Abstract
It is known that vision at the saccade goal is briefly enhanced before the eyes start to move. This enhancement is followed by a plummet in sensitivity as the eyes relocate the center of gaze. Recent work has shown that a similar modulation unfolds at the foveal scale for microsaccades. Here we examine and compare the extent and the time course of peri-microsaccadic and saccadic perception. Fixational eye movements were recorded with a high-resolution digital Dual Purkinjie Image eye-tracker while subjects performed a 2AFC discrimination task. Subjects (N=7) were required to shift their gaze to one of two possible locations surrounding a central fixation marker based on the direction indicated by a cue. Stimuli were flashed at those locations at variable times around the onset of the gaze shift. Stimuli appeared 0.3 deg and 5 deg away from the initial fixation, for microsaccades and saccades respectively. A response cue appeared after landing and subjects reported the orientation of the stimuli previously presented at the location indicated by this cue. Our findings show that stimuli at the microsaccade goal are perceptually enhanced (82%±7% vs 76%±4%, p<0.05) to the point that performance is comparable to when stimuli are presented directly at the preferred locus of fixation. This benefit occurs 30±19ms earlier in time compared to saccades. Similarly, discrimination of stimuli at the opposite location of the microsaccade goal is impaired (18%±5% performance drop) 30±6ms earlier than for saccades. Sensitivity recovered back to and beyond baseline upon microsaccade/saccade landing. These findings show that foveal vision is modulated around the time of microsaccades and that the time course of these pre-microsaccadic modulations differs compared to saccades; in particular pre-microsaccadic perceptual enhancements seem to occur earlier in time.