Visual cortical correlates of visible persistence.

In order to evaluate their possible role in visible persistence, cortical cells from area 17 of the cat were investigated with a stationary light bar flashed for different durations. Thirteen out of 72 cells with non-overlapping On and Off subregions were able to respond to the briefest On stimulus (12.5 msec) for low and moderate contrasts. The responses of these cells outlasted brief On stimuli and this neural persistence increased as the On duration was shortened, mimicking the inverse duration effect of visible persistence. The 30 cells with overlapping On and Off subregions were all able to respond to brief stimuli but their neural persistence was independent of stimulus duration. At very high contrast levels, the inverse duration effect, observed in cells with non-overlapping subregions, disappeared since the On responses were followed by Off rebound discharges regardless of stimulus duration. It is suggested that the latter responses are a possible cortical equivalent of positive afterimages.