Competition between opposing motion directions in the perception of apparent motion: A new look at an old stimulus

This study tested the hypothesis that the perception of 2-flash apparent motion (points of light are briefly presented in succession at a nearby locations) is the outcome of competition between two opposing motion directions activated by the stimulus. Experiment 1 replicated previous results obtained using 2-flash stimuli; motion was optimal for a non-zero inter-frame interval (Kolers, 1972; Wertheimer, 1912). In Experiment 2, stimuli were pared down to a single luminance change toward the background at one location, and a single luminance change away from the background at one location at another. Results were consistent with apparent motion being specified by the counter-changing luminance; motion was optimal for a non-zero inter-frame interval. A subtractive model based on counter-change stimulating opposing motion directions did not account for the results of the 2-flash experiment. An alternative model based on the combined transient responses of biphasic detectors is discussed.