The Invisible Gorilla

In 1999, at Harvard University, two researchers showed volunteers a short video of two teams passing a basketball, one in white shirts and the other in black. The task was to count how many passes the white team made. It seemed easy, and people concentrated hard.

In the middle of the scene, a person in a gorilla costume walked across the court, stopped in the center, thumped their chest, and left, after about nine seconds. When asked if they had seen anything strange, about half of the participants said no. Many didn't even believe it when they watched the video again.

That's the starting point of the book: we think we see everything that's in front of our eyes, but attention works like a flashlight. It only sees well what's under the light. The authors use this scene to open a series of everyday illusions, all tied to how we think our own mind works.

The technical name for the phenomenon is inattentional blindness. It happens when the mind is busy with a task and fails to register unexpected objects, even when they're in plain view. It isn't a vision problem, and it doesn't depend on intelligence. Anyone can experience it.

The authors point out that the error is stronger when the unexpected object is different from what we're looking for. In the video, people watching for white shirts were more likely to miss the black gorilla. Someone who knows how to look for something specific ends up filtering out the rest without realizing it.

The most treacherous part is the lack of warning. When attention fails, no alarm goes off in your head. That's why people tend to say this would never happen to them, which is the second illusion: believing we know how much we perceive.

This phenomenon explains an accident every American driver knows. A person glances at the rearview mirror, doesn't see the motorcycle, and changes lanes. Or crosses an intersection with a phone in hand and doesn't notice the cyclist coming from the right. The eyes passed over it, but attention was somewhere else.

Research on attention behind the wheel shows that talking on the phone is distracting even with speakerphone or earbuds, because the problem is mental, not an occupied hand. In the U.S., many states restrict phone use while driving, with fines and points on your license.

Drivers usually think they're above average and in command of the task. That's exactly the illusion the authors describe. If the mind is already overloaded, the gorilla can be a child running after a ball, and no one sees it.