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Movement Illusion in Film — Myths and Explanations

In spite of the history of psychologicians’ warnings against the persistence of vision explanation of the movement illusion in film (Muensterberg, Woodwort, Rock) and contemporary film psychologists’ campaign against it (Anderson, Brooks, Hochberg), the illusion of movement (psychologists predominantly speak about the apparent movement) is still persistently explained in this fashion. For quite some time the persistence of movement explanation has been supplemented by the subsumption of the movement illusion to phi phenomenon also, but without any attempt to clarify the queer methodological move of explaining one phenomenon by the two unrelated explanations.

One of the deeper reasons why persistence of vision explanation is still practiced, and why the two explanations are used side by side, is that — in the case of film — we are dealing with TWO ILLUSIONS, not one. One illusion is the illusion of light constancy of film image, contrary to the fact that the image is intermittently darkened by shatter mechanism during its projection. Persistence of vision is a pertinent explanation of this illusion, though there remains a question whether it is also an adequate explanation of the flicker fusion phenomenon — i. e. of the integration of intermittent flashes of film image on the screen (cf. Rushton). Second illusion is the movement illusion: we illusory see continuous movement within the film shot though what is projected is just a sequence of stills with no movement in them.

This illusion is pertinently categorized as a sort of phi phenomenon (or stroboscopic movement). Though both illusions do contribute to the final perceptual impact of film, they constitute two quite different and separate phenomena, i. e. one is not necessary for the occurrence of the other. There are three substantial arguments against mixing the two phenomena (flicker fusion and stroboscopic movement). The argument of double exposure (Brooks, Hochberg) states that persistence of vision alone would produce only double exposure effect (doubling of scenic features of the two successive images within one perceived image — as it occurs in thaumatrop). Apparent movement effect is not produced by persistence of vision. The argument of film cut states that light constancy (i. e. flicker fusion) occurs over the cut though typically there is no apparent movement from frame to frame over the cut. Again, flicker fusion is obviously dissociated from apparent movement. The argument of different frequencies states that flicker frequency required for critical flicker fusion (light constancy) is quite different from the frequency of intermittent movement of projected film images required for apparent movement effect.

Perfect apparent movement occurs at intermittent changes of 16 frames per second, while it is required a double shatter frequency — around 50-60 times per second — in order to eliminate a flickering effect in projected film image. Further demonstration that the two ’fusions’ — flicker fusion that produces light constancy and stroboscopic ’fusion’ that produces apparent movement — are not causally connected can be found in the fact that in early silent films the flicker effect was quite strong, while at the same time the movement illusion was full.

The problem with phi phenomenon approach to the movement illusion is that it is more an enlightening generic specification of the illusion than its proper explanation (i. e. elucidation of psycho-physiological mechanisms at the basis of different aspects of phi phenomenon). There are two problems behind the choice of explanation of apparent movement. Firstly, one can assume that perceptual mechanisms behind the apparent movement are quite different from mechanisms behind the proper movement perception.

Secondly, one can assume that only one mechanism is in question, but it is a mechanism that can be ’cheated’, perceptually ’mislead’ under specific stimulus conditions. The paper argues for the last approach: there is a limitation on the adaptational specificity of our perceptual processing of environment. The processing is tuned to the particular adaptationally important stimulus configuration (say to object movement, and observer’s proprio-movement) because it is highly improbable that particular configuration changes will ever belong to the scenes/objects of complete different ontological status (e. g. to a specific succession of closely placed and closely shaped static patterns).

But, if such an improbability does occur, if an object of completely different ontological status (e. g. a succession of film images) is producing the required stimulus configuration for particular processing (for movement processing), then the processing would be misled into illusory perception of movement (cf. Anderson, Brooks-Hochberg, Gibson, Palmer, Rock...).


1. ’Myth of persistence of vision’; 1.1. Persistence of vision as explanation of movement illusion; 1.2. Supplementary explanation by phi-phenomenon; 1.3. Harangue against the persistency explanation of apparent movement; 2. What is explained by the persistency of vision, and what is not; 2.1. The two basic illusions of film; 2.2. Argument of double exposure; 2.3. Argument of film cut; 2.4. Argument of different frequencies; 2.5. Conclusion; 3. Why darken an image in shooting and projecting a movie?; 3.1. Why shatter?; 3.2. Flicker fusion as solution; 4. Explanations of apparent movement in film; 4.1. Specificity theories of apparent movement; 4.2. Hypothesis of common processing of apparent and real movement; 4.3. Argument of superfluous parallelism; 4.4. Argument of equal proximal conditions for apparent and real movement; 4.5. Argument of common neuro-psychological mechanism; 4.6. Conclusion: functional ’typification’ of perception; 5. Status of apparent movement; 5.1. Apparent movement is illusory; 5.2. Perception of film movement is an illusion proper; 5.3. Special ontological status of apparent movement; 6. Resume and conclusion; Endnotes; Bibliography.

Hrvoje Turković

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