Definition for Phi phenomenon
From Biology Forums Dictionary
The phi phenomenon is an optical illusion defined by Max Wertheimer in the Gestalt psychology in 1912, in which the persistence of vision formed a part of the base of the theory of the cinema, applied by Hugo Münsterberg in 1916. This optical illusion is based in the principle that the human eye 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.
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.