Neural synchrony correlates with surface segregation rules

To analyse an image, the visual system must decompose the scene into its relevant parts. Identifying distinct surfaces is a basic operation in such analysis, and is believed to precede object recognition(1,2). Two superimposed gratings moving in different directions (plaid stimuli) may be perceived either as two surfaces, one being transparent and sliding on top of the other (component motion) or as a single pattern whose direction of motion is intermediate to the component vectors (pattern motion)(3-6). The degree of transparency, and hence the perception, can be manipulated by changing only the luminance of the grating intersections(7-12). Here we show that neurons in two visual cortical areas-A18 and PMLS-synchronize their discharges when responding to contours of the same surface but not when responding to contours belonging to different surfaces. The amplitudes of responses correspond to previously described rate predictions(3,13-16) for component and pattern motion, but, in contrast to synchrony, failed to reflect the transition from component to pattern motion induced by manipulating the degree of transparency. Thus, dynamic changes in synchronization could encode, in a context-dependent way, relations among simultaneous responses to spatially superimposed contours and thereby bias their association with distinct surfaces.