Persistence of vision

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 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 a stream of light is repeatedly interrupted for very brief instances and thus enters the eyes intermittently. 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 an important 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. Some natural phenomena and the principles of some optical toys have been attributed to the persistence of vision effect. Patrick d'Arcy recognised the effect in 'the luminous ring that we see by turning a torch quickly, the fire wheels in the fireworks, the flattened spindle shape we see in a vibrating cord, the continuous circle we see in a cogwheel that turns with speed'. Basically everything that resembles motion blur seen in fast moving objects could be regarded as 'persistence of vision'. The fact that a glowing coal appears as a line of light when it is moved around quickly has often been used to illustrate the idea of persistence of vision.It is known as the 'sparkler's trail effect', named after the trail that appears when a sparkler is moved around quickly.