Simons and Chabris's Invisible Gorilla Experiment

In 1999 Daniel Simons and Christopher Chabris, then at Harvard University, published a study of sustained inattentional blindness that became widely known as the invisible gorilla experiment. Participants watched a short video of two teams, one dressed in white and one in black, passing basketballs, and were asked to count the number of passes made by one team while ignoring the other. Partway through the video a person in a gorilla suit walked into the middle of the scene, stopped to face the camera and thump its chest, and then walked off, remaining visible for about nine seconds. Roughly half of the participants across the study's conditions failed to notice the gorilla at all, with noticing rates varying depending on how visually similar the counted and ignored teams were and how demanding the counting task was. Simons and Chabris concluded that when attention is tightly focused on a demanding task, even a highly salient and unexpected object can go completely unperceived, a phenomenon they termed sustained inattentional blindness. The study became one of the most widely reproduced and cited demonstrations of the limits of visual attention in psychology.