APPARENT RELATIVE MOTION FROM A CHECKERBOARD SURROUND

To better understand the Ouchi illusion in which a stationary picture generates illusory relative motion, the spatial properties of the cons tituent elements of the rectangular checkerboard background were exami ned. Results of experiment 1 revealed that the largest illusion was ob tained with elements of approximately 20-30 min in width and 4-6 min i n height, an orientation of the constituents that was orthogonal to th at of the test grating, and a phase shift of the alternate stripes tha t was close to 180 degrees. In experiment 2 it was found that the illu sion increased in magnitude with increasing achromatic contrast but wa s minimal with a pattern of high chromatic contrast near isoluminance. In experiment 3, two test patches were presented simultaneously in th e checkerboard background and were varied independently in their orien tation to explore whether or not their motions were perceived as coher ent (common fate). Patches having identical orientations, and nearly o rthogonal to the surround, were synchronized more strongly than those having reflected orientations. Hysteresis related to the gain control of spatially overlapping visual units differing in their polarity (ON/ OFF) was discussed as a possible cause of this phenomenon.