Microsaccades differentially modulate neural activity in the striate and extrastriate visual cortex.

Saccadic eye movements in primates continually shift the location at which a given stimulus strikes the retina. Even during periods of steady fixation, microsaccades frequently jerk the center of gaze by small but resolvable distances, yet perception remains stable and continuous, uninterrupted by sudden jumps or shifts. The effect of such fixational eye movements on the activity of single neurons was examined in several regions of the visual cortex in macaque monkeys. We found that the firing of many neurons in striate and extrastriate cortex is profoundly influenced by saccades much smaller than the neurons' receptive fields. In striate cortex (V1) many cells showed a transient decrease in their firing shortly following a saccade. In sharp contrast, cells in the extrastriate areas V2 and V4 showed strong excitatory responses that closely coincided in time with the striate depression. No appreciable activity change was observed in the inferotemporal cortex (IT) following saccades. This activity pattern is consistent with the notion that topographic extrastriate areas receive extraretinal input associated with saccadic events. Such signals may be necessary for the stable perception of objects and scenes during eye movements, mediating the mapping between central object representations and the constantly changing retinotopic input.