Beta movement
The Beta movement is an optical illusion, first described by Max Wertheimer
Max Wertheimer
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 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
Animation is the rapid display of a sequence of images of 2-D or 3-D artwork or model positions in order to create an illusion of movement. The effect is an optical illusion of motion due to the phenomenon of persistence of vision, and can be created and demonstrated in several ways...

. Wertheimer wrote his paper in the early days of motion pictures, and this may account for some of his findings, since people were unused to images moving at all.

Of course 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
Optical illusion
An optical illusion is characterized by visually perceived images that differ from objective reality. The information gathered by the eye is processed in the brain to give a perception that does not tally with a physical measurement of the stimulus source...

 is caused by the fact that the human optic nerve
Optic nerve
The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...

 responds to changes in light at about 10 cycles per second
Hz is the International Standard symbol for Hertz, the unit of frequencyHZ may also stand for:* Habitable zone, the distance from a star where a planet can maintain Earth-like life* Hamilton Zoo, in New Zealand...

, 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 a snake running clockwise around the four edges of the square picture. This is also seen commonly on LED writing board
LED writing board
The LED writing board is a reusable writing surface on which advertising and messages are made with fluorescent marker pens. It has many different names, such as the Multi Color Neon LED Menu Board, Multi Color Neon LED Message Board or the Flashing LED board...


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.

Phi phenomenon

The Beta phenomenon is often confused with the phi phenomenon
Phi phenomenon
The phi phenomenon is an optical illusion defined by Max Wertheimer in the Gestalt psychology in 1912, in which the persistence of vision formed a part of the base of the theory of the cinema, applied by Hugo Münsterberg in 1916....

 but they are quite different physiologically. The phi phenomenon can be considered to be an apparent movement caused by luminous impulses in sequence, (that is to say, it is lights going on and off at regular intervals), whereas the beta movement is an apparent movement caused by lights that do not move, but seem to.

Beta and Phi

The names beta and phi are simply the letters "β" and "Φ" from the Greek alphabet
Greek alphabet
The Greek alphabet is the script that has been used to write the Greek language since at least 730 BC . The alphabet in its classical and modern form consists of 24 letters ordered in sequence from alpha to omega...

, and have no particular significance beyond separating the two phenomena.
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