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The beta movement is an optical illusion, first described by Max Wertheimer in 1912. Its illusion is that fixed images seem to move, even though of course the image does not change. It might be considered similar to the effects of animation. The static images do not physically change but give the appearance of motion because of being rapidly changed faster than the eye can see.
This optical illusion is caused by the fact that the human optic nerve responds to changes in light at about 10 cycles per second, so changes about double of this are registered as motion instead of being separate distinct images.
Examples of use of beta movement
One example of the beta movement effect would be a set of LEDs, as shown at the picture on the right. The LEDs, electronically, are individually controlled, but our eyes and brains perceive them as a snake running clockwise around the four edges of the square picture. This is also seen commonly on LED displays.
Experiment of beta movement
The classic beta phenomenon experiment involved a viewer watching a screen, upon which the experimenter projected two images in succession. The first image depicted a ball on the left side of the frame. The second image depicted a ball on the right side of the frame. In the experiment, the images were first held steady, then switched between the two frames. The experimenter asked then what the audience thought they saw.
The beta phenomenon is often confused with the phi phenomenon but they are different. The phi phenomenon is the apparent motion caused by a changing static image, as in a motion picture. The beta phenomenon is the apparent motion between different light sources that are periodically switched on, as in chase lighting. In phi, there are different images or lights in a single place, whereas in beta the images or lights are in different locations. In both cases the images or lights are turned on and off rapidly to produce the effect.
Beta and phi
The names beta and phi are simply the letters "β" and "Φ" from the Greek alphabet, and have no particular significance beyond separating the two phenomena.
- Wertheimer, M. (1912). Experimentelle Studien über das Sehen von Bewegung. Zeitschrift für Psychologie, 61, 161–265.