Persistence of vision

Persistence of vision is the optical illusion that occurs when the visual perception of an object does not cease for some time after the rays of light proceeding from it have ceased to enter the eye.^[1] The illusion has also been described as "retinal persistence",^[2] "persistence of impressions",^[3] simply "persistence" and other variations. A very commonly given example of the phenomenon is the apparent fiery trail of a glowing coal or burning stick while it is whirled around in the dark.^[1]

Many explanations of the illusion actually seem to describe positive afterimages^[4] and the neurological effect can be compared to the technological effect of motion blur in photography (or in film and video).

"Persistence of vision" can also be understood to mean the same as "flicker fusion",^[5] the effect that vision seems to persist continuously when the light that enters the eyes is interrupted with short and regular intervals. When the frequency is too high for the visual system to discern differences between moments, light and dark impressions fuse together into a continuous impression of the scene with intermediate brightness.

Since its introduction, the term "persistence of vision" has often been mistaken to be the explanation for motion perception in optical toys like the phenakistiscope and the zoetrope, and later in cinema. This theory has been disputed since long before cinematography's breakthrough in 1895. The illusion of motion as a result of fast intermittent presentations of sequential images is a stroboscopic effect, as explained in 1833 by Simon Stampfer (one of the inventors of the stroboscopic disc, a.k.a. phenakistiscope).^[6]

Early descriptions of the illusion often attributed the effect purely to the physiology of the eye, particularly of the retina. Nerves and parts of the brain later became accepted as important factors.

Sensory memory has been cited as a cause.^[7]