Introduction to Psychology

Introduction to Psychology

Jorden A. Cummings and Lee Sanders

Jennifer Walinga, Charles Stangor, Paul C. Price, Rajiv S. Jhangiani, I-Chant A. Chiang, Dana C. Leighton, and Carrie Cuttler, David M. Buss, Eric Turkheimer, Ian Weaver, Aaron Benjamin, Ap Dijksterhuis, Ayelet Fishbach, Bertram Malle, Brice Kuhl, Cara Laney, Christia Spears Brown, Cynthia L. Pickett, David A. Schroeder, David Matsumoto, David Watson, Dennis L. Poepsel, Edward Diener, Elizabeth F. Loftus, Emily Hooker, Frances Friedrich, George Loewenstein, Gregory Murphy, Henry L. Roediger III, Hyisung Hwang, Jake Teeny, Jeanne Tsai, Jennifer A. Jewell, Jerry M. Burger, Jorden A. Cummings, Kathleen B. McDermott, Lee Sanders, Maferima Touré-Tillery, Marc Brackett, Mark E. Bouton, Max H. Bazerman, Neil Thin, Nicole Dudukovic, Peter Salovey, R. Chris Fraley, Richard E. Lucas, Robert A. Emmons, Robert Biswas-Diener, Robert V. Levine, Sarah Delaney, Sarah Pressman, Sudeep Bhatia, Susan T. Fiske, Yanine D. Hess, and Yoshihisa Kashima

University of Saskatchewan Open Press



About the Book


Introduction to Psychology, by Jorden A. Cummings (Associate Professor, Department of Psychology, University of Saskatchewan) and Lee Sanders (Sessional Lecturer, Department of Psychology, University of Saskatchewan), has been created from a combination of original content and materials compiled and adapted from several open educational resources (OERs), including Source Chapters from:

Attributions are more clearly delineated in the Source Chapter Attributions area of this book, including descriptions of which sections were edited prior to their inclusion.

All original and revised content is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License. Under the terms of the CC BY-NC-SA license, you are free to copy, redistribute, modify or adapt this book as long as you provide attribution. You may not use the material for commercial purposes. If you remix, transform, or build upon the material, you must distribute your contributions under the same license as the original. Additionally, if you redistribute this textbook, in whole or in part, in either a print or digital format, then you must retain on every physical and/or electronic page the following attribution:

The Key Terms list for each chapter and the Glossary for this book are new additions, compiled from a combination of existing definitions and vocabulary lists (taken from the Source Chapters) and new definitions. The Self-Tests provided with each chapter are also a new addition for this book; these were created using the H5P plugin for WordPress, and are available for others to download and use in their own instances of WordPress or Pressbooks.

OERs are defined as “teaching, learning, and research resources that reside in the public domain or have been released under an intellectual property license that permits their free use and re-purposing by others” (Hewlett Foundation). This textbook and the OERs from which it has been built are openly licensed using a Creative Commons license, and are offered in various digital and e-book formats free of charge. Printed editions of this book can be obtained for a nominal fee through the University of Saskatchewan bookstore.

Cover Attribution

Cover image by Yeshi Kangrang on Unsplash. Cover design by Rob Butz.


Source Chapter Attributions

Authors are indicated within each chapter throughout this book, but are also listed here, along with links to the original source OER. Edits to the original content, where they have taken place, are indicated on the list shown here. General formatting edits and reordering of figure and table numbers have also been done throughout the book.

All Key Terms, Self-Tests, and the Glossary are new additions to this textbook adaptation.

Chapter 1:

Chapter 2:

Chapter 3:

Chapter 4:

Chapter 5:

Chapter 6:

Chapter 7:

Chapter 8:

Chapter 9:

Chapter 10:

Chapter 11:

Chapter 12:

Chapter 13

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It truly takes a village to create an open textbook! This project was made possible by the efforts of many people over the past year – there are many thank-yous to give.

Thank you to Lisa Berg, Program Manager at the Distance Education Unit, and Gordon Sarty, Department Head of the Department of Psychology at the University of Saskatchewan, for their support of this project.

Thank you to Lee Sanders for your co-authorship and preparation of the PSY120 sections of this book.

This project was made possible by an Open Textbook Creation/Adaption Fund grant from the Gwenna Moss Centre for Teaching & Learning and the University of Saskatchewan. Thank you!

Thank you to Heather Ross (Gwenna Moss Centre for Teaching & Learning) for her unwavering confidence in this project and accompanying pep talks when needed, her enthusiasm, and her wisdom navigating open resources and helping us connect with the available resources that already exist.

Thank you to Julie Maier, Instructional Designer (Distance Education Unit) extraordinaire! This project could not have happened without your organization, amazing eye for detail, skills, and knowledge of how to maximize the success of the learning experience of students who will use this book. Thank you as well for building this book in Pressbooks and your “we’re almost there!” emails.

Thank you to Robb Larmer (Distance Education Unit) for your assistance with the test bank build and, as always, your Blackboard expertise.

Thank you to Rob Butz for your cover design, and to Rob and my parents for your encouragement over the past year as I navigated this new professional experience and worked a ridiculous number of evenings and weekends.

Thank you to Ryan Banow (Gwenna Moss Centre for Teaching & Learning) for your lesson on writing multiple choice questions for our test bank adventure.

Thank you to the authors whose work is used in this book. Without your work and willingness to share it openly, this book could not have happened.

Thank you to the graduate students without whom the ancillary resources would not have been possible: Amanda Sinclair, Jessica Campoli, Kirstie Gibson, Kathurina Mazurik, Christianne Rooke, and Austen Smith. You were fabulous company for multiple choice question writing.


–Jorden A. Cummings


Chapter 1. Introducing Psychology


Chapter 1 Introduction

Charles Stangor and Jennifer Walinga

Psychology is the scientific study of mind and behaviour. The word “psychology” comes from the Greek words “psyche,” meaning life, and “logos,” meaning explanation. Psychology is a popular major for students, a popular topic in the public media, and a part of our everyday lives. Television shows such as Dr. Phil feature psychologists who provide personal advice to those with personal or family difficulties. Psychological television crime dramas such as Cracked, Criminal Minds, Psyche, CSI, and others feature the work of forensic psychologists who use psychological principles to help solve crimes. And many people have direct knowledge of psychology because they have visited psychologists, such as school counsellors, family therapists, and religious, marriage, or bereavement counsellors.

Because we are frequently exposed to the work of psychologists in our everyday lives, we all have an idea about what psychology is and what psychologists do. In many ways I am sure that your conceptions are correct. Psychologists do work in forensic fields, and they do provide counselling and therapy for people in distress. But there are hundreds of thousands of psychologists in the world, and most of them work in other places, doing work that you are probably not aware of.

Most psychologists work in research laboratories, hospitals, and other field settings where they study the behaviour of humans and animals. For instance, my colleagues in the Psychology Department at the University of Maryland study such diverse topics as anxiety in children, the interpretation of dreams, the effects of caffeine on thinking, how birds recognize each other, how praying mantises hear, how people from different cultures react differently in negotiation, and the factors that lead people to engage in terrorism. Other psychologists study topics such as alcohol and drug addiction, memory, emotion, hypnosis, love, what makes people aggressive or helpful, and the psychologies of politics, prejudice, culture, and religion. Psychologists also work in schools and businesses, and they use a variety of methods, including observation, questionnaires, interviews, and laboratory studies, to help them understand behaviour.

This chapter provides an introduction to the broad field of psychology and the many approaches that psychologists take to understanding human behaviour. We will consider how psychologists conduct scientific research, with an overview of some of the most important approaches used and topics studied by psychologists, and also consider the variety of fields in which psychologists work and the careers that are available to people with psychology degrees. I expect that you may find that at least some of your preconceptions about psychology will be challenged and changed, and you will learn that psychology is a field that will provide you with new ways of thinking about your own thoughts, feelings, and actions.

Five photos. Long description available.
Figure 1.1 Psychology is in part the study of behaviour. Why do you think these people are behaving the way they are? [Long Description]

Image Attributions

Figure 1.1:

Long Descriptions

Figure 1.1 long description: Five photos:

  1. Man in hospital bed with broken leg; a soldier is lifting his leg as is if to give physical therapy.
  2. Young girl smoking a cigarette.
  3. A man doing a hand stand on a beach with sun setting in background.
  4. A man and woman yelling at each other with their heads touching.
  5. One man and four women dressed up like Star Trek characters and aliens.


1.1 Psychology as a Science

Charles Stangor and Jennifer Walinga

Learning Objectives

  1. Explain why using our intuition about everyday behaviour is insufficient for a complete understanding of the causes of behaviour.
  2. Describe the difference between values and facts and explain how the scientific method is used to differentiate between the two.

Despite the differences in their interests, areas of study, and approaches, all psychologists have one thing in common: they rely on scientific methods. Research psychologists use scientific methods to create new knowledge about the causes of behaviour, whereas psychologist-practitioners, such as clinical, counselling, industrial-organizational, and school psychologists, use existing research to enhance the everyday life of others. The science of psychology is important for both researchers and practitioners.

In a sense all humans are scientists. We all have an interest in asking and answering questions about our world. We want to know why things happen, when and if they are likely to happen again, and how to reproduce or change them. Such knowledge enables us to predict our own behaviour and that of others. We may even collect data (i.e., any information collected through formal observation or measurement) to aid us in this undertaking. It has been argued that people are “everyday scientists” who conduct research projects to answer questions about behaviour (Nisbett & Ross, 1980). When we perform poorly on an important test, we try to understand what caused our failure to remember or understand the material and what might help us do better the next time. When our good friends Monisha and Charlie break up, despite the fact that they appeared to have a relationship made in heaven, we try to determine what happened. When we contemplate the rise of terrorist acts around the world, we try to investigate the causes of this problem by looking at the terrorists themselves, the situation around them, and others’ responses to them.

The Problem of Intuition

The results of these “everyday” research projects can teach us many principles of human behaviour. We learn through experience that if we give someone bad news, he or she may blame us even though the news was not our fault. We learn that people may become depressed after they fail at an important task. We see that aggressive behaviour occurs frequently in our society, and we develop theories to explain why this is so. These insights are part of everyday social life. In fact, much research in psychology involves the scientific study of everyday behaviour (Heider, 1958; Kelley, 1967).

The problem, however, with the way people collect and interpret data in their everyday lives is that they are not always particularly thorough. Often, when one explanation for an event seems right, we adopt that explanation as the truth even when other explanations are possible and potentially more accurate. For example, eyewitnesses to violent crimes are often extremely confident in their identifications of the perpetrators of these crimes. But research finds that eyewitnesses are no less confident in their identifications when they are incorrect than when they are correct (Cutler & Wells, 2009; Wells & Hasel, 2008). People may also become convinced of the existence of extrasensory perception (ESP), or the predictive value of astrology, when there is no evidence for either (Gilovich, 1993). Furthermore, psychologists have also found that there are a variety of cognitive and motivational biases that frequently influence our perceptions and lead us to draw erroneous conclusions (Fiske & Taylor, 2007; Hsee & Hastie, 2006). In summary, accepting explanations for events without testing them thoroughly may lead us to think that we know the causes of things when we really do not.

Research Focus: Unconscious Preferences for the Letters of Our Own Name

A study reported in the Journal of Consumer Research (Brendl, Chattopadhyay, Pelham, & Carvallo, 2005) demonstrates the extent to which people can be unaware of the causes of their own behaviour. The research demonstrated that, at least under certain conditions (and although they do not know it), people frequently prefer brand names that contain the letters of their own name to brand names that do not contain the letters of their own name.

The research participants were recruited in pairs and were told that the research was a taste test of different types of tea. For each pair of participants, the experimenter created two teas and named them by adding the word stem “oki” to the first three letters of each participant’s first name. For example, for Jonathan and Elisabeth, the names of the teas would have been Jonoki and Elioki.

The participants were then shown 20 packets of tea that were supposedly being tested. Eighteen packets were labelled with made-up Japanese names (e.g., Mataku; Somuta), and two were labelled with the brand names constructed from the participants’ names. The experimenter explained that each participant would taste only two teas and would be allowed to choose one packet of these two to take home.

One of the two participants was asked to draw slips of paper to select the two brands that would be tasted at this session. However, the drawing was rigged so that the two brands containing the participants’ name stems were always chosen for tasting. Then, while the teas were being brewed, the participants completed a task designed to heighten their need for self-esteem, and that was expected to increase their desire to choose a brand that had the letters of their own name. Specifically, the participants all wrote about an aspect of themselves that they would like to change.

After the teas were ready, the participants tasted them and then chose to take a packet of one of the teas home with them. After they made their choice, the participants were asked why they chose the tea they had chosen, and then the true purpose of the study was explained to them.

The results of this study found that participants chose the tea that included the first three letters of their own name significantly more frequently (64% of the time) than they chose the tea that included the first three letters of their partner’s name (only 36% of the time). Furthermore, the decisions were made unconsciously; the participants did not know why they chose the tea they chose. When they were asked, more than 90% of the participants thought that they had chosen on the basis of taste, whereas only 5% of them mentioned the real cause — that the brand name contained the letters of their name.

Once we learn about the outcome of a given event (e.g., when we read about the results of a research project), we frequently believe that we would have been able to predict the outcome ahead of time. For instance, if half of a class of students is told that research concerning attraction between people has demonstrated that “opposites attract” and the other half is told that research has demonstrated that “birds of a feather flock together,” most of the students will report believing that the outcome that they just read about is true, and that they would have predicted the outcome before they had read about it. Of course, both of these contradictory outcomes cannot be true. (In fact, psychological research finds that “birds of a feather flock together” is generally the case.) The problem is that just reading a description of research findings leads us to think of the many cases we know that support the findings, and thus makes them seem believable. The tendency to think that we could have predicted something that has already occurred that we probably would not have been able to predict is called the hindsight bias.

Why Psychologists Rely on Empirical Methods

All scientists, whether they are physicists, chemists, biologists, sociologists, or psychologists, use empirical methods to study the topics that interest them. Empirical methods include the processes of collecting and organizing data and drawing conclusions about those data. The empirical methods used by scientists have developed over many years and provide a basis for collecting, analyzing, and interpreting data within a common framework in which information can be shared. We can label the scientific method as the set of assumptions, rules, and procedures that scientists use to conduct empirical research.

Although scientific research is an important method of studying human behaviour, not all questions can be answered using scientific approaches. Statements that cannot be objectively measured or objectively determined to be true or false are not within the domain of scientific inquiry. Scientists therefore draw a distinction between values and facts. Values are personal statements such as “Abortion should not be permitted in this country,” “I will go to heaven when I die,” or “It is important to study psychology.” Facts are objective statements determined to be accurate through empirical study. Examples are “There were more than 21,000 homicides in Canada in 2009” or “Research demonstrates that individuals who are exposed to highly stressful situations over long periods of time develop more health problems than those who are not.”

Because values cannot be considered to be either true or false, science cannot prove or disprove them. Nevertheless, as shown in Table 1.1, research can sometimes provide facts that can help people develop their values. For instance, science may be able to objectively measure the impact of unwanted children on a society or the psychological trauma suffered by women who have abortions. The effect of imprisonment on the crime rate in Canada may also be determinable. This factual information can and should be made available to help people formulate their values about abortion and incarceration, as well as to enable governments to articulate appropriate policies. Values also frequently come into play in determining what research is appropriate or important to conduct. For instance, the Canadian government has recently increased funding for university research, designating $37 million annually to the three major research councils dealing with health, social science, and the sciences (Research Canada, 2014).

Table 1.1 Examples of Values and Facts in Scientific Research.

Personal value Scientific fact
The environment should be protected. The Canadian government has reduced environmental funding by $200 million but annually pays more than $1.4 billion in subsidies to the oil and gas industry.
Practical work experience helps to develop skilled workers. More than $100 million for interest-free loans will be available in 2014 through the Canada Apprentice Loan program, an expansion of the Canada Student Loans Program.
Technology is increasingly necessary. The federal government in Canada will invest $305 million over five years to extend high-speed broadband to some 280,000 homes in 2014.
It is important to quit smoking. The Canadian government will raise the cost of cigarettes by more than $4 on a carton in 2014.
Source: Huffington Post, 2014.

Although scientists use research to help establish facts, the distinction between values and facts is not always clear-cut. Sometimes statements that scientists consider to be factual turn out later, on the basis of further research, to be partially or even entirely incorrect. Although scientific procedures do not necessarily guarantee that the answers to questions will be objective and unbiased, science is still the best method for drawing objective conclusions about the world around us. When old facts are discarded, they are replaced with new facts based on newer and more correct data. Although science is not perfect, the requirements of empiricism and objectivity result in a much greater chance of producing an accurate understanding of human behaviour than is available through other approaches.

Levels of Explanation in Psychology

The study of psychology spans many different topics at many different levels of explanation, which are the perspectives that are used to understand behaviour. Lower levels of explanation are more closely tied to biological influences, such as genes, neurons, neurotransmitters, and hormones, whereas the middle levels of explanation refer to the abilities and characteristics of individual people, and the highest levels of explanation relate to social groups, organizations, and cultures (Cacioppo, Berntson, Sheridan, & McClintock, 2000).

The same topic can be studied within psychology at different levels of explanation, as shown in Table 1.2, “Levels of Explanation.” For instance, the psychological disorder known as depression affects millions of people worldwide and is known to be caused by biological, social, and cultural factors. Studying and helping alleviate depression can be accomplished at low levels of explanation by investigating how chemicals in the brain influence the experience of depression. This approach has allowed psychologists to develop and prescribe drugs, such as Prozac, which may decrease depression in many individuals (Williams, Simpson, Simpson, & Nahas, 2009). At the middle levels of explanation, psychological therapy is directed at helping individuals cope with negative life experiences that may cause depression. And at the highest level, psychologists study differences in the prevalence of depression between men and women and across cultures. The occurrence of psychological disorders, including depression, is substantially higher for women than for men, and it is also higher in Western cultures, such as in Canada, the United States, and Europe, than in Eastern cultures, such as in India, China, and Japan (Chen, Wang, Poland, & Lin, 2009; Seedat et al., 2009). These sex and cultural differences provide insight into the factors that cause depression. The study of depression in psychology helps remind us that no one level of explanation can explain everything. All levels of explanation, from biological to personal to cultural, are essential for a better understanding of human behaviour.

Table 1.2 Levels of Explanation
Level of Explanation Underlying Process Examples
Lower Biological
  • Depression is in part genetically influenced.
  • Depression is influenced by the action of neurotransmitters in the brain.
Middle Interpersonal
  • People who are depressed may interpret the events that occur to them too negatively.
  • Psychotherapy can be used to help people talk about and combat depression
Higher Cultural and social
  • Women experience more depression than do men.
  • The prevalence of depression varies across cultures and historical time periods.

The Challenges of Studying Psychology

Understanding and attempting to alleviate the costs of psychological disorders such as depression is not easy because psychological experiences are extremely complex. The questions psychologists pose are as difficult as those posed by doctors, biologists, chemists, physicists, and other scientists, if not more so (Wilson, 1998).

A major goal of psychology is to predict behaviour by understanding its causes. Making predictions is difficult, in part because people vary and respond differently in different situations. Individual differences are the variations among people on physical or psychological dimensions. For instance, although many people experience at least some symptoms of depression at some times in their lives, the experience varies dramatically among people. Some people experience major negative events, such as severe physical injuries or the loss of significant others, without experiencing much depression, whereas other people experience severe depression for no apparent reason. Other important individual differences that we will discuss in the chapters to come include differences in extraversion, intelligence, self-esteem, anxiety, aggression, and conformity.

Because of the many individual difference variables that influence behaviour, we cannot always predict who will become aggressive or who will perform best in graduate school or on the job. The predictions made by psychologists (and most other scientists) are only probabilistic. We can say, for instance, that people who score higher on an intelligence test will, on average, do better than people who score lower on the same test, but we cannot make very accurate predictions about exactly how any one person will perform.

Another reason that it is difficult to predict behaviour is that almost all behaviour is multiply determined, or produced by many factors. And these factors occur at different levels of explanation. We have seen, for instance, that depression is caused by lower-level genetic factors, by medium-level personal factors, and by higher-level social and cultural factors. You should always be skeptical about people who attempt to explain important human behaviours, such as violence, child abuse, poverty, anxiety, or depression, in terms of a single cause.

Furthermore, these multiple causes are not independent of one another; they are associated such that when one cause is present, other causes tend to be present as well. This overlap makes it difficult to pinpoint which cause or causes are operating. For instance, some people may be depressed because of biological imbalances in neurotransmitters in their brain. The resulting depression may lead them to act more negatively toward other people around them, which then leads those other people to respond more negatively to them, which then increases their depression. As a result, the biological determinants of depression become intertwined with the social responses of other people, making it difficult to disentangle the effects of each cause.

Another difficulty in studying psychology is that much human behaviour is caused by factors that are outside our conscious awareness, making it impossible for us, as individuals, to really understand them. The role of unconscious processes was emphasized in the theorizing of the Austrian neurologist Sigmund Freud (1856-1939), who argued that many psychological disorders were caused by memories that we have repressed and thus remain outside our consciousness. Unconscious processes will be an important part of our study of psychology, and we will see that current research has supported many of Freud’s ideas about the importance of the unconscious in guiding behaviour.


Key Takeaways

  • Psychology is the scientific study of mind and behaviour.
  • Though it is easy to think that everyday situations have commonsense answers, scientific studies have found that people are not always as good at predicting outcomes as they think they are.
  • The hindsight bias leads us to think that we could have predicted events that we actually could not have predicted.
  • People are frequently unaware of the causes of their own behaviours.
  • Psychologists use the scientific method to collect, analyze, and interpret evidence.
  • Employing the scientific method allows the scientist to collect empirical data objectively, which adds to the accumulation of scientific knowledge.
  • Psychological phenomena are complex, and making predictions about them is difficult because of individual differences and because they are multiply determined at different levels of explanation.

Exercises and Critical Thinking

  1. Can you think of a time when you used your intuition to analyze an outcome, only to be surprised later to find that your explanation was completely incorrect? Did this surprise help you understand how intuition may sometimes lead us astray?
  2. Describe the scientific method in a way that someone who knows nothing about science could understand it.
  3. Consider a behaviour that you find to be important and think about its potential causes at different levels of explanation. How do you think psychologists would study this behaviour?


Brendl, C. M., Chattopadhyay, A., Pelham, B. W., & Carvallo, M. (2005). Name letter branding: Valence transfers when product specific needs are active. Journal of Consumer Research, 32(3), 405–415.

Cacioppo, J. T., Berntson, G. G., Sheridan, J. F., & McClintock, M. K. (2000). Multilevel integrative analyses of human behavior: Social neuroscience and the complementing nature of social and biological approaches. Psychological Bulletin, 126(6), 829–843.

Chen, P.-Y., Wang, S.-C., Poland, R. E., & Lin, K.-M. (2009). Biological variations in depression and anxiety between East and West. CNS Neuroscience & Therapeutics, 15(3), 283–294.

Cutler, B. L., & Wells, G. L. (2009). Expert testimony regarding eyewitness identification. In J. L. Skeem, S. O. Lilienfeld, & K. S. Douglas (Eds.), Psychological science in the courtroom: Consensus and controversy (pp. 100–123). New York, NY: Guilford Press.

Fiske, S. T., & Taylor, S. E. (2007). Social cognition: From brains to culture. New York, NY: McGraw-Hill.

Gilovich, T. (1993). How we know what isn’t so: The fallibility of human reason in everyday life. New York, NY: Free Press.

Heider, F. (1958). The psychology of interpersonal relations. Hillsdale, NJ: Erlbaum.

Hsee, C. K., & Hastie, R. (2006). Decision and experience: Why don’t we choose what makes us happy? Trends in Cognitive Sciences, 10(1), 31–37.

Hufffington Post. (2014). 2014 Canadian Budget Highlights: What You Need To Know. Retrieved May 2, 2104 from

Kelley, H. H. (1967). Attribution theory in social psychology. In D. Levine (Ed.), Nebraska symposium on motivation (Vol. 15, pp. 192–240). Lincoln: University of Nebraska Press.

Nisbett, R. E., & Ross, L. (1980). Human inference: Strategies and shortcomings of social judgment. Englewood Cliffs, NJ: Prentice Hall.

Research Canada. (2014). Budget 2014 – What it means for us. Retrieved May 2, 2014 from

Seedat, S., Scott, K. M., Angermeyer, M. C., Berglund, P., Bromet, E. J., Brugha, T. S., & Kessler, R. C. (2009). Cross-national associations between gender and mental disorders in the World Health Organization World Mental Health Surveys. Archives of General Psychiatry, 66(7), 785–795.

Wells, G. L., & Hasel, L. E. (2008). Eyewitness identification: Issues in common knowledge and generalization. In E. Borgida & S. T. Fiske (Eds.), Beyond common sense: Psychological science in the courtroom (pp. 159–176). Malden, NJ: Blackwell.

Williams, N., Simpson, A. N., Simpson, K., & Nahas, Z. (2009). Relapse rates with long-term antidepressant drug therapy: A meta-analysis. Human Psychopharmacology: Clinical and Experimental, 24(5), 401–408.

Wilson, E. O. (1998). Consilience: The unity of knowledge. New York, NY: Vintage Books.


1.2 The Evolution of Psychology: History, Approaches, and Questions

Charles Stangor and Jennifer Walinga

Learning Objectives

  1. Explain how psychology changed from a philosophical to a scientific discipline.
  2. List some of the most important questions that concern psychologists.
  3. Outline the basic schools of psychology and how each school has contributed to psychology.

In this section we will review the history of psychology with a focus on the important questions that psychologists ask and the major approaches (or schools) of psychological inquiry. The schools of psychology that we will review are summarized in Table 1.3, “The Most Important Approaches (Schools) of Psychology,” while Table 1.4, “History of Psychology,” presents a timeline of some of the most important psychologists, beginning with the early Greek philosophers and extending to the present day. Table 1.3 and Table 1.4 both represent a selection of the most important schools and people; to mention all the approaches and all the psychologists who have contributed to the field is not possible in one chapter. The approaches that psychologists have used to assess the issues that interest them have changed dramatically over the history of psychology. Perhaps most importantly, the field has moved steadily from speculation about behaviour toward a more objective and scientific approach as the technology available to study human behaviour has improved (Benjamin & Baker, 2004). There has also been an influx of women into the field. Although most early psychologists were men, now most psychologists, including the presidents of the most important psychological organizations, are women.

Table 1.3 The Most Important Approaches (Schools) of Psychology.
School of Psychology Description Important Contributors
Structuralism Uses the method of introspection to identify the basic elements or “structures” of psychological experience Wilhelm Wundt, Edward B. Titchener
Functionalism Attempts to understand why animals and humans have developed the particular psychological aspects that they currently possess William James
Psychodynamic Focuses on the role of our unconscious thoughts, feelings, and memories and our early childhood experiences in determining behaviour Sigmund Freud, Carl Jung, Alfred Adler, Erik Erickson
Behaviourism Based on the premise that it is not possible to objectively study the mind, and therefore that psychologists should limit their attention to the study of behaviour itself John B. Watson, B. F. Skinner
Cognitive The study of mental processes, including perception, thinking, memory, and judgments Hermann Ebbinghaus, Sir Frederic Bartlett, Jean Piaget
Social-cultural The study of how the social situations and the cultures in which people find themselves influence thinking and behaviour Fritz Heider, Leon Festinger, Stanley Schachter

Although most of the earliest psychologists were men, women are increasingly contributing to psychology. Here are some examples:

Although it cannot capture every important psychologist, the following timeline shows some of the most important contributors to the history of psychology. (Adapted by J. Walinga.)

Table 1.4 History of Psychology.
Date Psychologist(s) Description
428 to 347 BCE Plato Greek philosopher who argued for the role of nature in psychological development.
384 to 432 BCE Aristotle Greek philosopher who argued for the role of nurture in psychological development.
1588 to 1679 CE Thomas Hobbes English philosopher.
1596 to 1650 René Descartes French philosopher.
1632 to 1704 John Locke English philosopher.
1712 to 1778 Jean-Jacques Rousseau French philosopher.
1801 to 1887 Gustav Fechner German experimental psychologist who developed the idea of the “just noticeable difference” (JND), which is considered to be the first empirical psychological measurement.
1809 to 1882 Charles Darwin British naturalist whose theory of natural selection influenced the functionalist school and the field of evolutionary psychology.
1832 to 1920 Wilhelm Wundt German psychologist who opened one of the first psychology laboratories and helped develop the field of structuralism.
1842 to 1910 William James American psychologist who opened one of the first psychology laboratories and helped develop the field of functionalism.
1849 to 1936 Ivan Pavlov Russian psychologist whose experiments on learning led to the principles of classical conditioning.
1850 to 1909 Hermann Ebbinghaus German psychologist who studied the ability of people to remember lists of nonsense syllables under different conditions.
1856 to 1939 Sigmund Freud Austrian psychologist who founded the field of psychodynamic psychology.
1867 to 1927 Edward Bradford Titchener American psychologist  who contributed to the field of structuralism.
1878 to 1958 John B. Watson American psychologist  who contributed to the field of behavioralism.
1886 to 1969 Sir Frederic Bartlett British psychologist who studied the cognitive and social processes of remembering.
1896 to 1980 Jean Piaget Swiss psychologist  who developed an important theory of  cognitive development in children.
1904 to  1990 B. F. Skinner American psychologist who contributed to the school of behaviourism.
1926 to 1993 Donald Broadbent British cognitive psychologist who was  pioneer in the study of attention.
20th and 21st centuries Linda Bartoshuk; Daniel Kahneman; Elizabeth Loftus; Geroge Miller. American psychologists who contributed to the cognitive school of psychology by studying learning, memory, and judgment. An important contribution is the advancement of the field of neuroscience. Daniel Kahneman won the Nobel Prize in Economics for his work on psychological decision making.
1850 Dorothea Dix Canadian psychologist known for her contributions to mental health and opened one of the first mental hospitals in Halifax, New Brunswick.
1880 William Lyall; James Baldwin Canadian psychologists who wrote early psychology texts and created first Canadian psychology lab at the University of Toronto.
1950 James Olds; Brenda Milner; Wilder Penfield; Donald Hebb; Endel Telving Canadian psychologists who contributed to neurological psychology and opened the Montreal Neurological Institute.
1960 Albert Bandura Canadian psychologist who developed ‘social learning theory’ with his Bobo doll studies illustrating the impact that observation and interaction has on learning.
1970 Hans Selye Canadian psychologist who contributed significantly in the area of psychology of stress.

Although psychology has changed dramatically over its history, the most important questions that psychologists address have remained constant. Some of these questions follow, and we will discuss them both in this chapter and in the chapters to come:

Bird's eye view of black smoke and a town on fire.
Figure 1.2 Lac-Mégantic Derailment. Psychologists study the causes of poor judgments such as those made by executives like the three criminally charged in relation to the Lac-Mégantic train derailment in 2013. This picture was taken from a Sûreté du Québec helicopter on the day of the derailment.

Early Psychologists

The earliest psychologists that we know about are the Greek philosophers Plato (428-347 BC) and Aristotle (384-322 BC). These philosophers (see Figure 1.3) asked many of the same questions that today’s psychologists ask; for instance, they questioned the distinction between nature and nurture and the existence of free will. In terms of the former, Plato argued on the nature side, believing that certain kinds of knowledge are innate or inborn, whereas Aristotle was more on the nurture side, believing that each child is born as an “empty slate” (in Latin, a tabula rasa) and that knowledge is primarily acquired through learning and experience.

Figure 1.3 Early Psychologists. The earliest psychologists were the Greek Philosophers Plato (left) and Aristotle (right). Plato believed that much knowledge was innate, whereas Aristotle thought that each child was born as an “empty slate” and that knowledge was primarily acquired through learning and experience.

European philosophers continued to ask these fundamental questions during the Renaissance. For instance, the French philosopher René Descartes (1596-1650) also considered the issue of free will, arguing in its favour and believing that the mind controls the body through the pineal gland in the brain (an idea that made some sense at the time but was later proved incorrect). Descartes also believed in the existence of innate natural abilities. A scientist as well as a philosopher, Descartes dissected animals and was among the first to understand that the nerves controlled the muscles. He also addressed the relationship between mind (the mental aspects of life) and body (the physical aspects of life). Descartes believed in the principle of dualism: that the mind is fundamentally different from the mechanical body. Other European philosophers, including Thomas Hobbes (1588-1679), John Locke (1632-1704), and Jean-Jacques Rousseau (1712-1778), also weighed in on these issues. The fundamental problem that these philosophers faced was that they had few methods for settling their claims. Most philosophers didn’t conduct any research on these questions, in part because they didn’t yet know how to do it, and in part because they weren’t sure it was even possible to objectively study human experience. But dramatic changes came during the 1800s with the help of the first two research psychologists: the German psychologist Wilhelm Wundt (1832-1920), who developed a psychology laboratory in Leipzig, Germany, and the American psychologist William James (1842-1910), who founded a psychology laboratory at Harvard University.

Structuralism: Introspection and the Awareness of Subjective Experience

Wundt’s research in his laboratory in Leipzig focused on the nature of consciousness itself. Wundt and his students believed that it was possible to analyze the basic elements of the mind and to classify our conscious experiences scientifically. Wundt began the field known as structuralism, a school of psychology whose goal was to identify the basic elements or structures of psychological experience. Its goal was to create a periodic table of the elements of sensations, similar to the periodic table of elements that had recently been created in chemistry. Structuralists used the method of introspection to attempt to create a map of the elements of consciousness. Introspection involves asking research participants to describe exactly what they experience as they work on mental tasks, such as viewing colours, reading a page in a book, or performing a math problem. A participant who is reading a book might report, for instance, that he saw some black and coloured straight and curved marks on a white background. In other studies the structuralists used newly invented reaction time instruments to systematically assess not only what the participants were thinking but how long it took them to do so. Wundt discovered that it took people longer to report what sound they had just heard than to simply respond that they had heard the sound. These studies marked the first time researchers realized that there is a difference between the sensation of a stimulus and the perception of that stimulus, and the idea of using reaction times to study mental events has now become a mainstay of cognitive psychology.

Figure 1.4 Wundt and Titchener. Wilhelm Wundt (seated at left) and Edward Titchener (right) helped create the structuralist school of psychology. Their goal was to classify the elements of sensation through introspection.

Perhaps the best known of the structuralists was Edward Bradford Titchener (1867-1927). Titchener was a student of Wundt’s who came to the United States in the late 1800s and founded a laboratory at Cornell University (Figure 1.4). (Titchener was later rejected by McGill University (1903). Perhaps he was ahead of his time; Brenda Milner did not open the Montreal Neurological Institute until 1950.) In his research using introspection, Titchener and his students claimed to have identified more than 40,000 sensations, including those relating to vision, hearing, and taste. An important aspect of the structuralist approach was that it was rigorous and scientific. The research marked the beginning of psychology as a science, because it demonstrated that mental events could be quantified. But the structuralists also discovered the limitations of introspection. Even highly trained research participants were often unable to report on their subjective experiences. When the participants were asked to do simple math problems, they could easily do them, but they could not easily answer how they did them. Thus the structuralists were the first to realize the importance of unconscious processes—that many important aspects of human psychology occur outside our conscious awareness, and that psychologists cannot expect research participants to be able to accurately report on all of their experiences.

Functionalism and Evolutionary Psychology

In contrast to Wundt, who attempted to understand the nature of consciousness, William James and the other members of the school of functionalism aimed to understand why animals and humans have developed the particular psychological aspects that they currently possess (Hunt, 1993). For James, one’s thinking was relevant only to one’s behaviour. As he put it in his psychology textbook, “My thinking is first and last and always for the sake of my doing” (James, 1890). James and the other members of the functionalist school (Figure 1.5) were influenced by Charles Darwin’s (1809-1882) theory of natural selection, which proposed that the physical characteristics of animals and humans evolved because they were useful, or functional. The functionalists believed that Darwin’s theory applied to psychological characteristics too. Just as some animals have developed strong muscles to allow them to run fast, the human brain, so functionalists thought, must have adapted to serve a particular function in human experience.

Figure 1.5 Functionalist School. The functionalist school of psychology, founded by the American psychologist William James (left), was influenced by the work of Charles Darwin (right).

Although functionalism no longer exists as a school of psychology, its basic principles have been absorbed into psychology and continue to influence it in many ways. The work of the functionalists has developed into the field of evolutionary psychology, a branch of psychology that applies the Darwinian theory of natural selection to human and animal behaviour (Dennett, 1995; Tooby & Cosmides, 1992). Evolutionary psychology accepts the functionalists’ basic assumption, namely that many human psychological systems, including memory, emotion, and personality, serve key adaptive functions. As we will see in the chapters to come, evolutionary psychologists use evolutionary theory to understand many different behaviours, including romantic attraction, stereotypes and prejudice, and even the causes of many psychological disorders. A key component of the ideas of evolutionary psychology is fitness. Fitness refers to the extent to which having a given characteristic helps the individual organism survive and reproduce at a higher rate than do other members of the species who do not have the characteristic. Fitter organisms pass on their genes more successfully to later generations, making the characteristics that produce fitness more likely to become part of the organism’s nature than characteristics that do not produce fitness. For example, it has been argued that the emotion of jealousy has survived over time in men because men who experience jealousy are more fit than men who do not. According to this idea, the experience of jealousy leads men to be more likely to protect their mates and guard against rivals, which increases their reproductive success (Buss, 2000). Despite its importance in psychological theorizing, evolutionary psychology also has some limitations. One problem is that many of its predictions are extremely difficult to test. Unlike the fossils that are used to learn about the physical evolution of species, we cannot know which psychological characteristics our ancestors possessed or did not possess; we can only make guesses about this. Because it is difficult to directly test evolutionary theories, it is always possible that the explanations we apply are made up after the fact to account for observed data (Gould & Lewontin, 1979). Nevertheless, the evolutionary approach is important to psychology because it provides logical explanations for why we have many psychological characteristics.

Psychodynamic Psychology

Perhaps the school of psychology that is most familiar to the general public is the psychodynamic approach to understanding behaviour, which was championed by Sigmund Freud (1856-1939) and his followers. Psychodynamic psychology is an approach to understanding human behaviour that focuses on the role of unconscious thoughts, feelings, and memories. Freud (Figure 1.6) developed his theories about behaviour through extensive analysis of the patients that he treated in his private clinical practice. Freud believed that many of the problems that his patients experienced, including anxiety, depression, and sexual dysfunction, were the result of the effects of painful childhood experiences that they could no longer remember.

Figure 1.6 Sigmund Freud. Sigmund Freud and the other psychodynamic psychologists believed that many of our thoughts and emotions are unconscious. Psychotherapy was designed to help patients recover and confront their “lost” memories.

Freud’s ideas were extended by other psychologists whom he influenced, including Carl Jung (1875-1961), Alfred Adler (1870-1937), Karen Horney (1855-1952), and Erik Erikson (1902-1994). These and others who follow the psychodynamic approach believe that it is possible to help the patient if the unconscious drives can be remembered, particularly through a deep and thorough exploration of the person’s early sexual experiences and current sexual desires. These explorations are revealed through talk therapy and dream analysis in a process called psychoanalysis. The founders of the school of psychodynamics were primarily practitioners who worked with individuals to help them understand and confront their psychological symptoms. Although they did not conduct much research on their ideas, and although later, more sophisticated tests of their theories have not always supported their proposals, psychodynamics has nevertheless had substantial impact on the field of psychology, and indeed on thinking about human behaviour more generally (Moore & Fine, 1995). The importance of the unconscious in human behaviour, the idea that early childhood experiences are critical, and the concept of therapy as a way of improving human lives are all ideas that are derived from the psychodynamic approach and that remain central to psychology.

Behaviourism and the Question of Free Will

Although they differed in approach, both structuralism and functionalism were essentially studies of the mind. The psychologists associated with the school of behaviourism, on the other hand, were reacting in part to the difficulties psychologists encountered when they tried to use introspection to understand behaviour. Behaviourism is a school of psychology that is based on the premise that it is not possible to objectively study the mind, and therefore that psychologists should limit their attention to the study of behaviour itself. Behaviourists believe that the human mind is a black box into which stimuli are sent and from which responses are received. They argue that there is no point in trying to determine what happens in the box because we can successfully predict behaviour without knowing what happens inside the mind. Furthermore, behaviourists believe that it is possible to develop laws of learning that can explain all behaviours. The first behaviourist was the American psychologist John B. Watson (1878-1958). Watson was influenced in large part by the work of the Russian physiologist Ivan Pavlov (1849-1936), who had discovered that dogs would salivate at the sound of a tone that had previously been associated with the presentation of food. Watson and the other behaviourists began to use these ideas to explain how events that people and other organisms experienced in their environment (stimuli) could produce specific behaviours (responses). For instance, in Pavlov’s research the stimulus (either the food or, after learning, the tone) would produce the response of salivation in the dogs. In his research Watson found that systematically exposing a child to fearful stimuli in the presence of objects that did not themselves elicit fear could lead the child to respond with a fearful behaviour to the presence of the objects (Watson & Rayner, 1920; Beck, Levinson, & Irons, 2009). In the best known of his studies, an eight-month-old boy named Little Albert was used as the subject. Here is a summary of the findings: The boy was placed in the middle of a room; a white laboratory rat was placed near him and he was allowed to play with it. The child showed no fear of the rat. In later trials, the researchers made a loud sound behind Albert’s back by striking a steel bar with a hammer whenever the baby touched the rat. The child cried when he heard the noise. After several such pairings of the two stimuli, the child was again shown the rat. Now, however, he cried and tried to move away from the rat. In line with the behaviourist approach, the boy had learned to associate the white rat with the loud noise, resulting in crying.

Figure 1.7 Skinner. B. F. Skinner was a member of the behaviourist school of psychology. He argued that free will is an illusion and that all behaviour is determined by environmental factors.

The most famous behaviourist was Burrhus Frederick (B. F.) Skinner (1904 to 1990), who expanded the principles of behaviourism and also brought them to the attention of the public at large. Skinner (Figure 1.7) used the ideas of stimulus and response, along with the application of rewards or reinforcements, to train pigeons and other animals. And he used the general principles of behaviourism to develop theories about how best to teach children and how to create societies that were peaceful and productive. Skinner even developed a method for studying thoughts and feelings using the behaviourist approach (Skinner, 1957, 1972).

Research Focus: Do We Have Free Will?

The behaviourist research program had important implications for the fundamental questions about nature and nurture and about free will. In terms of the nature-nurture debate, the behaviourists agreed with the nurture approach, believing that we are shaped exclusively by our environments. They also argued that there is no free will, but rather that our behaviours are determined by the events that we have experienced in our past. In short, this approach argues that organisms, including humans, are a lot like puppets in a show who don’t realize that other people are controlling them. Furthermore, although we do not cause our own actions, we nevertheless believe that we do because we don’t realize all the influences acting on our behaviour.

Recent research in psychology has suggested that Skinner and the behaviourists might well have been right, at least in the sense that we overestimate our own free will in responding to the events around us (Libet, 1985; Matsuhashi & Hallett, 2008; Wegner, 2002). In one demonstration of the misperception of our own free will, neuroscientists Soon, Brass, Heinze, and Haynes (2008) placed their research participants in a functional magnetic resonance imaging (fMRI) brain scanner while they presented them with a series of letters on a computer screen. The letter on the screen changed every half second. The participants were asked, whenever they decided to, to press either of two buttons. Then they were asked to indicate which letter was showing on the screen when they decided to press the button. The researchers analyzed the brain images to see if they could predict which of the two buttons the participant was going to press, even before the letter at which he or she had indicated the decision to press a button. Suggesting that the intention to act occurred in the brain before the research participants became aware of it, the researchers found that the prefrontal cortex region of the brain showed activation that could be used to predict the button pressed as long as 10 seconds before the participants said that they had decided which button to press.

Research has found that we are more likely to think that we control our behaviour when the desire to act occurs immediately prior to the outcome, when the thought is consistent with the outcome, and when there are no other apparent causes for the behaviour. Aarts, Custers, and Wegner (2005) asked their research participants to control a rapidly moving square along with a computer that was also controlling the square independently. The participants pressed a button to stop the movement. When participants were exposed to words related to the location of the square just before they stopped its movement, they became more likely to think that they controlled the motion, even when it was actually the computer that stopped it. And Dijksterhuis, Preston, Wegner, and Aarts (2008) found that participants who had just been exposed to first-person singular pronouns, such as “I” and “me,” were more likely to believe that they controlled their actions than were people who had seen the words “computer” or “God.” The idea that we are more likely to take ownership for our actions in some cases than in others is also seen in our attributions for success and failure. Because we normally expect that our behaviours will be met with success, when we are successful we easily believe that the success is the result of our own free will. When an action is met with failure, on the other hand, we are less likely to perceive this outcome as the result of our free will, and we are more likely to blame the outcome on luck or our teacher (Wegner, 2003).

The behaviourists made substantial contributions to psychology by identifying the principles of learning. Although the behaviourists were incorrect in their beliefs that it was not possible to measure thoughts and feelings, their ideas provided new ideas that helped further our understanding regarding the nature-nurture debate and the question of free will. The ideas of behaviourism are fundamental to psychology and have been developed to help us better understand the role of prior experiences in a variety of areas of psychology.

The Cognitive Approach and Cognitive Neuroscience

Science is always influenced by the technology that surrounds it, and psychology is no exception. Thus it is no surprise that beginning in the 1960s, growing numbers of psychologists began to think about the brain and about human behaviour in terms of the computer, which was being developed and becoming publicly available at that time. The analogy between the brain and the computer, although by no means perfect, provided part of the impetus for a new school of psychology called cognitive psychology. Cognitive psychology is a field of psychology that studies mental processes, including perception, thinking, memory, and judgment. These actions correspond well to the processes that computers perform. Although cognitive psychology began in earnest in the 1960s, earlier psychologists had also taken a cognitive orientation. Some of the important contributors to cognitive psychology include the German psychologist Hermann Ebbinghaus (1850-1909), who studied the ability of people to remember lists of words under different conditions, and the English psychologist Sir Frederic Bartlett (1886-1969), who studied the cognitive and social processes of remembering. Bartlett created short stories that were in some ways logical but also contained some very unusual and unexpected events. Bartlett discovered that people found it very difficult to recall the stories exactly, even after being allowed to study them repeatedly, and he hypothesized that the stories were difficult to remember because they did not fit the participants’ expectations about how stories should go. The idea that our memory is influenced by what we already know was also a major idea behind the cognitive-developmental stage model of Swiss psychologist Jean Piaget (1896-1980). Other important cognitive psychologists include Donald E. Broadbent (1926-1993), Daniel Kahneman (1934-), George Miller (1920-2012), Eleanor Rosch (1938-), and Amos Tversky (1937-1996).

The War of the Ghosts

The War of the Ghosts is a story that was used by Sir Frederic Bartlett to test the influence of prior expectations on memory. Bartlett found that even when his British research participants were allowed to read the story many times, they still could not remember it well, and he believed this was because it did not fit with their prior knowledge. One night two young men from Egulac went down to the river to hunt seals, and while they were there it became foggy and calm. Then they heard war-cries, and they thought: “Maybe this is a war-party.” They escaped to the shore, and hid behind a log. Now canoes came up, and they heard the noise of paddles and saw one canoe coming up to them. There were five men in the canoe, and they said: “What do you think? We wish to take you along. We are going up the river to make war on the people.” One of the young men said, “I have no arrows.” “Arrows are in the canoe,” they said. “I will not go along. I might be killed. My relatives do not know where I have gone. But you,” he said, turning to the other, “may go with them.” So one of the young men went, but the other returned home. And the warriors went on up the river to a town on the other side of Kalama. The people came down to the water and they began to fight, and many were killed. But presently the young man heard one of the warriors say, “Quick, let us go home: that Indian has been hit.” Now he thought: “Oh, they are ghosts.” He did not feel sick, but they said he had been shot. So the canoes went back to Egulac and the young man went ashore to his house and made a fire. And he told everybody and said: “Behold I accompanied the ghosts, and we went to fight. Many of our fellows were killed, and many of those who attacked us were killed. They said I was hit, and I did not feel sick.” He told it all, and then he became quiet. When the sun rose he fell down. Something black came out of his mouth. His face became contorted. The people jumped up and cried. He was dead. (Bartlett, 1932)

In its argument that our thinking has a powerful influence on behaviour, the cognitive approach provided a distinct alternative to behaviourism. According to cognitive psychologists, ignoring the mind itself will never be sufficient because people interpret the stimuli that they experience. For instance, when a boy turns to a girl on a date and says, “You are so beautiful,” a behaviourist would probably see that as a reinforcing (positive) stimulus. And yet the girl might not be so easily fooled. She might try to understand why the boy is making this particular statement at this particular time and wonder if he might be attempting to influence her through the comment. Cognitive psychologists maintain that when we take into consideration how stimuli are evaluated and interpreted, we understand behaviour more deeply. Cognitive psychology remains enormously influential today, and it has guided research in such varied fields as language, problem solving, memory, intelligence, education, human development, social psychology, and psychotherapy. The cognitive revolution has been given even more life over the past decade as the result of recent advances in our ability to see the brain in action using neuroimaging techniques. Neuroimaging is the use of various techniques to provide pictures of the structure and function of the living brain (Ilardi & Feldman, 2001). These images are used to diagnose brain disease and injury, but they also allow researchers to view information processing as it occurs in the brain, because the processing causes the involved area of the brain to increase metabolism and show up on the scan. We have already discussed the use of one neuroimaging technique, functional magnetic resonance imaging (fMRI), in the research focus earlier in this section, and we will discuss the use of neuroimaging techniques in many areas of psychology in the chapters to follow.

Social-Cultural Psychology

A final school, which takes a higher level of analysis and which has had substantial impact on psychology, can be broadly referred to as the social-cultural approach. The field of social-cultural psychology is the study of how the social situations and the cultures in which people find themselves influence thinking and behaviour. Social-cultural psychologists are particularly concerned with how people perceive themselves and others, and how people influence each other’s behaviour. For instance, social psychologists have found that we are attracted to others who are similar to us in terms of attitudes and interests (Byrne, 1969), that we develop our own beliefs and attitudes by comparing our opinions to those of others (Festinger, 1954), and that we frequently change our beliefs and behaviours to be similar to those of the people we care about—a process known as conformity. An important aspect of social-cultural psychology are social normsthe ways of thinking, feeling, or behaving that are shared by group members and perceived by them as appropriate (Asch, 1952; Cialdini, 1993). Norms include customs, traditions, standards, and rules, as well as the general values of the group. Many of the most important social norms are determined by the culture in which we live, and these cultures are studied by cross-cultural psychologists. A culture represents the common set of social norms, including religious and family values and other moral beliefs, shared by the people who live in a geographical region (Fiske, Kitayama, Markus, & Nisbett, 1998; Markus, Kitayama, & Heiman, 1996; Matsumoto, 2001). Cultures influence every aspect of our lives, and it is not inappropriate to say that our culture defines our lives just as much as does our evolutionary experience (Mesoudi, 2009). Psychologists have found that there is a fundamental difference in social norms between Western cultures (including those in Canada, the United States, Western Europe, Australia, and New Zealand) and East Asian cultures (including those in China, Japan, Taiwan, Korea, India, and Southeast Asia). Norms in Western cultures are primarily oriented toward individualism, which is about valuing the self and one’s independence from others. Children in Western cultures are taught to develop and to value a sense of their personal self, and to see themselves in large part as separate from the other people around them. Children in Western cultures feel special about themselves; they enjoy getting gold stars on their projects and the best grade in the class. Adults in Western cultures are oriented toward promoting their own individual success, frequently in comparison to (or even at the expense of) others. Norms in the East Asian culture, on the other hand, are oriented toward interdependence or collectivism. In these cultures children are taught to focus on developing harmonious social relationships with others. The predominant norms relate to group togetherness and connectedness, and duty and responsibility to one’s family and other groups. When asked to describe themselves, the members of East Asian cultures are more likely than those from Western cultures to indicate that they are particularly concerned about the interests of others, including their close friends and their colleagues (Figure 1.8, “East vs West”).

Photo 1: An Asian family plays a board game. Photo 2: A blonde woman stands alone with her dog.
Figure 1.8 East vs West. In Western cultures social norms promote a focus on the self (individualism), whereas in Eastern cultures the focus is more on families and social groups (collectivism).

Another important cultural difference is the extent to which people in different cultures are bound by social norms and customs, rather than being free to express their own individuality without considering social norms (Chan, Gelfand, Triandis, & Tzeng, 1996). Cultures also differ in terms of personal space, such as how closely individuals stand to each other when talking, as well as the communication styles they employ. It is important to be aware of cultures and cultural differences because people with different cultural backgrounds increasingly come into contact with each other as a result of increased travel and immigration and the development of the Internet and other forms of communication. In Canada, for instance, there are many different ethnic groups, and the proportion of the population that comes from minority (non-White) groups is increasing from year to year. The social-cultural approach to understanding behaviour reminds us again of the difficulty of making broad generalizations about human nature. Different people experience things differently, and they experience them differently in different cultures.

The Many Disciplines of Psychology

Psychology is not one discipline but rather a collection of many subdisciplines that all share at least some common approaches and that work together and exchange knowledge to form a coherent discipline (Yang & Chiu, 2009). Because the field of psychology is so broad, students may wonder which areas are most suitable for their interests and which types of careers might be available to them. Table 1.5, “Some Career Paths in Psychology,” will help you consider the answers to these questions. You can learn more about these different fields of psychology and the careers associated with them at

Table 1.5 Some Career Paths in Psychology.
Psychology field Description Career opportunities
Biopsychology and neuroscience This field examines the physiological bases of behaviour in animals and humans by studying the functioning of different brain areas and the effects of hormones and neurotransmitters on behaviour. Most biopsychologists work in research settings—for instance, at universities, for the federal government, and in private research labs.
Clinical and counselling psychology These are the largest fields of psychology. The focus is on the assessment, diagnosis, causes, and treatment of mental disorders. Clinical and counseling psychologists provide therapy to patients with the goal of improving their life experiences. They work in hospitals, schools, social agencies, and private practice. Because the demand for this career is high, entry to academic programs is highly competitive.
Cognitive psychology This field uses sophisticated research methods, including reaction time and brain imaging, to study memory, language, and thinking of humans. Cognitive psychologists work primarily in research settings, although some (such as those who specialize in human-computer interactions) consult for businesses.
Developmental psychology These psychologists conduct research on the cognitive, emotional, and social changes that occur across the lifespan. Many work in research settings, although others work in schools and community agencies to help improve and evaluate the effectiveness of intervention programs such as Head Start.
Forensic psychology Forensic psychologists apply psychological principles to understand the behaviour of judges, lawyers, courtroom juries, and others in the criminal justice system. Forensic psychologists work in the criminal justice system. They may testify in court and may provide information about the reliability of eyewitness testimony and jury selection.
Health psychology Health psychologists are concerned with understanding how biology, behaviour, and the social situation influence health and illness. Health psychologists work with medical professionals in clinical settings to promote better health, conduct research, and teach at universities.
Industrial-organizational and environmental psychology Industrial-organizational psychology applies psychology to the workplace with the goal of improving the performance and well-being of employees. There are a wide variety of career opportunities in these fields, generally working in businesses. These psychologists help select employees, evaluate employee performance, and examine the effects of different working conditions on behaviour. They may also work to design equipment and environments that improve employee performance and reduce accidents.
Personality psychology These psychologists study people and the differences among them. The goal is to develop theories that explain the psychological processes of individuals, and to focus on individual differences. Most work in academic settings, but the skills of personality psychologists are also in demand in business—for instance, in advertising and marketing. PhD programs in personality psychology are often connected with programs in social psychology.
School and educational psychology This field studies how people learn in school, the effectiveness of school programs, and the psychology of teaching. School psychologists work in elementary and secondary schools or school district offices with students, teachers, parents, and administrators. They may assess children’s psychological and learning problems and develop programs to minimize the impact of these problems.
Social and cross-cultural psychology This field examines people’s interactions with other people. Topics of study include conformity, group behaviour, leadership, attitudes, and personal perception. Many social psychologists work in marketing, advertising, organizational, systems design, and other applied psychology fields.
Sports psychology This field studies the psychological aspects of sports behaviour. The goal is to understand the psychological factors that influence performance in sports, including the role of exercise and team interactions. Sports psychologists work in gyms, schools, professional sports teams, and other areas where sports are practiced.

Psychology in Everyday Life: How to Effectively Learn and Remember

One way that the findings of psychological research may be particularly helpful to you is in terms of improving your learning and study skills. Psychological research has provided a substantial amount of knowledge about the principles of learning and memory. This information can help you do better in this and other courses, and can also help you better learn new concepts and techniques in other areas of your life. The most important thing you can learn in college is how to better study, learn, and remember. These skills will help you throughout your life, as you learn new jobs and take on other responsibilities. There are substantial individual differences in learning and memory, such that some people learn faster than others. But even if it takes you longer to learn than you think it should, the extra time you put into studying is well worth the effort. And you can learn to learn—learning to study effectively and to remember information is just like learning any other skill, such as playing a sport or a video game.

To learn well, you need to be ready to learn. You cannot learn well when you are tired, when you are under stress, or if you are abusing alcohol or drugs. Try to keep a consistent routine of sleeping and eating. Eat moderately and nutritiously, and avoid drugs that can impair memory, particularly alcohol. There is no evidence that stimulants such as caffeine, amphetamines, or any of the many “memory-enhancing drugs” on the market will help you learn (Gold, Cahill, & Wenk, 2002; McDaniel, Maier, & Einstein, 2002). Memory supplements are usually no more effective than drinking a can of sugared soda, which releases glucose and thus improves memory slightly.

Psychologists have studied the ways that best allow people to acquire new information, to retain it over time, and to retrieve information that has been stored in our memories. One important finding is that learning is an active process. To acquire information most effectively, we must actively manipulate it. One active approach is rehearsal—repeating the information that is to be learned over and over again. Although simple repetition does help us learn, psychological research has found that we acquire information most effectively when we actively think about or elaborate on its meaning and relate the material to something else. When you study, try to elaborate by connecting the information to other things that you already know. If you want to remember the different schools of psychology, for instance, try to think about how each of the approaches is different from the others. As you compare the approaches, determine what is most important about each one and then relate it to the features of the other approaches.

In an important study showing the effectiveness of elaborative encoding, Rogers, Kuiper, and Kirker (1977) found that students learned information best when they related it to aspects of themselves (a phenomenon known as the self-reference effect). This research suggests that imagining how the material relates to your own interests and goals will help you learn it. An approach known as the method of loci involves linking each of the pieces of information that you need to remember to places that you are familiar with. You might think about the house that you grew up in and the rooms in it. You could put the behaviourists in the bedroom, the structuralists in the living room, and the functionalists in the kitchen. Then when you need to remember the information, you retrieve the mental image of your house and should be able to “see” each of the people in each of the areas.

One of the most fundamental principles of learning is known as the spacing effect. Both humans and animals more easily remember or learn material when they study the material in several shorter study periods over a longer period of time, rather than studying it just once for a long period of time. Cramming for an exam is a particularly ineffective way to learn. Psychologists have also found that performance is improved when people set difficult yet realistic goals for themselves (Locke & Latham, 2006). You can use this knowledge to help you learn. Set realistic goals for the time you are going to spend studying and what you are going to learn, and try to stick to those goals. Do a small amount every day, and by the end of the week you will have accomplished a lot.

Our ability to adequately assess our own knowledge is known as metacognition. Research suggests that our metacognition may make us overconfident, leading us to believe that we have learned material even when we have not. To counteract this problem, don’t just go over your notes again and again. Instead, make a list of questions and then see if you can answer them. Study the information again and then test yourself again after a few minutes. If you made any mistakes, study again. Then wait for a half hour and test yourself again. Then test again after one day and after two days. Testing yourself by attempting to retrieve information in an active manner is better than simply studying the material because it will help you determine if you really know it. In summary, everyone can learn to learn better. Learning is an important skill, and following the previously mentioned guidelines will likely help you learn better.

Key Takeaways

  • The first psychologists were philosophers, but the field became more empirical and objective as more sophisticated scientific approaches were developed and employed.
  • Some basic questions asked by psychologists include those about nature versus nurture, free will versus determinism, accuracy versus inaccuracy, and conscious versus unconscious processing.
  • The structuralists attempted to analyze the nature of consciousness using introspection.
  • The functionalists based their ideas on the work of Darwin, and their approaches led to the field of evolutionary psychology.
  • The behaviourists explained behaviour in terms of stimulus, response, and reinforcement, while denying the presence of free will.
  • Cognitive psychologists study how people perceive, process, and remember information.
  • Psychodynamic psychology focuses on unconscious drives and the potential to improve lives through psychoanalysis and psychotherapy.
  • The social-cultural approach focuses on the social situation, including how cultures and social norms influence our behaviour.

Exercises and Critical Thinking

  1. What type of questions can psychologists answer that philosophers might not be able to answer as completely or as accurately? Explain why you think psychologists can answer these questions better than philosophers can.
  2. Choose one of the major questions of psychology and provide some evidence from your own experience that supports one side or the other.
  3. Choose two of the fields of psychology discussed in this section and explain how they differ in their approaches to understanding behaviour and the level of explanation at which they are focused.


Aarts, H., Custers, R., & Wegner, D. M. (2005). On the inference of personal authorship: Enhancing experienced agency by priming effect information. Consciousness and Cognition: An International Journal, 14(3), 439–458.

Asch, S. E. (1952). Social Psychology. Englewood Cliffs, NJ: Prentice Hall.

Bartlett, F. C. (1932). Remembering. Cambridge: Cambridge University Press.

Beck, H. P., Levinson, S., & Irons, G. (2009). Finding Little Albert: A journey to John B. Watson’s infant laboratory. American Psychologist, 64(7), 605–614.

Benjamin, L. T., Jr., & Baker, D. B. (2004). From seance to science: A history of the profession of psychology in America. Belmont, CA: Wadsworth/Thomson.

Buss, D. M. (2000). The dangerous passion: Why jealousy is as necessary as love and sex. New York, NY: Free Press.

Byrne, D. (1969). Attitudes and attraction. In L. Berkowitz (Ed.), Advances in experimental social psychology (Vol. 4, pp. 35–89). New York, NY: Academic Press.

Chan, D. K. S., Gelfand, M. J., Triandis, H. C., & Tzeng, O. (1996). Tightness-looseness revisited: Some preliminary analyses in Japan and the United States. International Journal of Psychology, 31, 1–12.

Cialdini, R. B. (1993). Influence: Science and practice (3rd ed.). New York, NY: Harper Collins College.

Dennett, D. (1995). Darwin’s dangerous idea: Evolution and the meanings of life. New York, NY: Simon and Schuster.

Dijksterhuis, A., Preston, J., Wegner, D. M., & Aarts, H. (2008). Effects of subliminal priming of self and God on self-attribution of authorship for events. Journal of Experimental Social Psychology, 44(1), 2–9.

Festinger, L. (1954). A theory of social comparison processes. Human Relations, 7, 117–140.

Fiske, S. T. (2003). Social beings. Hoboken, NJ: John Wiley & Sons.

Fiske, A., Kitayama, S., Markus, H., & Nisbett, R. (1998). The cultural matrix of social psychology. In D. Gilbert, S. Fiske, & G. Lindzey (Eds.), The handbook of social psychology (4th ed., pp. 915–981). New York, NY: McGraw-Hill.

Gold, P. E., Cahill, L., & Wenk, G. L. (2002). Ginkgo biloba: A cognitive enhancer? Psychological Science in the Public Interest, 3(1), 2–11.

Gould, S. J., & Lewontin, R. C. (1979). The spandrels of San Marco and the Panglossian paradigm: A critique of the adaptationist programme. In Proceedings of the Royal Society of London (Series B), 205, 581–598.

Harris, J. (1998). The nurture assumption: Why children turn out the way they do. New York, NY: Touchstone Books.

Hunt, M. (1993). The story of psychology. New York, NY: Anchor Books.

Ilardi, S. S., & Feldman, D. (2001). The cognitive neuroscience paradigm: A unifying metatheoretical framework for the science and practice of clinical psychology. Journal of Clinical Psychology, 57(9), 1067–1088.

James, W. (1890). The principles of psychology. New York, NY: Dover.

Libet, B. (1985). Unconscious cerebral initiative and the role of conscious will in voluntary action. Behavioral and Brain Sciences, 8(4), 529–566.

Locke, E. A., & Latham, G. P. (2006). New directions in goal-setting theory. Current Directions in Psychological Science, 15(5), 265–268.

Markus, H. R., Kitayama, S., & Heiman, R. J. (1996). Culture and “basic” psychological principles. In E. T. Higgins & A. W. Kruglanski (Eds.), Social psychology: Handbook of basic principles (pp. 857–913). New York, NY: Guilford Press.

Matsuhashi, M., & Hallett, M. (2008). The timing of the conscious intention to move. European Journal of Neuroscience, 28(11), 2344–2351.

Matsumoto, D. (Ed.). (2001). The handbook of culture and psychology. New York, NY: Oxford University Press.

McDaniel, M.A., Maier, S.F., & Einstein, G.O. (2002). Brain-specific nutrients: A memory cure? Psychological Science in the Public Interest, 3, 11-37.

Mesoudi, A. (2009). How cultural evolutionary theory can inform social psychology and vice versa. Psychological Review, 116(4), 929–952.

Moore, B. E., & Fine, B. D. (1995). Psychoanalysis: The major concepts. New Haven, CT: Yale University Press.

Pinker, S. (2002). The blank slate: The modern denial of human nature. New York, NY: Penguin Putnam.

Rogers, T. B., Kuiper, N. A., & Kirker, W. S. (1977). Self-reference and the encoding of personal information. Journal of Personality & Social Psychology, 35(9), 677–688.

Skinner, B. (1957). Verbal behavior. Acton, MA: Copley; Skinner, B. (1968). The technology of teaching. New York, NY: Appleton-Century-Crofts.

Skinner, B. (1972). Beyond freedom and dignity. New York, NY: Vintage Books.

Soon, C. S., Brass, M., Heinze, H.-J., & Haynes, J.-D. (2008). Unconscious determinants of free decisions in the human brain. Nature Neuroscience, 11(5), 543–545.

Tooby, J., & Cosmides, L. (1992). The psychological foundations of culture. In J. H. Barkow & L. Cosmides (Eds.), The adapted mind: Evolutionary psychology and the generation of culture (p. 666). New York, NY: Oxford University Press.

Watson, J. B., & Rayner, R. (1920). Conditioned emotional reactions. Journal of Experimental Psychology, 3(1), 1–14.

Wegner, D. M. (2002). The illusion of conscious will. Cambridge, MA: MIT Press.

Wegner, D. M. (2003). The mind’s best trick: How we experience conscious will. Trends in Cognitive Sciences, 7(2), 65–69.

Yang, Y.-J., & Chiu, C.-Y. (2009). Mapping the structure and dynamics of psychological knowledge: Forty years of APA journal citations (1970–2009). Review of General Psychology, 13(4), 349–356.

Image Attributions

Figure 1.2:

Figure 1.3: Plato photo ( courtesy of Bust of Aristotle by Giovanni Dall’Orto, (, _Roma._Foto_di_Giovanni_Dall%27Orto.jpg) used under CC BY license.

Figure 1.4: Wundt research group by Kenosis, ( is in the public domain; Edward B. Titchener ( is in the public domain.

Figure 1.5: William James (,_philosopher.jpg). Charles Darwin by George Richmond ( is in public domain.

Figure 1.6: Sigmund Freud by Max Halberstadt ( is in public domain.

Figure 1.7: B.F. Skinner at Harvard circa 1950 ( _1950.jpg) used under CC BY 3.0 license (

Figure 1.8:West Wittering Wonderful As Always” by Gareth Williams ( is licensed under CC BY 2.0. “Family playing a board game” by Bill Branson ( is in public domain.



Chapter 1 Summary, Key Terms, and Self-Test

Charles Stangor, Jennifer Walinga, and Jorden A. Cummings


Psychology is the scientific study of mind and behaviour. Most psychologists work in research laboratories, hospitals, and other field settings where they study the behaviour of humans and animals. Some psychologists are researchers and others are practitioners, but all psychologists use scientific methods to inform their work.

Although it is easy to think that everyday situations have common sense answers, scientific studies have found that people are not always as good at predicting outcomes as they often think they are. The hindsight bias leads us to think that we could have predicted events that we could not actually have predicted.

Employing the scientific method allows psychologists to objectively and systematically understand human behaviour.

Psychologists study behaviour at different levels of explanation, ranging from lower biological levels to higher social and cultural levels. The same behaviours can be studied and explained within psychology at different levels of explanation.

The first psychologists were philosophers, but the field became more objective as more sophisticated scientific approaches were developed and employed. Some of the most important historical schools of psychology include structuralism, functionalism, behaviourism, and psychodynamic psychology. Cognitive psychology, evolutionary psychology, and social-cultural psychology are some important contemporary approaches.

Some of the basic questions asked by psychologists, both historically and currently, include those about the relative roles of nature versus nurture in behaviour, free will versus determinism, accuracy versus inaccuracy, and conscious versus unconscious processing.

Psychological phenomena are complex, and making predictions about them is difficult because they are multiply determined at different levels of explanation. Research has found that people are frequently unaware of the causes of their own behaviours.

There are a variety of available career choices within psychology that provide employment in many different areas of interest.

Key Terms

  • Behaviourism
  • Cognitive psychology
  • Collectivism
  • Conformity
  • Culture
  • Data
  • Depression
  • Dualism
  • Empirical methods
  • Evolutionary psychology
  • Facts
  • Fitness
  • Heritability of the characteristic
  • Hindsight bias
  • Individual differences
  • Individualism
  • Introspection
  • Levels of explanation
  • Multiply determined
  • Neuroimaging
  • Psychoanalysis
  • Psychodynamic psychology
  • Psychologist-practitioners
  • Psychology
  • Repressed
  • Research psychologists
  • School of functionalism
  • Scientific method
  • Social norms
  • Social-cultural psychology
  • Structuralism
  • Theory of natural selection

Self Test

An interactive or media element has been excluded from this version of the text. You can view it online here:

Direct link to self-test:


Chapter 2. Introduction to Major Perspectives


Chapter 2 Introduction

Jennifer Walinga

Scientific areas of study are often guided by a paradigm (prevailing model). In astronomy, Ptolemy placed Earth at the centre of the universe and thereby shaped the way people conceived of all things related to that science. Later, the Copernican paradigm placed the Sun at the centre of the universe, which shifted perspectives and understandings. A paradigm presents a generally accepted approach to the whole field during a particular era. A paradigm equips scientists and practitioners with a set of assumptions about what is to be studied as well as a set of research methods for how those phenomena should be examined. In physics, the Aristotelian view of the composition of matter prevailed until Newton’s 17th-century mechanical model emerged and overtook it, which in turn was expanded by Einstein’s 20th-century relativity paradigm (Watson, 1967). With each shift in knowledge and insight, a form of revolution occurs (Kuhn, 1970).

However, psychology lacks a guiding or prevailing paradigm due to its youth and scope. Instead, the field of psychology has travelled the course of several movements, schools of thought, or perspectives, which provide frameworks for organizing data and connecting theories but no overall guidance or stance. In psychology, each new line of thinking emerges in response to another. New ideas or ways of thinking challenge prior thinking and require further research in order to resolve, clarify, or expand tensions between concepts. Often, new methodologiesResearch study design principles. emerge as well, and new questions demand new tools or approaches in order to be answered.

Major psychological perspectives discussed by researchers and practitioners today include biological, psychodynamic, behaviouristic, humanistic, cognitive, and evolutionary perspectives (Figure 2.1, “Major Psychological Perspectives Timeline”). It appears that a new perspective emerges every 20 to 30 years.

Psychological perspectives over time. Long description available.
Figure 2.1  Major Psychological Perspectives Timeline [Long Description] (by J. Walinga)

This list of perspectives changes, of course, as the field of psychology grows and evolves, and as our conceptualization of psychology expands and develops. The first structuralist psychologists, such as Wilhelm Wundt and Edward B. Titchener of the late 1800s, thought of psychology in biological or physiological terms and focused on the elements of human experience and sensation — the “what” of human experience. But the wave of functionalist, behavioural, and cognitive psychologists to follow began to include the “how” of human experience. Influenced by Charles Darwin’s theories, William James and others later began to consider the “why” of human experience by focusing on interactions between mind and body, including perceptions and emotions, as well as the influence of environment on human experience (Figure 2.2, “The Elements of Psychology”).

Three elements of phsychology. Long description available.
Figure 2.2  The Elements of Psychology [Long Description] (by J. Walinga)

Reflecting on psychological developments today (e.g., positive psychology, multiple intelligences, systems thinking), we can foresee psychology moving toward an integrative approach that incorporates much of the prior learning that has come before it. Dr. Evan Thompson, a professor of philosophy at the University of British Columbia, who works in the fields of cognitive science, philosophy of mind, phenomenology, and cross-cultural philosophy, especially Asian philosophy and contemporary Buddhist philosophy in dialogue with Western philosophy and science, speaks and writes about an integrative psychology, which is psychology that combines the nature and actions of mind, body, and spirit (Varela, Rosch, & Thompson, 1992). Perhaps an integrative perspective will be the next developmental stage for the field of psychology and will move the field that much closer to its own established paradigm.


Freud, S. (1900). The interpretation of dreams. In J. Strachey (Ed. & Trans.), The standard edition of the complete works of Sigmund Freud (Vol. 4). London: Hogarth Press.

Kuhn, T. S. (1970). The structure of scientific revolutions (2nd ed.). Chicago: University of Chicago Press.

Maslow, A. H. (1954).  Motivation and personality. New York: Harper.

Neisser, U. (1967). Cognitive Psychology. Englewood Cliffs, NJ: Prentice Hall.

Pavlov, I. P. (1927). Conditional reflexes (G. V. Anrep, Trans.). New York: Oxford University Press.

Rogers, C. R. (1942). Counseling and psychotherapy: Newer concepts in practice. Boston: Houghton Mifflin.

Varela, Francisco J., Rosch, Eleanor, & Thompson, Evan. (1992). The Embodied Mind: Cognitive Science and Human Experience. Cambridge, MA: MIT Press.

Watson, R. I. (1967). Psychology: A prescriptive science. American Psychologist, 22, 435–443.

Long Descriptions

Figure 2.1 Long Description – Major Psychological Perspectives Timeline.
Physiological Perspective Year Person
Biological – Physiological Psychology 1874 Wundt
1898 Titchener
Phsychodynamic – Interpretation of Dreams 1990 Freud
Behaviouristic – Stimulus and Response 1927 Pavlov
1938 Skinner
Humanistic – Self Actualization 1942 Rogers
1954 Maslow
Cognitive – Information Processing 1967 Neisser
Evolutionary – Adaptation 1999 Buss

Figure 2.2 long description: There are three elements of psychology: Why? How? and What? “Why” deals with things like evolution, environment, and culture. “How” deals with things like cognition, behaviour, and subconscious. “What” deals with sensations, emotions, thoughts, perceptions, and actions.


2.1 Biological Psychology

Jennifer Walinga

Learning Objectives

  1. Understand the core premises of biological psychology and the early thinkers.
  2. Critically evaluate empirical support for various biological psychology theories.
  3. Explore applications and implications of key concepts from this perspective.

Biological psychologists are interested in measuring biological, physiological, or genetic variables in an attempt to relate them to psychological or behavioural variables. Because all behaviour is controlled by the central nervous system, biological psychologists seek to understand how the brain functions in order to understand behaviour. Key areas of focus include sensation and perception; motivated behaviour (such as hunger, thirst, and sex); control of movement; learning and memory; sleep and biological rhythms; and emotion. As technical sophistication leads to advancements in research methods, more advanced topics such as language, reasoning, decision making, and consciousness are now being studied.

Biological psychology has its roots in early structuralist and functionalist psychological studies, and as with all of the major perspectives, it has relevance today. In section 1.2, we discuss the history and development of functionalism and structuralism. In this chapter, we extend this discussion to include the theoretical and methodological aspects of these two approaches within the biological perspective and provide examples of relevant studies.

The early structural and functional psychologists believed that the study of conscious thoughts would be the key to understanding the mind. Their approaches to the study of the mind were based on systematic and rigorous observation, laying the foundation for modern psychological experimentation. In terms of research focus, Wundt and Titchener explored topics such as attention span, reaction time, vision, emotion, and time perception, all of which are still studied today.

Wundt’s primary method of research was introspection, which involves training people to concentrate and report on their conscious experiences as they react to stimuli. This approach is still used today in modern neuroscience research; however, many scientists criticize the use of introspection for its lack of empirical approach and objectivity. Structuralism was also criticized because its subject of interest – the conscious experience – was not easily studied with controlled experimentation. Structuralism’s reliance on introspection, despite Titchener’s rigid guidelines, was criticized for its lack of reliability. Critics argued that self-analysis is not feasible, and that introspection can yield different results depending on the subject. Critics were also concerned about the possibility of retrospection, or the memory of sensation rather than the sensation itself.

Today, researchers argue for introspective methods as crucial for understanding certain experiences and contexts.Two Minnesota researchers (Jones & Schmid, 2000) used autoethnography, a narrative approach to introspective analysis (Ellis, 1999), to study the phenomenological experience of the prison world and the consequent adaptations and transformations that it evokes. Jones, serving a year-and-a-day sentence in a maximum security prison, relied on his personal documentation of his experience to later study the psychological impacts of his experience.

From Structuralism to Functionalism

As structuralism struggled to survive the scrutiny of the scientific method, new approaches to studying the mind were sought. One important alternative was functionalism, founded by William James in the late 19th century, described and discussed in his two-volume publication The Principles of Psychology (1890) (see Chapter 1.2 for details). Built on structuralism’s concern for the anatomy of the mind, functionalism led to greater concern about the functions of the mind, and later on to behaviourism.

One of James’s students, James Angell, captured the functionalist perspective in relation to a discussion of free will in his 1906 text Psychology: An Introductory Study of the Structure and Function of Human Consciousness:

Inasmuch as consciousness is a systematising, unifying activity, we find that with increasing maturity our impulses are commonly coordinated with one another more and more perfectly. We thus come to acquire definite and reliable habits of action. Our wills become formed. Such fixation of modes of willing constitutes character. The really good man is not obliged to hesitate about stealing. His moral habits all impel him immediately and irrepressibly away from such actions. If he does hesitate, it is in order to be sure that the suggested act is stealing, not because his character is unstable. From one point of view the development of character is never complete, because experience is constantly presenting new aspects of life to us, and in consequence of this fact we are always engaged in slight reconstructions of our modes of conduct and our attitude toward life. But in a practical common-sense way most of our important habits of reaction become fixed at a fairly early and definite time in life.

Functionalism considers mental life and behaviour in terms of active adaptation to the person’s environment. As such, it provides the general basis for developing psychological theories not readily testable by controlled experiments such as applied psychology. William James’s functionalist approach to psychology was less concerned with the composition of the mind than with examining the ways in which the mind adapts to changing situations and environments. In functionalism, the brain is believed to have evolved for the purpose of bettering the survival of its carrier by acting as an information processor.A system for taking information in one form and transforming it into another. In processing information the brain is considered to execute functions similar to those executed by a computer and much like what is shown in Figure 2.3 below of a complex adaptive system.

Figure 2.3 Complex Adaptive System. Behaviour is influenced by information gathered from a changing external environment.

The functionalists retained an emphasis on conscious experience. John Dewey, George Herbert Mead, Harvey A. Carr, and especially James Angell were the additional proponents of functionalism at the University of Chicago. Another group at Columbia University, including James McKeen Cattell, Edward L. Thorndike, and Robert S. Woodworth, shared a functionalist perspective.

Biological psychology is also considered reductionist. For the reductionist, the simple is the source of the complex. In other words, to explain a complex phenomenon (like human behaviour) a person needs to reduce it to its elements. In contrast, for the holist, the whole is more than the sum of the parts. Explanations of a behaviour at its simplest level can be deemed reductionist. The experimental and laboratory approach in various areas of psychology (e.g., behaviourist, biological, cognitive) reflects a reductionist position. This approach inevitably must reduce a complex behaviour to a simple set of variables that offer the possibility of identifying a cause and an effect (i.e., the biological approach suggests that psychological problems can be treated like a disease and are therefore often treatable with drugs).

The brain and its functions (Figure 2.4) garnered great interest from the biological psychologists and continue to be a focus for psychologists today. Cognitive psychologists rely on the functionalist insights in discussing how affect, or emotion, and environment or events interact and result in specific perceptions. Biological psychologists study the human brain in terms of specialized parts, or systems, and their exquisitely complex relationships. Studies have shown neurogenesisThe generation or growth of new brain cells, specifically when neurons are created from neural stem cells. in the hippocampus (Gage, 2003). In this respect, the human brain is not a static mass of nervous tissue. As well, it has been found that influential environmental factors operate throughout the life span. Among the most negative factors, traumatic injury and drugs can lead to serious destruction. In contrast, a healthy diet, regular programs of exercise, and challenging mental activities can offer long-term, positive impacts on the brain and psychological development (Kolb, Gibb, & Robinson, 2003).

Figure 2.4 Functions of the Brain. Different parts of the brain are responsible for different things.

The brain comprises four lobes:

  1. Frontal lobe: also known as the motor cortex, this portion of the brain is involved in motor skills, higher level cognition, and expressive language.
  2. Occipital lobe: also known as the visual cortex, this portion of the brain is involved in interpreting visual stimuli and information.
  3. Parietal lobe: also known as the somatosensory cortex, this portion of the brain is involved in the processing of other tactile sensory information such as pressure, touch, and pain.
  4. Temporal lobe: also known as the auditory cortex, this portion of the brain is involved in the interpretation of the sounds and language we hear.

Another important part of the nervous system is the peripheral nervous system, which is divided into two parts:

  1. The somatic nervous system, which controls the actions of skeletal muscles.
  2. The autonomic nervous system, which regulates automatic processes such as heart rate, breathing, and blood pressure. The autonomic nervous system, in turn has two parts:
    1. The sympathetic nervous system, which controls the fight-or-flight response, a reflex that prepares the body to respond to danger in the environment.
    2. The parasympathetic nervous system, which works to bring the body back to its normal state after a fight-or-flight response.

Research Focus: Internal versus External Focus and Performance

Within the realm of sport psychology, Gabrielle Wulf and colleagues from the University of Las Vegas Nevada have studied the role of internal and external focus on physical performance outcomes such as balance, accuracy, speed, and endurance. In one experiment they used a ski-simulator and directed participants’ attention to either the pressure they exerted on the wheels of the platform on which they were standing (external focus), or to their feet that were exerting the force (internal focus). On a retention test, the external focus group demonstrated superior learning (i.e., larger movement amplitudes) compared with both the internal focus group and a control group without focus instructions. The researchers went on to replicate findings in a subsequent experiment that involved balancing on a stabilometer. Again, directing participants’ attention externally, by keeping markers on the balance platform horizontal, led to more effective balance learning than inducing an internal focus, by asking them to try to keep their feet horizontal. The researchers showed that balance performance or learning, as measured by deviations from a balanced position, is enhanced when the performers’ attention is directed to minimizing movements of the platform or disk as compared to those of their feet. Since the initial studies, numerous researchers have replicated the benefits of an external focus for other balance tasks (Wulf, Höß, & Prinz, 1998).

Another balance task, riding a paddle boat, was used by Totsika and Wulf (2003). With instructions to focus on pushing the pedals forward, participants showed more effective learning compared to participants with instructions to focus on pushing their feet forward. This subtle difference in instructions is important for researchers of attentional focus. The first instruction to push the pedal is external, with the participant focusing on the pedal and allowing the body to figure out how to push the pedal. The second instruction to push the feet forward is internal, with the participant concentrating on making his or her feet move.

In further biologically oriented psychological research at the University of Toronto, Schmitz, Cheng, and De Rosa (2010) showed that visual attentionthe brain’s ability to selectively filter unattended or unwanted information from reaching awareness — diminishes with age, leaving older adults less capable of filtering out distracting or irrelevant information. This age-related “leaky” attentional filter fundamentally impacts the way visual information is encoded into memory. Older adults with impaired visual attention have better memory for “irrelevant” information. In the study, the research team examined brain images using functional magnetic resonance imaging (fMRI) on a group of young (mean age = 22 years) and older adults (mean age = 77 years) while they looked at pictures of overlapping faces and places (houses and buildings). Participants were asked to pay attention only to the faces and to identify the gender of the person. Even though they could see the place in the image, it was not relevant to the task at hand (Read about the study’s findings at

The authors noted:

In young adults, the brain region for processing faces was active while the brain region for processing places was not. However, both the face and place regions were active in older people. This means that even at early stages of perception, older adults were less capable of filtering out the distracting information. Moreover, on a surprise memory test 10 minutes after the scan, older adults were more likely to recognize what face was originally paired with what house.

The findings suggest that under attentionally demanding conditions, such as a person looking for keys on a cluttered table, age-related problems with “tuning in” to the desired object may be linked to the way in which information is selected and processed in the sensory areas of the brain. Both the relevant sensory information — the keys — and the irrelevant information — the clutter — are perceived and encoded more or less equally. In older adults, these changes in visual attention may broadly influence many of the cognitive deficits typically observed in normal aging, particularly memory.

Key Takeaways

  • Biological psychology – also known as biopsychology or psychobiology – is the application of the principles of biology to the study of mental processes and behaviour.
  • Biological psychology as a scientific discipline emerged from a variety of scientific and philosophical traditions in the 18th and 19th centuries.
  • In The Principles of Psychology (1890), William James argued that the scientific study of psychology should be grounded in an understanding of biology.
  • The fields of behavioural neuroscience, cognitive neuroscience, and neuropsychology are all subfields of biological psychology.
  • Biological psychologists are interested in measuring biological, physiological, or genetic variables in an attempt to relate them to psychological or behavioural variables.

Exercises and Critical Thinking

  1. Try this exercise with your group: Take a short walk together without talking to or looking at one another. When you return to the classroom, have each group member write down what they saw, felt, heard, tasted, and smelled. Compare and discuss reflecting on some of the assumptions and beliefs of the structuralists. Consider what might be the reasons for the differences and similarities.
  2. Where can you see evidence of insights from biological psychology in some of the applications of psychology that you commonly experience today (e.g., sport, leadership, marketing, education)?
  3. Study the functions of the brain and reflect on whether you tend toward left- or right-brain tendencies.

Image Attributions

Figure 2.3: Complex Adaptive System by Acadac ( is in the public domain.

Figure 2.4: Left and Right Brain by Webber ( is in the public domain.


Angell, James Rowland. (1906).”Character and the Will”, Chapter 22 in Psychology: An Introductory Study of the Structure and Function of Human Consciousness, Third edition, revised. New York: Henry Holt and Company, p. 376-381.

Ellis, Carolyn. (1999). Heartful Autoethnography. Qualitative Health Research, 9(53), 669-683.

Gage, F. H. (2003, September). Brain, repair yourself. Scientific American, 46–53.

James, W. (1890). The Principles of Psychology. New York, NY: Henry Holt and Co.

Jones, R.S. & Schmid, T. J. (2000). Doing Time: Prison experience and identity. Stamford, CT: JAI Press.

Kolb, B., Gibb, K., & Robinson, T. E. (2003). Brain plasticity and behavior. Current Directions in Psychological Science, 12, 1–5.

Schmitz, T.W., Cheng, F.H. & De Rosa, E. (2010). Failing to ignore: paradoxical neural effects of perceptual load on early attentional selection in normal aging. Journal of Neuroscience, 30(44), 14750 –14758.

Totsika, V., & Wulf, G. (2003). The influence of external and internal foci of attention on transfer to novel situations and skills. Research Quarterly Exercise and Sport, 74, 220–225.

Wulf, G., Höß, M., & Prinz, W. (1998). Instructions for motor learning: Differential effects of internal versus external focus of attention. Journal of Motor Behavior, 30, 169–179.


2.2 Psychodynamic Psychology

Jennifer Walinga

Learning Objectives

  1. Understand some of the psychological forces underlying human behaviour.
  2. Identify levels of consciousness.
  3. Critically discuss various models and theories of psychodynamic and behavioural psychology.
  4. Understand the concept of psychological types and identify applications and examples in daily life.

Sigmund Freud

The psychodynamic perspective in psychology proposes that there are psychological forces underlying human behaviour, feelings, and emotions. Psychodynamics originated with Sigmund Freud (Figure 2.5) in the late 19th century, who suggested that psychological processes are flows of psychological energy (libido) in a complex brain. In response to the more reductionist approach of biological, structural, and functional psychology movements, the psychodynamic perspective marks a pendulum swing back toward more holistic, systemic, and abstract concepts and their influence on the more concrete behaviours and actions. Freud’s theory of psychoanalysis assumes that much of mental life is unconscious, and that past experiences, especially in early childhood, shape how a person feels and behaves throughout life.

Figure 2.5 Group Photo. Front row (left to right): Sigmund Freud, G. Stanley Hall, Carl Jung; Back row (left to right): Abraham A. Brill, Ernest Jones, Sándor Ferenczi.

Consciousness is the awareness of the self in space and time. It can be defined as human awareness of both internal and external stimuli. Researchers study states of human consciousness and differences in perception in order to understand how the body works to produce conscious awareness. Consciousness varies in both arousal and content, and there are two types of conscious experience: phenomenal, or in the moment, and access, which recalls experiences from memory.

First appearing in the historical records of the ancient Mayan and Incan civilizations, various theories of multiple levels of consciousness have pervaded spiritual, psychological, medical, and moral speculations in both Eastern and Western cultures. The ancient Mayans were among the first to propose an organized sense of each level of consciousness, its purpose, and its temporal connection to humankind. Because consciousness incorporates stimuli from the environment as well as internal stimuli, the Mayans believed it to be the most basic form of existence, capable of evolution. The Incas, however, considered consciousness to be a progression, not only of awareness but of concern for others as well.

Sigmund Freud divided human consciousness into three levels of awareness: the conscious, preconscious, and unconscious. Each of these levels corresponds to and overlaps with Freud’s ideas of the id, ego, and superego. The conscious level consists of all those things we are aware of, including things that we know about ourselves and our surroundings. The preconscious consists of those things we could pay conscious attention to if we so desired, and where many memories are stored for easy retrieval. Freud saw the preconscious as those thoughts that are unconscious at the particular moment in question, but that are not repressed and are therefore available for recall and easily capable of becoming conscious (e.g., the “tip of the tongue” effect). The unconscious consists of those things that are outside of conscious awareness, including many memories, thoughts, and urges of which we are not aware. Much of what is stored in the unconscious is thought to be unpleasant or conflicting; for example, sexual impulses that are deemed “unacceptable.” While these elements are stored out of our awareness, they are nevertheless thought to influence our behaviour.

Figure 2.6  The Levels of Consciousness.

Figure 2.6  illustrates the respective levels of id, ego, and superego. In this diagram, the bright blue line represents the divide between consciousness (above) and unconsciousness (below). Below this line, but above the id, is the preconscious level. The lowest segment is the unconscious.  Like the ego, the superego has conscious and unconscious elements, while the id is completely unconscious. When all three parts of the personality are in dynamic equilibrium, the individual is thought to be mentally healthy. However if the ego is unable to mediate between the id and the superego, an imbalance occurs in the form of psychological distress.

While Freud’s theory remains one of the best known, various schools within the field of psychology have developed their own perspectives. For example:

Most psychodynamic approaches use talk therapy, or psychoanalysis, to examine maladaptive functions that developed early in life and are, at least in part, unconscious.  Psychoanalysis is a type of analysis that involves attempting to affect behavioural change through having patients talk about their difficulties. Practising psychoanalysts today collect their data in much the same way as Freud did, through case studies, but often without the couch. The analyst listens and observes, gathering information about the patient. Psychoanalytic scientists today also collect data in formal laboratory experiments, studying groups of people in more restricted, controlled ways (Cramer, 2000; Westen, 1998).

Carl Jung

Carl Jung (1875-1961) expanded on Freud’s theories, introducing the concepts of the archetype, the collective unconscious, and individuation — or the psychological process of integrating the opposites, including the conscious with the unconscious, while still maintaining their relative autonomy (Figure 2.7). Jung focused less on infantile development and conflict between the id and superego, and more on integration between different parts of the person.

Figure 2.7  Jung’s Theory.

The following are Jung’s concepts that are still prevalent today:

Active imagination: This refers to activating our imaginal processes in waking life in order to tap into the unconscious meanings of our symbols.

Archetypes: These primordial images reflect basic patterns or universal themes common to us all and that are present in the unconscious. These symbolic images exist outside space and time. Examples are the shadow, animus, anima, the old wise person, and the innocent child. There are also nature archetypes, like fire, ocean, river, mountain.

  1. Anima is the archetype symbolizing the unconscious female component of the male psyche. Tendencies or qualities often thought of as feminine.
  2. Animus is the archetype symbolizing the unconscious male component of the female psyche. Tendencies or qualities often thought of as masculine.
  3. Self is the archetype symbolizing the totality of the personality. It represents the striving for unity, wholeness, and integration.
  4. Persona is the mask or image a person presents to the world. It is designed to make a particular impression on others, while concealing a person’s true nature.
  5. Shadow is the side of a personality that a person does not consciously display in public. It may have positive or negative qualities.
  6. Dreams are specific expressions of the unconscious that have a definite, purposeful structure indicating an underlying idea or intention. The general function of dreams is to restore a person’s total psychic equilibrium.
  7. Complexes are usually unconscious and repressed emotionally toned symbolic material that is incompatible with consciousness. Complexes can cause constant psychological disturbances and symptoms of neurosis. With intervention, they can become conscious and greatly reduced in their impact.

Individuation:  Jung believed that a human being is inwardly whole, but that most people have lost touch with important parts of themselves. Through listening to the messages of our dreams and waking imagination, we can contact and reintegrate our different parts. The goal of life is individuation, which is the process of integrating the conscious with the unconscious, synergizing the many components of the psyche. Jung asserted: “Trust that which gives you meaning and accept it as your guide” (Jung, 1951, p. 3). Each human being has a specific nature and calling uniquely his or her own, and unless these are fulfilled through a union of conscious and unconscious, the person can become sick. Today, the term “individuation” is used in the media industry to describe new printing and online technologies that permit “mass customization” of media (newspaper, online, television) so that its contents match each individual user’s unique interests, shifting from the mass media practice of producing the same contents for all readers, viewers, listeners, or online users (Chen, Wang, & Tseng, 2009). Marshall McLuhan, the communications theorist, alluded to this trend in customization when discussing the future of printed books in an electronically interconnected world (McLuhan & Nevitt, 1972).

Mandala: For Jung, the mandala (which is the Sanskrit word for “circle”) was a symbol of wholeness, completeness, and perfection, and symbolized the self.

Mystery: For Jung, life was a great mystery, and he believed that humans know and understand very little of it. He never hesitated to say, “I don’t know,” and he always admitted when he came to the end of his understanding.

Neurosis: Jung had a hunch that what passed for normality often was the very force that shattered the personality of the patient. He proposed that trying to be “normal” violates a person’s inner nature and is itself a form of pathology. In the psychiatric hospital, he wondered why psychiatrists were not interested in what their patients had to say.

Story: Jung concluded that every person has a story, and when derangement occurs, it is because the personal story has been denied or rejected. Healing and integration come when the person discovers or rediscovers his or her own personal story.

Symbol: A symbol is a name, term, or picture that is familiar in daily life, but for Jung it had other connotations besides its conventional and obvious meaning. To Jung, a symbol implied something vague and partially unknown or hidden, and was never precisely defined. Dream symbols carried messages from the unconscious to the rational mind.

Unconscious: This basic tenet, as expressed by Jung, states that all products of the unconscious are symbolic and can be taken as guiding messages. Within this concept, there are two types:

  1. Personal unconscious: This aspect of the psyche does not usually enter an individual’s awareness, but, instead, appears in overt behaviour or in dreams.
  2. Collective unconscious: This aspect of the unconscious manifests in universal themes that run through all human life. The idea of the collective unconscious assumes that the history of the human race, back to the most primitive times, lives on in all people.

Word association test: This is a research technique that Jung used to explore the complexes in the personal unconscious. It consisted of reading 100 words to someone, one at a time, and having the person respond quickly with a word of his or her own.

Psychological Types

According to Jung, people differ in certain basic ways, even though the instincts that drive us are the same. Jung distinguished two general attitudes–introversion and extraversion–and four functions–thinking, feeling, sensing, and intuiting:

  1. Introvert: Inner-directed; needs privacy and space; chooses solitude to recover energy; often reflective.
  2. Extravert: Outer-directed; needs sociability; chooses people as a source of energy; often action-oriented.
  3. Thinking function: Logical; sees cause and effect relations; cool, distant, frank, and questioning.
  4. Feeling function: Creative, warm, intimate; has a sense of valuing positively or negatively. (Note that this is not the same as emotion.)
  5. Sensing function: Sensory; oriented toward the body and senses; detailed, concrete, and present.
  6. Intuitive: Sees many possibilities in situations; goes with hunches; impatient with earthy details; impractical; sometimes not present

The Myers-Briggs Type Indicator (MBTI) assessment is a psychometric questionnaire designed to measure psychological preferences in how people perceive the world and make decisions. The original developers of the Myers-Briggs personality inventory were Katharine Cook Briggs and her daughter, Isabel Briggs-Myers (1980, 1995). Having studied the work of Jung, the mother-daughter team turned their interest in human behaviour into a practical application of the theory of psychological types. They began creating the indicator during World War II, believing that a knowledge of personality preferences would help women who were entering the industrial workforce for the first time to identify the sort of wartime jobs that would be “most comfortable and effective.”

The initial questionnaire became the Myers-Briggs Type Indicator (MBTI), first published in 1962 and emphasizing the value of naturally occurring differences (CAPT, 2012). These preferences were extrapolated from the typological theories proposed by Jung and first published in his 1921 book Psychological Types (Adler & Hull, 2014). Jung theorized that there are four principal psychological functions by which we experience the world: sensation, intuition, feeling, and thinking, with one of these four functions being dominant most of the time. The MBTI provides individuals with a measure of their dominant preferences based on the Jungian functions.

Research Focus: The Theory of Buyer Behaviour

Jungian theory influenced a whole realm of social psychology called Consumer Behaviour (Howard & Sheth, 1968). Consumer behaviour is the study of individuals, groups, or organizations and the processes they use to select, secure, and dispose of products, services, experiences, or ideas to satisfy needs, and the impacts that these processes have on the consumer and society. Blending psychology, sociology, social anthropology, marketing, and economics, the study of consumer behaviour attempts to understand the decision-making processes of buyers, such as how emotions affect buying behaviour (Figure 2.8); it also studies characteristics of individual consumers, such as demographics, and behavioural variables and external influences, such as family, education, and culture, in an attempt to understand people’s desires.

A fancy, fast car in an advertisement stimulates the hypothalams in the brain.
Figure 2.8 Neuromarketing.

The black box model (Sandhusen, 2000) captures this interaction of stimuli, consumer characteristics, decision processes, and consumer responses. Stimuli can be experienced as interpersonal stimuli (between people) or intrapersonal stimuli (within people). The black box model is related to the black box theory of behaviourism, where the focus is set not on the processes inside a consumer, but on the relation between the stimuli and the response of the consumer. The marketing stimuli are planned and processed by the companies, whereas the environmental stimuli are based on social, economic, political, and cultural circumstances of a society. The buyer’s black box contains the buyer characteristics and the decision process, which determines the buyer’s response (Table 2.1).

Table 2.1 Environmental Factors and Buyer’s Black Box Adapted from by J. Walinga.
Environmental Factors Buyer’s Black Box Buyer’s Response
Marketing Stimuli Environmental Stimuli Buyer Characteristics Decision Process
  • product
  • price
  • place
  • promotion
  • economic
  • technological
  • political
  • cultural
  • demographic
  • natural
  • attitudes
  • motivation
  • perceptions
  • personality
  • lifestyle
  • knowledge
  • problem recognition
  • information search
  • alternative evaluation
  • purchase decision
  • post-purchase behaviour
  • product choice
  • brand choice
  • dealer choice
  • purchase timing
  • purchase amount

Dreaming and Psychodynamic Psychology

Freud showed a great interest in the interpretation of human dreams, and his theory centred on the notion of repressed longing — the idea that dreaming allows us to sort through unresolved, repressed wishes. Freud’s theory described dreams as having both latent and manifest content. Latent content relates to deep unconscious wishes or fantasies, while manifest content is superficial and meaningless. Manifest content often masks or obscures latent content.

Theories emerging from the work of Freud include the following:

Threat-simulation theory suggests that dreaming should be seen as an ancient biological defence mechanism. Dreams are thought to provide an evolutionary advantage because of their capacity to repeatedly simulate potential threatening events. This process enhances the neurocognitive mechanisms required for efficient threat perception and avoidance. During much of human evolution, physical and interpersonal threats were serious enough to reward reproductive advantage to those who survived them. Therefore, dreaming evolved to replicate these threats and continually practice dealing with them. This theory suggests that dreams serve the purpose of allowing for the rehearsal of threatening scenarios in order to better prepare an individual for real-life threats.

Expectation fulfillment theory posits that dreaming serves to discharge emotional arousals (however minor) that haven’t been expressed during the day. This practice frees up space in the brain to deal with the emotional arousals of the next day and allows instinctive urges to stay intact. In effect, the expectation is fulfilled (i.e., the action is completed) in the dream, but only in a metaphorical form so that a false memory is not created. This theory explains why dreams are usually forgotten immediately afterwards.

Other neurobiological theories also exist:

Activation-synthesis theory: One prominent neurobiological theory of dreaming is the activation-synthesis theory, which states that dreams don’t actually mean anything. They are merely electrical brain impulses that pull random thoughts and imagery from our memories. The theory posits that humans construct dream stories after they wake up, in a natural attempt to make sense of the nonsensical. However, given the vast documentation of realistic aspects to human dreaming as well as indirect experimental evidence that other mammals (e.g., cats) also dream, evolutionary psychologists have theorized that dreaming does indeed serve a purpose.

Continual-activation theory: The continual-activation theory of dreaming proposes that dreaming is a result of brain activation and synthesis. Dreaming and REM sleep are simultaneously controlled by different brain mechanisms. The hypothesis states that the function of sleep is to process, encode, and transfer data from short-term memory to long-term memory through a process called “consolidation.” However, there is not much evidence to back up consolidation as a theory. NREM (non-rapid eye movement or non-REM) sleep processes the conscious-related memory (declarative memory), and REM (rapid eye movement) sleep processes the unconscious-related memory (procedural memory).

The underlying assumption of continual-activation theory is that during REM sleep, the unconscious part of a brain is busy processing procedural memory. Meanwhile, the level of activation in the conscious part of the brain descends to a very low level as the inputs from the senses are basically disconnected. This triggers the “continual-activation” mechanism to generate a data stream from the memory stores to flow through to the conscious part of the brain.

Nielsen and colleagues (2003) investigated the dimensional structure of dreams by administering the Typical Dreams Questionnaire (TDQ) to 1,181 first-year university students in three Canadian cities. A profile of themes was found that varied little by age, gender, or region; however, differences that were identified correlated with developmental milestones, personality attributes, or sociocultural factors. Factor analysis found that women’s dreams related mostly to negative factors (failure, loss of control, snakes/insects), while men’s dreams related primarily to positive factors (magic/myth, alien life).

Research Focus: Can Dreaming Enhance Problem Solving?

Stemming from Freudian and Jungian theories of dream states, researchers in Lancaster, UK (Sio & Ormerod, 2009; Sio Monaghan, & Ormerod, 2013) and in Alberta, Canada (Both, Needham, & Wood, 2004) explored the role of “incubation” in facilitating problem solving. Incubation is the concept of “sleeping on a problem,” or disengaging from actively and consciously trying to solve a problem, in order to allow, as the theory goes, the unconscious processes to work on the  problem. Incubation can take a variety of forms, such as taking a break, sleeping, or working on another kind of problem either more difficult or less challenging. Findings suggest that incubation can, indeed, have a positive impact on problem-solving outcomes. Interestingly, lower-level cognitive tasks (e.g.,  simple math or language tasks, vacuuming, putting items away) resulted in higher problem-solving outcomes than more challenging tasks (e.g., crossword puzzles, math problems). Educators have also found that taking active breaks increases children’s creativity and problem-solving abilities in classroom settings.

There are several hypotheses that aim to explain the conscious-unconscious effects on problem solving:

  1. Spreading activation: When problem solvers disengage from the problem-solving task, they naturally expose themselves to more information that can serve to inform the problem-solving process. Solvers are sensitized to certain information and can benefit from conceptual combination of disparate ideas related to the problem.
  2. Selective forgetting: Once disengaged from the problem-solving process, solvers are freer to let go of certain ideas or concepts that may be inhibiting the problem-solving process, allowing a cleaner, fresher view of the problem and revealing clearer pathways to solution.
  3. Problem restructuring: When problem solvers let go of the initial problem, they are then freed to restructure or reorganize their representation of the problem and thereby capitalize on relevant information not previously noticed, switch strategies, or rearrange problem information in a manner more conducive to solution pathways.

The study of neural correlates of consciousness (NCC) seeks to link activity within the brain to subjective human experiences in the physical world. Progress in neurophilosophy has come from focusing on the body rather than the mind (Squire, 2008). In this context, the neuronal correlates of consciousness may be viewed as its causes, and consciousness may be thought of as a state-dependent property of some undefined complex, adaptive, and highly interconnected biological system. The NCC constitute the smallest set of neural events and structures sufficient for a given conscious percept or explicit memory (Figure 2.9).

A person sees a dog and the NCC determines how the person consciously perceives the dog.
Figure 2.9  The Neuronal Correlates of Consciousness.

In the investigation into the NCC, our capacity to manipulate visual percepts in time and space has made vision a focus of study. Psychologists have perfected a number of techniques in which the seemingly simple relationship between a physical stimulus in the world and its associated principle in the subject’s mind is disturbed and therefore open for understanding. In this manner the neural mechanisms can be isolated, permitting visual consciousness to be tracked in the brain. In a perceptual illusion, the physical stimulus remains fixed while the perception fluctuates. The best known example is the Necker Cube (Koch, 2004): the 12 lines in the cube can be perceived in one of two different ways in depth (Figure 2.10).

This cube appears to be facing a different direction depending on how you look at it.
Figure 2.10 The Necker Cube.

A number of functional magnetic resonance imaging (fMRI) experiments have identified the activity underlying visual consciousness in humans and demonstrated quite conclusively that activity in various areas of the brain follows the mental perception and not the retinal stimulus (Rees & Frith, 2007), making it possible to link brain activity with perception (Figure 2.11).

A scan of a human brain. Some sections of the brain are lit up in red.
Figure 2.11  fMRI scan.

Key Takeaways

  • Psychodynamic psychology emphasizes the systematic study of the psychological forces that underlie human behaviour, feelings, and emotions and how they might relate to early experience.
  • Consciousness is the awareness of the self in space and time and is defined as human awareness to both internal and external stimuli.
  • Sigmund Freud divided human consciousness into three levels of awareness: the conscious, preconscious, and unconscious. Each of these levels corresponds and overlaps with his ideas of the id, ego, and superego.
  • Most psychodynamic approaches use talk therapy to examine maladaptive functions that developed early in life and are, at least in part, unconscious.
  • Carl Jung expanded upon Freud’s theories, introducing the concepts of the archetype, the collective unconscious, and individuation.
  • Freud’s theory describes dreams as having both latent and manifest content. Latent content relates to deep unconscious wishes or fantasies while manifest content is superficial and meaningless.
  • Unconscious processing includes several theories: threat simulation theory, expectation fulfillment theory, activation synthesis theory, continual activation theory.
  • One application of unconscious processing includes incubation as it relates to problem solving: the concept of “sleeping on a problem” or disengaging from actively and consciously trying to solve a problem in order to allow one’s unconscious processes to work on the  problem.
  • The study of neural correlates of consciousness seeks to link activity within the brain to subjective human experiences in the physical world.
  • In a perceptual illusion, like the Necker Cube, the physical stimulus remains fixed while the perception fluctuates, allowing the neural mechanisms to be isolated and permitting visual consciousness to be tracked in the brain.
  • Activity in the brain can be studied and captured using functional magnetic resonance imaging (fMRI) scans.

Exercises and Critical Thinking

  1. Utilize the principles of the psychodynamic school of thought to reflect on a recent dream you experienced. What might the dream imply or represent? Try to trace one of your qualities or characteristics to a prior experience or learning.
  2. Jung has influenced a variety of practices in psychology today including therapeutic and organizational. Can you identify other areas of society where “archetypes” may play a role?
  3. Debate with your group the value or danger of “mass customization.” What issues or controversies does the concept of customized marketing and product development pose?

Image Attributions

Figure 2.5: Freud Jung in front of Clark Hall ( is in the public domain.

Figure 2.6: Visual representation of Freud’s id, ego and superego and the level of consciousness ( used under CC BY SA 3.0 license (

Figure 2.7: Graphical model of Carl Jung’s theory – English version by Andrzej Brodziak ( used under CC-BY-SA 2.5 Generic license (

Figure 2.8: Neuromarketing schema by Benoit Rochon  ( used under CC BY 3.0 license (

Figure 2.9: Neural Correlates Of Consciousness by Christof Koch ( used under CC BY SA 3.0 license (

Figure 2.10: Necker’s cube, a type of optical illusion by Stevo-88 ( is in the public domain.

Figure 2.11: FMRI scan during working memory tasks by John Graner ( is in the public domain.


Adler, G., & Hull, R. F.C. (2014). Collected Works of C.G. Jung, Volume 6: Psychological Types. Princeton, NJ: Princeton University Press.

Both, L., Needham, D., & Wood, E. (2004). Examining Tasks that Facilitate the Experience of Incubation While Problem-Solving. Alberta Journal of Educational Research, 50(1), 57–67.

Briggs-Myers, Isabel, & Myers, Peter B. (1980, 1995). Gifts differing: Understanding personality type. Mountain View, CA: Davies-Black Publishing.

CAPT (Center for Applications of Psychological Type. (2012). The story of Isabel Briggs Myers. Retrieved from

Chen, Songlin, Wang, Yue, & Tseng, Mitchell (2009). Mass Customization as a Collaborative Engineering Effort. International Journal of Collaborative Engineering, 1(2), 152–167.

Cramer, P. (2000). Defense mechanisms in psychology today. American Psychologist, 55, 637–646.

Howard, J., & Sheth, J.N. (1968). Theory of Buyer Behavior. New York, NY: J. Wiley & Sons.

Jung, C. G. (1951). Aion: Researches into the Phenomenology of the Self (Collected Works Vol. 9 Part 2). Princeton, N.J.: Bollingen.

Koch, Christof (2004). The quest for consciousness: a neurobiological approach. Englewood, US-CO: Roberts & Company Publishers.

McLuhan, Marshall, & Nevitt, Barrington. (1972). Take today: The executive as dropout. New York, NY: Harcourt Brace.

Nielsen, Tore A.,  Zadra, Antonio L., Simard, Valérie Saucier, Sébastien Stenstrom, Philippe Smith, Carlyle, & Kuiken, Don (2003). The typical dreams of Canadian university students dreaming. Journal of the Association for the Study of Dreams, 13(4), 211–235.

Rees G., & Frith C. (2007). Methodologies for identifying the neural correlates of consciousness. In: The Blackwell Companion to Consciousness. Velmans, M. & Schneider, S., (Eds.), pp. 553–66. Blackwell: Oxford, UK.

Sandhusen, R. (2000). Marketing. New York, NY: Barron’s Educational Series.

Sio, U.N., & Ormerod, T.C. (2009). Does incubation enhance problem solving? A meta-analytic review. Psychological Bulletin,135(1), 94–120.

Sio U.N., Monaghan P., & Ormerod T. (2013). Sleep on it, but only if it is difficult: Effects of sleep on problem solving. Memory and Cognition, 41(2), 159–66.

Squire, Larry R. (2008). Fundamental neuroscience (3rd ed.). Waltham, Mass: Academic Press. p. 1256.

Westen, D. (1998). The scientific legacy of Sigmund Freud: Toward a psychodynamically informed psychological science. Psychological Bulletin, 124(3), 333–371.


2.3 Behaviourist Psychology

Jennifer Walinga

Learning Objectives

  1. Understand the principles of behaviourist psychology and how these differ from psychodynamic principles in terms of theory and application.
  2. Distinguish between classical and operant conditioning.
  3. Become familiar with key behaviourist theorists and approaches.
  4. Identify applications of the behaviourist models in modern life.

Emerging in contrast to psychodynamic psychology, behaviourism focuses on observable behaviour as a means to studying the human psyche. The primary tenet of behaviourism is that psychology should concern itself with the observable behaviour of people and animals, not with unobservable events that take place in their minds. The behaviourists criticized the mentalists for their inability to demonstrate empirical evidence to support their claims. The behaviourist school of thought maintains that behaviours can be described scientifically without recourse either to internal physiological events or to hypothetical constructs such as thoughts and beliefs, making behaviour a more productive area of focus for understanding human or animal psychology.

The main influences of behaviourist psychology were Ivan Pavlov (1849-1936), who investigated classical conditioning though often disagreeing with behaviourism or behaviourists; Edward Lee Thorndike (1874-1949), who introduced the concept of reinforcement and was the first to apply psychological principles to learning; John B. Watson (1878-1958), who rejected introspective methods and sought to restrict psychology to experimental methods; and B.F. Skinner (1904-1990), who conducted research on operant conditioning.

The first of these, Ivan Pavlov, is known for his work on one important type of learning, classical conditioning. As we learn, we alter the way we perceive our environment, the way we interpret the incoming stimuli, and therefore the way we interact, or behave. Pavlov, a Russian physiologist, actually discovered classical conditioning accidentally while doing research on the digestive patterns in dogs. During his experiments, he would put meat powder in the mouth of a dog who had tubes inserted into various organs to measure bodily responses. Pavlov discovered that the dog began to salivate before the meat powder was presented to it. Soon the dog began to salivate as soon as the person feeding it entered the room. Pavlov quickly began to gain interest in this phenomenon and abandoned his digestion research in favour of his now famous classical conditioning study.

Basically, Pavlov’s findings support the idea that we develop responses to certain stimuli that are not naturally occurring. When we touch a hot stove, our reflex pulls our hand back. We do this instinctively with no learning involved. The reflex is merely a survival instinct. Pavlov discovered that we make associations that cause us to generalize our response to one stimuli onto a neutral stimuli it is paired with. In other words, hot burner = ouch; stove = burner; therefore, stove = ouch.

In his research with the dogs, Pavlov began pairing a bell sound with the meat powder and found that even when the meat powder was not presented, a dog would eventually begin to salivate after hearing the bell. In this case, since the meat powder naturally results in salivation, these two variables are called the unconditioned stimulus (UCS) and the unconditioned response (UCR), respectively. In the experiment, the bell and salivation are not naturally occurring; the dog is conditioned to respond to the bell. Therefore, the bell is considered the conditioned stimulus (CS), and the salivation to the bell, the conditioned response (CR).

Many of our behaviours today are shaped by the pairing of stimuli. The smell of a cologne, the sound of a certain song, or the occurrence of a specific day of the year can trigger distinct memories, emotions, and associations. When we make these types of associations, we are experiencing classical conditioning.

Operant conditioning is another type of learning that refers to how an organism operates on the environment or how it responds to what is presented to it in the environment (Figure 2.12).

Figure 2.12 Operant Conditioning.

Examples of operant conditioning include the following:

Reinforcement means to strengthen, and is used in psychology to refer to any stimulus which strengthens or increases the probability of a specific response. For example, if you want your dog to sit on command, you may give him a treat every time he sits for you. The dog will eventually come to understand that sitting when told to will result in a treat. This treat is reinforcing the behaviour because the dog likes it and will result in him sitting when instructed to do so. There are four types of reinforcement: positive, negative, punishment, and extinction.

Research has found positive reinforcement is the most powerful of any of these types of operant conditioning responses. Adding a positive to increase a response not only works better, but allows both parties to focus on the positive aspects of the situation. Punishment, when applied immediately following the negative behaviour, can be effective, but results in extinction when it is not applied consistently. Punishment can also invoke other negative responses such as anger and resentment.

Thorndike’s (1898) work with cats and puzzle boxes illustrates the concept of conditioning. The puzzle boxes were approximately 50 cm long, 38 cm wide, and 30 cm tall (Figure 2.13). Thorndike’s puzzle boxes were built so that the cat, placed inside the box, could escape only if it pressed a bar or pulled a lever, which caused the string attached to the door to lift the weight and open the door. Thorndike measured the time it took the cat to perform the required response (e.g., pulling the lever). Once it had learned the response he gave the cat a reward, usually food.

Figure 2.13 Thorndike’s Puzzle Box.

Thorndike found that once a cat accidentally stepped on the switch, it would then press the switch faster in each succeeding trial inside the puzzle box. By observing and recording how long it took a variety of animals to escape through several trials, Thorndike was able to graph the learning curve (graphed as an S-shape). He observed that most animals had difficulty escaping at first, then began to escape faster and faster with each successive puzzle box trial, and eventually levelled off in their escape times. The learning curve also suggested that different species learned in the same way but at different speeds. His finding was that cats, for instance, consistently showed gradual learning.

From his research with puzzle boxes, Thorndike was able to create his own theory of learning (1932):

  1. Learning is incremental.
  2. Learning occurs automatically.
  3. All animals learn the same way.
  4. Law of effect. If an association is followed by satisfaction, it will be strengthened, and if it is followed by annoyance, it will be weakened.
  5. Law of use. The more often an association is used, the stronger it becomes.
  6. Law of disuse. The longer an association is unused, the weaker it becomes.
  7. Law of recency. The most recent response is most likely to reoccur.
  8. Multiple response. An animal will try multiple responses (trial and error) if the first response does not lead to a specific state of affairs.
  9. Set or attitude. Animals are predisposed to act in a specific way.
  10. Prepotency of elements. A subject can filter out irrelevant aspects of a problem and focus on and respond to significant elements of a problem.
  11. Response by analogy. Responses from a related or similar context may be used in a new context.
  12. Identical elements theory of transfer. The more similar the situations are, the greater the amount of information that will transfer. Similarly, if the situations have nothing in common, information learned in one situation will not be of any value in the other situation.
  13. Associative shifting. It is possible to shift any response from occurring with one stimulus to occurring with another stimulus. Associative shift maintains that a response is first made to situation A, then to AB, and then finally to B, thus shifting a response from one condition to another by associating it with that condition.
  14. Law of readiness. A quality in responses and connections that results in readiness to act. Behaviour and learning are influenced by the readiness or unreadiness of responses, as well as by their strength.
  15. Identifiability. Identification or placement of a situation is a first response of the nervous system, which can recognize it. Then connections may be made to one another or to another response, and these connections depend on the original identification. Therefore, a large amount of learning is made up of changes in the identifiability of situations.
  16. Availability. The ease of getting a specific response. For example, it would be easier for a person to learn to touch his or her nose or mouth with closed eyes than it would be to draw a line five inches long with closed eyes.

John B. Watson promoted a change in psychology through his address, Psychology as the Behaviorist Views It (1913), delivered at Columbia University. Through his behaviourist approach, Watson conducted research on animal behaviour, child rearing, and advertising while gaining notoriety for the controversial “Little Albert” experiment. Immortalized in introductory psychology textbooks, this experiment set out to show how the recently discovered principles of classical conditioning could be applied to condition fear of a white rat into Little Albert, an 11-month-old boy. Watson and Rayner (1920) first presented to the boy a white rat and observed that the boy was not afraid. Next they presented him with a white rat and then clanged an iron rod. Little Albert responded by crying. This second presentation was repeated several times. Finally, Watson and Rayner presented the white rat by itself and the boy showed fear. Later, in an attempt to see if the fear transferred to other objects, Watson presented Little Albert with a rabbit, a dog, and a fur coat. He cried at the sight of all of them. This study demonstrated how emotions could become conditioned responses.

Burrhus Frederic Skinner called his particular brand of behaviourism radical behaviourism (1974). Radical behaviourism is the philosophy of the science of behaviour. It seeks to understand behaviour as a function of environmental histories of reinforcing consequences. This applied behaviourism does not accept private events such as thinking, perceptions, and unobservable emotions in a causal account of an organism’s behaviour.

While a researcher at Harvard, Skinner invented the operant conditioning chamber, popularly referred to as the Skinner box (Figure 2.14), used to measure responses of organisms (most often rats and pigeons) and their orderly interactions with the environment. The box had a lever and a food tray, and a hungry rat inside the box could get food delivered to the tray by pressing the lever. Skinner observed that when a rat was first put into the box, it would wander around, sniffing and exploring, and would usually press the bar by accident, at which point a food pellet would drop into the tray. After that happened, the rate of bar pressing would increase dramatically and remain high until the rat was no longer hungry.

Figure 2.14 Skinner Box.

Negative reinforcement was also exemplified by Skinner placing rats into an electrified chamber that delivered unpleasant shocks. Levers to cut the power were placed inside these boxes. By running a current through the box, Skinner noticed that the rats, after accidentally pressing the lever in a frantic bid to escape, quickly learned the effects of the lever and consequently used this knowledge to stop the currents both during and prior to electrical shock. These two learned responses are known as escape learning and avoidance learning (Skinner, 1938). The operant chamber for pigeons involved a plastic disk in which the pigeon pecked in order to open a drawer filled with grain. The Skinner box led to the principle of reinforcement, which is the probability of something occurring based on the consequences of a behaviour.

Research Focus

Applying game incentives such as prompts, competition, badges, and rewards to ordinary activities, or gamification, is a growing approach to behaviour modification today. Health care has also applied some early innovative uses of gamification — from a Sony PS3 Move motion controller used to help children diagnosed with cancer to the launch of Games for Health, the first peer-reviewed journal dedicated to the research and design of health games and behavioural health strategies. Gamification is the process of taking an ordinary activity (like jogging or car sharing) and adding game mechanisms to it, including prompts, rewards, leader-boards, and competition between different players.

When used in social marketing and online health-promotion campaigns, gamification can be used to encourage a new, healthy behaviour such as regular exercise, improved diet, or completing actions required for treatment. Typically, gamification is web-based, usually with a mobile app or as a micro-site. Behavioural change campaigns require an understanding of human psychology, specifically the benefits and barriers associated with a behaviour. There have been several campaigns using gamification techniques that have had remarkable results. For example, organizations that wanted employees to exercise regularly have installed gyms in their offices and created a custom application that rewards employees for “checking in” to the gyms. Employees can form regionally based teams, check in to workouts, and chart their team’s progress on a leader-board. This has a powerful effect on creating and sustaining a positive behavioural change.

Similar game mechanics have been used in sustainability campaigns aimed at increasing household environmental compliance. Such sites use game mechanics such as points, challenges, and rewards to increase daily “green” habits like recycling and conserving water. Other behavioural change campaigns that have applied social gaming include using cameras to record speeding cars, which reduce the incidence of speeding, and offering products that allow users to track their healthy behaviours through the day, including miles travelled, calories burned, and stairs climbed.

Key Takeaways

  • Behaviourist psychology should concern itself with the observable behaviour of people and animals, not with unobservable events that take place in their minds.
  • The main influences of behaviourist psychology were Ivan Pavlov (1849-1936), Edward Lee Thorndike (1874-1949), John B. Watson (1878-1958), and B.F. Skinner (1904-1990).
  • The idea that we develop responses to certain stimuli that are not naturally occurring is called “classical conditioning.”
  • Operant conditioning refers to how an organism operates on the environment or how it responds to what is presented to it in the environment.
  • Reinforcement means to strengthen, and is used in psychology to refer to any stimulus that strengthens or increases the probability of a specific response.
  • There are four types of reinforcement: positive, negative, punishment, and extinction.
  • Behaviourist researchers used experimental methods (puzzle box, operant conditioning or Skinner box, Little Albert experiment) to investigate learning processes.
  • Today, behaviourism is still prominent in applications such as gamification.

Exercises and Critical Thinking

  1. Reflect on your educational experience and try to determine what aspects of behaviourism were employed.
  2. Research Skinner’s other inventions, such as the “teaching machine” or the “air crib,” and discuss with a group the underlying principles, beliefs, and values governing such “machines.” Do you disagree or agree with their use?
  3. What might be some other applications for gamification behavioural change strategies? Design a campaign or strategy for changing a behaviour of your choice (e.g., health, work, addiction, or sustainable practice).

Image Attributions

Figure 2.12: Operant conditioning diagram by studentne ( used under CC BY SA 3.0 license (

Figure 2.13: Thorndike’s Puzzle Box. by Jacob Sussman ( is in the public domain.

Figure 2.14: Skinner box scheme 01 by Andreas1 ( used under CC BY SA 3.0 license (


Skinner, B.F. (1938). The behavior of organisms: an experimental analysis. Oxford, England: Appleton-Century.

Skinner, B.F. (1974). About behaviorism. New York, NY: Random House.

Thorndike, Edward Lee. (1898). Animal intelligence. Princeton, NJ: MacMillan.

Thorndike, Edward (1932). The fundamentals of learning. New York, NY: AMS Press Inc.

Watson, J. B. (1913). Psychology as the behaviorist views it. Psychological Review, 20, 158-177.

Watson, J. B., & Rayner, R. (1920). Conditioned emotional reactions. Journal of Experimental Psychology, 3, 1-14.


2.4 Humanist, Cognitive, and Evolutionary Psychology

Jennifer Walinga

Learning Objectives

  1. Understand the key principles of humanistic psychology.
  2. Differentiate humanistic psychology from biological, psychodynamic, and behaviourist psychology.
  3. Critically discuss and differentiate between key humanistic concepts such as motivation, need, adaptation, and perception.
  4. Identify how humanistic psychology, and its related streams of cognitive and evolutionary psychology, have influenced aspects of daily life and work.

Humanistic psychology emerged as the third force in psychology after psychodynamic and behaviourist psychology. Humanistic psychology holds a hopeful, constructive view of human beings and of their substantial capacity to be self-determining. This wave of psychology is guided by a conviction that intentionality and ethical values are the key psychological forces determining human behaviour. Humanistic psychologists strive to enhance the human qualities of choice, creativity, the interaction of the body, mind, and spirit, and the capacity to become more aware, free, responsible, life-affirming, and trustworthy.

Emerging in the late 1950s, humanistic psychology began as a reaction against the two schools of thought then dominating American psychology. Behaviourism’s insistence on applying the methods of physical science to human behaviour caused adherents to neglect crucial subjective data, humanists believed. Similarly, psychoanalysis’s emphasis on unconscious drives relegated the conscious mind to relative unimportance.

The early humanistic psychologists sought to restore the importance of consciousness and offer a more holistic view of human life. Humanistic psychology acknowledges that the mind is strongly influenced by determining forces in society and the unconscious, and emphasizes the conscious capacity of individuals to develop personal competence and self-respect. The humanistic orientation has led to the development of therapies to facilitate personal and interpersonal skills and to enhance the quality of life. During the 1950s and 1960s, Carl Rogers, for instance, introduced what he called person or client-centred therapy, which relies on clients’ capacity for self-direction, empathy, and acceptance to promote clients’ development. Abraham Maslow (1908-1970) developed a hierarchy of motivation or hierarchy of needs culminating in self-actualization. Rollo May (1909 – 1994) brought European existential psychotherapy and phenomenology into the field by acknowledging human choice and the tragic aspects of human existence, and Fritz Perls developed gestalt therapy in his workshops and training programs at the Esalan Institute and elsewhere.

During the 1970s and 1980s, the ideas and values of humanistic psychology spread into many areas of society. As a result, humanistic psychology has many branches and extensions, as outlined in Table 2.2.

Table 2.2 Humanistic Therapies and their Theorists.Adapted by J. Walinga.
Humanistic Therapies Theorists
Analytical and Archetypal Psychology C.G. Jung, James Hillman
Authentic Movement Mary Whitehouse
Encounter Carl Rogers, Will Schultz
Existential Analysis Rollo May, James F.T Bugental
Focusing Eugene Gendin
Gestalt Art Therapy Janie Rhyne
Logotherapy Viktor Frankl
Neuro-Linguistic Programming Richard Bandler, John Grinder
Psychosynthesis Roberto Assagioli
Rational-Emotive Therapy Albert Ellis
Reality Therapy William Glasser
Self-Disclosure Sidney Jourard
Sensory Awareness though Movement Moshe Feldenkreis

Client-centred therapy provides a supportive environment in which clients can re-establish their true identity. Central to this thinking is the idea that the world is judgmental, and many people fear that if they share with the world their true identity, it would judge them relentlessly. People tend to suppress their beliefs, values, or opinions because they are not supported, not socially acceptable, or negatively judged. To re-establish a client’s true identity, the therapist relies on the techniques of unconditional positive regard and empathy. These two techniques are central to client-centred therapy because they build trust between the client and therapist by creating a nonjudgmental and supportive environment for the client.

Existential therapy contrasts the psychoanalysts’ focus on the self and focuses instead on “man in the world.” The counsellor and the client may reflect on how the client has answered life’s questions in the past, but attention ultimately emphasizes the choices to be made in the present and future and enabling a new freedom and responsibility to act. By accepting limitations and mortality, a client can overcome anxieties and instead view life as moments in which he or she is fundamentally free.

Gestalt therapy focuses on the skills and techniques that permit an individual to be more aware of their feelings. According to this approach, it is much more important to understand what patients are feeling and how they are feeling rather than to identify what is causing their feelings. Supporters of gestalt therapy argued that earlier theories spent an unnecessary amount of time making assumptions about what causes behaviour. Instead, gestalt therapy focuses on the here and now.

Research Focus

In his seminal work “Significant Aspects of Client-Centered Therapy,” Rogers described the discovery of the “capacity of the client” (1946):

Naturally the question is raised, what is the reason for this predictability in a type of therapeutic procedure in which the therapist serves only a catalytic function? Basically the reason for the predictability [page 418] of the therapeutic process lies in the discovery — and I use that word intentionally — that within the client reside constructive forces whose strength and uniformity have been either entirely unrecognized or grossly underestimated. It is the clearcut and disciplined reliance by the therapist upon those forces within the client, which seems to account for the orderliness of the therapeutic process, and its consistency from one client to the next.

I mentioned that I regarded this as a discovery. I would like to amplify that statement. We have known for centuries that catharsis and emotional release were helpful. Many new methods have been and are being developed to bring about release, but the principle is not new. Likewise, we have known since Freud’s time that insight, if it is accepted and assimilated by the client, is therapeutic. The principle is not new. Likewise we have realized that revised action patterns, new ways of behaving, may come about as a result of insight. The principle is not new.

But we have not known or recognized that in most if not all individuals there exist growth forces, tendencies toward self-actualization, which may act as the sole motivation for therapy. We have not realized that under suitable psychological conditions these forces bring about emotional release in those areas and at those rates which are most beneficial to the individual. These forces drive the individual to explore his own attitudes and his relationship to reality, and to explore these areas effectively.

We have not realized that the individual is capable of exploring his attitudes and feelings, including those which have been denied to consciousness, at a rate which does not cause panic, and to the depth required for comfortable adjustment. The individual is capable of discovering and perceiving, truly and spontaneously, the interrelationships between his own attitudes, and the relationship of himself to reality. The individual has the capacity and the strength to devise, quite unguided, the steps which will lead him to a more mature and more comfortable relationship to his reality. It is the gradual and increasing recognition of these capacities within the individual by the client-centered therapist that rates, I believe, the term discovery. All of these capacities I have described are released in the individual if a suitable psychological atmosphere is provided.

Rogers identified five characteristics of the fully functioning person:

  1. Open to experience: Both positive and negative emotions are accepted. Negative feelings are not denied, but worked through (rather than resort to ego defence mechanisms).
  2. Existential living: Being in touch with different experiences as they occur in life, avoiding prejudging and preconceptions. Being able to live in and fully appreciate the present, not always looking back to the past or forward to the future (i.e., living for the moment).
  3. Trust feelings: Feelings, instincts, and gut-reactions are paid attention to and trusted. A person’s own decisions are the right ones and we should trust ourselves to make the right choices.
  4. Creativity: Creative thinking and risk taking are features of a person’s life. A person does not play it safe all the time. This involves the ability to adjust and change and seek new experiences.
  5. Fulfilled life: A person is happy and satisfied with life, and always looking for new challenges and experiences.

Humanistic psychology recognizes that human existence consists of multiple layers of reality: the physical, the organic, and the symbolic. It contests the idea — traditionally held by the behavioural sciences — that the only legitimate research method is an experimental test using quantitative data. It argues for the use of additional methods specifically designed to study qualitative factors such as subjective experience, emotion, perception, memory, values, and beliefs. Whereas other approaches take an objective view of people — in essence asking, What is this person like? — humanistic psychologists give priority to understanding people’s subjectivity, asking, What is it like to be this person? (Clay, 2002).

Humanistic psychology has, of course, quietly influenced North American psychology and culture over many decades by informing the civil rights debate and the women’s rights movement, for example. In the academic world, however, humanistic psychology’s rejection of quantitative research in favour of qualitative methods caused its reputation to suffer and its adherents to be marginalized. But in recent years, there’s mounting evidence of renewal in the field itself.

Abraham Maslow’s view of human needs was more complex than Rogers’s. While Rogers believed that people needed unconditional positive regard, Maslow acknowledged that people have a variety of needs that differ in timing and priority (Figure 2.15).

Hierarchy of Needs. Long description available.
Figure 2.15 Maslow’s Hierarchy of Needs. [Long Description]

Maslow called the bottom four levels of the pyramid deficiency needs because a person does not feel anything if they are met, but becomes anxious if they are not. Thus, physiological needs such as eating, drinking, and sleeping are deficiency needs, as are safety needs, social needs such as friendship and sexual intimacy, and ego needs such as self-esteem and recognition. In contrast, Maslow called the fifth level of the pyramid a growth needA growth need allows one to reach full potential as a human being. because it enables a person to self-actualize or reach his or her fullest potential as a human being. Once a person has met the deficiency needs, he or she can attend to self-actualization; however, only a small minority of people are able to self-actualize because self-actualization requires uncommon qualities such as honesty, independence, awareness, objectivity, creativity, and originality.

Frederick Taylor’s scientific management principles of the early 1900s, born of the industrial revolution and focused on scientific study of productivity in the workplace, fostered the development of motivation theory, which held that all work consisted largely of simple, uninteresting tasks, and that the only viable method to get people to undertake these tasks was to provide incentives and monitor them carefully. In order to get as much productivity out of workers as possible, it was believed that a person must reward the desired behaviour and punish the rejected behaviour — otherwise known as the “carrot-and-stick” approach.

During this time, scientists believed in two main drives powering human behaviour: the biological drive, including hunger, thirst, and intimacy; and the reward-punishment drive. However, scientists began to encounter situations during their experiments where the reward-punishment drive wasn’t producing the expected performance results. In 1949, Harry F. Harlow, professor of psychology at the University of Wisconsin, began to argue for a third drive: intrinsic motivationthe joy of the task itself.

Harlow’s theory (1950) was based on studies of primate behaviour when solving puzzles. He found that when presented with a puzzle, monkeys seemed to enjoy solving the puzzles without the presence or expectation of rewards. He found these monkeys, driven by intrinsic motivation, solved the puzzles quicker and more accurately than monkeys that received food rewards.

Edward Deci and Richard Ryan (1985) went on to explore and replicate these findings with humans many times over in their studies of families, classrooms, teams, organizations, clinics, and cultures. They concluded that conditions supporting the individual’s experience of autonomy, competence, and relatedness foster the greatest motivation for and engagement in activities while enhancing performance, persistence, and creativity.

Dan Pink (2010) provides ample evidence to support the notion that a traditional carrot-and-stick approach can result in:

Research Focus: When the Lights Went on

The term “Hawthorne Effect” was coined in 1950 by Henry A. Landsberger when analyzing earlier experiments from 1924 to 1932 at the Hawthorne Works (a Western Electric factory outside Chicago). The Hawthorne Works had commissioned a study to see if their workers would become more productive in higher or lower levels of light. (Most industrial/occupational psychology and organizational behaviour textbooks refer to these illumination studies.) In these lighting studies, light intensity was altered to examine its effect on worker productivity. The workers’ productivity seemed to improve when changes were made, and slumped when the study ended. It was suggested that the productivity gain occurred as a result of the motivational effect on the workers of the interest being shown in them. George Elton Mayo (1945) described the Hawthorne Effect in terms of a positive emotional effect due to the perception of a sympathetic or interested observer. Although illumination research of workplace lighting formed the basis of the Hawthorne Effect, other changes such as maintaining clean work stations, clearing floors of obstacles, and even relocating work stations resulted in increased productivity for short periods. Today the term is used to identify any type of short-lived increase in productivity based on attention to human needs.

Humanistic psychology gave birth to the self-help movement, with concepts grounded in emotion and intuition. The recent positive psychology movement is one form of neo-humanistic psychology that combines emotion and intuition with reason and research. Similarly, modern crisis counselling’s emphasis on empathetic listening finds its roots in Rogers’s humanistic psychology work. In the wider culture, the growing popularity of personal and executive coaching also points to humanistic psychology’s success. Humanistic psychology’s principles may become increasingly relevant as the nation ages, creating a culture preoccupied with facing death and finding meaning in life.

In 1998, a paradigm shift in thinking occurred when University of Pennsylvania psychologist Martin Seligman, in his presidential address to the American Psychological Association (APA), urged psychology to “turn toward understanding and building the human strengths to complement our emphasis on healing damage” (1998b). Though not denying humanity’s flaws, the new approach suggested by positive psychologists recommends focusing on people’s strengths and virtues as a point of departure. Rather than analyze the psychopathology underlying alcoholism, for example, positive psychologists might study the resilience of those who have managed a successful recovery through Alcoholics Anonymous. Instead of viewing religion as a delusion and a crutch, as did Freud, they might identify the mechanisms through which a spiritual practice like meditation enhances mental and physical health. Their lab experiments might seek to define not the conditions that induce depraved behaviour, but those that foster generosity, courage, creativity, and laughter.

Seligman developed the concepts of learned optimism (1998a) and authentic happiness (2002). Learned optimism follows an ABCDE model:

In this model, when faced with adversity (A) such as a criticism or failure, a person might form the belief (B) that he or she is underperforming or incapable, and consider the consequence (C) of quitting. However, disputation (D) would challenge the underlying assumptions or beliefs that have formed. The person would then form a new belief in his or her capacity to grow from the critique or learn from the failure. From there, the person would become energized (E) as he or she pursues a new performance path.

In collaboration with Seligman, and within the positive psychology framework, Dr. Mihalyi Csikszentmihályi from Claremont University developed the theory of flow (1988; 1990). Flow is a state of optimal performance. A flow state can be entered while performing any activity, although it is most likely to occur when a person is wholeheartedly performing a task or activity for intrinsic purposes. Csikszentmihályi identified the following six factors as encompassing an experience of flow:

  1. Intense and focused concentration on the present moment
  2. Merging of action and awareness
  3. Loss of reflective self-consciousness
  4. Sense of personal control or agency over the situation or activity
  5. Distortion of temporal experience (i.e., a person’s subjective experience of time being altered)
  6. Experience of the activity being intrinsically rewarding (also referred to as an autotelic experience)

Flow theory suggests that three conditions have to be met to achieve a flow state. First, a person must be involved in an activity with a clear set of goals and progress. This adds direction and structure to the task. Second, the task at hand must have clear and immediate feedback. This helps the person negotiate any changing demands and allows him or her to adjust performance to maintain the flow state. And last, a person must have a good balance between the perceived challenges of the task at hand and his or her own perceived skills. The person must have confidence in his or her ability to complete the task at hand (Figure 2.16).

Mental state depending on a person’s skill and the task’s difficulty. Long description available
Figure 2.16 Factors of Flow State. [Long Description]

Cognitive Psychology

Cognitive psychology is the study of mental processes such as attention, memory, perception, language use, problem solving, creativity, and thinking. Much of the work derived from cognitive psychology has been integrated into various other modern disciplines of psychological study including social psychology, personality psychology, abnormal psychology, developmental psychology, educational psychology, and economics.

Ulric Neisser (1928-2012) is credited with formally coining the term cognitive psychology and defining it as “all processes by which the sensory input is transformed, reduced, elaborated, stored, recovered, and used” (1967, page 4). Cognition came to be seen as involved in everything a human being might possibly do: every psychological phenomenon is a cognitive phenomenon. Theories of cognition include developmental, cultural, neural, computational, and moral perspectives.

While behaviourism and cognitive schools of psychological thought may not agree theoretically, they have complemented each other in practical therapeutic applications, such as in cognitive-behavioural therapy (CBT) that has demonstrable utility in treating certain pathologies, such as simple phobias, post-traumatic stress disorder (PTSD), and addiction. CBT replaces maladaptive strategies with more adaptive ones by challenging ways of thinking and reacting. CBT techniques focus on helping individuals challenge their patterns and beliefs and replace erroneous thinking, such as overgeneralizing, magnifying negatives, or catastrophizing, with more realistic and effective thoughts, thus decreasing self-defeating emotions and behaviour and breaking what can otherwise become a negative cycle. These errors in thinking are known as “cognitive distortions.” CBT helps individuals take a more open, mindful, and aware posture toward their distorted thoughts and feelings so as to diminish their impact (Hayes, Villatte, Levin, & Hildebrandt, 2011).


The psychological definition of attention is a state of focused awareness on a subset of the available perceptual information. The key function of attention is to filter out irrelevant data, enabling the desired data to be distributed to the other mental processes. The human brain may, at times, simultaneously receive inputs in the form of auditory, visual, olfactory, taste, and tactile information. Without the ability to filter out some or most of that simultaneous information and focus on one or typically two inputs at most, the brain would become overloaded as a person attempted to process all the information.


Modern conceptions of memory typically break it down into three main subclasses:

  1. Procedural memory: memory for the performance of particular types of action, is often activated on a subconscious level, or at most requires a minimal amount of conscious effort (e.g., driving to work along the same route).
  2. Semantic memory: the encyclopedic knowledge that a person possesses, such as what the Eiffel Tower looks like, or the name of a friend from Grade 6.
  3. Episodic memory: memory of autobiographical events that can be explicitly stated, contains all memories that are temporal in nature, such as when you last brushed your teeth, or where you were when you heard about a major news event.


Perception involves both the physical senses (sight, smell, hearing, taste, touch, and proprioception) as well as the cognitive processes involved in selecting and interpreting those senses. It is how people come to understand the world around them through interpretation of stimuli.

Language use

Cognitive psychologists began exploring the cognitive processes involved with language in the 1870s when Carl Wernicke (1848-1905) proposed a model for the mental processing of language (1875/1995). Significant work has been done recently on understanding the timing of language acquisition and how it can be used to determine if a child has, or is at risk of developing, a learning disability.

Problem solving

Metacognition involves conscious thought about thought processes and might include monitoring a person’s performance on a given task, understanding a person’s capabilities on particular mental tasks, or observing a person’s ability to apply cognitive strategies. Much of the current study regarding metacognition within the field of cognitive psychology deals with its application within the area of education. Educators strive to increase students’ metacognitive abilities in order to enhance their learning, study habits, goal setting, and self-regulation.

Research Focus: Divided Attention

Relating to the field of cognitive psychology is the concept of divided attention, which refers to a person’s ability to focus on two or more things at one time. A number of early studies dealt with the ability of a person wearing headphones to discern meaningful conversation when presented with different messages in each ear. Key findings demonstrated the mind’s ability to focus on one message, while still being somewhat aware of information taken in by the ear that was not consciously attended to. Participants who were wearing earphones were told that they would be hearing separate messages in each ear and that they were expected to attend only to information related to basketball. When the experiment started, the message about basketball was presented to the left ear, and non-relevant information was presented to the right ear. At some point the message related to basketball was switched to the right ear, and the non-relevant information to the left ear. When this happened, the listener was usually able to repeat the entire message at the end, having attended to the left or right ear only when it was appropriate (Glucksberg & Cowan, 1970).

Evolutionary Psychology

Evolutionary psychology has emerged as a major perspective in psychology. It seeks to develop and understand ways of expanding the emotional connection between individuals and the natural world, thereby assisting individuals with developing sustainable lifestyles and remedying alienation from nature. The main premise of evolutionary psychology is that while today the human mind is shaped by the modern social world, it is adapted to the natural environment in which it evolved. According to the hypothesis of biologist E.O. Wilson, human beings have an innate instinct to connect emotionally with nature. What distinguishes evolutionary psychologists from many cognitive psychologists is the proposal that the relevant internal mechanisms are adaptations products of natural selection — that helped our ancestors get around the world, survive, and reproduce. Evolutionary psychology is founded on several core premises:

Evolutionary psychologists sometimes present their approach as potentially unifying, or providing a foundation for, all other work that aims to explain human behaviour (Tooby & Cosmides, 1992). This claim has been met with skepticism by many social scientists who see a role for multiple types of explanation of human behaviour, some of which are not reducible to biological explanations of any sort.

Key Takeaways

  • Humanistic psychology emerged as the “third force” in psychology after psychodynamic and behaviourist psychologies.
  • The key principles of humanistic psychology include human capacity for self-actualization, self-direction, and choice.
  • Carl Rogers identified five principles of a fully functioning person as open, present, trusting, creative, and fulfilled.
  • Humanistic psychology relies on subjective factors and utilizes qualitative methods of study.
  • Abraham Maslow introduced a hierarchy of human needs including physiological, safety, belonging, esteem, and self-actualization.
  • With the advance of humanistic psychology, human motivation theory shifted from a purely external or extrinsic focus to the acknowledgment of an intrinsic focus.
  • Positive psychology recommends focusing on people’s strengths and virtues as a point of departure rather than analyzing the underlying psychopathology.
  • Flow is a state of optimal performance that can be entered when a person is wholeheartedly performing a task or activity for intrinsic purposes.
  • Cognitive psychology is the study of mental processes such as attention, memory, perception, language use, problem solving, creativity, and thinking.
  • The main premise of evolutionary psychology is that while today the human mind is shaped by the modern social world, it is adapted to the natural environment in which it evolved.

Exercises and Critical Thinking

  1. What model do you believe the current educational system follows? Are students trained according to the behavioural model or do educators also address the subjective beliefs, thoughts, and feelings of the student?
  2. What are some of the psychological traits you possess that might contribute to your survival or “fitness”? Can you provide an example of when this trait contributed to your success?
  3. Can you see applications for the principles of evolutionary psychology in the workplace or community (e.g., certain psychological qualities will ensure that you perform more effectively in a job interview)?
  4. Conduct a cultural analysis of your family, cohort, or social group. What are some of the values and beliefs communicated in your family or group? In what shape or form are these values manifested or expressed? Through what ways of doing, artifacts, activities, and/or traditions are these values communicated or expressed?

Image Attributions

Figure 2.15: Diagram of Maslow’s hierarchy of needs. by J. Finkelstein (’s_hierarchy_of_needs.png) used under CC BY SA 3.0 license (

Figure 2.16: Challenge vs skill Commons by Dr. enh ( is in the public domain.


Clay, Rebecca A. (2002). A renaissance for humanistic psychology. American Psychological Association Monitor, 33 (8), 42.

Csikszentmihályi, M. (1988). The flow experience and its significance for human psychology, in Csikszentmihályi, M., (Ed.) Optimal experience: psychological studies of flow in consciousness, Cambridge, UK: Cambridge University Press, page. 15–35.

Csikszentmihályi, M. (1990). Flow: The psychology of optimal experience. New York: Harper & Row.

Deci, E. L., & Ryan, R. M. (1985). Intrinsic motivation and self-determination in human behavior. New York: Plenum.

Glucksberg, S., & Cowen, C. N., Jr. (1970). Memory for nonattended auditory material. Cognitive Psychology, I, 149-156.

Harlow, H.F. (1950). Early social deprivation and later behavior in the monkey. page. 154-173. In A.Abrams, H.H. Gurner & J.E.P. Tomal, (Eds.), Unfinished tasks in the behavioral sciences (1964). Baltimore: Williams & Wilkins.

Hayes, Steven C., Villatte, Matthieu, Levin, Michael, & Hildebrandt, Mikaela. (2011). Open, aware, and active: Contextual approaches as an emerging trend in the behavioral and cognitive therapies. Annual Review of Clinical Psychology, 7, 141–168.

Mayo, Elton (1945). Social problems of an industrial civilization. Boston: Division of Research, Graduate School of Business Administration, Harvard University, page 64.

Neisser, U. (1967). Cognitive psychology. Englewood Cliffs, NJ: Prentice Hall.

Pink, Daniel H. (2010). Drive – The surprising truth about what motivates us. Edinburgh, UK: Canongate Books.

Rogers, C. R. (1946). Significant aspects of client-centered therapy. American Psychologist, 1, 415-422.

Seligman, M. E. P. (1998a). Building human strength: Psychology’s forgotten mission. APA Monitor, 29(1).

Seligman, M.E.P. (1998b). Learned optimism: How to change your mind and your life. Second edition. New York: Pocket Books (Simon and Schuster).

Seligman, M. E. P. (2002). Authentic happiness: Using the new positive psychology to realize your potential for lasting fulfillment. New York: Free Press.

Tooby, J., & Cosmides, L. (1992). The psychological foundations of culture. In H. Barkow, L. Cosmides & J. Tooby (Eds.), The adapted mind, New York: Oxford University Press, page 19–136.

Wernicke, K. (1875/1995). The aphasia symptom-complex: A psychological study on an anatomical basis. In Paul Eling (Ed.) Reader in the history of aphasia. Amsterdam: John Benjamins Pub Co. page 69–89.

Long Descriptions

Figure 2.15 long description: In Maslow’s hierarchy of needs, there are five levels.

  1. Physiological needs: Breathing, food, water, sex, sleep, homeostasis, excretion.
  2. Safety needs: Security of body, of employment, of resources, of morality, of the family, of health, of property.
  3. Long and belonging needs: Friendship, family, sexual intimacy.
  4. Esteem needs: Self-esteem, confidence, chievement, respect of others, respect by others.
  5. Self-Actualization: Morality, creativity, spontaneity, problem solving, lack of prejudice, acceptance of facts.
Figure 2.16 long description: Factors of Flow State.
Low Skill Level Medium Skill Level High Skill Level
Low Challenge Apathy Boredom Relaxation
Medium Challenge Worry Control
High Challenge Anxiety Arousal Flow



Chapter 2 Summary, Key Terms, and Self-Test

Jennifer Walinga and Lee Sanders


There are many different ways to think about human experience, thought, and behaviour. The multiple perspectives in modern psychology provide researchers and students a variety of ways to approach problems and to understand, explain, predict, and resolve human thought and behaviour.

Perhaps the field of psychology struggles to find a unifying paradigm because human beings are so multifaceted, and human experience so diverse and complex. As with many areas of life, psychology is perhaps best understood through its complexity: psychology seems to move between poles and require a dialectical examination. Human beings are complex systems living within complex adaptive systems (Figure 2.17), possessing multiple ways of knowing and learning and therefore requiring multiple perspectives in order to shed light on the meaning of any one human experience.

Systems surrounding an individual. Long description available.
Figure 2.17  Complex Adaptive Systems. [Long Description]

The greatest challenge of modern psychology may be holding the whole of human system experience in our minds – biology, cognition, emotion, and belief over time and within an environment and culture – and distilling an understanding from the complex interactions of so many factors.

Key Terms

  • Access
  • Activation-synthesis theory
  • Active Imagination
  • Adaptations
  • Affect
  • Anima
  • Animus
  • Archetypes
  • Associative shifting
  • Attention
  • Authoethnography
  • Autonomic nervous system
  • Availability
  • Avoidance learning
  • Behaviourism
  • Biological drive
  • Biological psychology
  • Black box model
  • Classical conditioning
  • Client- or person-centred therapy
  • Cognitive-behavioural therapy (CBT)
  • Cognitive psychology
  • Collective unconscious
  • Complexes
  • Conscious
  • Consciousness
  • Continual-activation theory
  • Deficiency needs
  • Divided attention
  • Dreams
  • Episodic memory
  • Escape learning
  • Evolutionary psychology
  • Existential therapy
  • Expectation fulfillment theory
  • Extinction
  • Extravert
  • Feeling function
  • Fight-or-flight response
  • Frontal lobe
  • Functionalism (or school of functionalism)
  • Gamification
  • Gestalt therapy
  • Growth need
  • Holist
  • Humanistic psychology
  • Identical elements theory of transfer
  • Identifiability
  • Individuation
  • Information Processor
  • Integrative Psychology
  • Intrinsic motivation
  • Introspection
  • Introvert
  • Intuitive
  • Latent content
  • Law of disuse
  • Law of effect
  • Law of readiness
  • Law of recency
  • Law of use
  • Mandala
  • Manifest content
  • Methodologies
  • Metacognition
  • Motivation theory
  • Multiple response
  • Myers-Briggs Type Indicator
  • Mystery
  • Negative reinforcement
  • Neural correlates of consciousness (NCC)
  • Neurogenesis
  • Neurophilosophy
  • Neurosis
  • Non-rapid eye movement or non-REM (NREM) sleep
  • Occipital lobe
  • Operant conditioning
  • Paradigm
  • Parasympathetic nervous system
  • Peripheral nervous system
  • Persona
  • Personal unconscious
  • Phenomenal
  • Positive psychology
  • Positive reinforcement
  • Preconscious
  • Prepotency of elements
  • Problem restructuring
  • Procedural memory
  • Psychoanalysis
  • Psychodynamic psychology
  • Punishment
  • Radical behaviourism
  • Rapid eye movement (REM) sleep
  • Reductionist
  • Reinforcement
  • Response by analogy
  • Scientific management
  • Selective forgetting
  • Self
  • Self-actualize
  • Semantic memory
  • Sensing function
  • Set or attitude
  • Shadow
  • Skinner box
  • Story
  • Structuralism
  • Somatic nervous system
  • Spreading activation
  • Symbol
  • Sympathetic nervous system
  • Temporal lobe
  • Thinking function
  • Third force
  • Threat-simulation theory
  • Unconscious
  • Visual attention
  • Word association test


An interactive or media element has been excluded from this version of the text. You can view it online here:

Direct link to self-test:

Image Attributions

Figure 2.17: body by Sue Clark ( is in the public domain; bullseye from Wikipedia ( used under a CC-BY-SA license 3.0 Unported license (

Long Description

Figure 2.17 long description: The individual is surrounded by multiple systems which exercise influence on the individual.

  1. An individual’s sex, age, health, etc.
  2. Microsystem: Family, peers, church, health services, school.
  3. Mesosystem.
  4. Exosystem: Social services, neighbours, local politics, mass media, industry.
  5. Macrosystem: Attitudes and ideologies of the culture.


Chapter 3. Psychological Science & Research


Chapter 3 Introduction

Charles Stangor, Jennifer Walinga, Jorden A. Cummings, and Lee Sanders

Psychologists study the behaviour of both humans and animals. The main purpose of this research is to help us understand people and to improve the quality of human lives. The results of psychological research are relevant to problems such as learning and memory, homelessness, psychological disorders, family instability, and aggressive behaviour and violence. Psychological research is used in a range of important areas, from public policy to driver safety. It guides court rulings with respect to racism and sexism (Brown v. Board of Education, 1954; Fiske, Bersoff, Borgida, Deaux, & Heilman, 1991), as well as court procedure, in the use of lie detectors during criminal trials, for example (Saxe, Dougherty, & Cross, 1985). Psychological research helps us understand how driver behaviour affects safety (Fajen & Warren, 2003), which methods of educating children are most effective (Alexander & Winne, 2006; Woolfolk-Hoy, 2005), how to best detect deception (DePaulo et al., 2003), and the causes of terrorism (Borum, 2004).

Some psychological research is basic research. Basic research is research that answers fundamental questions about behaviour. For instance, biopsychologists study how nerves conduct impulses from the receptors in the skin to the brain, and cognitive psychologists investigate how different types of studying influence memory for pictures and words. There is no particular reason to examine such things except to acquire a better knowledge of how these processes occur. Applied research is research that investigates issues that have implications for everyday life and provides solutions to everyday problems. Applied research has been conducted to study, among many other things, the most effective methods for reducing depression, the types of advertising campaigns that serve to reduce drug and alcohol abuse, the key predictors of managerial success in business, and the indicators of effective government programs.

Basic research and applied research inform each other, and advances in science occur more rapidly when each type of research is conducted (Lewin, 1999). For instance, although research concerning the role of practice on memory for lists of words is basic in orientation, the results could potentially be applied to help children learn to read. Correspondingly, psychologist-practitioners who wish to reduce the spread of AIDS or to promote volunteering frequently base their programs on the results of basic research. This basic AIDS or volunteering research is then applied to help change people’s attitudes and behaviours.

Psychological studies start with a research design, which is the specific method a researcher uses to collect, analyze, and interpret data. Psychologists use three major types of research designs in their research, and each provides an essential avenue for scientific investigation. Descriptive research is research designed to provide a snapshot of the current state of affairsCorrelational research is research designed to discover relationships among variables and to allow the prediction of future events from present knowledgeExperimental research is research in which initial equivalence among research participants in more than one group is created, followed by a manipulation of a given experience for these groups and a measurement of the influence of the manipulation. Each of the three research designs varies according to its strengths and limitations, and it is important to understand how each differs.

It is important that research in psychology is conducted in an ethical, moral, and responsible manner. Our research ethics are interpreted by important moral principles like respecting people’s rights and dignity. These moral principles are then translated into ethical codes – or set of rules – that researchers must follow. These codes have developed over time, often in response to historical and scientific events. One example rule is that participants must give informed consent before participating in a research study. That is, they must be aware of the procedure, potential risks, and benefits before explicitly stating if they wish to participate.

The results of psychological research are reported primarily in research articles published in scientific journals, and your instructor may require you to read some of these. The research reported in scientific journals has been evaluated, critiqued, and improved by scientists in the field through the process of peer review. In this book there are many citations of original research articles, and I encourage you to read those reports when you find a topic interesting. Most of these papers are readily available online through your college or university library. It is only by reading the original reports that you will really see how the research process works. A list of some of the most important journals in psychology is provided here for your information.

Psychology is not without its share of contentious issues, like many areas of scientific inquiry. One of the most recent debates is about replicability – or ability for findings to be supported by multiple studies and generalize across time and situations – and whether or not replicability should even be a goal of psychological science. We will discuss this issue and its impact on our field.

Psychological Journals

The following is a list of some of the most important journals in various subdisciplines of psychology. The research articles in these journals are likely to be available in your college or university library. You should try to read the primary source material in these journals when you can.

General Psychology

  • American Journal of Psychology
  • American Psychologist
  • Behavioral and Brain Sciences
  • Canadian Journal of Behavioural Science
  • Canadian Journal of Experimental Psychology
  • Canadian Psychology
  • Psychological Bulletin
  • Psychological Methods
  • Psychological Review
  • Psychological Science

Biopsychology and Neuroscience

  • Behavioral Neuroscience
  • Journal of Comparative Psychology
  • Psychophysiology

Clinical and Counselling Psychology

  • Journal of Abnormal Psychology
  • Journal of Consulting and Clinical Psychology
  • Journal of Counselling Psychology

Cognitive Psychology

  • Canadian Journal of Experimental Psychology
  • Cognition
  • Cognitive Psychology
  • Journal of Memory and Language
  • Perception & Psychophysics

Cross-Cultural, Personality, and Social Psychology

  • Journal of Cross-Cultural Psychology
  • Journal of Experimental Social Psychology
  • Journal of Personality
  • Journal of Personality and Social Psychology
  • Personality and Social Psychology Bulletin

Developmental Psychology

  • Child Development
  • Developmental Psychology

Educational and School Psychology

  • Educational Psychologist
  • Journal of Educational Psychology
  • Review of Educational Research

Environmental, Industrial, and Organizational Psychology

  • Journal of Applied Psychology
  • Organizational Behavior and Human Decision Processes
  • Organizational Psychology
  • Organizational Research Methods
  • Personnel Psychology


Alexander, P. A., & Winne, P. H. (Eds.). (2006). Handbook of educational psychology (2nd ed.). Mahwah, NJ: Lawrence Erlbaum Associates.

Borum, R. (2004). Psychology of terrorism. Tampa: University of South Florida.

Brown v. Board of Education. (1954). 347 U.S, 483.

DePaulo, B. M., Lindsay, J. J., Malone, B. E., Muhlenbruck, L., Charlton, K., & Cooper, H. (2003). Cues to deception. Psychological Bulletin, 129(1), 74–118.

Fajen, B. R., & Warren, W. H. (2003). Behavioral dynamics of steering, obstacle avoidance, and route selection. Journal of Experimental Psychology: Human Perception and Performance, 29(2), 343–362.

Fiske, S. T., Bersoff, D. N., Borgida, E., Deaux, K., & Heilman, M. E. (1991). Social science research on trial: Use of sex stereotyping research in Price Waterhouse v. Hopkins. American Psychologist, 46(10), 1049–1060.

Lewin, K. (1999). The complete social scientist: A Kurt Lewin reader (M. Gold, Ed.). Washington, DC: American Psychological Association.

Saxe, L., Dougherty, D., & Cross, T. (1985). The validity of polygraph testing: Scientific analysis and public controversy. American Psychologist, 40, 355–366.

Woolfolk-Hoy, A. E. (2005). Educational psychology (9th ed.). Boston, MA: Allyn & Bacon.


3.1 Psychologists Use the Scientific Method to Guide Their Research

Charles Stangor, Jennifer Walinga, and Jorden A. Cummings

Learning Objectives

  1. Describe the principles of the scientific method and explain its importance in conducting and interpreting research.
  2. Differentiate laws from theories and explain how research hypotheses are developed and tested.
  3. Discuss the procedures that researchers use to ensure that their research with humans and with animals is ethical.

Psychologists aren’t the only people who seek to understand human behaviour and solve social problems. Philosophers, religious leaders, and politicians, among others, also strive to provide explanations for human behaviour. But psychologists believe that research is the best tool for understanding human beings and their relationships with others. Rather than accepting the claim of a philosopher that people do (or do not) have free will, a psychologist would collect data to empirically test whether or not people are able to actively control their own behaviour. Rather than accepting a politician’s contention that creating (or abandoning) a new centre for mental health will improve the lives of individuals in the inner city, a psychologist would empirically assess the effects of receiving mental health treatment on the quality of life of the recipients. The statements made by psychologists are empirical, which means they are based on systematic collection and analysis of data.

The Scientific Method

All scientists (whether they are physicists, chemists, biologists, sociologists, or psychologists) are engaged in the basic processes of collecting data and drawing conclusions about those data. The methods used by scientists have developed over many years and provide a common framework for developing, organizing, and sharing information. The scientific method is the set of assumptions, rules, and procedures scientists use to conduct research.

In addition to requiring that science be empirical, the scientific method demands that the procedures used be objective, or free from the personal bias or emotions of the scientist. The scientific method proscribes how scientists collect and analyze data, how they draw conclusions from data, and how they share data with others. These rules increase objectivity by placing data under the scrutiny of other scientists and even the public at large. Because data are reported objectively, other scientists know exactly how the scientist collected and analyzed the data. This means that they do not have to rely only on the scientist’s own interpretation of the data; they may draw their own, potentially different, conclusions.

Most new research is designed to replicate — that is, to repeat, add to, or modify — previous research findings. The scientific method therefore results in an accumulation of scientific knowledge through the reporting of research and the addition to and modification of these reported findings by other scientists.

Laws and Theories as Organizing Principles

One goal of research is to organize information into meaningful statements that can be applied in many situations. Principles that are so general as to apply to all situations in a given domain of inquiry are known as laws. There are well-known laws in the physical sciences, such as the law of gravity and the laws of thermodynamics, and there are some universally accepted laws in psychology, such as the law of effect and Weber’s law. But because laws are very general principles and their validity has already been well established, they are themselves rarely directly subjected to scientific test.

The next step down from laws in the hierarchy of organizing principles is theory. A theory is an integrated set of principles that explains and predicts many, but not all, observed relationships within a given domain of inquiry. One example of an important theory in psychology is the stage theory of cognitive development proposed by the Swiss psychologist Jean Piaget. The theory states that children pass through a series of cognitive stages as they grow, each of which must be mastered in succession before movement to the next cognitive stage can occur. This is an extremely useful theory in human development because it can be applied to many different content areas and can be tested in many different ways.

Good theories have four important characteristics. First, good theories are general, meaning they summarize many different outcomes. Second, they are parsimonious, meaning they provide the simplest possible account of those outcomes. The stage theory of cognitive development meets both of these requirements. It can account for developmental changes in behaviour across a wide variety of domains, and yet it does so parsimoniously — by hypothesizing a simple set of cognitive stages. Third, good theories provide ideas for future research. The stage theory of cognitive development has been applied not only to learning about cognitive skills, but also to the study of children’s moral (Kohlberg, 1966) and gender (Ruble & Martin, 1998) development.

Finally, good theories are falsifiable (Popper, 1959), which means the variables of interest can be adequately measured and the relationships between the variables that are predicted by the theory can be shown through research to be incorrect. The stage theory of cognitive development is falsifiable because the stages of cognitive reasoning can be measured and because if research discovers, for instance, that children learn new tasks before they have reached the cognitive stage hypothesized to be required for that task, then the theory will be shown to be incorrect.

No single theory is able to account for all behaviour in all cases. Rather, theories are each limited in that they make accurate predictions in some situations or for some people but not in other situations or for other people. As a result, there is a constant exchange between theory and data: existing theories are modified on the basis of collected data, and the new modified theories then make new predictions that are tested by new data, and so forth. When a better theory is found, it will replace the old one. This is part of the accumulation of scientific knowledge.

The Research Hypothesis

Theories are usually framed too broadly to be tested in a single experiment. Therefore, scientists use a more precise statement of the presumed relationship between specific parts of a theory — a research hypothesis — as the basis for their research. A research hypothesis is a specific and falsifiable prediction about the relationship between or among two or more variables, where a variable is any attribute that can assume different values among different people or across different times or places. The research hypothesis states the existence of a relationship between the variables of interest and the specific direction of that relationship. For instance, the research hypothesis “Using marijuana will reduce learning” predicts that there is a relationship between one variable, “using marijuana,” and another variable called “learning.” Similarly, in the research hypothesis “Participating in psychotherapy will reduce anxiety,” the variables that are expected to be related are “participating in psychotherapy” and “level of anxiety.”

When stated in an abstract manner, the ideas that form the basis of a research hypothesis are known as conceptual variables. Conceptual variables are abstract ideas that form the basis of research hypotheses. Sometimes the conceptual variables are rather simple — for instance, age, gender, or weight. In other cases the conceptual variables represent more complex ideas, such as anxiety, cognitive development, learning, self-esteem, or sexism.

The first step in testing a research hypothesis involves turning the conceptual variables into measured variables, which are variables consisting of numbers that represent the conceptual variables. For instance, the conceptual variable “participating in psychotherapy” could be represented as the measured variable “number of psychotherapy hours the patient has accrued,” and the conceptual variable “using marijuana” could be assessed by having the research participants rate, on a scale from 1 to 10, how often they use marijuana or by administering a blood test that measures the presence of the chemicals in marijuana.

Psychologists use the term operational definition to refer to a precise statement of how a conceptual variable is turned into a measured variable. The relationship between conceptual and measured variables in a research hypothesis is diagrammed in Figure 3.1. The conceptual variables are represented in circles at the top of the figure (Psychotherapy and anxiety), and the measured variables are represented in squares at the bottom (number of hours the patient has spent in psychotherapy and anxiety concerns as reported by the patient). The two vertical arrows, which lead from the conceptual variables to the measured variables, represent the operational definitions of the two variables. The arrows indicate the expectation that changes in the conceptual variables (psychotherapy and anxiety) will cause changes in the corresponding measured variables (number of hours in psychotherapy and reported anxiety concerns). The measured variables are then used to draw inferences about the conceptual variables.

Figure 3.1. Research Hypothesis. In this research hypothesis, the conceptual variable of attending psychotherapy is operationalized using the number of hours of psychotherapy the client has completed, and the conceptual variable of anxiety is operationalized using self-reported levels of anxiety. The research hypothesis is that more psychotherapy will be related to less reported anxiety.

Table 3.1 lists some potential operational definitions of conceptual variables that have been used in psychological research. As you read through this list, note that in contrast to the abstract conceptual variables, the measured variables are very specific. This specificity is important for two reasons. First, more specific definitions mean that there is less danger that the collected data will be misunderstood by others. Second, specific definitions will enable future researchers to replicate the research.

Table 3.1 Examples of the Operational Definitions of Conceptual Variables that Have Been Used in Psychological Research
Conceptual variable Operational definitions
  • Number of presses of a button that administers shock to another student
  • Number of seconds taken to honk the horn at the car ahead after a stoplight turns green
Interpersonal attraction
  • Number of inches that an individual places his or her chair away from another person
  • Number of millimeters of pupil dilation when one person looks at another
Employee satisfaction
  • Number of days per month an employee shows up to work on time
  • Rating of job satisfaction from 1 (not at all satisfied) to 9 (extremely satisfied)
Decision-making skills
  • Number of groups able to correctly solve a group performance task
  • Number of seconds in which a person solves a problem
  • Number of negative words used in a creative story
  • Number of appointments made with a psychotherapist

Characteristics of an Ethical Research Project Using Human Participants

  • Trust and positive rapport are created between the researcher and the participant.
  • The rights of both the experimenter and participant are considered, and the relationship between them is mutually beneficial.
  • The experimenter treats the participant with concern and respect and attempts to make the research experience a pleasant and informative one.
  • Before the research begins, the participant is given all information relevant to his or her decision to participate, including any possibilities of physical danger or psychological stress.
  • The participant is given a chance to have questions about the procedure answered, thus guaranteeing his or her free choice about participating.
  • After the experiment is over, any deception that has been used is made public, and the necessity for it is explained.
  • The experimenter carefully debriefs the participant, explaining the underlying research hypothesis and the purpose of the experimental procedure in detail and answering any questions.
  • The experimenter provides information about how he or she can be contacted and offers to provide information about the results of the research if the participant is interested in receiving it. (Stangor, 2011)

This list presents some of the most important factors that psychologists take into consideration when designing their research. The most direct ethical concern of the scientist is to prevent harm to the research participants. One example is the well-known research of Stanley Milgram (1974) investigating obedience to authority. In these studies, participants were induced by an experimenter to administer electric shocks to another person so that Milgram could study the extent to which they would obey the demands of an authority figure. Most participants evidenced high levels of stress resulting from the psychological conflict they experienced between engaging in aggressive and dangerous behaviour and following the instructions of the experimenter. Studies such as those by Milgram are no longer conducted because the scientific community is now much more sensitized to the potential of such procedures to create emotional discomfort or harm.

Another goal of ethical research is to guarantee that participants have free choice regarding whether they wish to participate in research. Students in psychology classes may be allowed, or even required, to participate in research, but they are also always given an option to choose a different study to be in, or to perform other activities instead. And once an experiment begins, the research participant is always free to leave the experiment if he or she wishes to. Concerns with free choice also occur in institutional settings, such as in schools, hospitals, corporations, and prisons, when individuals are required by the institutions to take certain tests, or when employees are told or asked to participate in research.

Researchers must also protect the privacy of the research participants. In some cases data can be kept anonymous by not having the respondents put any identifying information on their questionnaires. In other cases the data cannot be anonymous because the researcher needs to keep track of which respondent contributed the data. In this case, one technique is to have each participant use a unique code number to identify his or her data, such as the last four digits of the student ID number. In this way the researcher can keep track of which person completed which questionnaire, but no one will be able to connect the data with the individual who contributed them.

Perhaps the most widespread ethical concern to the participants in behavioural research is the extent to which researchers employ deception. Deception occurs whenever research participants are not completely and fully informed about the nature of the research project before participating in it. Deception may occur in an active way, such as when the researcher tells the participants that he or she is studying learning when in fact the experiment really concerns obedience to authority. In other cases the deception is more passive, such as when participants are not told about the hypothesis being studied or the potential use of the data being collected.

Some researchers have argued that no deception should ever be used in any research (Baumrind, 1985). They argue that participants should always be told the complete truth about the nature of the research they are in, and that when participants are deceived there will be negative consequences, such as the possibility that participants may arrive at other studies already expecting to be deceived. Other psychologists defend the use of deception on the grounds that it is needed to get participants to act naturally and to enable the study of psychological phenomena that might not otherwise get investigated. They argue that it would be impossible to study topics such as altruism, aggression, obedience, and stereotyping without using deception because if participants were informed ahead of time what the study involved, this knowledge would certainly change their behaviour. The codes of ethics of the Canadian Psychological Association and the Tri-Council Policy Statement of Canada’s three federal research agencies (the Canadian Institute of Health Research [CIHR], the Natural Sciences and Engineering Research Council of Canada [NSERC], and the Social Sciences and Humanities Research Council of Canada [SSHRC] or “the Agencies”) allow researchers to use deception, but these codes also require them to explicitly consider how their research might be conducted without the use of deception.

Research with Animals

Because animals make up an important part of the natural world, and because some research cannot be conducted using humans, animals are also participants in psychological research (Figure 3.3). Most psychological research using animals is now conducted with rats, mice, and birds, and the use of other animals in research is declining (Thomas & Blackman, 1992). As with ethical decisions involving human participants, a set of basic principles has been developed that helps researchers make informed decisions about such research; a summary is shown below.

Canadian Psychological Association Guidelines on Humane Care and Use of Animals in Research

The following are some of the most important ethical principles from the Canadian Psychological Association’s (CPA) guidelines on research with animals.

  • II.45 Not use animals in their research unless there is a reasonable expectation that the research will increase understanding of the structures and processes underlying behaviour, or increase understanding of the particular animal species used in the study, or result eventually in benefits to the health and welfare of humans or other animals.
  • II.46 Use a procedure subjecting animals to pain, stress, or privation only if an alternative procedure is unavailable and the goal is justified by its prospective scientific, educational, or applied value.
  • II.47 Make every effort to minimize the discomfort, illness, and pain of animals. This would include performing surgical procedures only under appropriate anaesthesia, using techniques to avoid infection and minimize pain during and after surgery and, if disposing of experimental animals is carried out at the termination of the study, doing so in a humane way. (Canadian Code of Ethics for Psychologists)
  • II.48 Use animals in classroom demonstrations only if the instructional objectives cannot be achieved through the use of video-tapes, films, or other methods, and if the type of demonstration is warranted by the anticipated instructional gain (Canadian Psychological Association, 2000).


An gloved hand holds a white rat.
Figure 3.2 Animal Research. Psychologists may use animals in their research, but they make reasonable efforts to minimize the discomfort the animals experience.

Because the use of animals in research involves a personal value, people naturally disagree about this practice. Although many people accept the value of such research (Plous, 1996), a minority of people, including animal-rights activists, believe that it is ethically wrong to conduct research on animals. This argument is based on the assumption that because animals are living creatures just as humans are, no harm should ever be done to them.

Most scientists, however, reject this view. They argue that such beliefs ignore the potential benefits that have come, and continue to come, from research with animals. For instance, drugs that can reduce the incidence of cancer or AIDS may first be tested on animals, and surgery that can save human lives may first be practised on animals. Research on animals has also led to a better understanding of the physiological causes of depression, phobias, and stress, among other illnesses. In contrast to animal-rights activists, then, scientists believe that because there are many benefits that accrue from animal research, such research can and should continue as long as the humane treatment of the animals used in the research is guaranteed.

Key Takeaways

  • Psychologists use the scientific method to generate, accumulate, and report scientific knowledge.
  • Basic research, which answers questions about behaviour, and applied research, which finds solutions to everyday problems, inform each other and work together to advance science.
  • Research reports describing scientific studies are published in scientific journals so that other scientists and laypersons may review the empirical findings.
  • Organizing principles, including laws, theories, and research hypotheses, give structure and uniformity to scientific methods.
  • Concerns for conducting ethical research are paramount. Researchers ensure that participants are given free choice to participate and that their privacy is protected. Informed consent and debriefing help provide humane treatment of participants.
  • A cost-benefit analysis is used to determine what research should and should not be allowed to proceed.

Exercises and Critical Thinking

  1. Give an example from personal experience of how you or someone you know has benefited from the results of scientific research.
  2. Find and discuss a research project that in your opinion has ethical concerns. Explain why you find these concerns to be troubling.
  3. Indicate your personal feelings about the use of animals in research. When should and should not animals be used? What principles have you used to come to these conclusions?

Image Attributions

Figure 3.2:Wistar rat” by Janet Stephens ( is in the public domain.


Baumrind, D. (1985). Research using intentional deception: Ethical issues revisited. American Psychologist, 40, 165–174.

Canadian Psychological Association. (2000). Canadian code of ethics for psychologists (third edition) [PDF]. Retrieved July 2014 from

Kohlberg, L. (1966). A cognitive-developmental analysis of children’s sex-role concepts and attitudes. In E. E. Maccoby (Ed.), The development of sex differences. Stanford, CA: Stanford University Press.

Milgram, S. (1974). Obedience to authority: An experimental view. New York, NY: Harper and Row.

Plous, S. (1996). Attitudes toward the use of animals in psychological research and education. Psychological Science, 7, 352–358.

Popper, K. R. (1959). The logic of scientific discovery. New York, NY: Basic Books.Rosenthal, R. (1994). Science and ethics in conducting, analyzing, and reporting psychological research. Psychological Science, 5, 127–134.

Ruble, D., & Martin, C. (1998). Gender development. In W. Damon (Ed.), Handbook of child psychology (5th ed., pp. 933–1016). New York, NY: John Wiley & Sons.

Stangor, C. (2011). Research methods for the behavioral sciences (4th ed.). Mountain View, CA: Cengage.

Thomas, G., & Blackman, D. (1992). The future of animal studies in psychology. American Psychologist, 47, 1678.

3.2 Moral Foundations of Ethical Research

Paul C. Price, Rajiv S. Jhangiani, I-Chant A. Chiang, Dana C. Leighton, and Carrie Cuttler

Learning Objectives

  1. Describe a simple framework for thinking about ethical issues in psychological research.
  2. Give examples of several ethical issues that arise in psychological research—including ones that affect research participants, the scientific community, and society more generally.

In 1998 a medical journal called The Lancet published an article of interest to many psychologists. The researchers claimed to have shown a statistical relationship between receiving the combined measles, mumps, and rubella (MMR) vaccine and the development of autism—suggesting furthermore that the vaccine might even cause autism. One result of this report was that many parents decided not to have their children vaccinated, which of course put them at higher risk for measles, mumps, and rubella. However, follow-up studies by other researchers consistently failed to find a statistical relationship between the MMR vaccine and autism—and it is widely accepted now in the scientific community that there is no relationship. In addition, several more serious problems with the original research were uncovered. Among them were that the lead researcher stood to gain financially from his conclusions because he had patented a competing measles vaccine. He had also used biased methods to select and test his research participants and had used unapproved and medically unnecessary procedures on them. In 2010 The Lancet retracted the article, and the lead researcher’s right to practice medicine was revoked (Burns, 2010).

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In the upcoming sections (3.2. 3.3, 3.4) we explore the ethics of scientific research in psychology. We begin with a general framework for thinking about the ethics of scientific research in psychology. Then we look at some specific ethical codes for biomedical and behavioral researchers —focusing on the Ethics Code of the American Psychological Association. Finally, we consider some practical tips for conducting ethical research in psychology.

Ethics is the branch of philosophy that is concerned with morality—what it means to behave morally and how people can achieve that goal. It can also refer to a set of principles and practices that provide moral guidance in a particular field. There is an ethics of business, medicine, teaching, and of course, scientific research. As the opening example illustrates, many kinds of ethical issues can arise in scientific research, especially when it involves human participants. For this reason, it is useful to begin with a general framework for thinking through these issues.

A Framework for Thinking About Research Ethics

Table 3.1 “A Framework for Thinking About Ethical Issues in Scientific Research” presents a framework for thinking through the ethical issues involved in psychological research. The rows of Table 3.1 “A Framework for Thinking About Ethical Issues in Scientific Research” represent four general moral principles that apply to scientific research: weighing risks against benefits, acting responsibly and with integrity, seeking justice, and respecting people’s rights and dignity. (These principles are adapted from those in the American Psychological Association [APA] Ethics Code.) The columns of Table 3.2 “A Framework for Thinking About Ethical Issues in Scientific Research” represent three groups of people that are affected by scientific research: the research participants, the scientific community, and society more generally. The idea is that a thorough consideration of the ethics of any research project must take into account how each of the four moral principles applies to each of the three groups of people.

Table 3.2 A Framework for Thinking About Ethical Issues in Scientific Research
Who is affected?
Moral principle Research participants Scientific community Society
Weighing risks against benefits
Acting responsibly and with integrity
Seeking justice
Respecting people’s rights and dignity

Moral Principles

Let us look more closely at each of the moral principles and how they can be applied to each of the three groups.

Weighing Risks Against Benefits

Scientific research in psychology can be ethical only if its risks are outweighed by its benefits. Among the risks to research participants are that a treatment might fail to help or even be harmful, a procedure might result in physical or psychological harm, and their right to privacy might be violated. Among the potential benefits are receiving a helpful treatment, learning about psychology, experiencing the satisfaction of contributing to scientific knowledge, and receiving money or course credit for participating. Scientific research can have risks and benefits to the scientific community and to society too (Rosenthal, 1994). A risk to science is that if a research question is uninteresting or a study is poorly designed, then the time, money, and effort spent on that research could have been spent on more productive research. A risk to society is that research results could be misunderstood or misapplied with harmful consequences. The research that mistakenly linked the measles, mumps, and rubella (MMR) vaccine to autism resulted in both of these kinds of harm. Of course, the benefits of scientific research to science and society are that it advances scientific knowledge and can contribute to the welfare of society.

It is not necessarily easy to weigh the risks of research against its benefits because the risks and benefits may not be directly comparable. For example, it is common for the risks of a study to be primarily to the research participants but the benefits primarily for science or society. Consider, for example, Stanley Milgram’s original study on obedience to authority (Milgram, 1963). The participants were told that they were taking part in a study on the effects of punishment on learning and were instructed to give electric shocks to another participant each time that participant responded incorrectly on a learning task. With each incorrect response, the shock became stronger—eventually causing the other participant (who was in the next room) to protest, complain about his heart, scream in pain, and finally fall silent and stop responding. If the first participant hesitated or expressed concern, the researcher said that he must continue. In reality, the other participant was a confederate of the researcher—a helper who pretended to be a real participant—and the protests, complaints, and screams that the real participant heard were an audio recording that was activated when he flipped the switch to administer the “shocks.” The surprising result of this study was that most of the real participants continued to administer the shocks right through the confederate’s protests, complaints, and screams. Although this is considered one of the most important results in psychology—with implications for understanding events like the Holocaust or the mistreatment of prisoners by US soldiers at Abu Ghraib—it came at the cost of producing severe psychological stress in the research participants.

Was It Worth It?

Much of the debate over the ethics of Milgram’s obedience study concerns the question of whether the resulting scientific knowledge was worth the harm caused to the research participants. To get a better sense of the harm, consider Milgram’s (1963) own description of it.

In a large number of cases, the degree of tension reached extremes that are rarely seen in sociopsychological laboratory studies. Subjects were observed to sweat, tremble, stutter, bite their lips, groan, and dig their fingernails into their flesh.…Fourteen of the 40 subjects showed definite signs of nervous laughter and smiling. The laughter seemed entirely out of place, even bizarre. Full blown uncontrollable seizures [of laughter] were observed for three subjects. On one occasion we observed a seizure so violently convulsive that it was necessary to call a halt to the experiment (p. 375).

Milgram also noted that another observer reported that within 20 minutes one participant “was reduced to a twitching, stuttering wreck, who was rapidly approaching the point of nervous collapse” (p. 377)

To Milgram’s credit, he went to great lengths to debrief his participants—including returning their mental states to normal—and to show that most of them thought the research was valuable and were glad to have participated.

Acting Responsibly and With Integrity

Researchers must act responsibly and with integrity. This means carrying out their research in a thorough and competent manner, meeting their professional obligations, and being truthful. Acting with integrity is important because it promotes trust, which is an essential element of all effective human relationships. Participants must be able to trust that researchers are being honest with them (e.g., about what the study involves), will keep their promises (e.g., to maintain confidentiality), and will carry out their research in ways that maximize benefits and minimize risk. An important issue here is the use of deception. Some research questions (such as Milgram’s) are difficult or impossible to answer without deceiving research participants. Thus acting with integrity can conflict with doing research that advances scientific knowledge and benefits society. We will consider how psychologists generally deal with this conflict shortly.

The scientific community and society must also be able to trust that researchers have conducted their research thoroughly and competently and that they have reported on it honestly. Again, the example at the beginning of the chapter illustrates what can happen when this trust is violated. In this case, other researchers wasted resources on unnecessary follow-up research and people avoided the MMR vaccine, putting their children at increased risk of measles, mumps, and rubella.

Seeking Justice

Researchers must conduct their research in a just manner. They should treat their participants fairly, for example, by giving them adequate compensation for their participation and making sure that benefits and risks are distributed across all participants. For example, in a study of a new and potentially beneficial psychotherapy, some participants might receive the psychotherapy while others serve as a control group that receives no treatment. If the psychotherapy turns out to be effective, it would be fair to offer it to participants in the control group when the study ends.

At a broader societal level, members of some groups have historically faced more than their fair share of the risks of scientific research, including people who are institutionalized, are disabled, or belong to racial or ethnic minorities. A particularly tragic example is the Tuskegee syphilis study conducted by the US Public Health Service from 1932 to 1972 (Reverby, 2009). The participants in this study were poor African American men in the vicinity of Tuskegee, Alabama, who were told that they were being treated for “bad blood.” Although they were given some free medical care, they were not treated for their syphilis. Instead, they were observed to see how the disease developed in untreated patients. Even after the use of penicillin became the standard treatment for syphilis in the 1940s, these men continued to be denied treatment without being given an opportunity to leave the study. The study was eventually discontinued only after details were made known to the general public by journalists and activists. It is now widely recognized that researchers need to consider issues of justice and fairness at the societal level.

“They Were Betrayed”

In 1997—65 years after the Tuskegee Syphilis Study began and 25 years after it ended—President Bill Clinton formally apologized on behalf of the US government to those who were affected. Here is an excerpt from the apology:

So today America does remember the hundreds of men used in research without their knowledge and consent. We remember them and their family members. Men who were poor and African American, without resources and with few alternatives, they believed they had found hope when they were offered free medical care by the United States Public Health Service. They were betrayed.

Read the full text of the apology at

Respecting People’s Rights and Dignity

Researchers must respect people’s rights and dignity as human beings. One element of this is respecting their autonomy—their right to make their own choices and take their own actions free from coercion. Of fundamental importance here is the concept of informed consent. This means that researchers obtain and document people’s agreement to participate in a study after having informed them of everything that might reasonably be expected to affect their decision. Consider the participants in the Tuskegee study. Although they agreed to participate in the study, they were not told that they had syphilis but would be denied treatment for it. Had they been told this basic fact about the study, it seems likely that they would not have agreed to participate. Likewise, had participants in Milgram’s study been told that they might be “reduced to a twitching, stuttering wreck,” it seems likely that many of them would not have agreed to participate. In neither of these studies did participants give true informed consent.

Another element of respecting people’s rights and dignity is respecting their privacy—their right to decide what information about them is shared with others. This means that researchers must maintain confidentiality, which is essentially an agreement not to disclose participants’ personal information without their consent or some appropriate legal authorization. Even more ideally participants can maintain anonymity, which is when their name and other personally identifiable information is not collected at all.

Unavoidable Ethical Conflict

It may already be clear that ethical conflict in psychological research is unavoidable. Because there is little, if any, psychological research that is completely risk-free, there will almost always be a conflict between risks and benefits. Research that is beneficial to one group (e.g., the scientific community) can be harmful to another (e.g., the research participants), creating especially difficult tradeoffs. We have also seen that being completely truthful with research participants can make it difficult or impossible to conduct scientifically valid studies on important questions.

Of course, many ethical conflicts are fairly easy to resolve. Nearly everyone would agree that deceiving research participants and then subjecting them to physical harm would not be justified by filling a small gap in the research literature. But many ethical conflicts are not easy to resolve, and competent and well-meaning researchers can disagree about how to resolve them. Consider, for example, an actual study on “personal space” conducted in a public men’s room (Middlemist, Knowles, & Matter, 1976). The researchers secretly observed their participants to see whether it took them longer to begin urinating when there was another man (a confederate of the researchers) at a nearby urinal. While some critics found this to be an unjustified assault on human dignity (Koocher, 1977), the researchers had carefully considered the ethical conflicts, resolved them as best they could, and concluded that the benefits of the research outweighed the risks (Middlemist, Knowles, & Matter, 1977). For example, they had interviewed some preliminary participants and found that none of them was bothered by the fact that they had been observed.

The point here is that although it may not be possible to eliminate ethical conflict completely, it is possible to deal with it in responsible and constructive ways. In general, this means thoroughly and carefully thinking through the ethical issues that are raised, minimizing the risks, and weighing the risks against the benefits. It also means being able to explain one’s ethical decisions to others, seeking feedback on them, and ultimately taking responsibility for them.


Key Takeaways

  • A wide variety of ethical issues arise in psychological research. Thinking them through requires considering how each of four moral principles (weighing risks against benefits, acting responsibly and with integrity, seeking justice, and respecting people’s rights and dignity) applies to each of three groups of people (research participants, science, and society).
  • Ethical conflict in psychological research is unavoidable. Researchers must think through the ethical issues raised by their research, minimize the risks, weigh the risks against the benefits, be able to explain their ethical decisions, seek feedback about these decisions from others, and ultimately take responsibility for them.


  1. Practice: Imagine a study testing the effectiveness of a new drug for treating obsessive-compulsive disorder. Give a hypothetical example of an ethical issue from each cell of Table 3.1 “A Framework for Thinking About Ethical Issues in Scientific Research” that could arise in this research.
  2. Discussion: It has been argued that researchers are not ethically responsible for the misinterpretation or misuse of their research by others. Do you agree? Why or why not?


Burns, J. F. (2010, May 24). British medical council bars doctor who linked vaccine to autism. The New York Times. Retrieved from

Rosenthal, R. M. (1994). Science and ethics in conducting, analyzing, and reporting psychological research. Psychological Science, 5, 127–133.

Milgram, S. (1963). Behavioral study of obedience. Journal of Abnormal and Social Psychology, 67, 371–378.

Milgram, S. (1963). Behavioral study of obedience. Journal of Abnormal and Social Psychology, 67, 371–378.

Reverby, S. M. (2009). Examining Tuskegee: The infamous syphilis study and its legacy. Chapel Hill, NC: University of North Carolina Press.

Middlemist, R. D., Knowles, E. S., & Matter, C. F. (1976). Personal space invasions in the lavatory: Suggestive evidence for arousal. Journal of Personality and Social Psychology, 33, 541–546.

Koocher, G. P. (1977). Bathroom behavior and human dignity. Journal of Personality and Social Psychology, 35, 120–121.

Middlemist, R. D., Knowles, E. S., & Matter, C. F. (1977). What to do and what to report: A reply to Koocher. Journal of Personality and Social Psychology, 35, 122–125.

3.3 From Moral Principles to Ethics Codes

Paul C. Price, Rajiv S. Jhangiani, I-Chant A. Chiang, Dana C. Leighton, and Carrie Cuttler

Learning Objectives

  1. Describe the history of ethics codes for scientific research with human participants.
  2. Summarize the American Psychological Association Ethics Code—especially as it relates to informed consent, deception, debriefing, research with nonhuman animals, and scholarly integrity.

The general moral principles of weighing risks against benefits, acting with integrity, seeking justice, and respecting people’s rights and dignity provide a useful starting point for thinking about the ethics of psychological research because essentially everyone agrees on them. As we have seen, however, even people who agree on these general principles can disagree about specific ethical issues that arise in the course of conducting research. This is why there also exist more detailed and enforceable ethics codes that provide guidance on important issues that arise frequently. In this section, we begin with a brief historical overview of such ethics codes and then look closely at the one that is most relevant to psychological research—that of the American Psychological Association (APA).

Historical Overview

One of the earliest ethics codes was the Nuremberg Code—a set of 10 principles written in 1947 in conjunction with the trials of Nazi physicians accused of shockingly cruel research on concentration camp prisoners during World War II. It provided a standard against which to compare the behavior of the men on trial—many of whom were eventually convicted and either imprisoned or sentenced to death. The Nuremberg Code was particularly clear about the importance of carefully weighing risks against benefits and the need for informed consent. The Declaration of Helsinki is a similar ethics code that was created by the World Medical Council in 1964. Among the standards that it added to the Nuremberg Code was that research with human participants should be based on a written protocol—a detailed description of the research—that is reviewed by an independent committee. The Declaration of Helsinki has been revised several times, most recently in 2004.

In the United States, concerns about the Tuskegee study and others led to the publication in 1978 of a set of federal guidelines called the Belmont Report. The Belmont Report explicitly recognized the principle of seeking justice, including the importance of conducting research in a way that distributes risks and benefits fairly across different groups at the societal level. It also recognized the importance of respect for persons, which translates to the need for informed consent. Finally, it recognized the principle of beneficence, which underscores the importance of maximizing the benefits of research while minimizing harms to participants and society. The Belmont Report became the basis of a set of laws—the Federal Policy for the Protection of Human Subjects—that apply to research conducted, supported, or regulated by the federal government. An extremely important part of these regulations is that universities, hospitals, and other institutions that receive support from the federal government must establish an ethical review board (ERB) or an institutional review board (IRB)—a committee that is responsible for reviewing research protocols for potential ethical problems. An IRB must consist of at least five people with varying backgrounds, including members of different professions, scientists and nonscientists, men and women, and at least one person not otherwise affiliated with the institution. The IRB helps to make sure that the risks of the proposed research are minimized, the benefits outweigh the risks, the research is carried out in a fair manner, and the informed consent procedure is adequate.

The federal regulations also distinguish research that poses three levels of risk. Exempt research includes research on the effectiveness of normal educational activities, the use of standard psychological measures and surveys of a nonsensitive nature that are administered in a way that maintains confidentiality, and research using existing data from public sources. It is called exempt because the regulations do not apply to it. Minimal risk research exposes participants to risks that are no greater than those encountered by healthy people in daily life or during routine physical or psychological examinations. Minimal risk research can receive an expedited review by one member of the IRB or by a separate committee under the authority of the IRB that can only approve minimal risk research. (Many departments of psychology have such separate committees.) Finally, at-risk research poses greater than minimal risk and must be reviewed by the full board of IRB members.

Ethics Codes

The link that follows the list—from the Office of Human Subjects Research at the National Institutes of Health—allows you to read the ethics codes discussed in this section in their entirety. They are all highly recommended and, with the exception of the Federal Policy, short and easy to read.

APA Ethics Code

The APA’s Ethical Principles of Psychologists and Code of Conduct (also known as the APA Ethics Code) was first published in 1953 and has been revised several times since then, most recently in 2010. It includes about 150 specific ethical standards that psychologists and their students are expected to follow. Much of the APA Ethics Code concerns the clinical practice of psychology—advertising one’s services, setting and collecting fees, having personal relationships with clients, and so on. For our purposes, the most relevant part is Standard 8: Research and Publication. Although Standard 8 is reproduced here in its entirety, we should consider some of its most important aspects—informed consent, deception, debriefing, the use of nonhuman animal subjects, and scholarly integrity—in more detail.

APA Ethics Code

Standard 8: Research and Publication

8.01 Institutional Approval

When institutional approval is required, psychologists provide accurate information about their research proposals and obtain approval prior to conducting the research. They conduct the research in accordance with the approved research protocol.

8.02 Informed Consent to Research

  1. When obtaining informed consent as required in Standard 3.10, Informed Consent, psychologists inform participants about (1) the purpose of the research, expected duration, and procedures; (2) their right to decline to participate and to withdraw from the research once participation has begun; (3) the foreseeable consequences of declining or withdrawing; (4) reasonably foreseeable factors that may be expected to influence their willingness to participate such as potential risks, discomfort, or adverse effects; (5) any prospective research benefits; (6) limits of confidentiality; (7) incentives for participation; and (8) whom to contact for questions about the research and research participants’ rights. They provide opportunity for the prospective participants to ask questions and receive answers. (See also Standards 8.03, Informed Consent for Recording Voices and Images in Research; 8.05, Dispensing With Informed Consent for Research; and 8.07, Deception in Research.)
  2. Psychologists conducting intervention research involving the use of experimental treatments clarify to participants at the outset of the research (1) the experimental nature of the treatment; (2) the services that will or will not be available to the control group(s) if appropriate; (3) the means by which assignment to treatment and control groups will be made; (4) available treatment alternatives if an individual does not wish to participate in the research or wishes to withdraw once a study has begun; and (5) compensation for or monetary costs of participating including, if appropriate, whether reimbursement from the participant or a third-party payor will be sought. (See also Standard 8.02a, Informed Consent to Research.)

8.03 Informed Consent for Recording Voices and Images in Research

Psychologists obtain informed consent from research participants prior to recording their voices or images for data collection unless (1) the research consists solely of naturalistic observations in public places, and it is not anticipated that the recording will be used in a manner that could cause personal identification or harm, or (2) the research design includes deception, and consent for the use of the recording is obtained during debriefing. (See also Standard 8.07, Deception in Research.)

8.04 Client/Patient, Student, and Subordinate Research Participants

  1. When psychologists conduct research with clients/patients, students, or subordinates as participants, psychologists take steps to protect the prospective participants from adverse consequences of declining or withdrawing from participation.
  2. When research participation is a course requirement or an opportunity for extra credit, the prospective participant is given the choice of equitable alternative activities.

8.05 Dispensing With Informed Consent for Research

Psychologists may dispense with informed consent only (1) where research would not reasonably be assumed to create distress or harm and involves (a) the study of normal educational practices, curricula, or classroom management methods conducted in educational settings; (b) only anonymous questionnaires, naturalistic observations, or archival research for which disclosure of responses would not place participants at risk of criminal or civil liability or damage their financial standing, employability, or reputation, and confidentiality is protected; or (c) the study of factors related to job or organization effectiveness conducted in organizational settings for which there is no risk to participants’ employability, and confidentiality is protected or (2) where otherwise permitted by law or federal or institutional regulations.

8.06 Offering Inducements for Research Participation

  1. Psychologists make reasonable efforts to avoid offering excessive or inappropriate financial or other inducements for research participation when such inducements are likely to coerce participation.
  2. When offering professional services as an inducement for research participation, psychologists clarify the nature of the services, as well as the risks, obligations, and limitations. (See also Standard 6.05, Barter With Clients/Patients.)

8.07 Deception in Research

  1. Psychologists do not conduct a study involving deception unless they have determined that the use of deceptive techniques is justified by the study’s significant prospective scientific, educational, or applied value and that effective nondeceptive alternative procedures are not feasible.
  2. Psychologists do not deceive prospective participants about research that is reasonably expected to cause physical pain or severe emotional distress.
  3. Psychologists explain any deception that is an integral feature of the design and conduct of an experiment to participants as early as is feasible, preferably at the conclusion of their participation, but no later than at the conclusion of the data collection, and permit participants to withdraw their data. (See also Standard 8.08, Debriefing.)

8.08 Debriefing

  1. Psychologists provide a prompt opportunity for participants to obtain appropriate information about the nature, results, and conclusions of the research, and they take reasonable steps to correct any misconceptions that participants may have of which the psychologists are aware.
  2. If scientific or humane values justify delaying or withholding this information, psychologists take reasonable measures to reduce the risk of harm.
  3. When psychologists become aware that research procedures have harmed a participant, they take reasonable steps to minimize the harm.

8.09 Humane Care and Use of Animals in Research

  1. Psychologists acquire, care for, use, and dispose of animals in compliance with current federal, state, and local laws and regulations, and with professional standards.
  2. Psychologists trained in research methods and experienced in the care of laboratory animals supervise all procedures involving animals and are responsible for ensuring appropriate consideration of their comfort, health, and humane treatment.
  3. Psychologists ensure that all individuals under their supervision who are using animals have received instruction in research methods and in the care, maintenance, and handling of the species being used, to the extent appropriate to their role. (See also Standard 2.05, Delegation of Work to Others.)
  4. Psychologists make reasonable efforts to minimize the discomfort, infection, illness, and pain of animal subjects.
  5. Psychologists use a procedure subjecting animals to pain, stress, or privation only when an alternative procedure is unavailable and the goal is justified by its prospective scientific, educational, or applied value.
  6. Psychologists perform surgical procedures under appropriate anesthesia and follow techniques to avoid infection and minimize pain during and after surgery.
  7. When it is appropriate that an animal’s life be terminated, psychologists proceed rapidly, with an effort to minimize pain and in accordance with accepted procedures.

8.10 Reporting Research Results

  1. Psychologists do not fabricate data. (See also Standard 5.01a, Avoidance of False or Deceptive Statements.)
  2. If psychologists discover significant errors in their published data, they take reasonable steps to correct such errors in a correction, retraction, erratum, or other appropriate publication means.

8.11 Plagiarism

Psychologists do not present portions of another’s work or data as their own, even if the other work or data source is cited occasionally.

8.12 Publication Credit

  1. Psychologists take responsibility and credit, including authorship credit, only for work they have actually performed or to which they have substantially contributed. (See also Standard 8.12b, Publication Credit.)
  2. Principal authorship and other publication credits accurately reflect the relative scientific or professional contributions of the individuals involved, regardless of their relative status. Mere possession of an institutional position, such as department chair, does not justify authorship credit. Minor contributions to the research or to the writing for publications are acknowledged appropriately, such as in footnotes or in an introductory statement.
  3. Except under exceptional circumstances, a student is listed as principal author on any multiple-authored article that is substantially based on the student’s doctoral dissertation. Faculty advisors discuss publication credit with students as early as feasible and throughout the research and publication process as appropriate. (See also Standard 8.12b, Publication Credit.)

8.13 Duplicate Publication of Data

Psychologists do not publish, as original data, data that have been previously published. This does not preclude republishing data when they are accompanied by proper acknowledgment.

8.14 Sharing Research Data for Verification

  1. After research results are published, psychologists do not withhold the data on which their conclusions are based from other competent professionals who seek to verify the substantive claims through reanalysis and who intend to use such data only for that purpose, provided that the confidentiality of the participants can be protected and unless legal rights concerning proprietary data preclude their release. This does not preclude psychologists from requiring that such individuals or groups be responsible for costs associated with the provision of such information.
  2. Psychologists who request data from other psychologists to verify the substantive claims through reanalysis may use shared data only for the declared purpose. Requesting psychologists obtain prior written agreement for all other uses of the data.

8.15 Reviewers

Psychologists who review material submitted for presentation, publication, grant, or research proposal review respect the confidentiality of and the proprietary rights in such information of those who submitted it.

Source: You can read the full APA Ethics Code at

Informed Consent

Standards 8.02 to 8.05 are about informed consent. Again, informed consent means obtaining and documenting people’s agreement to participate in a study, having informed them of everything that might reasonably be expected to affect their decision. This includes details of the procedure, the risks and benefits of the research, the fact that they have the right to decline to participate or to withdraw from the study, the consequences of doing so, and any legal limits to confidentiality. For example, some states require researchers who learn of child abuse or other crimes to report this information to authorities.

Although the process of obtaining informed consent often involves having participants read and sign a consent form, it is important to understand that this is not all it is. Although having participants read and sign a consent form might be enough when they are competent adults with the necessary ability and motivation, many participants do not actually read consent forms or read them but do not understand them. For example, participants often mistake consent forms for legal documents and mistakenly believe that by signing them they give up their right to sue the researcher (Mann, 1994). Even with competent adults, therefore, it is good practice to tell participants about the risks and benefits, demonstrate the procedure, ask them if they have questions, and remind them of their right to withdraw at any time—in addition to having them read and sign a consent form.

Note also that there are situations in which informed consent is not necessary. These include situations in which the research is not expected to cause any harm and the procedure is straightforward or the study is conducted in the context of people’s ordinary activities. For example, if you wanted to sit outside a public building and observe whether people hold the door open for people behind them, you would not need to obtain their informed consent. Similarly, if a college instructor wanted to compare two legitimate teaching methods across two sections of his research methods course, he would not need to obtain informed consent from his students.


Deception of participants in psychological research can take a variety of forms: misinforming participants about the purpose of a study, using confederates, using phony equipment like Milgram’s shock generator, and presenting participants with false feedback about their performance (e.g., telling them they did poorly on a test when they actually did well). Deception also includes not informing participants of the full design or true purpose of the research even if they are not actively misinformed (Sieber, Iannuzzo, & Rodriguez, 1995). For example, a study on incidental learning—learning without conscious effort—might involve having participants read through a list of words in preparation for a “memory test” later. Although participants are likely to assume that the memory test will require them to recall the words, it might instead require them to recall the contents of the room or the appearance of the research assistant.

Some researchers have argued that deception of research participants is rarely if ever ethically justified. Among their arguments are that it prevents participants from giving truly informed consent, fails to respect their dignity as human beings, has the potential to upset them, makes them distrustful and therefore less honest in their responding, and damages the reputation of researchers in the field (Baumrind, 1985).

Note, however, that the APA Ethics Code takes a more moderate approach—allowing deception when the benefits of the study outweigh the risks, participants cannot reasonably be expected to be harmed, the research question cannot be answered without the use of deception, and participants are informed about the deception as soon as possible. This approach acknowledges that not all forms of deception are equally bad. Compare, for example, Milgram’s study in which he deceived his participants in several significant ways that resulted in their experiencing severe psychological stress with an incidental learning study in which a “memory test” turns out to be slightly different from what participants were expecting. It also acknowledges that some scientifically and socially important research questions can be difficult or impossible to answer without deceiving participants. Knowing that a study concerns the extent to which they obey authority, act aggressively toward a peer, or help a stranger is likely to change the way people behave so that the results no longer generalize to the real world.


Standard 8.08 is about debriefing. This is the process of informing research participants as soon as possible of the purpose of the study, revealing any deception, and correcting any other misconceptions they might have as a result of participating. Debriefing also involves minimizing harm that might have occurred. For example, an experiment on the effects of being in a sad mood on memory might involve inducing a sad mood in participants by having them think sad thoughts, watch a sad video, and/or listen to sad music. Debriefing would be the time to return participants’ moods to normal by having them think happy thoughts, watch a happy video, or listen to happy music.

Nonhuman Animal Subjects

Standard 8.09 is about the humane treatment and care of nonhuman animal subjects. Although most contemporary research in psychology does not involve nonhuman animal subjects, a significant minority of it does—especially in the study of learning and conditioning, behavioral neuroscience, and the development of drug and surgical therapies for psychological disorders.

The use of nonhuman animal subjects in psychological research is similar to the use of deception in that there are those who argue that it is rarely, if ever, ethically acceptable (Bowd & Shapiro, 1993). Clearly, nonhuman animals are incapable of giving informed consent. Yet they can be subjected to numerous procedures that are likely to cause them suffering. They can be confined, deprived of food and water, subjected to pain, operated on, and ultimately euthanized. (Of course, they can also be observed benignly in natural or zoo-like settings.) Others point out that psychological research on nonhuman animals has resulted in many important benefits to humans, including the development of behavioral therapies for many disorders, more effective pain control methods, and antipsychotic drugs (Miller, 1985). It has also resulted in benefits to nonhuman animals, including alternatives to shooting and poisoning as means of controlling them.

As with deception, the APA acknowledges that the benefits of research on nonhuman animals can outweigh the costs, in which case it is ethically acceptable. However, researchers must use alternative methods when they can. When they cannot, they must acquire and care for their subjects humanely and minimize the harm to them. For more information on the APA’s position on nonhuman animal subjects, see the website of the APA’s Committee on Animal Research and Ethics (

Scholarly Integrity

Standards 8.10 to 8.15 are about scholarly integrity. These include the obvious points that researchers must not fabricate data or plagiarize. Plagiarism means using others’ words or ideas without proper acknowledgment. Proper acknowledgment generally means indicating direct quotations with quotation marks and providing a citation to the source of any quotation or idea used.

The remaining standards make some less obvious but equally important points. Researchers should not publish the same data a second time as though it were new, they should share their data with other researchers, and as peer reviewers they should keep the unpublished research they review confidential. Note that the authors’ names on published research—and the order in which those names appear—should reflect the importance of each person’s contribution to the research. It would be unethical, for example, to include as an author someone who had made only minor contributions to the research (e.g., analyzing some of the data) or for a faculty member to make himself or herself the first author on research that was largely conducted by a student.


Key Takeaways

  • There are several written ethics codes for research with human participants that provide specific guidance on the ethical issues that arise most frequently. These codes include the Nuremberg Code, the Declaration of Helsinki, the Belmont Report, and the Federal Policy for the Protection of Human Subjects.
  • The APA Ethics Code is the most important ethics code for researchers in psychology. It includes many standards that are relevant mainly to clinical practice, but Standard 8 concerns informed consent, deception, debriefing, the use of nonhuman animal subjects, and scholarly integrity in research.
  • Research conducted at universities, hospitals, and other institutions that receive support from the federal government must be reviewed by an institutional review board (IRB)—a committee at the institution that reviews research protocols to make sure they conform to ethical standards.
  • Informed consent is the process of obtaining and documenting people’s agreement to participate in a study, having informed them of everything that might reasonably be expected to affect their decision. Although it often involves having them read and sign a consent form, it is not equivalent to reading and signing a consent form.
  • Although some researchers argue that deception of research participants is never ethically justified, the APA Ethics Code allows for its use when the benefits of using it outweigh the risks, participants cannot reasonably be expected to be harmed, there is no way to conduct the study without deception, and participants are informed of the deception as soon as possible.


  1. Practice: Read the Nuremberg Code, the Belmont Report, and Standard 8of the APA Ethics Code. List five specific similarities and five specific differences among them.
  2. Discussion: In a study on the effects of disgust on moral judgment, participants were asked to judge the morality of disgusting acts, including people eating a dead pet and passionate kissing between a brother and sister (Haidt, Koller, & Dias, 1993). If you were on the IRB that reviewed this protocol, what concerns would you have with it? Refer to the appropriate sections of the APA Ethics Code.


Mann, T. (1994). Informed consent for psychological research: Do subjects comprehend consent forms and understand their legal rights? Psychological Science, 5, 140–143.

Sieber, J. E., Iannuzzo, R., & Rodriguez, B. (1995). Deception methods in psychology: Have they changed in 23 years? Ethics & Behavior, 5, 67–85.

Baumrind, D. (1985). Research using intentional deception: Ethical issues revisited. American Psychologist, 40, 165–174.

Bowd, A. D., & Shapiro, K. J. (1993). The case against animal laboratory research in psychology. Journal of Social Issues, 49, 133–142.

Miller, N. E. (1985). The value of behavioral research on animals. American Psychologist, 40, 423–440.

Haidt, J., Koller, S. H., & Dias, M. (1993). Affect, culture, and morality, or is it wrong to eat your dog? Journal of Personality and Social Psychology, 65, 613–628.

3.4 Putting Ethics Into Practice

Paul C. Price, Rajiv S. Jhangiani, I-Chant A. Chiang, Dana C. Leighton, and Carrie Cuttler

Learning Objectives

  1. Describe several strategies for identifying and minimizing risks and deception in psychological research.
  2. Create thorough informed consent and debriefing procedures, including a consent form.

In this section, we look at some practical advice for conducting ethical research in psychology. Again, it is important to remember that ethical issues arise well before you begin to collect data and continue to arise through publication and beyond.

Know and Accept Your Ethical Responsibilities

As the American Psychological Association (APA) Ethics Code notes in its introduction, “Lack of awareness or misunderstanding of an ethical standard is not itself a defense to a charge of unethical conduct.” This is why the very first thing that you must do as a new researcher is to know and accept your ethical responsibilities. At a minimum, this means reading and understanding the relevant sections of the APA Ethics Code, distinguishing minimal risk from at-risk research, and knowing the specific policies and procedures of your institution—including how to prepare and submit a research protocol for institutional review board (IRB) review. If you are conducting research as a course requirement, there may be specific course standards, policies, and procedures. If any standard, policy, or procedure is unclear—or you are unsure what to do about an ethical issue that arises—you must seek clarification. You can do this by reviewing the relevant ethics codes, reading about how similar issues have been resolved by others, or consulting with more experienced researchers, your IRB, or your course instructor. Ultimately, you as the researcher must take responsibility for the ethics of the research you conduct.

Identify and Minimize Risks

As you design your study, you must identify and minimize risks to participants. Start by listing all the risks, including risks of physical and psychological harm and violations of confidentiality. Remember that it is easy for researchers to see risks as less serious than participants do or even to overlook them completely. For example, one student researcher wanted to test people’s sensitivity to violent images by showing them gruesome photographs of crime and accident scenes. Because she was an emergency medical technician, however, she greatly underestimated how disturbing these images were to most people. Remember too that some risks might apply only to some participants. For example, while most people would have no problem completing a survey about their fear of various crimes, those who have been a victim of one of those crimes might become upset. This is why you should seek input from a variety of people, including your research collaborators, more experienced researchers, and even from nonresearchers who might be better able to take the perspective of a participant.

Once you have identified the risks, you can often reduce or eliminate many of them. One way is to modify the research design. For example, you might be able to shorten or simplify the procedure to prevent boredom and frustration. You might be able to replace upsetting or offensive stimulus materials (e.g., graphic accident scene photos) with less upsetting or offensive ones (e.g., milder photos of the sort people are likely to see in the newspaper). A good example of modifying a research design is a 2009 replication of Milgram’s study conducted by Jerry Burger. Instead of allowing his participants to continue administering shocks up to the 450-V maximum, the researcher always stopped the procedure when they were about to administer the 150-V shock (Burger, 2009). This made sense because in Milgram’s study (a) participants’ severe negative reactions occurred after this point and (b) most participants who administered the 150-V shock continued all the way to the 450-V maximum. Thus the researcher was able to compare his results directly with Milgram’s at every point up to the 150-V shock and also was able to estimate how many of his participants would have continued to the maximum—but without subjecting them to the severe stress that Milgram did. (The results, by the way, were that these contemporary participants were just as obedient as Milgram’s were.)

A second way to minimize risks is to use a pre-screening procedure to identify and eliminate participants who are at high risk. You can do this in part through the informed consent process. For example, you can warn participants that a survey includes questions about their fear of crime and remind them that they are free to withdraw if they think this might upset them. Prescreening can also involve collecting data to identify and eliminate participants. For example, Burger used an extensive pre-screening procedure involving multiple questionnaires and an interview with a clinical psychologist to identify and eliminate participants with physical or psychological problems that put them at high risk.

A third way to minimize risks is to take active steps to maintain confidentiality. You should keep signed consent forms separately from any data that you collect and in such a way that no individual’s name can be linked to his or her data. In addition, beyond people’s sex and age, you should only collect personal information that you actually need to answer your research question. If people’s sexual orientation or ethnicity is not clearly relevant to your research question, for example, then do not ask them about it. Be aware also that certain data collection procedures can lead to unintentional violations of confidentiality. When participants respond to an oral survey in a shopping mall or complete a questionnaire in a classroom setting, it is possible that their responses will be overheard or seen by others. If the responses are personal, it is better to administer the survey or questionnaire individually in private or to use other techniques to prevent the unintentional sharing of personal information.

Identify and Minimize Deception

Remember that deception can take a variety of forms, not all of which involve actively misleading participants. It is also deceptive to allow participants to make incorrect assumptions (e.g., about what will be on a “memory test”) or simply withhold information about the full design or purpose of the study. It is best to identify and minimize all forms of deception.

Remember that according to the APA Ethics Code, deception is ethically acceptable only if there is no way to answer your research question without it. Therefore, if your research design includes any form of active deception, you should consider whether it is truly necessary. Imagine, for example, that you want to know whether the age of college professors affects students’ expectations about their teaching ability. You could do this by telling participants that you will show them photos of college professors and ask them to rate each one’s teaching ability. But if the photos are not really of college professors but of your own family members and friends, then this would be deception. This deception could easily be eliminated, however, by telling participants instead to imagine that the photos are of college professors and to rate them as if they were.

In general, it is considered acceptable to wait until debriefing before you reveal your research question as long as you describe the procedure, risks, and benefits during the informed consent process. For example, you would not have to tell participants that you wanted to know whether the age of college professors affects people’s expectations about them until the study was over. Not only is this information unlikely to affect people’s decision about whether or not to participate in the study, but it has the potential to invalidate the results. Participants who know that age is the independent variable might rate the older and younger “professors” differently because they think you want them to. Alternatively, they might be careful to rate them the same so that they do not appear prejudiced. But even this extremely mild form of deception can be minimized by informing participants—orally, in writing, or both—that although you have accurately described the procedure, risks, and benefits, you will wait to reveal the research question until afterward. In essence, participants give their consent to be deceived or to have information withheld from them until later.

Weigh the Risks Against the Benefits

Once the risks of the research have been identified and minimized, you need to weigh them against the benefits. This requires identifying all the benefits. Remember to consider benefits to the research participants, to science, and to society. If you are a student researcher, remember that one of the benefits is the knowledge you will gain about how to conduct scientific research in psychology—knowledge you can then use to complete your studies and succeed in graduate school or in your career.

If the research poses minimal risk—no more than in people’s daily lives or routine physical or psychological examinations—then even a small benefit to participants, science, or society is generally considered enough to justify it. If it poses more than minimal risk, then there should be more benefits. If the research has the potential to upset some participants, for example, then it becomes more important that the study is well designed and can answer a scientifically interesting research question or have clear practical implications. It would be unethical to subject people to pain, fear, or embarrassment for no better reason than to satisfy one’s personal curiosity. In general, psychological research that has the potential to cause harm that is more than minor or lasts for more than a short time is rarely considered justified by its benefits.

Create Informed Consent and Debriefing Procedures

Once you have settled on a research design, you need to create your informed consent and debriefing procedures. Start by deciding whether informed consent is necessary according to APA Standard 8.05. If informed consent is necessary, there are several things you should do. First, when you recruit participants—whether it is through word of mouth, posted advertisements, or a participant pool—provide them with as much information about the study as you can. This will allow those who might find the study objectionable to avoid it. Second, prepare a script or set of “talking points” to help you explain the study to your participants in simple everyday language. This should include a description of the procedure, the risks and benefits, and their right to withdraw at any time. Third, create an informed consent form that covers all the points in Standard 8.02a that participants can read and sign after you have described the study to them. Your university, department, or course instructor may have a sample consent form that you can adapt for your own study. If not, an Internet search will turn up several samples. Remember that if appropriate, both the oral and written parts of the informed consent process should include the fact that you are keeping some information about the design or purpose of the study from them but that you will reveal it during debriefing.

Debriefing is similar to informed consent in that you cannot necessarily expect participants to read and understand written debriefing forms. So again it is best to write a script or set of talking points with the goal of being able to explain the study in simple, everyday language. During the debriefing, you should reveal the research question and full design of the study. For example, if participants are tested under only one condition, then you should explain what happened in the other conditions. If you deceived your participants, you should reveal this as soon as possible, apologize for the deception, explain why it was necessary, and correct any misconceptions that participants might have as a result. Debriefing is also a good time to provide additional benefits to research participants by giving them relevant practical information or referrals to other sources of help. For example, in a study of attitudes toward domestic abuse, you could provide pamphlets about domestic abuse and referral information to the university counseling center for those who might want it.

Remember to schedule plenty of time for the informed consent and debriefing processes. They cannot be effective if you have to rush through them.

Get Approval

The next step is to get institutional approval for your research based on the specific policies and procedures at your institution or for your course. This will generally require writing a protocol that describes the purpose of the study, the research design and procedure, the risks and benefits, the steps taken to minimize risks, and the informed consent and debriefing procedures. Do not think of the institutional approval process as merely an obstacle to overcome but as an opportunity to think through the ethics of your research and to consult with others who are likely to have more experience or different perspectives than you. If the IRB has questions or concerns about your research, address them promptly and in good faith. This might even mean making further modifications to your research design and procedure before resubmitting your protocol.

Follow Through

Your concern with ethics should not end when your study receives institutional approval. It now becomes important to stick to the protocol you submitted or to seek additional approval for anything other than a minor change. During the research, you should monitor your participants for unanticipated reactions and seek feedback from them during debriefing. One criticism of Milgram’s study is that although he did not know ahead of time that his participants would have such severe negative reactions, he certainly knew after he had tested the first several participants and should have made adjustments at that point (Baumrind, 1985). Be alert also for potential violations of confidentiality. Keep the consent forms and the data safe and separate from each other and make sure that no one, intentionally or unintentionally, has access to any participant’s personal information.

Finally, you must maintain your integrity through the publication process and beyond. Address publication credit—who will be authors on the research and the order of authors—with your collaborators early and avoid plagiarism in your writing. Remember that your scientific goal is to learn about the way the world actually is and that your scientific duty is to report on your results honestly and accurately. So do not be tempted to fabricate data or alter your results in any way. Besides, unexpected results are often as interesting, or more so, than expected ones.


Key Takeaways

  • It is your responsibility as a researcher to know and accept your ethical responsibilities.
  • You can take several concrete steps to minimize risks and deception in your research. These include making changes to your research design, prescreening to identify and eliminate high-risk participants, and providing participants with as much information as possible during informed consent and debriefing.
  • Your ethical responsibilities continue beyond IRB approval. You need to monitor participants’ reactions, be alert for potential violations of confidentiality, and maintain scholarly integrity through the publication process.


  1. Discussion: How could you conduct a study on the extent to which people obey authority in a way that minimizes risks and deception as much as possible? (Note: Such a study would not have to look at all like Milgram’s.)
  2. Practice: Find a study in a professional journal and create a consent form for that study. Be sure to include all the information in Standard 8.02.


Burger, J. M. (2009). Replicating Milgram: Would people still obey today? American Psychologist, 64, 1–11.

Baumrind, D. (1985). Research using intentional deception: Ethical issues revisited. American Psychologist, 40, 165–174.


3.5 Psychologists Use Descriptive, Correlational, and Experimental Research Designs to Understand Behaviour

Charles Stangor and Jennifer Walinga

Learning Objectives

  1. Differentiate the goals of descriptive, correlational, and experimental research designs and explain the advantages and disadvantages of each.
  2. Explain the goals of descriptive research and the statistical techniques used to interpret it.
  3. Summarize the uses of correlational research and describe why correlational research cannot be used to infer causality.
  4. Review the procedures of experimental research and explain how it can be used to draw causal inferences.

Psychologists agree that if their ideas and theories about human behaviour are to be taken seriously, they must be backed up by data. However, the research of different psychologists is designed with different goals in mind, and the different goals require different approaches. These varying approaches, summarized in Table 3.3, are known as research designs. A research design is the specific method a researcher uses to collect, analyze, and interpret data. Psychologists use three major types of research designs in their research, and each provides an essential avenue for scientific investigation. Descriptive research is research designed to provide a snapshot of the current state of affairs. Correlational research is research designed to discover relationships among variables and to allow the prediction of future events from present knowledge. Experimental research is research in which initial equivalence among research participants in more than one group is created, followed by a manipulation of a given experience for these groups and a measurement of the influence of the manipulation. Each of the three research designs varies according to its strengths and limitations, and it is important to understand how each differs.

Table 3.3 Characteristics of the Three Research Designs
Research design Goal Advantages Disadvantages
Descriptive To create a snapshot of the current state of affairs Provides a relatively complete picture of what is occurring at a given time. Allows the development of questions for further study. Does not assess relationships among variables. May be unethical if participants do not know they are being observed.
Correlational To assess the relationships between and among two or more variables Allows testing of expected relationships between and among variables and the making of predictions. Can assess these relationships in everyday life events. Cannot be used to draw inferences about the causal relationships between and among the variables.
Experimental To assess the causal impact of one or more experimental manipulations on a dependent variable Allows drawing of conclusions about the causal relationships among variables. Cannot experimentally manipulate many important variables. May be expensive and time consuming.
Source: Stangor, 2011.

Descriptive Research: Assessing the Current State of Affairs

Descriptive research is designed to create a snapshot of the current thoughts, feelings, or behaviour of individuals. This section reviews three types of descriptive research: case studies, surveys, and naturalistic observation (Figure 3.3).

Sometimes the data in a descriptive research project are based on only a small set of individuals, often only one person or a single small group. These research designs are known as case studies descriptive records of one or more individual’s experiences and behaviour. Sometimes case studies involve ordinary individuals, as when developmental psychologist Jean Piaget used his observation of his own children to develop his stage theory of cognitive development. More frequently, case studies are conducted on individuals who have unusual or abnormal experiences or characteristics or who find themselves in particularly difficult or stressful situations. The assumption is that by carefully studying individuals who are socially marginal, who are experiencing unusual situations, or who are going through a difficult phase in their lives, we can learn something about human nature.

Sigmund Freud was a master of using the psychological difficulties of individuals to draw conclusions about basic psychological processes. Freud wrote case studies of some of his most interesting patients and used these careful examinations to develop his important theories of personality. One classic example is Freud’s description of “Little Hans,” a child whose fear of horses the psychoanalyst interpreted in terms of repressed sexual impulses and the Oedipus complex (Freud, 1909/1964).

Man reading newspaper on park bench.
Figure 3.3 Descriptive Research. Political polls reported in newspapers and on the Internet are descriptive research designs that provide snapshots of the likely voting behaviour of a population.

Another well-known case study is Phineas Gage, a man whose thoughts and emotions were extensively studied by cognitive psychologists after a railroad spike was blasted through his skull in an accident. Although there are questions about the interpretation of this case study (Kotowicz, 2007), it did provide early evidence that the brain’s frontal lobe is involved in emotion and morality (Damasio et al., 2005). An interesting example of a case study in clinical psychology is described by Rokeach (1964), who investigated in detail the beliefs of and interactions among three patients with schizophrenia, all of whom were convinced they were Jesus Christ.

In other cases the data from descriptive research projects come in the form of a survey a measure administered through either an interview or a written questionnaire to get a picture of the beliefs or behaviours of a sample of people of interest. The people chosen to participate in the research (known as the sample) are selected to be representative of all the people that the researcher wishes to know about (the population). In election polls, for instance, a sample is taken from the population of all “likely voters” in the upcoming elections.

The results of surveys may sometimes be rather mundane, such as “Nine out of 10 doctors prefer Tymenocin” or “The median income in the city of Hamilton is $46,712.” Yet other times (particularly in discussions of social behaviour), the results can be shocking: “More than 40,000 people are killed by gunfire in the United States every year” or “More than 60% of women between the ages of 50 and 60 suffer from depression.” Descriptive research is frequently used by psychologists to get an estimate of the prevalence (or incidence) of psychological disorders.

A final type of descriptive research — known as naturalistic observation — is research based on the observation of everyday events. For instance, a developmental psychologist who watches children on a playground and describes what they say to each other while they play is conducting descriptive research, as is a biopsychologist who observes animals in their natural habitats. One example of observational research involves a systematic procedure known as the strange situation, used to get a picture of how adults and young children interact. The data that are collected in the strange situation are systematically coded in a coding sheet such as that shown in Table 3.4.

Table 3.4 Sample Coding Form Used to Assess Child’s and Mother’s Behaviour in the Strange Situation
Coder name: Olive
This table represents a sample coding sheet from an episode of the “strange situation,” in which an infant (usually about one year old) is observed playing in a room with two adults — the child’s mother and a stranger. Each of the four coding categories is scored by the coder from 1 (the baby makes no effort to engage in the behaviour) to 7 (the baby makes a significant effort to engage in the behaviour). More information about the meaning of the coding can be found in Ainsworth, Blehar, Waters, and Wall (1978).

Coding categories explained:

  • Proximity: The baby moves toward, grasps, or climbs on the adult.
  • Maintaining contact: The baby resists being put down by the adult by crying or trying to climb back up.
  • Resistance: The baby pushes, hits, or squirms to be put down from the adult’s arms.
  • Avoidance: The baby turns away or moves away from the adult.
Episode Coding categories
Proximity Contact Resistance Avoidance
Mother and baby play alone 1 1 1 1
Mother puts baby down 4 1 1 1
Stranger enters room 1 2 3 1
Mother leaves room; stranger plays with baby 1 3 1 1
Mother re-enters, greets and may comfort baby, then leaves again 4 2 1 2
Stranger tries to play with baby 1 3 1 1
Mother re-enters and picks up baby 6 6 1 2
Source: Stangor, 2011.

The results of descriptive research projects are analyzed using descriptive statistics numbers that summarize the distribution of scores on a measured variable. Most variables have distributions similar to that shown in Figure 3.4 where most of the scores are located near the centre of the distribution, and the distribution is symmetrical and bell-shaped. A data distribution that is shaped like a bell is known as a normal distribution.

Figure 3.4 Height Distribution. The distribution of the heights of the students in a class will form a normal distribution. In this sample the mean (M) = 67.12 inches and the standard deviation (s) = 2.74.


A distribution can be described in terms of its central tendency — that is, the point in the distribution around which the data are centred — and its dispersion, or spread. The arithmetic average, or arithmetic mean, symbolized by the letter M, is the most commonly used measure of central tendency. It is computed by calculating the sum of all the scores of the variable and dividing this sum by the number of participants in the distribution (denoted by the letter N). In the data presented in Figure 3.4 the mean height of the students is 67.12 inches (170.5 cm). The sample mean is usually indicated by the letter M.

In some cases, however, the data distribution is not symmetrical. This occurs when there are one or more extreme scores (known as outliers) at one end of the distribution. Consider, for instance, the variable of family income (see Figure 3.6), which includes an outlier (a value of $3,800,000). In this case the mean is not a good measure of central tendency. Although it appears from Figure 3.5 that the central tendency of the family income variable should be around $70,000, the mean family income is actually $223,960. The single very extreme income has a disproportionate impact on the mean, resulting in a value that does not well represent the central tendency.

The median is used as an alternative measure of central tendency when distributions are not symmetrical. The median is the score in the center of the distribution, meaning that 50% of the scores are greater than the median and 50% of the scores are less than the median. In our case, the median household income ($73,000) is a much better indication of central tendency than is the mean household income ($223,960).

Family income median versus mean. Long description available.
Figure 3.5 Family Income Distribution. The distribution of family incomes is likely to be nonsymmetrical because some incomes can be very large in comparison to most incomes. In this case the median or the mode is a better indicator of central tendency than is the mean. [Long Description]

A final measure of central tendency, known as the mode, represents the value that occurs most frequently in the distribution. You can see from Figure 3.5 that the mode for the family income variable is $93,000 (it occurs four times).

In addition to summarizing the central tendency of a distribution, descriptive statistics convey information about how the scores of the variable are spread around the central tendency. Dispersion refers to the extent to which the scores are all tightly clustered around the central tendency, as seen in Figure 3.6.

A line graph forms a narrow bell shape around the central tendency.
Figure 3.6


Or they may be more spread out away from it, as seen in Figure 3.7.


A line graph forms a wide bell shape around the central tendency.
Figure 3.7

One simple measure of dispersion is to find the largest (the maximum) and the smallest (the minimum) observed values of the variable and to compute the range of the variable as the maximum observed score minus the minimum observed score. You can check that the range of the height variable in Figure 3.4 is 72 – 62 = 10. The standard deviation, symbolized as s, is the most commonly used measure of dispersion. Distributions with a larger standard deviation have more spread. The standard deviation of the height variable is s = 2.74, and the standard deviation of the family income variable is s = $745,337.

An advantage of descriptive research is that it attempts to capture the complexity of everyday behaviour. Case studies provide detailed information about a single person or a small group of people, surveys capture the thoughts or reported behaviours of a large population of people, and naturalistic observation objectively records the behaviour of people or animals as it occurs naturally. Thus descriptive research is used to provide a relatively complete understanding of what is currently happening.

Despite these advantages, descriptive research has a distinct disadvantage in that, although it allows us to get an idea of what is currently happening, it is usually limited to static pictures. Although descriptions of particular experiences may be interesting, they are not always transferable to other individuals in other situations, nor do they tell us exactly why specific behaviours or events occurred. For instance, descriptions of individuals who have suffered a stressful event, such as a war or an earthquake, can be used to understand the individuals’ reactions to the event but cannot tell us anything about the long-term effects of the stress. And because there is no comparison group that did not experience the stressful situation, we cannot know what these individuals would be like if they hadn’t had the stressful experience.

Correlational Research: Seeking Relationships among Variables

In contrast to descriptive research, which is designed primarily to provide static pictures, correlational research involves the measurement of two or more relevant variables and an assessment of the relationship between or among those variables. For instance, the variables of height and weight are systematically related (correlated) because taller people generally weigh more than shorter people. In the same way, study time and memory errors are also related, because the more time a person is given to study a list of words, the fewer errors he or she will make. When there are two variables in the research design, one of them is called the predictor variable and the other the outcome variable. The research design can be visualized as shown in Figure 3.8, where the curved arrow represents the expected correlation between these two variables.

There is a expected correlation between predictor variables and outcome variables.
Figure 3.8 Predictor and Outcome Variables.

One way of organizing the data from a correlational study with two variables is to graph the values of each of the measured variables using a scatter plot. As you can see in Figure 3.9 a scatter plot is a visual image of the relationship between two variables. A point is plotted for each individual at the intersection of his or her scores for the two variables. When the association between the variables on the scatter plot can be easily approximated with a straight line, as in parts (a) and (b) of Figure 3.9 the variables are said to have a linear relationship.

When the straight line indicates that individuals who have above-average values for one variable also tend to have above-average values for the other variable, as in part (a), the relationship is said to be positive linear. Examples of positive linear relationships include those between height and weight, between education and income, and between age and mathematical abilities in children. In each case, people who score higher on one of the variables also tend to score higher on the other variable. Negative linear relationships, in contrast, as shown in part (b), occur when above-average values for one variable tend to be associated with below-average values for the other variable. Examples of negative linear relationships include those between the age of a child and the number of diapers the child uses, and between practice on and errors made on a learning task. In these cases, people who score higher on one of the variables tend to score lower on the other variable.

Relationships between variables that cannot be described with a straight line are known as nonlinear relationships. Part (c) of Figure 3.9 shows a common pattern in which the distribution of the points is essentially random. In this case there is no relationship at all between the two variables, and they are said to be independent. Parts (d) and (e) of Figure 3.9 show patterns of association in which, although there is an association, the points are not well described by a single straight line. For instance, part (d) shows the type of relationship that frequently occurs between anxiety and performance. Increases in anxiety from low to moderate levels are associated with performance increases, whereas increases in anxiety from moderate to high levels are associated with decreases in performance. Relationships that change in direction and thus are not described by a single straight line are called curvilinear relationships.

Different scatter plots. Long description available.
Figure 3.9 Examples of Scatter Plots. Some examples of relationships between two variables as shown in scatter plots. Note that the Pearson correlation coefficient (r) between variables that have curvilinear relationships will likely be close to zero. [Long Description] Source: Adapted from Stangor (2011).


The most common statistical measure of the strength of linear relationships among variables is the Pearson correlation coefficient, which is symbolized by the letter r. The value of the correlation coefficient ranges from r = –1.00 to r = +1.00. The direction of the linear relationship is indicated by the sign of the correlation coefficient. Positive values of r (such as r = .54 or r = .67) indicate that the relationship is positive linear (i.e., the pattern of the dots on the scatter plot runs from the lower left to the upper right), whereas negative values of r (such as r = –.30 or r = –.72) indicate negative linear relationships (i.e., the dots run from the upper left to the lower right). The strength of the linear relationship is indexed by the distance of the correlation coefficient from zero (its absolute value). For instance, r = –.54 is a stronger relationship than r = .30, and r = .72 is a stronger relationship than r = –.57. Because the Pearson correlation coefficient only measures linear relationships, variables that have curvilinear relationships are not well described by r, and the observed correlation will be close to zero.

It is also possible to study relationships among more than two measures at the same time. A research design in which more than one predictor variable is used to predict a single outcome variable is analyzed through multiple regression (Aiken & West, 1991). Multiple regression is a statistical technique, based on correlation coefficients among variables, that allows predicting a single outcome variable from more than one predictor variable. For instance, Figure 3.10 shows a multiple regression analysis in which three predictor variables (Salary, job satisfaction, and years employed) are used to predict a single outcome (job performance). The use of multiple regression analysis shows an important advantage of correlational research designs — they can be used to make predictions about a person’s likely score on an outcome variable (e.g., job performance) based on knowledge of other variables.

Figure 3.10 Prediction of Job Performance from Three Predictor Variables. Multiple regression allows scientists to predict the scores on a single outcome variable using more than one predictor variable.

An important limitation of correlational research designs is that they cannot be used to draw conclusions about the causal relationships among the measured variables. Consider, for instance, a researcher who has hypothesized that viewing violent behaviour will cause increased aggressive play in children. He has collected, from a sample of Grade 4 children, a measure of how many violent television shows each child views during the week, as well as a measure of how aggressively each child plays on the school playground. From his collected data, the researcher discovers a positive correlation between the two measured variables.

Measured variables showed that viewing violent TV is positively correlated with aggressive play.
Figure 3.11

Although this positive correlation appears to support the researcher’s hypothesis, it cannot be taken to indicate that viewing violent television causes aggressive behaviour. Although the researcher is tempted to assume that viewing violent television causes aggressive play, there are other possibilities. One alternative possibility is that the causal direction is exactly opposite from what has been hypothesized. Perhaps children who have behaved aggressively at school develop residual excitement that leads them to want to watch violent television shows at home (Figure 3.12):

Perhaps, aggressive play leads to watching violent TV.
Figure 3.12

Although this possibility may seem less likely, there is no way to rule out the possibility of such reverse causation on the basis of this observed correlation. It is also possible that both causal directions are operating and that the two variables cause each other (Figure 3.13).

Perhaps, aggressive play and watching violent TV encourage each other.
Figure 3.13

Still another possible explanation for the observed correlation is that it has been produced by the presence of a common-causal variable (also known as a third variable). A common-causal variable is a variable that is not part of the research hypothesis but that causes both the predictor and the outcome variable and thus produces the observed correlation between them. In our example, a potential common-causal variable is the discipline style of the children’s parents. Parents who use a harsh and punitive discipline style may produce children who like to watch violent television and who also behave aggressively in comparison to children whose parents use less harsh discipline (Figure 3.14)

Perhaps, the parents' discipline style causes children to watch violent TV and play aggressively.
Figure 3.14

In this case, television viewing and aggressive play would be positively correlated (as indicated by the curved arrow between them), even though neither one caused the other but they were both caused by the discipline style of the parents (the straight arrows). When the predictor and outcome variables are both caused by a common-causal variable, the observed relationship between them is said to be spurious. A spurious relationship is a relationship between two variables in which a common-causal variable produces and “explains away” the relationship. If effects of the common-causal variable were taken away, or controlled for, the relationship between the predictor and outcome variables would disappear. In the example, the relationship between aggression and television viewing might be spurious because by controlling for the effect of the parents’ disciplining style, the relationship between television viewing and aggressive behaviour might go away.

Common-causal variables in correlational research designs can be thought of as mystery variables because, as they have not been measured, their presence and identity are usually unknown to the researcher. Since it is not possible to measure every variable that could cause both the predictor and outcome variables, the existence of an unknown common-causal variable is always a possibility. For this reason, we are left with the basic limitation of correlational research: correlation does not demonstrate causation. It is important that when you read about correlational research projects, you keep in mind the possibility of spurious relationships, and be sure to interpret the findings appropriately. Although correlational research is sometimes reported as demonstrating causality without any mention being made of the possibility of reverse causation or common-causal variables, informed consumers of research, like you, are aware of these interpretational problems.

In sum, correlational research designs have both strengths and limitations. One strength is that they can be used when experimental research is not possible because the predictor variables cannot be manipulated. Correlational designs also have the advantage of allowing the researcher to study behaviour as it occurs in everyday life. And we can also use correlational designs to make predictions — for instance, to predict from the scores on their battery of tests the success of job trainees during a training session. But we cannot use such correlational information to determine whether the training caused better job performance. For that, researchers rely on experiments.

Experimental Research: Understanding the Causes of Behaviour

The goal of experimental research design is to provide more definitive conclusions about the causal relationships among the variables in the research hypothesis than is available from correlational designs. In an experimental research design, the variables of interest are called the independent variable (or variables) and the dependent variable. The independent variable in an experiment is the causing variable that is created (manipulated) by the experimenter. The dependent variable in an experiment is a measured variable that is expected to be influenced by the experimental manipulation. The research hypothesis suggests that the manipulated independent variable or variables will cause changes in the measured dependent variables. We can diagram the research hypothesis by using an arrow that points in one direction. This demonstrates the expected direction of causality (Figure 3.15):

Viewing violence (independent variable) and its relation to aggressive behaviour (dependent variable
Figure 3.15

Research Focus: Video Games and Aggression

Consider an experiment conducted by Anderson and Dill (2000). The study was designed to test the hypothesis that viewing violent video games would increase aggressive behaviour. In this research, male and female undergraduates from Iowa State University were given a chance to play with either a violent video game (Wolfenstein 3D) or a nonviolent video game (Myst). During the experimental session, the participants played their assigned video games for 15 minutes. Then, after the play, each participant played a competitive game with an opponent in which the participant could deliver blasts of white noise through the earphones of the opponent. The operational definition of the dependent variable (aggressive behaviour) was the level and duration of noise delivered to the opponent. The design of the experiment is shown in Figure 3.16

Figure 3.16 An Experimental Research Design.

Two advantages of the experimental research design are (a) the assurance that the independent variable (also known as the experimental manipulation) occurs prior to the measured dependent variable, and (b) the creation of initial equivalence between the conditions of the experiment (in this case by using random assignment to conditions).

Experimental designs have two very nice features. For one, they guarantee that the independent variable occurs prior to the measurement of the dependent variable. This eliminates the possibility of reverse causation. Second, the influence of common-causal variables is controlled, and thus eliminated, by creating initial equivalence among the participants in each of the experimental conditions before the manipulation occurs.

The most common method of creating equivalence among the experimental conditions is through random assignment to conditions, a procedure in which the condition that each participant is assigned to is determined through a random process, such as drawing numbers out of an envelope or using a random number table. Anderson and Dill first randomly assigned about 100 participants to each of their two groups (Group A and Group B). Because they used random assignment to conditions, they could be confident that, before the experimental manipulation occurred, the students in Group A were, on average, equivalent to the students in Group B on every possible variable, including variables that are likely to be related to aggression, such as parental discipline style, peer relationships, hormone levels, diet — and in fact everything else.

Then, after they had created initial equivalence, Anderson and Dill created the experimental manipulation — they had the participants in Group A play the violent game and the participants in Group B play the nonviolent game. Then they compared the dependent variable (the white noise blasts) between the two groups, finding that the students who had viewed the violent video game gave significantly longer noise blasts than did the students who had played the nonviolent game.

Anderson and Dill had from the outset created initial equivalence between the groups. This initial equivalence allowed them to observe differences in the white noise levels between the two groups after the experimental manipulation, leading to the conclusion that it was the independent variable (and not some other variable) that caused these differences. The idea is that the only thing that was different between the students in the two groups was the video game they had played.

Despite the advantage of determining causation, experiments do have limitations. One is that they are often conducted in laboratory situations rather than in the everyday lives of people. Therefore, we do not know whether results that we find in a laboratory setting will necessarily hold up in everyday life. Second, and more important, is that some of the most interesting and key social variables cannot be experimentally manipulated. If we want to study the influence of the size of a mob on the destructiveness of its behaviour, or to compare the personality characteristics of people who join suicide cults with those of people who do not join such cults, these relationships must be assessed using correlational designs, because it is simply not possible to experimentally manipulate these variables.


Key Takeaways

  • Descriptive, correlational, and experimental research designs are used to collect and analyze data.
  • Descriptive designs include case studies, surveys, and naturalistic observation. The goal of these designs is to get a picture of the current thoughts, feelings, or behaviours in a given group of people. Descriptive research is summarized using descriptive statistics.
  • Correlational research designs measure two or more relevant variables and assess a relationship between or among them. The variables may be presented on a scatter plot to visually show the relationships. The Pearson Correlation Coefficient (r) is a measure of the strength of linear relationship between two variables.
  • Common-causal variables may cause both the predictor and outcome variable in a correlational design, producing a spurious relationship. The possibility of common-causal variables makes it impossible to draw causal conclusions from correlational research designs.
  • Experimental research involves the manipulation of an independent variable and the measurement of a dependent variable. Random assignment to conditions is normally used to create initial equivalence between the groups, allowing researchers to draw causal conclusions.

Exercises and Critical Thinking

  1. There is a negative correlation between the row that a student sits in in a large class (when the rows are numbered from front to back) and his or her final grade in the class. Do you think this represents a causal relationship or a spurious relationship, and why?
  2. Think of two variables (other than those mentioned in this book) that are likely to be correlated, but in which the correlation is probably spurious. What is the likely common-causal variable that is producing the relationship?
  3. Imagine a researcher wants to test the hypothesis that participating in psychotherapy will cause a decrease in reported anxiety. Describe the type of research design the investigator might use to draw this conclusion. What would be the independent and dependent variables in the research?

Image Attributions

Figure 3.3:Reading newspaper” by Alaskan Dude ( is licensed under CC BY 2.0


Aiken, L., & West, S. (1991). Multiple regression: Testing and interpreting interactions. Newbury Park, CA: Sage.

Ainsworth, M. S., Blehar, M. C., Waters, E., & Wall, S. (1978). Patterns of attachment: A psychological study of the strange situation. Hillsdale, NJ: Lawrence Erlbaum Associates.

Anderson, C. A., & Dill, K. E. (2000). Video games and aggressive thoughts, feelings, and behavior in the laboratory and in life. Journal of Personality and Social Psychology, 78(4), 772–790.

Damasio, H., Grabowski, T., Frank, R., Galaburda, A. M., Damasio, A. R., Cacioppo, J. T., & Berntson, G. G. (2005). The return of Phineas Gage: Clues about the brain from the skull of a famous patient. In Social neuroscience: Key readings. (pp. 21–28). New York, NY: Psychology Press.

Freud, S. (1909/1964). Analysis of phobia in a five-year-old boy. In E. A. Southwell & M. Merbaum (Eds.), Personality: Readings in theory and research (pp. 3–32). Belmont, CA: Wadsworth. (Original work published 1909).

Kotowicz, Z. (2007). The strange case of Phineas Gage. History of the Human Sciences, 20(1), 115–131.

Rokeach, M. (1964). The three Christs of Ypsilanti: A psychological study. New York, NY: Knopf.

Stangor, C. (2011). Research methods for the behavioural sciences (4th ed.). Mountain View, CA: Cengage.

Long Descriptions

Figure 3.5 long description: There are 25 families. 24 families have an income between $44,000 and $111,000 and one family has an income of $3,800,000. The mean income is $223,960 while the median income is $73,000.

Figure 3.9 long description: Types of scatter plots.

  1. Positive linear, r=positive .82. The plots on the graph form a rough line that runs from lower left to upper right.
  2. Negative linear, r=negative .70. The plots on the graph form a rough line that runs from upper left to lower right.
  3. Independent, r=0.00. The plots on the graph are spread out around the centre.
  4. Curvilinear, r=0.00. The plots of the graph form a rough line that goes up and then down like a hill.
  5. Curvilinear, r=0.00. The plots on the graph for a rough line that goes down and then up like a ditch.


3.6 You Can Be an Informed Consumer of Psychological Research

Charles Stangor and Jennifer Walinga

Learning Objectives

  1. Outline the four potential threats to the validity of research and discuss how they may make it difficult to accurately interpret research findings.
  2. Describe how confounding may reduce the internal validity of an experiment.
  3. Explain how generalization, replication, and meta-analyses are used to assess the external validity of research findings.

Good research is valid research. When research is valid, the conclusions drawn by the researcher are legitimate. For instance, if a researcher concludes that participating in psychotherapy reduces anxiety, or that taller people are smarter than shorter people, the research is valid only if the therapy really works or if taller people really are smarter. Unfortunately, there are many threats to the validity of research, and these threats may sometimes lead to unwarranted conclusions. Often, and despite researchers’ best intentions, some of the research reported on websites as well as in newspapers, magazines, and even scientific journals is invalid. Validity is not an all-or-nothing proposition, which means that some research is more valid than other research. Only by understanding the potential threats to validity will you be able to make knowledgeable decisions about the conclusions that can or cannot be drawn from a research project. There are four major types of threats to the validity of research, and informed consumers of research are aware of each type.

Threats to the Validity of Research

  1. Threats to construct validity. Although it is claimed that the measured variables measure the conceptual variables of interest, they actually may not.
  2. Threats to statistical conclusion validity. Conclusions regarding the research may be incorrect because no statistical tests were made or because the statistical tests were incorrectly interpreted.
  3. Threats to internal validity. Although it is claimed that the independent variable caused the dependent variable, the dependent variable actually may have been caused by a confounding variable.
  4. Threats to external validity. Although it is claimed that the results are more general, the observed effects may actually only be found under limited conditions or for specific groups of people. (Stangor, 2011)

One threat to valid research occurs when there is a threat to construct validity. Construct validity refers to the extent to which the variables used in the research adequately assess the conceptual variables they were designed to measure. One requirement for construct validity is that the measure be reliable, where reliability refers to the consistency of a measured variable. A bathroom scale is usually reliable, because if we step on and off it a couple of times, the scale will consistently measure the same weight every time. Other measures, including some psychological tests, may be less reliable, and thus less useful.

Normally, we can assume that the researchers have done their best to assure the construct validity of their measures, but it is not inappropriate for you, as an informed consumer of research, to question this. It is always important to remember that the ability to learn about the relationship between the conceptual variables in a research hypothesis is dependent on the operational definitions of the measured variables. If the measures do not really measure the conceptual variables that they are designed to assess (e.g., if a supposed IQ test does not really measure intelligence), then they cannot be used to draw inferences about the relationship between the conceptual variables (Nunnally, 1978).

The statistical methods that scientists use to test their research hypotheses are based on probability estimates. You will see statements in research reports indicating that the results were statistically significant or not statistically significant. These statements will be accompanied by statistical tests, often including statements such as p < 0.05 or about confidence intervals. These statements describe the statistical significance of the data that have been collected. Statistical significance refers to the confidence with which a scientist can conclude that data are not due to chance or random error. When a researcher concludes that a result is statistically significant, he or she has determined that the observed data was very unlikely to have been caused by chance factors alone. Hence, there is likely a real relationship between or among the variables in the research design. Otherwise, the researcher concludes that the results were not statistically significant.

Statistical conclusion validity refers to the extent to which we can be certain that the researcher has drawn accurate conclusions about the statistical significance of the research. Research will be invalid if the conclusions made about the research hypothesis are incorrect because statistical inferences about the collected data are in error. These errors can occur either because the scientist inappropriately infers that the data do support the research hypothesis when in fact they are due to chance, or when the researcher mistakenly fails to find support for the research hypothesis. Normally, we can assume that the researchers have done their best to ensure the statistical conclusion validity of a research design, but we must always keep in mind that inferences about data are probabilistic and never certain — this is why research never proves a theory.

Internal validity refers to the extent to which we can trust the conclusions that have been drawn about the causal relationship between the independent and dependent variables (Campbell & Stanley, 1963). Internal validity applies primarily to experimental research designs, in which the researcher hopes to conclude that the independent variable has caused the dependent variable. Internal validity is maximized when the research is free from the presence of confounding variables variables other than the independent variable on which the participants in one experimental condition differ systematically from those in other conditions.

Consider an experiment in which a researcher tested the hypothesis that drinking alcohol makes members of the opposite sex look more attractive. Participants older than 21 years of age were randomly assigned to drink either orange juice mixed with vodka or orange juice alone. To eliminate the need for deception, the participants were told whether or not their drinks contained vodka. After enough time had passed for the alcohol to take effect, the participants were asked to rate the attractiveness of pictures of members of the opposite sex. The results of the experiment showed that, as predicted, the participants who drank the vodka rated the photos as significantly more attractive.

If you think about this experiment for a minute, it may occur to you that although the researcher wanted to draw the conclusion that the alcohol caused the differences in perceived attractiveness, the expectation of having consumed alcohol is confounded with the presence of alcohol. That is, the people who drank alcohol also knew they drank alcohol, and those who did not drink alcohol knew they did not. It is possible that simply knowing that they were drinking alcohol, rather than the effect of the alcohol itself, may have caused the differences (see Figure 3.17, “An Example of Confounding”). One solution to the problem of potential expectancy effects is to tell both groups that they are drinking orange juice and vodka but really give alcohol to only half of the participants (it is possible to do this because vodka has very little smell or taste). If differences in perceived attractiveness are found, the experimenter could then confidently attribute them to the alcohol rather than to the expectancy about having consumed alcohol.

Figure 3.17 An Example of Confounding. Confounding occurs when a variable that is not part of the research hypothesis is “mixed up,” or confounded, with the variable in the research hypothesis. In the bottom panel, alcohol consumed and alcohol expectancy are confounded, but in the top panel they are separate (independent). Confounding makes it impossible to be sure that the independent variable (rather than the confounding variable) caused the dependent variable.

Another threat to internal validity can occur when the experimenter knows the research hypothesis and also knows which experimental condition the participants are in. The outcome is the potential for experimenter bias, a situation in which the experimenter subtly treats the research participants in the various experimental conditions differently, resulting in an invalid confirmation of the research hypothesis. In one study demonstrating experimenter bias, Rosenthal and Fode (1963) sent 12 students to test a research hypothesis concerning maze learning in rats. Although it was not initially revealed to the students, they were actually the participants in an experiment. Six of the students were randomly told that the rats they would be testing had been bred to be highly intelligent, whereas the other six students were led to believe that the rats had been bred to be unintelligent. In reality there were no differences among the rats given to the two groups of students. When the students returned with their data, a startling result emerged. The rats run by students who expected them to be intelligent showed significantly better maze learning than the rats run by students who expected them to be unintelligent. Somehow the students’ expectations influenced their data. They evidently did something different when they tested the rats, perhaps subtly changing how they timed the maze running or how they treated the rats. And this experimenter bias probably occurred entirely out of their awareness.

To avoid experimenter bias, researchers frequently run experiments in which the researchers are blind to condition. This means that although the experimenters know the research hypotheses, they do not know which conditions the participants are assigned to. Experimenter bias cannot occur if the researcher is blind to condition. In a double-blind experiment, both the researcher and the research participants are blind to condition. For instance, in a double-blind trial of a drug, the researcher does not know whether the drug being given is the real drug or the ineffective placebo, and the patients also do not know which they are getting. Double-blind experiments eliminate the potential for experimenter effects and at the same time eliminate participant expectancy effects.

While internal validity refers to conclusions drawn about events that occurred within the experiment, external validity refers to the extent to which the results of a research design can be generalized beyond the specific way the original experiment was conducted. Generalization refers to the extent to which relationships among conceptual variables can be demonstrated in a wide variety of people and a wide variety of manipulated or measured variables.

Psychologists who use university students as participants in their research may be concerned about generalization, wondering if their research will generalize to people who are not college students. And researchers who study the behaviours of employees in one company may wonder whether the same findings would translate to other companies. Whenever there is reason to suspect that a result found for one sample of participants would not hold up for another sample, then research may be conducted with these other populations to test for generalization.

Recently, many psychologists have been interested in testing hypotheses about the extent to which a result will replicate across people from different cultures (Heine, 2010). For instance, a researcher might test whether the effects on aggression of viewing violent video games are the same for Japanese children as they are for Canadian children by showing violent and nonviolent films to a sample of both Japanese and Canadian schoolchildren. If the results are the same in both cultures, then we say that the results have generalized, but if they are different, then we have learned a limiting condition of the effect (see Table 3.5, “A Cross-Cultural Replication”).

Table 3.5 A Cross-Cultural Replication.
Canada Japan Gaming behaviour
More aggressive behaviour observed ??? Violent Games
Less aggressive behaviour observed ??? Nonviolent Games
Source: Adapted by J. Walinga.

In a cross-cultural replication, external validity is observed if the same effects that have been found in one culture are replicated in another culture. If they are not replicated in the new culture, then a limiting condition of the original results is found.

Unless the researcher has a specific reason to believe that generalization will not hold, it is appropriate to assume that a result found in one population (even if that population is college or university students) will generalize to other populations. Because the investigator can never demonstrate that the research results generalize to all populations, it is not expected that the researcher will attempt to do so. Rather, the burden of proof rests on those who claim that a result will not generalize.

Because any single test of a research hypothesis will always be limited in terms of what it can show, important advances in science are never the result of a single research project. Advances occur through the accumulation of knowledge that comes from many different tests of the same theory or research hypothesis. These tests are conducted by different researchers using different research designs, participants, and operationalizations of the independent and dependent variables. The process of repeating previous research, which forms the basis of all scientific inquiry, is known as replication.

Scientists often use a procedure known as meta-analysis to summarize replications of research findings. A meta-analysis is a statistical technique that uses the results of existing studies to integrate and draw conclusions about those studies. Because meta-analyses provide so much information, they are very popular and useful ways of summarizing research literature.

A meta-analysis provides a relatively objective method of reviewing research findings because it (a) specifies inclusion criteria that indicate exactly which studies will or will not be included in the analysis, (b) systematically searches for all studies that meet the inclusion criteria, and (c) provides an objective measure of the strength of observed relationships. Frequently, the researchers also include — if they can find them — studies that have not been published in journals.

Psychology in Everyday Life: Critically Evaluating the Validity of Websites

The validity of research reports published in scientific journals is likely to be high because the hypotheses, methods, results, and conclusions of the research have been rigorously evaluated by other scientists, through peer review, before the research was published. For this reason, you will want to use peer-reviewed journal articles as your major source of information about psychological research.

Although research articles are the gold standard for validity, you may also need and desire to get at least some information from other sources. The Internet is a vast source of information from which you can learn about almost anything, including psychology. Search engines — such as Google or Yahoo! — bring hundreds or thousands of hits on a topic, and online encyclopedias, such as Wikipedia, provide articles about relevant topics.

Although you will naturally use the web to help you find information about fields such as psychology, you must also realize that it is important to carefully evaluate the validity of the information you get from the web. You must try to distinguish information that is based on empirical research from information that is based on opinion, and between valid and invalid data. The following material may be helpful to you in learning to make these distinctions.

The techniques for evaluating the validity of websites are similar to those that are applied to evaluating any other source of information. Ask first about the source of the information. Is the domain a “.com” or “.ca” (business), “.gov” (government), or “.org” (nonprofit) entity? This information can help you determine the author’s (or organization’s) purpose in publishing the website. Try to determine where the information is coming from. Is the data being summarized from objective sources, such as journal articles or academic or government agencies? Does it seem that the author is interpreting the information as objectively as possible, or is the data being interpreted to support a particular point of view? Consider what groups, individuals, and political or commercial interests stand to gain from the site. Is the website potentially part of an advocacy group whose web pages reflect the particular positions of the group? Material from any group’s site may be useful, but try to be aware of the group’s purposes and potential biases.

Also, ask whether or not the authors themselves appear to be a trustworthy source of information. Do they hold positions in an academic institution? Do they have peer-reviewed publications in scientific journals? Many useful web pages appear as part of organizational sites and reflect the work of that organization. You can be more certain of the validity of the information if it is sponsored by a professional organization, such as the Canadian Psychological Association or the Canadian Mental Health Association.

Try to check on the accuracy of the material and discern whether the sources of information seem current. Is the information cited so that you can read it in its original form? Reputable websites will probably link to other reputable sources, such as journal articles and scholarly books. Try to check the accuracy of the information by reading at least some of these sources yourself.

It is fair to say that all authors, researchers, and organizations have at least some bias and that the information from any site can be invalid. But good material attempts to be fair by acknowledging other possible positions, interpretations, or conclusions. A critical examination of the nature of the websites you browse for information will help you determine if the information is valid and will give you more confidence in the information you take from it.


Key Takeaways

  • Research is said to be valid when the conclusions drawn by the researcher are legitimate. Because all research has the potential to be invalid, no research ever “proves” a theory or research hypothesis.
  • Construct validity, statistical conclusion validity, internal validity, and external validity are all types of validity that people who read and interpret research need to be aware of.
  • Construct validity refers to the assurance that the measured variables adequately measure the conceptual variables.
  • Statistical conclusion validity refers to the assurance that inferences about statistical significance are appropriate.
  • Internal validity refers to the assurance that the independent variable has caused the dependent variable. Internal validity is greater when confounding variables are reduced or eliminated.
  • External validity is greater when effects can be replicated across different manipulations, measures, and populations. Scientists use meta-analyses to better understand the external validity of research.

Exercises and Critical Thinking

  1. The Pepsi-Cola Company, now PepsiCo Inc., conducted the “Pepsi Challenge” by randomly assigning individuals to taste either a Pepsi or a Coke. The researchers labelled the glasses with only an “M” (for Pepsi) or a “Q” (for Coke) and asked the participants to rate how much they liked the beverage. The research showed that subjects overwhelmingly preferred glass “M” over glass “Q,” and the researchers concluded that Pepsi was preferred to Coke. Can you tell what confounding variable is present in this research design? How would you redesign the research to eliminate the confound?
  2. Locate a research report of a meta-analysis. Determine the criteria that were used to select the studies and report on the findings of the research.


Campbell, D. T., & Stanley, J. C. (1963). Experimental and quasi-experimental designs for research. Chicago: Rand McNally.

Heine, S. J. (2010). Cultural psychology. In S. T. Fiske, D. T. Gilbert, & G. Lindzey (Eds.), Handbook of social psychology (5th ed., Vol. 2, pp. 1423–1464). Hoboken, NJ: John Wiley & Sons.

Nunnally, J. C. (1978). Pyschometric theory. New York, NY: McGraw-Hill.

Rosenthal, R., & Fode, K. L. (1963). The effect of experimenter bias on the performance of the albino rat. Behavioral Science, 8, 183–189.

Stangor, C. (2011). Research methods for the behavioral sciences (4th ed.). Mountain View, CA: Cengage.


3.7 The Replication Crisis in Psychology

Edward Diener and Robert Biswas-Diener

In science, replication is the process of repeating research to determine the extent to which findings generalize across time and across situations. Recently, the science of psychology has come under criticism because a number of research findings do not replicate. In this module we discuss reasons for non-replication, the impact this phenomenon has on the field, and suggest solutions to the problem.

Learning Objectives

  1. Define “replication”
  2. Explain the difference between exact and conceptual replication
  3. List 4 explanations for non-replication
  4. Name 3 potential solutions to the replication crisis

The Disturbing Problem


Four pirates
Figure 3.18: If you saw a pirate you might not believe it; but if you saw another one you would feel more confident in your observation. In science, this is the process of replication.

If you were driving down the road and you saw a pirate standing at an intersection you might not believe your eyes. But if you continued driving and saw a second, and then a third, you might become more confident in your observations. The more pirates you saw the less likely the first sighting would be a false positive (you were driving fast and the person was just wearing an unusual hat and billowy shirt) and the more likely it would be the result of a logical reason (there is a pirate themed conference in town). This somewhat absurd example is a real-life illustration of replication: the repeated findings of the same results.

The replication of findings is one of the defining hallmarks of science. Scientists must be able to replicate the results of studies or their findings do not become part of scientific knowledge. Replication protects against false positives (seeing a result that is not really there) and also increases confidence that the result actually exists. If you collect satisfaction data among homeless people living in Kolkata, India, for example, it might seem strange that they would report fairly high satisfaction with their food (which is exactly what we found in Biswas-Diener & Diener, 2001). If you find the exact same result, but at a different time, and with a different sample of homeless people living in Kolkata, however, you can feel more confident that this result is true (as we did in Biswas-Diener & Diener, 2006).

In modern times, the science of psychology is facing a crisis. It turns out that many studies in psychology—including many highly cited studies—do not replicate. In an era where news is instantaneous, the failure to replicate research raises important questions about the scientific process in general and psychology specifically. People have the right to know if they can trust research evidence. For our part, psychologists also have a vested interest in ensuring that our methods and findings are as trustworthy as possible.

Psychology is not alone in coming up short on replication. There have been notable failures to replicate findings in other scientific fields as well. For instance, in 1989 scientists reported that they had produced “cold fusion,” achieving nuclear fusion at room temperatures. This could have been an enormous breakthrough in the advancement of clean energy. However, other scientists were unable to replicate the findings. Thus, the potentially important results did not become part of the scientific canon, and a new energy source did not materialize. In medical science as well, a number of findings have been found not to replicate—which is of vital concern to all of society. The non-reproducibility of medical findings suggests that some treatments for illness could be ineffective. One example of non-replication has emerged in the study of genetics and diseases: when replications were attempted to determine whether certain gene-disease findings held up, only about 4% of the findings consistently did so.

The non-reproducibility of findings is disturbing because it suggests the possibility that the original research was done sloppily. Even worse is the suspicion that the research may have been falsified. In science, faking results is the biggest of sins, the unforgivable sin, and for this reason the field of psychology has been thrown into an uproar. However, as we will discuss, there are a number of explanations for non-replication, and not all are bad.

What is Replication?


Top image - group of 8 men presented with lines a varying length. Bottom image - group of two men and two women presented with varying types of fruit.
Figure 3.19: Example of direct replication and conceptual replication of Asch’s conformity experiment.

There are different types of replication. First, there is a type called “exact replication” (also called “direct replication“). In this form, a scientist attempts to exactly recreate the scientific methods used in conditions of an earlier study to determine whether the results come out the same. If, for instance, you wanted to exactly replicate Asch’s (1956) classic findings on conformity, you would follow the original methodology: you would use only male participants, you would use groups of 8, and you would present the same stimuli (lines of differing lengths) in the same order. The second type of replication is called “conceptual replication.” This occurs when—instead of an exact replication, which reproduces the methods of the earlier study as closely as possible—a scientist tries to confirm the previous findings using a different set of specific methods that test the same idea. The same hypothesis is tested, but using a different set of methods and measures. A conceptual replication of Asch’s research might involve both male and female confederates purposefully misidentifying types of fruit to investigate conformity—rather than only males misidentifying line lengths.

Both exact and conceptual replications are important because they each tell us something new. Exact replications tell us whether the original findings are true, at least under the exact conditions tested. Conceptual replications help confirm whether the theoretical idea behind the findings is true, and under what conditions these findings will occur. In other words, conceptual replication offers insights into how generalizable the findings are.


Enormity of the Current Crisis

Percentage of findings published in prestigious journals which have replicated: (1) Journal of Personality and Social Psychology - Social, 23%, (2) Journal of Experimental Psychology - Learning, Memory, and Cognition, 48%, (3) Psychological Science - social articles, 29%, (4) Psychological Science - cognitive articles, 53%
Table 3.6: The Reproducibility of Psychological Science

Recently, there has been growing concern as psychological research fails to replicate. To give you an idea of the extent of non-replicability of psychology findings, Table 3.6 shows data reported in 2015 by the Open Science Collaboration project, led by University of Virginia psychologist Brian Nosek (Open Science Collaboration, 2015). Because these findings were reported in the prestigious journal, Science, they received widespread attention from the media. Here are the percentages of research that replicated—selected from several highly prestigious journals:

Clearly, there is a very large problem when only about 1/3 of the psychological studies in premier journals replicate! It appears that this problem is particularly pronounced for social psychology but even the 53% replication level of cognitive psychology is cause for concern.

The situation in psychology has grown so worrisome that the Nobel Prize-winning psychologist Daniel Kahneman called on social psychologists to clean up their act (Kahneman, 2012). The Nobel laureate spoke bluntly of doubts about the integrity of psychology research, calling the current situation in the field a “mess.” His missive was pointed primarily at researchers who study social “priming,” but in light of the non-replication results that have since come out, it might be more aptly directed at the behavioral sciences in general.

Examples of Non-replications in Psychology

A stereotypical image of a professor - a white, middle-aged man with glasses and a beard, dressed in a coat and tie stands with chalk in hand in front of a blackboard which displays a mathematical formula.
Figure 3.20: In one study, researchers enhanced test performance by priming participants with stereotypes of intelligence. But subsequent studies have not been able to replicate those results.

A large number of scientists have attempted to replicate studies on what might be called “metaphorical priming,” and more often than not these replications have failed. Priming is the process by which a recent reference (often a subtle, subconscious cue) can increase the accessibility of a trait. For example, if your instructor says, “Please put aside your books, take out a clean sheet of paper, and write your name at the top,” you might find your pulse quickening. Over time, you have learned that this cue means you are about to be given a pop quiz. This phrase primes all the features associated with pop quizzes: they are anxiety-provoking, they are tricky, your performance matters.

One example of a priming study that, at least in some cases, does not replicate, is the priming of the idea of intelligence. In theory, it might be possible to prime people to actually become more intelligent (or perform better on tests, at least). For instance, in one study, priming students with the idea of a stereotypical professor versus soccer hooligans led participants in the “professor” condition to earn higher scores on a trivia game (Dijksterhuis & van Knippenberg, 1998). Unfortunately, in several follow-up instances this finding has not replicated (Shanks et al, 2013). This is unfortunate for all of us because it would be a very easy way to raise our test scores and general intelligence. If only it were true.

Another example of a finding that seems not to replicate consistently is the use of spatial distance cues to prime people’s feelings of emotional closeness to their families (Williams & Bargh, 2008). In this type of study, participants are asked to plot points on graph paper, either close together or far apart. The participants are then asked to rate how close they are to their family members. Although the original researchers found that people who plotted close-together points on graph paper reported being closer to their relatives, studies reported on PsychFileDrawer—an internet repository of replication attempts—suggest that the findings frequently do not replicate. Again, this is unfortunate because it would be a handy way to help people feel closer to their families.

As one can see from the examples, some of the studies that fail to replicate report extremely interesting findings—even counterintuitive findings that appear to offer new insights into the human mind. Critics claim that psychologists have become too enamored with such newsworthy, surprising “discoveries” that receive a lot of media attention. Which raises the question of timing: might the current crisis of non-replication be related to the modern, media-hungry context in which psychological research (indeed, all research) is conducted? Put another way: is the non-replication crisis new?

Nobody has tried to systematically replicate studies from the past, so we do not know if published studies are becoming less replicable over time. In 1990, however, Amir and Sharon were able to successfully replicate most of the main effects of six studies from another culture, though they did fail to replicate many of the interactions. This particular shortcoming in their overall replication may suggest that published studies are becoming less replicable over time, but we cannot be certain. What we can be sure of is that there is a significant problem with replication in psychology, and it’s a trend the field needs to correct. Without replicable findings, nobody will be able to believe in scientific psychology.

Reasons for Non-replication

When findings do not replicate, the original scientists sometimes become indignant and defensive, offering reasons or excuses for non-replication of their findings—including, at times, attacking those attempting the replication. They sometimes claim that the scientists attempting the replication are unskilled or unsophisticated, or do not have sufficient experience to replicate the findings. This, of course, might be true, and it is one possible reason for non-replication.

One reason for defensive responses is the unspoken implication that the original results might have been falsified. Faked results are only one reason studies may not replicate, but it is the most disturbing reason. We hope faking is rare, but in the past decade a number of shocking cases have turned up. Perhaps the most well-known come from social psychology. Diederik Stapel, a renowned social psychologist in the Netherlands, admitted to faking the results of a number of studies. Marc Hauser, a popular professor at Harvard, apparently faked results on morality and cognition. Karen Ruggiero at the University of Texas was also found to have falsified a number of her results (proving that bad behavior doesn’t have a gender bias). Each of these psychologists—and there are quite a few more examples—was believed to have faked data. Subsequently, they all were disgraced and lost their jobs.

Another reason for non-replication is that, in studies with small sample sizes, statistically-significant results may often be the result of chance. For example, if you ask five people if they believe that aliens from other planets visit Earth and regularly abduct humans, you may get three people who agree with this notion—simply by chance. Their answers may, in fact, not be at all representative of the larger population. On the other hand, if you survey one thousand people, there is a higher probability that their belief in alien abductions reflects the actual attitudes of society. Now consider this scenario in the context of replication: if you try to replicate the first study—the one in which you interviewed only five people—there is only a small chance that you will randomly draw five new people with exactly the same (or similar) attitudes. It’s far more likely that you will be able to replicate the findings using another large sample, because it is simply more likely that the findings are accurate.

Another reason for non-replication is that, while the findings in an original study may be true, they may only be true for some people in some circumstances and not necessarily universal or enduring. Imagine that a survey in the 1950s found a strong majority of respondents to have trust in government officials. Now imagine the same survey administered today, with vastly different results. This example of non-replication does not invalidate the original results. Rather, it suggests that attitudes have shifted over time.

A final reason for non-replication relates to the quality of the replication rather than the quality of the original study. Non-replication might be the product of scientist-error, with the newer investigation not following the original procedures closely enough. Similarly, the attempted replication study might, itself, have too small a sample size or insufficient statistical power to find significant results.

In Defense of Replication Attempts

Failures in replication are not all bad and, in fact, some non-replication should be expected in science. Original studies are conducted when an answer to a question is uncertain. That is to say, scientists are venturing into new territory. In such cases we should expect some answers to be uncovered that will not pan out in the long run. Furthermore, we hope that scientists take on challenging new topics that come with some amount of risk. After all, if scientists were only to publish safe results that were easy to replicate, we might have very boring studies that do not advance our knowledge very quickly. But, with such risks, some non-replication of results is to be expected.

A woman analyzing data on a computer. Researchers use statistical software to store, analyze and share data.
Figure 3.21: Researchers use specialized statistical software to store, analyze, and share data. Saving data over time and sharing data with others can be useful in conducting replications.

A recent example of risk-taking can be seen in the research of social psychologist Daryl Bem. In 2011, Bem published an article claiming he had found in a number of studies that future events could influence the past. His proposition turns the nature of time, which is assumed by virtually everyone except science fiction writers to run in one direction, on its head. Needless to say, attacks on Bem’s article came fast and furious, including attacks on his statistics and methodology (Ritchie, Wiseman & French, 2012). There were attempts at replication and most of them failed, but not all. A year after Bem’s article came out, the prestigious journal where it was published, Journal of Personality and Social Psychology, published another paper in which a scientist failed to replicate Bem’s findings in a number of studies very similar to the originals (Galak, Lebeouf, Nelson & Simmons, 2012).

Some people viewed the publication of Bem’s (2011) original study as a failure in the system of science. They argued that the paper should not have been published. But the editor and reviewers of the article had moved forward with publication because, although they might have thought the findings provocative and unlikely, they did not see obvious flaws in the methodology. We see the publication of the Bem paper, and the ensuing debate, as a strength of science. We are willing to consider unusual ideas if there is evidence to support them: we are open-minded. At the same time, we are critical and believe in replication. Scientists should be willing to consider unusual or risky hypotheses but ultimately allow good evidence to have the final say, not people’s opinions.

Solutions to the Problem

Dissemination of Replication Attempts

The fact that replications, including failed replication attempts, now have outlets where they can be communicated to other researchers is a very encouraging development, and should strengthen the science considerably. One problem for many decades has been the near-impossibility of publishing replication attempts, regardless of whether they’ve been positive or negative.

More Systematic Programs of Scientific Research

The six principles of open science: open data, open source, open access, open methodology, open peer review, open educational resources.
Figure 3.22: 6 Principles of Open Science – adapted from openscienceASAP.

The reward structure in academia has served to discourage replication. Many psychologists—especially those who work full time at universities—are often rewarded at work—with promotions, pay raises, tenure, and prestige—through their research. Replications of one’s own earlier work, or the work of others, is typically discouraged because it does not represent original thinking. Instead, academics are rewarded for high numbers of publications, and flashy studies are often given prominence in media reports of published studies.

Psychological scientists need to carefully pursue programmatic research. Findings from a single study are rarely adequate, and should be followed up by additional studies using varying methodologies. Thinking about research this way—as if it were a program rather than a single study—can help. We would recommend that laboratories conduct careful sets of interlocking studies, where important findings are followed up using various methods. It is not sufficient to find some surprising outcome, report it, and then move on. When findings are important enough to be published, they are often important enough to prompt further, more conclusive research. In this way scientists will discover whether their findings are replicable, and how broadly generalizable they are. If the findings do not always replicate, but do sometimes, we will learn the conditions in which the pattern does or doesn’t hold. This is an important part of science—to discover how generalizable the findings are.

When researchers criticize others for being unable to replicate the original findings, saying that the conditions in the follow-up study were changed, this is important to pay attention to as well. Not all criticism is knee-jerk defensiveness or resentment. The replication crisis has stirred heated emotions among research psychologists and the public, but it is time for us to calm down and return to a more scientific attitude and system of programmatic research.

Textbooks and Journals

Some psychologists blame the trend toward non-replication on specific journal policies, such as the policy of Psychological Science to publish short single studies. When single studies are published we do not know whether even the authors themselves can replicate their findings. The journal Psychological Science has come under perhaps the harshest criticism. Others blame the rash of nonreplicable studies on a tendency of some fields for surprising and counterintuitive findings that grab the public interest. The irony here is that such counterintuitive findings are in fact less likely to be true precisely because they are so strange—so they should perhaps warrant more scrutiny and further analysis.

The criticism of journals extends to textbooks as well. In our opinion, psychology textbooks should stress true science, based on findings that have been demonstrated to be replicable. There are a number of inaccuracies that persist across common psychology textbooks, including small mistakes in common coverage of the most famous studies, such as the Stanford Prison Experiment (Griggs & Whitehead, 2014) and the Milgram studies (Griggs & Whitehead, 2015). To some extent, the inclusion of non-replicated studies in textbooks is the product of market forces. Textbook publishers are under pressure to release new editions of their books, often far more frequently than advances in psychological science truly justify. As a result, there is pressure to include “sexier” topics such as controversial studies.

Ultimately, people also need to learn to be intelligent consumers of science. Instead of getting overly-excited by findings from a single study, it’s wise to wait for replications. When a corpus of studies is built on a phenomenon, we can begin to trust the findings. Journalists must be educated about this too, and learn not to readily broadcast and promote findings from single flashy studies. If the results of a study seem too good to be true, maybe they are. Everyone needs to take a more skeptical view of scientific findings, until they have been replicated.


Outside Resources

Article: New Yorker article on the “replication crisis”

Web: Collaborative Replications and Education Project – This is a replication project where students are encouraged to conduct replications as part of their courses.

Web: Commentary on what makes for a convincing replication.

Web: Open Science Framework – The Open Science Framework is an open source software project that facilitates open collaboration in science research.

Web: Psych File Drawer – A website created to address “the file drawer problem”. allows users to upload results of serious replication attempts in all research areas of psychology.

Discussion Questions

  1. Why do scientists see replication by other laboratories as being so crucial to advances in science?
  2. Do the failures of replication shake your faith in what you have learned about psychology? Why or why not?
  3. Can you think of any psychological findings that you think might not replicate?
  4. What findings are so important that you think they should be replicated?
  5. Why do you think quite a few studies do not replicate?
  6. How frequently do you think faking results occurs? Why? How might we prevent that?

Image Attributions

Figure 3.18: Dave Hamster,, CC BY 2.0,

Figure 3.20: CC0 Public Domain,

Figure 3.21: Kwantlen Polytechnic University Psychology Department, CC BY 2.0,

Figure 3.22: Underlying Image: Greg Emmerich,, CC BY-SA 2.0,


Amir, Y., & Sharon, I. (1990). Replication research: A “must” for the scientific advancement of psychology.Journal of Social Behavior and Personality, Special Issue, 5, 51-69.

Asch, S. E. (1956). Studies of independence and conformity: I. A minority of one against a unanimous majority. Psychological Monographs, 70 (9, Whole No. 416).

Bem, DJ (March 2011). “Feeling the future: experimental evidence for anomalous retroactive influences on cognition and affect.” Journal of personality and social psychology, 100, 407–25.

Biswas-Diener, R., & Diener, E. (2006). Subjective well-being of the homeless, and lessons for happiness. Social Indicators Research. 76, 185-205.

Biswas-Diener, R. , & Diener, E. (2001). Making the best of a bad situation: Satisfaction in the slums of Calcutta. Social Indicators Research, 55, 329-352.

Dijksterhuis, A., & van Knippenberg, A. (1998). The relation between perception and behavior or how to win a game of Trivial Pursuit. Journal of Personality and Social Psychology, 74, 865–877.

Galak, J., LeBoeuf, R. A., Nelson, L. D., & Simmons, J. P. (2012, August 27). Correcting the Past: Failures to Replicate Psi. Journal of Personality and Social Psychology.

Griggs & Whitehead (2015). Coverage of Milgram’s obedience experiments in social psychology textbooks: Where have all the criticisms gone? Teaching of Psychology, 42, 315-322.

Griggs, R. A. & Whitehead, G. I. (2014). Coverage of the Stanford Prison Experiment in Introductory Social Psychology textbooks. Teaching of Psychology, 41, 318-324.

Kahneman, D. (2012). A proposal to deal with questions about priming effects. An open letter to the scientific community:!/suppinfoFile/Kahneman%20Letter.pdf

Nosek, B. A., Aarts, A. A., Anderson, C. J., Anderson, J. E., Kappes, H. B., & Open Science Collaboration. (2015). Estimating the reproducibility of psychological science. Science, 349(6251), aac4716-aac4716.

Ritchie, S. J., Wiseman, R., & French, C. C. (2012). Failing the future: Three unsuccessful attempts to replicate Bem’s ‘retroactive facilitation of recall’ effect. PLOS One. DOI: 10.1371/journal.pone.0033423

Shanks, D. R., Newell, B., Lee, E. H., Balikrishnan, D., Ekelund, L., Cenac, Z., Kavvadia, F. & Moore, C. (2013). Priming intelligent behavior: Elusive phenomenon. PLOS One. DOI: 10.1371/journal.pone.0056515

Williams, L. E., & Bargh, J. A. (2008). Keeping one’s distance: The influence of spatial distance cues on affect and evaluation. Psychological Science, 19, 302-308.


Chapter 3 Summary, Key Terms, and Self-Test

Charles Stangor, Jennifer Walinga, Jorden A. Cummings, and Lee Sanders


Psychologists study the behaviour of both humans and animals in order to understand and improve the quality of human lives.

Psychological research may be either basic or applied in orientation. Basic research and applied research inform each other, and advances in science occur more rapidly when both types of research are conducted.

The results of psychological research are reported primarily in research reports in scientific journals. These research reports have been evaluated, critiqued, and improved by other scientists through the process of peer review.

The methods used by scientists have developed over many years and provide a common framework through which information can be collected, organized, and shared.

The scientific method is the set of assumptions, rules, and procedures that scientists use to conduct research. In addition to requiring that science be empirical, the scientific method demands that the procedures used be objective, or free from personal bias.

Scientific findings are organized by theories, which are used to summarize and make new predictions, but theories are usually framed too broadly to be tested in a single experiment. Therefore, scientists normally use the research hypothesis as a basis for their research.

Good theories are falsifiable. This means that the relationships between the variables that are predicted by the theory can be shown through research to be incorrect.

Scientists use operational definitions to turn the ideas of interest — conceptual variables — into measured variables.

It is important for psychological research using humans and animals to be ethical. Our ethics codes are developed from the moral principles of weighing risks against benefits, acting responsibly and with integrity, seeking justice, and respecting people’s rights and dignity.

Researchers must follow specific ethics codes, providing rules for how to conduct studies. Some historical events that impacted our ethics codes today are the Nuremberg trials, the Declaration of Helsinki, and the Belmont Report.

Decisions about whether psychological research using human and animals is ethical are made using established ethical codes developed by scientific organizations and on the basis of judgments made by the local Ethical Review Board. Informed consent, deception, and debriefing are all considered when deciding if research will be approved.

Psychological studies start with a research design that vary according to its strengths and limitations, and it is important to understand how each differs.

Descriptive research is designed to provide a snapshot of the current state of affairs. Descriptive research allows the development of questions for further study but does not assess relationships among variables. The results of descriptive research projects are analyzed using descriptive statistics.

Correlational research assesses the relationships between and among two or more variables. It allows making predictions but cannot be used to draw inferences about the causal relationships between and among the variables. Linear relationships between variables are normally analyzed using the Pearson correlation coefficient.

The goal of experimental research is to assess the causal impact of one or more experimental manipulations on a dependent variable. Because experimental research creates initial equivalence among the participants in the different experimental conditions, it allows drawing conclusions about the causal relationships among variables. Experimental designs are not always possible because many important variables cannot be experimentally manipulated.

Because all research has the potential for invalidity, research never “proves” a theory or hypothesis.

Threats to construct validity involve potential inaccuracies in the measurement of the conceptual variables.

Threats to statistical conclusion validity involve potential inaccuracies in the statistical testing of the relationships among variables.

Threats to internal validity involve potential inaccuracies in assumptions about the causal role of the independent variable on the dependent variable.

Threats to external validity involve potential inaccuracy regarding the generality of observed findings.

Informed consumers of research are aware of the strengths of research but are also aware of its potential limitations.

The replication of findings is an important hallmark of science. Replication projects in psychology have had mixed results, with many studies not being replicated. There are multiple reasons why study results might not be replicable.

Key Terms

  • Anonymity
  • APA Ethical Code
  • Applied Research
  • Arithmetic Mean (M)
  • At-Risk Research
  • Autonomy
  • Basic Research
  • Belmont Report
  • Beneficence
  • Blind to Condition
  • Case Studies
  • Central Tendency
  • Common-Causal Variable
  • Conceptual Replication
  • Conceptual Variables
  • Confederate
  • Confidentiality
  • Confounding Variables
  • Consent Form
  • Construct Validity
  • Correlational Research
  • Cost-Benefit Analysis
  • Curvilinear Relationship
  • Debriefing
  • Deception
  • Declaration of Helsinki
  • Dependent Variable
  • Descriptive Research
  • Descriptive Statistics
  • Dispersion
  • Distribution
  • Double-Blind Experiment
  • Ethical Review Board (ERB) (also known as Institutional Review Board, IRB)
  • Ethics
  • Empirical
  • Exact (or Direct) Replication
  • Exempt Research
  • Experimenter Bias
  • Experimental Research
  • External Validity
  • Falsified Data (or faked data)
  • Federal Policy for the Protection of Human Subjects
  • Generalization
  • Incidence
  • Independent Variable
  • Informed Consent
  • Internal Validity
  • Justice
  • Laws
  • Linear Relationship
  • Limiting Condition
  • Maximum Observed Score
  • Measured Variables
  • Median
  • Meta-Analysis
  • Minimum Observed Score
  • Minimal Risk Research
  • Mode
  • Multiple Regression
  • Naturalistic Observations
  • Negative Linear Relationship
  • No Relationship
  • Nonlinear Relationship
  • Normal Distribution
  • Nuremberg Code
  • Objective
  • Operational Definition
  • Outliers
  • Pearson Correlation Coefficient (r)
  • Positive Linear Relationship
  • Pre-Screening
  • Priming
  • Privacy
  • Protocol
  • Random Assignment to Conditions
  • Range
  • Reliability
  • Replicate
  • Replication
  • Research Design
  • Research Hypothesis
  • Respect for Persons
  • Sample
  • Sample Size
  • Scatter Plot
  • Scientific Method
  • Single-Blind Experiment
  • Spurious Relationship
  • Stage Theory of Cognitive Development
  • Standard Deviation
  • Statistical Conclusion Validity
  • Statistical Significance
  • Surveys
  • Theory
  • Traits of Good Theories: General; Parsimonious; Falsifiable
  • Valid
  • Variables


An interactive or media element has been excluded from this version of the text. You can view it online here:

Direct link to self-test:


Chapter 4. Genetics and Evolution


Chapter 4 Introduction

Lee Sanders

As discussed in Chapter 2, the biological perspective in psychology emphasizes bodily events and changes associated with behaviour. Biological psychology applies the principles of biology to the study of mental processes and behaviour. Psychologists in this framework study human behaviours that are both different and alike. We will begin this chapter with a discussion if the nature versus nurture debate. In this debate, psychological scientists seek to determine the origins of behavioural traits as being either biological or due to environment. Both sides of the debate contribute to the question, ‘why do we behave the way we do?”

Genetic and evolutionary approaches are biological perspective that inform this question. Genetic influence on behavior is a relatively recent discovery. Behavioural genetics is an interdisciplinary field concerned with how genes and the environment influence individual behaviour and traits including brain function. The focus of this field is on the genetic bases of individual difference in how we think and act.

Heredity and environment are constantly interacting to influence our psychological and physical traits. Epigenetics is the study of heritable changes in gene expression that does not involve changes to the underlying DNA sequence. Epigenetic research seeks to understand the influence of genes on our behaviour and mental processes, and how the environment affects our genes, and influences their expression through biological mechanisms that switch them on and off.

Behavioural genomics is the of study of DNA, inherited traits, and the ways in which specific genes are related to behaviour. This framework involves a shift in focus away from the influence of specific individual genes on behaviour to the entire genome which is an organism’s complete set of genes in each cell with the exceptions of sperm and egg cells. Researchers are interested in the interaction of multiple genes and numerous environmental factors that influence human behaviour. Methods using twin and adoption studies are engaged calculate heritability, which is a measure of variability of behavioural traits among individuals that can be accounted for by genetic factors. Variability in IQ scores, for example, can be denoted by a heritability coefficient, which is a statistic expressed as a number between zero and one that represents the degree to which genetic differences between individuals contribute to individual differences in a behaviour or trait found in a population. 

While behavioural genetics and genomics perspectives focus on the roles of genes, heredity, and environment in explaining individual differences in behaviour, researchers in evolutionary psychology concentrate on the evolutionary mechanisms that might explain the commonalities that aid in our survival and reproductive success, including human cognition, development, emotion, and social practices. Evolutionary psychology is a field of psychology that emphasizes the evolutionary mechanisms at work in the similarities of human behaviour including cognition, emotion, development, and social practice. An evolutionary approach aims to interpret and explain modern human behaviour in terms of how our brains and behaviours have been shaped by the physical and social environment encountered by our ancestors, and the forces that acted upon them.

The theories of Charles Darwin have a profound influence on evolutionary psychology. Natural selection is a theory developed through his observations of the fitness of a species’ characteristics to its environment. Natural selection refers to the ability for a species to adapt to its environment, find food and water, and mate in order to stay alive long enough to reproduce and pass on genetic traits favorable to that setting. Evolution through natural selection requires a trait to be heritable, and individuals within the breeding population must have a reproductive advantage for having the trait. Evolutionary useful behaviors have had a beneficial function in the cognitive development of our species. The brain, for example, has a set of cognitive adaptations for solving problems related to survival and reproductive fitness. Individuals with advantageous traits are more likely to survive and reproduce offspring with similar genes.

While natural selection suggests that some traits and adaptations make an individual more likely to survive, certain traits evolve to help some individuals increase their chances of mating and passing on their genes. Darwin proposed a second theory to explain the fate of genes. Sexual selection theory suggests that certain traits evolve to help some individuals increase their chances of mating and passing on their genes. Members of the same sex will compete for access to the other sex in a process called intrasexual selection. Intersexual selection refers to the influence of physical factors signalling reproductive health and fitness, and cultural factors that indicate social security.

Sexual strategies theory is a comprehensive evolutionary theory of human mating that defines the menu of mating strategies humans pursue (e.g., short-term casual sex, long-term committed mating), the adaptive problems women and men face when pursuing these strategies, and the evolved solutions to these mating problems. Sexual overperception bias, for example, is a mating theory that suggests that males often misread sexual interest from women to prevent the costs of missing out on an opportunity for reproduction. Evolutionary research on attraction also highlights the importance of facial symmetry to mate selection and reproduction.

Sociobiology contends that evolution has given us a genetic tendency to act in ways that maximize our chances of passing on our genes onto the next generations. Psychological traits are thought to be ‘selected’ to aid individuals in propagating their genes. Hunter-gatherer theory illustrates sex differences and suggests that our labour was divided based on sex and sex role socialization as a means of survival (Buss & Barnes, 1986; Silverman & Eals, 1992). For example, this theory suggests that males hunted, and females gathered because of physical and behavioural skills that are reproductively fit to this environment, an also, that some competencies selected for during the process of human evolution are still present today. This can be a very controversial area of theory and research as you will see in the highlight ‘How We Talk (or Do Not Talk) about Intelligence’ in Chapter 9.

Biopsychosocial theory takes a complex approach to understanding human behaviour. Aspects of biology (genes), psychological components (thoughts, personality, mood), and social conditions (family support, stress, culture) are all considered in analyses of why we do what we do from this perspective.

Research in the evolutionary perspective also applies the principles of biology to the study of human behaviour. Evolutionary psychologists start from the position that cognitive structures are designed by natural selection to serve survival and reproduction (Hagen 2004). From this perspective, hearing, smell, vision, pain, and motor control are examined as functions of the nervous system that have been involved in survival and reproduction for thousands of generations and years.


Buss, D. M., & Barnes, M. (1986). Preferences in human mate selection. Journal of personality and social psychology, 50(3), 559.

Hagen, E. H. (2004). The evolutionary psychology FAQ. NOBA Open Textbook Project. Retrieved from

Silverman, I., & Eals, M. (1992). Sex differences in spatial abilities: Evolutionary theory and data. In Portions of this paper were presented at the meetings of the International Society for Human Ethology in Binghamton, NY, Jun 1990, the Human Behavior and Evolution Society in Los Angeles, CA, Aug 1990, and the European Sociobiological Society in Prague, Czechoslovakia, Aug 1991. Oxford University Press.


4.1 The Nature-Nurture Question

Eric Turkheimer

People have a deep intuition about what has been called the “nature–nurture question.” Some aspects of our behavior feel as though they originate in our genetic makeup, while others feel like the result of our upbringing or our own hard work. The scientific field of behavior genetics attempts to study these differences empirically, either by examining similarities among family members with different degrees of genetic relatedness, or, more recently, by studying differences in the DNA of people with different behavioral traits. The scientific methods that have been developed are ingenious, but often inconclusive. Many of the difficulties encountered in the empirical science of behavior genetics turn out to be conceptual, and our intuitions about nature and nurture get more complicated the harder we think about them. In the end, it is an oversimplification to ask how “genetic” some particular behavior is. Genes and environments always combine to produce behavior, and the real science is in the discovery of how they combine for a given behavior.

Learning Objectives

  1. Understand what the nature–nurture debate is and why the problem fascinates us.
  2. Understand why nature–nurture questions are difficult to study empirically.
  3. Know the major research designs that can be used to study nature–nurture questions.
  4. Appreciate the complexities of nature–nurture and why questions that seem simple turn out not to have simple answers.


There are three related problems at the intersection of philosophy and science that are fundamental to our understanding of our relationship to the natural world: the mind–body problem, the free will problem, and the nature–nurture problem. These great questions have a lot in common. Everyone, even those without much knowledge of science or philosophy, has opinions about the answers to these questions that come simply from observing the world we live in. Our feelings about our relationship with the physical and biological world often seem incomplete. We are in control of our actions in some ways, but at the mercy of our bodies in others; it feels obvious that our consciousness is some kind of creation of our physical brains, at the same time we sense that our awareness must go beyond just the physical. This incomplete knowledge of our relationship with nature leaves us fascinated and a little obsessed, like a cat that climbs into a paper bag and then out again, over and over, mystified every time by a relationship between inner and outer that it can see but can’t quite understand.

It may seem obvious that we are born with certain characteristics while others are acquired, and yet of the three great questions about humans’ relationship with the natural world, only nature–nurture gets referred to as a “debate.” In the history of psychology, no other question has caused so much controversy and offense: We are so concerned with nature–nurture because our very sense of moral character seems to depend on it. While we may admire the athletic skills of a great basketball player, we think of his height as simply a gift, a payoff in the “genetic lottery.” For the same reason, no one blames a short person for his height or someone’s congenital disability on poor decisions: To state the obvious, it’s “not their fault.” But we do praise the concert violinist (and perhaps her parents and teachers as well) for her dedication, just as we condemn cheaters, slackers, and bullies for their bad behavior.

The problem is, most human characteristics aren’t usually as clear-cut as height or instrument-mastery, affirming our nature–nurture expectations strongly one way or the other. In fact, even the great violinist might have some inborn qualities—perfect pitch, or long, nimble fingers—that support and reward her hard work. And the basketball player might have eaten a diet while growing up that promoted his genetic tendency for being tall. When we think about our own qualities, they seem under our control in some respects, yet beyond our control in others. And often the traits that don’t seem to have an obvious cause are the ones that concern us the most and are far more personally significant. What about how much we drink or worry? What about our honesty, or religiosity, or sexual orientation? They all come from that uncertain zone, neither fixed by nature nor totally under our own control.

Two nearly identical puppies stand side by side." title="Two nearly identical puppies stand side by side.
Figure 4.1: Researchers have learned a great deal about the nature-nurture dynamic by working with animals. But of course many of the techniques used to study animals cannot be applied to people. Separating these two influences in human subjects is a greater research challenge.

One major problem with answering nature-nurture questions about people is, how do you set up an experiment? In nonhuman animals, there are relatively straightforward experiments for tackling nature–nurture questions. Say, for example, you are interested in aggressiveness in dogs. You want to test for the more important determinant of aggression: being born to aggressive dogs or being raised by them. You could mate two aggressive dogs—angry Chihuahuas—together, and mate two nonaggressive dogs—happy beagles—together, then switch half the puppies from each litter between the different sets of parents to raise. You would then have puppies born to aggressive parents (the Chihuahuas) but being raised by nonaggressive parents (the Beagles), and vice versa, in litters that mirror each other in puppy distribution. The big questions are: Would the Chihuahua parents raise aggressive beagle puppies? Would the beagle parents raise nonaggressive Chihuahua puppies? Would the puppies’ nature win out, regardless of who raised them? Or… would the result be a combination of nature and nurture? Much of the most significant nature–nurture research has been done in this way (Scott & Fuller, 1998), and animal breeders have been doing it successfully for thousands of years. In fact, it is fairly easy to breed animals for behavioral traits.

With people, however, we can’t assign babies to parents at random, or select parents with certain behavioral characteristics to mate, merely in the interest of science (though history does include horrific examples of such practices, in misguided attempts at “eugenics,” the shaping of human characteristics through intentional breeding). In typical human families, children’s biological parents raise them, so it is very difficult to know whether children act like their parents due to genetic (nature) or environmental (nurture) reasons. Nevertheless, despite our restrictions on setting up human-based experiments, we do see real-world examples of nature-nurture at work in the human sphere—though they only provide partial answers to our many questions.

The science of how genes and environments work together to influence behavior is called behavioral genetics. The easiest opportunity we have to observe this is the adoption study. When children are put up for adoption, the parents who give birth to them are no longer the parents who raise them. This setup isn’t quite the same as the experiments with dogs (children aren’t assigned to random adoptive parents in order to suit the particular interests of a scientist) but adoption still tells us some interesting things, or at least confirms some basic expectations. For instance, if the biological child of tall parents were adopted into a family of short people, do you suppose the child’s growth would be affected? What about the biological child of a Spanish-speaking family adopted at birth into an English-speaking family? What language would you expect the child to speak? And what might these outcomes tell you about the difference between height and language in terms of nature-nurture?

Twin boys sit together dressed in matching clothes and hats and holding similar stuffed animals." title="Twin boys sit together dressed in matching clothes and hats and holding similar stuffed animals.
Figure 4.2: Studies focused on twins have led to important insights about the biological origins of many personality characteristics.

Another option for observing nature-nurture in humans involves twin studies. There are two types of twins: monozygotic (MZ) and dizygotic (DZ). Monozygotic twins, also called “identical” twins, result from a single zygote (fertilized egg) and have the same DNA. They are essentially clones. Dizygotic twins, also known as “fraternal” twins, develop from two zygotes and share 50% of their DNA. Fraternal twins are ordinary siblings who happen to have been born at the same time. To analyze nature–nurture using twins, we compare the similarity of MZ and DZ pairs. Sticking with the features of height and spoken language, let’s take a look at how nature and nurture apply: Identical twins, unsurprisingly, are almost perfectly similar for height. The heights of fraternal twins, however, are like any other sibling pairs: more similar to each other than to people from other families, but hardly identical. This contrast between twin types gives us a clue about the role genetics plays in determining height. Now consider spoken language. If one identical twin speaks Spanish at home, the co-twin with whom she is raised almost certainly does too. But the same would be true for a pair of fraternal twins raised together. In terms of spoken language, fraternal twins are just as similar as identical twins, so it appears that the genetic match of identical twins doesn’t make much difference.

Twin and adoption studies are two instances of a much broader class of methods for observing nature-nurture called quantitative genetics, the scientific discipline in which similarities among individuals are analyzed based on how biologically related they are. We can do these studies with siblings and half-siblings, cousins, twins who have been separated at birth and raised separately (Bouchard, Lykken, McGue, & Segal, 1990; such twins are very rare and play a smaller role than is commonly believed in the science of nature–nurture), or with entire extended families (see Plomin, DeFries, Knopik, & Neiderhiser, 2012, for a complete introduction to research methods relevant to nature–nurture).

For better or for worse, contentions about nature–nurture have intensified because quantitative genetics produces a number called a heritability coefficient, varying from 0 to 1, that is meant to provide a single measure of genetics’ influence of a trait. In a general way, a heritability coefficient measures how strongly differences among individuals are related to differences among their genes. But beware: Heritability coefficients, although simple to compute, are deceptively difficult to interpret. Nevertheless, numbers that provide simple answers to complicated questions tend to have a strong influence on the human imagination, and a great deal of time has been spent discussing whether the heritability of intelligence or personality or depression is equal to one number or another.

A DNA single strand
Figure 4.3: Quantitative genetics uses statistical methods to study the effects that both heredity and environment have on test subjects. These methods have provided us with the heritability coefficient which measures how strongly differences among individuals for a trait are related to differences among their genes.

One reason nature–nurture continues to fascinate us so much is that we live in an era of great scientific discovery in genetics, comparable to the times of Copernicus, Galileo, and Newton, with regard to astronomy and physics. Every day, it seems, new discoveries are made, new possibilities proposed. When Francis Galton first started thinking about nature–nurture in the late-19th century he was very influenced by his cousin, Charles Darwin, but genetics per se was unknown. Mendel’s famous work with peas, conducted at about the same time, went undiscovered for 20 years; quantitative genetics was developed in the 1920s; DNA was discovered by Watson and Crick in the 1950s; the human genome was completely sequenced at the turn of the 21st century; and we are now on the verge of being able to obtain the specific DNA sequence of anyone at a relatively low cost. No one knows what this new genetic knowledge will mean for the study of nature–nurture, but as we will see in the next section, answers to nature–nurture questions have turned out to be far more difficult and mysterious than anyone imagined.

What Have We Learned About Nature–Nurture?

It would be satisfying to be able to say that nature–nurture studies have given us conclusive and complete evidence about where traits come from, with some traits clearly resulting from genetics and others almost entirely from environmental factors, such as childrearing practices and personal will; but that is not the case. Instead, everything has turned out to have some footing in genetics. The more genetically-related people are, the more similar they are—for everything: height, weight, intelligence, personality, mental illness, etc. Sure, it seems like common sense that some traits have a genetic bias. For example, adopted children resemble their biological parents even if they have never met them, and identical twins are more similar to each other than are fraternal twins. And while certain psychological traits, such as personality or mental illness (e.g., schizophrenia), seem reasonably influenced by genetics, it turns out that the same is true for political attitudes, how much television people watch (Plomin, Corley, DeFries, & Fulker, 1990), and whether or not they get divorced (McGue & Lykken, 1992).

A father and his young son sit together on a blanket on the lawn on a sunny day. Each have their shirts removed and are dressed almost identically including straw hats, sunglasses, and pipes." title="A father and his young son sit together on a blanket on the lawn on a sunny day. Each have their shirts removed and are dressed almost identically including straw hats, sunglasses, and pipes.
Figure 4.4: Research over the last half century has revealed how central genetics are to behavior. The more genetically related people are the more similar they are not just physically but also in terms of personality and behavior.

It may seem surprising, but genetic influence on behavior is a relatively recent discovery. In the middle of the 20th century, psychology was dominated by the doctrine of behaviorism, which held that behavior could only be explained in terms of environmental factors. Psychiatry concentrated on psychoanalysis, which probed for roots of behavior in individuals’ early life-histories. The truth is, neither behaviorism nor psychoanalysis is incompatible with genetic influences on behavior, and neither Freud nor Skinner was naive about the importance of organic processes in behavior. Nevertheless, in their day it was widely thought that children’s personalities were shaped entirely by imitating their parents’ behavior, and that schizophrenia was caused by certain kinds of “pathological mothering.” Whatever the outcome of our broader discussion of nature–nurture, the basic fact that the best predictors of an adopted child’s personality or mental health are found in the biological parents he or she has never met, rather than in the adoptive parents who raised him or her, presents a significant challenge to purely environmental explanations of personality or psychopathology. The message is clear: You can’t leave genes out of the equation. But keep in mind, no behavioral traits are completely inherited, so you can’t leave the environment out altogether, either.

Trying to untangle the various ways nature-nurture influences human behavior can be messy, and often common-sense notions can get in the way of good science. One very significant contribution of behavioral genetics that has changed psychology for good can be very helpful to keep in mind: When your subjects are biologically-related, no matter how clearly a situation may seem to point to environmental influence, it is never safe to interpret a behavior as wholly the result of nurture without further evidence. For example, when presented with data showing that children whose mothers read to them often are likely to have better reading scores in third grade, it is tempting to conclude that reading to your kids out loud is important to success in school; this may well be true, but the study as described is inconclusive, because there are genetic as well asenvironmental pathways between the parenting practices of mothers and the abilities of their children. This is a case where “correlation does not imply causation,” as they say. To establish that reading aloud causes success, a scientist can either study the problem in adoptive families (in which the genetic pathway is absent) or by finding a way to randomly assign children to oral reading conditions.

The outcomes of nature–nurture studies have fallen short of our expectations (of establishing clear-cut bases for traits) in many ways. The most disappointing outcome has been the inability to organize traits from more– to less-genetic. As noted earlier, everything has turned out to be at least somewhat heritable (passed down), yet nothing has turned out to be absolutely heritable, and there hasn’t been much consistency as to which traits are more heritable and which are less heritable once other considerations (such as how accurately the trait can be measured) are taken into account (Turkheimer, 2000). The problem is conceptual: The heritability coefficient, and, in fact, the whole quantitative structure that underlies it, does not match up with our nature–nurture intuitions. We want to know how “important” the roles of genes and environment are to the development of a trait, but in focusing on “important” maybe we’re emphasizing the wrong thing. First of all, genes and environment are both crucial to every trait; without genes the environment would have nothing to work on, and too, genes cannot develop in a vacuum. Even more important, because nature–nurture questions look at the differences among people, the cause of a given trait depends not only on the trait itself, but also on the differences in that trait between members of the group being studied.

The classic example of the heritability coefficient defying intuition is the trait of having two arms. No one would argue against the development of arms being a biological, genetic process. But fraternal twins are just as similar for “two-armedness” as identical twins, resulting in a heritability coefficient of zero for the trait of having two arms. Normally, according to the heritability model, this result (coefficient of zero) would suggest all nurture, no nature, but we know that’s not the case. The reason this result is not a tip-off that arm development is less genetic than we imagine is because people do not vary in the genes related to arm development—which essentially upends the heritability formula. In fact, in this instance, the opposite is likely true: the extent that people differ in arm number is likely the result of accidents and, therefore, environmental. For reasons like these, we always have to be very careful when asking nature–nurture questions, especially when we try to express the answer in terms of a single number. The heritability of a trait is not simply a property of that trait, but a property of the trait in a particular context of relevant genes and environmental factors.

Another issue with the heritability coefficient is that it divides traits’ determinants into two portions—genes and environment—which are then calculated together for the total variability. This is a little like asking how much of the experience of a symphony comes from the horns and how much from the strings; the ways instruments or genes integrate is more complex than that. It turns out to be the case that, for many traits, genetic differences affect behavior under some environmental circumstances but not others—a phenomenon called gene-environment interaction, or G x E. In one well-known example, Caspi et al. (2002) showed that among maltreated children, those who carried a particular allele of the MAOA gene showed a predisposition to violence and antisocial behavior, while those with other alleles did not. Whereas, in children who had not been maltreated, the gene had no effect. Making matters even more complicated are very recent studies of what is known as epigenetics (see module, “Epigenetics”, a process in which the DNA itself is modified by environmental events, and those genetic changes transmitted to children.

A mother smiles broadly as she nuzzle noses with her toddler son.
Figure 4.5: The answer to the nature –nurture question has not turned out to be as straightforward as we would like. The many questions we can ask about the relationships among genes, environments, and human traits may have many different answers, and the answer to one tells us little about the answers to the others.

Some common questions about nature–nurture are, how susceptible is a trait to change, how malleable is it, and do we “have a choice” about it? These questions are much more complex than they may seem at first glance. For example, phenylketonuria is an inborn error of metabolism caused by a single gene; it prevents the body from metabolizing phenylalanine. Untreated, it causes mental retardation and death. But it can be treated effectively by a straightforward environmental intervention: avoiding foods containing phenylalanine. Height seems like a trait firmly rooted in our nature and unchangeable, but the average height of many populations in Asia and Europe has increased significantly in the past 100 years, due to changes in diet and the alleviation of poverty. Even the most modern genetics has not provided definitive answers to nature–nurture questions. When it was first becoming possible to measure the DNA sequences of individual people, it was widely thought that we would quickly progress to finding the specific genes that account for behavioral characteristics, but that hasn’t happened. There are a few rare genes that have been found to have significant (almost always negative) effects, such as the single gene that causes Huntington’s disease, or the Apolipoprotein gene that causes early onset dementia in a small percentage of Alzheimer’s cases. Aside from these rare genes of great effect, however, the genetic impact on behavior is broken up over many genes, each with very small effects. For most behavioral traits, the effects are so small and distributed across so many genes that we have not been able to catalog them in a meaningful way. In fact, the same is true of environmental effects. We know that extreme environmental hardship causes catastrophic effects for many behavioral outcomes, but fortunately extreme environmental hardship is very rare. Within the normal range of environmental events, those responsible for differences (e.g., why some children in a suburban third-grade classroom perform better than others) are much more difficult to grasp.

The difficulties with finding clear-cut solutions to nature–nurture problems bring us back to the other great questions about our relationship with the natural world: the mind-body problem and free will. Investigations into what we mean when we say we are aware of something reveal that consciousness is not simply the product of a particular area of the brain, nor does choice turn out to be an orderly activity that we can apply to some behaviors but not others. So it is with nature and nurture: What at first may seem to be a straightforward matter, able to be indexed with a single number, becomes more and more complicated the closer we look. The many questions we can ask about the intersection among genes, environments, and human traits—how sensitive are traits to environmental change, and how common are those influential environments; are parents or culture more relevant; how sensitive are traits to differences in genes, and how much do the relevant genes vary in a particular population; does the trait involve a single gene or a great many genes; is the trait more easily described in genetic or more-complex behavioral terms?—may have different answers, and the answer to one tells us little about the answers to the others.

It is tempting to predict that the more we understand the wide-ranging effects of genetic differences on all human characteristics—especially behavioral ones—our cultural, ethical, legal, and personal ways of thinking about ourselves will have to undergo profound changes in response. Perhaps criminal proceedings will consider genetic background. Parents, presented with the genetic sequence of their children, will be faced with difficult decisions about reproduction. These hopes or fears are often exaggerated. In some ways, our thinking may need to change—for example, when we consider the meaning behind the fundamental American principle that all men are created equal. Human beings differ, and like all evolved organisms they differ genetically. The Declaration of Independence predates Darwin and Mendel, but it is hard to imagine that Jefferson—whose genius encompassed botany as well as moral philosophy—would have been alarmed to learn about the genetic diversity of organisms. One of the most important things modern genetics has taught us is that almost all human behavior is too complex to be nailed down, even from the most complete genetic information, unless we’re looking at identical twins. The science of nature and nurture has demonstrated that genetic differences among people are vital to human moral equality, freedom, and self-determination, not opposed to them. As Mordecai Kaplan said about the role of the past in Jewish theology, genetics gets a vote, not a veto, in the determination of human behavior. We should indulge our fascination with nature–nurture while resisting the temptation to oversimplify it.



Outside Resources

Web: Institute for Behavioral Genetics

Discussion Questions

  1. Is your personality more like one of your parents than the other? If you have a sibling, is his or her personality like yours? In your family, how did these similarities and differences develop? What do you think caused them?
  2. Can you think of a human characteristic for which genetic differences would play almost no role? Defend your choice.
  3. Do you think the time will come when we will be able to predict almost everything about someone by examining their DNA on the day they are born?
  4. Identical twins are more similar than fraternal twins for the trait of aggressiveness, as well as for criminal behavior. Do these facts have implications for the courtroom? If it can be shown that a violent criminal had violent parents, should it make a difference in culpability or sentencing?

Image Attributions

Figure 4.1: Sebastián Dario,, CC BY-NC 2.0,

Figure 4.2: CCO Creative Commons

Figure 4.3: EMSL,, CC BY-NC-SA 2.0,

Figure 4.4: Paul Altobelli,, CC BY 2.0,

Figure 4.5: Sundaram Ramaswamy,, CC BY 2.0,


Bouchard, T. J., Lykken, D. T., McGue, M., & Segal, N. L. (1990). Sources of human psychological differences: The Minnesota study of twins reared apart. Science, 250(4978), 223–228.

Caspi, A., McClay, J., Moffitt, T. E., Mill, J., Martin, J., Craig, I. W., Taylor, A. & Poulton, R. (2002). Role of genotype in the cycle of violence in maltreated children. Science, 297(5582), 851–854.

McGue, M., & Lykken, D. T. (1992). Genetic influence on risk of divorce. Psychological Science, 3(6), 368–373.

Plomin, R., Corley, R., DeFries, J. C., & Fulker, D. W. (1990). Individual differences in television viewing in early childhood: Nature as well as nurture. Psychological Science, 1(6), 371–377.

Plomin, R., DeFries, J. C., Knopik, V. S., & Neiderhiser, J. M. (2012). Behavioral genetics. New York, NY: Worth Publishers.

Scott, J. P., & Fuller, J. L. (1998). Genetics and the social behavior of the dog. Chicago, IL: University of Chicago Press.

Turkheimer, E. (2000). Three laws of behavior genetics and what they mean. Current Directions in Psychological Science, 9(5), 160–164.


4.2 Evolutionary Theories in Psychology

David M. Buss

Evolution or change over time occurs through the processes of natural and sexual selection. In response to problems in our environment, we adapt both physically and psychologically to ensure our survival and reproduction. Sexual selection theory describes how evolution has shaped us to provide a mating advantage rather than just a survival advantage and occurs through two distinct pathways: intrasexual competition and intersexual selection. Gene selection theory, the modern explanation behind evolutionary biology, occurs through the desire for gene replication. Evolutionary psychology connects evolutionary principles with modern psychology and focuses primarily on psychological adaptations: changes in the way we think in order to improve our survival. Two major evolutionary psychological theories are described: Sexual strategies theory describes the psychology of human mating strategies and the ways in which women and men differ in those strategies. Error management theory describes the evolution of biases in the way we think about everything.

Learning Objectives

  1. Learn what “evolution” means.
  2. Define the primary mechanisms by which evolution takes place.
  3. Identify the two major classes of adaptations.
  4. Define sexual selection and its two primary processes.
  5. Define gene selection theory.
  6. Understand psychological adaptations.
  7. Identify the core premises of sexual strategies theory.
  8. Identify the core premises of error management theory, and provide two empirical examples of adaptive cognitive biases.


A couple holding hands on a bench.
Figure 4.6: It may seem like just a casual date, but don’t doubt that the forces of evolution are hard at work below the surface.

If you have ever been on a first date, you’re probably familiar with the anxiety of trying to figure out what clothes to wear or what perfume or cologne to put on. In fact, you may even consider flossing your teeth for the first time all year. When considering why you put in all this work, you probably recognize that you’re doing it to impress the other person. But how did you learn these particular behaviors? Where did you get the idea that a first date should be at a nice restaurant or someplace unique? It is possible that we have been taught these behaviors by observing others. It is also possible, however, that these behaviors—the fancy clothes, the expensive restaurant—are biologically programmed into us. That is, just as peacocks display their feathers to show how attractive they are, or some lizards do push-ups to show how strong they are, when we style our hair or bring a gift to a date, we’re trying to communicate to the other person: “Hey, I’m a good mate! Choose me! Choose me!”

However, we all know that our ancestors hundreds of thousands of years ago weren’t driving sports cars or wearing designer clothes to attract mates. So how could someone ever say that such behaviors are “biologically programmed” into us? Well, even though our ancestors might not have been doing these specific actions, these behaviors are the result of the same driving force: the powerful influence of evolution. Yes, evolution—certain traits and behaviors developing over time because they are advantageous to our survival. In the case of dating, doing something like offering a gift might represent more than a nice gesture. Just as chimpanzees will give food to mates to show they can provide for them, when you offer gifts to your dates, you are communicating that you have the money or “resources” to help take care of them. And even though the person receiving the gift may not realize it, the same evolutionary forces are influencing his or her behavior as well. The receiver of the gift evaluates not only the gift but also the gift-giver’s clothes, physical appearance, and many other qualities, to determine whether the individual is a suitable mate. But because these evolutionary processes are hardwired into us, it is easy to overlook their influence.

To broaden your understanding of evolutionary processes, this module will present some of the most important elements of evolution as they impact psychology. Evolutionary theory helps us piece together the story of how we humans have prospered. It also helps to explain why we behave as we do on a daily basis in our modern world: why we bring gifts on dates, why we get jealous, why we crave our favorite foods, why we protect our children, and so on. Evolution may seem like a historical concept that applies only to our ancient ancestors but, in truth, it is still very much a part of our modern daily lives.

Basics of Evolutionary Theory

Evolution simply means change over time. Many think of evolution as the development of traits and behaviors that allow us to survive this “dog-eat-dog” world, like strong leg muscles to run fast, or fists to punch and defend ourselves. However, physical survival is only important if it eventually contributes to successful reproduction. That is, even if you live to be a 100-year-old, if you fail to mate and produce children, your genes will die with your body. Thus, reproductive success, not survival success, is the engine of evolution by natural selection. Every mating success by one person means the loss of a mating opportunity for another. Yet every living human being is an evolutionary success story. Each of us is descended from a long and unbroken line of ancestors who triumphed over others in the struggle to survive (at least long enough to mate) and reproduce. However, in order for our genes to endure over time—to survive harsh climates, to defeat predators—we have inherited adaptive, psychological processes designed to ensure success.

At the broadest level, we can think of organisms, including humans, as having two large classes of adaptations—or traits and behaviors that evolved over time to increase our reproductive success. The first class of adaptations are called survival adaptations: mechanisms that helped our ancestors handle the “hostile forces of nature.” For example, in order to survive very hot temperatures, we developed sweat glands to cool ourselves. In order to survive very cold temperatures, we developed shivering mechanisms (the speedy contraction and expansion of muscles to produce warmth). Other examples of survival adaptations include developing a craving for fats and sugars, encouraging us to seek out particular foods rich in fats and sugars that keep us going longer during food shortages. Some threats, such as snakes, spiders, darkness, heights, and strangers, often produce fear in us, which encourages us to avoid them and thereby stay safe. These are also examples of survival adaptations. However, all of these adaptations are for physical survival, whereas the second class of adaptations are for reproduction, and help us compete for mates. These adaptations are described in an evolutionary theory proposed by Charles Darwin, called sexual selection theory.

Sexual Selection Theory

Darwin noticed that there were many traits and behaviors of organisms that could not be explained by “survival selection.” For example, the brilliant plumage of peacocks should actually lower their rates of survival. That is, the peacocks’ feathers act like a neon sign to predators, advertising “Easy, delicious dinner here!” But if these bright feathers only lower peacocks’ chances at survival, why do they have them? The same can be asked of similar characteristics of other animals, such as the large antlers of male stags or the wattles of roosters, which also seem to be unfavorable to survival. Again, if these traits only make the animals less likely to survive, why did they develop in the first place? And how have these animals continued to survive with these traits over thousands and thousands of years? Darwin’s answer to this conundrum was the theory of sexual selection: the evolution of characteristics, not because of survival advantage, but because of mating advantage.

Professional boxers throw punches in the middle of a ring.
Figure 4.7: Modern sports like boxing can be seen as modified/stylized versions of the evolutionary behavior of intrasexual competition.

Sexual selection occurs through two processes. The first, intrasexual competition, occurs when members of one sex compete against each other, and the winner gets to mate with a member of the opposite sex. Male stags, for example, battle with their antlers, and the winner (often the stronger one with larger antlers) gains mating access to the female. That is, even though large antlers make it harder for the stags to run through the forest and evade predators (which lowers their survival success), they provide the stags with a better chance of attracting a mate (which increases their reproductive success). Similarly, human males sometimes also compete against each other in physical contests: boxing, wrestling, karate, or group-on-group sports, such as football. Even though engaging in these activities poses a “threat” to their survival success, as with the stag, the victors are often more attractive to potential mates, increasing their reproductive success. Thus, whatever qualities lead to success in intrasexual competition are then passed on with greater frequency due to their association with greater mating success.

The second process of sexual selection is preferential mate choice, also called intersexual selection. In this process, if members of one sex are attracted to certain qualities in mates—such as brilliant plumage, signs of good health, or even intelligence—those desired qualities get passed on in greater numbers, simply because their possessors mate more often. For example, the colorful plumage of peacocks exists due to a long evolutionary history of peahens’ (the term for female peacocks) attraction to males with brilliantly colored feathers.

In all sexually-reproducing species, adaptations in both sexes (males and females) exist due to survival selection and sexual selection. However, unlike other animals where one sex has dominant control over mate choice, humans have “mutual mate choice.” That is, both women and men typically have a say in choosing their mates. And both mates value qualities such as kindness, intelligence, and dependability that are beneficial to long-term relationships—qualities that make good partners and good parents.

Gene Selection Theory

In modern evolutionary theory, all evolutionary processes boil down to an organism’s genes. Genes are the basic “units of heredity,” or the information that is passed along in DNA that tells the cells and molecules how to “build” the organism and how that organism should behave. Genes that are better able to encourage the organism to reproduce, and thus replicate themselves in the organism’s offspring, have an advantage over competing genes that are less able. For example, take female sloths: In order to attract a mate, they will scream as loudly as they can, to let potential mates know where they are in the thick jungle. Now, consider two types of genes in female sloths: one gene that allows them to scream extremely loudly, and another that only allows them to scream moderately loudly. In this case, the sloth with the gene that allows her to shout louder will attract more mates—increasing reproductive success—which ensures that her genes are more readily passed on than those of the quieter sloth.

Essentially, genes can boost their own replicative success in two basic ways. First, they can influence the odds for survival and reproduction of the organism they are in (individual reproductive success or fitness—as in the example with the sloths). Second, genes can also influence the organism to help other organisms who also likely contain those genes—known as “genetic relatives”—to survive and reproduce (which is called inclusive fitness). For example, why do human parents tend to help their own kids with the financial burdens of a college education and not the kids next door? Well, having a college education increases one’s attractiveness to other mates, which increases one’s likelihood for reproducing and passing on genes. And because parents’ genes are in their own children (and not the neighborhood children), funding their children’s educations increases the likelihood that the parents’ genes will be passed on.

Understanding gene replication is the key to understanding modern evolutionary theory. It also fits well with many evolutionary psychological theories. However, for the time being, we’ll ignore genes and focus primarily on actual adaptations that evolved because they helped our ancestors survive and/or reproduce.

Evolutionary Psychology

Evolutionary psychology aims the lens of modern evolutionary theory on the workings of the human mind. It focuses primarily on psychological adaptations: mechanisms of the mind that have evolved to solve specific problems of survival or reproduction. These kinds of adaptations are in contrast to physiological adaptations, which are adaptations that occur in the body as a consequence of one’s environment. One example of a physiological adaptation is how our skin makes calluses. First, there is an “input,” such as repeated friction to the skin on the bottom of our feet from walking. Second, there is a “procedure,” in which the skin grows new skin cells at the afflicted area. Third, an actual callus forms as an “output” to protect the underlying tissue—the final outcome of the physiological adaptation (i.e., tougher skin to protect repeatedly scraped areas). On the other hand, a psychological adaptation is a development or change of a mechanism in the mind. For example, take sexual jealousy. First, there is an “input,” such as a romantic partner flirting with a rival. Second, there is a “procedure,” in which the person evaluates the threat the rival poses to the romantic relationship. Third, there is a behavioral output, which might range from vigilance (e.g., snooping through a partner’s email) to violence (e.g., threatening the rival).

Evolutionary psychology is fundamentally an interactionist framework, or a theory that takes into account multiple factors when determining the outcome. For example, jealousy, like a callus, doesn’t simply pop up out of nowhere. There is an “interaction” between the environmental trigger (e.g., the flirting; the repeated rubbing of the skin) and the initial response (e.g., evaluation of the flirter’s threat; the forming of new skin cells) to produce the outcome.

In evolutionary psychology, culture also has a major effect on psychological adaptations. For example, status within one’s group is important in all cultures for achieving reproductive success, because higher status makes someone more attractive to mates. In individualistic cultures, such as the United States, status is heavily determined by individual accomplishments. But in more collectivist cultures, such as Japan, status is more heavily determined by contributions to the group and by that group’s success. For example, consider a group project. If you were to put in most of the effort on a successful group project, the culture in the United States reinforces the psychological adaptation to try to claim that success for yourself (because individual achievements are rewarded with higher status). However, the culture in Japan reinforces the psychological adaptation to attribute that success to the whole group (because collective achievements are rewarded with higher status). Another example of cultural input is the importance of virginity as a desirable quality for a mate. Cultural norms that advise against premarital sex persuade people to ignore their own basic interests because they know that virginity will make them more attractive marriage partners. Evolutionary psychology, in short, does not predict rigid robotic-like “instincts.” That is, there isn’t one rule that works all the time. Rather, evolutionary psychology studies flexible, environmentally-connected and culturally-influenced adaptations that vary according to the situation.

Psychological adaptations are hypothesized to be wide-ranging, and include food preferences, habitat preferences, mate preferences, and specialized fears. These psychological adaptations also include many traits that improve people’s ability to live in groups, such as the desire to cooperate and make friends, or the inclination to spot and avoid frauds, punish rivals, establish status hierarchies, nurture children, and help genetic relatives. Research programs in evolutionary psychology develop and empirically test predictions about the nature of psychological adaptations. Below, we highlight a few evolutionary psychological theories and their associated research approaches.

Sexual Strategies Theory

Sexual strategies theory is based on sexual selection theory. It proposes that humans have evolved a list of different mating strategies, both short-term and long-term, that vary depending on culture, social context, parental influence, and personal mate value (desirability in the “mating market”).

In its initial formulation, sexual strategies theory focused on the differences between men and women in mating preferences and strategies (Buss & Schmitt, 1993). It started by looking at the minimum parental investment needed to produce a child. For women, even the minimum investment is significant: after becoming pregnant, they have to carry that child for nine months inside of them. For men, on the other hand, the minimum investment to produce the same child is considerably smaller—simply the act of sex.

A pregnant woman smiles as she looks down at her belly.
Figure 4.8: Because women bear responsibility for pregnancy, they may use different sexual selection strategies than men do.

These differences in parental investment have an enormous impact on sexual strategies. For a woman, the risks associated with making a poor mating choice is high. She might get pregnant by a man who will not help to support her and her children, or who might have poor-quality genes. And because the stakes are higher for a woman, wise mating decisions for her are much more valuable. For men, on the other hand, the need to focus on making wise mating decisions isn’t as important. That is, unlike women, men 1) don’t biologically have the child growing inside of them for nine months, and 2) do not have as high a cultural expectation to raise the child. This logic leads to a powerful set of predictions: In short-term mating, women will likely be choosier than men (because the costs of getting pregnant are so high), while men, on average, will likely engage in more casual sexual activities (because this cost is greatly lessened). Due to this, men will sometimes deceive women about their long-term intentions for the benefit of short-term sex, and men are more likely than women to lower their mating standards for short-term mating situations.

An extensive body of empirical evidence supports these and related predictions (Buss & Schmitt, 2011). Men express a desire for a larger number of sex partners than women do. They let less time elapse before seeking sex. They are more willing to consent to sex with strangers and are less likely to require emotional involvement with their sex partners. They have more frequent sexual fantasies and fantasize about a larger variety of sex partners. They are more likely to regret missed sexual opportunities. And they lower their standards in short-term mating, showing a willingness to mate with a larger variety of women as long as the costs and risks are low.

However, in situations where both the man and woman are interested in long-term mating, both sexes tend to invest substantially in the relationship and in their children. In these cases, the theory predicts that both sexes will be extremely choosy when pursuing a long-term mating strategy. Much empirical research supports this prediction, as well. In fact, the qualities women and men generally look for when choosing long-term mates are very similar: both want mates who are intelligent, kind, understanding, healthy, dependable, honest, loyal, loving, and adaptable.

Nonetheless, women and men do differ in their preferences for a few key qualities in long-term mating, because of somewhat distinct adaptive problems. Modern women have inherited the evolutionary trait to desire mates who possess resources, have qualities linked with acquiring resources (e.g., ambition, wealth, industriousness), and are willing to share those resources with them. On the other hand, men more strongly desire youth and health in women, as both are cues to fertility. These male and female differences are universal in humans. They were first documented in 37 different cultures, from Australia to Zambia (Buss, 1989), and have been replicated by dozens of researchers in dozens of additional cultures (for summaries, see Buss, 2012).

As we know, though, just because we have these mating preferences (e.g., men with resources; fertile women), people don’t always get what they want. There are countless other factors which influence who people ultimately select as their mate. For example, the sex ratio (the percentage of men to women in the mating pool), cultural practices (such as arranged marriages, which inhibit individuals’ freedom to act on their preferred mating strategies), the strategies of others (e.g., if everyone else is pursuing short-term sex, it’s more difficult to pursue a long-term mating strategy), and many others all influence who we select as our mates.

Sexual strategies theory—anchored in sexual selection theory— predicts specific similarities and differences in men and women’s mating preferences and strategies. Whether we seek short-term or long-term relationships, many personality, social, cultural, and ecological factors will all influence who our partners will be.

Error Management Theory

A narrow path covered in leaves passes through a forest.
Figure 4.9: If you were walking in the woods and heard a sound in the bushes you might be startled and act on the worst case scenario—such as the threat of a wild animal—by moving in the opposite direction. This is evolutionary psychology at work, keeping you safe so you can survive and reproduce.

Error management theory (EMT) deals with the evolution of how we think, make decisions, and evaluate uncertain situations—that is, situations where there’s no clear answer how we should behave. (Haselton & Buss, 2000; Haselton, Nettle, & Andrews, 2005). Consider, for example, walking through the woods at dusk. You hear a rustle in the leaves on the path in front of you. It could be a snake. Or, it could just be the wind blowing the leaves. Because you can’t really tell why the leaves rustled, it’s an uncertain situation. The important question then is, what are the costs of errors in judgment? That is, if you conclude that it’s a dangerous snake so you avoid the leaves, the costs are minimal (i.e., you simply make a short detour around them). However, if you assume the leaves are safe and simply walk over them—when in fact it is a dangerous snake—the decision could cost you your life.

Now, think about our evolutionary history and how generation after generation was confronted with similar decisions, where one option had low cost but great reward (walking around the leaves and not getting bitten) and the other had a low reward but high cost (walking through the leaves and getting bitten). These kinds of choices are called “cost asymmetries.” If during our evolutionary history we encountered decisions like these generation after generation, over time an adaptive bias would be created: we would make sure to err in favor of the least costly (in this case, least dangerous) option (e.g., walking around the leaves). To put it another way, EMT predicts that whenever uncertain situations present us with a safer versus more dangerous decision, we will psychologically adapt to prefer choices that minimize the cost of errors.

EMT is a general evolutionary psychological theory that can be applied to many different domains of our lives, but a specific example of it is the visual descent illusion. To illustrate: Have you ever thought it would be no problem to jump off of a ledge, but as soon as you stood up there, it suddenly looked much higher than you thought? The visual descent illusion (Jackson & Cormack, 2008) states that people will overestimate the distance when looking down from a height (compared to looking up) so that people will be especially wary of falling from great heights—which would result in injury or death. Another example of EMT is the auditory looming bias: Have you ever noticed how an ambulance seems closer when it’s coming toward you, but suddenly seems far away once it’s immediately passed? With the auditory looming bias, people overestimate how close objects are when the sound is moving toward them compared to when it is moving away from them. From our evolutionary history, humans learned, “It’s better to be safe than sorry.” Therefore, if we think that a threat is closer to us when it’s moving toward us (because it seems louder), we will be quicker to act and escape. In this regard, there may be times we ran away when we didn’t need to (a false alarm), but wasting that time is a less costly mistake than not acting in the first place when a real threat does exist.

EMT has also been used to predict adaptive biases in the domain of mating. Consider something as simple as a smile. In one case, a smile from a potential mate could be a sign of sexual or romantic interest. On the other hand, it may just signal friendliness. Because of the costs to men of missing out on chances for reproduction, EMT predicts that men have a sexual overperception bias: they often misread sexual interest from a woman, when really it’s just a friendly smile or touch. In the mating domain, the sexual overperception bias is one of the best-documented phenomena. It’s been shown in studies in which men and women rated the sexual interest between people in photographs and videotaped interactions. As well, it’s been shown in the laboratory with participants engaging in actual “speed dating,” where the men interpret sexual interest from the women more often than the women actually intended it (Perilloux, Easton, & Buss, 2012). In short, EMT predicts that men, more than women, will over-infer sexual interest based on minimal cues, and empirical research confirms this adaptive mating bias.


Sexual strategies theory and error management theory are two evolutionary psychological theories that have received much empirical support from dozens of independent researchers. But, there are many other evolutionary psychological theories, such as social exchange theory for example, that also make predictions about our modern day behavior and preferences, too. The merits of each evolutionary psychological theory, however, must be evaluated separately and treated like any scientific theory. That is, we should only trust their predictions and claims to the extent they are supported by scientific studies. However, even if the theory is scientifically grounded, just because a psychological adaptation was advantageous in our history, it doesn’t mean it’s still useful today. For example, even though women may have preferred men with resources in generations ago, our modern society has advanced such that these preferences are no longer apt or necessary. Nonetheless, it’s important to consider how our evolutionary history has shaped our automatic or “instinctual” desires and reflexes of today, so that we can better shape them for the future ahead.


Outside Resources


Web: Articles and books on evolutionary psychology

Web: Main international scientific organization for the study of evolution and human behavior, HBES

Discussion Questions

  1. How does change take place over time in the living world?
  2. Which two potential psychological adaptations to problems of survival are not discussed in this module?
  3. What are the psychological and behavioral implications of the fact that women bear heavier costs to produce a child than men do?
  4. Can you formulate a hypothesis about an error management bias in the domain of social interaction?

Image Attributions

Figure 4.6: Best Couples,, CC BY-SA 2.0,

Figure 4.7: Dave Hogg,, CC BY 2.0,

Figure 4.8: CC0 Public Domain,

Figure 4.9: Nicholas T,, CC BY 2.0,


Buss, D. M. (2012). Evolutionary psychology: The new science of the mind (4th ed.). Boston, MA: Allyn & Bacon.

Buss, D. M. (1989). Sex differences in human mate preferences: Evolutionary hypotheses tested in 37 cultures. Behavioral & Brain Sciences, 12, 1–49.

Buss, D. M., & Schmitt, D. P. (2011). Evolutionary psychology and feminism. Sex Roles, 64, 768–787.

Buss, D. M., & Schmitt, D. P. (1993). Sexual strategies theory: An evolutionary perspective on human mating. Psychological Review, 100, 204–232.

Haselton, M. G., & Buss, D. M. (2000). Error management theory: A new perspective on biases in cross-sex mind reading. Journal of Personality and Social Psychology, 78, 81–91.

Haselton, M. G., Nettle, D., & Andrews, P. W. (2005). The evolution of cognitive bias. In D. M. Buss (Ed.), The handbook of evolutionary psychology (pp. 724–746). New York, NY: Wiley.

Jackson, R. E., & Cormack, J. K. (2008). Evolved navigation theory and the environmental vertical illusion. Evolution and Human Behavior, 29, 299–304.

Perilloux, C., Easton, J. A., & Buss, D. M. (2012). The misperception of sexual interest. Psychological Science, 23, 146–151.


4.3 Epigenetics in Psychology

Ian Weaver

Early life experiences exert a profound and long-lasting influence on physical and mental health throughout life. The efforts to identify the primary causes of this have significantly benefited from studies of the epigenome—a dynamic layer of information associated with DNA that differs between individuals and can be altered through various experiences and environments. The epigenome has been heralded as a key “missing piece” of the etiological puzzle for understanding how development of psychological disorders may be influenced by the surrounding environment, in concordance with the genome. Understanding the mechanisms involved in the initiation, maintenance, and heritability of epigenetic states is thus an important aspect of research in current biology, particularly in the study of learning and memory, emotion, and social behavior in humans. Moreover, epigenetics in psychology provides a framework for understanding how the expression of genes is influenced by experiences and the environment to produce individual differences in behavior, cognition, personality, and mental health. In this module, we survey recent developments revealing epigenetic aspects of mental health and review some of the challenges of epigenetic approaches in psychology to help explain how nurture shapes nature.

Learning Objectives

  1. Explain what the term epigenetics means and the molecular machinery involved.
  2. Name and discuss important neural and developmental pathways that are regulated by epigenetic factors, and provide examples of epigenetic effects on personality traits and cognitive behavior.
  3. Understand how misregulation of epigenetic mechanisms can lead to disease states, and be able to discuss examples.
  4. Recognize how epigenetic machinery can be targets for therapeutic agents, and discuss examples.


A strand of DNA.
Figure 4.10: DNA stands for Deoxyribonucleic Acid, and although each person’s DNA is unique to that individual, it is 99.9% similar to every other human on the planet. 

Early childhood is not only a period of physical growth; it is also a time of mental development related to changes in the anatomy, physiology, and chemistry of the nervous system that influence mental health throughout life. Cognitive abilities associated with learning and memory, reasoning, problem solving, and developing relationships continue to emerge during childhood. Brain development is more rapid during this critical or sensitive period than at any other, with more than 700 neural connections created each second. Herein, complex gene–environment interactions (or genotype–environment interactions, G×E) serve to increase the number of possible contacts between neurons, as they hone their adult synaptic properties and excitability. Many weak connections form to different neuronal targets; subsequently, they undergo remodeling in which most connections vanish and a few stable connections remain. These structural changes (or plasticity) may be crucial for the development of mature neural networks that support emotional, cognitive, and social behavior. The generation of different morphology, physiology, and behavioral outcomes from a single genome in response to changes in the environment forms the basis for “phenotypic plasticity,” which is fundamental to the way organisms cope with environmental variation, navigate the present world, and solve future problems.

The challenge for psychology has been to integrate findings from genetics and environmental (social, biological, chemical) factors, including the quality of infant–mother attachments, into the study of personality and our understanding of the emergence of mental illness. These studies have demonstrated that common DNA sequence variation and rare mutations account for only a small fraction (1%–2%) of the total risk for inheritance of personality traits and mental disorders (Dick, Riley, & Kendler, 2010; Gershon, Alliey-Rodriguez, & Liu, 2011). Additionally, studies that have attempted to examine the mechanisms and conditions under which DNA sequence variation influences brain development and function have been confounded by complex cause-and-effect relationships (Petronis, 2010). The large unaccounted heritability of personality traits and mental health suggests that additional molecular and cellular mechanisms are involved.

Epigenetics has the potential to provide answers to these important questions and refers to the transmission of phenotype in terms of gene expression in the absence of changes in DNA sequence—hence the name epi- (Greek: επί- over, above) genetics (Waddington, 1942; Wolffe & Matzke, 1999). The advent of high-throughput techniques such as sequencing-based approaches to study the distributions of regulators of gene expression throughout the genome led to the collective description of the “epigenome.” In contrast to the genome sequence, which is static and the same in almost all cells, the epigenome is highly dynamic, differing among cell types, tissues, and brain regions (Gregg et al., 2010). Recent studies have provided insights into epigenetic regulation of developmental pathways in response to a range of external environmental factors (Dolinoy, Weidman, & Jirtle, 2007). These environmental factors during early childhood and adolescence can cause changes in expression of genes conferring risk of mental health and chronic physical conditions. Thus, the examination of genetic–epigenetic–environment interactions from a developmental perspective may determine the nature of gene misregulation in psychological disorders.

This module will provide an overview of the main components of the epigenome and review themes in recent epigenetic research that have relevance for psychology, to form the biological basis for the interplay between environmental signals and the genome in the regulation of individual differences in physiology, emotion, cognition, and behavior.

Molecular control of gene expression: the dynamic epigenome

75-year-old identical twins wearing identical dresses.
Figure 4.11: Identical twins are the perfect example of epigenetics. Although they share exactly the same DNA, their unique experiences in life will cause some genes (and not others) to express themselves. This is why, over time, identical twins come to look and behave differently. 

Almost all the cells in our body are genetically identical, yet our body generates many different cell types, organized into different tissues and organs, and expresses different proteins. Within each type of mammalian cell, about 2 meters of genomic DNA is divided into nuclear chromosomes. Yet the nucleus of a human cell, which contains the chromosomes, is only about 2 μm in diameter. To achieve this 1,000,000-fold compaction, DNA is wrapped around a group of 8 proteins called histones. This combination of DNA and histone proteins forms a special structure called a “nucleosome,” the basic unit of chromatin, which represents a structural solution for maintaining and accessing the tightly compacted genome. These factors alter the likelihood that a gene will be expressed or silenced. Cellular functions such as gene expression, DNA replication, and the generation of specific cell types are therefore influenced by distinct patterns of chromatin structure, involving covalent modification of both histones (Kadonaga, 1998) and DNA (Razin, 1998).

Importantly, epigenetic variation also emerges across the lifespan. For example, although identical twins share a common genotype and are genetically identical and epigenetically similar when they are young, as they age they become more dissimilar in their epigenetic patterns and often display behavioral, personality, or even physical differences, and have different risk levels for serious illness. Thus, understanding the structure of the nucleosome is key to understanding the precise and stable control of gene expression and regulation, providing a molecular interface between genes and environmentally induced changes in cellular activity.

The primary epigenetic mark: DNA modification

DNA methylation is the best-understood epigenetic modification influencing gene expression. DNA is composed of four types of naturally occurring nitrogenous bases: adenine (A), thymine (T), guanine (G), and cytosine (C). In mammalian genomes, DNA methylation occurs primarily at cytosine residues in the context of cytosines that are followed by guanines (CpG dinucleotides), to form 5-methylcytosine in a cell-specific pattern (Goll & Bestor, 2005; Law & Jacobsen, 2010; Suzuki & Bird, 2008). The enzymes that perform DNA methylation are called DNA methyltransferases (DNMTs), which catalyze the transfer of a methyl group to the cytosine (Adams, McKay, Craig, & Burdon, 1979). These enzymes are all expressed in the central nervous system and are dynamically regulated during development (Feng, Chang, Li, & Fan, 2005; Goto et al., 1994). The effect of DNA methylation on gene function varies depending on the period of development during which the methylation occurs and location of the methylated cytosine. Methylation of DNA in gene regulatory regions (promoter and enhancer regions) usually results in gene silencing and reduced gene expression (Ooi, O’Donnell, & Bestor, 2009; Suzuki & Bird, 2008; Sutter and Doerfler, 1980; Vardimon et al., 1982). This is a powerful regulatory mechanism that ensures that genes are expressed only when needed. Thus DNA methylation may broadly impact human brain development, and age-related misregulation of DNA methylation is associated with the molecular pathogenesis of neurodevelopmental disorders.

Histone modification and the histone code

Model of a histone protein.
Figure 4.12: Life experiences, like a stressful event in childhood, can cause the modification of histone proteins (pictured) to help adapt to one’s environment. For example, in response to a stressful event, histone modification of one’s DNA might occur to encourage a more cautions personality—in order to avoid future, stressful encounters. 

The modification of histone proteins comprises an important epigenetic mark related to gene expression. One of the most thoroughly studied modifications is histone acetylation, which is associated with gene activation and increased gene expression (Wade, Pruss, & Wolffe, 1997). Acetylation on histone tails is mediated by the opposing enzymatic activities of histone acetyltransferases (HATs) and histone deacetylases (HDACs) (Kuo & Allis, 1998). For example, acetylation of histone in gene regulatory regions by HAT enzymes is generally associated with DNA demethylation, gene activation, and increased gene expression (Hong, Schroth, Matthews, Yau, & Bradbury, 1993; Sealy & Chalkley, 1978). On the other hand, removal of the acetyl group (deacetylation) by HDAC enzymes is generally associated with DNA methylation, gene silencing, and decreased gene expression (Davie & Chadee, 1998). The relationship between patterns of histone modifications and gene activity provides evidence for the existence of a “histone code” for determining cell-specific gene expression programs (Jenuwein & Allis, 2001). Interestingly, recent research using animal models has demonstrated that histone modifications and DNA methylation of certain genes mediates the long-term behavioral effects of the level of care experienced during infancy.

Early childhood experience

The development of an individual is an active process of adaptation that occurs within a social and economic context. For example, the closeness or degree of positive attachment of the parent (typically mother)–infant bond and parental investment (including nutrient supply provided by the parent) that define early childhood experience also program the development of individual differences in stress responses in the brain, which then affect memory, attention, and emotion. In terms of evolution, this process provides the offspring with the ability to physiologically adjust gene expression profiles contributing to the organization and function of neural circuits and molecular pathways that support (1) biological defensive systems for survival (e.g., stress resilience), (2) reproductive success to promote establishment and persistence in the present environment, and (3) adequate parenting in the next generation (Bradshaw, 1965).

Parental investment and programming of stress responses in the offspring

The most comprehensive study to date of variations in parental investment and epigenetic inheritance in mammals is that of the maternally transmitted responses to stress in rats. In rat pups, maternal nurturing (licking and grooming) during the first week of life is associated with long-term programming of individual differences in stress responsiveness, emotionality, cognitive performance, and reproductive behavior (Caldji et al., 1998; Francis, Diorio, Liu, & Meaney, 1999; Liu et al., 1997; Myers, Brunelli, Shair, Squire, & Hofer, 1989; Stern, 1997). In adulthood, the offspring of mothers that exhibit increased levels of pup licking and grooming over the first week of life show increased expression of the glucocorticoid receptor in the hippocampus (a brain structure associated with stress responsivity as well as learning and memory) and a lower hormonal response to stress compared with adult animals reared by low licking and grooming mothers (Francis et al., 1999; Liu et al., 1997). Moreover, rat pups that received low levels of maternal licking and grooming during the first week of life showed decreased histone acetylation and increased DNA methylation of a neuron-specific promoter of the glucocorticoid receptor gene (Weaver et al., 2004). The expression of this gene is then reduced, the number of glucocorticoid receptors in the brain is decreased, and the animals show a higher hormonal response to stress throughout their life. The effects of maternal care on stress hormone responses and behaviour in the offspring can be eliminated in adulthood by pharmacological treatment (HDAC inhibitor trichostatin A, TSA) or dietary amino acid supplementation (methyl donor L-methionine), treatments that influence histone acetylation, DNA methylation, and expression of the glucocorticoid receptor gene (Weaver et al., 2004; Weaver et al., 2005). This series of experiments shows that histone acetylation and DNA methylation of the glucocorticoid receptor gene promoter is a necessary link in the process leading to the long-term physiological and behavioral sequelae of poor maternal care. This points to a possible molecular target for treatments that may reverse or ameliorate the traces of childhood maltreatment.

A young father and mother are all smiles as they hold their infant.
Figure 4.13: Parental care during one’s childhood has important and consequential effects on the development of an individual, effects that persist even into adulthood. 

Several studies have attempted to determine to what extent the findings from model animals are transferable to humans. Examination of post-mortem brain tissue from healthy human subjects found that the human equivalent of the glucocorticoid receptor gene promoter (NR3C1 exon 1F promoter) is also unique to the individual (Turner, Pelascini, Macedo, & Muller, 2008). A similar study examining newborns showed that methylation of the glucocorticoid receptor gene promoter maybe an early epigenetic marker of maternal mood and risk of increased hormonal responses to stress in infants 3 months of age (Oberlander et al., 2008). Although further studies are required to examine the functional consequence of this DNA methylation, these findings are consistent with our studies in the neonate and adult offspring of low licking and grooming mothers that show increased DNA methylation of the promoter of the glucocorticoid receptor gene, decreased glucocorticoid receptor gene expression, and increased hormonal responses to stress (Weaver et al., 2004). Examination of brain tissue from suicide victims found that the human glucocorticoid receptor gene promoter is also more methylated in the brains of individuals who had experienced maltreatment during childhood (McGowan et al., 2009). These finding suggests that DNA methylation mediates the effects of early environment in both rodents and humans and points to the possibility of new therapeutic approaches stemming from translational epigenetic research. Indeed, similar processes at comparable epigenetic labile regions could explain why the adult offspring of high and low licking/grooming mothers exhibit widespread differences in hippocampal gene expression and cognitive function (Weaver, Meaney, & Szyf, 2006).

However, this type of research is limited by the inaccessibility of human brain samples. The translational potential of this finding would be greatly enhanced if the relevant epigenetic modification can be measured in an accessible tissue. Examination of blood samples from adult patients with bipolar disorder, who also retrospectively reported on their experiences of childhood abuse and neglect, found that the degree of DNA methylation of the human glucocorticoid receptor gene promoter was strongly positively related to the reported experience of childhood maltreatment decades earlier. For a relationship between a molecular measure and reported historical exposure, the effects size is extraordinarily large. This opens a range of new possibilities: given the large effect size and consistency of this association, measurement of the GR promoter methylation may effectively become a blood test measuring the physiological traces left on the genome by early experiences. Although this blood test cannot replace current methods of diagnosis, this unique and addition information adds to our knowledge of how disease may arise and be manifested throughout life. Near-future research will examine whether this measure adds value over and above simple reporting of early adversities when it comes to predicting important outcomes, such as response to treatment or suicide.

Child nutrition and the epigenome

A mother and daughter shopping for vegetables at the supermarket.
Figure 4.14: Whether or not your parents knew the science behind it, telling you to eat your veggies as a kid really does make you healthier and stronger—at least your DNA, that is. 

The old adage “you are what you eat” might be true on more than just a physical level: The food you choose (and even what your parents and grandparents chose) is reflected in your own personal development and risk for disease in adult life (Wells, 2003). Nutrients can reverse or change DNA methylation and histone modifications, thereby modifying the expression of critical genes associated with physiologic and pathologic processes, including embryonic development, aging, and carcinogenesis. It appears that nutrients can influence the epigenome either by directly inhibiting enzymes that catalyze DNA methylation or histone modifications, or by altering the availability of substrates necessary for those enzymatic reactions. For example, rat mothers fed a diet low in methyl group donors during pregnancy produce offspring with reduced DNMT-1 expression, decreased DNA methylation, and increased histone acetylation at promoter regions of specific genes, including the glucocorticoid receptor, and increased gene expression in the liver of juvenile offspring (Lillycrop, Phillips, Jackson, Hanson, & Burdge, 2005) and adult offspring (Lillycrop et al., 2007). These data suggest that early life nutrition has the potential to influence epigenetic programming in the brain not only during early development but also in adult life, thereby modulating health throughout life. In this regard, nutritional epigenetics has been viewed as an attractive tool to prevent pediatric developmental diseases and cancer, as well as to delay aging-associated processes.

The best evidence relating to the impact of adverse environmental conditions development and health comes from studies of the children of women who were pregnant during two civilian famines of World War II: the Siege of Leningrad (1941–44) (Bateson, 2001) and the Dutch Hunger Winter (1944–1945) (Stanner et al., 1997). In the Netherlands famine, women who were previously well nourished were subjected to low caloric intake and associated environmental stressors. Women who endured the famine in the late stages of pregnancy gave birth to smaller babies (Lumey & Stein, 1997) and these children had an increased risk of insulin resistance later in life (Painter, Roseboom, & Bleker, 2005). In addition, offspring who were starved prenatally later experienced impaired glucose tolerance in adulthood, even when food was more abundant (Stanner et al., 1997). Famine exposure at various stages of gestation was associated with a wide range of risks such as increased obesity, higher rates of coronary heart disease, and lower birth weight (Lumey & Stein, 1997). Interestingly, when examined 60 years later, people exposed to famine prenatally showed reduced DNA methylation compared with their unexposed same-sex siblings (Heijmans et al., 2008).

Epigenetic regulation of learning and memory

Cortical neuron tissue.
Figure 4.15: Neural plasticity is the change of neural pathways and synapses which allows for our ability to learn new things and remember them. 

Memories are recollections of actual events stored within our brains. But how is our brain able to form and store these memories? Epigenetic mechanisms influence genomic activities in the brain to produce long-term changes in synaptic signaling, organization, and morphology, which in turn support learning and memory (Day & Sweatt, 2011).

Neuronal activity in the hippocampus of mice is associated with changes in DNA methylation (Guo et al., 2011), and disruption to genes encoding the DNA methylation machinery cause learning and memory impairments (Feng et al., 2010). DNA methylation has also been implicated in the maintenance of long-term memories, as pharmacological inhibition of DNA methylation and impaired memory (Day & Sweatt, 2011; Miller et al., 2010). These findings indicate the importance of DNA methylation in mediating synaptic plasticity and cognitive functions, both of which are disturbed in psychological illness.

Changes in histone modifications can also influence long-term memory formation by altering chromatin accessibility and the expression of genes relevant to learning and memory. Memory formation and the associated enhancements in synaptic transmission are accompanied by increases in histone acetylation (Guan et al., 2002) and alterations in histone methylation (Schaefer et al., 2009), which promote gene expression. Conversely, a neuronal increase in histone deacetylase activity, which promotes gene silencing, results in reduced synaptic plasticity and impairs memory (Guan et al., 2009). Pharmacological inhibition of histone deacetylases augments memory formation (Guan et al., 2009; Levenson et al., 2004), further suggesting that histone (de)acetylation regulates this process.

In humans genetic defects in genes encoding the DNA methylation and chromatin machinery exhibit profound effects on cognitive function and mental health (Jiang, Bressler, & Beaudet, 2004). The two best-characterized examples are Rett syndrome (Amir et al., 1999) and Rubinstein-Taybi syndrome (RTS) (Alarcon et al., 2004), which are profound intellectual disability disorders. Both MECP2 and CBP are highly expressed in neurons and are involved in regulating neural gene expression (Chen et al., 2003; Martinowich et al., 2003).

Rett syndrome patients have a mutation in their DNA sequence in a gene called MECP2. MECP2 plays many important roles within the cell: One of these roles is to read the DNA sequence, checking for DNA methylation, and to bind to areas that contain methylation, thereby preventing the wrong proteins from being present. Other roles for MECP2 include promoting the presence of particular, necessary, proteins, ensuring that DNA is packaged properly within the cell and assisting with the production of proteins. MECP2 function also influences gene expression that supports dendritic and synaptic development and hippocampus-dependent memory (Li, Zhong, Chau, Williams, & Chang, 2011; Skene et al., 2010). Mice with altered MECP2 expression exhibit genome-wide increases in histone acetylation, neuron cell death, increased anxiety, cognitive deficits, and social withdrawal (Shahbazian et al., 2002). These findings support a model in which DNA methylation and MECP2 constitute a cell-specific epigenetic mechanism for regulation of histone modification and gene expression, which may be disrupted in Rett syndrome.

RTS patients have a mutation in their DNA sequence in a gene called CBP. One of these roles of CBP is to bind to specific histones and promote histone acetylation, thereby promoting gene expression. Consistent with this function, RTS patients exhibit a genome-wide decrease in histone acetylation and cognitive dysfunction in adulthood (Kalkhoven et al., 2003). The learning and memory deficits are attributed to disrupted neural plasticity (Korzus, Rosenfeld, & Mayford, 2004). Similar to RTS in humans, mice with a mutation of CBP perform poorly in cognitive tasks and show decreased genome-wide histone acetylation (for review, see Josselyn, 2005). In the mouse brain CBP was found to act as an epigenetic switch to promote the birth of new neurons in the brain. Interestingly, this epigenetic mechanism is disrupted in the fetal brains of mice with a mutation of CBP, which, as pups, exhibit early behavioral deficits following removal and separation from their mother (Wang et al., 2010). These findings provide a novel mechanism whereby environmental cues, acting through histone modifying enzymes, can regulate epigenetic status and thereby directly promote neurogenesis, which regulates neurobehavioral development.

Together, these studies demonstrate that misregulation of epigenetic modifications and their regulatory enzymes is capable of orchestrating prominent deficits in neuronal plasticity and cognitive function. Knowledge from these studies may provide greater insight into other mental disorders such as depression and suicidal behaviors.

Epigenetic mechanisms in psychological disorders

Two models of chromatin.
Figure 4.16: Pictured above is a chromatin, the spiral-looking macromolecule involved in depression.

Epigenome-wide studies have identified several dozen sites with DNA methylation alterations in genes involved in brain development and neurotransmitter pathways, which had previously been associated with mental illness (Mill et al., 2008). These disorders are complex and typically start at a young age and cause lifelong disability. Often, limited benefits from treatment make these diseases some of the most burdensome disorders for individuals, families, and society. It has become evident that the efforts to identify the primary causes of complex psychiatric disorders may significantly benefit from studies linking environmental effects with changes observed within the individual cells.

Epigenetic events that alter chromatin structure to regulate programs of gene expression have been associated with depression-related behavior and action of antidepressant medications, with increasing evidence for similar mechanisms occurring in post-mortem brains of depressed individuals. In mice, social avoidance resulted in decreased expression of hippocampal genes important in mediating depressive responses (Tsankova et al., 2006). Similarly, chronic social defeat stress was found to decrease expression of genes implicated in normal emotion processing (Lutter et al., 2008). Consistent with these findings, levels of histone markers of increased gene expression were down regulated in human post-mortem brain samples from individuals with a history of clinical depression (Covington et al., 2009).

Administration of antidepressants increased histone markers of increased gene expression and reversed the gene repression induced by defeat stress (Lee, Wynder, Schmidt, McCafferty, & Shiekhattar, 2006; Tsankova et al., 2006; Wilkinson et al., 2009). These results provide support for the use of HDAC inhibitors against depression. Accordingly, several HDAC inhibitors have been found to exert antidepressant effects by each modifying distinct cellular targets (Cassel et al., 2006; Schroeder, Lin, Crusio, & Akbarian, 2007).

There is also increasing evidence that aberrant gene expression resulting from altered epigenetic regulation is associated with the pathophysiology of suicide (McGowan et al., 2008; Poulter et al., 2008). Thus, it is tempting to speculate that there is an epigenetically determined reduced capacity for gene expression, which is required for learning and memory, in the brains of suicide victims.

Epigenetic strategy to understanding gene-environment interactions

An unhappy-looking little boy sits with his teddy bear on the floor of a closet.
Figure 4.17: Although there is some evidence that a dysfunctional upbringing can increase one’s likelihood for schizophrenia (an epigenetically inherited disease), some people who have both the predisposition and the stressful environment never develop the mental illness.

While the cellular and molecular mechanisms that influence on physical and mental health have long been a central focus of neuroscience, only in recent years has attention turned to the epigenetic mechanisms behind the dynamic changes in gene expression responsible for normal cognitive function and increased risk for mental illness. The links between early environment and epigenetic modifications suggest a mechanism underlying gene-environment interactions. Early environmental adversity alone is not a sufficient cause of mental illness, because many individuals with a history of severe childhood maltreatment or trauma remain healthy. It is increasingly becoming evident that inherited differences in the segments of specific genes may moderate the effects of adversity and determine who is sensitive and who is resilient through a gene-environment interplay. Genes such as the glucocorticoid receptor appear to moderate the effects of childhood adversity on mental illness. Remarkably, epigenetic DNA modifications have been identified that may underlie the long-lasting effects of environment on biological functions. This new epigenetic research is pointing to a new strategy to understanding gene-environment interactions.

The next decade of research will show if this potential can be exploited in the development of new therapeutic options that may alter the traces that early environment leaves on the genome. However, as discussed in this module, the epigenome is not static and can be molded by developmental signals, environmental perturbations, and disease states, which present an experimental challenge in the search for epigenetic risk factors in psychological disorders (Rakyan, Down, Balding, & Beck, 2011). The sample size and epigenomic assay required is dependent on the number of tissues affected, as well as the type and distribution of epigenetic modifications. The combination of genetic association maps studies with epigenome-wide developmental studies may help identify novel molecular mechanisms to explain features of inheritance of personality traits and transform our understanding of the biological basis of psychology. Importantly, these epigenetic studies may lead to identification of novel therapeutic targets and enable the development of improved strategies for early diagnosis, prevention, and better treatment of psychological and behavioral disorders.


Outside Resources

Reference: The “Encyclopedia of DNA Elements” (ENCODE) project

Reference: THREADS – A new way to explore the ENCODE Project

Web: Explore, view, and download genome-wide maps of DNA and histone modifications from the NCBI Epigenomics Portal

Web: NOVA ScienceNOW – Introduction to Epigenetics

Web: The University of Utah’s Genetic Science Learning Center

Discussion Questions

  1. Describe the physical state of the genome when genes are active and inactive.
  2. Often, the physical characteristics of genetically identical twins become increasingly different as they age, even at the molecular level. Explain why this is so (use the terms “environment” and “epigenome”).
  3. Name 3–4 environmental factors that influence the epigenome and describe their effects.
  4. The rat nurturing example shows us how parental behavior can shape the behavior of offspring on a biochemical level. Discuss how this relates to humans and include the personal and social implications.
  5. Explain how the food we eat affects gene expression.
  6. Can the diets of parents affect their offspring’s epigenome?
  7. Why is converging evidence the best kind of evidence in the study of brain function?
  8. If you were interested in whether a particular brain area was involved in a specific behavior, what neuroscience methods could you use?
  9. If you were interested in the precise time in which a particular brain process occurred, which neuroscience methods could you use?

Image Attributions

Figure 4.10: CC0 Public Domain,

Figure 4.11: M.,, CC BY-NC-SA 2.0,

Figure 4.12: Zephyris,, CC BY-SA 3.0,

Figure 4.13: The White Ribbon Alliance,, CC BY-NC-SA 2.0,

Figure 4.14: U.S. Department of Agriculture,, CC BY 2.0,

Figure 4.15: Gerry Shaw,, CC BY-SA 3.0,

Figure 4.16: Zephyris,, CC BY-SA 3.0,

Figure 4.17: Steve White, CC0 Public Domain,


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4.4 Is Personality More Nature or More Nurture? Behavioural and Molecular Genetics

Charles Stangor and Jennifer Walinga

Learning Objectives

  1. Explain how genes transmit personality from one generation to the next.
  2. Outline the methods of behavioural genetics studies and the conclusions that we can draw from them about the determinants of personality.
  3. Explain how molecular genetics research helps us understand the role of genetics in personality.

One question that is exceedingly important for the study of personality concerns the extent to which it is the result of nature or nurture. If nature is more important, then our personalities will form early in our lives and will be difficult to change later. If nurture is more important, however, then our experiences are likely to be particularly important, and we may be able to flexibly alter our personalities over time. In this section we will see that the personality traits of humans and animals are determined in large part by their genetic makeup, and thus it is no surprise that identical twins Paula Bernstein and Elyse Schein turned out to be very similar even though they had been raised separately. But we will also see that genetics does not determine everything.

In the nucleus of each cell in your body are 23 pairs of chromosomes. One of each pair comes from your father, and the other comes from your mother. The chromosomes are made up of strands of the molecule DNA (deoxyribonucleic acid), and the DNA is grouped into segments known as genes. A gene is the basic biological unit that transmits characteristics from one generation to the next. Human cells have about 25,000 genes.

The genes of different members of the same species are almost identical. The DNA in your genes, for instance, is about 99.9% the same as the DNA in my genes and in the DNA of every other human being. These common genetic structures lead members of the same species to be born with a variety of behaviours that come naturally to them and that define the characteristics of the species. These abilities and characteristics are known as instincts — complex inborn patterns of behaviours that help ensure survival and reproduction (Tinbergen, 1951). Different animals have different instincts. Birds naturally build nests, dogs are naturally loyal to their human caretakers, and humans instinctively learn to walk and to speak and understand language.

But the strength of different traits and behaviours also varies within species. Rabbits are naturally fearful, but some are more fearful than others; some dogs are more loyal than others to their caretakers; and some humans learn to speak and write better than others do. These differences are determined in part by the small amount (in humans, the 0.1%) of the differences in genes among the members of the species.

Personality is not determined by any single gene, but rather by the actions of many genes working together. There is no “IQ gene” that determines intelligence and there is no “good marriage-partner gene” that makes a person a particularly good marriage bet. Furthermore, even working together, genes are not so powerful that they can control or create our personality. Some genes tend to increase a given characteristic and others work to decrease that same characteristic — the complex relationship among the various genes, as well as a variety of random factors, produces the final outcome. Furthermore, genetic factors always work with environmental factors to create personality. Having a given pattern of genes doesn’t necessarily mean that a particular trait will develop, because some traits might occur only in some environments. For example, a person may have a genetic variant that is known to increase his or her risk for developing emphysema from smoking. But if that person never smokes, then emphysema most likely will not develop.

Studying Personality Using Behavioural Genetics

Perhaps the most direct way to study the role of genetics in personality is to selectively breed animals for the trait of interest. In this approach the scientist chooses the animals that most strongly express the personality characteristics of interest and breeds these animals with each other. If the selective breeding creates offspring with even stronger traits, then we can assume that the trait has genetic origins. In this manner, scientists have studied the role of genetics in how worms respond to stimuli, how fish develop courtship rituals, how rats differ in play, and how pigs differ in their responses to stress.

Although selective breeding studies can be informative, they are clearly not useful for studying humans. For this psychologists rely on behavioural genetics — a variety of research techniques that scientists use to learn about the genetic and environmental influences on human behaviour by comparing the traits of biologically and nonbiologically related family members (Baker, 2004). Behavioural genetics is based on the results of family studies, twin studies, and adoptive studies.

A family study starts with one person who has a trait of interest — for instance, a developmental disorder such as autism — and examines the individual’s family tree to determine the extent to which other members of the family also have the trait. The presence of the trait in first-degree relatives (parents, siblings, and children) is compared with the prevalence of the trait in second-degree relatives (aunts, uncles, grandchildren, grandparents, and nephews or nieces) and in more distant family members. The scientists then analyze the patterns of the trait in the family members to see the extent to which it is shared by closer and more distant relatives.

Although family studies can reveal whether a trait runs in a family, it cannot explain why. In a twin study, researchers study the personality characteristics of twins. Twin studies rely on the fact that identical (or monozygotic) twins have essentially the same set of genes, while fraternal (or dizygotic) twins have, on average, a half-identical set. The idea is that if the twins are raised in the same household, then the twins will be influenced by their environments to an equal degree, and this influence will be pretty much equal for identical and fraternal twins. In other words, if environmental factors are the same, then the only factor that can make identical twins more similar than fraternal twins is their greater genetic similarity.

In a twin study, the data from many pairs of twins are collected and the rates of similarity for identical and fraternal pairs are compared. A correlation coefficient is calculated that assesses the extent to which the trait for one twin is associated with the trait in the other twin. Twin studies divide the influence of nature and nurture into three parts:

In the typical twin study, all three sources of influence are operating simultaneously, and it is possible to determine the relative importance of each type.

An adoption study compares biologically related people, including twins, who have been reared either separately or apart. Evidence for genetic influence on a trait is found when children who have been adopted show traits that are more similar to those of their biological parents than to those of their adoptive parents. Evidence for environmental influence is found when the adoptee is more like his or her adoptive parents than the biological parents.

The results of family, twin, and adoption studies are combined to get a better idea of the influence of genetics and environment on traits of interest. Table 4.1, “Data from Twin and Adoption Studies on the Heritability of Various Characteristics,” presents data on the correlations and heritability estimates for a variety of traits based on the results of behavioural genetics studies (Bouchard, Lykken, McGue, Segal, & Tellegen, 1990).

Table 4.1 Data from Twin and Adoption Studies on the Heritability of Various Characteristics.
Correlation between children raised together Correlation between children raised apart Estimated percent of total due to
Identical twins Fraternal twins Identical twins Fraternal twins Heritability (%) Shared environment (%) Nonshared environment (%)
Age of puberty 45 5 50
Aggression 0.43 0.14 0.46 0.06
Alzheimer disease 0.54 0.16
Fingerprint patterns 0.96 0.47 0.96 0.47 100 0 0
General cognitive ability 56 0 44
Likelihood of divorce 0.52 0.22
Sexual orientation 0.52 0.22 18–39 0–17 61–66
Big Five dimensions 40–50
This table presents some of the observed correlations and heritability estimates for various characteristics.
Sources: Långström, et al, 2010; Loehlin, 1992; McGue & Lykken, 1992; Plomin et al, 1997; Tellegen et al, 1988.

If you look in the second column of Table 4.1 , “Data from Twin and Adoption Studies on the Heritability of Various Characteristics,” you will see the observed correlations for the traits between identical twins who have been raised together in the same house by the same parents. This column represents the pure effects of genetics, in the sense that environmental differences have been controlled to be a small as possible. You can see that these correlations are higher for some traits than for others. Fingerprint patterns are very highly determined by our genetics (r = .96), whereas the Big Five trait dimensions have a heritability of 40% to 50%.

You can also see from the table that, overall, there is more influence of nature than of parents. Identical twins, even when they are raised in separate households by different parents (column 4), turn out to be quite similar in personality, and are more similar than fraternal twins who are raised in separate households (column 5). These results show that genetics has a strong influence on personality, and helps explain why Elyse and Paula were so similar when they finally met.

Despite the overall role of genetics, you can see in Table 4.1, “Data from Twin and Adoption Studies on the Heritability of Various Characteristics,” that the correlations between identical twins (column 2) and heritability estimates for most traits (column 6) are substantially less than 1.00, showing that the environment also plays an important role in personality (Turkheimer & Waldron, 2000). For instance, for sexual orientation the estimates of heritability vary from 18% to 39% of the total across studies, suggesting that 61% to 82% of the total influence is due to environment.

You might at first think that parents would have a strong influence on the personalities of their children, but this would be incorrect. As you can see by looking in column 7 of Table 4.1,” research finds that the influence of shared environment (i.e., the effects of parents or other caretakers) plays little or no role in adult personality (Harris, 2006). Shared environment does influence the personality and behaviour of young children, but this influence decreases rapidly as the child grows older. By the time we reach adulthood, the impact of shared environment on our personalities is weak at best (Roberts & DelVecchio, 2000). What this means is that although parents must provide a nourishing and stimulating environment for children, no matter how hard they try they are not likely to be able to turn their children into geniuses or into professional athletes, nor will they be able to turn them into criminals.

If parents are not providing the environmental influences on the child, then what is? The last column in Table 4.1,” the influence of nonshared environment, represents whatever is “left over” after removing the effects of genetics and parents. You can see that these factors — the largely unknown things that happen to us that make us different from other people — often have the largest influence on personality.

Studying Personality Using Molecular Genetics

In addition to the use of behavioural genetics, our understanding of the role of biology in personality recently has been dramatically increased through the use of molecular genetics, which is the study of which genes are associated with which personality traits (Goldsmith et al., 2003; Strachan & Read, 1999). These advances have occurred as a result of new knowledge about the structure of human DNA made possible through the Human Genome Project and related work that has identified the genes in the human body (Human Genome Project, 2010). Molecular genetics researchers have also developed new techniques that allow them to find the locations of genes within chromosomes and to identify the effects those genes have when activated or deactivated.

Figure 4.18 Laboratory Mice. These “knockout” mice are participating in studies in which some of their genes have been deactivated to determine the influence of the genes on behaviour.

One approach that can be used in animals, usually in laboratory mice, is the knockout study (as shown in Figure 4.18, “Laboratory Mice”). In this approach the researchers use specialized techniques to remove or modify the influence of a gene in a line of knockout mice (Crusio, Goldowitz, Holmes, & Wolfer, 2009). The researchers harvest embryonic stem cells from mouse embryos and then modify the DNA of the cells. The DNA is created so that the action of certain genes will be eliminated or knocked out. The cells are then injected into the embryos of other mice that are implanted into the uteruses of living female mice. When these animals are born, they are studied to see whether their behaviour differs from a control group of normal animals. Research has found that removing or changing genes in mice can affect their anxiety, aggression, learning, and socialization patterns.

In humans, a molecular genetics study normally begins with the collection of a DNA sample from the participants in the study, usually by taking some cells from the inner surface of the cheek. In the lab, the DNA is extracted from the sampled cells and is combined with a solution containing a marker for the particular genes of interest as well as a fluorescent dye. If the gene is present in the DNA of the individual, then the solution will bind to that gene and activate the dye. The more the gene is expressed, the stronger the reaction.

In one common approach, DNA is collected from people who have a particular personality characteristic and also from people who do not. The DNA of the two groups is compared to see which genes differ between them. These studies are now able to compare thousands of genes at the same time. Research using molecular genetics has found genes associated with a variety of personality traits including novelty-seeking (Ekelund, Lichtermann, Järvelin, & Peltonen, 1999), attention-deficit/hyperactivity disorder (Waldman & Gizer, 2006), and smoking behaviour (Thorgeirsson et al., 2008).

Reviewing the Literature: Is Our Genetics Our Destiny?

Over the past two decades scientists have made substantial progress in understanding the important role of genetics in behaviour. Behavioural genetics studies have found that, for most traits, genetics is more important than parental influence. And molecular genetics studies have begun to pinpoint the particular genes that are causing these differences. The results of these studies might lead you to believe that your destiny is determined by your genes, but this would be a mistaken assumption.

For one, the results of all research must be interpreted carefully. Over time we will learn even more about the role of genetics, and our conclusions about its influence will likely change. Current research in the area of behavioural genetics is often criticized for making assumptions about how researchers categorize identical and fraternal twins, about whether twins are in fact treated in the same way by their parents, about whether twins are representative of children more generally, and about many other issues. Although these critiques may not change the overall conclusions, it must be kept in mind that these findings are relatively new and will certainly be updated with time (Plomin, 2000).

Furthermore, it is important to reiterate that although genetics is important, and although we are learning more every day about its role in many personality variables, genetics does not determine everything. In fact, the major influence on personality is nonshared environmental influences, which include all the things that occur to us that make us unique individuals. These differences include variability in brain structure, nutrition, education, upbringing, and even interactions among the genes themselves.

The genetic differences that exist at birth may be either amplified or diminished over time through environmental factors. The brains and bodies of identical twins are not exactly the same, and they become even more different as they grow up. As a result, even genetically identical twins have distinct personalities, resulting in large part from environmental effects.

Because these nonshared environmental differences are nonsystematic and largely accidental or random, it will be difficult to ever determine exactly what will happen to a child as he or she grows up. Although we do inherit our genes, we do not inherit personality in any fixed sense. The effect of our genes on our behaviour is entirely dependent on the context of our life as it unfolds day to day. Based on your genes, no one can say what kind of human being you will turn out to be or what you will do in life.


Key Takeaways

  • Genes are the basic biological units that transmit characteristics from one generation to the next.
  • Personality is not determined by any single gene, but rather by the actions of many genes working together.
  • Behavioural genetics refers to a variety of research techniques that scientists use to learn about the genetic and environmental influences on human behaviour.
  • Behavioural genetics is based on the results of family studies, twin studies, and adoptive studies.
  • Overall, genetics has more influence than parents do on shaping our personality.
  • Molecular genetics is the study of which genes are associated with which personality traits.
  • The largely unknown environmental influences, known as the nonshared environmental effects, have the largest impact on personality. Because these differences are nonsystematic and largely accidental or random, we do not inherit our personality in any fixed sense.

Exercises and Critical Thinking

  1. Think about the twins you know. Do they seem to be very similar to each other, or does it seem that their differences outweigh their similarities?
  2. Describe the implications of the effects of genetics on personality, overall. What does it mean to say that genetics “determines” or “does not determine” our personality?

Image Attributions

Figure 4.18:Laboratory mice” by Aaron Logan is licensed under CC BY 1.0 license (


Baker, C. (2004). Behavioral genetics: An introduction to how genes and environments interact through development to shape differences in mood, personality, and intelligence. [PDF] Retrieved from

Bouchard, T. J., Lykken, D. T., McGue, M., Segal, N. L., & Tellegen, A. (1990). Sources of human psychological differences: The Minnesota study of twins reared apartScience, 250(4978), 223–228. Retrieved from

Crusio, W. E., Goldowitz, D., Holmes, A., & Wolfer, D. (2009). Standards for the publication of mouse mutant studies. Genes, Brain & Behavior, 8(1), 1–4.

Ekelund, J., Lichtermann, D., Järvelin, M. R., & Peltonen, L. (1999). Association between novelty seeking and the type 4 dopamine receptor gene in a large Finnish cohort sample. American Journal of Psychiatry, 156, 1453–1455.

Goldsmith, H., Gernsbacher, M. A., Crabbe, J., Dawson, G., Gottesman, I. I., Hewitt, J.,…Swanson, J. (2003). Research psychologists’ roles in the genetic revolution. American Psychologist, 58(4), 318–319.

Harris, J. R. (2006). No two alike: Human nature and human individuality. New York, NY: Norton.

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Långström, N., Rahman, Q., Carlström, E., & Lichtenstein, P. (2010). Genetic and environmental effects on same-sex sexual behaviour: A population study of twins in Sweden. Archives of Sexual Behaviour, 39(1), 75-80.

Loehlin, J. C. (1992). Genes and environment in personality development. Thousand Oaks, CA: Sage Publications, Inc.

McGue, M., & Lykken, D. T. (1992). Genetic influence on risk of divorce. Psychological Science, 3(6), 368–373.

Plomin, R. (2000). Behavioural genetics in the 21st century. International Journal of Behavioral Development, 24(1), 30–34.

Plomin, R., Fulker, D. W., Corley, R., & DeFries, J. C. (1997). Nature, nurture, and cognitive development from 1 to 16 years: A parent-offspring adoption study. Psychological Science, 8(6), 442–447.

Roberts, B. W., & DelVecchio, W. F. (2000). The rank-order consistency of personality traits from childhood to old age: A quantitative review of longitudinal studies. Psychological Bulletin, 126(1), 3–25.

Strachan, T., & Read, A. P. (1999). Human molecular genetics (2nd ed.). Retrieved from

Tellegen, A., Lykken, D. T., Bouchard, T. J., Wilcox, K. J., Segal, N. L., & Rich, S. (1988). Personality similarity in twins reared apart and together. Journal of Personality and Social Psychology, 54(6), 1031–1039.

Thorgeirsson, T. E., Geller, F., Sulem, P., Rafnar, T., Wiste, A., Magnusson, K. P.,…Stefansson, K. (2008). A variant associated with nicotine dependence, lung cancer and peripheral arterial disease. Nature, 452(7187), 638–641.

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Chapter 4 Summary, Key Terms, and Self-Test

Lee Sanders


The biological perspective emphasizes bodily events and changes associated with behaviour. Biological psychology emerged from scientific and philosophical traditions of the 18th and 19th centuries, including the ideas of William James (1890), who argued that psychological science should be grounded in biology.

Biological psychology applies the principles of biology to the study of mental processes and behaviour. Psychologists in this framework study human behaviours that are both different and alike.

Genetic and evolutionary approaches inform the nature versus nurture debate and seek to determine the origins of behavioural traits as being either biological or due to environment. Both frameworks contribute to the question, ‘why do we behave the way we do?”

The genetic influence on behavior is a relatively recent discovery. Behavioural genetics is an interdisciplinary field concerned with how genes and the environment influence individual behaviour and traits including brain function.

Human genetic code is unique and sets us apart from other species, but the focus of this field is on the genetic bases of individual difference in how we think and act.

Our code involves genes, located on chromosomes, which are the rod-shaped structures found in the centre or ‘nucleus’ of every cell of the body. This genetic material is composed of thread-like strands of deoxyribonucleic acid or ‘DNA’.  DNA refers to the chromosomal molecule that transfers genetic characteristics by way of coded instructions.

Cells that develop from the union of sperm and ova (egg) will produce a karyotype of 46 chromosomes arranged in 23 pairs that an individual will inherit at conception. 22 of the pairs are autosomal chromosomes and one pair consists of two sex chromosomes.

DNA contains the four nucleotides adenine, cytosine, guanine, and thymine. Each coded gene is a unique combination of the four nucleotides, abbreviated using the first letter of each (A, C, G, T).

Gene sequences are responsible for guiding the process that creates the structure of proteins. Genes provide the instructions to make the proteins that we need to carry out life functions. Proteins make up our physical structures and regulate development and physiological process throughout the lifespan.

Some genes contribute directly to the development of individual traits while others are inherited in the same way for all humans. Offspring will inherit a combination of dominant and recessive alleles, the variations of a given gene, from their parents. The variation is sometimes observable as in the case of the interaction and variation of the genes involved in eye color.

The sum of this inherited information is called genotype. Genotype represent the unique set of genes that comprise an individual’s unique code. Heredity also results in phenotype, which refers to the inherited physical traits and behavioural characteristics that show genetic variation in attributes like eye colour, height, and body weight, and personality and intelligence as well. Error in copying the original DNA sequence during division of sperm and egg cells are referred to as mutations that result from environmental hazards, toxins, and radiation.

Heredity and environment are constantly interacting to influence our psychological and physical traits. Genes affect the kind of experiences we have but experience also affects our genes.

Epigenetics is the study of heritable changes in gene expression that does not involve changes to the underlying DNA sequence. Epigenetic research seeks to understand the influence of genes on our behaviour and mental processes, and how the environment affects our genes, and influences their expression through biological mechanisms that switch them on and off. Epigenetics research also helps us to understand that the influence of nature and nurture on behaviour is more than an either-or equation.

While our genetic code is found in the nucleus of most of the cells in our body, cells also contain noncoding DNA that contributes indirectly to a trait by switching certain genes on or off over the course of a lifetime. Genes also contain information about environmental factors that influence whether a gene is ‘expressed’ or stays inactive. Whether a gene is expressed or not depends on heredity and environment.

Behavioural genomics is a complementary interdisciplinary field in the study of DNA, inherited traits, and the ways in which specific genes are related to behaviour. This perspective involves a shift in focus away from the influence of specific individual genes to genome, which refers to an organism’s complete set of genes in each cell with the exceptions of sperm and egg cells.

Genetics research involves looking at markers across complete sets of DNA or genome, in the cells of many people to identify genetic variations associated with a disease or disorder.

Behavioural genomics research questions the role of genomes, genetics, heritability, and environmental factors as main contributors to behaviour. Research in this framework addresses the differences between genotypes of groups of people in order to determine and better understand the relevance of genome to health conditions in the population.

Researchers examine the influence of genomes on behaviour to understand the heritability of traits, and which genomes cause certain conditions. The technology behind the Human Genome Project has opened doors for research on complex diseases and behaviours affecting human populations including mental illness

Researchers are also interested in the interaction of multiple genes and numerous environmental factors that influence human behaviour. The Human Genome Project, for example, involves classifying the sequences of billions of nucleotides (ACGT) making up the genes. Between 20,000 to 25,000 genes have been identified in scientific research so far.

Behavioural genetics researchers use the methods of twin and adoption studies to calculate heritability, which is a measure of variability of behavioural traits among individuals that can be accounted for by genetic factors. Variability in IQ scores, for example, can be denoted by a heritability coefficient, which is a statistic expressed as a number between zero and one that represents the degree to which genetic differences between individuals contribute to individual differences in a behaviour or trait found in a population. This method is used to compare people of different levels of relatedness and measure any similarities or resemblance for a specific trait of interest.

Behavioural genomics research also involves twin studies to identify specific genes than can be linked to behavioural phenotypes.

Linkage mapping is also used to indicate the order of genes on a chromosome in behavioural genetics research.

The Candidate Gene approach involves assessing the impact of genes on inherited disorders by comparing the genome of people who express a trait or behaviour with those who do not.

Whole-genome association like the Human Genome and HapMap studies are undertaken with the goal of better detection, treatment, and prevention of physical and mental disease.

While behavioural genetics and genomics perspectives focus on the roles of genes, heredity, and environment in explaining individual differences in behaviour, researchers in evolutionary psychology concentrate on the evolutionary mechanisms that might explain the commonalities that aid in our survival and reproductive success, including human cognition, development, emotion, and social practices.

The focus of the evolutionary perspective is on the genetic dispositions that shape our similarities relating to survival and reproductive success. It is an approach that interprets and explains modern human behaviour in terms of forces acting upon our distant ancestors.

Evolutionary psychology is a field of psychology that emphasizes the evolutionary mechanisms at work in the commonalities of human behaviour including cognition, emotion, development, and social practice.

An evolutionary approach aims to interpret and explain modern human behaviour in terms of how our brains and behaviours have been shaped by the physical and social environment encountered by our ancestors, and the forces that acted upon them.

Genes hold messages about the past and our shared evolutionary heritage. While researchers in the perspectives of behavioural genetics and genomics search for the influence of genetics on human differences, evolutionary psychologists look for the genetic bases of our similarities.

The theories of Charles Darwin have a profound influence on evolutionary psychology. Natural selection and sexual selection are theories developed through his observations of the fitness of a species’ characteristics to its environment.

Natural selection refers to the ability for a species to adapt to its environment, find food and water, and mate in order to stay alive long enough to reproduce and pass on genetic traits favorable to that setting. When this pattern continues, more offspring are born with adaptive traits that are ‘selected’ by reproductive success and spread throughout the species.  In this theory, Darwin proposed that nature determines the fate of genes in terms of which genes survive and reproduce. Species without adaptive traits are more likely to die before being able to reproduce and if this pattern continues, the species will eventually disappear.

Gene selection theory is a modern theory of evolution by selection, that suggests differential gene replication is the defining process of evolutionary change. Evolution through natural selection requires a trait to be heritable, and individuals within the breeding population must have a reproductive advantage for having the trait. If there is an environmental pressure – a change in climate or shortage of food for example – a certain trait may be better suited to survival and this will produce an increase in that trait within a population.

Darwin’s theories can be applied to human behavior as well. All modern species are versions of the species that were the ‘fittest’ for their specific time and environment. Humans have several innate physical adaptations or traits that we are either born with or develop quickly thanks to the evolution of our species that enhance the chance of our survival. We have the physical ability to respond to temperature including sweat glands and shivering mechanisms. We crave foods rich in vitamins, fats, and sugars. We have a fear response to snakes, spiders, darkness, heights, and strangers.

Humans also have a ‘thinking’ capacity to solve inevitable problems with creative solutions regarding our survival and reproduction. The human brain contains specialized adaptations for performing certain cognitive and behavioural functions including perception.

What makes Homo sapiens stand out in evolutionary history is our roomy prefrontal cortex. This extra space enabled the development of more brain cells, which led to higher cognitive functions including logic and intelligence. The ability to calculate and ‘think’ our way out of challenging situations helped our ancestors overcome environmental problems.

Evolutionary useful behaviors have had a beneficial function in the cognitive development of our species. The brain, for example, has a set of cognitive adaptations for solving problems related to survival and reproductive fitness. A guiding assumption among many evolutionary psychologists is that the human mind developed as a collection of mental modules to help handle specific survival problems.

Error management theory (EMT) is a theory that deals with the evolution of how we think and evaluate certain situations to minimize costly mistakes that can cause death or damage, and impact on our survival and the ability to reproduce. We psychologically adapt to make choices that minimize a ‘cost’ in judgement, or error. Visual descent illusion, auditory looming bias, and sexual overperception bias are all examples of psychological adaptations in this regard.

All modern species are versions of the species that were the ‘fittest’ for their specific time and environment. Humans have several innate traits that we are either born with or develop quickly thanks to the evolution of our species. We pass physical and behavioural traits from one generation to the next through sexual reproduction.  The ability to anticipate and solve problems helped our ancestors overcome food shortages and other environmental problems. Individuals with these advantageous traits are more likely to survive and reproduce offspring with similar genes.

Humans also have adaptations for reproduction as proposed in Darwin’s sexual selection theory. Sexual selection theory attempts to explain the fate of genes by suggesting that certain traits evolve to help some individuals increase their chances of mating and passing on their genes. Members of the same sex will compete for access to the other sex in a process called intrasexual selection.

Intersexual selection refers to the influence of physical factors signalling reproductive health and fitness, including a preference for youthful and beautiful females for males, and a preference for tall and muscular males by females.

Cultural factors are also important influences for female preferences including love, kindness, and social security.

Evolutionary research on attraction also highlights the importance of facial symmetry as an indicator of reproductive health in mate selection and reproduction.

Members of the same sex will compete for access to the other sex in a process called intrasexual selection.

Sexual strategies theory is a comprehensive evolutionary theory of human mating that defines the menu of mating strategies humans pursue, the adaptive problems women and men face when pursuing these strategies, and the evolved solutions to these mating problems.

Sexual overperception bias is a mating theory that suggests that males often misread sexual interest from women to prevent the costs of missing out on an opportunity for reproduction.

Evolutionary research on attraction highlights the importance of facial symmetry to mate selection and reproduction. Humans are genetically programmed to have, and to recognize symmetrical features. There is no sex difference in mate selection behaviour in this context.

An evolutionary psychologist would suggest that an individual with a symmetrical face is more likely to be fertile and in possession of good genes. Symmetry signals health to a potential mate, however, sometimes disease or environmental factors slightly alter facial symmetry.

Sociobiology contends that evolution has given us a genetic tendency to act in ways that maximize our chances of passing on our genes onto the next generations. Psychological traits are thought to be ‘selected’ to aid individuals in propagating their genes. Male and female problem-solving skills sometimes differ because of different survival issues. Physical characteristics often play a role in initial attraction and influence our desire to approach. For example, humans show a preference for body symmetry in mate selection. Sex role socialization appears to be another factor in mate selection in American samples.

One notable field is the study of sex differences in cognitive abilities examined in the framework of hunter-gatherer theory. Hunter-gatherer theory illustrates sex differences and suggests that our labour was divided based on sex as a means of survival.  This theory suggests that males hunted, and females gathered because of physical and behavioural skills that are reproductively fit to this environment. Also, that the competencies selected for during the process of human evolution are still present today, including cognitive abilities and tasks with varying results.

The hunter-gather theory of human spatial sex differences starts from the premise that most of our time on earth has been spent living on the lands of the African savannah. In this environment, our labour was divided based on sex. Because of their size and strength, males took on the role of hunter and tracker of animals, and females remained closer to the home to care for children and gather plants and medicines rich in the vitamins needed for health.

Sex roles required individuals to use certain behavioural skills or ‘competencies’ needed to thrive and survive in their environment). Males required stamina and good wayfaring, orienteering, and spatial skills to be able to travel great distances without getting lost, as well as good coordination for throwing weapons used in the hunt. Females had to have good memory for the location and variety of edible plants. The theory further suggests that males with good spatial skills and females with good location memory would have been more successful or ‘fit’ to this environment, than males and females without these skills.

Biopsychosocial theory takes a complex approach to understanding human behaviour. Aspects of biology (genes), psychological components (thoughts, personality, mood), and social conditions (family support, stress, culture) are all considered in analyses of why we do what we do from this perspective. Research on specialized adaptation also relates to how the brain processes attraction.  Cross-cultural studies have found “universals” in feelings of attraction.

Research in the evolutionary perspective also applies the principles of biology to the study of human behaviour. Evolutionary psychologists start from the position that cognitive structures are designed by natural selection to serve survival and reproduction. From this perspective, hearing, smell, vision, pain, and motor control are examined as functions of the nervous system that have been involved in survival and reproduction for thousands of generations and years.

Key Terms

  • Adaptations
  • Adoption study
  • Behavioral genetics
  • Chromosomes
  • DNA methylation
  • DNA Methyltransferases (DNMTs)
  • Error Management Theory (EMT)
  • Epigenetics
  • Epigenome
  • Evolution
  • Family study
  • Gene
  • Gene Selection Theory
  • Genotype
  • Heritability
  • Heritability Coefficient
  • Histone Acetyltransferases (HATs) and Histone Deacetylases (HDACs)
  • Histone modifications
  • Identical twins
  • Instincts
  • Intrasexual competition
  • Intersexual selection
  • Knocked out
  • Molecular genetics
  • Natural selection
  • Nonshared environment
  • Phenotype
  • Physiological adaptations
  • Psychological adaptations
  • Sexual selection
  • Shared environment
  • Twin studies
  • Quantitative genetics


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Chapter 5. Brains, Bodies, and Behaviour


Chapter 5 Introduction

Charles Stangor and Jennifer Walinga

Did a Neurological Disorder Cause a Musician to Compose Boléro and an Artist to Paint It 66 Years Later?

In 1986, Anne Adams was working as a cell biologist at the University of Toronto in Ontario, Canada. She took a leave of absence from her work to care for a sick child, and while she was away, she completely changed her interests, dropping biology entirely and turning her attention to art. In 1994 she completed her painting Unravelling Boléro, a translation of Maurice Ravel’s famous orchestral piece onto canvas. As you can see on the New Scientist website (, this artwork is filled with themes of repetition. Each bar of music is represented by a lacy vertical figure, with the height representing volume, the shape representing note quality, and the colour representing the music’s pitch. Like Ravel’s music (see the video below), which is a hypnotic piece consisting of two melodial themes repeated eight times over 340 musical bars, the theme in the painting repeats and builds, leading to a dramatic change in colour from blue to orange and pink, a representation of Boléro’s sudden and dramatic climax.


An interactive or media element has been excluded from this version of the text. You can view it online here:

Video: Maurice Ravel’s composition Boléro (1928) []. This is a video clip of Maurice Ravel’s Boléro, composed in 1928 during the early phase of his illness.

Shortly after finishing the painting, Adams began to experience behavioural problems, including increased difficulty speaking. Neuroimages of Adams’s brain taken during this time show that regions in the front part of her brain, which are normally associated with language processing, had begun to deteriorate, while at the same time, regions of the brain responsible for the integration of information from the five senses were unusually well developed (Seeley et al., 2008). The deterioration of the frontal cortex is a symptom of frontotemporal dementia, a disease that is associated with changes in artistic and musical tastes and skills (Miller, Boone, Cummings, Read, & Mishkin, 2000), as well as with an increase in repetitive behaviours (Aldhous, 2008).

What Adams did not know at the time was that her brain may have been undergoing the same changes that Ravel’s had undergone 66 years earlier. In fact, it appears that Ravel may have suffered from the same neurological disorder. Ravel composed Boléro at age 53, when he himself was beginning to show behavioural symptoms that were interfering with his ability to move and speak. Scientists have concluded, based on an analysis of his written notes and letters, that Ravel was also experiencing the effects of frontotemporal dementia (Amaducci, Grassi, & Boller, 2002). If Adams and Ravel were both affected by the same disease, this could explain why they both became fascinated with the repetitive aspects of their arts, and it would present a remarkable example of the influence of our brains on behaviour.

Every behaviour begins with biology. Our behaviours, as well as our thoughts and feelings, are produced by the actions of our brains, nerves, muscles, and glands. In this chapter we will begin our journey into the world of psychology by considering the biological makeup of the human being, including the most remarkable of human organs—the brain. We’ll consider the structure of the brain and also the methods that psychologists use to study the brain and to understand how it works.

We will see that the body is controlled by an information highway known as the nervous system, a collection of hundreds of billions of specialized and interconnected cells through which messages are sent between the brain and the rest of the body. The nervous system consists of the central nervous system (CNS), made up of the brain and the spinal cord, and the peripheral nervous system (PNS), the neurons that link the CNS to our skin, muscles, and glands. And we will see that our behaviour is also influenced in large part by the endocrine system, the chemical regulator of the body that consists of glands that secrete hormones.

Although this chapter begins at a very low level of explanation, and although the topic of study may seem at first to be far from the everyday behaviours that we all engage in, a full understanding of the biology underlying psychological processes is an important cornerstone of your new understanding of psychology. We will consider throughout the chapter how our biology influences important human behaviours, including our mental and physical health, our reactions to drugs, as well as our aggressive responses and our perceptions of other people. This chapter is particularly important for contemporary psychology because the ability to measure biological aspects of behaviour, including the structure and function of the human brain, is progressing rapidly, and understanding the biological foundations of behaviour is an increasingly important line of psychological study.


Aldhous, P. (2008, April 7). “Boléro”: Beautiful symptom of a terrible disease. New Scientist. Retrieved from

Amaducci, L., Grassi, E., & Boller, F. (2002). Maurice Ravel and right-hemisphere musical creativity: Influence of disease on his last musical works? European Journal of Neurology, 9(1), 75–82.

Miller, B. L., Boone, K., Cummings, J. L., Read, S. L., & Mishkin, F. (2000). Functional correlates of musical and visual ability in frontotemporal dementia. British Journal of Psychiatry, 176, 458–463.

Seeley, W. W., Matthews, B. R., Crawford, R. K., Gorno-Tempini, M. L., Foti, D., Mackenzie, I. R., & Miller, B. L. (2008). “Unravelling Boléro”: Progressive aphasia, transmodal creativity, and the right posterior neocortex. Brain, 131(1), 39–49.


5.1 The Neuron Is the Building Block of the Nervous System

Charles Stangor and Jennifer Walinga

Learning Objectives

  1. Describe the structure and functions of the neuron.
  2. Draw a diagram of the pathways of communication within and between neurons.
  3. List three of the major neurotransmitters and describe their functions.

The nervous system is composed of more than 100 billion cells known as neurons. A neuron is a cell in the nervous system whose function it is to receive and transmit information. As you can see in Figure 5.1, “Components of the Neuron,” neurons are made up of three major parts: a cell body, or soma, which contains the nucleus of the cell and keeps the cell alive; a branching treelike fibre known as the dendrite, which collects information from other cells and sends the information to the soma; and a long, segmented fibre known as the axon, which transmits information away from the cell body toward other neurons or to the muscles and glands. Figure 5.2 shows a photograph of neurons taken using confocal microscopy.

Figure 5.1 Components of the Neuron.
Figure 5.2 The nervous system, including the brain, is made up of billions of interlinked neurons. This vast interconnected web is responsible for all human thinking, feeling, and behaviour.

Some neurons have hundreds or even thousands of dendrites, and these dendrites may themselves be branched to allow the cell to receive information from thousands of other cells. The axons are also specialized, and some, such as those that send messages from the spinal cord to the muscles in the hands or feet, may be very long — even up to several feet in length. To improve the speed of their communication, and to keep their electrical charges from shorting out with other neurons, axons are often surrounded by a myelin sheath. The myelin sheath is a layer of fatty tissue surrounding the axon of a neuron that both acts as an insulator and allows faster transmission of the electrical signal. Axons branch out toward their ends, and at the tip of each branch is a terminal button.

Neurons Communicate Using Electricity and Chemicals

The nervous system operates using an electrochemical process. An electrical charge moves through the neuron itself, and chemicals are used to transmit information between neurons. Within the neuron, when a signal is received by the dendrites, it is transmitted to the soma in the form of an electrical signal, and, if the signal is strong enough, it may then be passed on to the axon and then to the terminal buttons. If the signal reaches the terminal buttons, they are signalled to emit chemicals known as neurotransmitters, which communicate with other neurons across the spaces between the cells, known as synapses.


An interactive or media element has been excluded from this version of the text. You can view it online here:

Video: The Electrochemical Action of the Neuron []. This video clip shows a model of the electrochemical action of the neuron and neurotransmitters.

The electrical signal moves through the neuron as a result of changes in the electrical charge of the axon. Normally, the axon remains in the resting potential, a state in which the interior of the neuron contains a greater number of negatively charged ions than does the area outside the cell. When the segment of the axon that is closest to the cell body is stimulated by an electrical signal from the dendrites, and if this electrical signal is strong enough that it passes a certain level or threshold, the cell membrane in this first segment opens its gates, allowing positively charged sodium ions that were previously kept out to enter. This change in electrical charge that occurs in a neuron when a nerve impulse is transmitted is known as the action potential. Once the action potential occurs, the number of positive ions exceeds the number of negative ions in this segment, and the segment temporarily becomes positively charged.

As you can see in Figure 5.3, “The Myelin Sheath and the Nodes of Ranvier,” the axon is segmented by a series of breaks between the sausage-like segments of the myelin sheath. Each of these gaps is a node of Ranvier.The break in the myelin sheath of a nerve fibre. The electrical charge moves down the axon from segment to segment, in a set of small jumps, moving from node to node. When the action potential occurs in the first segment of the axon, it quickly creates a similar change in the next segment, which then stimulates the next segment, and so forth as the positive electrical impulse continues all the way down to the end of the axon. As each new segment becomes positive, the membrane in the prior segment closes up again, and the segment returns to its negative resting potential. In this way the action potential is transmitted along the axon, toward the terminal buttons. The entire response along the length of the axon is very fast — it can happen up to 1,000 times each second.

Figure 5.3 The Myelin Sheath and the Nodes of Ranvier. The myelin sheath wraps around the axon but also leaves small gaps called the nodes of Ranvier. The action potential jumps from node to node as it travels down the axon.

An important aspect of the action potential is that it operates in an all or nothing manner. What this means is that the neuron either fires completely, such that the action potential moves all the way down the axon, or it does not fire at all. Thus neurons can provide more energy to the neurons down the line by firing faster but not by firing more strongly. Furthermore, the neuron is prevented from repeated firing by the presence of a refractory period a brief time after the firing of the axon in which the axon cannot fire again because the neuron has not yet returned to its resting potential.

Neurotransmitters: The Body’s Chemical Messengers

Not only do the neural signals travel via electrical charges within the neuron, but they also travel via chemical transmission between the neurons. Neurons are separated by junction areas known as synapses,The small gap between neurons across which nerve impulses are transmitted. areas where the terminal buttons at the end of the axon of one neuron nearly, but don’t quite, touch the dendrites of another. The synapses provide a remarkable function because they allow each axon to communicate with many dendrites in neighbouring cells. Because a neuron may have synaptic connections with thousands of other neurons, the communication links among the neurons in the nervous system allow for a highly sophisticated communication system.

When the electrical impulse from the action potential reaches the end of the axon, it signals the terminal buttons to release neurotransmitters into the synapse. A neurotransmitter is a chemical that relays signals across the synapses between neurons. Neurotransmitters travel across the synaptic space between the terminal button of one neuron and the dendrites of other neurons, where they bind to the dendrites in the neighbouring neurons. Furthermore, different terminal buttons release different neurotransmitters, and different dendrites are particularly sensitive to different neurotransmitters. The dendrites will admit the neurotransmitters only if they are the right shape to fit in the receptor sites on the receiving neuron. For this reason, the receptor sites and neurotransmitters are often compared to a lock and key (Figure 5.4, “The Synapse”).

Figure 5.4 The Synapse. When the nerve impulse reaches the terminal button, it triggers the release of neurotransmitters into the synapse. The neurotransmitters fit into receptors on the receiving dendrites in the manner of a lock and key.

When neurotransmitters are accepted by the receptors on the receiving neurons, their effect may be either excitatory (i.e., they make the cell more likely to fire) or inhibitory (i.e., they make the cell less likely to fire). Furthermore, if the receiving neuron is able to accept more than one neurotransmitter, it will be influenced by the excitatory and inhibitory processes of each. If the excitatory effects of the neurotransmitters are greater than the inhibitory influences of the neurotransmitters, the neuron moves closer to its firing threshold; if it reaches the threshold, the action potential and the process of transferring information through the neuron begins.

Neurotransmitters that are not accepted by the receptor sites must be removed from the synapse in order for the next potential stimulation of the neuron to happen. This process occurs in part through the breaking down of the neurotransmitters by enzymes, and in part through reuptake, a process in which neurotransmitters that are in the synapse are reabsorbed into the transmitting terminal buttons, ready to again be released after the neuron fires.

More than 100 chemical substances produced in the body have been identified as neurotransmitters, and these substances have a wide and profound effect on emotion, cognition, and behaviour. Neurotransmitters regulate our appetite, our memory, our emotions, as well as our muscle action and movement. And as you can see in Table 5.1, “The Major Neurotransmitters and Their Functions,” some neurotransmitters are also associated with psychological and physical diseases.

Drugs that we might ingest — either for medical reasons or recreationally — can act like neurotransmitters to influence our thoughts, feelings, and behaviour. An agonist is a drug that has chemical properties similar to a particular neurotransmitter and thus mimics the effects of the neurotransmitter. When an agonist is ingested, it binds to the receptor sites in the dendrites to excite the neuron, acting as if more of the neurotransmitter had been present. As an example, cocaine is an agonist for the neurotransmitter dopamine. Because dopamine produces feelings of pleasure when it is released by neurons, cocaine creates similar feelings when it is ingested. An antagonist is a drug that reduces or stops the normal effects of a neurotransmitter. When an antagonist is ingested, it binds to the receptor sites in the dendrite, thereby blocking the neurotransmitter. As an example, the poison curare is an antagonist for the neurotransmitter acetylcholine. When the poison enters the brain, it binds to the dendrites, stops communication among the neurons, and usually causes death. Still other drugs work by blocking the reuptake of the neurotransmitter itself — when reuptake is reduced by the drug, more neurotransmitter remains in the synapse, increasing its action.

Table 5.1 The Major Neurotransmitters and Their Functions
Neurotransmitter Description and function Notes
Acetylcholine (ACh) A common neurotransmitter used in the spinal cord and motor neurons to stimulate muscle contractions. It’s also used in the brain to regulate memory, sleeping, and dreaming. Alzheimer’s disease is associated with an undersupply of acetylcholine. Nicotine is an agonist that acts like acetylcholine.
Dopamine Involved in movement, motivation, and emotion, Dopamine produces feelings of pleasure when released by the brain’s reward system, and it’s also involved in learning. Schizophrenia is linked to increases in dopamine, whereas Parkinson’s disease is linked to reductions in dopamine (and dopamine agonists may be used to treat it).
Endorphins Released in response to behaviours such as vigorous exercise, orgasm, and eating spicy foods. Endorphins are natural pain relievers. They are related to the compounds found in drugs such as opium, morphine, and heroin. The release of endorphins creates the runner’s high that is experienced after intense physical exertion.
GABA (gamma-aminobutyric acid) The major inhibitory neurotransmitter in the brain. A lack of GABA can lead to involuntary motor actions, including tremors and seizures. Alcohol stimulates the release of GABA, which inhibits the nervous system and makes us feel drunk. Low levels of GABA can produce anxiety, and GABA agonists (tranquilizers) are used to reduce anxiety.
Glutamate The most common neurotransmitter, it’s released in more than 90% of the brain’s synapses. Glutamate is found in the food additive MSG (monosodium glutamate). Excess glutamate can cause overstimulation, migraines, and seizures.
Serotonin Involved in many functions, including mood, appetite, sleep, and aggression. Low levels of serotonin are associated with depression, and some drugs designed to treat depression (known as selective serotonin reuptake inhibitors, or SSRIs) serve to prevent their reuptake.


Key Takeaways

  • The central nervous system (CNS) is the collection of neurons that make up the brain and the spinal cord.
  • The peripheral nervous system (PNS) is the collection of neurons that link the CNS to our skin, muscles, and glands.
  • Neurons are specialized cells, found in the nervous system, which transmit information. Neurons contain a dendrite, a soma, and an axon.
  • Some axons are covered with a fatty substance known as the myelin sheath, which surrounds the axon, acting as an insulator and allowing faster transmission of the electrical signal.
  • The dendrite is a treelike extension that receives information from other neurons and transmits electrical stimulation to the soma.
  • The axon is an elongated fibre that transfers information from the soma to the terminal buttons.
  • Neurotransmitters relay information chemically from the terminal buttons and across the synapses to the receiving dendrites using a lock and key type of system.
  • The many different neurotransmitters work together to influence cognition, memory, and behaviour.
  • Agonists are drugs that mimic the actions of neurotransmitters, whereas antagonists are drugs that block the actions of neurotransmitters.

Exercises and Critical Thinking

  1. Draw a picture of a neuron and label its main parts.
  2. Imagine an action that you engage in every day and explain how neurons and neurotransmitters might work together to help you engage in that action.

Image Attributions

Figure 5.2:Confocal microscopy of mouse brain, cortex” by ZEISS Microscopy ( used under CC BY-NC-ND 2.0  ( license.


5.2 Our Brains Control Our Thoughts, Feelings, and Behaviour

Charles Stangor and Jennifer Walinga

Learning Objectives

  1. Describe the structures and function of the “old brain” and its influence on behaviour.
  2. Explain the structure of the cerebral cortex (its hemispheres and lobes) and the function of each area of the cortex.
  3. Define the concepts of brain plasticity, neurogenesis, and brain lateralization.

If you were someone who understood brain anatomy and were to look at the brain of an animal that you had never seen before, you would nevertheless be able to deduce the likely capacities of the animal. This is because the brains of all animals are very similar in overall form. In each animal the brain is layered, and the basic structures of the brain are similar (see Figure 5.5, “The Major Structures in the Human Brain”). The innermost structures of the brain — the parts nearest the spinal cord — are the oldest part of the brain, and these areas carry out the same functions they did for our distant ancestors. The “old brain” regulates basic survival functions, such as breathing, moving, resting, and feeding, and creates our experiences of emotion. Mammals, including humans, have developed further brain layers that provide more advanced functions — for instance, better memory, more sophisticated social interactions, and the ability to experience emotions. Humans have a very large and highly developed outer layer known as the cerebral cortex (see Figure 5.6, “Cerebral Cortex”), which makes us particularly adept at these processes.

The many lobes and parts of the brain.
Figure 5.5 The Major Structures in the Human Brain.
Figure 5.6 Cerebral Cortex. Humans have a very large and highly developed outer brain layer known as the cerebral cortex. The cortex provides humans with excellent memory, outstanding cognitive skills, and the ability to experience complex emotions.

The Old Brain: Wired for Survival

The brain stem is the oldest and innermost region of the brain. It’s designed to control the most basic functions of life, including breathing, attention, and motor responses (Figure 5.7, “The Brain Stem and the Thalamus”). The brain stem begins where the spinal cord enters the skull and forms the medulla, the area of the brain stem that controls heart rate and breathing. In many cases the medulla alone is sufficient to maintain life — animals that have the remainder of their brains above the medulla severed are still able to eat, breathe, and even move. The spherical shape above the medulla is the pons, a structure in the brain stem that helps control the movements of the body, playing a particularly important role in balance and walking.

Running through the medulla and the pons is a long, narrow network of neurons known as the reticular formation. The job of the reticular formation is to filter out some of the stimuli that are coming into the brain from the spinal cord and to relay the remainder of the signals to other areas of the brain. The reticular formation also plays important roles in walking, eating, sexual activity, and sleeping. When electrical stimulation is applied to the reticular formation of an animal, it immediately becomes fully awake, and when the reticular formation is severed from the higher brain regions, the animal falls into a deep coma.

Figure 5.7 The Brain Stem and the Thalamus. The brain stem is an extension of the spinal cord, including the medulla, the pons, the thalamus, and the reticular formation.

Above the brain stem are other parts of the old brain that also are involved in the processing of behaviour and emotions (see Figure 5.8, “The Limbic System”). The thalamus is the egg-shaped structure above the brain stem that applies still more filtering to the sensory information that is coming up from the spinal cord and through the reticular formation, and it relays some of these remaining signals to the higher brain levels (Sherman & Guillery, 2006). The thalamus also receives some of the higher brain’s replies, forwarding them to the medulla and the cerebellum. The thalamus is also important in sleep because it shuts off incoming signals from the senses, allowing us to rest.

Figure 5.8 The Limbic System. This diagram shows the major parts of the limbic system, as well as the pituitary gland, which is controlled by it.

The cerebellum (literally, “little brain”) consists of two wrinkled ovals behind the brain stem. It functions to coordinate voluntary movement. People who have damage to the cerebellum have difficulty walking, keeping their balance, and holding their hands steady. Consuming alcohol influences the cerebellum, which is why people who are drunk have more difficulty walking in a straight line. Also, the cerebellum contributes to emotional responses, helps us discriminate between different sounds and textures, and is important in learning (Bower & Parsons, 2003).

Whereas the primary function of the brain stem is to regulate the most basic aspects of life, including motor functions, the limbic system is largely responsible for memory and emotions, including our responses to reward and punishment. The limbic system is a brain area, located between the brain stem and the two cerebral hemispheres, that governs emotion and memory. It includes the amygdala, the hypothalamus, and the hippocampus.

The amygdala consists of two “almond-shaped” clusters (amygdala comes from the Latin word for “almond”) and is primarily responsible for regulating our perceptions of, and reactions to, aggression and fear. The amygdala has connections to other bodily systems related to fear, including the sympathetic nervous system (which we will see later is important in fear responses), facial responses (which perceive and express emotions), the processing of smells, and the release of neurotransmitters related to stress and aggression (Best, 2009). In one early study, Klüver and Bucy (1939) damaged the amygdala of an aggressive rhesus monkey. They found that the once angry animal immediately became passive and no longer responded to fearful situations with aggressive behaviour. Electrical stimulation of the amygdala in other animals also influences aggression. In addition to helping us experience fear, the amygdala also helps us learn from situations that create fear. When we experience events that are dangerous, the amygdala stimulates the brain to remember the details of the situation so that we learn to avoid it in the future (Sigurdsson, Doyère, Cain, & LeDoux, 2007).

Located just under the thalamus (hence its name), the hypothalamus is a brain structure that contains a number of small areas that perform a variety of functions, including the regulation of hunger and sexual behaviour, as well as linking the nervous system to the endocrine system via the pituitary gland. Through its many interactions with other parts of the brain, the hypothalamus helps regulate body temperature, hunger, thirst, and sex, and responds to the satisfaction of these needs by creating feelings of pleasure. Olds and Milner (1954) discovered these reward centres accidentally after they had momentarily stimulated the hypothalamus of a rat. The researchers noticed that after being stimulated, the rat continued to move to the exact spot in its cage where the stimulation had occurred, as if it were trying to re-create the circumstances surrounding its original experience. Upon further research into these reward centres, Olds (1958) discovered that animals would do almost anything to re-create enjoyable stimulation, including crossing a painful electrified grid to receive it. In one experiment a rat was given the opportunity to electrically stimulate its own hypothalamus by pressing a pedal. The rat enjoyed the experience so much that it pressed the pedal more than 7,000 times per hour until it collapsed from sheer exhaustion.

The hippocampus consists of two “horns” that curve back from the amygdala. The hippocampus is important in storing information in long-term memory. If the hippocampus is damaged, a person cannot build new memories, living instead in a strange world where everything he or she experiences just fades away, even while older memories from the time before the damage are untouched.

The Cerebral Cortex Creates Consciousness and Thinking

All animals have adapted to their environments by developing abilities that help them survive. Some animals have hard shells, others run extremely fast, and some have acute hearing. Human beings do not have any of these particular characteristics, but we do have one big advantage over other animals — we are very, very smart.

You might think that we should be able to determine the intelligence of an animal by looking at the ratio of the animal’s brain weight to the weight of its entire body. But this does not really work. The elephant’s brain is one-thousandth of its weight, but the whale’s brain is only one ten-thousandth of its body weight. On the other hand, although the human brain is one-sixtieth of its body weight, the mouse’s brain represents one-fortieth of its body weight. Despite these comparisons, elephants do not seem 10 times smarter than whales, and humans definitely seem smarter than mice.

The key to the advanced intelligence of humans is not found in the size of our brains. What sets humans apart from other animals is our larger cerebral cortex the outer bark-like layer of our brain that allows us to so successfully use language, acquire complex skills, create tools, and live in social groups (Gibson, 2002). In humans, the cerebral cortex is wrinkled and folded, rather than smooth as it is in most other animals. This creates a much greater surface area and size, and allows increased capacities for learning, remembering, and thinking. The folding of the cerebral cortex is referred to as corticalization.

Although the cortex is only about one-tenth of an inch thick, it makes up more than 80% of the brain’s weight. The cortex contains about 20 billion nerve cells and 300 trillion synaptic connections (de Courten-Myers, 1999). Supporting all these neurons are billions more glial cells (glia), cells that surround and link to the neurons, protecting them, providing them with nutrients, and absorbing unused neurotransmitters. The glia come in different forms and have different functions. For instance, the myelin sheath surrounding the axon of many neurons is a type of glial cell. The glia are essential partners of neurons, without which the neurons could not survive or function (Miller, 2005).

The cerebral cortex is divided into two hemispheres, and each hemisphere is divided into four lobes, each separated by folds known as fissures. If we look at the cortex starting at the front of the brain and moving over the top (see Figure 5.9, “The Two Hemispheres”), we see first the frontal lobe (behind the forehead), which is responsible primarily for thinking, planning, memory, and judgment. Following the frontal lobe is the parietal lobe, which extends from the middle to the back of the skull and which is responsible primarily for processing information about touch. Then comes the occipital lobe at the very back of the skull, which processes visual information. Finally, in front of the occipital lobe (pretty much between the ears) is the temporal lobe, responsible primarily for hearing and language.

Figure 5.9 The Two Hemispheres. The brain is divided into two hemispheres (left and right), each of which has four lobes (temporal, frontal, occipital, and parietal). Furthermore, there are specific cortical areas that control different processes.

Functions of the Cortex

When the German physicists Gustav Fritsch and Eduard Hitzig (1870/2009) applied mild electric stimulation to different parts of a dog’s cortex, they discovered that they could make different parts of the dog’s body move. Furthermore, they discovered an important and unexpected principle of brain activity. They found that stimulating the right side of the brain produced movement in the left side of the dog’s body, and vice versa. This finding follows from a general principle about how the brain is structured, called contralateral control, meaning the brain is wired such that in most cases the left hemisphere receives sensations from and controls the right side of the body, and vice versa.

Figure 5.10 The Sensory Cortex and the Motor Cortex. The portion of the sensory and motor cortex devoted to receiving messages that control specific regions of the body is determined by the amount of fine movement that area is capable of performing. Thus the hand and fingers have as much area in the cerebral cortex as does the entire trunk of the body.

Fritsch and Hitzig also found that the movement that followed the brain stimulation only occurred when they stimulated a specific arch-shaped region that runs across the top of the brain from ear to ear, just at the front of the parietal lobe (see Figure 5.10, “The Sensory Cortex and the Motor Cortex”). Fritsch and Hitzig had discovered the motor cortex, the part of the cortex that controls and executes movements of the body by sending signals to the cerebellum and the spinal cord. More recent research has mapped the motor cortex even more fully, by providing mild electronic stimulation to different areas of the motor cortex in fully conscious patients while observing their bodily responses (because the brain has no sensory receptors, these patients feel no pain). As you can see in Figure 5.10, “The Sensory Cortex and the Motor Cortex,” this research has revealed that the motor cortex is specialized for providing control over the body, in the sense that the parts of the body that require more precise and finer movements, such as the face and the hands, also are allotted the greatest amount of cortical space.

Just as the motor cortex sends out messages to the specific parts of the body, the somatosensory cortex, an area just behind and parallel to the motor cortex at the back of the frontal lobe, receives information from the skin’s sensory receptors and the movements of different body parts. Again, the more sensitive the body region, the more area is dedicated to it in the sensory cortex. Our sensitive lips, for example, occupy a large area in the sensory cortex, as do our fingers and genitals.

Other areas of the cortex process other types of sensory information. The visual cortex is the area located in the occipital lobe (at the very back of the brain) that processes visual information. If you were stimulated in the visual cortex, you would see flashes of light or colour, and perhaps you remember having had the experience of “seeing stars” when you were hit in, or fell on, the back of your head. The temporal lobe, located on the lower side of each hemisphere, contains the auditory cortex, which is responsible for hearing and language. The temporal lobe also processes some visual information, providing us with the ability to name the objects around us (Martin, 2007).

The motor and sensory areas of the cortex account for a relatively small part of the total cortex. The remainder of the cortex is made up of association areas in which sensory and motor information is combined and associated with our stored knowledge. These association areas are the places in the brain that are responsible for most of the things that make human beings seem human. The association areas are involved in higher mental functions, such as learning, thinking, planning, judging, moral reflecting, figuring, and spatial reasoning.

The Brain Is Flexible: Neuroplasticity

The control of some specific bodily functions, such as movement, vision, and hearing, is performed in specified areas of the cortex, and if these areas are damaged, the individual will likely lose the ability to perform the corresponding function. For instance, if an infant suffers damage to facial recognition areas in the temporal lobe, it is likely that he or she will never be able to recognize faces (Farah, Rabinowitz, Quinn, & Liu, 2000). On the other hand, the brain is not divided up in an entirely rigid way. The brain’s neurons have a remarkable capacity to reorganize and extend themselves to carry out particular functions in response to the needs of the organism and to repair damage. As a result, the brain constantly creates new neural communication routes and rewires existing ones. Neuroplasticity refers to the brain’s ability to change its structure and function in response to experience or damage. Neuroplasticity enables us to learn and remember new things and adjust to new experiences.

Our brains are the most “plastic” when we are young children, as it is during this time that we learn the most about our environment. On the other hand, neuroplasticity continues to be observed even in adults (Kolb & Fantie, 1989). The principles of neuroplasticity help us understand how our brains develop to reflect our experiences. For instance, accomplished musicians have a larger auditory cortex compared with the general population (Bengtsson et al., 2005) and also require less neural activity to move their fingers over the keys than do novices (Münte, Altenmüller, & Jäncke, 2002). These observations reflect the changes in the brain that follow our experiences.

Plasticity is also observed when there is damage to the brain or to parts of the body that are represented in the motor and sensory cortexes. When a tumour in the left hemisphere of the brain impairs language, the right hemisphere will begin to compensate to help the person recover the ability to speak (Thiel et al., 2006). And if a person loses a finger, the area of the sensory cortex that previously received information from the missing finger will begin to receive input from adjacent fingers, causing the remaining digits to become more sensitive to touch (Fox, 1984).

Although neurons cannot repair or regenerate themselves as skin or blood vessels can, new evidence suggests that the brain can engage in neurogenesis, the forming of new neurons (Van Praag, Zhao, Gage, & Gazzaniga, 2004). These new neurons originate deep in the brain and may then migrate to other brain areas, where they form new connections with other neurons (Gould, 2007). This leaves open the possibility that someday scientists might be able to “rebuild” damaged brains by creating drugs that help grow neurons.

Research Focus: Identifying the Unique Functions of the Left and Right Hemispheres Using Split-Brain Patients

We have seen that the left hemisphere of the brain primarily senses and controls the motor movements on the right side of the body, and vice versa. This fact provides an interesting way to study brain lateralization the idea that the left and the right hemispheres of the brain are specialized to perform different functions. Gazzaniga, Bogen, and Sperry (1965) studied a patient, known as W. J., who had undergone an operation to relieve severe seizures. In this surgery, the region that normally connects the two halves of the brain and supports communication between the hemispheres, known as the corpus callosum, is severed. As a result, the patient essentially becomes a person with two separate brains. Because the left and right hemispheres are separated, each hemisphere develops a mind of its own, with its own sensations, concepts, and motivations (Gazzaniga, 2005).In their research, Gazzaniga and his colleagues tested the ability of W. J. to recognize and respond to objects and written passages that were presented to only the left or to only the right brain hemispheres (see Figure 5.11, “Visual and Verbal Processing in the Split-Brain Patient”). The researchers had W. J. look straight ahead and then flashed, for a fraction of a second, a picture of a geometrical shape to the left of where he was looking. By doing so, they ensured that — because the two hemispheres had been separated — the image of the shape was experienced only in the right brain hemisphere (remember that sensory input from the left side of the body is sent to the right side of the brain). Gazzaniga and his colleagues found that W. J. was able to identify what he had been shown when he was asked to pick the object from a series of shapes, using his left hand, but that he could not do this when the object was shown in the right visual field. On the other hand, W. J. could easily read written material presented in the right visual field (and thus experienced in the left hemisphere) but not when it was presented in the left visual field.

Figure 5.11 Visual and Verbal Processing in the Split-Brain Patient. The information that is presented on the left side of our field of vision is transmitted to the right brain hemisphere, and vice versa. In split-brain patients, the severed corpus callosum does not permit information to be transferred between hemispheres, which allows researchers to learn about the functions of each hemisphere. In the sample on the left, the split-brain patient could not choose which image had been presented because the left hemisphere cannot process visual information. In the sample on the right the patient could not read the passage because the right brain hemisphere cannot process language.

This research, and many other studies following it, has demonstrated that the two brain hemispheres specialize in different abilities. In most people the ability to speak, write, and understand language is located in the left hemisphere. This is why W. J. could read passages that were presented on the right side and thus transmitted to the left hemisphere, but could not read passages that were only experienced in the right brain hemisphere. The left hemisphere is also better at math and at judging time and rhythm. It is also superior in coordinating the order of complex movements — for example, lip movements needed for speech. The right hemisphere, on the other hand, has only very limited verbal abilities, and yet it excels in perceptual skills. The right hemisphere is able to recognize objects, including faces, patterns, and melodies, and it can put a puzzle together or draw a picture. This is why W. J. could pick out the image when he saw it on the left, but not the right, visual field.

Although Gazzaniga’s research demonstrated that the brain is in fact lateralized, such that the two hemispheres specialize in different activities, this does not mean that when people behave in a certain way or perform a certain activity they are only using one hemisphere of their brains at a time. That would be drastically oversimplifying the concept of brain differences. We normally use both hemispheres at the same time, and the difference between the abilities of the two hemispheres is not absolute (Soroker et al., 2005).

Psychology in Everyday Life: Why Are Some People Left-Handed?

Across cultures and ethnic groups, about 90% of people are mainly right-handed, whereas only 10% are primarily left-handed (Peters, Reimers, & Manning, 2006). This fact is puzzling, in part because the number of left-handers is so low, and in part because other animals, including our closest primate relatives, do not show any type of handedness. The existence of right-handers and left-handers provides an interesting example of the relationship among evolution, biology, and social factors and how the same phenomenon can be understood at different levels of analysis (Harris, 1990; McManus, 2002).At least some handedness is determined by genetics. Ultrasound scans show that nine out of 10 fetuses suck the thumb of their right hand, suggesting that the preference is determined before birth (Hepper, Wells, & Lynch, 2005), and the mechanism of transmission has been linked to a gene on the X chromosome (Jones & Martin, 2000). It has also been observed that left-handed people are likely to have fewer children, and this may be in part because the mothers of left-handers are more prone to miscarriages and other prenatal problems (McKeever, Cerone, Suter, & Wu, 2000).

But culture also plays a role. In the past, left-handed children were forced to write with their right hands in many countries, and this practice continues, particularly in collectivistic cultures, such as India and Japan, where left-handedness is viewed negatively as compared with individualistic societies, such as Canada and the United States. For example, India has about half as many left-handers as the United States (Ida & Mandal, 2003).

There are both advantages and disadvantages to being left-handed in a world where most people are right-handed. One problem for lefties is that the world is designed for right-handers. Automatic teller machines (ATMs), classroom desks, scissors, microscopes, drill presses, and table saws are just some examples of everyday machinery designed with the most important controls on the right side. This may explain in part why left-handers suffer somewhat more accidents than do right-handers (Dutta & Mandal, 2006).

Despite the potential difficulty living and working in a world designed for right-handers, there seem to be some advantages to being left-handed. Throughout history, a number of prominent artists have been left-handed, including Leonardo da Vinci, Michelangelo, Pablo Picasso, and Max Escher. Because the right hemisphere is superior in imaging and visual abilities, there may be some advantage to using the left hand for drawing or painting (Springer & Deutsch, 1998). Left-handed people are also better at envisioning three-dimensional objects, which may explain why there is such a high number of left-handed architects, artists, and chess players in proportion to their numbers (Coren, 1992). However, there are also more left-handers among those with reading disabilities, allergies, and migraine headaches (Geschwind & Behan, 2007), perhaps due to the fact that a small minority of left-handers owe their handedness to a birth trauma, such as being born prematurely (Betancur, Vélez, Cabanieu, & le Moal, 1990).

In sports in which handedness may matter, such as tennis, boxing, fencing, or judo, left-handers may have an advantage. They play many games against right-handers and learn how to best handle their styles. Right-handers, however, play very few games against left-handers, which may make them more vulnerable. This explains why a disproportionately high number of left-handers are found in sports where direct one-on-one action predominates. In other sports, such as golf, there are fewer left-handed players because the handedness of one player has no effect on the competition.

The fact that left-handers excel in some sports suggests the possibility that they may have also had an evolutionary advantage because their ancestors may have been more successful in important skills such as hand-to-hand combat (Bodmer & McKie, 1994). At this point, however, this idea remains only a hypothesis, and determinants of human handedness are yet to be fully understood.


Key Takeaways

  • The old brain — including the brain stem, medulla, pons, reticular formation, thalamus, cerebellum, amygdala, hypothalamus, and hippocampus — regulates basic survival functions, such as breathing, moving, resting, feeding, emotions, and memory.
  • The cerebral cortex, made up of billions of neurons and glial cells, is divided into the right and left hemispheres and into four lobes.
  • The frontal lobe is primarily responsible for thinking, planning, memory, and judgment. The parietal lobe is primarily responsible for bodily sensations and touch. The temporal lobe is primarily responsible for hearing and language. The occipital lobe is primarily responsible for vision. Other areas of the cortex act as association areas, responsible for integrating information.
  • The brain changes as a function of experience and potential damage in a process known as plasticity. The brain can generate new neurons through neurogenesis.
  • The motor cortex controls voluntary movements. Body parts requiring the most control and dexterity take up the most space in the motor cortex.
  • The sensory cortex receives and processes bodily sensations. Body parts that are the most sensitive occupy the greatest amount of space in the sensory cortex.
  • The left cerebral hemisphere is primarily responsible for language and speech in most people, whereas the right hemisphere specializes in spatial and perceptual skills, visualization, and the recognition of patterns, faces, and melodies.
  • The severing of the corpus callosum, which connects the two hemispheres, creates a “split-brain patient,” with the effect of creating two separate minds operating in one person.
  • Studies with split-brain patients as research participants have been used to study brain lateralization.
  • Neuroplasticity allows the brain to adapt and change as a function of experience or damage.

Exercises and Critical Thinking

  1. Do you think that animals experience emotion? What aspects of brain structure might lead you to believe that they do or do not?
  2. Consider your own experiences and speculate on which parts of your brain might be particularly well developed as a result of these experiences.
  3. Which brain hemisphere are you likely to be using when you search for a fork in the silverware drawer? Which brain hemisphere are you most likely to be using when you struggle to remember the name of an old friend?
  4. Do you think that encouraging left-handed children to use their right hands is a good idea? Why or why not?

Image Attributions

Figure 5.5: Anatomy of the Brain by artlessstacey ( is in the public domain.

Figure 5.6: Adapted from Wikia Education. (n.d.). Cerebral cortex. Retrieved from


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5.3 Putting It All Together: The Nervous System and the Endocrine System

Charles Stangor and Jennifer Walinga

Learning Objectives

  1. Summarize the primary functions of the CNS and of the subsystems of the PNS.
  2. Explain how the electrical components of the nervous system and the chemical components of the endocrine system work together to influence behaviour.

Now that we have considered how individual neurons operate and the roles of the different brain areas, it is time to ask how the body manages to put it all together. How do the complex activities in the various parts of the brain, the simple all-or-nothing firings of billions of interconnected neurons, and the various chemical systems within the body work together to allow the body to respond to the social environment and engage in everyday behaviours? In this section we will see that the complexities of human behaviour are accomplished through the joint actions of electrical and chemical processes in the nervous system and the endocrine system.

Electrical Control of Behaviour: The Nervous System

The nervous system (see Figure 5.12, “The Functional Divisions of the Nervous System”), the electrical information highway of the body, is made up of nerves bundles of interconnected neurons that fire in synchrony to carry messages. The central nervous system (CNS), made up of the brain and spinal cord, is the major controller of the body’s functions, charged with interpreting sensory information and responding to it with its own directives. The CNS interprets information coming in from the senses, formulates an appropriate reaction, and sends responses to the appropriate system to respond accordingly. Everything that we see, hear, smell, touch, and taste is conveyed to us from our sensory organs as neural impulses, and each of the commands that the brain sends to the body, both consciously and unconsciously, travels through this system as well.

The nervous system. Long description available
Figure 5.12 The Functional Divisions of the Nervous System. [Long Description]

Nerves are differentiated according to their function. A sensory (or afferent) neuron carries information from the sensory receptors, whereas a motor (or efferent) neuron transmits information to the muscles and glands. An interneuron, which is by far the most common type of neuron, is located primarily within the CNS and is responsible for communicating among the neurons. Interneurons allow the brain to combine the multiple sources of available information to create a coherent picture of the sensory information being conveyed.

The spinal cord is the long, thin, tubular bundle of nerves and supporting cells that extends down from the brain. It is the central throughway of information for the body. Within the spinal cord, ascending tracts of sensory neurons relay sensory information from the sense organs to the brain while descending tracts of motor neurons relay motor commands back to the body. When a quicker-than-usual response is required, the spinal cord can do its own processing, bypassing the brain altogether. A reflex is an involuntary and nearly instantaneous movement in response to a stimulus. Reflexes are triggered when sensory information is powerful enough to reach a given threshold and the interneurons in the spinal cord act to send a message back through the motor neurons without relaying the information to the brain (see Figure 5.13, “The Reflex”). When you touch a hot stove and immediately pull your hand back, or when you fumble your cell phone and instinctively reach to catch it before it falls, reflexes in your spinal cord order the appropriate responses before your brain even knows what is happening.

Figure 5.13 The Reflex. The central nervous system can interpret signals from sensory neurons and respond to them extremely quickly via the motor neurons without any need for the brain to be involved. These quick responses, known as reflexes, can reduce the damage that we might experience as a result of, for instance, touching a hot stove.

If the central nervous system is the command centre of the body, the peripheral nervous system (PNS) represents the front line. The PNS links the CNS to the body’s sense receptors, muscles, and glands. As you can see in Figure 5.14, “The Autonomic Nervous System,” the peripheral nervous system is itself divided into two subsystems, one controlling internal responses and one controlling external responses.

The autonomic nervous system (ANS) is the division of the PNS that governs the internal activities of the human body, including heart rate, breathing, digestion, salivation, perspiration, urination, and sexual arousal. Many of the actions of the ANS, such as heart rate and digestion, are automatic and out of our conscious control, but others, such as breathing and sexual activity, can be controlled and influenced by conscious processes.

The somatic nervous system (SNS) is the division of the PNS that controls the external aspects of the body, including the skeletal muscles, skin, and sense organs. The somatic nervous system consists primarily of motor nerves responsible for sending brain signals for muscle contraction.

The autonomic nervous system itself can be further subdivided into the sympathetic and parasympathetic systems. The sympathetic division of the ANS is involved in preparing the body for behaviour, particularly in response to stress, by activating the organs and the glands in the endocrine system. The parasympathetic division of the ANS tends to calm the body by slowing the heart and breathing and by allowing the body to recover from the activities that the sympathetic system causes. The sympathetic and the parasympathetic divisions normally function in opposition to each other, with the sympathetic division acting a bit like the accelerator pedal on a car and the parasympathetic division acting like the brake.

Figure 5.14 The Autonomic Nervous System. The autonomic nervous system has two divisions: The sympathetic division acts to energize the body, preparing it for action. The parasympathetic division acts to calm the body, allowing it to rest. [Long Description]

Our everyday activities are controlled by the interaction between the sympathetic and parasympathetic nervous systems. For example, when we get out of bed in the morning, we would experience a sharp drop in blood pressure if it were not for the action of the sympathetic system, which automatically increases blood flow through the body. Similarly, after we eat a big meal, the parasympathetic system automatically sends more blood to the stomach and intestines, allowing us to efficiently digest the food. And perhaps you have had the experience of not being at all hungry before a stressful event, such as a sports game or an exam (when the sympathetic division was primarily in action), but suddenly finding yourself feeling starved afterward, as the parasympathetic takes over. The two systems work together to maintain vital bodily functions, resulting in homeostasis, the natural balance in the body’s systems.

The Body’s Chemicals Help Control Behaviour: The Endocrine System

The nervous system is designed to protect us from danger through its interpretation of and reactions to stimuli. But a primary function of the sympathetic and parasympathetic nervous systems is to interact with the endocrine system to elicit chemicals that provide another system for influencing our feelings and behaviours.

A gland in the endocrine system is made up of groups of cells that function to secrete hormones. A hormone is a chemical that moves throughout the body to help regulate emotions and behaviours. When the hormones released by one gland arrive at receptor tissues or other glands, these receiving receptors may trigger the release of other hormones, resulting in a series of complex chemical chain reactions. The endocrine system works together with the nervous system to influence many aspects of human behaviour, including growth, reproduction, and metabolism. And the endocrine system plays a vital role in emotions. Because the glands in men and women differ, hormones also help explain some of the observed behavioural differences between men and women. The major glands in the endocrine system are shown in Figure 5.15, “The Major Glands of the Endocrine System.”

Figure 5.15 The Major Glands of the Endocrine System. The male is shown on the left and the female on the right.

The pituitary gland, a small pea-sized gland located near the centre of the brain, is responsible for controlling the body’s growth, but it also has many other influences that make it of primary importance to regulating behaviour. The pituitary secretes hormones that influence our responses to pain as well as hormones that signal the ovaries and testes to make sex hormones. The pituitary gland also controls ovulation and the menstrual cycle in women. Because the pituitary has such an important influence on other glands, it is sometimes known as the “master gland.”

Other glands in the endocrine system include the pancreas, which secretes hormones designed to keep the body supplied with fuel to produce and maintain stores of energy; the pineal gland, located in the middle of the brain, which secretes melatonin, a hormone that helps regulate the wake-sleep cycle; and the thyroid and parathyroid glands, which are responsible for determining how quickly the body uses energy and hormones, and controlling the amount of calcium in the blood and bones.

The body has two triangular adrenal glands, one atop each kidney. The adrenal glands produce hormones that regulate salt and water balance in the body, and they are involved in metabolism, the immune system, and sexual development and function. The most important function of the adrenal glands is to secrete the hormones epinephrine (also known as adrenaline) and norepinephrine (also known as noradrenaline) when we are excited, threatened, or stressed. Epinephrine and norepinephrine stimulate the sympathetic division of the ANS, causing increased heart and lung activity, dilation of the pupils, and increases in blood sugar, which give the body a surge of energy to respond to a threat. The activity and role of the adrenal glands in response to stress provide an excellent example of the close relationship and interdependency of the nervous and endocrine systems. A quick-acting nervous system is essential for immediate activation of the adrenal glands, while the endocrine system mobilizes the body for action.

The male sex glands, known as the testes, secrete a number of hormones, the most important of which is testosterone, the male sex hormone. Testosterone regulates body changes associated with sexual development, including enlargement of the penis, deepening of the voice, growth of facial and pubic hair, and the increase in muscle growth and strength. The ovaries, the female sex glands, are located in the pelvis. They produce eggs and secrete the female hormones estrogen and progesterone. Estrogen is involved in the development of female sexual features, including breast growth, the accumulation of body fat around the hips and thighs, and the growth spurt that occurs during puberty. Both estrogen and progesterone are also involved in pregnancy and the regulation of the menstrual cycle.

Recent research has pinpointed some of the important roles of the sex hormones in social behaviour. Dabbs, Hargrove, and Heusel (1996) measured the testosterone levels of 240 men who were members of 12 fraternities at two universities. They also obtained descriptions of the fraternities from university officials, fraternity officers, yearbook and chapter house photographs, and researcher field notes. The researchers correlated the testosterone levels and the descriptions of each fraternity. They found that the fraternities with the highest average testosterone levels were also more wild and unruly, and one of these fraternities was known across campus for the crudeness of its behaviour. On the other hand, the fraternities with the lowest average testosterone levels were more well behaved, friendly and pleasant, academically successful, and socially responsible. Banks and Dabbs (1996) found that juvenile delinquents and prisoners who had high levels of testosterone also acted more violently, and Tremblay and colleagues (1998) found that testosterone was related to toughness and leadership behaviours in adolescent boys. Although testosterone levels are higher in men than in women, the relationship between testosterone and aggression is not limited to males. Studies have also shown a positive relationship between testosterone and aggression and related behaviours (such as competitiveness) in women (Cashdan, 2003).

Keep in mind that the observed relationships between testosterone levels and aggressive behaviour that have been found in these studies do not prove that testosterone causes aggression — the relationships are only correlational. In fact, there is evidence that the relationship between violence and testosterone also goes in the other direction: playing an aggressive game, such as tennis or even chess, increases the testosterone levels of the winners and decreases the testosterone levels of losers (Gladue, Boechler, & McCaul, 1989; Mazur, Booth, & Dabbs, 1992), and perhaps this is why excited soccer fans sometimes riot when their team wins.

Recent research has also begun to document the role that female sex hormones may play in reactions to others. A study about hormonal influences on social-cognitive functioning (Macrae, Alnwick, Milne, & Schloerscheidt, 2002) found that women were more easily able to perceive and categorize male faces during the more fertile phases of their menstrual cycles. Although researchers did not directly measure the presence of hormones, it is likely that phase-specific hormonal differences influenced the women’s perceptions.

At this point you can begin to see the important role the hormones play in behaviour. But the hormones we have reviewed in this section represent only a subset of the many influences that hormones have on our behaviours. In the chapters to come we will consider the important roles that hormones play in many other behaviours, including sleeping, sexual activity, and helping and harming others.


Key Takeaways

  • The body uses both electrical and chemical systems to create homeostasis.
  • The CNS is made up of bundles of nerves that carry messages to and from the PNS.
  • The peripheral nervous system is composed of the autonomic nervous system (ANS) and the peripheral nervous system (PNS). The ANS is further divided into the sympathetic (activating) and parasympathetic (calming) nervous systems. These divisions are activated by glands and organs in the endocrine system.
  • Specific nerves, including sensory neurons, motor neurons, and interneurons, each have specific functions.
  • The spinal cord may bypass the brain by responding rapidly using reflexes.
  • The pituitary gland is a master gland, affecting many other glands.
  • Hormones produced by the pituitary and adrenal glands regulate growth, stress, sexual functions, and chemical balance in the body.
  • The adrenal glands produce epinephrine and norepinephrine, the hormones responsible for our reactions to stress.
  • The sex hormones, testosterone, estrogen, and progesterone, play an important role in sex differences.

Exercises and Critical Thinking

  1. Recall a time when you were threatened or stressed. What physiological reactions did you experience in the situation, and what aspects of the endocrine system do you think created those reactions?
  2. Consider the emotions that you have experienced over the past several weeks. What hormones do you think might have been involved in creating those emotions?


Banks, T., & Dabbs, J. M., Jr. (1996). Salivary testosterone and cortisol in delinquent and violent urban subculture. Journal of Social Psychology, 136(1), 49–56.

Cashdan, E. (2003). Hormones and competitive aggression in women. Aggressive Behavior, 29(2), 107–115.

Dabbs, J. M., Jr., Hargrove, M. F., & Heusel, C. (1996). Testosterone differences among college fraternities: Well-behaved vs. rambunctious. Personality and Individual Differences, 20(2), 157–161.

Gladue, B. A., Boechler, M., & McCaul, K. D. (1989). Hormonal response to competition in human males. Aggressive Behavior, 15(6), 409–422.

Macrae, C. N., Alnwick, K. A., Milne, A. B., & Schloerscheidt, A. M. (2002). Person perception across the menstrual cycle: Hormonal influences on social-cognitive functioning. Psychological Science, 13(6), 532–536.

Mazur, A., Booth, A., & Dabbs, J. M. (1992). Testosterone and chess competition. Social Psychology Quarterly, 55(1), 70–77.

Tremblay, R. E., Schaal, B., Boulerice, B., Arseneault, L., Soussignan, R. G., Paquette, D., & Laurent, D. (1998). Testosterone, physical aggression, dominance, and physical development in early adolescence. International Journal of Behavioral Development, 22(4), 753–777.

Long Descriptions

Figure 5.12 long description: The nervous system is made up of two parts: The central nervous system consisting of the brain and spinal cord and the peripheral nervous system. The peripheral nervous system is both autonomic (controlling internal activities of organs and glands) and somatic (controlling external actions of skin and muscles).

Figure 5.14 long description:

Sympathetic Nervous System Parasympathetic Nervous System
Dilates pupil Contracts pupil
Accelerates heartbeat Slows heartbeat
Inhibits digestive activity Stimulates digestive activity
Stimulates glucose release
Stimulates secretion of epinephrine and norepinephrine



5.4 Psychologists Study the Brain Using Many Different Methods

Charles Stangor and Jennifer Walinga

Learning Objective

  1. Compare and contrast the techniques that scientists use to view and understand brain structures and functions.

One problem in understanding the brain is that it is difficult to get a good picture of what is going on inside it. But there are a variety of empirical methods that allow scientists to look at brains in action, and the number of possibilities has increased dramatically in recent years with the introduction of new neuroimaging techniques. In this section we will consider the various techniques that psychologists use to learn about the brain. Each of the different techniques has some advantages, and when we put them together, we begin to get a relatively good picture of how the brain functions and which brain structures control which activities. Perhaps the most immediate approach to visualizing and understanding the structure of the brain is to directly analyze the brains of human cadavers. When Albert Einstein died in 1955, his brain was removed and stored for later analysis. Researcher Marian Diamond (1999) later analyzed a section of Einstein’s cortex to investigate its characteristics. Diamond was interested in the role of glia, and she hypothesized that the ratio of glial cells to neurons was an important determinant of intelligence. To test this hypothesis, she compared the ratio of glia to neurons in Einstein’s brain with the ratio in the preserved brains of 11 other more “ordinary” men. However, Diamond was able to find support for only part of her research hypothesis. Although she found that Einstein’s brain had relatively more glia in all the areas that she studied than did the control group, the difference was only statistically significant in one of the areas she tested. Diamond admits a limitation in her study is that she had only one Einstein to compare with 11 ordinary men.

Lesions Provide a Picture of What Is Missing

An advantage of the cadaver approach is that the brains can be fully studied, but an obvious disadvantage is that the brains are no longer active. In other cases, however, we can study living brains. The brains of living human beings may be damaged — as a result of strokes, falls, automobile accidents, gunshots, or tumours, for instance. These damages are called lesions. In rare occasions, brain lesions may be created intentionally through surgery, such as that designed to remove brain tumours or (as in split-brain patients) reduce the effects of epilepsy. Psychologists also sometimes intentionally create lesions in animals to study the effects on their behaviour. In so doing, they hope to be able to draw inferences about the likely functions of human brains from the effects of the lesions in animals. Lesions allow the scientist to observe any loss of brain function that may occur. For instance, when an individual suffers a stroke, a blood clot deprives part of the brain of oxygen, killing the neurons in the area and rendering that area unable to process information. In some cases, the result of the stroke is a specific lack of ability. For instance, if the stroke influences the occipital lobe, then vision may suffer, and if the stroke influences the areas associated with language or speech, these functions will suffer. In fact, our earliest understanding of the specific areas involved in speech and language were gained by studying patients who had experienced strokes.

A skull with a bar piercing down through the top of the head and through the jaw.
Figure 5.16 Phineas Gage. Areas in the frontal lobe of Phineas Gage were damaged when a metal rod blasted through it.

It is now known that a good part of our moral reasoning abilities is located in the frontal lobe, and at least some of this understanding comes from lesion studies. For instance, consider the well-known case of Phineas Gage (Figure 5.16) , a 25-year-old railroad worker who, as a result of an explosion, had an iron rod driven into his cheek and out through the top of his skull, causing major damage to his frontal lobe (Macmillan, 2000). Although, remarkably, Gage was able to return to work after the wounds healed, he no longer seemed to be the same person to those who knew him. The amiable, soft-spoken Gage had become irritable, rude, irresponsible, and dishonest. Although there are questions about the interpretation of this case study (Kotowicz, 2007), it did provide early evidence that the frontal lobe is involved in emotion and morality (Damasio et al., 2005). More recent and more controlled research has also used patients with lesions to investigate the source of moral reasoning. Michael Koenigs and his colleagues (Koenigs et al., 2007) asked groups of normal persons, individuals with lesions in the frontal lobes, and individuals with lesions in other places in the brain to respond to scenarios that involved doing harm to a person, even though the harm ultimately saved the lives of other people (Miller, 2008). In one of the scenarios the participants were asked if they would be willing to kill one person in order to prevent five other people from being killed. As you can see in Figure 5.17, “The Frontal Lobe and Moral Judgment,” they found that the individuals with lesions in the frontal lobe were significantly more likely to agree to do the harm than were individuals from the two other groups.

Frontal Lobe and Moral Judgment graph. Long description available.
Figure 5.17 The Frontal Lobe and Moral Judgment. Koenigs and his colleagues (2007) found that the frontal lobe is important in moral judgment. Persons with lesions in the frontal lobe were more likely to be willing to harm one person in order to save the lives of five others than were control participants or those with lesions in other parts of the brain. [Long Description]

Recording Electrical Activity in the Brain

In addition to lesion approaches, it is also possible to learn about the brain by studying the electrical activity created by the firing of its neurons. One approach, primarily used with animals, is to place detectors in the brain to study the responses of specific neurons. Research using these techniques has found, for instance, that there are specific neurons, known as feature detectors, in the visual cortex that detect movement, lines and edges, and even faces (Kanwisher, 2000).

Figure 5.18 EEG Study. A participant in an EEG study with a number of electrodes placed around his head.

A less invasive approach, and one that can be used on living humans, is electroencephalography (EEG), as shown in Figure 5.18. The EEG is a technique that records the electrical activity produced by the brain’s neurons through the use of electrodes that are placed around the research participant’s head. An EEG can show if a person is asleep, awake, or anesthetized because the brainwave patterns are known to differ during each state. EEGs can also track the waves that are produced when a person is reading, writing, and speaking, and are useful for understanding brain abnormalities, such as epilepsy. A particular advantage of EEG is that the participant can move around while the recordings are being taken, which is useful when measuring brain activity in children, who often have difficulty keeping still. Furthermore, by following electrical impulses across the surface of the brain, researchers can observe changes over very fast time periods.

Peeking inside the Brain: Neuroimaging

Although the EEG can provide information about the general patterns of electrical activity within the brain, and although the EEG allows the researcher to see these changes quickly as they occur in real time, the electrodes must be placed on the surface of the skull, and each electrode measures brainwaves from large areas of the brain. As a result, EEGs do not provide a very clear picture of the structure of the brain. But techniques exist to provide more specific brain images. Functional magnetic resonance imaging (fMRI) is a type of brain scan that uses a magnetic field to create images of brain activity in each brain area. The patient lies on a bed within a large cylindrical structure containing a very strong magnet. Neurons that are firing use more oxygen, and the need for oxygen increases blood flow to the area. The fMRI detects the amount of blood flow in each brain region, and thus is an indicator of neural activity. Very clear and detailed pictures of brain structures can be produced via fMRI (see Figure 5.19, “fMRI Image”). Often, the images take the form of cross-sectional “slices” that are obtained as the magnetic field is passed across the brain. The images of these slices are taken repeatedly and are superimposed on images of the brain structure itself to show how activity changes in different brain structures over time. When the research participant is asked to engage in tasks while in the scanner (e.g., by playing a game with another person), the images can show which parts of the brain are associated with which types of tasks. Another advantage of the fMRI is that it is noninvasive. The research participant simply enters the machine and the scans begin. Although the scanners themselves are expensive, the advantages of fMRIs are substantial, and they are now available in many university and hospital settings. The fMRI is now the most commonly used method of learning about brain structure.

Figure 5.19 fMRI Image. The fMRI creates images of brain structure and activity. The red and yellow areas represent increased blood flow and thus increased activity.

There is still one more approach that is being more frequently implemented to understand brain function, and although it is new, it may turn out to be the most useful of all. Transcranial magnetic stimulation (TMS) is a procedure in which magnetic pulses are applied to the brain of a living person with the goal of temporarily and safely deactivating a small brain region. In TMS studies the research participant is first scanned in an fMRI machine to determine the exact location of the brain area to be tested. Then the electrical stimulation is provided to the brain before or while the participant is working on a cognitive task, and the effects of the stimulation on performance are assessed. If the participant’s ability to perform the task is influenced by the presence of the stimulation, the researchers can conclude that this particular area of the brain is important to carrying out the task. The primary advantage of TMS is that it allows the researcher to draw causal conclusions about the influence of brain structures on thoughts, feelings, and behaviours. When the TMS pulses are applied, the brain region becomes less active, and this deactivation is expected to influence the research participant’s responses. Current research has used TMS to study the brain areas responsible for emotion and cognition and their roles in how people perceive intention and approach moral reasoning (Kalbe et al., 2010; Van den Eynde et al., 2010; Young, Camprodon, Hauser, Pascual-Leone, & Saxe, 2010). TMS is also used as a treatment for a variety of psychological conditions, including migraine, Parkinson’s disease, and major depressive disorder.

Research Focus: Cyberostracism

Neuroimaging techniques have important implications for understanding our behaviour, including our responses to those around us. Naomi Eisenberger and her colleagues (2003) tested the hypothesis that people who were excluded by others would report emotional distress and that images of their brains would show that they experienced pain in the same part of the brain where physical pain is normally experienced. In the experiment, 13 participants were each placed into an fMRI brain-imaging machine. The participants were told that they would be playing a computer “Cyberball” game with two other players who were also in fMRI machines (the two opponents did not actually exist, and their responses were controlled by the computer). Each of the participants was measured under three different conditions. In the first part of the experiment, the participants were told that as a result of technical difficulties, the link to the other two scanners could not yet be made, and thus at first they could not engage in, but only watch, the game play. This allowed the researchers to take a baseline fMRI reading. Then, during a second, inclusion, scan, the participants played the game, supposedly with the two other players. During this time, the other players threw the ball to the participants. In the third, exclusion, scan, however, the participants initially received seven throws from the other two players but were then excluded from the game because the two players stopped throwing the ball to the participants for the remainder of the scan (45 throws). The results of the analyses showed that activity in two areas of the frontal lobe was significantly greater during the exclusion scan than during the inclusion scan. Because these brain regions are known from prior research to be active for individuals who are experiencing physical pain, the authors concluded that these results show that the physiological brain responses associated with being socially excluded by others are similar to brain responses experienced upon physical injury. Further research (Chen, Williams, Fitness, & Newton, 2008; Wesselmann, Bagg, & Williams, 2009) has documented that people react to being excluded in a variety of situations with a variety of emotions and behaviours. People who feel that they are excluded, or even those who observe other people being excluded, not only experience pain, but feel worse about themselves and their relationships with people more generally, and they may work harder to try to restore their connections with others.


Key Takeaways

  • Studying the brains of cadavers can lead to discoveries about brain structure, but these studies are limited because the brain is no longer active.
  • Lesion studies are informative about the effects of lesions on different brain regions.
  • Electrophysiological recording may be used in animals to directly measure brain activity.
  • Measures of electrical activity in the brain, such as electroencephalography (EEG), are used to assess brainwave patterns and activity.
  • Functional magnetic resonance imaging (fMRI) measures blood flow in the brain during different activities, providing information about the activity of neurons and thus the functions of brain regions.
  • Transcranial magnetic stimulation (TMS) is used to temporarily and safely deactivate a small brain region, with the goal of testing the causal effects of the deactivation on behaviour.

Exercise and Critical Thinking

  1. Consider the different ways that psychologists study the brain, and think of a psychological characteristic or behaviour that could be studied using each of the different techniques.

Image Attributions

Figure 5.16:Phineas gage – 1868 skull diagram” by John M. Harlow, M.D. ( is in the public domain.

Figure 5.18:EEG cap” by Thuglas ( is in the public domain.

Figure 5.19: Face recognition by National Institutes of Health ( is in public domain.


Chen, Z., Williams, K. D., Fitness, J., & Newton, N. C. (2008). When hurt will not heal: Exploring the capacity to relive social and physical pain. Psychological Science, 19(8), 789–795.

Damasio, H., Grabowski, T., Frank, R., Galaburda, A. M., Damasio, A. R., Cacioppo, J. T., & Berntson, G. G. (2005). The return of Phineas Gage: Clues about the brain from the skull of a famous patient. In Social neuroscience: Key readings (pp. 21–28). New York, NY: Psychology Press.

Diamond, M. C. (1999). Why Einstein’s brain? New Horizons for Learning. Retrieved from

Eisenberger, N. I., Lieberman, M. D., & Williams, K. D. (2003). Does rejection hurt? An fMRI study of social exclusion. Science, 302(5643), 290–292.

Kalbe, E., Schlegel, M., Sack, A. T., Nowak, D. A., Dafotakis, M., Bangard, C., & Kessler, J. (2010). Dissociating cognitive from affective theory of mind: A TMS study. Cortex: A Journal Devoted to the Study of the Nervous System and Behavior, 46(6), 769–780.

Kanwisher, N. (2000). Domain specificity in face perception. Nature Neuroscience, 3(8), 759–763.

Koenigs, M., Young, L., Adolphs, R., Tranel, D., Cushman, F., Hauser, M., & Damasio, A. (2007). Damage to the prefontal cortex increases utilitarian moral judgments. Nature, 446(7138), 908–911.

Kotowicz, Z. (2007). The strange case of Phineas Gage. History of the Human Sciences, 20(1), 115–131.

Macmillan, M. (2000). An odd kind of fame: Stories of Phineas Gage. Cambridge, MA: MIT Press.

Miller, G. (2008). The roots of morality. Science, 320, 734–737.

Van den Eynde, F., Claudino, A. M., Mogg, A., Horrell, L., Stahl, D., & Schmidt, U. (2010). Repetitive transcranial magnetic stimulation reduces cue-induced food craving in bulimic disorders. Biological Psychiatry, 67(8), 793–795.

Wesselmann, E. D., Bagg, D., & Williams, K. D. (2009). “I feel your pain”: The effects of observing ostracism on the ostracism detection system. Journal of Experimental Social Psychology, 45(6), 1308–1311.

Young, L., Camprodon, J. A., Hauser, M., Pascual-Leone, A., & Saxe, R. (2010). Disruption of the right temporoparietal junction with transcranial magnetic stimulation reduces the role of beliefs in moral judgments. PNAS Proceedings of the National Academy of Sciences of the United States of America, 107(15), 6753–6758.

Long Descriptions

Figure 5.17 long description: The Frontal Lobe and Moral Judgement

Control Participants Participants with lesions in areas other than the frontal lobes Participants with lesions in the frontal lobes
Proportion of participants who engaged in harm 0.23 0.20 0.46



Chapter 5 Summary, Key Terms, and Self-Test

Charles Stangor, Jennifer Walinga, and Lee Sanders


All human behaviour, thoughts, and feelings are produced by the actions of our brains, nerves, muscles, and glands.

The body is controlled by the nervous system, consisting of the central nervous system (CNS) and the peripheral nervous system (PNS) and the endocrine system, which is made up of glands that create and control hormones.

Neurons are the cells in the nervous system. Neurons are composed of a soma that contains the nucleus of the cell; a dendrite that collects information from other cells and sends the information to the soma; and a long segmented fiber, known as the axon, which transmits information away from the cell body toward other neurons and to the muscles and glands.

The nervous system operates using an electrochemical process. An electrical charge moves through the neuron itself, and chemicals are used to transmit information between neurons. Within the neuron, the electrical charge occurs in the form of an action potential. The action potential operates in an all-or-nothing manner.

Neurons are separated by junction areas known as synapses. Neurotransmitters travel across the synaptic space between the terminal button of one neuron and the dendrites of other neurons, where they bind to the dendrites in the neighboring neurons. More than 100 chemical substances produced in the body have been identified as neurotransmitters, and these substances have a wide and profound effect on emotion, cognition, and behaviour.

Drugs that we ingest may either mimic (agonists) or block (antagonists) the operations of neurotransmitters.

The brains of all animals are layered and generally quite similar in overall form.

The brain stem is the oldest and innermost region of the brain. It controls the most basic functions of life, including breathing, attention, and motor responses. The brain stem includes the medulla, the pons, and the reticular formation.

Above the brain stem are other parts of the old brain involved in the processing of behaviour and emotions, including the thalamus, the cerebellum, and the limbic system. The limbic system includes the amygdala, the hypothalamus, and the hippocampus.

The cerebral cortex contains about 20 billion nerve cells and 300 trillion synaptic connections, and it’s supported by billions more glial cells that surround and link to the neurons. The cerebral cortex is divided into two hemispheres, and each hemisphere is divided into four lobes, each separated by folds known as fissures.

The frontal lobe is primarily responsible for thinking, planning, memory, and judgment. The parietal lobe is responsible for processing information about touch. The occipital lobe processes visual information, and the temporal lobe is responsible for hearing and language. The cortex also includes the motor cortex, the somatosensory cortex, the visual cortex, the auditory cortex, and the association areas.

The brain can develop new neurons, a process known as neurogenesis, as well as new routes for neural communications (neuroplasticity).

Psychologists study the brain using cadaver and lesion approaches, as well as through neuroimaging techniques that include electroencephalography (EEG), functional magnetic resonance imaging (fMRI), and transcranial magnetic stimulation (TMS).

Sensory (afferent) neurons carry information from the sensory receptors, whereas motor (efferent) neurons transmit information to the muscles and glands. Interneurons, by far the most common of neurons, are located primarily within the CNS and responsible for communicating among the neurons.

The peripheral nervous system is itself divided into two subsystems, one controlling internal responses (the autonomic nervous system, ANS) and one controlling external responses (the somatic nervous system). The sympathetic division of the ANS is involved in preparing the body for behaviour by activating the organs and the glands in the endocrine system. The parasympathetic division of the ANS tends to calm the body by slowing the heart and breathing and by allowing the body to recover from the activities that the sympathetic system causes.

Glands in the endocrine system include the pituitary gland, the pancreas, the adrenal glands, and the male and female sex glands. The male sex hormone testosterone and the female sex hormones estrogen and progesterone play important roles in behaviour and contribute to gender differences.

Key Terms

  • Action potential
  • Adrenal glands
  • Agonist
  • Amygdala
  • Antagonist
  • Auditory cortex
  • Autonomic Nervous System (ANS)
  • Association areas
  • Axon
  • Brain lateralization
  • Brain stem
  • Central Nervous System (CNS)
  • Cerebellum
  • Cerebral cortex
  • Contralateral control
  • Corpus callosum
  • Dendrite
  • Electroencephalography (EEG)
  • Endocrine system
  • Estrogen
  • Excitatory
  • Feature detectors
  • Frontal lobe
  • Functional Magnetic Resonance Imaging (fMRI)
  • Gland
  • Glial cells
  • Hippocampus
  • Homeostasis
  • Hormone
  • Hypothalamus
  • Inhibitory
  • Interneuron
  • Lesions
  • Limbic system
  • Nerves
  • Nervous system
  • Neurogenesis
  • Neuron
  • Neuroplasticity
  • Neurotransmitter
  • Node of Ranvier
  • Medulla
  • Motor cortex
  • Motor neuron (or Efferent neuron)
  • Myelin sheath
  • Occipital lobe
  • Ovaries
  • Pancreas
  • Parasympathetic division
  • Parathyroid gland
  • Parietal lobe
  • Peripheral Nervous System (PNS)
  • Pineal gland
  • Pituitary gland
  • Pons
  • Reflex
  • Refractory period
  • Resting potential
  • Reticular formation
  • Reuptake
  • Sensory neuron (or Afferent neuron)
  • Soma
  • Somatic Nervous System (SNS)
  • Somatosensory Cortex
  • Spinal cord
  • Sympathetic division
  • Synapses
  • Temporal lobe
  • Testes
  • Testosterone
  • Thalamus
  • Thyroid gland
  • Transcranial Magnetic Stimulation (TMS)
  • Visual cortex


An interactive or media element has been excluded from this version of the text. You can view it online here:

Direct link to self-test:


Chapter 6. Sensing and Perceiving


Chapter 6 Introduction

Charles Stangor and Jennifer Walinga

Misperception by Those Trained to Accurately Perceive a Threat

On September 6, 2007, the Asia-Pacific Economic Cooperation (APEC) leaders’ summit was being held in downtown Sydney, Australia. World leaders were attending the summit. Many roads in the area were closed for security reasons, and police presence was high.

As a prank, eight members of the Australian television satire The Chaser’s War on Everything assembled a false motorcade made up of two black four-wheel-drive vehicles, a black sedan, two motorcycles, bodyguards, and chauffeurs (see the video below). Group member Chas Licciardello was in one of the cars disguised as Osama bin Laden. The motorcade drove through Sydney’s central business district and entered the security zone of the meeting. The motorcade was waved on by police, through two checkpoints, until the Chaser group decided it had taken the gag far enough and stopped outside the InterContinental Hotel where former U.S. president George W. Bush was staying. Licciardello stepped out onto the street and complained, in character as bin Laden, about not being invited to the APEC Summit. Only at this time did the police belatedly check the identity of the group members, finally arresting them.

Watch the video: The Chaser – APEC Stunt []

Afterward, the group testified that it had made little effort to disguise its attempt as anything more than a prank. The group’s only realistic attempt to fool police was its Canadian-flag-marked vehicles. Other than that, the group used obviously fake credentials, and its security passes were printed with “JOKE,” “Insecurity,” and “It’s pretty obvious this isn’t a real pass,” all clearly visible to any police officer who might have been troubled to look closely as the motorcade passed. The required APEC 2007 official vehicle stickers had the name of the group’s show printed on them, and this text: “This dude likes trees and poetry and certain types of carnivorous plants excite him.” In addition, a few of the “bodyguards” were carrying camcorders, and one of the motorcyclists was dressed in jeans, both details that should have alerted police that something was amiss.

The Chaser pranksters later explained the primary reason for the stunt. They wanted to make a statement about the fact that bin Laden, a world leader, had not been invited to an APEC Summit where issues of terror were being discussed. The secondary motive was to test the event’s security. The show’s lawyers approved the stunt, under the assumption that the motorcade would be stopped at the APEC meeting.

The ability to detect and interpret the events that are occurring around us allows us to respond to these stimuli appropriately (Gibson & Pick, 2000). In most cases the system is successful, but as you can see from the above example, it is not perfect. In this chapter we will discuss the strengths and limitations of these capacities, focusing on both sensation awareness resulting from the stimulation of a sense organ — and perception the organization and interpretation of sensations. Sensation and perception work seamlessly together to allow us to experience the world through our eyes, ears, nose, tongue, and skin, but also to combine what we are currently learning from the environment with what we already know about it to make judgments and to choose appropriate behaviours.

The study of sensation and perception is exceedingly important for our everyday lives because the knowledge generated by psychologists is used in so many ways to help so many people. Psychologists work closely with mechanical and electrical engineers, with experts in defence and military contractors, and with clinical, health, and sports psychologists to help them apply this knowledge to their everyday practices. The research is used to help us understand and better prepare people to cope with such diverse events as driving cars, flying planes, creating robots, and managing pain (Fajen & Warren, 2003).

Photo 1: Kids playing hockey. Photo 2: Kids playing arcade games. Photo 3: A large bridge.
Figure 6.1 Sports psychologists, video game designers, and mechanical engineers use knowledge about sensation and perception to create and improve everyday objects and behaviours.

We will begin the chapter with a focus on the six senses of seeing, hearing, smelling, touching, tasting, and monitoring the body’s positions (proprioception). We will see that sensation is sometimes relatively direct, in the sense that the wide variety of stimuli around us inform and guide our behaviours quickly and accurately, but nevertheless is always the result of at least some interpretation. We do not directly experience stimuli, but rather we experience those stimuli as they are created by our senses. Each sense accomplishes the basic process of transduction the conversion of stimuli detected by receptor cells to electrical impulses that are then transported to the brain — in different, but related, ways.

After we have reviewed the basic processes of sensation, we will turn to the topic of perception, focusing on how the brain’s processing of sensory experience can not only help us make quick and accurate judgments, but also mislead us into making perceptual and judgmental errors, such as those that allowed the Chaser group to breach security at the APEC meeting.

Image Attributions

Figure 6.1: Caroline ouellette by Genevieve2 ( used under CC BY SA 3.0 license (; Arcade by Belinda Hankins Miller ( used under CC BY 2.0 license (; Niagara Bridge, Canada by Tony Hisgett (,_Canada.jpg) used under CC BY 2.0 license (


Fajen, B. R., & Warren, W. H. (2003). Behavioral dynamics of steering, obstacle avoidance, and route selection. Journal of Experimental Psychology: Human Perception and Performance, 29(2), 343–362.

Gibson, E. J., & Pick, A. D. (2000). An ecological approach to perceptual learning and development. New York, NY: Oxford University Press.


6.1 We Experience Our World through Sensation

Charles Stangor, Jennifer Walinga, and Lee Sanders

Learning Objectives

  1. Review and summarize the capacities and limitations of human sensation.
  2. Explain the difference between sensation and perception and describe how psychologists measure sensory and difference thresholds.

Sensory Thresholds: What Can We Experience?

Humans possess powerful sensory capacities that allow us to sense the kaleidoscope of sights, sounds, smells, and tastes that surround us. Our eyes detect light energy and our ears pick up sound waves. Our skin senses touch, pressure, hot, and cold. Our tongues react to the molecules of the foods we eat, and our noses detect scents in the air. The human perceptual system is wired for accuracy, and people are exceedingly good at making use of the wide variety of information available to them (Stoffregen & Bardy, 2001).

In many ways our senses are quite remarkable. The human eye can detect the equivalent of a single candle flame burning 30 miles away and can distinguish among more than 300,000 different colours. The human ear can detect sounds as low as 20 hertz (vibrations per second) and as high as 20,000 hertz, and it can hear the tick of a clock about 20 feet away in a quiet room. We can taste a teaspoon of sugar dissolved in two gallons of water, and we are able to smell one drop of perfume diffused in a three-room apartment. We can feel the wing of a bee on our cheek dropped from one centimeter above (Galanter, 1962).

Test your hearing

To get an idea of the range of sounds that the human ear can sense, test your hearing by watching the following video. Use headphones!

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Video: How Old Are Your Ears? (Hearing Test) []

Figure 6.2 Smell. The dog’s highly sensitive sense of smell is useful for searches of missing persons, explosives, foods, and drugs.

Although there is much that we do sense, there is even more that we do not. Dogs (Figure 6.2), bats, whales, and some rodents all have much better hearing than we do, and many animals have a far richer sense of smell. Birds are able to see the ultraviolet light that we cannot (see Figure 6.3, “Ultraviolet Light and Bird Vision”) and can also sense the pull of the earth’s magnetic field. Cats have an extremely sensitive and sophisticated sense of touch, and they are able to navigate in complete darkness using their whiskers. The fact that different organisms have different sensations is part of their evolutionary adaptation. Each species is adapted to sensing the things that are most important to them, while being blissfully unaware of the things that don’t matter.

We see a black bird while birds see a purple, green, and blue bird.
Figure 6.3 Ultraviolet Light and Bird Vision. Birds can see ultraviolet light; humans cannot. What looks like a black bird to us is in colour for a bird.

Measuring Sensation

Psychophysics is the branch of psychology that studies the effects of physical stimuli on sensory perceptions and mental states. The field of psychophysics was founded by the German psychologist Gustav Fechner (1801-1887), who was the first to study the relationship between the strength of a stimulus and a person’s ability to detect the stimulus.

The measurement techniques developed by Fechner and his colleagues are designed in part to help determine the limits of human sensation. One important criterion is the ability to detect very faint stimuli. The absolute threshold of a sensation is defined as the intensity of a stimulus that allows an organism to just barely detect it.

In a typical psychophysics experiment, an individual is presented with a series of trials in which a signal is sometimes presented and sometimes not, or in which two stimuli are presented that are either the same or different. Imagine, for instance, that you were asked to take a hearing test. On each of the trials your task is to indicate either “yes” if you heard a sound or “no” if you did not. The signals are purposefully made to be very faint, making accurate judgments difficult.

The problem for you is that the very faint signals create uncertainty. Because our ears are constantly sending background information to the brain, you will sometimes think that you heard a sound when none was there, and you will sometimes fail to detect a sound that is there. Your task is to determine whether the neural activity that you are experiencing is due to the background noise alone or is the result of a signal within the noise.

The responses that you give on the hearing test can be analyzed using signal detection analysis. Signal detection analysis is a technique used to determine the ability of the perceiver to separate true signals from background noise (Macmillan & Creelman, 2005; Wickens, 2002). As you can see in Figure 6.4, “Outcomes of a Signal Detection Analysis,” each judgment trial creates four possible outcomes: A hit occurs when you, as the listener, correctly say “yes” when there was a sound. A false alarm occurs when you respond “yes” to no signal. In the other two cases you respond “no” — either a miss (saying “no” when there was a signal) or a correct rejection (saying “no” when there was in fact no signal).

Figure 6.4 Outcomes of a Signal Detection Analysis. Our ability to accurately detect stimuli is measured using a signal detection analysis. Two of the possible decisions (hits and correct rejections) are accurate; the other two (misses and false alarms) are errors.

The analysis of the data from a psychophysics experiment creates two measures. One measure, known as sensitivity, refers to the true ability of the individual to detect the presence or absence of signals. People who have better hearing will have higher sensitivity than will those with poorer hearing. The other measure, response bias, refers to a behavioural tendency to respond “yes” to the trials, which is independent of sensitivity.

Imagine, for instance, that rather than taking a hearing test, you are a soldier on guard duty, and your job is to detect the very faint sound of the breaking of a branch that indicates that an enemy is nearby. You can see that in this case making a false alarm by alerting the other soldiers to the sound might not be as costly as a miss (a failure to report the sound), which could be deadly. Therefore, you might well adopt a very lenient response bias in which whenever you are at all unsure, you send a warning signal. In this case your responses may not be very accurate (your sensitivity may be low because you are making a lot of false alarms) and yet the extreme response bias can save lives.

Another application of signal detection occurs when medical technicians study body images for the presence of cancerous tumours. Again, a miss (in which the technician incorrectly determines that there is no tumour) can be very costly, but false alarms (referring patients who do not have tumours to further testing) also have costs. The ultimate decisions that the technicians make are based on the quality of the signal (clarity of the image), their experience and training (the ability to recognize certain shapes and textures of tumours), and their best guesses about the relative costs of misses versus false alarms.

Although we have focused to this point on the absolute threshold, a second important criterion concerns the ability to assess differences between stimuli. The difference threshold (or just noticeable difference [JND]), refers to the change in a stimulus that can just barely be detected by the organism. The German physiologist Ernst Weber (1795-1878) made an important discovery about the JND — namely, that the ability to detect differences depends not so much on the size of the difference but on the size of the difference in relation to the absolute size of the stimulus. Weber’s law maintains that the just noticeable difference of a stimulus is a constant proportion of the original intensity of the stimulus. As an example, if you have a cup of coffee that has only a very little bit of sugar in it (say one teaspoon), adding another teaspoon of sugar will make a big difference in taste. But if you added that same teaspoon to a cup of coffee that already had five teaspoons of sugar in it, then you probably wouldn’t taste the difference as much (in fact, according to Weber’s law, you would have to add five more teaspoons to make the same difference in taste).

One interesting application of Weber’s law is in our everyday shopping behaviour. Our tendency to perceive cost differences between products is dependent not only on the amount of money we will spend or save, but also on the amount of money saved relative to the price of the purchase. For example, if you were about to buy a soda or candy bar in a convenience store, and the price of the items ranged from $1 to $3, you would likely think that the $3 item cost “a lot more” than the $1 item. But now imagine that you were comparing between two music systems, one that cost $397 and one that cost $399. Probably you would think that the cost of the two systems was “about the same,” even though buying the cheaper one would still save you $2.

Research Focus: Influence without Awareness

If you study Figure 6.5, “Absolute Threshold,” you will see that the absolute threshold is the point where we become aware of a faint stimulus. After that point, we say that the stimulus is conscious because we can accurately report on its existence (or its nonexistence) more than 50% of the time. But can subliminal stimuli (events that occur below the absolute threshold and of which we are not conscious) have an influence on our behaviour?

Figure 6.5 Absolute Threshold. As the intensity of a stimulus increases, we are more likely to perceive it. Stimuli below the absolute threshold can still have at least some influence on us, even though we cannot consciously detect them.

A variety of research programs have found that subliminal stimuli can influence our judgments and behaviour, at least in the short term (Dijksterhuis, 2010). But whether the presentation of subliminal stimuli can influence the products that we buy has been a more controversial topic in psychology. In one relevant experiment, Karremans, Stroebe, and Claus (2006) had Dutch college students view a series of computer trials in which a string of letters such as BBBBBBBBB or BBBbBBBBB were presented on the screen. To be sure they paid attention to the display, the students were asked to note whether the strings contained a small b. However, immediately before each of the letter strings, the researchers presented either the name of a drink that is popular in Holland (Lipton Ice) or a control string containing the same letters as Lipton Ice (NpeicTol). These words were presented so quickly (for only about one-fiftieth of a second) that the participants could not see them.

Then the students were asked to indicate their intention to drink Lipton Ice by answering questions such as “If you would sit on a terrace now, how likely is it that you would order Lipton Ice,” and also to indicate how thirsty they were at the time. The researchers found that the students who had been exposed to the “Lipton Ice” words (and particularly those who indicated that they were already thirsty) were significantly more likely to say that they would drink Lipton Ice than were those who had been exposed to the control words.

If they were effective, procedures such as this (we can call the technique “subliminal advertising” because it advertises a product outside awareness) would have some major advantages for advertisers, because it would allow them to promote their products without directly interrupting the consumers’ activity and without the consumers’ knowing they are being persuaded. People cannot counterargue with, or attempt to avoid being influenced by, messages received outside awareness. Due to fears that people may be influenced without their knowing, subliminal advertising has been banned in many countries, including Australia, Canada, Great Britain, the United States, and Russia.

Although it has been proven to work in some research, subliminal advertising’s effectiveness is still uncertain. Charles Trappey (1996) conducted a meta-analysis in which he combined 23 leading research studies that had tested the influence of subliminal advertising on consumer choice. The results showed that subliminal advertising had a negligible effect on consumer choice. Saegert (1987, p. 107) concluded that “marketing should quit giving subliminal advertising the benefit of the doubt,” arguing that the influences of subliminal stimuli are usually so weak that they are normally overshadowed by the person’s own decision making about the behaviour.

Taken together then, the evidence for the effectiveness of subliminal advertising is weak, and its effects may be limited to only some people and in only some conditions. You probably don’t have to worry too much about being subliminally persuaded in your everyday life, even if subliminal ads are allowed in your country. But even if subliminal advertising is not all that effective itself, there are plenty of other indirect advertising techniques that are used and that do work. For instance, many ads for automobiles and alcoholic beverages are subtly sexualized, which encourages the consumer to indirectly (even if not subliminally) associate these products with sexuality. And there is the ever more frequent “product placement” technique, where images of brands (cars, sodas, electronics, and so forth) are placed on websites and in popular television shows and movies. Harris, Bargh, & Brownell (2009) found that being exposed to food advertising on television significantly increased child and adult snacking behaviours, again suggesting that the effects of perceived images, even if presented above the absolute threshold, may nevertheless be very subtle.

Another example of processing that occurs outside our awareness is seen when certain areas of the visual cortex are damaged, causing blindsight, a condition in which people are unable to consciously report on visual stimuli but nevertheless are able to accurately answer questions about what they are seeing. When people with blindsight are asked directly what stimuli look like, or to determine whether these stimuli are present at all, they cannot do so at better than chance levels. They report that they cannot see anything. However, when they are asked more indirect questions, they are able to give correct answers. For example, people with blindsight are able to correctly determine an object’s location and direction of movement, as well as identify simple geometrical forms and patterns (Weiskrantz, 1997). It seems that although conscious reports of the visual experiences are not possible, there is still a parallel and implicit process at work, enabling people to perceive certain aspects of the stimuli.


Key Takeaways

  • Sensation is the process of receiving information from the environment through our sensory organs. Perception is the process of interpreting and organizing the incoming information so that we can understand it and react accordingly.
  • Transduction is the conversion of stimuli detected by receptor cells to electrical impulses that are transported to the brain.
  • Although our experiences of the world are rich and complex, humans — like all species — have their own adapted sensory strengths and sensory limitations.
  • Sensation and perception work together in a fluid, continuous process.
  • Our judgments in detection tasks are influenced by both the absolute threshold of the signal as well as our current motivations and experiences. Signal detection analysis is used to differentiate sensitivity from response biases.
  • The difference threshold, or just noticeable difference, is the ability to detect the smallest change in a stimulus about 50% of the time. According to Weber’s law, the just noticeable difference increases in proportion to the total intensity of the stimulus.
  • Research has found that stimuli can influence behaviour even when they are presented below the absolute threshold (i.e., subliminally). The effectiveness of subliminal advertising, however, has not been shown to be of large magnitude.

Exercises and Critical Thinking

  1. Leaf through a magazine or watch several advertisements on television and pay attention to the persuasive techniques being used. What impact are these ads having on your senses? Based on what you know about psychophysics, sensation, and perception, what are some of the reasons why subliminal advertising might be banned in some countries?
  2. If we pick up two letters, one that weighs one ounce and one that weighs two ounces, we can notice the difference. But if we pick up two packages, one that weighs three pounds one ounce, and one that weighs three pounds two ounces, we can’t tell the difference. Why?
  3. Take a moment and lie down quietly in your bedroom. Notice the variety and levels of what you can see, hear, and feel. Does this experience help you understand the idea of the absolute threshold?

Image Attributions

Figure 6.2: Police officer with sniffer dog by Harald Dettenborn, used under CC BY 3.0 license(

Figure 6.3: Adapted from Fatal Light Awareness Program. (2008),


Dijksterhuis, A. (2010). Automaticity and the unconscious. In S. T. Fiske, D. T. Gilbert, & G. Lindzey (Eds.), Handbook of social psychology (5th ed., Vol. 1, pp. 228–267). Hoboken, NJ: John Wiley & Sons.

Galanter, E. (1962). Contemporary Psychophysics. In R. Brown, E. Galanter, E. H. Hess, & G. Mandler (Eds.), New directions in psychology. New York, NY: Holt, Rinehart and Winston.

Harris, J. L., Bargh, J. A., & Brownell, K. D. (2009). Priming effects of television food advertising on eating behavior. Health Psychology, 28(4), 404–413.

Karremans, J. C., Stroebe, W., & Claus, J. (2006). Beyond Vicary’s fantasies: The impact of subliminal priming and brand choice. Journal of Experimental Social Psychology, 42(6), 792–798.

Macmillan, N. A., & Creelman, C. D. (2005). Detection theory: A user’s guide (2nd ed). Mahwah, NJ: Lawrence Erlbaum Associates.

Saegert, J. (1987). Why marketing should quit giving subliminal advertising the benefit of the doubt. Psychology and Marketing, 4(2), 107–120.

Stoffregen, T. A., & Bardy, B. G. (2001). On specification and the senses. Behavioral and Brain Sciences, 24(2), 195–261.

Trappey, C. (1996). A meta-analysis of consumer choice and subliminal advertising. Psychology and Marketing, 13, 517–530.

Weiskrantz, L. (1997). Consciousness lost and found: A neuropsychological exploration. New York, NY: Oxford University Press.

Wickens, T. D. (2002). Elementary signal detection theory. New York, NY: Oxford University Press.


6.2 Seeing

Charles Stangor and Jennifer Walinga

Learning Objectives

  1. Identify the key structures of the eye and the role they play in vision.
  2. Summarize how the eye and the visual cortex work together to sense and perceive the visual stimuli in the environment, including processing colours, shape, depth, and motion.

Whereas other animals rely primarily on hearing, smell, or touch to understand the world around them, human beings rely in large part on vision. A large part of our cerebral cortex is devoted to seeing, and we have substantial visual skills. Seeing begins when light falls on the eyes, initiating the process of transduction. Once this visual information reaches the visual cortex, it is processed by a variety of neurons that detect colours, shapes, and motion, and that create meaningful perceptions out of the incoming stimuli.

The air around us is filled with a sea of electromagnetic energy: pulses of energy waves that can carry information from place to place. As you can see in Figure 6.6, “The Electromagnetic Spectrum,” electromagnetic waves vary in their wavelength the distance between one wave peak and the next wave peak — with the shortest gamma waves being only a fraction of a millimeter in length and the longest radio waves being hundreds of kilometers long. Humans are blind to almost all of this energy — our eyes detect only the range from about 400 to 700 billionths of a meter, the part of the electromagnetic spectrum known as the visible spectrum.

Figure 6.6 The Electromagnetic Spectrum

The Sensing Eye and the Perceiving Visual Cortex

As you can see in Figure 6.7, “Anatomy of the Human Eye,” light enters the eye through the cornea, a clear covering that protects the eye and begins to focus the incoming light. The light then passes through the pupil, a small opening in the centre of the eye. The pupil is surrounded by the iris, the coloured part of the eye that controls the size of the pupil by constricting or dilating in response to light intensity. When we enter a dark movie theatre on a sunny day, for instance, muscles in the iris open the pupil and allow more light to enter. Complete adaptation to the dark may take up to 20 minutes.

Behind the pupil is the lens, a structure that focuses the incoming light on the retina, the layer of tissue at the back of the eye that contains photoreceptor cells. As our eyes move from near objects to distant objects, a process known as visual accommodation occurs. Visual accommodation is the process of changing the curvature of the lens to keep the light entering the eye focused on the retina. Rays from the top of the image strike the bottom of the retina and vice versa, and rays from the left side of the image strike the right part of the retina and vice versa, causing the image on the retina to be upside down and backward. Furthermore, the image projected on the retina is flat, and yet our final perception of the image will be three dimensional.

Figure 6.7 Anatomy of the Human Eye. Light enters the eye through the transparent cornea, passing through the pupil at the centre of the iris. The lens adjusts to focus the light on the retina, where it appears upside down and backward. Receptor cells on the retina send information via the optic nerve to the visual cortex.

Accommodation is not always perfect (Figure 6.8) if the focus is in front of the retina, we say that the person is nearsighted, and when the focus is behind the retina, we say that the person is farsighted. Eyeglasses and contact lenses correct this problem by adding another lens in front of the eye, and laser eye surgery corrects the problem by reshaping the eye’s own lens.

Figure 6.8 Normal, Nearsighted, and Farsighted Eyes. For people with normal vision (left), the lens properly focuses incoming light on the retina. For people who are nearsighted (centre), images from far objects focus too far in front of the retina, whereas for people who are farsighted (right), images from near objects focus too far behind the retina. Eyeglasses solve the problem by adding a secondary, corrective lens.

The retina contains layers of neurons specialized to respond to light (see Figure 6.9, “The Retina with Its Specialized Cells”). As light falls on the retina, it first activates receptor cells known as rods and cones. The activation of these cells then spreads to the bipolar cells and then to the ganglion cells, which gather together and converge, like the strands of a rope, forming the optic nerve. The optic nerve is a collection of millions of ganglion neurons that sends vast amounts of visual information, via the thalamus, to the brain. Because the retina and the optic nerve are active processors and analyzers of visual information, it is appropriate to think of these structures as an extension of the brain itself.

Figure 6.9 The Retina with Its Specialized Cells. When light falls on the retina, it creates a photochemical reaction in the rods and cones at the back of the retina. The reactions then continue to the bipolar cells, the ganglion cells, and eventually to the optic nerve.

Rods are visual neurons that specialize in detecting black, white, and gray colours. There are about 120 million rods in each eye. The rods do not provide a lot of detail about the images we see, but because they are highly sensitive to shorter-waved (darker) and weak light, they help us see in dim light — for instance, at night. Because the rods are located primarily around the edges of the retina, they are particularly active in peripheral vision (when you need to see something at night, try looking away from what you want to see). Cones are visual neurons that are specialized in detecting fine detail and colours. The five million or so cones in each eye enable us to see in colour, but they operate best in bright light. The cones are located primarily in and around the fovea, which is the central point of the retina.

To demonstrate the difference between rods and cones in attention to detail, choose a word in this text and focus on it. Do you notice that the words a few inches to the side seem more blurred? This is because the word you are focusing on strikes the detail-oriented cones, while the words surrounding it strike the less-detail-oriented rods, which are located on the periphery.

Margaret Livingstone (2000) (Figure 6.10) found an interesting effect that demonstrates the different processing capacities of the eye’s rods and cones — namely, that the Mona Lisa’s smile, which is widely referred to as “elusive,” is perceived differently depending on how one looks at the painting. Because Leonardo da Vinci painted the smile in low-detail brush strokes, these details are better perceived by our peripheral vision (the rods) than by the cones. Livingstone found that people rated the Mona Lisa as more cheerful when they were instructed to focus on her eyes than they did when they were asked to look directly at her mouth. As Livingstone put it, “She smiles until you look at her mouth, and then it fades, like a dim star that disappears when you look directly at it.”

Figure 6.10 Mona Lisa’s Smile.

As you can see in Figure 6.11, “Pathway of Visual Images through the Thalamus and into the Visual Cortex,” the sensory information received by the retina is relayed through the thalamus to corresponding areas in the visual cortex, which is located in the occipital lobe at the back of the brain. Although the principle of contralateral control might lead you to expect that the left eye would send information to the right brain hemisphere and vice versa, nature is smarter than that. In fact, the left and right eyes each send information to both the left and the right hemisphere, and the visual cortex processes each of the cues separately and in parallel. This is an adaptational advantage to an organism that loses sight in one eye, because even if only one eye is functional, both hemispheres will still receive input from it.

Figure 6.11 Pathway of Visual Images through the Thalamus and into the Visual Cortex. The left and right eyes each send information to both the left and the right brain hemisphere.

The visual cortex is made up of specialized neurons that turn the sensations they receive from the optic nerve into meaningful images. Because there are no photoreceptor cells at the place where the optic nerve leaves the retina, a hole or blind spot in our vision is created (see Figure 6.12, “Blind Spot Demonstration”). When both of our eyes are open, we don’t experience a problem because our eyes are constantly moving, and one eye makes up for what the other eye misses. But the visual system is also designed to deal with this problem if only one eye is open — the visual cortex simply fills in the small hole in our vision with similar patterns from the surrounding areas, and we never notice the difference. The ability of the visual system to cope with the blind spot is another example of how sensation and perception work together to create meaningful experience.

Figure 6.12 Blind Spot Demonstration. You can get an idea of the extent of your blind spot (the place where the optic nerve leaves the retina) by trying this: close your left eye and stare with your right eye at the cross in the diagram. You should be able to see the elephant image to the right (don’t look at it, just notice that it is there). If you can’t see the elephant, move closer or farther away until you can. Now slowly move so that you are closer to the image while you keep looking at the cross. At one distance (probably a foot or so), the elephant will completely disappear from view because its image has fallen on the blind spot.

Perception is created in part through the simultaneous action of thousands of feature detector neurons specialized neurons, located in the visual cortex, that respond to the strength, angles, shapes, edges, and movements of a visual stimulus (Kelsey, 1997; Livingstone & Hubel, 1988). The feature detectors work in parallel, each performing a specialized function. When faced with a red square, for instance, the parallel line feature detectors, the horizontal line feature detectors, and the red colour feature detectors all become activated. This activation is then passed on to other parts of the visual cortex, where other neurons compare the information supplied by the feature detectors with images stored in memory. Suddenly, in a flash of recognition, the many neurons fire together, creating the single image of the red square that we experience (Rodriguez et al., 1999). See Figure 6.13 for an explanation about the Necker cube.

Figure 6.13 The Necker Cube. The Necker cube is an example of how the visual system creates perceptions out of sensations. We do not see a series of lines but, rather, a cube. Which cube we see varies depending on the momentary outcome of perceptual processes in the visual cortex.

Some feature detectors are tuned to selectively respond to particularly important objects, such as faces, smiles, and other parts of the body (Downing, Jiang, Shuman, & Kanwisher, 2001; Haxby et al., 2001). When researchers disrupted face recognition areas of the cortex using the magnetic pulses of transcranial magnetic stimulation (TMS), people were temporarily unable to recognize faces, and yet they were still able to recognize houses (McKone, Kanwisher, & Duchaine, 2007; Pitcher, Walsh, Yovel, & Duchaine, 2007).

Perceiving Colour

It has been estimated that the human visual system can detect and discriminate among seven million colour variations (Geldard, 1972), but these variations are all created by the combinations of the three primary colours: red, green, and blue. The shade of a colour, known as hue, is conveyed by the wavelength of the light that enters the eye (we see shorter wavelengths as more blue and longer wavelengths as more red), and we detect brightness from the intensity or height of the wave (bigger or more intense waves are perceived as brighter), as shown in Figure 6.14.

Figure 6.14 Low- and High-Frequency Sine Waves and Low- and High-Intensity Sine Waves and Their Corresponding Colours. Light waves with shorter frequencies are perceived as more blue than red; light waves with higher intensity are seen as brighter.

In his important research on colour vision, Hermann von Helmholtz (1821-1894) theorized that colour is perceived because the cones in the retina come in three types. One type of cone reacts primarily to blue light (short wavelengths), another reacts primarily to green light (medium wavelengths), and a third reacts primarily to red light (long wavelengths). The visual cortex then detects and compares the strength of the signals from each of the three types of cones, creating the experience of colour. According to this Young-Helmholtz trichromatic colour theory what colour we see depends on the mix of the signals from the three types of cones. If the brain is receiving primarily red and blue signals, for instance, it will perceive purple; if it is receiving primarily red and green signals it will perceive yellow; and if it is receiving messages from all three types of cones it will perceive white.

The different functions of the three types of cones are apparent in people who experience colour blindness the inability to detect green and/or red colours. About one in 50 people, mostly men, lack functioning in the red- or green-sensitive cones, leaving them only able to experience either one or two colours (Figure 6.15).

Figure 6.15 Colour Blindness. People with normal colour vision can see the number 42 in the first image and the number 12 in the second (they are vague but apparent). However, people who are colour blind cannot see the numbers at all.

The trichromatic colour theory cannot explain all of human vision, however. For one, although the colour purple does appear to us as a mix of red and blue, yellow does not appear to be a mix of red and green. And people with colour blindness, who cannot see either green or red, nevertheless can still see yellow. An alternative approach to the Young-Helmholtz theory, known as the opponent-process colour theory, proposes that we analyze sensory information not in terms of three colours but rather in three sets of “opponent colours”: red-green, yellow-blue, and white-black. Evidence for the opponent-process theory comes from the fact that some neurons in the retina and in the visual cortex are excited by one colour (e.g., red) but inhibited by another colour (e.g., green).

One example of opponent processing occurs in the experience of an afterimage. If you stare at the shape on the top left side of Figure 6.16, “Afterimages,” for about 30 seconds (the longer you look, the better the effect), and then move your eyes to the blank area to the right of it, you will see the afterimage. Now try this by staring at the image of the Italian flag below and then shifting your eyes to the blank area beside it. When we stare at the green stripe, our green receptors habituate and begin to process less strongly, whereas the red receptors remain at full strength. When we switch our gaze, we see primarily the red part of the opponent process. Similar processes create blue after yellow and white after black.

Figure 6.16 Afterimages.

The tricolour and the opponent-process mechanisms work together to produce colour vision. When light rays enter the eye, the red, blue, and green cones on the retina respond in different degrees and send different strength signals of red, blue, and green through the optic nerve. The colour signals are then processed both by the ganglion cells and by the neurons in the visual cortex (Gegenfurtner & Kiper, 2003).

Perceiving Form

One of the important processes required in vision is the perception of form. German psychologists in the 1930s and 1940s, including Max Wertheimer (1880-1943), Kurt Koffka (1886-1941), and Wolfgang Köhler (1887-1967), argued that we create forms out of their component sensations based on the idea of the gestalt, a meaningfully organized whole. The idea of the gestalt is that the “whole is more than the sum of its parts.” Some examples of how gestalt principles lead us to see more than what is actually there are summarized in Table 6.1, “Summary of Gestalt Principles of Form Perception.”

Table 6.1 Summary of Gestalt Principles of Form Perception.
Principle Description Example Image
Figure and ground We structure input so that we always see a figure (image) against a ground (background). At right, you may see a vase or you may see two faces, but in either case, you will organize the image as a figure against a ground.



Similarity Stimuli that are similar to each other tend to be grouped together. You are more likely to see three similar columns among the XYX characters at right than you are to see four rows.
Xs and Ys
Proximity We tend to group nearby figures together. Do you see four or eight images at right? Principles of proximity suggest that you might see only four.


Continuity We tend to perceive stimuli in smooth, continuous ways rather than in more discontinuous ways. At right, most people see a line of dots that moves from the lower left to the upper right, rather than a line that moves from the left and then suddenly turns down. The principle of continuity leads us to see most lines as following the smoothest possible path.
Closure We tend to fill in gaps in an incomplete image to create a complete, whole object. Closure leads us to see a single spherical object at right rather than a set of unrelated cones.

Perceiving Depth

Depth perception is the ability to perceive three-dimensional space and to accurately judge distance. Without depth perception, we would be unable to drive a car, thread a needle, or simply navigate our way around the supermarket (Howard & Rogers, 2001). Research has found that depth perception is in part based on innate capacities and in part learned through experience (Witherington, 2005).

Psychologists Eleanor Gibson and Richard Walk (1960) tested the ability to perceive depth in six- to 14-month-old infants by placing them on a visual cliff, a mechanism that gives the perception of a dangerous drop-off, in which infants can be safely tested for their perception of depth (Figure 6.17 “Visual Cliff”). The infants were placed on one side of the “cliff,” while their mothers called to them from the other side. Gibson and Walk found that most infants either crawled away from the cliff or remained on the board and cried because they wanted to go to their mothers, but the infants perceived a chasm that they instinctively could not cross. Further research has found that even very young children who cannot yet crawl are fearful of heights (Campos, Langer, & Krowitz, 1970). On the other hand, studies have also found that infants improve their hand-eye coordination as they learn to better grasp objects and as they gain more experience in crawling, indicating that depth perception is also learned (Adolph, 2000).

A baby on the edge of a table.
Figure 6.17 Visual Cliff. Babies appear to have the innate ability to perceive depth, as seen by this baby’s reluctance to cross the “visual cliff.”

Depth perception is the result of our use of depth cues, messages from our bodies and the external environment that supply us with information about space and distance. Binocular depth cues are depth cues that are created by retinal image disparity — that is, the space between our eyes — and which thus require the coordination of both eyes. One outcome of retinal disparity is that the images projected on each eye are slightly different from each other. The visual cortex automatically merges the two images into one, enabling us to perceive depth. Three-dimensional movies make use of retinal disparity by using 3-D glasses that the viewer wears to create a different image on each eye. The perceptual system quickly, easily, and unconsciously turns the disparity into 3-D.

An important binocular depth cue is convergence, the inward turning of our eyes that is required to focus on objects that are less than about 50 feet away from us. The visual cortex uses the size of the convergence angle between the eyes to judge the object’s distance. You will be able to feel your eyes converging if you slowly bring a finger closer to your nose while continuing to focus on it. When you close one eye, you no longer feel the tension — convergence is a binocular depth cue that requires both eyes to work.

The visual system also uses accommodation to help determine depth. As the lens changes its curvature to focus on distant or close objects, information relayed from the muscles attached to the lens helps us determine an object’s distance. Accommodation is only effective at short viewing distances, however, so while it comes in handy when threading a needle or tying shoelaces, it is far less effective when driving or playing sports.

Although the best cues to depth occur when both eyes work together, we are able to see depth even with one eye closed. Monocular depth cues are depth cues that help us perceive depth using only one eye (Sekuler & Blake, 2006). Some of the most important are summarized in Table 6.2, “Monocular Depth Cues That Help Us Judge Depth at a Distance.”

Table 6.2 Monocular Depth Cues That Help Us Judge Depth at a Distance.
Name Description Example Image
Position We tend to see objects higher up in our field of vision as farther away. The fence posts at right appear farther away not only because they become smaller but also because they appear higher up in the picture. Fences
Relative size Assuming that the objects in a scene are the same size, smaller objects are perceived as farther away. At right, the cars in the distance appear smaller than those nearer to us.
Traffic on a busy street
Linear perspective Parallel lines appear to converge at a distance. We know that the tracks at right are parallel. When they appear closer together, we determine they are farther away.
Train Tracks
Light and shadow The eye receives more reflected light from objects that are closer to us. Normally, light comes from above, so darker images are in shadow. We see the images at right as extending and indented according to their shadowing. If we invert the picture, the images will reverse.
Interposition When one object overlaps another object, we view it as closer. At right, because the blue star covers the pink bar, it is seen as closer than the yellow moon.
A yellow moon shape is behind a purple bar and a blue star shape is in front of the purple bar.
Aerial perspective Objects that appear hazy, or that are covered with smog or dust, appear farther away. The artist who painted the picture on the right used aerial perspective to make the clouds more hazy and thus appear farther away.
A sunset painting

Perceiving Motion

Many animals, including human beings, have very sophisticated perceptual skills that allow them to coordinate their own motion with the motion of moving objects in order to create a collision with that object. Bats and birds use this mechanism to catch up with prey, dogs use it to catch a Frisbee, and humans use it to catch a moving football. The brain detects motion partly from the changing size of an image on the retina (objects that look bigger are usually closer to us) and in part from the relative brightness of objects.

We also experience motion when objects near each other change their appearance. The beta effect refers to the perception of motion that occurs when different images are presented next to each other in succession (see “Beta Effect and Phi Phenomenon”). The visual cortex fills in the missing part of the motion and we see the object moving. The beta effect is used in movies to create the experience of motion. A related effect is the phi phenomenon, in which we perceive a sensation of motion caused by the appearance and disappearance of objects that are near each other. The phi phenomenon looks like a moving zone or cloud of background colour surrounding the flashing objects. The beta effect and the phi phenomenon are other examples of the importance of the gestalt — our tendency to “see more than the sum of the parts.”

Beta Effect and Phi Phenomenon

In the beta effect, our eyes detect motion from a series of still images, each with the object in a different place. This is the fundamental mechanism of motion pictures (movies). In the phi phenomenon, the perception of motion is based on the momentary hiding of an image.

Phi phenomenon:

Beta effect:


Key Takeaways

  • Vision is the process of detecting the electromagnetic energy that surrounds us. Only a small fraction of the electromagnetic spectrum is visible to humans.
  • The visual receptor cells on the retina detect shape, colour, motion, and depth.
  • Light enters the eye through the transparent cornea and passes through the pupil at the centre of the iris. The lens adjusts to focus the light on the retina, where it appears upside down and backward. Receptor cells on the retina are excited or inhibited by the light and send information to the visual cortex through the optic nerve.
  • The retina has two types of photoreceptor cells: rods, which detect brightness and respond to black and white, and cones, which respond to red, green, and blue. Colour blindness occurs when people lack function in the red- or green-sensitive cones.
  • Feature detector neurons in the visual cortex help us recognize objects, and some neurons respond selectively to faces and other body parts.
  • The Young-Helmholtz trichromatic colour theory proposes that colour perception is the result of the signals sent by the three types of cones, whereas the opponent-process colour theory proposes that we perceive colour as three sets of opponent colours: red-green, yellow-blue, and white-black.
  • The ability to perceive depth occurs as the result of binocular and monocular depth cues.
  • Motion is perceived as a function of the size and brightness of objects. The beta effect and the phi phenomenon are examples of perceived motion.

Exercises and Critical Thinking

  1. Consider some ways that the processes of visual perception help you engage in an everyday activity, such as driving a car or riding a bicycle.
  2. Imagine for a moment what your life would be like if you couldn’t see. Do you think you would be able to compensate for your loss of sight by using other senses?

Image Attributions

Figure 6.10: Mona Lisa detail face ( is in the public domain.

Figure 6.15: Ishihara Plate No.11 ( and Ishihara Plate No.23 ( is in the public domain.

Figure 6.16: Nachbild by Freddy2001 ( and Italian Flag Inverted by Pcessna ( is in the public domain.

Figure 6.17: Perception-Conception ( used with CC-BY-SA 3.0 (


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Campos, J. J., Langer, A., & Krowitz, A. (1970). Cardiac responses on the visual cliff in prelocomotor human infants. Science, 170(3954), 196–197.

Downing, P. E., Jiang, Y., Shuman, M., & Kanwisher, N. (2001). A cortical area selective for visual processing of the human body. Science, 293(5539), 2470–2473.

Gegenfurtner, K. R., & Kiper, D. C. (2003). Color vision. Annual Review of Neuroscience, 26, 181–206.

Geldard, F. A. (1972). The human senses (2nd ed.). New York, NY: John Wiley & Sons.

Gibson, E. J., & Walk, R. D. (1960). The “visual cliff.” Scientific American, 202(4), 64–71.

Haxby, J. V., Gobbini, M. I., Furey, M. L., Ishai, A., Schouten, J. L., & Pietrini, P. (2001). Distributed and overlapping representations of faces and objects in ventral temporal cortex. Science, 293(5539), 2425–2430.

Howard, I. P., & Rogers, B. J. (2001). Seeing in depth: Basic mechanisms (Vol. 1). Toronto, ON: Porteous.

Kelsey, C.A. (1997). Detection of visual information. In W. R. Hendee & P. N. T. Wells (Eds.), The perception of visual information (2nd ed.). New York, NY: Springer Verlag.

Livingstone, M., & Hubel, D. (1998). Segregation of form, color, movement, and depth: Anatomy, physiology, and perception. Science, 240, 740–749.

Livingstone M. S. (2000). Is it warm? Is it real? Or just low spatial frequency? Science, 290, 1299.

McKone, E., Kanwisher, N., & Duchaine, B. C. (2007). Can generic expertise explain special processing for faces? Trends in Cognitive Sciences, 11, 8–15.

Pitcher, D., Walsh, V., Yovel, G., & Duchaine, B. (2007). TMS evidence for the involvement of the right occipital face area in early face processing. Current Biology, 17, 1568–1573.

Rodriguez, E., George, N., Lachaux, J.-P., Martinerie, J., Renault, B., & Varela, F. J. (1999). Perception’s shadow: Long-distance synchronization of human brain activity. Nature, 397(6718), 430–433.

Sekuler, R., & Blake, R. (2006). Perception (5th ed.). New York, NY: McGraw-Hill.

Witherington, D. C. (2005). The development of prospective grasping control between 5 and 7 months: A longitudinal study. Infancy, 7(2), 143–161.


6.3 Hearing

Charles Stangor and Jennifer Walinga

Learning Objectives

  1. Draw a picture of the ear, label its key structures and functions, and describe the role they play in hearing.
  2. Describe the process of transduction in hearing.

Like vision and all the other senses, hearing begins with transduction. Sound waves that are collected by our ears are converted into neural impulses, which are sent to the brain where they are integrated with past experience and interpreted as the sounds we experience. The human ear is sensitive to a wide range of sounds, from the faint tick of a clock in a nearby room to the roar of a rock band at a nightclub, and we have the ability to detect very small variations in sound. But the ear is particularly sensitive to sounds in the same frequency as the human voice. A mother can pick out her child’s voice from a host of others, and when we pick up the phone we quickly recognize a familiar voice. In a fraction of a second, our auditory system receives the sound waves, transmits them to the auditory cortex, compares them to stored knowledge of other voices, and identifies the caller.

The Ear

Just as the eye detects light waves, the ear detects sound waves. Vibrating objects (such as the human vocal cords or guitar strings) cause air molecules to bump into each other and produce sound waves, which travel from their source as peaks and valleys, much like the ripples that expand outward when a stone is tossed into a pond. Unlike light waves, which can travel in a vacuum, sound waves are carried within media such as air, water, or metal, and it is the changes in pressure associated with these media that the ear detects.

As with light waves, we detect both the wavelength and the amplitude of sound waves. The wavelength of the sound wave (known as frequency) is measured in terms of the number of waves that arrive per second and determines our perception of pitch, the perceived frequency of a sound. Longer sound waves have lower frequency and produce a lower pitch, whereas shorter waves have higher frequency and a higher pitch.

The amplitude, or height of the sound wave, determines how much energy it contains and is perceived as loudness (the degree of sound volume). Larger waves are perceived as louder. Loudness is measured using the unit of relative loudness known as the decibel. Zero decibels represent the absolute threshold for human hearing, below which we cannot hear a sound. Each increase in 10 decibels represents a tenfold increase in the loudness of the sound (see Figure 6.18, “Sounds in Everyday Life”). The sound of a typical conversation (about 60 decibels) is 1,000 times louder than the sound of a faint whisper (30 decibels), whereas the sound of a jackhammer (130 decibels) is 10 billion times louder than the whisper.

Sounds in Everyday Life
Figure 6.18 Sounds in Everyday Life. The human ear can comfortably hear sounds up to 80 decibels. Prolonged exposure to sounds above 80 decibels can cause hearing loss. [Long Description]

Audition begins in the pinna, the external and visible part of the ear, which is shaped like a funnel to draw in sound waves and guide them into the auditory canal. At the end of the canal, the sound waves strike the tightly stretched, highly sensitive membrane known as the tympanic membrane (or eardrum), which vibrates with the waves. The resulting vibrations are relayed into the middle ear through three tiny bones, known as the ossicles — the hammer (or malleus), anvil (or incus), and stirrup (or stapes) — to the cochlea, a snail-shaped liquid-filled tube in the inner ear that contains the cilia. The vibrations cause the oval window, the membrane covering the opening of the cochlea, to vibrate, disturbing the fluid inside the cochlea (Figure 6.19).

The movements of the fluid in the cochlea bend the hair cells of the inner ear, in much the same way that a gust of wind bends over wheat stalks in a field. The movements of the hair cells trigger nerve impulses in the attached neurons, which are sent to the auditory nerve and then to the auditory cortex in the brain. The cochlea contains about 16,000 hair cells, each of which holds a bundle of fibres known as cilia on its tip. The cilia are so sensitive that they can detect a movement that pushes them the width of a single atom. To put things in perspective, cilia swaying the width of an atom is equivalent to the tip of the Eiffel Tower swaying half an inch (Corey et al., 2004).

Figure 6.19 The Human Ear. Sound waves enter the outer ear and are transmitted through the auditory canal to the eardrum. The resulting vibrations are moved by the three small ossicles into the cochlea, where they are detected by hair cells and sent to the auditory nerve.

Although loudness is directly determined by the number of hair cells that are vibrating, two different mechanisms are used to detect pitch. The frequency theory of hearing proposes that whatever the pitch of a sound wave, nerve impulses of a corresponding frequency will be sent to the auditory nerve. For example, a tone measuring 600 hertz will be transduced into 600 nerve impulses a second. This theory has a problem with high-pitched sounds, however, because the neurons cannot fire fast enough. To reach the necessary speed, the neurons work together in a sort of volley system in which different neurons fire in sequence, allowing us to detect sounds up to about 4,000 hertz.

Not only is frequency important, but location is critical as well. The cochlea relays information about the specific area, or place, in the cochlea that is most activated by the incoming sound. The place theory of hearing proposes that different areas of the cochlea respond to different frequencies. Higher tones excite areas closest to the opening of the cochlea (near the oval window). Lower tones excite areas near the narrow tip of the cochlea, at the opposite end. Pitch is therefore determined in part by the area of the cochlea firing the most frequently.

Just as having two eyes in slightly different positions allows us to perceive depth, so the fact that the ears are placed on either side of the head enables us to benefit from stereophonic, or three-dimensional, hearing. If a sound occurs on your left side, the left ear will receive the sound slightly sooner than the right ear, and the sound it receives will be more intense, allowing you to quickly determine the location of the sound. Although the distance between our two ears is only about six inches, and sound waves travel at 750 miles an hour, the time and intensity differences are easily detected (Middlebrooks & Green, 1991). When a sound is equidistant from both ears, such as when it is directly in front, behind, beneath, or overhead, we have more difficulty pinpointing its location. It is for this reason that dogs (and people, too) tend to cock their heads when trying to pinpoint a sound, so that the ears receive slightly different signals.

Hearing Loss

In 2006, 1,266,120 (5.0%) Canadians aged 15 and older reported having a hearing limitation. Over eight in 10 (83.2%) hearing limitations were mild in nature, while the remaining 16.8% were classified as severe (Statistics Canada, 2006). Conductive hearing loss is caused by physical damage to the ear (such as to the eardrums or ossicles) that reduces the ability of the ear to transfer vibrations from the outer ear to the inner ear. Sensorineural hearing loss, which is caused by damage to the cilia or to the auditory nerve, is less common overall but frequently occurs with age (Tennesen, 2007). The cilia are extremely fragile, and by the time we are 65 years old, we will have lost 40% of them, particularly those that respond to high-pitched sounds (Chisolm, Willott, & Lister, 2003).

Prolonged exposure to loud sounds will eventually create sensorineural hearing loss as the cilia are damaged by the noise. People who constantly operate noisy machinery without using appropriate ear protection are at high risk of hearing loss, as are people who listen to loud music on their headphones or who engage in noisy hobbies, such as hunting or motorcycling. Sounds that are 85 decibels or more can cause damage to your hearing, particularly if you are exposed to them repeatedly. Sounds of more than 130 decibels are dangerous even if you are exposed to them infrequently. People who experience tinnitus (a ringing or a buzzing sensation) after being exposed to loud sounds have very likely experienced some damage to their cilia. Taking precautions when being exposed to loud sounds is important, as cilia do not grow back.

While conductive hearing loss can often be improved through hearing aids that amplify the sound, they are of little help to sensorineural hearing loss. But if the auditory nerve is still intact, a cochlear implant may be used. A cochlear implant is a device made up of a series of electrodes that are placed inside the cochlea. The device serves to bypass the hair cells by stimulating the auditory nerve cells directly. The latest implants utilize place theory, enabling different spots on the implant to respond to different levels of pitch. The cochlear implant can help children who would normally be deaf hear. If the device is implanted early enough, these children can frequently learn to speak, often as well as children born without hearing loss do (Dettman, Pinder, Briggs, Dowell, & Leigh, 2007; Dorman & Wilson, 2004).


Key Takeaways

  • Sound waves vibrating through media such as air, water, or metal are the stimulus energy that is sensed by the ear.
  • The hearing system is designed to assess frequency (pitch) and amplitude (loudness).
  • Sound waves enter the outer ear (the pinna) and are sent to the eardrum via the auditory canal. The resulting vibrations are relayed by the three ossicles, causing the oval window covering the cochlea to vibrate. The vibrations are detected by the cilia (hair cells) and sent via the auditory nerve to the auditory cortex.
  • There are two theories as to how we perceive pitch: The frequency theory of hearing suggests that as a sound wave’s pitch changes, nerve impulses of a corresponding frequency enter the auditory nerve. The place theory of hearing suggests that we hear different pitches because different areas of the cochlea respond to higher and lower pitches.
  • Conductive hearing loss is caused by physical damage to the ear or eardrum and may be improved by hearing aids or cochlear implants. Sensorineural hearing loss, caused by damage to the hair cells or auditory nerves in the inner ear, may be produced by prolonged exposure to sounds of more than 85 decibels.

Exercise and Critical Thinking

  1. Given what you have learned about hearing in this chapter, are you engaging in any activities that might cause long-term hearing loss? If so, how might you change your behaviour to reduce the likelihood of suffering damage?


Chisolm, T. H., Willott, J. F., & Lister, J. J. (2003). The aging auditory system: Anatomic and physiologic changes and implications for rehabilitation. International Journal of Audiology, 42(Suppl. 2), 2S3–2S10.

Corey, D. P., García-Añoveros, J., Holt, J. R., Kwan, K. Y., Lin, S.-Y., Vollrath, M. A., Amalfitano, A.,…Zhang, D.-S. (2004). TRPA1 is a candidate for the mechano-sensitive transduction channel of vertebrate hair cells. Nature, 432, 723–730. Retrieved from

Dettman, S. J., Pinder, D., Briggs, R. J. S., Dowell, R. C., & Leigh, J. R. (2007). Communication development in children who receive the cochlear implant younger than 12 months: Risk versus benefits. Ear and Hearing, 28(2, Suppl.), 11S–18S.

Dorman, M. F., & Wilson, B. S. (2004). The design and function of cochlear implants. American Scientist, 92, 436–445.

Middlebrooks, J. C., & Green, D. M. (1991). Sound localization by human listeners. Annual Review of Psychology, 42, 135–159.

Statistics Canada. (2006). Participation and activity limitation survey, 2006. Retrieved June 2014 from

Tennesen, M. (2007, March 10). Gone today, hear tomorrow. New Scientist, 2594, 42–45.

Long Description

Figure 6.18 long description: Levels of Noise

Decibels (dB) Description Examples
140 Painful and dangerous, use hearing protection or avoid. Fireworks, gunshots, custom car stereos (at full volume)
130 Painful and dangerous, use hearing protection or avoid. Jackhammers, ambulances
120 Uncomfortable, dangerous over 30 seconds Jet planes (during takeoff)
110 Very loud, dangerous over 30 seconds Concerts, car horns, sporting events
100 Very loud, dangerous over 30 seconds Snowmobiles, MP3 players (at full volume)
90 Very loud, dangerous over 30 seconds Lawnmowers, power tools, blenders, hair dryers
 85 Over 85 dB for extended periods can cause permanent hearing loss.
80 Loud Alarm clocks
70 Loud Traffic, vacuum cleaners
60 Moderate Normal conversation, dishwashers
50 Moderate Moderate raindall
40 Soft Quiet library
20 Faint Leaves rustling



6.4 Tasting, Smelling, and Touching

Charles Stangor and Jennifer Walinga

Learning Objectives

  1. Summarize how the senses of taste and olfaction transduce stimuli into perceptions.
  2. Describe the process of transduction in the senses of touch and proprioception.
  3. Outline the gate control theory of pain. Explain why pain matters and how it may be controlled.

Although vision and hearing are by far the most important senses, human sensation is rounded out by four others, each of which provides an essential avenue to a better understanding of and response to the world around us. These other senses are touch, taste, and smell, and our sense of body position and movement (proprioception).


Taste is important not only because it allows us to enjoy the food we eat, but, even more crucial, because it leads us toward foods that provide energy (sugar, for instance) and away from foods that could be harmful. Many children are picky eaters for a reason — they are biologically predisposed to be very careful about what they eat. Together with the sense of smell, taste helps us maintain appetite, assess potential dangers (such as the odour of a gas leak or a burning house), and avoid eating poisonous or spoiled food.

Our ability to taste begins at the taste receptors on the tongue. The tongue detects six different taste sensations, known respectively as sweet, salty, sour, bitter, piquancy (spicy), and umami (savory). Umami is a meaty taste associated with meats, cheeses, soy, seaweed, and mushrooms, and is particularly found in monosodium glutamate (MSG), a popular flavour enhancer (Ikeda, 1909/2002; Sugimoto & Ninomiya, 2005).

Our tongues are covered with taste buds, which are designed to sense chemicals in the mouth. Most taste buds are located in the top outer edges of the tongue, but there are also receptors at the back of the tongue as well as on the walls of the mouth and at the back of the throat. As we chew food, it dissolves and enters the taste buds, triggering nerve impulses that are transmitted to the brain (Northcutt, 2004). Human tongues are covered with 2,000 to 10,000 taste buds, and each bud contains between 50 and 100 taste receptor cells. Taste buds are activated very quickly; a salty or sweet taste that touches a taste bud for even one-tenth of a second will trigger a neural impulse (Kelling & Halpern, 1983). On average, taste buds live for about five days, after which new taste buds are created to replace them. As we get older, however, the rate of creation decreases, making us less sensitive to taste. This change helps explain why some foods that seem so unpleasant in childhood are more enjoyable in adulthood.

The area of the sensory cortex that responds to taste is in a very similar location to the area that responds to smell, a fact that helps explain why the sense of smell also contributes to our experience of the things we eat. You may remember having had difficulty tasting food when you had a bad cold, and if you block your nose and taste slices of raw potato, apple, and parsnip, you will not be able to taste the differences between them. Our experience of texture in a food (the way we feel it on our tongues) also influences how we taste it.


As we breathe in air through our nostrils, we inhale airborne chemical molecules, which are detected by the 10 million to 20 million receptor cells embedded in the olfactory membrane of the upper nasal passage. The olfactory receptor cells are topped with tentacle-like protrusions that contain receptor proteins. When an odour receptor is stimulated, the membrane sends neural messages up the olfactory nerve to the brain (see Figure 6.20. “Smell Receptors”).

Figure 6.20 Smell Receptors. There are more than 1,000 types of odour receptor cells in the olfactory membrane.

We have approximately 1,000 types of odour receptor cells (Bensafi et al., 2004), and it is estimated that we can detect 10,000 different odours (Malnic, Hirono, Sato, & Buck, 1999). The receptors come in many different shapes and respond selectively to different smells. Like a lock and key, different chemical molecules fit into different receptor cells, and odours are detected according to their influence on a combination of receptor cells. Just as the 10 digits from 0 to 9 can combine in many different ways to produce an endless array of phone numbers, odour molecules bind to different combinations of receptors, and these combinations are decoded in the olfactory cortex. As you can see in Figure 6.21, “Age Differences in Smell,” the sense of smell peaks in early adulthood and then begins a slow decline. By ages 60 to 70, the sense of smell has become sharply diminished. In addition, women tend to have a more acute sense of smell than men.

A scatter plot showing a declining ability to identify common odours as people age.
Figure 6.21 Age Differences in Smell. The ability to identify common odourants declines markedly between 20 and 70 years of age.


The sense of touch is essential to human development. Infants thrive when they are cuddled and attended to, but not if they are deprived of human contact (Baysinger, Plubell, & Harlow, 1973; Feldman, 2007; Haradon, Bascom, Dragomir, & Scripcaru, 1994). Touch communicates warmth, caring, and support, and is an essential part of the enjoyment we gain from our social interactions with close others (Field et al., 1997; Keltner, 2009).

The skin, the largest organ in the body, is the sensory organ for touch. The skin contains a variety of nerve endings, combinations of which respond to particular types of pressures and temperatures. When you touch different parts of the body, you will find that some areas are more ticklish, whereas other areas respond more to pain, cold, or heat.

The thousands of nerve endings in the skin respond to four basic sensations — pressure, hot, cold, and pain — but only the sensation of pressure has its own specialized receptors. Other sensations are created by a combination of the other four. For instance:

The skin is important not only in providing information about touch and temperature, but also in proprioception the ability to sense the position and movement of our body parts. Proprioception is accomplished by specialized neurons located in the skin, joints, bones, ears, and tendons, which send messages about the compression and the contraction of muscles throughout the body. Without this feedback from our bones and muscles, we would be unable to play sports, walk, or even stand upright.

The ability to keep track of where the body is moving is also provided by the vestibular system, a set of liquid-filled areas in the inner ear that monitors the head’s position and movement, maintaining the body’s balance. As you can see in Figure 6.22, “The Vestibular System,” the vestibular system includes the semicircular canals and the vestibular sacs. These sacs connect the canals with the cochlea. The semicircular canals sense the rotational movements of the body, and the vestibular sacs sense linear accelerations. The vestibular system sends signals to the neural structures that control eye movement and to the muscles that keep the body upright.

Figure 6.22 The Vestibular System. The vestibular system includes the semicircular canals (brown) that transduce the rotational movements of the body, and the vestibular sacs (blue) that sense linear accelerations.

Experiencing Pain

We do not enjoy it, but the experience of pain is how the body informs us that we are in danger. The burn when we touch a hot radiator and the sharp stab when we step on a nail lead us to change our behaviour, preventing further damage to our bodies. People who cannot experience pain are in serious danger of damage from wounds that others with pain would quickly notice and attend to.

The gate control theory of pain proposes that pain is determined by the operation of two types of nerve fibres in the spinal cord. One set of smaller nerve fibres carries pain from the body to the brain, whereas a second set of larger fibres is designed to stop or start (as a gate would) the flow of pain (Melzack & Wall, 1996). It is for this reason that massaging an area where you feel pain may help alleviate it — the massage activates the large nerve fibres that block the pain signals of the small nerve fibres (Wall, 2000).

Experiencing pain is a lot more complicated than simply responding to neural messages, however. It is also a matter of perception. We feel pain less when we are busy focusing on a challenging activity (Bantick et al., 2002), which can help explain why sports players may feel their injuries only after the game. We also fee