The 1912 publication of Wertheimer’s article on the phi phenomenon usually marks the founding of the Gestalt school of psychology. The phi phenomenon indicates that conscious experience cannot be reduced to sensory experience. Koffka and Köhler worked with Wertheimer on his early perception experiments and are usually considered cofounders of Gestalt psychology. Wertheimer assumed that forces in the brain distribute themselves as they do in any physical system (symmetrically and evenly) and that these force fields interact with sensory information to determine conscious experience. The contention that force fields in the brain
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determine consciousness was called psychophysical isomorphism, and the contention that brain activity is always distributed in the most simple, symmetrical, and organized way was called the law of Prägnanz. The term perceptual constancy refers to the way we respond to objects or events as the same even when we experience them under a wide variety of circumstances.