A breathtaking and insightful journey

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More Praise for

the invisible gorilla

“Should be required reading by every judge and jury member in our crimi- nal justice system, along with every battlefi eld commander, corporate CEO, member of Congress, and, well, you and me . . . because the mental illusions so wonderfully explicated in this book can fool every one of us.”

—Michael Shermer, publisher of Skeptic magazine, monthly columnist for

Scientifi c American, and author of Why People Believe Weird Things

“A breathtaking and insightful journey through the illusions that infl u- ence every moment of our lives.”

—Richard Wiseman, author of Quirkology:

How We Discover the Big Truths in Small Things

“Not just witty and engaging but also insightful. . . . Reading this book won’t cure you of all these limitations, but it will at least help you recognize and compensate for them.”

—Thomas W. Malone, author of The Future of Work and

founder of the MIT Center for Collective Intelligence

“Everyday illusions trick us into thinking that we see—and know—more than we really do, and that we can predict the future when we can’t. The Invisible Gorilla teaches us exactly why, and it does so in an incredibly engaging way. Chabris and Simons provide terrifi c tips on how to cast off our illusions and get things right. Whether you’re a driver wanting to steer clear of on- coming motorcycles, a radiologist hoping to spot every tumor, or just an aver- age person curious about how your mind really works, this is a must-read.”

—Elizabeth Loftus, PhD, Distinguished Professor, University of

California–Irvine, and author of Memory and Eyewitness Testimony

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“An eye-opening book. After reading The Invisible Gorilla you will look at yourself and the world around you differently. Like its authors, the book is both funny and smart, fi lled with insights into the everyday illusions that we all walk around with. No matter what your job is or what you do in life, you will learn something from this book.”

—Joseph T. Hallinan, Pulitzer Prize–winning

author of Why We Make Mistakes

“Cognitive scientists Chris Chabris and Dan Simons deliver an entertaining tour of the many ways our brains mislead us every day. The Invisible Gorilla is engaging, accurate, and packed with real-world examples—some of which made me laugh out loud. Read it to fi nd out why weathermen might make good money managers, and what Homer Simpson can teach you about thinking clearly.”

—Sandra Aamodt, PhD, coauthor of Welcome to Your Brain

and former editor, Nature Neuroscience

“Wonderfully refreshing . . . The Invisible Gorilla makes us smarter by reminding us how little we know. Through a lively tour of the brain’s blind spots, this book will change the way you drive your car, hire your employees, and invest your money.”

—Amanda Ripley, senior writer, Time magazine,

and author of The Unthinkable

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the invisible gorilla

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Christopher Chabris

and Daniel Simons

c r o w n New York

the invisible gorilla And Other Ways Our Intuitions Deceive Us

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Copyright © 2010 by Christopher F. Chabris and Daniel J. Simons

All rights reserved. Published in the United States by Crown Publishers, an imprint of the Crown Publishing Group, a division of Random House, Inc., New York. www .crownpublishing .com

CROWN and the Crown colophon are registered trademarks of Random House, Inc.

Library of Congress Cataloging- in- Publication Data

Chabris, Christopher F. The invisible gorilla : and other ways our intuitions deceive us / Christopher F. Chabris and Daniel J. Simons. p. cm. Includes bibliographical references and index. 1. Perception. 2. Memory. 3. Thought and thinking. I. Simons, Daniel J. II. Title.

BF321.C43 2010 153.7’4—dc22

2009045325

ISBN 978- 0- 307- 45965- 7

Printed in the United States of America

Design by Ralph Fowler / rlf design

10 9 8 7 6 5 4 3 2 1

First Edition

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C O N T E N T S

Introduction: Everyday Illusions ix

1. “I Think I Would Have Seen That” 1

2. The Coach Who Choked 43

3. What Smart Chess Players and Stupid Criminals Have in Common 80

4. Should You Be More Like a Weather Forecaster or a Hedge Fund Manager? 116

5. Jumping to Conclusions 150

6. Get Smart Quick! 185

Conclusion: The Myth of Intuition 224

Ac know ledg ments 243

Notes 247

Index 291

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I N T R O D U C T I O N

everyday illusions

“There are three things extremely hard: steel,

a diamond, and to know one’s self.”

—Benjamin Franklin, Poor Richard’s Almanack (1750)

About twelve years ago, we conducted a simple experiment with the students in a psychology course we were teaching at Harvard University. To our surprise, it has become one of the best- known experiments in psychology. It appears in textbooks and is taught in introductory psychology courses throughout the world. It has been featured in magazines such as Newsweek and The New Yorker and on tele vi sion programs, including Dateline NBC. It has even been exhib- ited in the Exploratorium in San Francisco and in other museums. The experiment is pop u lar because it reveals, in a humorous way, something unexpected and deep about how we see our world— and about what we don’t see.

You’ll read about our experiment in the fi rst chapter of this book. As we’ve thought about it over the years, we’ve realized that it illustrates a broader principle about how the mind works. We all believe that we are

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x INTRODUCTION

capable of seeing what’s in front of us, of accurately remembering im- portant events from our past, of understanding the limits of our knowl- edge, of properly determining cause and effect. But these intuitive beliefs are often mistaken ones that mask critically important limita- tions on our cognitive abilities.

We must be reminded not to judge a book by its cover because we take outward appearances to be accurate advertisements of inner, un- seen qualities. We need to be told that a penny saved is a penny earned because we think about cash coming in differently from money we al- ready have. Aphorisms like these exist largely to help us avoid the mis- takes that intuition can cause. Likewise, Benjamin Franklin’s observation about extremely hard things suggests that we should question the intui- tive belief that we understand ourselves well. As we go through life, we act as though we know how our minds work and why we behave the way we do. It is surprising how often we really have no clue.

The Invisible Gorilla is a book about six everyday illusions that pro- foundly infl uence our lives: the illusions of attention, memory, confi – dence, knowledge, cause, and potential. These are distorted beliefs we hold about our minds that are not just wrong, but wrong in dangerous ways. We will explore when and why these illusions affect us, the conse- quences they have for human affairs, and how we can overcome or min- imize their impact.

We use the word “illusions” as a deliberate analogy to visual illusions like M. C. Escher’s famous never- ending staircase: Even after you realize that something about the picture as a whole is not right, you still can’t stop yourself from seeing each individual segment as a proper staircase. Everyday illusions are similarly per sis tent: Even after we know how our beliefs and intuitions are fl awed, they remain stubbornly resistant to change. We call them everyday illusions because they affect our behav- ior literally every day. Every time we talk on a cell phone while driving, believing we’re still paying enough attention to the road, we’ve been af- fected by one of these illusions. Every time we assume that someone who misremembers their past must be lying, we’ve succumbed to an illusion. Every time we pick a leader for a team because that person expresses the

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INTRODUCTION xi

most confi dence, we’ve been infl uenced by an illusion. Every time we start a new project convinced that we know how long it will take to com- plete, we are under an illusion. Indeed, virtually no realm of human be- havior is untouched by everyday illusions.

As professors who design and run psychology experiments for a living, we’ve found that the more we study the nature of the mind, the more we see the impact of these illusions in our own lives. You can develop the same sort of x-ray vision into the workings of your own mind. When you fi nish this book, you will be able to glimpse the man behind the curtain and some of the tiny gears and pulleys that govern your thoughts and be- liefs. Once you know about everyday illusions, you will view the world differently and think about it more clearly. You will see how illusions affect your own thoughts and actions, as well as the behavior of every- one around you. And you will recognize when journalists, managers, advertisers, and politicians— intentionally or accidentally— take advan- tage of illusions in an attempt to obfuscate or persuade. Understanding everyday illusions will lead you to recalibrate the way you approach your life to account for the limitations— and the true strengths— of your mind. You might even come up with ways to exploit these insights for fun and profi t. Ultimately, seeing through the veils that distort how we perceive ourselves and the world will connect you— for perhaps the fi rst time— with reality.

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the invisible gorilla

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1C H A P T E R “ i think i would have

seen that”

Around two o’clock on the cold, overcast morning of January 25, 1995, a group of four black men left the scene of a shooting at a hamburger restaurant in the Grove Hall section of Boston.1 As they drove away in a gold Lexus, the police radio erroneously announced that the victim was a cop, leading offi cers from several districts to join in a ten- mile high- speed chase. In the fi fteen to twenty minutes of mayhem that ensued, one police car veered off the road and crashed into a parked van. Eventually the Lexus skidded to a stop in a cul- de- sac on Wood- ruff Way in the Mattapan neighborhood. The suspects fl ed the car and ran in different directions.

One suspect, Robert “Smut” Brown III, age twenty- four, wearing a dark leather jacket, exited the back passenger side of the car and sprinted toward a chain- link fence on the side of the cul- de- sac. The fi rst car in pursuit, an unmarked police vehicle, stopped to the left of the Lexus. Michael Cox, a decorated offi cer from the police antigang unit who’d grown up in the nearby Roxbury area, got out of the passenger seat and took off after Brown. Cox, who also is black, was in plainclothes that night; he wore jeans, a black hoodie, and a parka.2

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2 THE INVISIBLE GORILLA

Cox got to the fence just after Smut Brown. As Brown scrambled over the top, his jacket got stuck on the metal. Cox reached for Brown and tried to pull him back, but Brown managed to fall to the other side. Cox prepared to scale the fence in pursuit, but just as he was starting to climb, his head was struck from behind by a blunt object, perhaps a baton or a fl ashlight. He fell to the ground. Another police offi cer had mistaken him for a suspect, and several offi cers then beat up Cox, kick- ing him in the head, back, face, and mouth. After a few moments, some- one yelled, “Stop, stop, he’s a cop, he’s a cop.” At that point, the offi cers fl ed, leaving Cox lying unconscious on the ground with facial wounds, a concussion, and kidney damage.3

Meanwhile, the pursuit of the suspects continued as more cops ar- rived. Early on the scene was Kenny Conley, a large, athletic man from South Boston who had joined the police force four years earlier, not long after graduating from high school. Conley’s cruiser came to a stop about forty feet away from the gold Lexus. Conley saw Smut Brown scale the fence, drop to the other side, and run. Conley followed Brown over the fence, chased him on foot for about a mile, and eventually captured him at gunpoint and handcuffed him in a parking lot on River Street. Conley wasn’t involved in the assault on Offi cer Cox, but he began his pursuit of Brown right as Cox was being pulled from the fence, and he scaled the fence right next to where the beating was happening.

Although the other murder suspects were caught and that case was considered solved, the assault on Offi cer Cox remained wide open. For the next two years, internal police investigators and a grand jury sought answers about what happened at the cul- de- sac. Which cops beat Cox? Why did they beat him? Did they simply mistake their black colleague for one of the black suspects? If so, why did they fl ee rather than seek medical help? Little headway was made, and in 1997, the local prose- cutors handed the matter over to federal authorities so they could investigate possible civil rights violations.

Cox named three offi cers whom he said had attacked him that night, but all of them denied knowing anything about the assault. Initial po- lice reports said that Cox sustained his injuries when he slipped on a

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“I THINK I WOULD HAVE SEEN THAT” 3

patch of ice and fell against the back of one of the police cars. Although many of the nearly sixty cops who were on the scene must have known what happened to Cox, none admitted knowing anything about the beating. Here, for example, is what Kenny Conley, who apprehended Smut Brown, said under oath:

Q: So your testimony is that you went over the fence within seconds of seeing him go over the fence?

A: Yeah.

Q: And in that time, you did not see any black plainclothes police offi cer chasing him?

A: No, I did not.

Q: In fact, no black plainclothes offi cer was chasing him, accord- ing to your testimony?

A: I did not see any black plainclothes offi cer chasing him.

Q: And if he was chasing him, you would have seen it?

A: I should have.

Q: And if he was holding the suspect as the suspect was at the top of the fence, he was lunging at him, you would have seen that, too?

A: I should have.

When asked directly if he would have seen Cox trying to pull Smut Brown from the fence, he responded, “I think I would have seen that.” Conley’s terse replies suggested a reluctant witness who had been advised by lawyers to stick to yes or no answers and not volunteer information. Since he was the cop who had taken up the chase, he was in an ideal posi- tion to know what happened. His per sis tent refusal to admit to having seen Cox effectively blocked the federal prosecutors’ attempt to indict the offi – cers involved in the attack, and no one was ever charged with the assault.

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4 THE INVISIBLE GORILLA

The only person ever charged with a crime in the case was Kenny Conley himself. He was indicted in 1997 for perjury and obstruction of justice. The prosecutors were convinced that Conley was “testilying”— outlandishly claiming, under oath, not to have seen what was going on right before his eyes. According to this theory, just like the offi cers who fi led reports denying any knowledge of the beating, Conley wouldn’t rat out his fellow cops. Indeed, shortly after Conley’s indictment, prom- inent Boston- area investigative journalist Dick Lehr wrote that “the Cox scandal shows a Boston police code of silence . . . a tight inner circle of offi cers protecting themselves with false stories.”4

Kenny Conley stuck with his story, and his case went to trial. Smut Brown testifi ed that Conley was the cop who arrested him. He also said that after he dropped over the fence, he looked back and saw a tall white cop standing near the beating. Another police offi cer also testifi ed that Conley was there. The jurors were incredulous at the notion that Conley could have run to the fence in pursuit of Brown without noticing the beating, or even seeing Offi cer Cox. After the trial, one juror explained, “It was hard for me to believe that, even with all the chaos, he didn’t see something.” Juror Burgess Nichols said that another juror had told him that his father and uncle had been police offi cers, and offi cers are taught “to observe everything” because they are “trained professionals.”5

Unable to reconcile their own expectations—and Conley’s—with Conley’s testimony that he didn’t see Cox, the jury convicted him. Kenny Conley was found guilty of one count each of perjury and ob- struction of justice, and he was sentenced to thirty- four months in jail.6 In 2000, after the U.S. Supreme Court declined to hear his case, he was fi red from the Boston police force. While his lawyers kept him out of jail with new appeals, Conley took up a new career as a carpenter.7

Dick Lehr, the journalist who reported on the Cox case and the “blue wall of silence,” never actually met with Kenny Conley until the summer of 2001. After this interview, Lehr began to wonder whether Conley might actually be telling the truth about what he saw and expe- rienced during his pursuit of Smut Brown. That’s when Lehr brought the former cop to visit Dan’s laboratory at Harvard.

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“I THINK I WOULD HAVE SEEN THAT” 5

Gorillas in Our Midst

The two of us met over a de cade ago when Chris was a graduate student in the Harvard University psychology department and Dan had just arrived as a new assistant professor. Chris’s offi ce was down the hall from Dan’s lab, and we soon discovered our mutual interest in how we perceive, remember, and think about our visual world. The Kenny Conley case was in full swing when Dan taught an undergraduate course in research methods with Chris as his teaching assistant. As part of their classwork, the students assisted us in conducting some experi- ments, one of which has become famous. It was based on an ingenious series of studies of visual attention and awareness conducted by the pio- neering cognitive psychologist Ulric Neisser in the 1970s. Neisser had moved to Cornell University when Dan was in his fi nal year of graduate school there, and their many conversations inspired Dan to build on Neisser’s earlier, groundbreaking research.

With our students as actors and a temporarily vacant fl oor of the psy- chology building as a set, we made a short fi lm of two teams of people moving around and passing basketballs. One team wore white shirts and the other wore black. Dan manned the camera and directed. Chris co- ordinated the action and kept track of which scenes we needed to shoot. We then digitally edited the fi lm and copied it to videotapes, and our students fanned out across the Harvard campus to run the experiment.8

They asked volunteers to silently count the number of passes made by the players wearing white while ignoring any passes by the players wearing black. The video lasted less than a minute. If you want to try the task yourself, stop reading now and go to the website for our book, www . theinvisiblegorilla .com, where we provide links to many of the experi- ments we discuss, including a short version of the basketball-passing video. Watch the video carefully, and be sure to include both aerial passes and bounce passes in your count.

Immediately after the video ended, our students asked the subjects to report how many passes they’d counted. In the full-length version, the correct answer was thirty- four—or maybe thirty- fi ve. To be honest, it

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6 THE INVISIBLE GORILLA

doesn’t matter. The pass- counting task was intended to keep people en- gaged in doing something that demanded attention to the action on the screen, but we weren’t really interested in pass- counting ability. We were actually testing something else: Halfway through the video, a female stu- dent wearing a full- body gorilla suit walked into the scene, stopped in the middle of the players, faced the camera, thumped her chest, and then walked off, spending about nine seconds onscreen. After asking subjects about the passes, we asked the more important questions:

Q: Did you notice anything unusual while you were doing the counting task?

A: No.

Q: Did you notice anything other than the players?

A: Well, there were some elevators, and S’s painted on the wall. I don’t know what the S’s were there for.

Q: Did you notice anyone other than the players?

A: No.

Q: Did you notice a gorilla?

A: A what?!?

Amazingly, roughly half of the subjects in our study did not notice the gorilla! Since then the experiment has been repeated many times, under different conditions, with diverse audiences, and in multiple countries, but the results are always the same: About half the people fail to see the gorilla. How could people not see a gorilla walk directly in front of them, turn to face them, beat its chest, and walk away? What made the gorilla invisible? This error of perception results from a lack of attention to an unexpected object, so it goes by the scientifi c name “inattentional blind- ness.” This name distinguishes it from forms of blindness resulting from a damaged visual system; here, people don’t see the gorilla, but not be- cause of a problem with their eyes. When people devote their attention to

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“I THINK I WOULD HAVE SEEN THAT” 7

a par tic u lar area or aspect of their visual world, they tend not to notice unexpected objects, even when those unexpected objects are salient, po- tentially important, and appear right where they are looking.9 In other words, the subjects were concentrating so hard on counting the passes that they were “blind” to the gorilla right in front of their eyes.

What prompted us to write this book, however, was not inattentional blindness in general or the gorilla study in par tic u lar. The fact that people miss things is important, but what impressed us even more was the sur- prise people showed when they realized what they had missed. When they watched the video again, this time without counting passes, they all saw the gorilla easily, and they were shocked. Some spontaneously said, “I missed that?!” or “No way!” A man who was tested later by the producers of Dateline NBC for their report on this research said, “I know that gorilla didn’t come through there the fi rst time.” Other subjects accused us of switching the tape while they weren’t looking.

The gorilla study illustrates, perhaps more dramatically than any other, the powerful and pervasive infl uence of the illusion of attention: We experience far less of our visual world than we think we do. If we were fully aware of the limits to attention, the illusion would vanish. While writing this book we hired the polling fi rm SurveyUSA to contact a representative sample of American adults and ask them a series of questions about how they think the mind works. We found that more than 75 percent of people agreed that they would notice such unexpected events, even when they were focused on something else.10 (We’ll talk about other fi ndings of this survey throughout the book.)

It’s true that we vividly experience some aspects of our world, par- ticularly those that are the focus of our attention. But this rich experi- ence inevitably leads to the erroneous belief that we pro cess all of the detailed information around us. In essence, we know how vividly we see some aspects of our world, but we are completely unaware of those aspects of our world that fall outside of that current focus of attention. Our vivid visual experience masks a striking mental blindness— we as- sume that visually distinctive or unusual objects will draw our atten- tion, but in reality they often go completely unnoticed.11

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8 THE INVISIBLE GORILLA

Since our experiment was published in the journal Perception in 1999, under the title “Gorillas in Our Midst,”12 it has become one of the most widely demonstrated and discussed studies in all of psychology. It earned us an Ig Nobel Prize in 2004 (awarded for “achievements that fi rst make people laugh, and then make them think”) and was even discussed by characters in an episode of the television drama CSI.13 And we’ve lost count of the number of times people have asked us whether we have seen the video with the basketball players and the gorilla.

Kenny Conley’s Invisible Gorilla

Dick Lehr brought Kenny Conley to Dan’s laboratory because he had heard about our gorilla experiment, and he wanted to see how Conley would do in it. Conley was physically imposing, but stoic and taciturn; Lehr did most of the talking that day. Dan led them to a small, window- less room in his laboratory and showed Conley the gorilla video, asking him to count the passes by the players wearing white. In advance, there was no way to know whether or not Conley would notice the unex- pected gorilla— about half of the people who watch the video see the gorilla. Moreover, Conley’s success or failure in noticing the gorilla would not tell us whether or not he saw Michael Cox being beaten on Woodruff Way six years earlier. (These are both important points, and we will return to them shortly.) But Dan was still curious about how Conley would react when he heard about the science.

Conley counted the passes accurately and saw the gorilla. As is usual for people who do see the gorilla, he seemed genuinely surprised that anyone else could possibly miss it. Even when Dan explained that people often miss unexpected events when their attention is otherwise en- gaged, Conley still had trouble accepting that anyone else could miss what seemed so obvious to him.

The illusion of attention is so ingrained and pervasive that everyone involved in the case of Kenny Conley was operating under a false no- tion of how the mind works: the mistaken belief that we pay attention to— and therefore should notice and remember— much more of the

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“I THINK I WOULD HAVE SEEN THAT” 9

world around us than we actually do. Conley himself testifi ed that he should have seen the brutal beating of Michael Cox had he actually run right past it. In their appeal of his conviction, Conley’s lawyers tried to show that he hadn’t run past the beating, that the testimony about his presence near the beating was wrong, and that descriptions of the inci- dent from other police offi cers were inaccurate. All of these arguments were founded on the assumption that Conley could only be telling the truth if he didn’t have the opportunity to see the beating. But what if, instead, in the cul- de- sac on Woodruff Way, Conley found himself in a real- life version of our gorilla experiment? He could have been right next to the beating of Cox, and even focused his eyes on it, without ever actually seeing it.

Conley was worried about Smut Brown scaling the fence and escap- ing, and he pursued his suspect with a single- minded focus that he de- scribed as “tunnel vision.” Conley’s prosecutor ridiculed this idea, saying that what prevented Conley from seeing the beating was not tunnel vision but video editing—“a deliberate cropping of Cox out of the picture.”14

But if Conley was suffi ciently focused on Brown, in the way our sub- jects were focused on counting the basketball passes, it is entirely possible that he ran right past the assault and still failed to see it. If so, the only inaccurate part of Conley’s testimony was his stated belief that he should have seen Cox. What is most striking about this case is that Conley’s own testimony was the primary evidence that put him near the beating, and that evidence, combined with a misunderstanding of how the mind works, and the blue wall of silence erected by the other cops, led prosecutors to charge him with perjury and obstruction of justice. They, and the jury that convicted him, assumed that he too was protecting his comrades.

Kenny Conley’s conviction was eventually overturned on appeal and set aside in July 2005. But Conley prevailed not because the prosecutors or a judge were convinced that he actually was telling the truth. Instead, the appeals court in Boston ruled that he had been denied a fair trial be- cause the prosecution didn’t tell his defense attorneys about an FBI memo that cast doubt on the credibility of one of the government’s witnesses.15 When the government decided not to retry him in September 2005,

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10 THE INVISIBLE GORILLA

Conley’s legal troubles were fi nally over. On May 19, 2006, more than eleven years after the original incident on Woodruff Way that changed his life, Conley was reinstated as a Boston police offi cer— but only after being forced to redo, at age thirty- seven, the same police academy training a new recruit has to endure.16 He was granted $647,000 in back pay for the years he was off the force,17 and in 2007 he was promoted to detective.18

Throughout this book, we will present many examples and anec- dotes, like the story of Kenny Conley, that show how everyday illusions can have tremendous infl uence on our lives. However, two important caveats are in order. First, as Robert Pirsig writes in Zen and the Art of Motorcycle Maintenance, “The real purpose of scientifi c method is to make sure Nature hasn’t misled you into thinking you know something that you actually don’t.”19 But science can only go so far, and although it can tell us in general how galaxies form, how DNA is transcribed into proteins, and how our minds perceive and remember our world, it is nearly impotent to explain a single event or individual case. The nature of everyday illusions almost never allows for proof that any par tic u lar incident was caused entirely by a specifi c mental mistake. There is no certainty that Conley missed the beating because of inattentional blind- ness, nor is there even certainty that he missed it at all (he could have seen it and then consistently lied). Without doing a study of attention under the same conditions Conley faced (at night, running after some- one climbing a fence, the danger in chasing a murder suspect, the unfa- miliar surroundings, and a gang of men attacking someone), we cannot estimate the probability that Conley missed what he said he missed.

We can, however, say that the intuitions of the people who condemned and convicted him were way off the mark. What is certain is that the police investigators, the prosecutors, and the jurors, and to some extent Kenny Conley himself, were all operating under the illusion of atten- tion and failed to consider the possibility— which we argue is a strong possibility— that Conley could have been telling the truth about both where he was and what he didn’t see on that January night in Boston.

The second important point to keep in mind is this: We use stories and anecdotes to convey our arguments because narratives are compel-

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“I THINK I WOULD HAVE SEEN THAT” 11

ling, memorable, and easily understood. But people tend to believe con- vincing, retrospective stories about why something happened even when there is no conclusive evidence of the event’s true causes. For that reason, we try to back up all of our examples with scientifi c research of the high- est quality, using endnotes to document our sources and provide addi- tional information along the way.

Our goals are to show you how everyday illusions infl uence our thoughts, decisions, and actions, and to convince you that they have large effects on our lives. We believe that once you have considered our argu- ments and evidence, you will agree, and that you will think about your own mind and your own behavior much differently. We hope that you will then act accordingly. So as you read on, read critically, keeping your mind open to the possibility that it doesn’t work the way you think it does.

The Nuclear Submarine and the Fishing Boat

Do you remember the fi rst major international incident of George W. Bush’s presidency? It happened less than a month after he took offi ce, on February 9, 2001.20 At approximately 1:40 p.m., Commander Scott Waddle, captaining the nuclear submarine USS Greene ville near Ha- waii, ordered a surprise maneuver known as an “emergency deep,” in which the submarine suddenly dives. He followed this with an “emer- gency main ballast tank blow,” in which high- pressure air forces water from the main ballasts, causing the submarine to surface as fast as it can. In this kind of maneuver, shown in movies like The Hunt for Red October, the bow of the submarine actually heaves out of the water. As the Greeneville zoomed toward the surface, the crew and passengers heard a loud noise, and the entire ship shook. “Jesus!” said Waddle. “What the hell was that?”

His ship had surfaced, at high speed, directly under a Japa nese fi sh- ing vessel, the Ehime Maru. The Greeneville’s rudder, which had been specially reinforced for penetrating ice packs in the Arctic, sliced the fi shing boat’s hull from one side to the other. Diesel fuel began to leak and the Ehime Maru took on water. Within minutes, it tipped up and

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12 THE INVISIBLE GORILLA

sank by its stern as the people onboard scrambled forward toward the bow. Many of them reached the three lifeboats and were rescued, but three crew members and six passengers died. The Greeneville received only minor damage, and no one onboard was injured.

What went wrong? How could a modern, technologically advanced submarine, equipped with state- of- the- art sonar and manned by an experienced crew, not detect a nearly two- hundred- foot- long fi shing boat so close by? In attempting to explain this accident, the National Transportation Safety Board’s fi fty- nine- page report exhaustively doc- uments all of the ways in which the offi cers failed to follow procedure, all of the distractions they faced in accommodating a delegation of civilian visitors, all of the errors they made along the way, and all of the miscommunication that contributed to poor tracking of the Ehime Maru’s actual position. It contains no evidence of alcohol, drugs, mental illness, fatigue, or personality confl icts infl uencing the crew’s ac- tions. The report is most interesting, however, for the crucial issue it does not even attempt to resolve: why Commander Waddle and the of- fi cer of the deck failed to see the Ehime Maru when they looked through the periscope.

Before a submarine performs an emergency deep maneuver, it re- turns to periscope depth so the commander can make sure no other ships are in the vicinity. The Ehime Maru should have been visible through the periscope, and Commander Waddle looked right toward it, but he still missed it. Why? The NTSB report emphasized the brevity of the periscope scan, as did Dateline NBC correspondent Stone Phillips: “. . . had Waddle stayed on the periscope longer, or raised it higher, he might have seen the Ehime Maru. He says there is no doubt he was look- ing in the right direction.” None of these reports consider any other reasons why Waddle could have failed to see the nearby vessel— a failure that surprised Waddle himself. But the results of our gorilla experiment tell us that the USS Greeneville’s commanding offi cer, with all his expe- rience and expertise, could indeed have looked right at another ship and just not have seen it. The key lies in what he thought he would see when he looked: As he said later, “I wasn’t looking for it, nor did I expect it.”21

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“I THINK I WOULD HAVE SEEN THAT” 13

Submarines rarely surface into other ships, so don’t lose sleep over the prospect on your next boat trip. But this kind of “looked but failed to see” accident is quite common on land. Perhaps you have had the experience of starting to turn out of a parking lot or a side road and then having to stop suddenly to avoid hitting a car you hadn’t seen be- fore that moment. After accidents, drivers regularly claim, “I was look- ing right there and they came out of nowhere . . . I never saw them.”22 These situations are especially troubling because they run counter to our intuitions about the mental pro cesses involved in attention and per- ception. We think we should see anything in front of us, but in fact we are aware of only a small portion of our visual world at any moment. The idea that we can look but not see is fl atly incompatible with how we understand our own minds, and this mistaken understanding can lead to incautious or overconfi dent decisions.

In this chapter, when we talk about looking, as in “looking without seeing,” we don’t mean anything abstract or vague or meta phorical. We literally mean looking right at something. We truly are arguing that directing our eyes at something does not guarantee that we will con- sciously see it. A skeptic might question whether a subject in the gorilla experiment or an offi cer chasing a suspect or a submarine commander bringing his ship to the surface actually looked right at the unexpected object or event. To perform these tasks, though (to count the passes, pursue a suspect, or sweep the area for ships), they needed to look right where the unexpected object appeared. It turns out that there is a way, in a laboratory situation at least, to mea sure exactly where on a screen a person fi xates their eyes (a technical way of saying “where they are look- ing”) at any moment. This technique, which uses a device called an “eye tracker,” can provide a continuous trace showing where and for how long a subject is looking during any period of time— such as the time of watching the gorilla video. Sports scientist Daniel Memmert of Heidelberg University ran our gorilla experiment using his eye tracker and found that the subjects who failed to notice the gorilla had spent, on average, a full second looking right at it— the same amount of time as those who did see it!23

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14 THE INVISIBLE GORILLA

Ben Roethlisberger’s Worst Interception

In February 2006, at the age of twenty- three and in just his second season as a professional football player, Ben Roethlisberger became the youn gest quarterback in NFL history to win a Super Bowl. During the off- season, on June 12 of that same year, he was riding his black 2005 Suzuki motorcycle heading outbound from downtown Pittsburgh on Second Avenue.24 As he neared the intersection at Tenth Street, a Chrysler New Yorker driven by Martha Fleishman approached in the opposite direction on Second Avenue. Both vehicles had green lights when Fleishman then turned left onto Tenth Street, cutting off Roeth- lisberger’s motorcycle. According to witnesses, Roethlisberger was thrown from his motorcycle, hit the Chrysler’s windshield, tumbled over the roof and off the trunk, and fi nally landed on the street. His jaw and nose were broken, many of his teeth were knocked out, and he re- ceived a large laceration on the back of his head, as well as a number of other minor injuries. He required seven hours of emergency surgery, but considering that he wasn’t wearing a helmet, he was lucky to survive the crash at all. Fleishman had a nearly perfect driving record— the only mark against her was a speeding ticket nine years earlier. Roeth- lisberger was cited for not wearing a helmet and for driving without the right type of license; Fleishman was cited and fi ned for failing to yield. Roethlisberger eventually made a full recovery from the accident and was ready to resume his role as the starting quarterback by the season opener in September.

Accidents like this one are unfortunately common. More than half of all motorcycle accidents are collisions with another vehicle. Nearly 65 percent of those happen much like Roethlisberger’s— a car violates the motorcycle’s right-of-way, turning left in front of the motorcyclist (or turning right in countries where cars drive on the left side of the road).25 In some cases, the car turns across oncoming traffi c onto a side street. In others, the car turns across a lane of traffi c onto the main street. In the typical accident of this sort, the driver of the car often says something like, “I signaled to turn left, and started out when it was

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“I THINK I WOULD HAVE SEEN THAT” 15

clear. Then something hit my car and I later saw the motorcycle and the guy lying in the street. I never saw him!” The motorcyclist in such ac- cidents says, “All of a sudden this car pulled out in front of me. The driver was looking right at me.” This experience leads some motor- cyclists to assume that car drivers violate their right- of- way intentionally— that they see the motorcyclist and turn anyway.

Why do drivers turn in front of motorcyclists? We favor, at least for some cases, an explanation that appeals to the illusion of attention. People don’t see the motorcyclists because they aren’t looking for motor- cyclists. If you are trying to make a diffi cult left turn across traffi c, most of the vehicles blocking your path are cars, not motorcycles (or bicycles, or horses, or rickshaws . . . ). To some extent, then, motorcycles are un- expected. Much like the subjects in our gorilla experiment, drivers often fail to notice unexpected events, even ones that are important. Criti- cally, though, they assume they will notice— that as long as they are looking in the right direction, unexpected objects and events will grab their attention.

How can we remedy this situation? Motorcycle safety advocates pro- pose a number of solutions, most of which we think are doomed to fail. Posting signs that implore people to “look for motorcycles” might lead drivers to adjust their expectations and become more likely to notice a motorcycle appearing shortly after the sign. Yet, after a few minutes of not seeing any motorcycles, their visual expectations will reset, leading them to again expect what they see most commonly— cars. Such adver- tising campaigns assume that the mechanisms of attention are perme- able, subject to infl uence from our intentions and thoughts. Yet, the wiring of our visual expectations is almost entirely insulated from our conscious control. As we will discuss extensively in Chapter 4, our brains are built to detect patterns automatically, and the pattern we ex- perience when driving features a preponderance of cars and a dearth of motorcycles. In other words, the ad campaign itself falls prey to the il- lusion of attention.

Suppose that one morning, we told you to watch for gorillas. Then, at some point a week later, you participated in our gorilla experiment.

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16 THE INVISIBLE GORILLA

Do you think our warning would have any effect? Most likely not; in the time between the warning and the experiment, your expectations would have been reset by your daily experience of seeing no gorillas. The warning would only be useful if we gave it shortly before showing you the video.

Only when people regularly look for and expect motorcycles will they be more likely to notice. In fact, a detailed analysis of sixty- two accident reports involving cars and motorcycles found that none of the car drivers had any experience riding motorcycles themselves.26 Perhaps the experience of riding a motorcycle can mitigate the effects of inat- tentional blindness for motorcycles. Or, put another way, the experi- ence of being unexpected yourself might make you better able to notice similar unexpected events.

Another common recommendation to improve the safety of motor- cycles is for riders to wear bright clothing rather than the typical attire of leather jacket, dark pants, and boots. The intuition seems right: A yellow jumpsuit should make the rider more visually distinctive and easier to notice. But as we’ve noted, looking is not the same as seeing. You can look right at the gorilla— or at a motorcycle— without seeing it. If the gorilla or motorcycle were physically imperceptible, that would be trivially true—nobody would be surprised if you failed to see a gorilla that was perfectly camoufl aged in a scene. What makes the evi- dence for inattentional blindness important and counterintuitive is that the gorilla is so obvious once you know it is there. So looking is neces- sary for seeing— if you don’t look at it, you can’t possibly see it. But looking is not suffi cient for seeing— looking at something doesn’t guar- antee that you will notice it. Wearing conspicuous clothing and riding a brightly colored motorcycle will increase your visibility, making it easier for people who are looking for you to see you. Such bright clothing doesn’t guarantee that you will be noticed, though.

We did not always realize this ourselves. When we fi rst designed the gorilla experiment, we assumed that making the “gorilla” more distinc- tive would lead to greater detection— of course people would notice a bright red gorilla. Given the rarity of red gorilla suits, we and our col-

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“I THINK I WOULD HAVE SEEN THAT” 17

leagues Steve Most (then a graduate student in Dan’s lab and now a professor at the University of Delaware) and Brian Scholl (then a post- doctoral fellow in the psychology department and now a professor at Yale) created a computerized version of the “gorilla” video in which the players were replaced by letters and the gorilla was replaced by a red cross (+) that unexpectedly traversed the display.27 Subjects counted how many times the white letters touched the sides of the display win- dow while ignoring the black letters.

Even jaded researchers like us were surprised by the result: 30 per- cent of viewers missed the bright red cross, even though it was the only cross, the only colored object, and the only object that moved in a straight path through the display. We thought the gorilla had gone un- noticed, at least in part, because it didn’t really stand out: It was dark- colored, like the players wearing black. Our belief that a distinctive object should “pop out” overrode our knowledge of the phenomenon of inattentional blindness. This “red gorilla” experiment shows that when something is unexpected, distinctiveness does not at all guarantee that we will notice it.

Refl ective clothing helps increase visibility for motorcyclists, but it doesn’t override our expectations. Motorcyclists are analogous to the cross in this experiment. People fail to see them, but not just because they are smaller or less distinctive than the other vehicles on the road. They fail to see the motorcycles precisely because they stand out. Wear- ing highly visible clothing is better than wearing invisible clothing (and less of a technological challenge), but increasing the visual distinctive- ness of the rider might be of limited use in helping drivers notice motor- cyclists. Ironically, what likely would work to increase detection of motorcycles is to make them look more like cars. For example, giving motorcycles two headlights separated as much as possible, to resemble the visual pattern of a car’s headlights, could well increase their detectability.

There is one proven way to eliminate inattentional blindness, though: Make the unexpected object or event less unexpected. Accidents with bicyclists and pedestrians are much like motorcycle accidents in that car drivers often hit the bikers or walkers without ever seeing them.

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18 THE INVISIBLE GORILLA

Peter Jacobsen, a public health con sul tant in California, examined the rates of accidents involving cars and either pedestrians or bicyclists across a range of cities in California and in a number of Eu ro pe an countries.28 For each city, he collected data on the number of injuries or fatalities per million kilometers people traveled by biking and by walk- ing in the year 2000. The pattern was clear, and surprising: Walking and biking were the least dangerous in the cities where they were done the most, and the most dangerous where they were done the least.

Why are motorists less likely to hit pedestrians or bicyclists where there are more people bicycling or walking? Because they are more used to seeing pedestrians. Think of it this way: Would you be safer cross- ing the pedestrian- clogged streets of London, where drivers are used to seeing people swarm around cars, or the wide, almost suburban boule- vards of Los Angeles, where drivers are less accustomed to people pop- ping up right in front of their cars without warning? Jacobsen’s data show that if you were to move to a town with twice as many pedestri- ans, you would reduce your chance of being hit by a car while walking by one- third.

In one of the most striking demonstrations of the power of expecta- tions,29 Steve Most, who led the “red gorilla” study, and his colleague Robert Astur of the Olin Neuropsychiatry Research Center in Hart- ford, Connecticut, conducted an experiment using a driving simulator. Just before arriving at each intersection, subjects looked for a blue arrow that indicated which way they should turn, and they ignored yellow ar- rows. Just as subjects entered one of the intersections, a motorcycle un- expectedly drove right into their path and stopped. When the motorcycle was blue, the same color as the attended direction arrows, almost all of the drivers noticed it. When it was yellow, matching the ignored direc- tion arrows, 36 percent of them hit the motorcycle, and two of them failed to apply their brakes at all! Your moment- to- moment expecta- tions, more than the visual distinctiveness of the object, determine what you see— and what you miss.

Of course, not every automobile- versus- motorcycle collision is en- tirely the fault of the person driving the car. In the Ben Roethlisberger

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“I THINK I WOULD HAVE SEEN THAT” 19

accident, the driver and the rider both had green lights, but Roethlis- berger was going straight and had the right-of-way. A witness at the scene quoted Martha Fleishman, the driver of the car, as saying, “I was watching him approach but he was not looking at me.”30 Roethlisberger might never have seen Fleishman’s car, even though it was right in front of him. Had he seen it, he might have been able to avoid the accident.

A Hard Landing

NASA research scientist Richard Haines spent much of his career at Ames Research Center, a space and aeronautics think tank in northern California. He is best known publicly for his attempts to document UFO experiences. But in the late 1970s and early 1980s, he and his col- leagues Edith Fischer and Toni Price conducted a pioneering study on pi lots and information display technologies using a fl ight simulator.31 Their experiment is important because it is one of the most dramatic demonstrations of looking without seeing. They tested commercial air- line pi lots who were rated to fl y the Boeing 727, one of the most com- mon planes of the time. Commercial airline pi lots tend to be among the most experienced and expert pilots— many fl ew in the military for years, and only the top pi lots get to fl y the larger commercial planes, where they have responsibility for hundreds of passengers on every fl ight. The subjects in this study were either fi rst offi cers or captains who had fl own 727s commercially for over one thousand hours.

During the experiment, the pi lots underwent extensive training on the use of a “head- up display.” This technology, which was relatively new at the time, displayed much of the critical instrumentation needed to fl y and land the simulated 727— altitude, bearing, speed, fuel status, and so on— in video form directly on the windshield in front of the pi- lots, rather than below or around it as in an ordinary cockpit. Over the course of multiple sessions, the pi lots fl ew a number of simulated land- ings under a wide range of weather conditions, either with or without the head- up display. Once they were practiced with the simulator, Haines inserted a surprise into one of the landing trials. As the pi lots

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