A report on Beta movement, Phi phenomenon and Animation

The illusion of motion caused by animation and film is sometimes believed to rely on beta movement, as an alternative to the older explanation known as persistence of vision.

In contrast to beta movement, seen at lower frequencies, the stimuli themselves do not appear to move.

This includes especially beta movement, which has been regarded as the illusion of motion in cinema and animation, although it can be argued that beta movement indicates long-range apparent motion rather than the short-range apparent motion seen in film.

The illusion of animation—as in motion pictures in general—has traditionally been attributed to persistence of vision and later to the phi phenomenon and/or beta movement, but the exact neurological causes are still uncertain.

Wertheimer used the Greek letter φ (phi) to designate illusions of motion and thought of the high-frequency objectless illusion as a "pure phi phenomenon", which he supposed was a more direct sensory experience of motion.