Phi phenomenon
The phi phenomenon is a perceptual illusion in which a disembodied perception of motion is produced by a succession of still images. Confusingly, the term "phi phenomena" is used to refer to both phi phenomenon and beta movement, a related illusion. This results in phi phenomenon often being confused with beta movement.
Discovery
Phi phenomena were described by Max Wertheimer in his 1912 paper Experimental Studies on the Seeing of Motion.
Description
The classic phi phenomenon experiment involves a viewer or audience watching a screen, upon which the experimenter projects two images in succession. The first image depicts a line on the left side of the frame. The second image depicts a line on the right side of the frame. The images may be shown quickly, in rapid succession, or each frame may be given several seconds of viewing time. Once both images have been projected, the experimenter asks the viewer or audience to describe what they saw.
At certain combinations of spacing and timing of the two images, a viewer will report a sensation of motion in the space between and around the two lines, even though the viewer also perceives two distinct lines and not the continuous motion of objects referred to as beta movement. The phi phenomenon looks like a moving zone or cloud of background color surrounding the flashing objects. Phi phenomenon generally takes place at much higher switching speeds than beta movement.
Computerized demonstrations of phi phenomenon often show a circular group of smaller circles, which switch on and off in quick sequence. Phi is described as "pure movement" that always takes on the background color. In beta movement, it appears that the circles (or other figures) are moving. With phi, the circles appear stationary, but movement is perceived around them.
Explanation
Scientists do not yet fully understand what causes the illusion of apparent motion with beta movement or phi phenomenon. Most theories involve a physiological, rather than psychological explanation, and have to do with the various ways the brain and optic nerves communicate.
Applications
The discovery of phi phenomenon played a significant role in Gestalt psychology, as it changed the way perception was studied. Illusions like phi phenomenon continue to help scientists find new ways to study the way the human brain and visual system perceive and interpret information.
External links
- Phi is not Beta – An explanation of the difference between the beta and phi phenomena, with online demonstrations of both, and a stronger version of phi than that found by Wertheimer.
- The Myth of Persistence of Vision Revisited – A detailed explanation of how the perception of motion in film and video differs from the simplest notions of "persistence of vision," with mention of the erroneous use of phi as a revised explanation.
ReferencesISBN links support NWE through referral fees
- Chang, Freddy., Daniel Gerstman., P.A. Pietsch and Linda Locke. MEPC: Optometry: Examination Review. March, 1994. McGraw-Hill Medical. Publishing. ISBN 0838574491
- Hartmann, George Wilfried. 2006. "Gestalt Psychology: A Survey of Facts and Principles". Kessinger Publishing. ISBN 142545285X
- Schwartz, Steven H. 2004. "Visual Perception". McGraw-Hill Medical. ISBN 0071411879
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