MAGNITUDE OF LUMINANCE MODULATION SPECIFIES AMPLITUDE OF PERCEIVED MOVEMENT

A compelling impression of movement, which is perceptually indistingui shable from a real displacement, can be elicited by patterns containin g no spatially displaced elements. An apparent oscillation, w-movement , was generated by a stationary pattern containing a large number of h orizontal pairs of spatially adjacent dots modulated in brightness. Th e observer's task was to adjust the perceived amplitude of the w-motio n to match the amplitude of a real oscillation. All of the data can be accounted for by a simple rule: If the relative change in the luminan ce, W = Delta L/L, between two adjacent stationary dots is kept consta nt, the distance over which these dots appeared to travel in space com prises a fixed fraction of the total distance by which they are separa ted. The apparent amplitude of the w-motion increases strictly in prop ortion with luminance contrast, provided that the contrast is represen ted in the motion-encoding system by a rapidly saturating compressive Weibull transformation. These findings can be explained in terms of bi local motion encoders comparing two luminance modulations occurring at two different locations.