Conceptually, the explanation of the regulation and interaction of internal signals and sensory signals to direct and coordinate body movements. It requires a copy of each activation of a motor unit by the processing unit. This copy then fixes the reference value or parameter required to execute the movement, until the reference from the sensory unit to the processing unit gives an indication of accordance with the value or set point. The concept can be used to explain some perceptual phenomena. For instance signals from neural units controlling how the eye moves. Hypothetically, this could be used in combination with reafferent signals across the retina to determine motion.