Elevation of Visual Threshold by Displacement of Retinal Image

THERE have been many reports that the threshold for perception of a test flash is raised during a saccadic eye movement1–4. Even with a flash brief enough to eliminate any blurring of its retinal image during the saccade, an elevation of threshold by half a log unit is common3, although there have been significant exceptions5. Of particular interest is the finding that this reduction in visibility may apply to flashes occurring as much as 40 ms before the onset of a saccade. Not unnaturally, this has been widely interpreted as evidence of some central inhibitory process, set in motion as part of the preparation of a voluntary eye movement.