Abstract
Apparent motion is the experience of motion from the quick successive stimulation of nearby spatial locations. We report here a phenomenon of reverse apparent motion from three frames that is consistent with a re-ordering of successive frames. In contrast to other reverse motion reports in the literature (e.g. Shioiri & Cavanagh, 1990, Vision Research), the present reversal is not obtained by manipulating the moving stimulus itself. Instead, the same physical stimulus is perceived moving forward or in reverse direction depending on what is presented just before. Observers had to decide on the direction of rotation of a test movie. The test movie consisted of 3 frames of 4 dots placed at the corners of a virtual square centered on the fixation point. On each frame, the dots rotated 30 degrees, either clockwise or counter-clockwise randomly across trials. The inter-stimulus interval (ISI) between two successive frames (1-2 or 2-3) was fixed to 100ms, and the other ISI varied from trial to trial from 0 to 200ms. Before the test movie, 4 frames of 4 dots were presented, either at 4 random locations (baseline condition), or at the location of the dots in one frame of the test movie (adapting condition). The baseline condition confirmed that without adaptation, the physical movie was correctly perceived in its forward direction. When the second frame of the movie was adapted, perceived motion was consistently reversed for short ISIs, but importantly forward motion was recovered for long ISIs. When either the first or last frame was adapted, forward motion was perceived. The results are discussed in relationship to different models, including a confusion of the order of successive frames, a change of the impulse response function, and a late interpretation of past events at the end of a temporal window.