Read the book: «The Invisible Gorilla: And Other Ways Our Intuition Deceives Us»
The Invisible Gorilla
And Other Ways Our Intuition Deceives Us
Christopher Chabris
& Daniel Simons
Table of Contents
Cover Page
Title Page
INTRODUCTION everyday illusions
CHAPTER 1 “i think i would have seen that”
CHAPTER 2 the coach who choked
CHAPTER 3 what smart chess players and stupid criminals have in common
CHAPTER 4 should you be more like a weather forecaster or a hedge fund manager?
CHAPTER 5 jumping to conclusions
CHAPTER 6 get smart quick!
conclusion the myth of intuition
NOTES
INDEX
Acknowledgments
More Praise for the INVISIBLE GORILLA
Copyright
About the Publisher
INTRODUCTION 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 television programs, including Dateline NBC. It has even been exhibited in the Exploratorium in San Francisco and in other museums. The experiment is popular 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 first 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 capable of seeing what’s in front of us, of accurately remembering important events from our past, of understanding the limits of our knowledge, of properly determining cause and effect. But these intuitive beliefs are often mistaken ones that mask critically important limitations 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, unseen 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 already have. Aphorisms like these exist largely to help us avoid the mistakes that intuition can cause. Likewise, Benjamin Franklin’s observation about extremely hard things suggests that we should question the intuitive 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 profoundly influence our lives: the illusions of attention, memory, confidence, 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 consequences they have for human affairs, and how we can overcome or minimize 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 persistent: Even after we know how our beliefs and intuitions are flawed, they remain stubbornly resistant to change. We call them everyday illusions because they affect our behavior 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 affected 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 most confidence, we’ve been influenced by an illusion. Every time we start a new project convinced that we know how long it will take to complete, we are under an illusion. Indeed, virtually no realm of human behavior 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 finish 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 beliefs. 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 everyone around you. And you will recognize when journalists, managers, advertisers, and politicians—intentionally or accidentally—take advantage 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 profit. Ultimately, seeing through the veils that distort how we perceive ourselves and the world will connect you—for perhaps the first time—with reality.
CHAPTER 1 “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 officers from several districts to join in a ten-mile high-speed chase. In the fifteen 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 Woodruff Way in the Mattapan neighborhood. The suspects fled 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 first car in pursuit, an unmarked police vehicle, stopped to the left of the Lexus. Michael Cox, a decorated officer 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
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 flashlight. He fell to the ground. Another police officer had mistaken him for a suspect, and several officers then beat up Cox, kicking him in the head, back, face, and mouth. After a few moments, someone yelled, “Stop, stop, he’s a cop, he’s a cop.” At that point, the officers fled, 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 arrived. 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 Officer 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 Officer 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 flee rather than seek medical help? Little headway was made, and in 1997, the local prosecutors handed the matter over to federal authorities so they could investigate possible civil rights violations.
Cox named three officers whom he said had attacked him that night, but all of them denied knowing anything about the assault. Initial police reports said that Cox sustained his injuries when he slipped on a 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 officer chasing him?
A: No, I did not.
Q: In fact, no black plainclothes officer was chasing him, according to your testimony?
A: I did not see any black plainclothes officer 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 position to know what happened. His persistent refusal to admit to having seen Cox effectively blocked the federal prosecutors’ attempt to indict the officers involved in the attack, and no one was ever charged with the assault.
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 officers who filed reports denying any knowledge of the beating, Conley wouldn’t rat out his fellow cops. Indeed, shortly after Conley’s indictment, prominent Boston-area investigative journalist Dick Lehr wrote that “the Cox scandal shows a Boston police code of silence…a tight inner circle of officers protecting themselves with false stories.”4
Kenny Conley stuck with his story, and his case went to trial. Smut Brown testified 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 officer also testified 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 Officer 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 officers, and officers 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 obstruction 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 fired 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 experienced during his pursuit of Smut Brown. That’s when Lehr brought the former cop to visit Dan’s laboratory at Harvard.
Gorillas in Our Midst
The two of us met over a decade 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 office 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 experiments, one of which has become famous. It was based on an ingenious series of studies of visual attention and awareness conducted by the pioneering cognitive psychologist Ulric Neisser in the 1970s. Neisser had moved to Cornell University when Dan was in his final 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 floor of the psychology building as a set, we made a short film 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 coordinated the action and kept track of which scenes we needed to shoot. We then digitally edited the film 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 experiments 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-five. To be honest, it doesn’t matter. The pass-counting task was intended to keep people engaged 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 student 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 scientific name “inattentional blindness.” This name distinguishes it from forms of blindness resulting from a damaged visual system; here, people don’t see the gorilla, but not because of a problem with their eyes. When people devote their attention to a particular area or aspect of their visual world, they tend not to notice unexpected objects, even when those unexpected objects are salient, potentially 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 particular. The fact that people miss things is important, but what impressed us even more was the surprise 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 first 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 influence 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 firm 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 findings of this survey throughout the book.)
It’s true that we vividly experience some aspects of our world, particularly those that are the focus of our attention. But this rich experience inevitably leads to the erroneous belief that we process 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 assume that visually distinctive or unusual objects will draw our attention, but in reality they often go completely unnoticed.11
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 first 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.
