STUDIES AND RESEARCH
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...).
ANALITICAL CONTENT OF THE PAPER:
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 |
