Rebounding V1 activity and a new visual aftereffect.

A serendipitous observation led to this study of V1 activity rebounds, which occur well after stimulus offset, and their relationship to visual aftereffects. We found that when a stimulus bar and background were simultaneously turned off, there was strong delayed rebounding activity (distinct from any off response). The neural rebound started 350-500 ms after stimulus offset, and its magnitude and duration were correlated with the prior visual response of the cell. In human psychophysical experiments, we found a delayed aftereffect that may be a perceptual correlate of the activity rebound. Both the rebound activity and the perceptual aftereffect disappeared if the stimulus bar and background were not extinguished together. The magnitude of the rebound varied with the spatial scale of the background even though background size had little effect on the visual response. It thus appeared that rebound magnitude was determined by a relatively large integration area. The aftereffect was not seen when the bar and background offsets were presented to different eyes, suggesting an early neural (monocular) basis for the aftereffect. Overall, we find a strong correlation between rebound activity and the perceived aftereffect. In addition to providing a possible explanation and neural correlate of a visual aftereffect, rebounding activity may provide new insight into the dynamics of early visual processing.