“A subject is seated in a darkened room and two spots of light are flashed off and on alternately. When the interval between flashes is more than 0.2 sec, the subject sees two flashing lights; but when the interval is less than 0.2 sec the subject sees one light in continuous motion. . . . This phenomenon underlies our experience of movies, which are actually a rapidly displayed series of still photographs. . . . Apparent motion is an experience that emerges from simple sensations but cannot plausibly be reduced to them. It is, in short, a perceptual whole (Gestalt, in German), given immediately to consciousness and deserving direct study. The Gestal psychologists advocated a holistic psychology based on the mind’s perception of complete forms.

This experimental demonstration (called the phi phenomenon), which shows that conscious experience is not usefully reducible to bundles of discrete sensations, was the starting point of the Gestalt movement.”

—Thomas Hardy Leahey, from A History of Psychology: Main Currents in Psychological Thought, second edition, 1987.