Beta movement is a perceptual illusion whereby two or more still images are combined by the brain into surmised motion. Beta movement is one of two illusions referred to as "phi phenomena." (Confusingly, the other illusion is referred to as the phi phenomenon).
These illusions are distortions of sensory input, revealing how the brain organizes and interprets the information we receive from the world. Through studying this type of illusion scientists are able to discover how our minds function in informing us about the environment. In addition to providing ways to research human abilities, illusions like beta movement intrigue and entertain people, reflecting our cognitive curiosity and appreciation for creativity that is part of human nature.
The phi phenomenon was first discovered by Max Wertheimer, who noticed that the light appeared to jump from one lamp to another when he turned them on and off in quick succession. Wertheimer published his findings in his 1912 paper Experimental Studies on the Seeing of Motion. This formed the beginnings of Gestalt psychology, which led to fundamental changes in the way psychologists approached the study of perception.
Beta movement is a specific form of this apparent movement illusion. It involves the viewer perceiving the objects (lights) actually moving themselves, not just the sensation of pure movement between them characterized by Wertheimer's phi phenomenon. The effect known as beta movement was first reported in 1913 by F. Kenkel.
The classic beta phenomenon experiment involves a viewer or audience watching a screen, upon which the experimenter projects two images in succession. The first image depicts a ball on the left side of the frame. The second image depicts a ball 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. Viewers generally claim to see one ball move from left to right, not two balls flashing in succession.
The beta phenomenon can also create the illusion of motion toward and away from an audience. When the first image is of a large object, and the second is of a small object (or vice-versa), viewers generally report that the object moved away from them. Additionally, if the first frame depicts a brightly-colored object against a solid background, and the second depicts the same object but in colors similar to the background, viewers report that the object moved away from them.
Beta movement is commonly found in computer generated examples as a circle of dots that disappear in a clockwise or counterclockwise sequence, making it seem as though dots are jumping into the empty space next to them. A similar image is used to show the related illusion of phi phenomenon, the only difference being the speed of the sequence of disappearing circles.
Scientists do not yet fully understand what causes the illusion of apparent motion with beta movement. Most theories involve a physiological, rather than psychological explanation, and have to do with the various ways the brain and optic nerves communicate.
Beta movement is often seen in strings of decorative holiday lights, which sometimes blink on and off in sequence. It can also be found on old theater marquees or other such signs, where individual lights appear to travel around the perimeter of the sign. Beta movement can also be found in neon signs, where a figure or object appears to change position.
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