Beta movement

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 1833, Joseph Plateau introduced what became known as the phenakistiscope,[2] an early animation device based on a stroboscopic effect.

Most authors who have since described the illusion of seeing motion in the fast succession of stationary images,[3] maintained that the effect is due to persistence of vision, either in the form of afterimages on the retina or with a mental process filling in the intervals between the images.

[1] In 1875, Sigmund Exner showed that, under the right conditions, people will see two quick, spatially separated but stationary electrical sparks as a single light moving from place to place, while quicker flashes were interpreted as motion between two stationary lights.

[4] In 1912, Max Wertheimer wrote an influential article that would lead to the foundation of Gestalt psychology.

In the discussed experiments, he asked test subjects what they saw when viewing successive tachistoscope projections of two similar shapes at two alternating locations on a screen.

At low frequencies, successive appearances of similar figures at different spots were perceived.

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.

Kenkel, a co-worker of Koffka, gave the optimal illusion of motion (with the appearance of one figure moving from one place to the next) the designation "β-Bewegung" (beta movement).

There are many factors that determine whether one will experience beta movement or the phi phenomenon in a particular circumstance.