Imagine watching a short video of two teams passing basketballs, one team in white shirts and the other in black. Your task is to count how many passes the players in white make. Partway through, a person in a gorilla costume walks into the middle of the group, turns toward the camera, and walks off again. Would you notice?
In a well-known study published in 1999, the psychologists Daniel Simons and Christopher Chabris showed a video like this one to a large number of volunteers. Roughly half of the volunteers who watched the gorilla version did not see it at all. People who watch the video again are often surprised that they missed something so obvious. When the counting task was made more difficult, even fewer people noticed the gorilla.
The researchers did not conclude that the volunteers had poor eyesight. The gorilla was in plain view, and their eyes almost certainly passed over it. The problem was attention. Because the brain cannot process everything the eyes take in, it concentrates on what matters for the current task and filters out much of the rest. An unexpected object that has nothing to do with the task can pass through the filter unnoticed.
Psychologists call this inattentional blindness. The study showed that people can miss something right in front of them when their attention is busy with something else.
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