An onset-onset law for one case of apparent motion and metacontrast

Ss rated the quality of apparent motion and of metacontrast in computer-controlled sequences of two or of three outlined squares. For brief stimuli, the dependence of the two effects on temporal factors of stimulation is virtually identical. Motion and metacontrast depend solely on the asynchrony of onsets between the two exposures (SOA) over a wide range of duration and interstimulus intervals (lSI). Metacontrast suppression is interpreted as a case of impossible motion. The temporal determinants of apparent motion are summarized in a model in which the effect occurs when the temporal overlap between the perceptual responses to the successive stimuli is intermediate in value.