The phi phenomenon is an optical illusion defined by Max Wertheimer

Max Wertheimer

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 in the Gestalt psychology

Gestalt psychology

Gestalt psychology or gestaltism is a theory of mind and brain of the Berlin School; the operational principle of gestalt psychology is that the brain is holistic, parallel, and analog, with self-organizing tendencies...

 in 1912, in which the persistence of vision

Persistence of vision

Persistence of vision is the phenomenon of the eye by which an afterimage is thought to persist for approximately one twenty-fifth of a second on the retina....

 formed a part of the base of the theory of the cinema, applied by Hugo Münsterberg

Hugo Münsterberg

Hugo Münsterberg was a German-American psychologist. He was one of the pioneers in applied psychology, extending his research and theories to Industrial/Organizational , legal, medical, clinical, educational and business settings. Münsterberg encountered immense turmoil with the outbreak of the...

 in 1916.
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 based in the principle that the human eye

Human eye

The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...

 is capable of perceiving movement from pieces of information, for example, a succession of images. In other words, from a slideshow of a group of frozen images at a certain speed of images per second, we are going to observe constant movement.

Phi phenomenon

The phi phenomenon is an optical illusion of our brains and eyes that allows us to perceive constant movement instead of a sequence of images. We are supplying information that does not exist (between image and image) that creates the illusion of a smooth movement.
The phi phenomenon, which might be considered the basis of the correct working of the cinema, is only a limitation of the human eye, which depends on the persistence of visual sensations.

Persistence of vision

The "persistence of vision" refers to that phenomenon in which the human perception of the decay of a visual stimulus is slower than the true decay of that stimulus. An image will stay on one's eye for a brief amount of time after its cause has, in reality, disappeared.

The phenomenon of the persistence of vision is popularly taught as the reason that humans perceive motion in such things as zoetropes and classically projected films, but it is in reality not connected with motion perception. It is merely the reason that we do not see the black frames that come between each "real" frame while watching a movie. The true reason for motion perception is the phi phenomenon.

Examples of use of the phi phenomenon

Cinema

Film

A film, also called a movie or motion picture, is a series of still or moving images. It is produced by recording photographic images with cameras, or by creating images using animation techniques or visual effects...

 and other popular forms of animation are, of course, the best example of this phenomenon at work. However, some of its predecessors are as follows:

Phenakistoscope

The phenakistoscope

Phenakistoscope

The phenakistoscope was an early animation device that used the persistence of vision principle to create an illusion of motion.-History:...

 was an early animation device. It preceded the zoetrope.

Zoetrope

Meaning "wheel of life," the zoetrope

Zoetrope

A zoetrope is a device that produces an illusion of action from a rapid succession of static pictures. The term zoetrope is from the Greek words "ζωή – zoe", "life" and τρόπος – tropos, "turn". It may be taken to mean "wheel of life"....

 is a device that produces the illusion of motion by presenting static pictures in quick succession. It accomplishes this by way of a spinning drum with slits in the top through which one watches the animation, which has usually been drawn on a strip of paper that sits at the bottom of the drum.

Experiment of the phi phenomenon

The classic phi phenomenon experiment involves a viewer or audience watching a screen, upon which the experimenter projects two images in succession. The first image depicts a line on the left side of the frame. The second image depicts a line on the right side of the frame. The images may be shown quickly, in rapid succession, or each frame may be given several seconds of viewing time. Once both images have been projected, the experimenter asks the viewer or audience to describe what they saw.

At a certain combinations of spacing and timing of the two images, a viewer will report a sensation of motion in the space between and around the two lines,.In these cases, the line that seems to move is actually a figure that first appears in the right of the screen and then in the left.

The phi phenomenon is not beta movement

Although both cause sensation of movement, the phi phenomenon can be considered to be an apparent movement caused by luminous impulses in sequence, whereas the beta movement

Beta movement

The Beta movement is an optical illusion, first described by Max Wertheimer 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...

is an apparent movement caused by luminous stationary impulses

External links

• The Myth of Persistence of Vision Revisited – A detailed explanation of how the perception of motion in film and video differs from the simplest notions of "persistence of vision", with mention of the erroneous use of phi as a revised explanation.
• Phi phenomenon activity – Application that lets us change some parameters to experiment with the phi phenomenon.