COOPERATIVE INTERACTIONS AND THE PERCEPTION OF MOTION AND STATIONARITY FOR DIRECTIONALLY AMBIGUOUS APPARENT-MOTION STIMULI

Evidence is reported that stationarity rather than motion can be perce ived for displaced stimuli, not because of insufficient motion energy for the stimulus to activate individual motion detectors, but because of cooperative interactions that actively suppress the perception of m otion. A long row of evenly spaced dots was presented in counterphase; the dots presented during each 180 ms frame were located midway betwe en the dots presented during the previous frame. When either a blank i nterval as brief as 15 ms was inserted between successive frames or th e luminance polarity of the dots was reversed on successive frames, th e unidirectional motion pattern perceived for small interdot distances (small displacements) was replaced by the perception of stationarity. However, when under the same conditions a single dot was displaced ov er the same small distances, motion rather than stationarity was perce ived. The contrasting results for the long row of displaced dots and t he single displaced dot indicated that when the activation of motion d etectors is weakened (by nonzero interframe intervals and/or the rever sal of luminance polarity), the perception of motion can be actively s uppressed by the collective effects of inhibitory interactions among t he large ensemble of detectors that is activated by the long row of do ts.