Effects of luminance and color on apparent motion.

The present study explored the effects of luminance, color, and distance on apparent motion direction of some repeated stimuli of alternating colors. Two experiments were performed to specify what affects apparent motion direction when the stroboscopic alternative is between proximity and similarity in color. In Exp. 1 the influence of luminance on apparent motion was systematically studied with seven different background luminance values. Analysis pointed out that apparent motion direction depends on the discriminability among the disks, in relation also to the background values. A formula to predict the apparent motion direction from luminance values was proposed. In Exp. 2 the influence of hue on apparent motion was studied. Stimuli with equiluminant disks on different backgrounds were used. Analysis pointed out that the stroboscopic unification was based mainly on proximity and that discriminability between the disks was rather poor, especially when apparent motion occurred also on an equiluminant background, as already pointed out by Ramachandran and Gregory in 1978. A different influence on apparent motion of the red-blue and red-green disks, as opposed to that of the blue-green ones, was also noted.