Persistence of vision

The optical illusion that occurs when visual perception of an object does not cease for some time after the rays of light proceeding from it has ceased to enter the eye.

Persistence of vision traditionally refers to the optical illusion that occurs when 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. The illusion has also been described as "retinal persistence", "persistence of impressions", simply "persistence" and other variations. According to this definition, the illusion would be the same as, or very similar to positive afterimages.

"Persistence of vision" can also be understood to mean the same as "flicker fusion", the effect that vision seems to persist continuously when the light that enters the eyes is interrupted with short and regular intervals.

Since its introduction, the term "persistence of vision" has been believed to be the explanation for motion perception in optical toys like the phenakistiscope and the zoetrope, and later in cinema. However, this theory has been disputed even before cinema was introduced in 1895. If "persistence of vision" is explained as "flicker fusion", it can be seen as a factor in the illusion of moving pictures in cinema and related optical toys, but not as its sole principle.

Early descriptions of the illusion often attributed the effect purely to imperfections of the eye, particularly of the retina. Nerves and parts of the brain later became part of explanations.

Sensory memory has been cited as a cause.

The idea that the motion effects in so-called "optical toys", like the phénakisticope and the zoetrope, is caused by images lingering on the retina was questioned in an 1868 article by William Benjamin Carpenter. He suggested that the illusion was "rather a mental than a retinal phenomenon".

Narrowly defined, the theory of persistence of vision is the belief that human perception of motion (brain centered) is the result of the persistence of vision (eye centered). That version of the theory was discarded well before the invention of film and also disproved in the context of the film in 1912 by Wertheimer but persists in citations in many classic and modern film-theory texts. A more plausible theory to explain motion perception (at least on a descriptive level) are two distinct perceptual illusions: phi phenomenon and beta movement.

A visual form of memory known as iconic memory has been described as the cause of this phenomenon. Although psychologists and physiologists have rejected the relevance of this theory to film viewership, film academics and theorists generally have not. Some scientists nowadays consider the entire theory of iconic memory a myth.

When contrasting the theory of persistence of vision with that of phi phenomena, an understanding emerges that the eye is not a camera and does not see in frames per second. In other words, vision is not as simple as light registering on a medium, since the brain has to make sense of the visual data the eye provides and construct a coherent picture of reality. Joseph Anderson and Barbara Fisher argue that the phi phenomena privileges a more constructionist approach to the cinema (David Bordwell, Noël Carroll, Kirstin Thompson) whereas the persistence of vision privileges a realist approach (André Bazin, Christian Metz, Jean-Louis Baudry).

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