Saccadic masking

Saccadic masking, also known as (visual) saccadic suppression, is the phenomenon in visual perception where the brain selectively blocks visual processing during eye movements in such a way that neither the motion of the eye (and subsequent motion blur of the image) nor the gap in visual perception is noticeable to the viewer. Saccadic masking, also known as (visual) saccadic suppression, is the phenomenon in visual perception where the brain selectively blocks visual processing during eye movements in such a way that neither the motion of the eye (and subsequent motion blur of the image) nor the gap in visual perception is noticeable to the viewer. The phenomenon was first described by Erdmann and Dodge in 1898, when it was noticed during unrelated experiments that an observer could never see the motion of their own eyes. This can easily be duplicated by looking into a mirror, and looking from one eye to another. The eyes can never be observed in motion, yet an external observer clearly sees the motion of the eyes. The phenomenon is often used to help explain a temporal illusion by the name of chronostasis, which momentarily occurs following a rapid eye-movement. A saccade is a fast eye motion, and because it is a motion that is optimised for speed, there is inevitable blurring of the image on the retina, as the retina is sweeping the visual field. Blurred retinal images are not of much use, and the eye has a mechanism that 'cuts off' the processing of retinal images when it becomes blurred. Humans become effectively blind during a saccade. This phenomenon is called saccadic masking or saccadic suppression. There are two major types of saccadic masking, flash suppression (the inability to see a flash of light during a saccade) and saccadic suppression of image displacement (characterized by the inability to perceive whether a target has moved or not during a saccade). Because saccadic suppression starts before the actual onset of the saccade, it cannot be triggered by retinal motion and must be centrally activated by the brain. Supporting this idea, a significant reduction of the cortical signals retinotopically encoding stimuli briefly presented immediately before the execution of a saccade has been found as early as in primary visual cortex.