Alteration of visual perception prior to microsaccades.

Gaze fixation is an active process, with the incessant occurrence of tiny eye movements, including microsaccades. While the retinal consequences of microsaccades may be presumed minimal because of their minute size, a significant perceptual consequence of these movements can also stem from active extraretinal mechanisms associated with corollaries of their motor generation. Here I show that prior to microsaccade onset, spatial perception is altered in a very specific manner: foveal stimuli are erroneously perceived as more eccentric, whereas peripheral stimuli are rendered more foveal. The mechanism for this perceptual "compression of space" is consistent with a spatially specific gain modulation of visual representations caused by the upcoming eye movements, as is hypothesized to happen for much larger saccades. I then demonstrate that this perimicrosaccadic perceptual alteration has at least one important functional consequence: it mediates visual-performance alterations similar to ones classically attributed to the cognitive process of covert visual attention.