Abstract
Eye movements play a major role in the perspective that vision is performed through an active sensing mechanism. Saccades enable humans and monkeys to sample the visual scene while moving the desired region into the fovea, the center of the visual field, where visual acuity is highest. Recent human behavioral studies reported on stimulus feature-specific enhancements at the fovea, preceding saccades or microsaccades towards visual targets. However, the underlying neurophysiological mechanisms were barely studied thus far. We investigated the neural mechanisms involved in the transfer of visual information between parafoveal and foveal regions to the central fovea, in relation to fixational saccades. Using voltage-sensitive dye imaging (VSDI) we characterized the spatio-temporal patterns of neural population activity in the primary visual cortex (V1) of behaving monkeys. VSDI enables to measure the population response at a high spatial (meso-scale) and temporal resolution (msec), simultaneously. A monkey was trained on a target detection task and we analyzed correct trials where the animal performed fixational saccades landing on the target. The imaged V1 area included a continuous retinotopic map ranging from the central fovea to parafoveal eccentricities. This enabled to measure the full extent of spatio-temporal patterns evoked by a visual target shifting from parafoveal to foveal regions, at pre-saccadic and post-saccadic times. The target onset evoked a clear patch of activation in V1. Following a fixational saccade to the target, the population response encoding the target shifted to the central fovea. Interestingly, the neural activity in the fovea started to increase before microsaccade onset, thus preceding and predicting the target landing at the central fovea. These results were not observed in trials with fixation only or trials with microsaccades elsewhere. Therefore, this effect can reflect information transfer between parafoveal to foveal regions, before microsaccade onset, which can support a mechanism for visual stabilization.