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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.

      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, windowless 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 unexpected 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 engaged, 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 notion of how the mind works: the mistaken belief that we pay attention to—and therefore should notice and remember—much more of the world around us than we actually do. Conley himself testified 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 incident from other police officers 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 escaping, and he pursued his suspect with a single-minded focus that he described 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 sufficiently focused on Brown, in the way our subjects 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

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