The Invisible Gorilla: And Other Ways Our Intuition Deceives Us. Christopher Chabris

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       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 unseen 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 similarlooking 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

      Similarly, we expect lifeguards at swimming pools to notice anyone in danger of drowning, but this is a false sense of safety brought on by the illusion of attention. Lifeguards have the nearly impossible task of scanning a large expanse of water and detecting the rare event of someone drowning.⁵² The difficulty of their task is exacerbated because swimmers regularly do things that look like drowning but aren’t, such as swimming under water, lying on the bottom of the pool, splashing frantically, and so on. Lifeguards take regular breaks, change their viewing stations repeatedly during shifts, and take many other steps to maintain their vigilance, but vigilance, besides being subject to its own limitations, cannot eliminate inattentional blindness. The lifeguards simply cannot see everything, but the illusion of attention makes us believe they will.

      Only becoming aware of the illusion of attention can help us to take steps to avoid missing what we need to see. In some cases, like lifeguarding, technological innovations such as automated scanning could help. Without awareness of our limitations, though, technological intervention can hurt. Head-up displays might improve our ability to navigate and to keep our eyes on the road, but they might impair our ability to detect unexpected events. Similarly, in-car GPS navigation systems might help us find our way, but when trusted implicitly, they can lead us to drive without noticing where we are going.⁵³ A driver in Germany followed his navigation instructions despite several “closed for construction” signs and barricades, eventually barreling his Mercedes into a pile of sand. Twice in 2008, drivers in New York State blindly followed their GPS instructions and turned onto a set of train tracks in front of an oncoming train (neither was injured, fortunately). A driver in Britain caused a train crash after unwittingly driving onto the Newcastle-Carlisle rail line tracks.

      A more common problem in Britain occurs when truck drivers follow their GPS commands onto streets that are too small for their trucks. In one case, a driver wedged his truck so firmly into a country lane that he couldn’t move backward, move forward, or even open his door. He had to sleep in his cab for three days before being towed out by a tractor. The problem, of course, is that the navigation system doesn’t know or take account of the size of the vehicle—and some of us don’t know that it doesn’t know. Our favorite example of GPS-induced blindness comes from the British town of Luckington. In April 2006, rising waters made a ford through the start of the Avon River temporarily impassable, so it was closed and markers were put on both sides. Every day during the two weeks following the closure, one or two cars drove right past the warning signs and into the river. These drivers apparently were so focused on their navigation displays that they didn’t see what was right in front of them.

      Technology can help us to overcome the limits on our abilities, but only if we recognize that any technological aid will have limits too. If we misunderstand the limits of the technology, these aids can actually make us less likely to notice what is around us. In a sense, we tend to generalize our illusion of attention to the aids we use to overcome the limits on our attention. In the next chapter, we will consider this question: If we successfully pay attention to something and notice it, will it then be remembered? Most people think yes, but we will argue that this too is an illusion—the illusion of memory.