Failure to detect displacement of the visual world during saccadic eye movements.

Perception of the rapid displacement of a target is suppressed during saccadic eye movements. Suppression is complete if eye movement is more than about three times larger than target displacement, and some suppression occurs even for target displacements of 4’. These results can be interpreted with the addition of a threshold element to the algebraic sum of the corollary discharge and the visual signal. The common observation that one’s own rapid eye movements (saccades) are not visible in a mirror has never been explained and raises the more general question of the perception of object displacement during saccades. The perceptual stability of the visual world despite saccades has classically been explained by postulating two parallel discharges from eye movement centers: one to the extraocular muscles, and a corollary discharge (CD) to the visual system to accurately subtract the effects ofeye movement from the internal (as opposed to retinal) representation of the visual world (Helmholtz. 1867; Sperry, 1950; von Hoist and Mettelstaedt, 1950). Difficulties arise for CD theories if object displacement is not detected for any displacement of a target in the world during a saccade creates a retinal target displacement different in magnitude from that of the CD, so that the target displacement should be detected. The experiment reported here shows, however, that target displacement during saccades often goes undetected quantifying the mirror observation.