Experimental Psychology Tutorials > Apparent Motion

Phi Phenomenon (aka "Apparent Motion")

This sequence of a running horse is actually a series of still pictures. The photographer, Eadweard (sic) Muybridge (1830 - 1904), was answering the question of whether or not a horse ever had all four feet off the ground while running. Muybridge sat up a series of still cameras with strings attached to each control stretched across the track. As the horse ran by it triggered, one by one, each camera. The photos answered the question. By flipping through the photos motion was seen. The photographs were taken in 1872 to settle a $25,000 bet between Leland Stanford and a rival horse breeder. Incidently, Stanford won.

As you no doubt know, the stimuli for moving pictures and TV screens is a series of still pictures--one still picture flashed after the other. Our perceptual system (and that of other animals) accepts the flashed still pictures and represents the sequence of stills as objects in motion. Isaac Asimov has a Science Fact article, "The Illusion of Motion" in the January 1991 Fantasy & Science Fiction Magazine giving a short history of the development of motion pictures.

Apparent Motion (aka "Phi Phenomenon") describes a situation where we perceive movement but the stimuli are not moving. This phenomenon is the basis of the motion we perceive in motion pictures, television, animated films, and theater marquees. Max Wertheimer, a founder of Gestalt Psychology, realized that Apparent Motion was an important phenomenon because the perception (motion) was not simply copying the stimulus (still pictures flashed one after the other).

I have the animation on my opening web page because my doctoral specialization was perception and my way of thinking about behavioral and psychological phenomenon remains that of a perceptual psychologist.

••••• In Appreciation •••••

Appreciation and thanks to my perception mentors, Harry Helson (who helped introduce Gestalt Psychology to the United States), and Irvin Rock (who wrote THE text in perception now sadly out of print).

Special appreciation to my colleague of 20 years, Bill Hepler, who continually taught me that teaching is important.

Modified Wednesday, July 20, 2005