a concept developed to explain the regulation and interaction of internal signals and sensory signals in directing and coordinating bodily movements. It requires storage of a copy of each spontaneous activation of a motor unit by the processing unit (see corollary discharge). This copy fixes the reference value of the parameters required to execute the movement, which guides the response until the reafference from a sensory unit to the processing unit indicates an accordance with the reference value or set point. The reafference principle has also been used to explain some perceptual phenomena. For example, a corollary discharge signal from neural units controlling how the eye moves has been hypothesized to be used in combination with reafferent motion signals from the retina to determine the motion of objects in the world. See also preafference.