Persistence of sight
Persistence of Vision ( English Persistence of Vision ) is an established in the 19th century term to the realistic motion perception when viewing moving images to explain, for example in film or television. In German, the terms afterimage effect or sluggishness of the eye are often used in this context . The traditional explanation claims that a perceived image persists for a certain time after it disappears on the retina and merges with the following image to form a unit, which causes the perception of seamless movement. This explanatory model has been refuted by more recent findings, but has persisted in the literature.
Two separate aspects are important as the reason why moving images convey a real impression: firstly, why a sequence of images merges into one image, and secondly, why movements reproduced in these images, which are not reproduced continuously and continuously, nevertheless appear realistic . The latter is explained by the stroboscopic movement . For the first point, i.e. to merge sequential images into one overall image, they must be repeated with sufficient frequency. In order for it to be perceived flicker-free, it must be above the flicker fusion frequency . The terms “persistence of seeing”, “afterimage effect” and “indolence of the eye” are now only related to this aspect. The term "afterimage effect" is very unfortunate, however, since retinal afterimages do not play a role here.
Flicker fusion
To ensure continuity for the outline of a figure, 4 to 5 images per second are sufficient. In order to be able to perceive the inside of a figure without flickering, however, much higher frequencies are necessary; these also depend primarily on the brightness of the pixels. As a rule, 48 or 72 images per second are shown in the cinema, whereby there are only 24 different images per second that are repeated two or three times. The flicker fusion frequency is the cut-off frequency from which the human eye can no longer distinguish a periodic light stimulus from a uniformly luminous one.
Visual persistence
As already mentioned, frequencies of 4 to 5 Hertz are sufficient for contours to be perceived as persistent. This is because of the visual persistence that is part of the iconic memory . Retinal afterimages do not play a role here, it is not a sensory but a cortical function. It is also the explanation for the perception of the thaumatrope , in which two different images are shown on the front and back of a disk and when the disk is rotated quickly, the images are perceived as merged.
Individual evidence
- ↑ Joseph and Barbara Anderson: The Myth of Persistence of Vision Revisited. In: Journal of Film and Video. Volume 45, Number 1, 1993, pp. 3-12 ( JSTOR 20687993 ).
- ↑ Bill Nichols, Susan J. Lederman: Flicker and Motion in Film. In: Teresa DeLauretis, Stephen Heath: Cinematic Apparatus. Springer, London 1980, pp. 96-105 ( Google books ).
- ↑ Steven J. Luck, Andrew Hollingworth (Eds.): Visual Memory. Oxford University Press, New York 2008, ISBN 978-0-19-530548-7 , p. 9 ( Google books ).
- ↑ a b Yves Galifret: Visual persistence and cinema? In: Comptes Rendus Biologies. , Vol. 329, No. 5-6, 2006, pp. 369-385 ( PMID 16731495 ; abstract).