Does segregation of differently moving areas depend on relative or absolute displacement?

We have examined the occurrence of segregation in random dot kinematograms in which a central patch of dots, and the surrounding area, were each coherently displaced, either in the same or opposite directions (Fig. 1), by varying amounts. The limiting displacement for segregation to occur is determined primarily by the displacement of each region alone, rather than the relative displacement of neighbouring regions (Fig 2). We conclude that the "correspondence problem" is solved by means of a short range motion detection process acting on each region separately; segregation is achieved by comparing the results of this process for adjacent regions.