inattentional blindness
a failure to notice unexpected but perceptible stimuli in a visual scene while one’s attention is focused on something else in the scene. This phenomenon occurs even when items are visible for several seconds. In two classic experiments, many participants focusing on judging the line lengths of a cross failed to notice a simultaneously presented square, and many focusing on counting the number of passes made by a basketball team failed to notice a person dressed in a gorilla suit walk by. Real-world examples are also common, such as magic tricks in which observers fail to see the magician’s sleight of hand in front of them and accidents in which drivers fail to see others on the road. Various factors affect the rate of inattentional blindness, including the visual relationship of the unexpected item to other items, the meaningfulness of the unexpected item, and—most significantly—the observer’s attentional set and cognitive load: Inattentional blindness is especially pronounced for task-irrelevant stimuli and in situations with high task-processing demands. Some researchers have suggested that inattentional blindness is in fact a kind of inattentional amnesia, in which people consciously perceive unattended objects but quickly forget them. In this view, attention is critical not for engaging the perceptual processes but rather for encoding the products of those processes into short-term memory. See also attentional blindness; change blindness; repetition blindness; selective perception. [term coined in 1998 by U.S. psychologists Arien Mack (1931– ) and Irvin Rock (1922–1995)]