Appearance and disappearance, an unrecognized form of grouping and form perception from common fate.

Perceptual grouping by common fate has been studied for more than one hundred years: visible stimulus elements that move together (e.g., with the same speed and direction) are perceptually grouped into a single entity distinct from its background. Yet other forms of common fate also exist. In the current study we evaluated the potential informativeness of common appearance and disappearance. In common appearance, a textured object that was not present in an initial view (which contained a textured background identical in nature to that of the object) suddenly appeared in a second view. In common disappearance, a textured object that was perfectly camouflaged in the initial view disappeared in a second view (revealing background texture that had previously been occluded). In both events in the current experiment, the rectangular object was not visible in either the first or second image -- nevertheless, the common appearance or disappearance of stimulus texture elements permitted the perception of object shape. Thirty younger and older adults effectively discriminated shape (horizontal versus vertical rectangles) defined by common appearance and disappearance. The duration of an interstimulus interval and age significantly modulated the visibility of stimulus objects defined by common appearance and disappearance.