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Global edition Forty Studies that Changed Psychology Explorations into the History of Psychological Research SeventH edition Roger R. Hock

FORTY STUDIES THAT CHANGED P SYC H O LO G Y

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FORTY STUDIES THAT CHANGED P SYC H O LO G Y Explorations into the History of Psychological Research Global Edition Seventh Edition Roger R. Hock, Ph.D. Mendocino College Boston Columbus Indianapolis New York San Francisco Upper Saddle River Amsterdam Cape Town Dubai London Madrid Milan Munich Paris Montréal Toronto Delhi Mexico City São Paulo Sydney Hong Kong Seoul Singapore Taipei Tokyo

Editorial Director: Craig Campanella Director of Marketing: Brandy Dawson Editor in Chief: Jessica Mosher Managing Editor: Denise Forlow Head of Learning Asset Acquisition, Senior Project Manager/Liaison: Harriet Tellem Operations Specialist: Diane Peirano Global Edition: Laura Dent Senior Manufacturing and Operations Executive Acquisitions Editor: Stephen Frail Editorial Assistant: Madelyn Schricker Manager for Arts & Sciences: Mary Fischer Acquisitions Editor, Global Edition: Cover Designer: Lumina Datamatics Cover Photo: © Alexey Losevich/Shutterstock Vrinda Malik Full-Service Project Management: Project Editor, Global Edition: Daniel Luiz Media Producer, Global Edition: GEX Publishing Services M. Vikram Kumar Senior Manufacturing Controller, Production, Global Edition: Trudy Kimber Pearson Education Limited Edinburgh Gate Harlow Essex CM20 2JE England and Associated Companies throughout the world Visit us on the World Wide Web at: www.pearsonglobaleditions.com © Pearson Education Limited 2015 The rights of Roger R. Hock to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988. Authorized adaptation from the United States edition, entitled Forty Studies That Changed Psychology: Explorations into the History of Psychological Research, 7th edition, ISBN 978-0-205-91839-3, by Roger R. Hock, published by Pearson Education © 2013. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without either the prior written permission of the publisher or a license permitting restricted copying in the United Kingdom issued by the Copyright Licensing Agency Ltd, Saffron House, 6–10 Kirby Street, London EC1N 8TS. All trademarks used herein are the property of their respective owners. The use of any trade- mark in this text does not vest in the author or publisher any trademark ownership rights in such trademarks, nor does the use of such trademarks imply any affiliation with or endorsement of this book by such owners. ISBN 10: 1-292-07096-X ISBN 13: 978-1-292-07096-4 (Print) ISBN 13: 978-1-292-07097-1 (PDF) British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library 14 13 12 11 10 9 8 7 6 5 4 3 2 1 Typeset in New Baskerville Std Roman by GEX Publishing Services. Printed and bound by Courier Westford in The United States of America.

For Diane Perin Hock and Caroline Mei Perin Hock

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CONTENTS Preface 11 CHAPTER I THE BIOLOGICAL BASIS OF HUmAN BEHAvIOR 19 reading 1: One Brain Or TwO? 19 Gazzaniga, M. S. (1967). The split brain in man. Scientific American, 217(2), 24–29. reading 2: MOre exPerience = Bigger Brain 30 Rosenzweig, M. R., Bennett, E. L., & Diamond, M. C. (1972). Brain changes in response to experience. Scientific American, 226(2), 22–29. reading 3: are YOu a “naTural”? 37 Bouchard, T., Lykken, D., McGue, M., Segal, N., & Tellegen, A. (1990). Sources of human psychological differences: The Minnesota study of twins reared apart. Science, 250, 223–229. reading 4: waTch OuT fOr The Visual cliff! 45 Gibson, E. J., & Walk, R. D. (1960). The “visual cliff.” Scientific American, 202(4), 67–71. CHAPTER II CONSCIOUSNESS AND THE SENSES 53 reading 5: Take a lOng lOOk 54 Fantz, R. L. (1961). The origin of form perception. Scientific American, 204, 61–72. reading 6: TO sleeP, nO dOuBT TO dreaM . . . 60 Aserinsky, E., & Kleitman, N. (1953). Regularly occurring periods of eye mobility and concomitant phenomena during sleep. Science, 118, 273–274. Dement, W. (1960). The effect of dream deprivation. Science, 131, 1705–1707. reading 7: as a caTegOrY, iT’s a naTural 67 Rosch, Eleanor H. (1973). Natural categories. Cognitive Psychology, 4, 328–350. reading 8: acTing as if YOu are hYPnOTized 75 Spanos, N. P. (1982). Hypnotic behavior: A cognitive, social, psychological perspective. Research Communications in Psychology, Psychiatry, and Behavior, 7, 199–213. 7

8 Contents CHAPTER III CONDITIONING AND LEARNING 83 reading 9: iT’s nOT JusT aBOuT saliVaTing dOgs! 83 Pavlov, I. P. (1927). Conditioned reflexes. London: Oxford University Press. reading 10: liTTle eMOTiOnal alBerT 90 Watson, J. B., & Rayner, R. (1920). Conditioned emotional responses. Journal of Experimental Psychology, 3, 1–14. reading 11: knOck wOOd! 96 Skinner, B. F. (1948). Superstition in the pigeon. Journal of Experimental Psychology, 38, 168–172. reading 12: see aggressiOn . . . dO aggressiOn! 103 Bandura, A., Ross, D., & Ross, S. A. (1961). Transmission of aggression through imitation of aggressive models. Journal of Abnormal and Social Psychology, 63, 575–582. CHAPTER Iv COGNITION, mEmORY, AND INTELLIGENCE 111 reading 13: whaT YOu exPecT is whaT YOu geT 111 Rosenthal, R., & Jacobson, L. (1966). Teachers’ expectancies: Determinates of pupils’ IQ gains. Psychological Reports, 19, 115–118. reading 14: JusT How are YOu inTelligenT? 118 Gardner, H. (1983) Frames of mind: The theory of multiple intelligences. New York: Basic Books. reading 15: MaPs in YOur Mind 128 Tolman, E. C. (1948). Cognitive maps in rats and men. Psychological Review, 55, 189–208. reading 16: Thanks fOr The MeMOries! 135 Loftus, E. F. (1975). Leading questions and the eyewitness report. Cognitive Psychology, 7, 560–572. CHAPTER v CHANGES OvER THE HUmAN LIFESPAN 144 reading 17: discOVering lOVe 144 Harlow, H. F. (1958). The nature of love. American Psychologist, 13, 673–685. reading 18: OuT Of sighT, BuT Not OuT Of Mind 152 Piaget, J. (1954). The development of object concept. In J. Piaget, The construction of reality in the child (pp. 3–96). New York: Basic Books. reading 19: hOw MOral are YOu? 161 Kohlberg, L. (1963). The development of children’s orientations toward a moral order: Sequence in the development of moral thought. Vita Humana, 6, 11–33. reading 20: in cOnTrOl and glad Of iT! 168 Langer, E. J., & Rodin, J. (1976). The effects of choice and enhanced personal responsibility for the aged: A field experiment in an institutional setting. Journal of Personality and Social Psychology, 34, 191–198.

Contents 9 CHAPTER vI mOTIvATION AND EmOTION 176 reading 21: a sexual MOTiVaTiOn 176 Masters, W. H., & Johnson, V. E. (1966). Human sexual response. Boston: Little, Brown. reading 22: i can see iT all OVer YOur face! 186 Ekman, P., & Friesen, W. V. (1971). Constants across cultures in the face and emotion. Journal of Personality and Social Psychology, 17, 124–129. reading 23: watcHiNg YOur eMOTiOns? 193 Ross, P. (2003). Mind readers. Scientific American, 289(3), 74–77. reading 24: ThOughTs OuT Of Tune 199 Festinger, L., & Carlsmith, J. M. (1959). Cognitive consequences of forced compliance. Journal of Abnormal and Social Psychology, 58, 203–210. CHAPTER vII PERSONALITY 207 reading 25: are YOu The MasTer Of YOur faTe? 208 Rotter, J. B. (1966). Generalized expectancies for internal versus external control of reinforcement. Psychological Monographs, 80, 1–28. reading 26: Masculine Or feMinine . . . Or BOTh? 216 Bem, S. L. (1974). The measurement of psychological androgyny. Journal of Consulting and Clinical Psychology, 42, 155–162. reading 27: racing againsT YOur hearT 226 Friedman, M., & Rosenman, R. H. (1959). Association of specific overt behavior pattern with blood and cardiovascular findings. Journal of the American Medical Association, 169, 1286–1296. reading 28: The One, The ManY 233 Triandis, H., Bontempo, R., Villareal, M., Asai, M., & Lucca, N. (1988). Individualism and collectivism: Cross-cultural perspectives on self-ingroup relationships. Journal of Personality and Social Psychology, 54, 323–338. CHAPTER vIII PSYCHOLOGICAL DISORDERS 243 reading 29: whO’s crazY here, anYwaY? 243 Rosenhan, D. L. (1973). On being sane in insane places. Science, 179, 250–258. reading 30: YOu’re geTTing defensiVe again! 251 Freud, A. (1946). The ego and the mechanisms of defense. New York: International Universities Press. reading 31: learning TO Be dePressed 258 Seligman, M. E. P., & Maier, S. F. (1967). Failure to escape traumatic shock. Journal of Experimental Psychology, 74, 1–9. reading 32: crOwding inTO The BehaViOral sink 265 Calhoun, J. B. (1962). Population density and social pathology. Scientific American, 206(3), 139–148.

10 Contents CHAPTER IX THERAPY 274 reading 33: chOOsing YOur PsYchOTheraPisT 274 Smith, M. L., & Glass, G. V. (1977). Meta-analysis of psychotherapy outcome studies. American Psychologist, 32, 752–760. reading 34: relaxing YOur fears awaY 280 Wolpe, J. (1961). The systematic desensitization treatment of neuroses. Journal of Nervous and Mental Diseases, 132, 180–203. reading 35: PrOJecTiOns Of whO YOu are 287 Rorschach, H. (1942). Psychodiagnostics: A diagnostic test based on perception. New York: Grune & Stratton. reading 36: PicTure This! 294 Murray, H. A. (1938). Explorations in personality (pp. 531–545). New York: Oxford University Press. CHAPTER X HUmAN INTERACTION AND SOCIAL BEHAvIOR 302 reading 37: a PrisOn BY anY OTher naMe . . . 303 Zimbardo, P. G. (1972). The pathology of imprisonment. Society, 9(6), 4–8. Haney, C., Banks, W. C., & Zimbardo, P. G. (1973). Interpersonal dynamics in a simulated prison. International Journal of Criminology & Penology, 1, 69–97. reading 38: The POwer Of cOnfOrMiTY 310 Asch, S. E. (1955). Opinions and social pressure. Scientific American, 193(5), 31–35. reading 39: TO helP Or nOT TO helP 315 Darley, J. M., & Latané, B. (1968). Bystander intervention in emergencies: Diffusion of responsibility. Journal of Personality and Social Psychology, 8, 377–383. reading 40: OBeY aT anY cOsT? 324 Milgram, S. (1963). Behavioral study of obedience. Journal of Abnormal and Social Psychology, 67, 371–378. auThOr index 334 suBJecT index 339

PREFACE Welcome to the seventh edition of Forty Studies that Changed Psychology. For over 20 years this book has been a mainstay for many college and high school courses around the world and has been translated into six languages. The majority of the studies included in this edition are the same ones that made up a large part of the first edition. This demonstrates how these land- mark studies continue today to exert their influence over psychological thought and research. These original studies and the ones that have been added or changed over the years provide a fascinating glimpse into the birth and growth of the science of psychology, and into the insights we have acquired trying to unravel the complexities of human nature. Many studies of human behavior have made remarkable and lasting impacts on the various disciplines that comprise the vast field of psychology. The findings generated from this research have changed our knowledge of human behavior, and they have set the stage for countless subsequent projects and research programs. Even when the results of some of these pivotal studies have later been drawn into controversy and question, their effect and influence in a historical context never diminish. They continue to be cited in new articles; they continue to be the topic of academic discussion, they continue to form the foundation for hundreds of textbook chapters, and they continue to hold a special place in the minds of psychologists. The concept for this book originated from my three decades of teaching psychology. Most psychology textbooks are based on key studies that have shaped the science of psychology over its relatively brief history. Textbooks, however, seldom give the original, core studies the attention they richly deserve. The original research processes and findings often are summarized and diluted to the point that little of the life and excitement of the discoveries remain. Sometimes, research results are reported in ways that may even mislead the reader about the study’s real impact and influence about what we know and how we know it. This is in no way a criticism of the textbook writers who work under length constraints and must make many difficult choices about what gets included and in how much detail. The situation is, however, unfortunate because the foundation of all of modern psychology is scientific research, and through over a century of ingenious and elegant studies, our knowledge and understanding of human behavior have been expanded and refined to the advanced level of sophistication that exists today. This book is an attempt to fill the gap between all those psychology text- books and the research that made them possible. It is a journey through the headline history of psychology. My hope is that the way the 40 chosen studies are 11

12 Preface presented will bring every one of them back to life so that you can experience them for yourself. This book is intended for anyone, in any course, who wishes a greater understanding of the true roots of psychology. CHOOSING THE STUDIES The studies included in this book have been carefully chosen from those found in psychology texts and journals and from those suggested by leading authori- ties in the many branches of psychology. As the studies were selected, 40 seemed to be a realistic number both from a historical point of view and in terms of length. The studies chosen are arguably among the most famous, the most important, or the most influential in the history of psychology. I use the word arguably because many who read this book may wish to dispute some of the choices. One thing is sure: No single list of 40 studies would satisfy everyone. However, the studies included here stirred up a great deal of controversy when they were published, sparked the most subsequent related research, opened new fields of psychological exploration, changed dramatically our knowledge of human behavior, and continue to be cited frequently. These studies are organized by chapter according to the major psychology branches into which they best fit: The Biological Basis of Human Behavior; Consciousness and the Senses; Conditioning and Learning; Cognition, Memory, and Intelligence; Changes over the Human Lifespan; Motivation and Emotion; Personality; Psychological Disorders; Therapy; and Human Interaction and Social Behavior. PRESENTING THE STUDIES The original studies themselves are not included in their entirety in this book. Instead, I have discussed and summarized them in a consistent format through- out the book to promote a clear understanding of the studies presented. Each reading contains the following: 1. An exact, readily available reference for where the original study can be found 2. A brief introduction summarizing the background in the field leading up to the study and the reasons the researcher carried out the project 3. The theoretical propositions or hypotheses on which the research rests 4. A detailed account of the experimental design and methods used to carry out the research, including, where appropriate, who the partici- pants were and how they were recruited; descriptions of any apparatus and materials used; and the actual procedures followed in carrying out the research 5. A summary of the results of the study in clear, understandable, nontech- nical, nonstatistical, no-jargon language 6. An interpretation of the meaning of the findings based on the author’s own discussion in the original article 7. The significance of the study to the field of psychology

Preface 13 8. A brief discussion of supportive or contradictory follow-up research find- ings and subsequent questioning or criticism from others in the field 9. A sampling of recent applications and citations of the study in others’ articles to demonstrate its continuing influence 10. References for additional and updated readings relating to the study Often, scientists speak in languages that are not easily understood (even by other scientists!). The primary goal of this book is to make these discover- ies meaningful and accessible to the reader and to allow you to experience the excitement and drama of these remarkable and important discoveries. Where possible and appropriate, I have edited and simplified some of the studies presented here for ease of reading and understanding. However, this has been done carefully, so that the meaning and elegance of the work are preserved and the impact of the research is distilled and clarified. NEW TO THE SEVENTH EDITION This seventh edition of Forty Studies offers numerous noteworthy and substan- tive changes and additions. I have added two of the most influential studies in the history of psychology about how we perceive the world. The first is Eleanor Rosch’s revolutionary discovery from 1973 of an ingenious method to allow us to study our brains’ categorization of colors. The second is a comparatively recent report on how the human brain is now literally visible for research purposed with the use of highly technical instruments, primarily the MRI. In addition, many of the Recent Applications sections near the end of the readings have been updated. These sections sample recent citations of the 40 studies into the 21st century. The 40 studies discussed in this book are referred to in over 1,000 research articles every year! A small sampling of those articles is briefly summarized throughout this edition to allow you to experience the ongoing influence of each or more of these 40 studies that changed psychology. All these recently cited studies are fully referenced at the end of each reading along with other relevant sources. As you read through them, you will be able to appreciate the breadth and richness of the contribu- tions still being made today by the 40 studies that comprise this book. Over the several years since completing the sixth edition, I have contin- ued to enjoy numerous conversations with, and helpful suggestions from, colleagues in many branches of psychological research about potential changes in the selection of studies for this new edition. Two studies I have for some time considered including have been mentioned frequently by fellow researchers, and are in many psychology texts so I have added them to this edition. Each of these two newly incorporated studies, in their own significant ways, expanded our perceptions of two very basic aspects of human nature and added to our knowledge of the complexity and diversity of the human experience. One of the “newly added” studies in this edition is actually a revisit to a study that was included in the very first edition over 20 years ago. Many

14 Preface colleagues have told me over the years that it is still too important to be dropped from the book. It is a study conducted by Eleanor Rosch that provided evidence that we are born with “built-in” categories for colors, and that many colors are not learned at all, but instead are accessed by our pre-existing color “prototypes”—already programmed into our brains and passed down to us through evolution. This makes sense when you consider that recognition of colors could play an important role in early humans’ survival and the survival of the human species. Although these early human would not have these color words, the survival value of color may have worked something like this: “Last time I ate that yellow leaf I got really sick, so I’m staying away from it; next time it might kill me!” The second study added to this new edition is a bit different from the rest in that it is relatively recent (2003), especially in comparison to all the other studies. However, I have included it because it involves a major scientific shift in how we study the human brain and are able to reveal how it functions. This new paradigm has the potential to allow researchers to watch your brain function as you carry out mental functions. It might even eventually be able to “see” what you are thinking! The tool that allows us to do this is Magnetic Resonance Imaging (the MRI). The MRI is not particularly new in itself, but researchers are now observing the brains of people while they are thinking; while they are functioning. This is referred to as the functional MRI or fMRI. This protocol for the MRI is still in the development stages, even today, and its ultimate potential remains controversial. But as you read, you will see the amazing feats the fMRI can, and has, accomplish. All the studies, regardless of vintage, discussed in the upcoming pages have one issue in common: research ethics. Perhaps the most important building block of psychological science is a strict understanding and adherence to a clear set of professional ethical guidelines in any research involving humans or ani- mals. Let’s consider briefly the ethical principles social scientists work diligently to follow as they make their discoveries. THE ETHICS OF RESEARCH INVOLVING HUMAN OR ANIMAL PARTICIPANTS Without subjects, scientific research is virtually impossible. In physics, the sub- jects are matter and energy; in botany, they are plantlife; in chemistry, they are molecules, atoms, and subatomic particles; and in psychology, the participants are people. Sometimes, certain types of research do not ethically permit the use of human participants, so animal subjects are substituted. However, the ultimate goal of animal research in psychology is to understand human behavior better, not to study the animals themselves. In this book, you will be reading about research involving both human and animal subjects. Some of the studies may cause you to question the ethics of the researchers in regard to the procedures used with the subjects. When painful or stressful procedures are part of a study, the question of ethics is noted in the chapter. However, because this is such a volatile

Preface 15 and topical issue, a brief discussion of the ethical guidelines followed by present-day psychologists in all research is included here in advance of the specific studies described in this book. research with human Participants The American Psychological Association (APA) has issued strict and clear guidelines that researchers must follow when carrying out experiments involv- ing human participants. A portion of the introduction to those guidelines reads as follows: Psychologists strive to benefit those with whom they work and take care to do no harm. In their professional actions, psychologists seek to safeguard the welfare and rights of those with whom they interact. . . . When conflicts occur among psychologists’ obligations or concerns, they attempt to resolve these conflicts in a responsible fashion that avoids or minimizes harm. . . . Psychologists uphold professional standards of conduct, clarify their professional roles and obliga- tions, accept appropriate responsibility for their behavior, and seek to manage conflicts of interest that could lead to exploitation or harm. . . . Psychologists respect the dignity and worth of all people, and the rights of individuals to privacy, confidentiality, and self-determination. (excerpted from Ethical Principles of Psychologists and Code of Conduct, 2003; see http://apa.org/ethics) Researchers today take great care to adhere to those principles by following basic ethical principles in carrying out all studies involving human participants. These principles may be summarized as follows: 1. Protection from harm. This may seem overly obvious to you: Of course researchers have the duty to protect their research participants from harm; don’t they? The answer is yes! But this was not always a hard and fast rule. As you will see in a few of the studies in this book, debates have long ensued over whether the rights of the volunteers were violated and whether researchers truly followed the other following guidelines. Moreover, the protection must extend beyond the experiments so that if a participant has any disturbing thoughts later on, he or she may contact the researchers and discuss them. 2. Informed consent. A researcher must explain to potential participants what the experiment is about and what procedures will be used so that the individual is able to make an informed decision about whether or not to participate. If the person then agrees to participate, this is called informed consent. As you will see in this book, sometimes the true purposes of an experiment cannot be revealed because this would alter the behavior of the participants and contaminate the results. In such cases, when decep- tion is used, a subject still must be given adequate information for informed consent, and the portions of the experiment that are hidden must be both justifiable based on the importance of the potential find- ings and revealed to the participants at the end of their involvement in the study. In research involving children or minors, parent or guardian consent is required and the same ethical guidelines apply.

16 Preface 3. Freedom to withdraw at any time. Part of informed consent is the principle that all human participants in all research projects must be aware that they may withdraw freely from the study at any time. This may appear to be an unnecessary rule, because it would seem obvious that any subject who is too uncomfortable with the procedures can simply leave. However, this is not always so straightforward. For example, undergraduate students are often given course credit for participating as participants in psycho- logical experiments. If they feel that withdrawing will influence the credit they need, they may not feel free to do so. When participants are paid to participate, if they are made to feel that their completion of the experi- ment is a requirement for payment, this could produce an unethical inducement to avoid withdrawing if they wish to do so. To avoid this problem, participants should be given credit or paid at the beginning of the procedure just for showing up. 4. Confidentiality. All results based on participants in experiments should be kept in complete confidence unless specific agreements have been made with the participants. This does not mean that results cannot be reported and published, but this is done in such a way that individual data cannot be identified. Often, no identifying information is even acquired from participants, and all data are combined to arrive at average differences among groups. 5. Debriefing. Most psychological research involves methods that are com- pletely harmless, both during and after the study. However, even seem- ingly harmless procedures can sometimes produce negative effects, such as frustration, embarrassment, or concern. One common safeguard against those effects is the ethical requirement of debriefing. After partici- pants have completed an experiment, especially one involving any form of deception, they should be debriefed. During debriefing, the true pur- pose and goals of the experiment are explained to them, and they are given the opportunity to ask any questions about their experiences. If there is any possibility of lingering aftereffects from the experiment, the researchers should provide participants with contact information if participants might have any concerns in the future. As you read through the studies included in this book, you may find a few studies that appear to have violated some of these ethical principles. Those studies were carried out long before formal ethical guidelines existed and the research could not be replicated under today’s ethical principles. The lack of guidelines, however, does not excuse past researchers for abuses. Judgment of those investigators and their actions must now be made by each of us individu- ally, and we must learn, as psychologists have, from past mistakes. research with animal subjects One of the hottest topics of discussion inside and outside the scientific com- munity is the question of the ethics of animal research. Animal-rights groups are growing in number and are becoming increasingly vocal and militant.

Preface 17 More controversy exists today over animal subjects than human participants, probably because animals cannot be protected, as humans can, with informed consent, freedom to withdraw, or debriefing. In addition, the most radical animal rights activists take the view that all living things are ordered in value by their ability to sense pain. In this conceptualization, animals are equal in value to humans and, therefore, any use of animals by humans is seen as unethical. This use includes eating a chicken, wearing leather, and owning pets (which, according to some animal-rights activists, is a form of slavery). At one end of the spectrum, many people believe that research with animals is inhumane and unethical and should be prohibited. However, nearly all scientists and most Americans believe that the limited and humane use of animals in scientific research is necessary and beneficial. Many lifesav- ing drugs and medical techniques have been developed through the use of animal experimental subjects. Animals have also often been subjects in psychological research to study issues such as depression, brain development, overcrowding, and learning processes. The primary reason animals are used in research is that to carry out similar research on humans clearly would be unethical. For example, suppose you wanted to study the effect on brain development and intelligence of raising infants in an enriched environment with many activities and toys, versus an impoverished environment with little to do. To assign human infants to these different conditions would simply not be possible. However, most people would agree that rats could be studied without major ethical concerns to reveal findings potentially important to humans (see Reading 2 on research by Rosenzweig and Bennett). The APA, in addition to its guidelines on human participants, has strict rules governing research with animal subjects that are designed to ensure humane treatment. These rules require that research animals receive proper housing, feeding, cleanliness, and health care. All unnecessary pain to the animal is prohibited. A portion of the APA’s Guidelines for the Ethical Conduct in the Care and Use of Animals (2004) reads as follows: Animals are to be provided with humane care and healthful conditions during their stay in the facility. . . . Psychologists are encouraged to consider enriching the environments of their laboratory animals and should keep abreast of litera- ture on well-being and enrichment for the species with which they work.  .  . . When alternative behavioral procedures are available, those that minimize discomfort to the animal should be used. When using aversive conditions, psychologists should adjust the parameters of stimulation to levels that appear minimal, though compatible with the aims of the research. Psychologists are encouraged to test painful stimuli on themselves, whenever reasonable. (see http://apa.org/science/anguide.html) In this book, several studies involve animal subjects. In addition to the eth- ical considerations of such research, difficulties also arise in applying findings from animals to humans. These issues are discussed in this book within each reading that includes animal research. Each individual, whether a researcher or a student of psychology, must make his or her own decisions about animal research in general and the justifiability of using animal subjects in any specific instance. If you allow for the idea that animal research is acceptable under some

18 Preface circumstances, then, for each study involving animals in this book, you must decide if the value of the study’s findings supports the methods used. One final note related to this issue of animal subjects involves a development that is a response to public concerns about potential mistreatment. The city of Cambridge, Massachusetts, one of the major research centers of the world and home to institutions such as Harvard University and the Massachusetts Institute of Technology (MIT), has led the way by creating the position of Commissioner of Laboratory Animals within the Cambridge Health Department (see http://www.cambridgepublichealth.org/services/regulatory-activities/ lab-animals). This was the first such governmental position in the United States. Cambridge, and the many research universities there, is home to 44 laboratories that house over 200,000 animals. The commissioner’s charge is to ensure humane and proper treatment of all animal subjects in all aspects of the research process, from the animals’ living quarters to the methods used in administering the research protocols. If a lab is found to be in violation of Cambridge’s strict laws concerning the humane care of lab animals, the commissioner is author- ized to impose fines of up to $300 per day. As of this writing, only one such fine has been imposed; it amounted to $40,000 (for 133 days in violation) on a facility that appeared to have deliberately disregarded animal treatment laws (Dr. Julie Medley, Commissioner of Laboratory Animals, e-mail, April 15, 2012). In all other cases, any facility that has been found in violation has willingly and quickly corrected the problem. The studies you are about to experience in this book have benefited all of humankind in many ways and to varying degrees. The history of psychological research is a relatively short one, but it is brimming with the richness and excitement of discovering human nature. ACKNOWLEDGMENTS I would like to express my sincere gratitude to Charlyce Jones Owen, publisher, who supported and believed in this project from its inception. I am also very grateful to Jessica Mosher, editor in chief of psychology at Pearson for her support and continuing, talented assistance on this project. For this edition my sincere thanks go out to Stephen Frail, executive psychology editor at Pearson, Maddy Schricker, development editor for the project, and Michelle Durgerian, project manager at GEX Publishing Services for the 7th Edition. I must offer my personal appreciation to Bruce Kenselaar and Suzanne Behnke for lending their considerable talents in designing the cover of this and past editions over the years. Thank you to my psychology colleagues in the field who have taken the time, interest, and effort to communicate to me their comments, suggestions, and wisdom relating to this and previous editions of Forty Studies. I have attempted at every opportunity to incorporate their valued insights into each edition. To my family, my friends, and my students who have participated in the history of this book in so many tangible and intangible ways over the past 20+ years (you know who you are), I extend my continuing best wishes and heartfelt thanks. Roger R. Hock

Chapter I The BiOlOgical Basis Of human BehaviOR Reading 1 One BRain OR TwO? Reading 2 MORe expeRience = BiggeR BRain Reading 3 aRe YOu a “naTuRal”? Reading 4 waTch OuT fOR The Visual cliff! Nearly all general psychology texts begin with chapters relating to the biology of human behavior. This is due not simply to convention but rather because basic biological processes underlie all behavior. The various branches of psychol- ogy rest, to varying degrees, on this biological foundation. The area of psychology that studies these biological functions is typically called psychobiology or biological psychology. This field focuses on the actions of your brain and nervous system, the processes of receiving stimulation and information from the environment through your senses, the ways your brain organizes sensory information to create your perceptions of the world, and how all of this affects your body and behavior. The studies chosen to represent this basic component of psychological research include a wide range of research and are among the most influential and most often cited. The first study discusses a famous research program on right-brain/left-brain specialization that shaped much of our present knowl- edge about how the brain functions. Next is a study that surprised the scien- tific community by demonstrating how a stimulating “childhood” might result in a more highly developed brain. The third study represents a fundamental change in the thinking of many psychologists about the basic causes of human behavior, personality, and social interaction—namely, a new appreciation for the significance of your genes. Fourth is the invention of the famous visual cliff method of studying infants’ abilities to perceive depth. All these studies, along with several others in this book, also address an issue that underlies and con- nects nearly all areas of psychology and provides the fuel for an ongoing and fascinating debate: the nature–nurture controversy. Reading 1: One BRain OR TwO? Gazzaniga, M. S. (1967). The split brain in man. Scientific American, 217(2), 24–29. You are probably aware that the two halves of your brain are not the same and that they perform different functions. For example, in general the left side of your brain is responsible for movement in the right side of your body, and 19

20 Chapter I The Biological Basis of Human Behavior vice versa. Beyond this, though, the two brain hemispheres appear to have much greater specialized abilities. It has come to be rather common knowledge that, for most of us, the left brain controls our ability to use language while the right is involved in spatial relationships, such as those needed for artistic activities. Stroke or head-injury patients who suffer damage to the left side of the brain will usually lose, to varying degrees, their ability to speak (often this skill returns with therapy and training). Many people believe that each half, or hemisphere, of your brain may actually be a completely separate mental system with its own individual abili- ties for learning, remembering, perceiving the world, and feeling emotions. The concepts underlying this view of the brain rest on early scientific research on the effects of splitting the brain into two separate hemispheres. That research was pioneered by Roger W. Sperry (1913–1994), beginning about 15 years prior to the article examined in this chapter. In his early work with animal subjects, Sperry made many remarkable discoveries. For example, in one series of studies, cats’ brains were surgically altered to sever the connec- tion between the two halves of the brain and to alter the optic nerves so that the left eye transmitted information only to the left hemisphere and the right eye only to the right hemisphere. Following surgery, the cats appeared to behave normally and exhibited virtually no ill effects. Then, with the right eye covered, the cats learned a new behavior, such as walking through a short maze to find food. After the cats became skilled at maneuvering through the maze, the eye cover was shifted to the cats’ left eyes. Now, when the cats were placed back in the maze, their right brains had no idea where to turn, and the animals had to relearn the entire maze from the beginning. Sperry conducted many related studies over the next 30 years, and in 1981 he received the Nobel Prize for his work on the specialized abilities of the two hemispheres of the brain. When his research endeavors turned to human participants in the early 1960s, he was joined in his work at the California Institute of Technology (Caltech) by Michael Gazzaniga. Although Sperry is considered to be the founder of split-brain research, Gazzaniga’s article has been chosen here because it is a clear, concise summary of their early collaborative work with human participants and it, along with other related research by Gazzaniga, is cited often in psychology texts. Its selection is in no way intended to overlook or overshadow either Sperry’s leadership in this field or his great contributions. Gazzaniga, in large part, owes his early research, and his discoveries in the area of hemispheric specialization, to Roger W. Sperry (see Sperry, 1968; Puente, 1995). To understand split-brain research, some knowledge of human physiol- ogy is required. The two hemispheres of your brain are in constant communi- cation with one another via the corpus callosum, a structure made up of about 200 million nerve fibers (Figure 1-1). If your corpus callosum is cut, this major line of communication is disrupted, and the two halves of your brain must then function independently. If we want to study each half of your brain sepa- rately, all we need to do is surgically sever your corpus callosum.

Reading 1 One Brain or Two? 21 Corpus Callosum Figure 1-1 The Corpus Callosum. (3D4Medical/Photo Researchers, Inc.) But can scientists surgically divide the brains of humans for research purposes? That sounds more like a Frankenstein movie than real science! Obviously, research ethics would never allow such drastic methods simply for the purpose of studying the specialized abilities of the brain’s two hemi- spheres. However, in the late 1950s, the field of medicine provided psycho- logists with a golden opportunity. In some people with very rare and very extreme cases of uncontrollable epilepsy, seizures could be greatly reduced or virtually eliminated by surgically severing the corpus callosum. This operation was (and is) successful, as a last resort, for those patients who cannot be helped by any other means. When this article was written in 1966, 10 such operations had been undertaken, and four of the patients consented to participate in examination and testing by Sperry and Gazzaniga to determine how their perceptual and intellectual skills were affected by this surgical treatment. TheoreTical ProPosiTions The researchers wanted to explore the extent to which the two halves of the human brain are able to function independently, as well as whether they have separate and unique abilities. If the information traveling between the two halves

22 Chapter I The Biological Basis of Human Behavior of your brain is interrupted, would the right side of your body suddenly be unable to coordinate with the left? If language is controlled by the left side of the brain, how would your ability to speak and understand words be affected by this surgery? Would thinking and reasoning processes exist in both halves separately? If the brain is really two separate brains, would a person be capable of function- ing normally when these two brains are no longer able to communicate? Considering that we receive sensory input from both the right and the left brains, how would the senses of vision, hearing, and touch be affected? Sperry and Gazzaniga attempted to answer these and many other questions in their studies of split-brain individuals. MeThod The researchers developed three types of tests to explore a wide range of men- tal and perceptual capabilities of the patients. One was designed to examine visual abilities. They devised a technique that allowed a picture of an object, a word, or parts of words to be transmitted only to the visual area (called a field) in either the right or left brain hemisphere, but not to both. Normally, both of your eyes send information to both sides of your brain. However, with exact placement of items or words in front of you, and with your eyes fixed on a specific point, images can be fed to the right or the left visual field of your brain independently. Another testing situation was designed for tactile (touch) stimulation. Participants could feel, but not see, an object, a block letter, or even a word in cutout block letters. The apparatus consisted of a screen with a space under it for the participant to reach through and touch the items without being able to see them. The visual and the tactile devices could be used simultaneously so that, for example, a picture of a pen could be projected to one side of the brain and the same object could be searched for by either hand among various objects behind the screen (see Figure 1-2). What do What do you see? you see? X X I see I see a ball. nothing. Figure 1-2 A typical visual testing device for split-brain participants.

Reading 1 One Brain or Two? 23 Testing auditory abilities was somewhat trickier. When sound enters either of your ears, sensations are sent to both sides of your brain. Therefore, it is not possible to limit auditory input to only one side of the brain even in split-brain patients. However, it is possible to limit the response to such input to one brain hemisphere. Here is how this was done: Imagine that several com- mon objects (a spoon, a pen, a marble) are placed into a cloth bag and you are then asked, verbally, to find certain items by touch. You would probably have no trouble doing so. If you place your left hand in the bag, it is being controlled by the right side of your brain, and vice versa. Do you think either side of your brain could do this task alone? As you will see in a moment, both halves of the brain are not equally capable of responding to this auditory task. What if you are not asked for specific objects but are asked simply to reach into the bag and identify objects by touch? Again, this would not be difficult for you, but it would be quite difficult for a split-brain patient. Gazzaniga combined all these testing techniques to reveal some fascinat- ing findings about how the brain functions. resulTs First, you should know that following this radical brain surgery, the patients’ intelligence level, personality, typical emotional reactions, and so on were relatively unchanged. They were very happy and relieved that they were now free of seizures. Gazzaniga reported that one patient, while still groggy from surgery, joked that he had “a splitting headache.” When testing began, however, these participants demonstrated many unusual mental abilities. Visual abilities One of the first tests involved a board with a horizontal row of lights. When a patient sat in front of this board and stared at a point in the middle of the lights, the bulbs would flash across both the right and left visual fields. However, when the patients were asked to explain what they saw, they said that only the lights on the right side of the board had flashed. Next, when the researchers flashed only the lights on the left side of the visual field, the patients claimed to have seen nothing. A logical conclusion from these find- ings was that the right side of the brain was blind. Then an amazing thing happened. The lights were flashed again, only this time the patients were asked to point to the lights that had flashed. Although they had said they only saw the lights on the right, they pointed to all the lights in both visual fields. Using this method of pointing, it was found that both halves of the brain had seen the lights and were equally skilled in visual perception. The important point here is that when the patients failed to say that they had seen all the lights, it was not because they didn’t see them but because the center for speech is located in the brain’s left hemisphere. In other words, for you to say you saw something, the object has to have been seen by the left side of your brain.

24 Chapter I The Biological Basis of Human Behavior Tactile abilities You can try this test yourself. Put your hands behind your back. Then have someone place familiar objects (a spoon, a pen, a book, a watch) in either your right or your left hand and see if you can identify the object. You would not find this task to be very difficult, would you? This is basically what Sperry and Gazzaniga did with the split-brain patients. When an object was placed in the right hand in such a way that the patient could not see or hear it, messages about the object would travel to the left hemisphere and the patient was able to name the object and describe it and its uses. However, when the same objects were placed in the left hand (connected to the right hemisphere), the patients could not name them or describe them in any way. But did the patients know in their right brain what the object was? To find out, the researchers asked the participants to match the object in their left hand (without seeing it, remember) to a group of various objects presented to them. This they could do as easily as you or I could. Again, this places verbal ability in the left hemisphere of the brain. Keep in mind that the reason you are able to name unseen objects in your left hand is that the information from the right side of your brain is transmitted via the corpus callosum to the left side, where your center for language says, “That’s a spoon!” Visual Plus Tactile Tests Combining these two types of tests provided support for the preceding find- ings and also offered additional interesting results. If participants were shown a picture of an object to the right hemisphere only, they were unable to name it or describe it. In fact, they might display no verbal response at all or even deny that anything had been presented. However, if the patients were allowed to reach under the screen with their left hand (still using only the right hemi- sphere) and touch a selection of objects, they were always able to find the one that had been presented visually. The right hemisphere can think about and analyze objects as well. Gazzaniga reported that when the right hemisphere was shown a picture of an item such as a cigarette, the participants could touch 10 objects behind the screen, all of which did not include a cigarette, and select an object that was most closely related to the item pictured—in this case, an ashtray. He went on to explain the following: Oddly enough, however, even after their correct response, and while they were holding the ashtray in their left hand, they were unable to name or describe the object or the picture of the cigarette. Evidently, the left hemisphere was com- pletely divorced, in perception and knowledge, from the right. (p. 26) Other tests were conducted to shed additional light on the language- processing abilities of the right hemisphere. One very famous, ingenious, and revealing use of the visual apparatus came when the word heart was pro- jected to the patients so that he was sent to the right visual field and art was sent to the left. Now, keeping in mind (your connected mind) the functions

Reading 1 One Brain or Two? 25 of the two hemispheres, what do you think the patients verbally reported seeing? If you said art, you were correct. However, and here is the revealing part, when the participants were presented with two cards with the words he and art printed on them and asked to point with the left hand to the word they had seen, they all pointed to he! This demonstrated that the right hemi- sphere is able to comprehend language, although it does so in a different way from the left: in a nonverbal way. The auditory tests conducted with the patients produced similar results. When patients were asked to reach with their left hand into a grab bag hidden from view and pull out certain specific objects (a watch, a marble, a comb, a coin), they had no trouble. This demonstrated that the right hemisphere was comprehending language. It was even possible to describe a related aspect of an item with the same accurate results. An example given by Gazzaniga was when the patients were asked to find in a grab bag full of plastic fruit “the fruit monkeys like best,” they retrieved a banana. Or when told “Sunkist sells a lot of them,” they pulled out an orange. However, if these same pieces of fruit were placed out of view in the patients’ left hand, they were unable to say what they were. In other words, when a verbal response was required, the right hemisphere was unable to speak. One last example of this amazing difference between the two hemi- spheres involved plastic block letters on the table behind the screen. When patients were asked to spell various words by feel with the left hand, they had an easy time doing so. Even if three or four letters that spelled specific words were placed behind the screen, they were able, left-handed, to arrange them correctly into words. However, immediately after completing this task, the par- ticipants could not name the word they had just spelled. Clearly, the left hemi- sphere of the brain is superior to the right for speech (in some left-handed people, this is reversed). But in what skills, if any, does the right hemisphere excel? Sperry and Gazzaniga found in this early work that visual tasks involv- ing spatial relationships and shapes were performed with greater proficiency by the left hand (even though these patients were all right-handed). As can be seen in Figure 1-3, participants who copy three-dimensional drawings (using the pencil behind the screen) were much more successful when using their left hand. The researchers wanted to explore emotional reactions of split-brain patients. While performing visual experiments, Sperry and Gazzaniga sud- denly flashed a picture of a nude woman to either the left or right hemisphere. In one instance, when this picture was shown to the left hemisphere of a female patient: She laughed and verbally identified the picture of a nude. When it was later presented to the right hemisphere, she said .  .  . she saw nothing, but almost immediately a sly smile spread over her face and she began to chuckle. Asked what she was laughing at, she said: “I don’t know . . . nothing . . . oh—that funny machine.” Although the right hemisphere could not describe what it had seen, the sight nevertheless elicited an emotional response like the one evoked in the left hemisphere. (p. 29)

26 Chapter I The Biological Basis of Human Behavior EXAMPLE LEFT HAND RIGHT HAND 1 2 3 Figure 1-3 Drawings made by split-brain patients. (Adapted from p. 27, “The Split Brain in Man,” by Michael S. Gazzaniga.) discussion The overall conclusion drawn from the research reported in this article was that two different brains exist within each person’s cranium—each with com- plex abilities. Gazzaniga notes the possibility that if our brain is really two brains, then perhaps we have the potential to process twice as much informa- tion if the two halves are divided. Indeed, some research evidence suggests that split-brain patients have the ability to perform two cognitive tasks as fast as a normal person can carry out one. significance of findings These findings and subsequent research carried out by Sperry, Gazzaniga, and others were extremely significant and far-reaching. They demonstrated that the two halves of your brain have many specialized skills and functions. Your left brain is “better” at speaking, writing, mathematical calculation, and read- ing, and it is the primary center for language. Your right hemisphere, however, possesses superior capabilities for recognizing faces, solving problems involv- ing spatial relationships, symbolic reasoning, and artistic activities. In the

Reading 1 One Brain or Two? 27 years since Sperry and Gazzaniga’s “split-brain” discoveries, psychobiological researchers have continued to uncover the amazing complexities of the human brain. Our brains are far more divided and compartmentalized than merely two hemispheres. We now know that a multitude of specific structures within the brain serve very specialized cognitive and behavioral functions. Our increased knowledge of the specialized functioning of the brain allows us to treat victims of stroke or head injury more effectively. By knowing the location of the damage, we can predict what deficits are likely to exist as a patient recovers. Through this knowledge, therapists can employ appropriate relearning and rehabilitation strategies to help patients recover as fully and quickly as possible. Gazzaniga and Sperry, after years of continuous work in this area, sug- gested that each hemisphere of your brain really is a mind of its own. In a later study, split-brain patients were tested on much more complex problems than have been discussed here. One question asked was “What profession would you choose?” A male patient verbally (left hemisphere) responded that he would choose to be a draftsman, but his left hand (right hemisphere) spelled, by touch in block letters, automobile racer (Gazzaniga & LeDoux, 1978). Gazzaniga has taken this theory a step further. He has proposed that even in people whose brains are normal and intact, the two hemispheres may not be in complete communication (Gazzaniga, 1985). For example, if certain bits of information, such as those forming an emotion, are not stored in a linguistic format, the left hemisphere may not have access to it. The result of this is that you may feel sad and not be able to say why. As this is an uncomfortable cognitive dilemma, the left hemisphere may try to find a verbal reason to explain the sadness (after all, language is its main job). However, because your left hemisphere does not have all the necessary data, its explanation may actually be wrong! criTicisMs The findings from the split-brain studies carried out over the years by Sperry, Gazzaniga, and others have rarely been disputed. The main body of criticism about this research has focused instead on the way the idea of right- and left- brain specialization has filtered down to popular culture and the media. A widely believed myth states that some people are more right-brained or more left-brained, or that one side of your brain needs to be developed in order for you to improve certain skills (more on this next). Jerre Levy, a psy- chobiologist at the University of Chicago, has been in the forefront of scien- tists trying to dispel the notion that we have two separately functioning brains. She claims that it is precisely because each hemisphere has separate functions that they must integrate their abilities instead of separating them, as is commonly believed. Through such integration, your brain is able to perform in ways that are greater than and different from the abilities of either side alone. When you read a story, for example, your right hemisphere is specializ- ing in emotional content (humor, pathos), picturing visual descriptions,

28 Chapter I The Biological Basis of Human Behavior keeping track of the story structure as a whole, and appreciating artistic writing style (such as the use of metaphors). While all this is happening, your left hemisphere understands the written words, deriving meaning from the complex relationships among words and sentences, and translating words into their phonetic sounds so that they can be understood as language. The reason you are able to read, understand, and appreciate a story is that your brain functions as a single, integrated structure (Levy, 1985). In fact, Levy explains that no human activity uses only one side of the brain: “The popular myths are interpretations and wishes, not the observa- tions of scientists. Normal people have not half a brain, nor two brains, but one gloriously differentiated brain, with each hemisphere contributing its specialized abilities” (Levy, 1985, p. 44). recenT aPPlicaTions The continuing influence of the split-brain research by Sperry and Gazzaniga echoes the quote from Levy. A review of recent medical and psychological literature reveals numerous articles in various fields referring to the early work and methodology of Roger Sperry, as well as to more recent findings by Gazzaniga and his associates. For example, a study from 1998 conducted in France (Hommet & Billard, 1998) has questioned the very foundations of the Sperry and Gazzaniga studies—namely, that severing the corpus callosum actually divides the hemispheres of the brain. The French study found that children who were born without a corpus callosum (a rare brain malforma- tion) demonstrated that information was being transmitted between their brain hemispheres. The researchers concluded that significant connections other than the corpus callosum must exist in these children. Whether such subcortical connections are indeed present in split-brain individuals remains unclear. Recent research has sounded an additional note of caution in how edu- cators might be tempted to apply Gazzaniga’s findings (Alferink & Farmer- Dougan, 2010). The widespread belief that different brain hemispheres control distinct cognitive functions has been clearly demonstrated only in a select number of patients who, for specific medical reasons have undergone the surgical procedure of severing the corpus callosum, We should not make the unwarranted assumption that the findings from these individuals should apply to everyone whose brains are intact. To leap from the assumption that different brain hemispheres are responsible for unique tasks to formulating education models based on these findings is risky. The point some researchers make is that the patients on whom this research was based displayed non-typical brain function even before the surgery. Therefore, to assume that educational methodology should focus on one hemisphere or the other for those with normal nonsevered brain functioning should be avoided. Nevertheless, researchers continue to explore the idea that our two brain hemispheres have separate, yet distinct, functions and influences.

Reading 1 One Brain or Two? 29 One such study (Morton, 2003) demonstrated how your dominant hemisphere may lead you toward specific interests and professions. Morton’s research made two discoveries in this regard. Using a special written test called “The Best Hand Test,” which measures hemisphericity (whether a person is right- or left-brain oriented), Morton found that among 400 students enrolled in first-year, general college courses, 56% were left-brain oriented. However, when the same methods were applied to 180 students in various, specialized upper-level courses, the range of left-brain students ranged from 38% to 65%. This difference indicated that something about a person’s brain hemi- spheres was associated with spreading students out over a variety of college degrees and interests. Second, and more revealing, Morton employed the same method in determining the hemispheric orientation of members of various professions in university settings. The findings indicated that hemi- spheric specialization appears to be predictive of professional choices. For example, among biochemists Morton found that 83% were left-brain ori- ented, while among astronomers only 29% showed a left-brain preference (p. 319). You can see how this would make sense in relation to Sperry and Gazzaniga’s work. Biology and chemistry rely more heavily on linguistic abili- ties, whereas astronomers must have greater abilities in spatial relationships (no pun intended). conclusion Some have carried this, separate-brain idea a step further and applied it to some psychological disorders, such as dissociative, multiple personality disor- der (e.g., Schiffer, 1996). The idea behind this notion is that in some people with intact, “nonsplit” brains, the right hemisphere may be able to function at a greater-than-normal level of independence from the left, and it may even take control of a person’s consciousness for periods of time. Is it possible that multiple personality disorder might be the expression of hidden personalities contained in our right hemispheres? It’s something to think about . . . with both of your hemispheres. Alferink, L., & Farmer-Dougan, V. (2010). Brain-(not) based education: Dangers of misunder- standing and misapplication of neuroscience research. Exceptionality, 18, 42–52. Gazzaniga, M. S. (1985). The social brain. New York: Basic Books. Gazzaniga, M. S., & LeDoux, J. E. (1978). The integrated mind. New York: Plenum Press. Hommet, C., & Billard, C. (1998). Corpus callosum syndrome in children. Neurochirurgie, 44(1), 110–112. Levy, J. (1985, May). Right brain, left brain: Fact and fiction. Psychology Today, 42–44. Morton, B. E. (2003). Line bisection-based hemisphericity estimates of university students and professionals: Evidence of sorting during higher education and career selection. Brain and Cognition, 52(3), 319–325. Puente, A. E. (1995). Roger Wolcott Sperry (1913–1994). American Psychologist, 50(11), 940–941. Schiffer, F. (1996). Cognitive ability of the right-hemisphere: Possible contributions to psycho- logical function. Harvard Review of Psychiatry, 4(3), 126–138. Sperry, R. W. (1968). Hemisphere disconnection and unity in conscious awareness. American Psychologist, 23, 723–733.

30 Chapter I The Biological Basis of Human Behavior Reading 2: mORe expeRience = BiggeR BRain Rosenzweig, M. R., Bennett, E. L., & Diamond, M. C. (1972). Brain changes in response to experience. Scientific American, 226(2), 22–29. If you were to enter the baby’s room in a typical American middle-class home today, you would probably see a crib full of stuffed animals and various colorful toys dangling directly over or within reach of the infant. Some of these toys may light up, move, play music, or do all three. What do you suppose is the parents’ reasoning behind providing infants with so much to see and do? Aside from the fact that babies seem to enjoy and respond positively to these toys, most parents believe, whether they verbalize it or not, that children need a stimulat- ing environment for optimal intellectual development and brain growth. The question of whether certain experiences produce physical changes in the brain has been a topic of conjecture and research among philosophers and scientists for centuries. In 1785, Vincenzo Malacarne, an Italian anato- mist, studied pairs of dogs from the same litter and pairs of birds from the same batches of eggs. For each pair, he would train one participant extensively over a long period of time while the other would be equally well cared for but untrained. He discovered later, in autopsies of the animals, that the brains of the trained animals appeared more complex, with a greater number of folds and fissures. However, this line of research was, for unknown reasons, discontinued. In the late 19th century, attempts were made to relate the circumference of the human head with the amount of learning a person had experienced. Although some early findings claimed such a relationship, later research determined that this was not a valid measure of brain development. By the 1960s, new technologies had been developed that gave scientists the ability to measure brain changes with precision using high-magnification techniques and assessment of levels of various brain enzymes and neurotrans- mitter chemicals. Mark Rosenzweig and his colleagues Edward Bennett and Marian Diamond, at the University of California at Berkeley, incorporated those technologies in an ambitious series of 16 experiments over a period of 10 years to try to address the issue of the effect of experience on the brain. Their findings were reported in the article discussed in this chapter. For rea- sons that will become obvious, they did not use humans in their studies, but rather, as in many classic psychological experiments, their subjects were rats. TheoreTical ProPosiTions Because psychologists are ultimately interested in humans, not rats, the valid- ity of using nonhuman subjects must be demonstrated. In these studies, the authors explained that, for several reasons, using rodents rather than higher mammals such as primates was scientifically sound as well as more convenient. The part of the brain that is the main focus of this research is smooth in the rat, not folded and complex as it is in higher animals. Therefore, it can be examined and measured more easily. In addition, rats are small and inexpen- sive, which is an important consideration in the world of research laboratories

Reading 2 More Experience = Bigger Brain 31 (usually underfunded and lacking in space). Rats bear large litters, and this allows for members from the same litters to be assigned to different experi- mental conditions. The authors point out that various strains of inbred rats have been produced, and this allows researchers to include the effects of genetics in their studies if desired. Implicit in Rosenzweig’s research was the belief that animals raised in highly stimulating environments will demonstrate differences in brain growth and chemistry when compared with animals reared in plain or dull circum- stances. In each of the experiments reported in this article, 12 sets of 3 male rats, each set from the same litter, were studied. MeThod Three male rats were chosen from each litter. They were then randomly assigned to one of three conditions. One rat remained in the laboratory cage with the rest of the colony, another was assigned to what Rosenzweig termed the “enriched” environment cage, and the third was assigned to the “impover- ished” cage. Remember, 12 rats were placed in each of these conditions for each of the 16 experiments. The three different environments (Figure 2-1) were described as follows: 1. The standard laboratory colony cage contained several rats in an adequate space with food and water always available. Figure 2-1 Rosenzweig’s three cage environments.

32 Chapter I The Biological Basis of Human Behavior 2. The impoverished environment was a slightly smaller cage isolated in a separate room in which the rat was placed alone with adequate food and water. 3. The enriched environment was virtually a rat’s Disneyland (no offense intended to Mickey!). Six to eight rats lived in a “large cage furnished with a variety of objects with which they could play. A new set of playthings, drawn out of a pool of 25 objects, was placed in the cage every day” (p. 22). The rats were allowed to live in these different environments for various periods of time, ranging from 4 to 10 weeks. Following this differential treat- ment period, the experimental rodents were examined to determine if any differences had developed in brain development. To be sure that no experi- menter bias would occur, the examinations were done in random order by code number so that the person doing the autopsy would not know in which condition the rat was raised. The rats’ brains were then measured, weighed, and analyzed to deter- mine the amount of cell growth and levels of neurotransmitter activity. In this latter measurement, one brain enzyme was of particular interest: acetylcho- linesterase. This chemical is important because it allows for faster and more efficient transmission of impulses among brain cells. Did Rosenzweig and his associates find differences in the brains of rats raised in enriched versus impoverished environments? The following are their results. resulTs Results indicated that the brains of the enriched rats were indeed different from those of the impoverished rats in many ways. The cerebral cortex (the part of the brain that responds to experience and is responsible for move- ment, memory, learning, and sensory input: vision, hearing, touch, taste, and smell) of the enriched rats was significantly heavier and thicker. Also, greater activity of the nervous system enzyme acetylcholinesterase, men- tioned previously, was found in the brain tissue of the rats with the enriched experience. Although no significant differences were found between the two groups of rats in the number of brain cells (neurons), the enriched environment produced larger neurons. Related to this was the finding that the ratio of RNA to DNA, the two most important brain chemicals for cell growth, was greater for the enriched rats. This implied that a higher level of chemical activity had taken place in the enriched rats’ brains. Rosenzweig and his colleagues stated that “although the brain differ- ences induced by environment are not large, we are confident that they are genuine. When the experiments are replicated, the same pattern of differ- ences is found repeatedly . . . . The most consistent effect of experience on the brain that we found was the ratio of the weight of the cortex to the weight of

Reading 2 More Experience = Bigger Brain 33 8 7 6 Percent difference 5 4 3 2 1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Experiment number Figure 2-2 Ratio of cortex to the rest of the brain: enriched compared with impoverished environment. (Results in exper- iments 2 through 16 were statistically significant.) (Adapted from Rosenzweig, Bennett, & Diamond, p. 26.) the rest of the brain: the sub-cortex. It appears that the cortex increases in weight quite readily in response to experience, whereas the rest of the brain changes little” (p. 25). This measurement of the ratio of the cortex to the rest of the brain was the most accurate measurement of brain changes because the overall weight of the brain may vary with the overall weight of each animal. By considering this ratio, such individual differences are canceled out. Figure 2-2 illustrates this finding for all 16 studies. As you can see, in only one experi- ment was the difference not statistically significant. The researchers reported a finding relating to the two rat groups’ brain synapses (the points at which two neurons meet). Most brain activity occurs at the synapse, where a nerve impulse is either passed from one neuron to the next so that it continues on, or it is inhibited and stopped. Under great mag- nification using the electron microscope, the researchers found that the synapses of the enriched rats’ brains were 50% larger than those of the impoverished rats, potentially allowing for increased brain activity. discussion and criTicisMs After nearly 10 years of research, Rosenzweig, Bennett, and Diamond were willing to state with confidence, “There can now be no doubt that many aspects of brain anatomy and brain chemistry are changed by experience” (p. 27). However, they were also quick to acknowledge that, when they first reported their findings, many other scientists were skeptical because such

34 Chapter I The Biological Basis of Human Behavior effects had not been so clearly demonstrated in past research. Some criticism contended that perhaps it was not the enriched environment that produced the brain changes but rather other differences in the treatment of the rats, such as mere handling or stress. The criticism of differential handling was a valid one in that the enriched rats were handled twice each day when they were removed from the cage as the toys were being changed, but the impoverished rats were not handled. It was possible, therefore, that the handling alone might have caused the results and not the enriched environment. To respond to this potentially confound- ing factor, the researchers handled one group of rats every day and did not handle another group of their litter mates (all were raised in the same envi- ronment). Rosenzweig and his associates found no differences in the brains of these two groups. In addition, in their later studies, both the enriched and impoverished rats were handled equally and, still, the same pattern of results was found. As for the criticisms relating to stress, the argument was that the isola- tion experienced by the impoverished rats was stressful, and this was the rea- son for their less-developed brains. Rosenzweig et al. cited other research that had exposed rats to a daily routine of stress (cage rotation or mild electric shock) and had found no evidence of changes in brain development due to stress alone. One of the problems of any research carried out in a laboratory is that it is nearly always an artificial environment. Rosenzweig and his colleagues were curious about how various levels of stimulation might affect the brain develop- ment of animals in their natural environments. They pointed out that labora- tory rats and mice often have been raised in artificial environments for as many as a hundred generations and bear little genetic resemblance to rats in the wild. To explore this intriguing possibility, they began studying wild deer mice. After the mice were trapped, they were randomly placed in either natural outdoor conditions or the enriched laboratory cages. After 4 weeks, the outdoor mice showed greater brain development than did those in the enriched laboratory environment: “This indicates that even the enriched laboratory environment is indeed impoverished in comparison with a natural environment” (p. 27). The most important criticism of any research involving animal subjects is the question of its application, if any, to humans. Without a doubt, this line of research could never be performed on humans, but it is nevertheless the responsibility of the researchers to address this issue, and these scientists did so. The authors explained that it is difficult to generalize from the findings of one set of rats to another set of rats, and consequently it is much more dif- ficult to try to apply rat findings to monkeys or humans. And, although they report similar findings with several species of rodents, they admit that more research would be necessary before any assumptions could be made responsi- bly about the effects of experience on the human brain. They proposed, how- ever, that the value of this kind of research on animals is that “it allows us to

Reading 2 More Experience = Bigger Brain 35 test concepts and techniques, some of which may later prove useful in research with human subjects” (p. 27). Several potential benefits of this research were suggested by the authors. One possible application pertained to the study of memory. Changes in the brain due to experience might lead to a better understanding of how memo- ries are stored in the brain. This could, in turn, lead to new techniques for improving memory and preventing memory loss due to aging. Another area in which this research might prove helpful was in explaining the relationship between malnutrition and intelligence. The concept proposed by the authors in this regard was that malnutrition may be a person’s responsiveness to the stimulation available in the environment and consequently may limit brain development. The authors also noted that other studies suggested that the effects of malnutrition on brain growth may be either reduced by environ- mental enrichment or increased by deprivation. relaTed research and recenT aPPlicaTions This work by Rosenzweig, Bennett, and Diamond has served as a catalyst for continued research in this developmental area that continues today. Over the decades since the publication of their article, these scientists and many others have continued to confirm, refine, and expand their findings. For example, research has demonstrated that learning itself is enhanced by enriched envi- ronmental experiences and that even the brains of adult animals raised in impoverished conditions can be improved when placed in an enriched envi- ronment (see Bennett, 1976, for a complete review). Some evidence exists to indicate that experience does indeed alter brain development in humans. Through careful autopsies of humans who have died naturally, it appears that as a person develops a greater number of skills and abilities, the brain actually becomes more complex and heavier. Other find- ings have come from examinations during autopsies of the brains of people who were unable to have certain experiences. For example, in a blind person’s brain, the portion of the cortex used for vision is significantly less developed, less convoluted, and thinner than in the brain of a person with normal sight. Marian Diamond, one of the authors of this original article, has applied the results of work in this area to the process of human intellectual develop- ment throughout life. She says, “For people’s lives, I think we can take a more optimistic view of the aging brain . . . . The main factor is stimulation. The nerve cells are designed for stimulation. And I think curiosity is a key factor. If one maintains curiosity for a lifetime, that will surely stimulate neural tissue and the cortex may in turn respond .  .  .  . I looked for people who were extremely active after 88 years of age. I found that the people who use their brains don’t lose them. It was that simple” (in Hopson, 1984, p. 70). Two recent studies have elaborated on Rosenzweig, Diamond, and Bennett’s notions of environmental influences on brain development in very diverse applications. Weiss and Bellinger (2006) expanded on the research by

36 Chapter I The Biological Basis of Human Behavior suggesting that studies of the effects of environmental toxins on early brain development in humans must encompass not only the toxicity of the chemical but also should consider all the factors present within the individual’s overall life context, including genetic tendencies and enriched or impoverished envi- ronments. The authors proposed that, in humans, the effects of exposure to toxic substances tend to be directly related to growing up in an enriched ver- sus an impoverished environment. In other words, when children are raised in poverty, not only is their developmental environment likely to be impover- ished, but they may also be at a greater risk of exposure to neurotoxic chemicals. Moreover, the environmental factors that are present can affect the outcome of the toxic exposure on brain development. Weiss and Bellinger asserted that when researchers have studied environmental toxins, the ten- dency has been to focus on the toxic substance itself and to minimize the accompanying situational variables. As the authors stated, We argue that the outcomes of exposure to neurotoxic chemicals early in life are shaped by the nature of a child’s social environment, including that prevailing before birth . . . . We contend that a true evaluation of toxic potential and its neurobehavioral consequences is inseparable from the ecologic setting [such as environmental richness] in which they act and which creates unique, enduring individual vulnerabilities. (p. 1497) Another article cites Rosenzweig’s 1972 study in critiquing some recent attempts to oversimplify enrichment strategies in attempts to enhance children’s brain development ( Jones & Zigler, 2002). As you can imagine, when the public learns about research such as Rosenzweig’s, a popular movement may be born that sounds attractive but has little basis in scientific fact. One of these from the 1990s, which you may have heard about, has become known as the “Mozart Effect.” This fad began with some preliminary research showing that when chil- dren listen to Mozart (but not other classical composers) they become better learners. This idea has grown to the point that entire Web sites are devoted to the benefits of the “Mozart Effect” for children and adults alike, involving claims that certain music can enhance overall health, improve memory, treat attention deficit disorder, reduce depression, and speed healing from physical injuries. conclusion Jones and Zigler (2002) maintain that such popular applications of the research are ineffective and even dangerous. They contend, “Brain research is being misappropriated to the service of misguided ‘quick fix’ solutions to more complicated, systemic issues” (p. 355). They further suggest that when scientific brain and learning research is applied carefully and correctly, it can make a “substantive contribution of high quality, intensive, multidomain interventions to early cognitive and social development” (p. 355). Bennett, E. L. (1976). Cerebral effects of differential experience and training. In M. R. Rosen- zweig & E. L. Bennett (Eds.), Neural mechanisms of learning and memory. Cambridge, MA: MIT Press.

Reading 3 Are You a “Natural”? 37 Hopson, J. (1984). A love affair with the brain: A PT conversation with Marian Diamond. Psychology Today, 11, 62–75. Jones, S., & Zigler, E. (2002). The Mozart Effect: Not learning from history. Journal of Applied Developmental Psychology, 23, 355–372. Weiss, B., & Bellinger, D. C. (2006). Social ecology of children’s vulnerability to environmental pollutants. (Commentary). Environmental Health Perspectives, 114, 1479–1485. Reading 3: aRe YOu a “naTuRal”? Bouchard, T., Lykken, D., McGue, M., Segal, N., & Tellegen, A. (1990). Sources of human psychological differences: The Minnesota study of twins reared apart. Science, 250, 223–229. This study represents a relatively recent and ongoing fundamental change in the way many psychologists view human nature in its broadest sense. You can relate to this change in a personal way by first taking a moment to answer in your mind the following question: “Who are you?” Think for a moment about some of your individual characteristics: your “personality traits.” Are you high strung or laid-back? Are you shy or outgoing? Are you adventurous, or do you seek out comfort and safety? Are you easy to get along with, or do you tend toward the disagreeable? Are you usually optimistic or more pessimistic about the outcome of future events? Think about yourself in terms of these or any other questions you feel are relevant. Take your time .  .  .  . Finished? Now, answer this next, and, for this reading, more important question: “Why are you who you are?” In other words, what factors contributed to “creating” the person you are today? If you are like most people, you will point to the child-rearing practices of your parents and the values, goals, and priorities they instilled in you. You might also credit the influences of brothers, sisters, grandparents, aunts, uncles, peers, teachers, and other mentors who played key roles in molding you. Still others of you will focus on key life-changing events, such as an ill- ness, the loss of a loved one, or the decision to attend a specific college, choose a major, or take a particular life course that seemed to lead you toward becom- ing your current self. All these influences share one characteristic: They are all environmental phenomena. Hardly anyone ever replies to the question “Why are you who you are?” with “I was born to be who I am; it’s all in my genes.” Everyone acknowledges that physical attributes, such as height, hair color, eye color, and body type, are genetic. More and more people are real- izing that tendencies toward many illnesses, such as cancer, heart disease, and high blood pressure, have significant genetic components. However, almost no one thinks of genes as the main force behind who they are psychologically. This may strike you as odd when you stop to think about it, but in reality very understandable reasons explain our “environmental bias.” First of all, psychology during the second half of the 20th century was dominated by the behaviorism theory of human nature. Basically, that theory states that all human behavior is controlled by environmental factors, including

38 Chapter I The Biological Basis of Human Behavior the stimuli that provoke behaviors and the consequences that follow response choices. Strict behaviorists believed that the internal psychological workings of the human mind were not only impossible to study scientifically but also that such study was unnecessary and irrelevant to a complete explanation for human behavior. Whether the wider culture accepted or even understood formal theories of behaviorism is not as important as the reality of their influence on today’s firmly entrenched popular belief that experience is the primary or exclusive architect of human nature. Another understandable reason for the pervasive acceptance of environ- mental explanations of behavior is that genetic and biological factors do not provide visible evidence of their influence. It’s easy for someone to say “I became a writer because I was deeply inspired and encouraged by my seventh- grade composition teacher.” You remember those sorts of influences; you see them. They are part of your past and present conscious experiences. You would find it much more difficult to recognize biological influences and say “I became a writer because my DNA contains a gene that has been expressed in me that predisposes me to write well.” You can’t see, touch, or remember the influence of your genes, and you don’t even know where in your body they might be located! In addition, many people are uncomfortable with the idea that they might be the product of their genes rather than the choices they have made in their lives. Such ideas smack of determinism and a lack of free will. Most peo- ple have a strong dislike for any theory that might in some way limit their conscious ability to determine the outcomes in their lives. Consequently, genetic causes of behavior and personality tend to be avoided or rejected. In reality, genetic influences interact with experience to mold a complete human, and the only question is this: Which is more dominant? Or, to phrase the ques- tion as it frequently appears in the media, “Is it nature or nurture?” The article by Thomas Bouchard, David Lykken, and their associates at the University of Minnesota in Minneapolis that is referenced in this chapter is a review of research that began in 1979 to examine the question of how much influence your genes have in determining your personal psychological qualities. This research grew out of a need for a scientific method to separate genetic influences (nature) from environmental forces (nurture) on people’s behavior and personality. This is no simple task when you consider that nearly every one of you, assuming you were not adopted, grew and developed under the direct environmental influence of your genetic donors (your parents). You might, for example, have the same sense of humor as your father (no offense!) because you learned it from him (nurture) or because you inherited his “sense-of-humor” gene (nature). No systematic approach can tease those two influences apart, right? Well, Bouchard and Lykken would say “wrong.” They have found a way to determine with a reasonable degree of confidence which psychological characteristics appear to be determined primarily by genetic factors and which are molded more by your environment.

Reading 3 Are You a “Natural”? 39 TheoreTical ProPosiTions It’s simple, really. All you have to do is take two humans who have exactly the same genes, separate them at birth, and raise them in significantly different environments. Then you can assume that those behavioral and personality characteristics they have in common as adults must be genetic. But how on earth can researchers possibly find pairs of identical people? (Don’t say “cloning”; we’re not there yet!) And even if they could, it would be unethical to force them into diverse environments, wouldn’t it? As you’ve already guessed, the researchers didn’t have to do that. Society had already done it for them. Identical twins have virtually the same genetic structure. They are called monozygotic twins because they start as one fertilized egg, called a zygote, and then split into two identical embryos. Fraternal twins are the result of two separate eggs fertilized by two separate sperm cells and are referred to as dizygotic twins. Fraternal twins are only as genetically similar as any two non- twin siblings. As unfortunate as it sounds, twin infants are sometimes given up for adoption and placed in separate homes. Adoption agencies will try to keep siblings, especially twins, together, but the more important goal is to find good homes for them even if it means separation. Over time, thousands of identical and fraternal twins have been adopted into separate homes and raised, fre- quently without the knowledge that they were a twin, in different and often contrasting environmental settings. In 1983 Bouchard and Lykken began to identify, locate, and bring together pairs of these twins. This 1990 article reports on results from 56 pairs of monozygotic reared-apart (MZA) twins from the United States and seven other countries who agreed to participate in weeklong sessions of intensive psychological and physiological tests and measurements (that this research is located in Minneapolis, one half of “the Twin Cities” is an irony that has not, by any means, gone unnoticed). These twins were compared with mono- zygotic twins reared together (MZT). The surprising findings continue to reverberate throughout the biological and behavioral sciences. MeThod Participants The first challenge for this project was to find sets of monozygotic twins who were separated early in life, reared apart for all or most of their lives, and reunited as adults. Most of the participants were found through word of mouth as news of the study began to spread. The twins themselves or their friends or family members would contact the research institute—the Minnesota Center for Twin and Adoption Research (MICTAR)—various social-services professionals in the adoption arena would serve as contacts, or in some cases one member of a twin-pair would contact the center for assist- ance in locating and reuniting with his or her sibling. All twins were tested to ensure that they were indeed monozygotic before beginning their participa- tion in the study.

40 Chapter I The Biological Basis of Human Behavior Procedure The researchers wanted to be sure they obtained as much data as possible during the twins’ one-week visit. Each twin completed approximately 50 hours of testing on nearly every human dimension you might imagine. They com- pleted four personality trait scales, three aptitude and occupational interest inventories, and two intelligence tests. In addition, the participants filled in checklists of household belongings (such as power tools, telescope, original artwork, unabridged dictionary) to assess the similarity of their family resources and a family environment scale that measured how they felt about the parenting they received from their adoptive parents. They were also administered a life history interview, a psychiatric interview, and a sexual his- tory interview. All these assessments were carried out individually so that it was not possible for one twin to inadvertently influence the answers and responses of the other. As you might imagine, the hours of testing created a huge database of information. The most important and surprising results are discussed here. resulTs Table 3-1 summarizes the similarities for some of the characteristics measured in the monozygotic twins reared apart (MZA) and includes the same data for monozygotic twins reared together (MZT). The degree of similarity is Table 3-1 Comparison of Correlations (r) of Selected Characteristics for identical Twins reared apart (MZa) and identical Twins reared Together (MZT)* chaRacTeRisTic r (MZa) siMilaRiTY r (MZT) r (MZa) ÷ r (MZT)** physiological — Brain wave activity .80 —— Blood pressure .64 .81 .987 heart rate .49 .70 .914 — .54 .907 intelligence .69 —— wais iQ .78 .88 .784 Raven intelligence Test — .76 1.03 —— personality Multidimensional personality Questionnaire .50 .49 1.02 (MpQ) .48 .49 .979 california personality inventory —— — .39 .48 .813 psychological interests .40 .49 .816 strong campbell interest inventory —— — Minnesota Occupational interest scale .49 .51 .961 .34 .28 1.21 social attitudes Religiosity nonreligious social attitudes *adapted from Table 4, p. 226. **1.00 would imply that MZa twin pairs were found to be exactly as similar as MZT twin pairs.

Reading 3 Are You a “Natural”? 41 expressed in the table as correlations or r values. The larger the correlation, the greater the similarity. The logic here is that if environment is responsible for individual differences, the MZT twins who shared the same environment as they grew up should be significantly more similar than the MZA twins. As you can see, this is not what the researchers found. The last column in Table 3-1 expresses the difference in similarity by dividing the MZA correlation on each characteristic by the MZT correlation. If both correlations were the same, the result would be 1.00; if they were entirely dissimilar, the result could be as low as 0.00. Examining column 4 in the table carefully, you’ll find that the correlations for characteristics were remarkably similar—that is, close to 1.00 and no lower than .700 for MZA and MZT twin pairs. discussion and iMPlicaTions of findings These findings indicate that genetic factors (or the genome) appear to account for most of the variations in a remarkable variety of human characteristics. This finding was demonstrated by the data in two important ways. One is that genetically identical humans (monozygotic twins), who were raised in sepa- rate and often very different settings, grew into adults who were extraordinar- ily similar, not only in appearance but also in basic psychology and personality. The second demonstration in this study of the dominance of genes is the fact that there appeared to be little effect of the environment on identical twins who were raised in the same setting. Here’s Bouchard and Lykken’s take on these discoveries: For almost every behavioral trait so far investigated, from reaction time to religiosity, an important fraction of the variation among people turns out to be associated with genetic variation. This fact need no longer be subject to debate; rather, it is time to consider its implications. Of course, some will argue with Bouchard and Lykken’s notion that the time to debate these issues is over. Some varying views are discussed in the next section. However, a discussion of the implications of this and other simi- lar studies by these same researchers is clearly warranted. In what ways do the genetic findings reported in this study change psychologists’ and, for that matter, all of our views of human nature? As mentioned previously, psychol- ogy and Western culture have been dominated for over 50 years by environ- mental thinking. Many of our basic beliefs about parenting, education, crime and punishment, psychotherapy, skills and abilities, interests, occupational goals, and social behavior, just to name a few, have been interpreted from the perspective that people’s experience molds their personalities, not their genes. Very few of us look at someone’s behavior and think, “That person was born to behave like that!” We want to believe that people learned their behav- ior patterns because that allows us to feel some measure of confidence that parenting makes a difference; that positive life experiences can win out over negative ones; and that unhealthy, ineffective behaviors can be unlearned.

42 Chapter I The Biological Basis of Human Behavior The notion that personality is a done deal the moment we are born leaves us with the temptation to say “Why bother?” Why bother working hard to be good parents? Why bother trying to help those who are down and out? Why bother trying to offer quality education? And so on. Bouchard and Lykken would want to be the first to disagree with such an interpretation of their findings. In this article, they offer three of their own implications of their provocative conclusions: 1. Clearly, intelligence is primarily determined by genetic factors (70% of the variation in intelligence appears to be due to genetic influence). However, as the authors state very clearly, [T]hese findings do not imply that traits like IQ cannot be enhanced . . . . A survey covering 14 countries has shown that the average IQ test score has increased in recent years. The present findings, therefore, do not define or limit what might be conceivably achieved in an optimal environment. (p. 227) Basically, what the authors are saying is that although 70% of the variation in IQ is due to naturally occurring genetic variation, 30% of the variation remains subject to increases or decreases due to environmental influences. These influences include many that are well-known, such as education, family setting, toxic substances, and socioeconomic status. 2. The basic underlying assumption in Bouchard and Lykken’s research is that human characteristics are determined by some combination of genetic and environmental influences. When the environment exerts less influence, differences must be attributed more to genes. The con- verse is also true: As environmental forces create a stronger influence on differences in a particular characteristic, genetic influences will be weaker. For example, most children in the United States have the oppor- tunity to learn to ride a bicycle. This implies that the environment’s effect on bicycle riding is somewhat similar for all children, so differ- ences in riding ability will be more affected by genetic forces. On the other hand, variation in, say, food preferences in the United States are more likely to be explained by environmental factors because food and taste experiences in childhood and throughout life are very diverse and will, therefore, leave less room for genetic forces to function. Here’s the interesting part of the researchers’ point: They maintain that personality is more like bicycle riding than food preferences. The authors are saying, in essence, that family environments exert less influence over who the kids grow up to be than do the genes they inherit from birth. Understandably, most parents do not want to hear or believe this. They are working hard to be good parents and to raise their children to be happy individuals and good citizens. The only parents who might take some comfort from these findings are those who are nearing their wits’ end with out-of-control or incorrigible sons or daughters and would appreciate being able to take less of the blame! However, Bouchard and Lykken are quick to point out that genes are

Reading 3 Are You a “Natural”? 43 not necessarily destiny and that devoted parents can still influence their children in positive ways, even if they are only working on a small per- centage of the total variation. 3. The most intriguing implication that Bouchard and Lykken suggest is that it’s not the environment influencing people’s characteristics, but vice versa. That is, people’s genetic tendencies actually mold their envi- ronments! The following is an example of the idea behind this theory. The fact that some people are more affectionate than others is usu- ally seen as evidence that some parents were more affectionate with their children than were other parents. In other words, affectionate kids come from affectionate environments. When this kind of assumption has been studied, it is usually found to be true. Affectionate people have, indeed, received more affection from their parents. Bouchard and Lykken are proposing, however, that variation in “affectionateness” may be, in real- ity, genetically determined so that some children are just born more affectionate than others. Their inborn tendency toward affectionate behavior causes them to respond to affection from their parents in ways that reinforce the parents’ behavior much more than genetically nonaf- fectionate children. This, in turn produces the affectionate behavior in the parents, not the other way around. The researchers contend that genes function in this way for many, if not most, human characteristics. They state it this way: The proximal [most immediate] cause of most psychological variance probably involves learning through experience, just as radical environ- mentalists have always believed. The effective experiences, however, to an important extent are self-selected, and that selection is guided by the steady pressure of the genome. (p. 228) criTicisMs and relaTed research As you might imagine, a great many related studies have been carried out using the database of twins developed by Bouchard and Lykken. In general, the findings continue to indicate that many human personality characteristics and behaviors are strongly influenced by genes. Many attributes that have been seen as stemming largely or completely from environmental sources are being reevaluated as twin studies reveal that heredity contributes either the majority of the variation or a significantly larger proportion than was previously contemplated. For example, studies from the University of Minnesota team found not only that the vocation you choose is largely determined by your genes but also that about 30% of the variation in your overall job satisfaction and work ethic appears due to genetic factors (Arvey et al., 1989; Arvey et al., 1994) even when the physical requirements of various professions were held con- stant. Other studies comparing identical (monozygotic) twins with fraternal (dizygotic) twins, both reared together and reared apart, have focused more directly on specific personality traits that are thought to be influential and

44 Chapter I The Biological Basis of Human Behavior stable in humans (Bouchard, 1994; Loehlin, 1992). These and other studies’ findings determined that the people’s variation on the characteristics of extra- version–introversion (outgoing versus shy), neuroticism (tendency to suffer from high anxiety and extreme emotional reactions), and conscientiousness (degree to which a person is competent, responsible, and thorough) is explained more (65%) by genetic differences than by environmental factors. Of course, not everyone in the scientific community is willing to accept these findings at face value. The criticisms of Bouchard and Lykken’s work take several directions (see Billings et al., 1992). Some studies claim that the researchers are not publishing their data as fully and completely as they should, and, therefore, their findings cannot be independently evaluated. These same critics also claim that many articles are reporting on case studies demonstrating strong environmental influences on twins that Bouchard and Lykken fail to consider. In addition, some researchers have voiced a major criticism of one aspect of twin research in general, referred to as the “equal environment assumption” (e.g., Joseph, 2002). This argument maintains that many of the conclusions drawn by Bouchard and Lykken about genetic influence assume that monozygotic and dizygotic twins raised together develop in identical environments. These critics maintain that such an assumption is not valid and that fraternal twins are treated far more differently than are identical twins. This, they contend, draws the entire method of twin research as a determi- nant of genetic influences into question. However, several other articles have refuted this criticism and supported the “equal environment assumption” (e.g., Kendler et al., 1993). recenT aPPlicaTions In 1999, Bouchard reviewed the nature–nurture evidence from the Minnesota twin registries (Bouchard, 1999). He concluded that, overall, 40% of the vari- ability in personality and 50% of the variability in intelligence appears to be genetically based. He also reiterated his position, discussed previously, that your genes drive your selection of environments and your selection or avoid- ance of specific personality-molding environments and behaviors. Research at the Minnesota Center for Twin and Adoption Research con- tinues to be very active. Some fascinating research has examined very complex human characteristics and behaviors that few would have even guessed to be genetically driven, such as love, divorce, and even death (see Minnesota Twin Family Study, 2007). These researchers have studied people’s selection of a mate to see if “falling in love” with Mr. or Ms. Right is genetically predisposed. It turns out that it is not. However, the researchers have found a genetic link to the likelihood of divorce, eating disorders, and age at the time of death. Bouchard and Lykken’s research has been applied to the larger philo- sophical discussion of human cloning (see Agar, 2003). If a human being is ever successfully cloned, the question is, as you are probably thinking, to what extent will a person’s essence—an individual’s personality—be transferred to

Reading 4 Watch out for the Visual Cliff! 45 his or her clone? The fear that human identity might be changed, degraded, or lost has been a common argument of those opposed to cloning. On the other hand, results of twin studies, such as those of Bouchard and Lykken sug- gest that “the cloned person may, under certain circumstances, be seen as surviving, to some degree, in the clone . . . . However . . . rather than warrant- ing concern, the potential for survival by cloning ought to help protect against the misuse of the technology” (Agar, 2003, p. 9). In a separate study examin- ing the issue of identical twins and cloning (Prainsack & Spector, 2006), researchers found that identical twins rarely consider the genetic aspects of their real-life experience of being identical twins. In addition, from a personal perspective, they did not view the idea of human cloning as unnatural or immoral but were more concerned about the ethics underlying the reasons for human cloning. Of course, this is a philosophical discussion so far, but as the prospect of human cloning looms ever closer, it becomes increasingly important and interesting food for thought. Agar, N. (2003). Cloning and identity. Journal of Medicine and Philosophy, 28, 9–26. Arvey, R., Bouchard, T., Segal, N., & Abraham, L. (1989). Job satisfaction: Environmental and genetic components. Journal of Applied Psychology, 74(2), 187–195. Arvey, R., McCall, B., Bouchard, T., & Taubman, P. (1994). Genetic influences on job satisfaction and work value. Personality and Individual Differences, 17(1), 21–33. Billings, P., Beckwith, J., & Alper, J. (1992). The genetic analysis of human behavior: A new era? Social Science and Medicine, 35(3), 227–238. Bouchard, T. (1994). Genes, environment, and personality. Science, 264(5166), 1700–1702. Bouchard, T. (1999). Genes, environment, and personality. In S. Ceci, et al. (Eds.), The nature– nurture debate: The essential readings, pp. 97–103. Malden, MA: Blackwell. Joseph, J. (2002). Twin studies in psychiatry and psychology: Science or pseudoscience? Psychiatric Quarterly, 73, 71–82. Kendler K., Neale M., Kessler R., Heath A., & Eaves L. (1993). A test of the equal environment assumption in twin studies of psychiatric illness. Behavioral Genetics, 23, 21–27. Loehlin, J. (1992). Genes and environment in personality development. Newbury Park, CA: Sage Publications. Minnesota Twin Family Study. (2007). What’s special about twins to science? Retrieved March 10, 2007, from http://www.psych.umn.edu/psylabs/mtfs/special.htm. Prainsack, B., & Spector, T. D. (2006). Twins: a cloning experience. Social Science & Medicine, 63(10), 2739–2752. Reading 4: waTch OuT fOR The visual cliff! Gibson, E. J., & Walk, R. D. (1960). The “visual cliff.” Scientific American, 202(4), 67–71. One of the most often told anecdotes in psychology concerns a man called S. B. (initials used to protect his privacy). S. B. had been blind his entire life until the age of 52, when he underwent a newly developed operation (the now-common corneal transplant) and his sight was restored. However, S. B.’s new ability to see did not mean that he automatically perceived what he saw the way the rest of us do. One important example of this became evident soon after the operation, before his vision had cleared completely. S. B. looked out his hospital window and was curious about the small objects he could see

46 Chapter I The Biological Basis of Human Behavior moving on the ground below. He began to crawl out on his window ledge, thinking he would lower himself down by his hands and have a look. Fortunately, the hospital staff prevented him from trying this. He was on the fourth floor, and those small moving things were cars! Even though S. B. could now see, he was not able to perceive depth. Our visual ability to sense and interpret the world around us is an area of interest to experimental psychologists because, obviously, it affects our behav- ior in important ways. In addition, within this ability lies the central question of whether our sensory processes are inborn or learned: the nature–nurture issue once again. Many psychologists believe that our most important visual skill is depth perception. You can imagine how difficult, and probably impos- sible, survival of the human species would have been if we could not perceive depth. We might have run headlong into things, been unable to judge how far away a predator was, or stepped right off cliffs. Therefore, it might be logical to assume that depth perception is an inborn survival mechanism that does not require experience to develop. However, as Eleanor Gibson and Richard Walk point out in their article, Human infants at the creeping and toddling stage are notoriously prone to falls from more or less high places. They must be kept from going over the brink by side panels on their cribs, gates on stairways, and the vigilance of adults. As their muscular coordination matures, they begin to avoid such accidents on their own. Common sense might suggest that the child learns to recognize falling-off places by experience—that is, by falling and hurting himself. (p. 64) These researchers wanted to study this visual ability of depth perception scientifically in the laboratory. To do this, they conceived of and developed a remarkable research tool they called the visual cliff. TheoreTical ProPosiTions If you wanted to find out at what point in the early developmental process animals or people are able to perceive depth, one way to do this would be to put them on the edge of a cliff and see if they are able to avoid falling off. This is a ridiculous suggestion because of the ethical considerations of the poten- tial injury to participants who were unable to perceive depth (or, more specifi- cally, height). The visual cliff avoids this problem because it presents the participant with what appears to be a drop-off, when no drop-off actually exists. Exactly how this is done will be explained shortly, but it is important first to recognize that the importance of this apparatus lies in the fact that human or animal infants can be placed on the visual cliff to see if they are able to perceive the drop-off and avoid it. If they are unable to do this and step off the “cliff,” there is no danger of falling. Gibson and Walk took a “nativist” position on this topic: They believed that depth perception and the avoidance of a drop-off appear automatically as part of our original biological equipment and are not, therefore, products of experience. The opposing view, held by empiricists, contends that such abilities

Reading 4 Watch out for the Visual Cliff! 47 are learned. Gibson and Walk’s visual cliff allowed them to ask these questions: At what stage in development can a person or animal respond effectively to the stimuli of depth and height? Do these responses appear at different times with animals of different species and habitats? Are these responses preprogrammed at birth or do they develop as a result of experience and learning? MeThod The visual cliff is comprised of a table about 4 feet high with a top made from a piece of thick, clear glass (Figures 4-1 and 4-2). Directly under half of the glass on the table (the shallow side) is a solid surface with a red-and-white checkered pattern. Under the other half is the same pattern, but it is down at the level of the floor underneath the table (the deep side). At the edge of the shallow side, then, is the appearance of a sudden drop-off to the floor, although, in reality, the glass extends all the way across. Between the shallow and the deep sides is a center board about a foot wide. The process of testing infants using this device was extremely simple. The participants for this study were 36 infants between the ages of 6 months and 14 months. The mothers of the infants also participated. Each infant was placed on the center board of the visual cliff and was then called by the mother, first from the deep side and then from the shallow side. To compare the development of depth perception in humans with that in other baby animals, the visual cliff allowed for similar tests with other 12” Center 42.5” Platform 6’ Shallow Side 8’ Deep Side Figure 4-1 Gibson and Walk’s visual cliff.

48 Chapter I The Biological Basis of Human Behavior Figure 4-2 The visual cliff in a testing situation. (Mark Richards/PhotoEdit, Inc.) species (without a mother’s beckoning, however). The baby animals were placed on the center board and observed to see if they could discriminate between the shallow and deep sides and avoid stepping off “the cliff.” You can imagine the rather unique situation in the psychology labs at Cornell University when the various baby animals were brought in for testing. They included chicks, turtles, rats, lambs, kids (baby goats, that is), pigs, kittens, and puppies. One has to wonder if they were all tested on the same day! Remember that the goal of this research was to examine whether depth perception is learned or innate. What makes this method so ingenious is that it allowed that question to at least begin to be answered. Infants, whether human or animal, cannot be asked if they perceive depth, and, as mentioned, human infants cannot be tested on real cliffs. In psychology, answers to per- plexing questions are often found through the development of new methods for studying the questions. The results of Gibson and Walk’s early study provide an excellent example of this. resulTs and discussion Nine children in the study refused to move at all off the center board. This was not explained by the researchers, but perhaps it was just infant stubbornness. When the mothers of the other 27 called to them from the shallow side, all the infants crawled off the board and crossed the glass. Only three of them, however, crept, with great hesitation, off the brink of the visual cliff when called by their mothers from the deep side. When called from the “cliff” side, most of the children either crawled away from the mother on the shallow side or cried in frustration at being unable to reach the mother

Reading 4 Watch out for the Visual Cliff! 49 without moving over the “cliff.” There was little question that the children were perceiving the depth of the “cliff ”: “Often they would peer down through the glass of the deep side and then back away. Others would pat the glass with their hands, yet despite this tactile assurance of solidity would refuse to cross” (p. 64). Do these results prove that humans’ ability to perceive depth is innate rather than learned? It does not, because all the children in this study had at least 6 months of life experience in which to learn about depth through trial and error. However, human infants cannot be tested in this way prior to 6 months of age because they do not have adequate locomotor abilities. It was for this reason that Gibson and Walk decided to test various other animals as a comparison. As you know, most nonhuman animals gain the ability to move about much sooner than humans. The results of the animal tests were extremely interesting in that the ability of the various animals to perceive depth devel- oped in relation to when the species needed such a skill for survival. For example, baby chickens must begin to scratch for their own food soon after hatching. When they were tested on the visual cliff at less than 24 hours of age, they never made the mistake of stepping off onto the deep side. Kids and lambs are able to stand and walk very soon after birth. From the moment they first stood up, their response on the visual cliff was as accu- rate and predictable as that of the chicks. Not one error was made. When one of the researchers placed a one-day-old baby goat on the deep side of the glass, the goat became frightened and froze in a defensive posture. If it was then pushed over the shallow side, it would relax and jump forward onto the seemingly solid surface. This indicated that the visual sense was in complete control and that the animals’ ability to feel the solidity of the glass on the deep side had no effect on the response. For the rats, it was a different story. They did not appear to show any significant preference for the shallow side of the table. Why do you suppose this difference was found? Before you conclude that rats are just stupid, con- sider Gibson and Walk’s much more likely explanation: A rat does not depend very much on vision to survive. Because it is nocturnal, a rat locates food by smell and moves around in the dark using cues from the stiff whiskers on its nose. So when a rat was placed on the center board, it was not fooled by the visual cliff because it was not using vision to decide which way to go. To the rat’s whiskers, the glass on the deep side felt the same as the glass on the shallow side and, thus, the rat was just as likely to move off the center board to the deep side as to the shallow side. You might expect the same results from kittens. They are basically noc- turnal and have sensitive whiskers. However, cats are predators, not scavengers like rats. Therefore, they depend more on vision. And, accordingly, kittens were found to have excellent depth perception as soon as they were able to move on their own: at about 4 weeks. Although at times this research article, and this discussion, risk sound- ing like a children’s animal story, it has to be reported that the species with the