Phi phenomenon
As phi phenomenon is in the narrower sense, a slip movement referred to, which at a fairly high with frequency is perceived alternating representation of relatively closely spaced optical stimuli. In contrast to the beta movement , which can be perceived at a lower frequency, no movement of the depicted objects themselves is perceived, but a diffuse, shapeless, shadow-like something that jumps back and forth between the depicted objects and seems to cover them alternately. This shadow is usually perceived roughly in the color of the background. This pseudo movement was first described by Max Wertheimer in his post- doctoral thesis Experimental Studies on Seeing Movement , published in 1912 .
In a broader sense, especially when speaking of Phi phenomena in the plural , the term encompasses all pseudo -movements that can be perceived when two optical stimuli are presented alternately, i.e. especially beta movement , which is important when perceiving moving images . In any case, when Wertheimer introduced the term “φ phenomenon” in 1912, he referred it to all of the pseudo-movements described in his publication; he called the shadow-like, objectless movement “pure φ”. However, some scientists are convinced that with the Greek letter Phi he only meant objectless movement.
Experimental reproduction
In the classic experiment, analogous to that of Wertheimer, to reproduce the pure, objectless Phi phenomenon, a test person is presented with two lines in succession on a screen. First one on the left, then one on the right. This sequence is repeated several times. The test subjects can perceive the Phi phenomenon at certain, very short time intervals between changing sides and at a suitable distance between the two lines.
However, it turns out to be far more difficult than with the beta movement to produce stable and convincing test results. To facilitate perception, a test arrangement was therefore designed in which more than two elements are used. In this variant of the experiment, also known as “Magni-phi”, disks of the same type are arranged in a circle and one of the objects is faded out in quick succession either clockwise or counterclockwise. This seems to make this shadowy movement easier to perceive. In addition, this test arrangement is less sensitive to changes in parameters such as timing, size of the panes, intensity or visual distance.
It was also found that even with a display that only uses two elements in accordance with the original test arrangement, better results can be achieved if a negative interstimulus interval (ISI) is used, i.e. the presentation times of the two elements overlap. Then the two stimuli shown alternately are perceived as stationary objects. This means that the observer subconsciously assumes that when the stimulus reappears on one side, it is the object previously shown at this point and not that of the opposite side, as in the beta movement. The decisive factor for this perception is the shortness of the interruption of the stimulus on each side. This is supported by the fact that the following two parameters must be suitably selected so that the pure Phi phenomenon is perceived: On the one hand, the absolute interval of the stimulus interruption per side must not be greater than 150 ms. In addition, the interruption interval may not exceed 40% of the period duration.
Research history
In his habilitation thesis Experimental Studies on Seeing Movement , published in 1912 , Max Wertheimer introduced the symbol φ ( Phi ) in the following way:
“Successively two objects are given as stimuli; these are felt; a is seen first, b last; between them was the 'movement from a to b seen'; without the corresponding movement respectively. the space-time-continuous intermediate layers between a and b would really have been exposed as stimuli. The psychological situation is - without any prejudice - denoted by a φ b. "
In addition to the “optimal movement”, which was later given the name beta movement, and partial movements of the two objects, Wertheimer also described cases that he described as “pure movement phenomena”. As for this, he summarized the descriptions of his test subjects as follows:
“These cases showed up in such a way that the thought was not there either: an object had moved over; what was available of objects was given in the two layers; not one or one of them or anything like that involved the movement; but between them there was movement; not an object movement. Neither: the object moves over, I just don't see it. But there was simply movement; not related to an object. "
Wertheimer attached great importance to these observations because, in his opinion, they prove that the perception of movement is a direct sensory perception that does not necessarily have to be inferred from the individual perception of two optical stimuli at a temporal and spatial distance. This aspect of his work from 1912 may have been an important impetus for the Gestalt psychology that he later co-founded .
From the middle of the 20th century, confusion arose in scientific literature about what the Phi phenomenon was all about. On the one hand, this was probably due to the fact that the English-speaking researchers found it difficult to understand Wertheimer's publication, which was written in German. Furthermore, it is not clear from Wertheimer's work with which parameters this “pure movement phenomenon” was observed, and the experimental reproduction of this is relatively difficult. Edwin Boring's influential standard work on sensory impression and perception, first published in 1942, probably contributed significantly to this confusion . In this he recapitulated the list of Wertheimer's cases and sorted them in ascending order according to the length of the interstimulus interval. In doing so, he classified the pure Phi phenomenon incorrectly, namely as the impression of movement with the longest interval, the further lengthening of which would no longer produce any impression of movement, but instead the observer would only perceive two objects appearing separately one after the other.
This confusion probably also contributed to the fact that the pure Phi phenomenon was "rediscovered" by other researchers, for example as "omega motion", "afterimage motion" or "shadow motion".
Explanation of the pure Phi phenomenon
Possibly due to the contradicting scientific literature, hardly any sensory or neurophysiological theories have been put forward to interpret the pure Phi phenomenon.
One explanation is to interpret the movement perception as the movement of a covering “curtain” in front of the depicted object. This would be supported by the fact that when comparing the timing of pure phi movement with beta movement, the interruption intervals roughly correspond to the presentation intervals in terms of the relative duration. As can be seen in the Kanizsa triangle , what is interpreted as an object and what is interpreted as a background in visual perception can depend on subtle factors. Thus, one could interpret the Phi phenomenon in such a way that the object actually presented is interpreted as a background that is covered by a moving “virtual curtain”. However, this explanatory approach would assume that purely temporal factors can also be sufficient to influence the interpretation of visual perception, what is interpreted as an object and what is interpreted as a background. If this were the case, the pure Phi phenomenon would actually not be an objectless perception of movement, as Wertheimer assumed.
See also
Web links
- Beta movement and Phi phenomenon. A pictorial explanation of the difference between the beta and phi phenomena in the strict sense
- Color Phi Phenomenon. Interactive display of the color change Phi phenomenon
Individual evidence
- ↑ a b c d Vebjørn Ekroll, Franz Faul, Jürgen Golz: Classification of apparent motion percepts based on temporal factors. In: Journal of Vision. Volume 8, 2008, No. 31, pp. 1-22 ( online ).
- ↑ a b c d Max Wertheimer : Experimental studies on seeing movement . In: Zeitschrift für Psychologie , Volume 61, 1912, pp. 161–265; gestalttheory.net (PDF; 8.6 MB).
- ↑ Friedrich Kenkel: Investigations into the connection between appearance size and appearance movement in some so-called optical illusions. In: F. Schumann (Ed.): Zeitschrift für Psychologie , Volume 67, Leipzig 1913, p. 363
- ↑ Martha Blassnigg: Time, Memory, Consciousness and the Cinema Experience: Revisiting Ideas on Matter and Spirit. Edision Rodopi, Amsterdam / New York 2009, ISBN 90-420-2640-5 , p. 126 ( books.google.de ).
- ↑ a b c d e f Robert M. Steinman, Zygmunt Pizlob, Filip J. Pizlob: Phi is not beta, and why Wertheimer's discovery launched the Gestalt revolution. In: Vision Research , Volume 40, 2000, pp. 2257-2264, PMID 10927113 .
- ↑ Robert Sekuler: Motion Perception: A Modern View of Wertheimer's 1912 monograph. In: Perception. Volume 25, pp. 1243-1258, doi: 10.1068 / p251243 .
- ↑ Edwin Boring: Sensation And Perception In The History Of Experimental Psychology. Appleton-Century-Crofts, New York 1942 ( archive.org ).