Two experiments were performed to examine which is important, intercentral or intercontour distance between the stimuli, to affect visual stream segregation (VISS). VISS is a phenomenon of two sets of apparent motion, which is seen among four lights, A, B, C, D on a vertical row presented at a fast rate alternately in the order of A, C, B, and D. Eight undergraduates were required to find the upper limits of the interstimulus interval (ISI) for producing VISS under each condition of intercentral and intercontour distances. The ISI increased with intercentral distance, but was constant irrespective of the intercontour distance. The results show that it is not intercontour but intercentral distance between the stimuli that is important to decide VISS and apparent motion between two stimuli.