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Shlomit Yuval-Greenberg, Elisha P. Merriam, David J. Heeger; Cortical activity in visual cortex coincident with microsaccades. Journal of Vision 2012;12(9):1016. doi: https://doi.org/10.1167/12.9.1016.
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Purpose: Our eyes are in constant rapid motion, and each such movement (saccade) generates a displacement of the visual image on the retina. Despite these displacements, our visual perception remains stable. It has long been hypothesized that the visual system maintains perceptual stability by compensating for these displacements by means of extraretinal information which it receives from oculomotor areas (corollary discharge). Most of the procedures previously used to study the corollary discharge employed peripheral cues as saccade targets. Such peripheral stimulation confounds the visual activity related to extraretinal neural processes with that related to retinal stimulation. The purpose of this research was to circumvent this confound by using involuntary small saccades (microsaccades) recorded in complete darkness, allowing us to avoid peripheral visual stimulation. Using this procedure we are able to demonstrate visual activation during saccade execution which is unrelated to retinal stimulation.
Method: We scanned subjects either while viewing a large, high contrast radial checkerboard (control), or while fixating on a small dot in an otherwise completely dark environment (main experiment). Cortical responses were measured with fMRI, time-locked to microsaccade onset.
Results: In the control experiment, several striate and extrastriate visual areas showed microsaccade-related activity. In the main experiment most of the early visual activity was not evident but significant responses remained in dorsal visual areas V3A and V6.
Conclusions: Activity in the control experiment (static stimulus) was likely the result of visually-evoked neural responses due to retinal displacement. The results of the main experiment cannot be attributed to retinal slip because it was conducted in complete darkness. Rather, visual activity in the main experiment may be related to corollary discharge signals fed back to visual cortex at the time of each eye movement.
Meeting abstract presented at VSS 2012
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