Being Wrong - Kathryn Schulz [29]
This point merits some emphasis: being wrong is often a side effect of a system that is functioning exactly right. Remember size constancy, our automatic ability to recalibrate scale according to distance? This is a handy trick 99.99 percent of the time. The other 0.01 percent occurs when, say, you find yourself on a ship in the Arctic looking at very large mountains, which you therefore conclude are very nearby. In this case (and in many others, as we’ll see), mistakes arise when a basically reliable system leads us astray. That’s part of what makes optical illusions, and errors more generally, so unforeseeable and surprising: not only do they arise from processes we can’t feel, they arise from processes that, under normal circumstances, work to our advantage.
Illusions, then, are the misleading outcomes of normal (and normally beneficial) perceptual processes. This isn’t just true of the visual kind. If you’ve ever seen a ventriloquist, you’ve been duped by another of these processes—in this case, one that automatically integrates information from your visual and auditory systems. (Thus if you hear speech and see a moving mouth, you’ll register the speech as coming from that mouth—even if it belongs to a three-foot tall wooden puppet.) Other auditory illusions are even more common. If you have either a cell phone or a baby, you are familiar with the experience of hearing your particular phone ringing, or your particular baby crying, when in fact it is (for once) quiet. Then there are tactile illusions, of which by far the most famous is that of the phantom limb: the amputee’s persistent, unshakable sense of experiencing sensation in his or her missing body part. Those of us fortunate enough to have all our limbs sometimes experience a similar if sillier feeling known as—no joke—the phantom hat. In this illusion, we continue to feel the presence of a tightly worn accessory, bandage, or article of clothing for some time after it has been removed.*
As this brief catalogue makes clear, and as I suggested earlier, most sensory illusions are not terribly important. Unless you are a vision scientist or an amputee or Captain John Ross, they have pretty much the status of parlor tricks. Occasionally, though, the quirks of our perceptual system leave us vulnerable to more serious errors. Take, for instance, a phenomenon known as inattentional blindness. There is a rather amazing experiment—which I’m about to ruin for you—in which subjects are shown a video of a group of people playing a fast-paced ball game and are asked to count how many times the ball is passed back and forth. At some point during the video, a gorilla (more precisely, a person in a gorilla costume) wanders into the middle of the group of players, stands around for a bit, beats its chest a few times, and then wanders off again. Here’s the amazing part: between 33 and 50 percent of subjects don’t see this happen. Perhaps this bears repeating: one-third to one-half of people instructed to pay close attention to a video fail to see a gorilla beating its chest in the middle of it.
This is inattentional blindness in action. It turns out that when we ask people to look for something specific, they develop a startling inability to see things in general. This cognitive peculiarity has been recorded since at least the 1970s, but you have to hand it to the designers of this study—the psychologists Daniel Simons and Christopher Chabris—for going well beyond what less inspired thinkers might have imagined was the logical extreme in order to demonstrate its potency. (The video is available on the website of the Visual Cognition Lab of the University of Illinois. But be warned: having read this paragraph, you will not fail to see the gorilla. It’s as if, rather than asking you to count the number of basketball passes,