Stimulus factors affecting illusory rebound motion

Stimulus attributes that influence a recently reported illusion called "illusory rebound motion" (IRM; [Hsieh, P.-J., Caplovitz, G. P., & Tse, P. U. (2005). Illusory rebound motion and the motion continuity heuristic. Vision Research, 45, 2972-2985.]) are described. When a bar alternates between two different colors, IRM can be observed to traverse the bar as if the color were shooting back and forth like the opening and closing of a zipper, even though each color appears in fact all at once. Here, we tested IRM over dynamic squares or disks defined by random dot or checkerboard textures to show that (1) IRM can be perceived in the absence of first-order motion-energy (or when the direction of net first-order motion-energy is ambiguous); (2) the direction of IRM is multistable and can change spontaneously or be changed volitionally; and (3) the perceived frequency of IRM is affected by several factors such as the contours of the stimulus, stimulus texture, and motion-energy.