The effects of motion adaptation and disparity in motion integration.

Abstract

Two experiments examined the effects of pattern vs component adaptation on motion integration in stimuli with or without disparity. Observers adapted to either downward pattern motion, downward component motion, or a grey screen, and were then tested with plaids containing either crossed, uncrossed or zero binocular disparity, moving downward. In a second experiment, the same test conditions were employed following adaptation to upward pattern motion. The total amount of time that coherence or transparent sliding was perceived was measured. Adaptation to component motion increased the amount of perceived coherent motion whereas adaptation to pattern motion decreased it. The second experiment revealed that adaptation to the upward-moving pattern had no effect on perceived coherence. The results demonstrate the complex nature of the interaction between depth and motion mechanisms in motion integration. Under prolonged inspection, a moving squarewave plaid 1 yields bistable percepts: Perception switches between separate gratings sliding over one another in their respective directions, and a coherent plaid moving in a third direction. The "separate" percept implies that each grating is processed by an appropriate direction-sensitive mechanism and that both are operating simultaneously. This is also referred to as the stage of component motion. The "coherent" percept implies a further stage of processing, whereby the two component gratings are integrated into a new pattern, a plaid, which moves in a composite direction, different from the two original directions. This stage has been referred to as pattern motion, and models have been developed to describe the perceived pattern direction (Adelson & Movshon, 1982; 1 Plaid stimuli are constructed by superimposing two grating stimuli of different orientations that may also differ in terms of their spatial frequency and contrast and other parameters. Each individual grating moves in a direction perpendicular to its orientation. The areas where the grating lines cross each other are called intersections and have a luminance that may differ from those of the peaks and troughs of the gratings, thus giving the plaid-like appearance of the compound stimulus.