Motion Grouping
Motion Grouping
A disk is clearly visible as long as it is in motion, but vanishes completely when it stops. "Motion grouping" is the tendency of the visual system to perceive objects that move together as wholes. As long as the black and white specks that make up the disk are in motion, we see a disk rather than individual bits of black and white. But when the disk is at rest, the visual system has no clues to differentiate it from the background, and with perfect camouflage, it vanishes.