APA Dictionary of Psychology

an illusion of depth in the motion of a stimulus that moves only in two dimensions, such as a pendulum. The illusion is induced by allowing one eye to view the motion before the other eye and never allowing both eyes to view the motion at the same time. The delay between the signals from the two eyes is interpreted by the visual system as binocular disparity, a normal depth cue. Compare Pulfrich effect. [Ernst Mach; Vinko Dvorak (1848–1922), Czech physicist]