Two experiments were performed to examine the effect of stimulus intensity on VISS (visual stream segregation) which is a kind of beta movement first described by Bregman and Achim (1973). Six subjects were required to find the upper threshold of ISI for producing VISS under various conditions of the stumulus intensity in each experiment. The ISI threshold decreased as the stimulus intensity was increased. The result showed that VISS follows Korte's second law of apparent motion. When two of the four lights were flashed in high intensity and the rest in low intensity, the ISI thresholds varied with the arrangement of intensity among the four lights (stimulus intensity pattern). The results suggest that VISS is affected by the factor of similarity resulting from the intensity patterns of the lights.
