It’s still possible—even reasonable—to suspect that people differ in their ability to focus attention on a primary task, but that this ability isn’t related to general intelligence or educational achievement. If individual differences in the ability to focus attention lead to differences in noticing unexpected objects, then people for whom the counting task is easier should be more likely to notice the gorilla—they are devoting fewer resources to the counting task and have more left over.
Dan and his graduate student Melinda Jensen recently conducted an experiment to test exactly this hypothesis. They first measured how well people could do a computer-based tracking task like the one we used in the “red gorilla” experiment and then looked to see whether those who performed the task well were more likely to notice an unexpected object. They weren’t. Apparently, whether you detect unexpected objects and events doesn’t depend on your capacity for attention. Consistent with this conclusion, Dan and sports scientist Daniel Memmert, the researcher who tracked children’s eye movements while they watched the gorilla video, found that who noticed and who missed an unexpected object was unrelated to several basic measures of attention capacity. These findings have an important practical implication: Training people to improve their attention abilities may do nothing to help them detect unexpected objects. If an object is truly unexpected, people are unlikely to notice it no matter how good (or bad) they are at focusing attention.
As far as we can tell, there are no such people as “noticers” and “missers”—at least, no people who consistently notice or consistently miss unexpected events in a variety of contexts and situations. There is one way, however, to predict how likely a person is to see the unexpected. But it is not a simple trait of the individual or a quality of the event; it is the combination of a fact about the individual and a fact about the situation in which the unexpected event occurs. Only seven people out of more than one thousand stopped to listen to Joshua Bell playing in the L’Enfant Plaza subway station. One had been to a concert Bell had given just three weeks earlier. Two of the remaining six were musicians themselves. Their expertise helped them recognize his skill—and the pieces he was playing—through the din. One, George Tindley, worked in a nearby Au Bon Pain restaurant. “You could tell in one second that this guy was good, that he was clearly a professional,” he told Weingarten. The other, John Picarello, said, “This was a superb violinist. I’ve never heard anyone of that caliber. He was technically proficient, with very good phrasing. He had a good fiddle, too, with a big, lush sound.”
Experiments support this observation. Experienced basketball players are more likely to notice the gorilla in the original basketball-passing video than are novice basketball players. In contrast, team handball players are no more likely to notice unexpected objects even though they are experts in a team sport that places demands on attention comparable to those of basketball.45 Expertise helps you notice unexpected events, but only when the event happens in the context of your expertise. Put experts in a situation where they have no special skill, and they are ordinary novices, taxing their attention just to keep up with the primary task. And no matter what the situation, experts are not immune to the illusory belief that people notice far more than they do. Gene Weingarten described John Picarello’s behavior as he watched Bell play: “On the video, you can see Picarello look around him now and then, almost bewildered. ‘Yeah, other people just were not getting it. It just wasn’t registering. That was baffling to me.’”
How Many Doctors Does It Take …
Even within their field of specialty, experts are not immune to inattentional blindness or the illusion of attention. Radiologists are medical specialists responsible for reading x-rays, CT scans, MRIs, and other images in order to detect and diagnose tumors and other abnormalities. Radiologists perform this visual detection task under controlled conditions every day of their careers. In the United States, their training involves four years of medical school, followed by up to five years in residency at a teaching hospital. Those who specialize in specific body systems spend another year or two in fellowship training. In total, they often have more than ten years of post-undergraduate training, followed by on-the-job experience in studying dozens of films each day. Despite their extensive training, radiologists can still miss subtle problems when they “read” medical images.
Consider a recent case described by Frank Zwemer and his colleagues at the University of Rochester School of Medicine.46 An ambulance brought a woman in her forties to the emergency room with severe vaginal bleeding. Doctors attempted to insert an intravenous line in a peripheral vein, but failed, so they instead inserted a central line via a catheter in the femoral vein, the largest vein in the groin. Getting the line in correctly requires also inserting a guidewire, which is removed once the line is in place.
The line was introduced successfully, but due to an oversight, the physician neglected to remove the guidewire.47 To address her blood loss, the patient was given transfusions, but she then developed difficulty breathing due to pulmonary edema (a swelling or fluid buildup in the lungs). She was intubated for respiratory support, and a chest x-ray was taken to confirm the diagnosis and make sure that the breathing tube was placed correctly. The ER doctor and the attending radiologist agreed on the diagnosis, but neither of them noticed the guidewire. The patient went next to the intensive care unit for several days of treatment, and after she improved she went to a standard unit. There she developed shortness of breath, which was caused by pulmonary embolism—a blood clot in her lung. During this time she received two more x-rays, as well as an echocardiogram and a CT scan. Only on the fifth day of her stay in the hospital did a physician happen to notice and remove the guidewire while performing a procedure to correct the pulmonary embolism. The patient then made a full recovery. (It was determined later that the guidewire probably didn’t cause the embolism because it was constructed of so-called nonthrombogenic material specifically intended not to promote blood clotting.)
When the various medical images were examined afterward, the guidewire was clearly visible on all three x-rays and on the CT, but none of the many doctors on the case noticed it. Their failure to see the anomalous guidewire illustrates yet again the dangers of inattentional blindness. The radiologists and other physicians who reviewed the chest images looked at them carefully, but they did not see the guidewire because they did not expect to see it.
Radiologists have a tremendously difficult task. They often review a large number of images at a time, typically looking for a specific problem—a broken bone, a tumor, and so on. They can’t take in everything in the image, so they focus their attention on the critical aspects of the image, just as the subjects in the gorilla study focused on counting the passes of one team of players. Due to the limits of attention, radiologists are unlikely to notice aspects of the image that are unexpected, like the presence of a guidewire. But people assume that radiologists should notice any problem in a medical image regardless of whether it is expected; any failure to do so must therefore be the result of the doctor’s negligence. Radiologists are regularly sued for missing small tumors or other problems.48 These lawsuits are often based on the illusion of attention—people assume that radiologists will notice anything anomalous in an image, when in reality they, like the rest of us, tend to see best what they are looking for in the image. If you tell radiologists to find the guidewire in a chest x-ray, they will expect to see one and will notice it. But if you tell them to find a pulmonary embolism, they may not notice the guidewire. (It’s also possible that when searching for the guidewire, they will miss more pulmonary embolisms.) An unexpected tumor that was missed during the original reading might seem obvious in hindsight.
Unfortunately, people often confuse what is easily noticed when it is expected with what should be noticed when it is unexpected. Moreover, the procedures frequently used in hospitals when reviewing radiographs are affected by the illusion of attention; doctors themselves also assume that they will
notice unexpected problems in an image, even when they are looking for something else. To reduce the effects of inattentional blindness, one can deliberately reexamine the same images with an eye toward the unexpected. When participants in our studies know that something unexpected might happen, they consistently see the gorilla—the unexpected has become the target of focused attention. Devoting attention to the unexpected is not a cure-all, however. We have limited attention resources, and devoting some attention to unexpected events means that we have less attention available for our primary task. It would be imprudent to ask radiologists to take time and resources away from detecting the expected problem in an x-ray (“Doctor, can you confirm that this patient has a pulmonary embolism so that we can begin treatment?”) to focus instead on things that are unlikely to be there (“Doctor, can you tell us whether we left anything behind in this patient’s body?”). A more effective strategy would be for a second radiologist, unfamiliar with the case and the tentative diagnosis, to examine the images and to look for secondary problems that might not have been noticed the first time through.
So it turns out that even experts with a decade of training in their medical specialty can miss unexpected objects in their domain of expertise. Although radiologists are better able than laypeople to detect unusual aspects of radiographs, they suffer from the same limits on attention as everyone else. Their expertise lies not in greater attention, but in more precise expectations formed by their experience and training in perceiving the important features of the images. Experience guides them to look for common problems rather than rare anomalies, and in most cases, that strategy is wise.
What Can We Do About the Illusion of Attention?
If this illusion of attention is so pervasive, how has our species survived to write about it? Why weren’t our would-be ancestors all eaten by unnoticed predators? In part, inattentional blindness and the accompanying illusion of attention are a consequence of modern society. Although our ancestors must have had similar limitations on awareness, in a less complex world there was less to be aware of. And few objects or events needed immediate attention. In contrast, the advance of technology has given us devices that require greater amounts of attention, more and more often, with shorter and shorter lead times. Our neurological circuits for vision and attention are built for pedestrian speeds, not for driving speeds. When you are walking, a delay of a few seconds in noticing an unexpected event is likely inconsequential. When you are driving, though, a delay of even one-tenth of a second in noticing an unexpected event can kill you (or someone else). The effects of inattention are amplified at high speeds, since any delay in noticing happens at the highest speed.
The effects of inattention are further amplified by any device or activity that takes attention away from what we are trying to do. Such devices and activities were rare in the BlackBerryless, iPhone-free, pre-GPS past, but they’re common today. Fortunately, accidents are still rare, because most of the time, nothing unexpected happens. But it is those rare unexpected events that matter. People are confident that they can drive and talk on the phone simultaneously precisely because they almost never encounter evidence that they cannot. And by “evidence” we don’t mean a news story about accident rates or a safety institute’s latest report, or even a story of a friend who zoned out while driving and almost hit something. We mean a personal experience, like a collision or a near miss, that was unambiguously caused by a depletion of attention and that cannot be explained away as the other person’s fault (a rationalization we are as good at making as we are at overestimating our own levels of attention). We will almost never be aware of the more subtle evidence of our distraction. Drivers who make mistakes usually don’t notice them; after all, they’re distracted.
The problem is that we lack positive evidence for our lack of attention. That is the basis of the illusion of attention. We are aware only of the unexpected objects we do notice, not the ones we have missed. Consequently, all the evidence we have is for good perception of our world. It takes an experience like missing the chest-thumping gorilla, which is hard to explain away (and which we have little incentive to explain away), to show us how much of the world around us we must be missing.
If the mechanisms of attention are opaque to us, how can we eliminate inattentional blindness so that we can be sure to spot the gorilla? The answer isn’t simple. In order to eliminate inattentional blindness, we would effectively have to eliminate focused attention. We would have to watch the gorilla video without bothering to focus on counting passes or even to focus on what we found interesting in the display. We would have to watch the display without expectations and without goals. But for the human mind, expectations and goals are inextricably intertwined with the most basic processes of perception and are not readily extinguished. Expectations are based on our prior experiences of the world, and perception builds on that experience. Our experience and expectations help us to make sense of what we see, and without them, the visual world would just be an unstructured array of light, a “blooming, buzzing confusion” in the classic words of William James.49
For the human brain, attention is essentially a zero-sum game: If we pay more attention to one place, object, or event, we necessarily pay less attention to others. Inattentional blindness is thus a necessary, if unfortunate, by-product of the normal operation of attention and perception. If we are right that inattentional blindness results from inherent limits on the capacity of visual attention, it might be impossible to reduce or eliminate it in general. In essence, trying to eliminate inattentional blindness would be equivalent to asking people to try flying by flapping their arms really rapidly. The structure of the human body doesn’t permit us to fly, just as the structure of the mind doesn’t permit us to consciously perceive everything around us.
The issue of how best to allocate our limited attention relates to a larger principle of attention. For the most part, inattentional blindness isn’t a problem. In fact, it is a consequence of the way attention works; it is the cost of our exceptional—and exceptionally useful—ability to focus our minds. Focused attention allows us to avoid distraction and use our limited resources more effectively; we don’t want to be distracted by everything else around us. Most drivers follow the rules of the road, most doctors don’t leave guidewires in patients, most fishing vessels aren’t floating right above submarines, most planes aren’t guided in to land right on top of other planes, most cops don’t viciously beat suspects, and most world-class violinists don’t play in the subway. And gorillas rarely saunter through basketball games. Unexpected events are unexpected for a good reason: They are rare. More important, in most cases, failing to spot the unexpected has little consequence.
Attention Writ Large
The illusion of attention affects us all in both mundane and potentially life-threatening ways—it truly is an everyday illusion. It contributes to everything from traffic accidents and airplane cockpit displays to cell phones, medicine, and even subway busking. As the gorilla experiment has become more widely known, it has been used to explain countless failures of awareness, from the concrete to the abstract, in diverse domains. It’s not just limited to visual attention, but applies equally well to all of our senses and even to broader patterns in the world around us. The gorilla experiment is powerful because it forces people to confront the illusion of attention. It provides an effective metaphor precisely because the illusion of attention has such broad reach. Here are some examples:50
A trainer uses it to show people how they can miss safety infractions that are right in front of them.
A Harvard professor uses it to explain how discriminatory practices in the workplace can go unnoticed even by intelligent, fair-minded individuals.
Antiterrorism experts cited it to explain how Australian intelligence officials could have missed the presence in their own country of the Jemaah Islamiyah group, which was responsible for the 2002 Bali bombings that killed 202 people.
A weight-loss website compares the uns
een gorilla to an unplanned snack that can ruin your diet.
Promoter of the paranormal Dean Radin likens the inattentional blindness of our subjects to the failure of scientists to see the “reality” of ESP and other extrasensory phenomena.
A high school principal uses inattentional blindness to explain how teachers and administrators often fail to notice bullying.
An Episcopal priest used it in a sermon to explain how easily people can miss evidence of God all around them.
A British ad campaign encouraged drivers to watch for bicyclists by creating a television and viral Web advertisement based on our video, with the chest-thumping gorilla replaced by a moonwalking bear.
Within the realm of visual perception, noticing suffers from even more limitations than the ones we have discussed so far. For example, it is hard to look for multiple things at once, to distinguish similar-looking objects, and to remain vigilant over long periods of time performing the same task. Our underappreciation of these constraints can have dire consequences for our safety and security. We expect airport baggage scanners to spot weapons in luggage, but they regularly fail to notice contraband items planted by authorities during tests of security procedures. The task of security scanners is much like the task of radiologists (though the training is, shall we say, much less extensive), and it is difficult if not impossible to see everything in a briefly viewed image. That’s especially true given that the things being searched for are rare.51
The Invisible Gorilla: And Other Ways Our Intuitions Deceive Us Page 5