ABSTRACT
Psychology.—Motor action is understood to mean the occurrence of a movement made up of three stages: planning, programming, and motor execution. Only the last stage is directly observable and brings about a change in the environment. The first two stages, elaborated mentally before the onset of the action, determine the goal and the strategy to adopt (planning), and the sequence of movements to make (programming). Proper execution of a motor action requires the subject to process two types of sensory information (→INFORMATION, PERCEPTION): (1) exteroceptive information drawn from “external space” (outside the body), which can be auditory, visual, olfactory, or somesthetic, and which acts both as a trigger and a guide for the motor action as it occurs in the environment; and (2) proprioceptive information drawn from “internal space” (inside the body). For an action to be performed efficiently, subjects must know their position relative to external space (→SPACE) and sense the position of their body segments, both before beginning to move (statesthesia) and during motion (kinesthesia). Motor actions can be distinguished from movement reflexes, which are elementary, rapid responses to external demands integrated at the bone marrow level, as well as from automatic responses (→AUTOMATISM), executed essentially in the brainstem and basal ganglia. A motor action is a voluntary movement (→CONTROL, WILL) to the extent that it is an expression of the individual’s intentions. It originates in a neural command generated in the cortex (see neuroscience below), either consecutive to or simultaneously with the integration of exteroceptive and proprioceptive sensory information.
