Numerosity Adaptation Effect

The numerosity adaptation effect is a perceptual phenomenon in numerical cognition, first described in 2008, in which a person's sense of how many items are in a visual display is automatically distorted after sustained viewing of another display containing a different number of items. After roughly thirty seconds spent viewing a display with many dots, a second display can come to look distinctly more or less numerous than it actually is, even though a viewer can verify the counts are equal. The effect cannot be explained simply by the size, density or contrast of the dots, since it persists when those non-numerical properties are manipulated, and it operates immediately and without conscious control, pointing to an automatic perceptual system for sensing approximate quantity that works much like the perceptual systems for other basic visual properties.