by Daniel Simons, as told to Discover’s Valerie Ross. Simons is a professor of psychology at the University of Illinois, where he studies attention, perception, and memory---and how much worse people are with those skills than they think. He is the co-author, with fellow psychologist Chris Chabris, of

The Invisible Gorilla.Late one January night in 1995, Boston police officer Kenny Conley ran right past the site of a brutal beating without doing a thing about it. The case received extensive media coverage because the victim was an undercover police officer and the aggressors were other cops. Conley steadfastly refused to admit having seen anything, and he was tried and convicted of perjury and obstruction of justice. Prosecutors, jurors, and judges took Conley’s denial to reflect an unwillingness to testify against other cops, a lie by omission. How could you run right past something as dramatic as a violent attack without seeing it? Chris Chabris and I used this example to open our book because it illustrates two fundamental aspects of how our minds work. First, we experience inattentional blindness, a failure to notice unexpected events that fall outside the focus of our attention. Second, we are largely oblivious to the limits of perception, attention, and awareness; we think that we are far more likely to notice unexpected events than we actually are. Chabris and I have studied this phenomenon of inattentional blindness for many years. Our best-known study was based on earlier work by Ulric Neisser: We asked subjects to count how many times three players wearing white shirts passed a basketball while ignoring players wearing black who passed their own ball. We found that about 50 percent of subjects failed to notice when a person in a gorilla suit unexpectedly walked through the scene. http://www.youtube.com/watch?v=vJG698U2Mvo The mismatch between what we see and what we think we see has profound implications for our court system. As our research has shown, we can fail to notice something obvious if we are focused on something else. Yet, most jurors likely hold the mistaken belief that we should see anything that happens right before our eyes. Kenny Conley was convicted on the strength of that intuitive belief. Many others likely languish in jail due to similarly mistaken beliefs about the accuracy of memory. By studying these limits of attention and memory and our beliefs about them, we identify cases in which our beliefs diverge from reality. Ideally, we can then reveal these “invisible gorillas” in the court system. In Conley’s case, the beating took place in the middle of the night, following a high-speed chase through the streets of Boston that culminated in Conley chasing a suspect on foot and apprehending him nearly a mile later. Conley presumably was focused on chasing the suspect, much like our subjects were intently focused on counting passes. And, that intent focus meant that he, like our subjects, was less likely to notice unexpected events falling outside that focus of attention. Although the analogy from inattentional blindness in the lab to the situation faced by Conley seems reasonable, Chabris and I had a nagging concern: No studies had tested the effects of inattentional blindness under real-world conditions like those faced by Conley. There is plenty of anecdotal evidence (as well as observational studies) showing that people do miss unexpected events in the real world, but we wanted to verify that our “inattentional blindness” explanation for Conley’s experience was plausible. In the study we published in i-Perception (conducted by Chabris and his students, Adam Weinberger and Matthew Fontaine, at Union College), we did our best to simulate some of the key aspects of Conley’s experience. Our subjects were asked to jog behind an experimenter, monitoring how many times the experimenter touched his hat. As they were jogging along a predefined route, they ran past a simulated fight scene in which two other experimenters were “beating” a third experimenter. We found that even in broad daylight, only 56 percent of subjects noticed the fight. At night, only 35 percent did. Presumably, even fewer people would have noticed had we been able to ramp up the intensity to something consistent with a high-speed police chase of a murder suspect. Coupled with the Conley case, this finding illustrates how flawed our thinking about inattentional blindness can be. The jury convicted Conley at least partly because they intuitively believed that he must have seen the beating. That belief, what we call an illusion of attention, is one of many ways that we misunderstand our own minds. It follows naturally from how we experience our world. We are only aware of those unexpected events we happen to see, and we are unaware of all the ones we never saw. The pattern we experience, then, is of always noticing unexpected events, and it’s rare that we experience our failures of awareness. If you missed the gorilla and nobody ever asked you about it or showed you what you missed, you would continue believing that you would notice it. Inattentional blindness is not the only courtroom problem caused by our imperfect brains. For example, when we recall a vivid experience, it often passes before our mind’s eye in great detail. But we rarely check the accuracy of that imagery, and when we do, the details often are distorted. Our assumptions lead us to trust confident testimony about memories (“That’s the guy who robbed me. I’m sure of it.”) when decades of research on memory, such as the great work by people like Elizabeth Loftus, reveals its fallibility. These assumptions we make about our memory lead to flawed decisions by juries: we assume someone must be lying when they simply can’t remember; we trust confident witnesses more than we should; we believe that people must have noticed anything falling within their field of view. This summer, Chabris and I published a paper in PLoS One based on a national survey we conducted to explore how pervasive these mistaken beliefs about memory actually are. The survey was a representative sample of the American population, and we found that 63 percent thought memory works like a video camera and 78 percent believed that unexpected objects will automatically grab notice, even when attention is focused elsewhere. These flawed intuitions help explain how so many people can be convicted of murder on the basis of eyewitness testimony, only to be exonerated later via DNA testing. Unless we can inform lawyers, judges, and juries about these assumptions and the limits of perception, we will continue to see innocent people convicted solely on the basis of eyewitness testimony. One of the big remaining questions in the study of the limits of attention and perception is whether some people are better able to notice and remember than others. Undoubtedly there are individual differences, but my guess is that the variability across people is far smaller than the similarities among us.While some people may notice a bit more than others, we all have severe limits on how much of the world around us actually reaches our awareness at any moment. Correction: The study in i-Perception was conducted by Chris Chabris and his students Adam Weinberger and Matthew Fontaine, not Daniel Blakely.