Abstract
Saccade execution is known to modulate visual perception in distinctive ways; sensitivity is briefly enhanced at the saccade goal location before the eyes start to move, and a drop in sensitivity follows at the commencement of the saccade. Recent work has shown that microsaccades induce similar modulations at the scale of the fovea. Here we compare the temporal dynamics of pre-microsaccadic and saccadic perception. Eye movements were recorded with a high-resolution digital Dual-Purkinje Image eye tracker while subjects performed a 2AFC discrimination task. Subjects (N=6) were required to move their gaze to one of two possible locations surrounding a central fixation marker based on the direction indicated by the cue. Stimuli were flashed at both locations at a variable time before the gaze shift, either 0.3 deg or 5 deg away from fixation, in the microsaccade and saccade task respectively. At the end of the trial, subjects reported the orientation of the stimuli previously presented at the location indicated by a response cue. Our findings show that the pre-microsaccadic and pre-saccadic perceptual enhancements at the goal location are characterized by a comparable duration (59 ± 16 ms vs. 60 ± 12 ms, p = 0.8). Yet, the enhancement associated with microsaccades begins approximately 30 ms earlier than for saccades (p < 0.01). At both scales the enhancement is followed by a suppression that begins before the gaze shift onset. Differently from perceptual enhancement, suppression lasts 34 ± 27 ms longer for microsaccades than saccades (p < 0.05). These findings suggest that although saccades and microsaccades induce similar perceptual modulations, the enhancement and suppression unfold following different dynamics likely as a result of the longer latencies characterizing microsaccades.