The motor system includes the components of the central and peripheral nervous system along with the muscles, joints and bones that enable movement. Motor control is the study of how body movements are planned by the brain and performed by the body. Woodworth stated that there were two phases: an impulse phase in which the brain calculates the necessary movements and a control phase where vision is the key to accuracy.

The degrees of freedom of a joint is the number of ways it can move. The degrees of freedom problem refers to the choice of how to move the body when there are countless possible ways to do so. There are several theories of movement planning:

1. Equilibrium point hypothesis (mass-spring model)
   This is a theory of motor control that emphasizes how the problem of control can be simplified by taking into account muscle properties. The muscle tension determines the movement. If one muscle increases tension, another muscle decreases tension (because most muscles are arranged in an agonist/antagonist system) and this causes the correct movement.
2. Dynamical systems
   Muscles and joints work together in a certain way. Movement is determined by the physical properties of the body (e.g: the difference between walking and running is determined by speed and transitions automatically). The dynamical systems cause movement to be performed correctly.
3. Optimal control theory
   This is a theory of motor control that states that movement that is the most efficient and the most optimal is selected. The most efficient movement is the movement that causes the least amount of torque change at the joints. This system uses forward models. This predicts the relationship between actions and their consequences. The body tries to predict sensory feedback (e.g: we can type relatively quickly and this wouldn’t be possible if we didn’t predict feedback, because we move too quickly to first process it and then act according to the perceived feedback). The control policy provides a set of rules that determine what to do given a particular goal. It takes as input the current state estimate and has a motor command as output. Aspects of the control policy seem to be located in the basal ganglia.

The associative chain theory states that the end of one particular action is associated with stimulating the start of the next action in the sequence, much like a chain. This theory explains how sequences of action arise from linking together associations between individual action components. This theory becomes problematic when one action has to produce multiple other actions. Langley stated that there is a hierarchy of actions, most clearly shown in language production and speech. Parallel processing is the ability to divide the process of solving a problem into multiple parts and work simultaneously on each part. Estes states that each node of the hierarchy corresponds to a particular action schema.

The use of hierarchical structures becomes problematic when explaining how currently desired units can be activated whilst others can be suppressed (e.g: when opening a locker, you don’t need to close the locker while you are taking things out of the locker). This is explained using recurrent networks. These are a type of artificial neural network with connections between units arranged so to obtain a cycle of activation. This design allows a temporal context to be designed into the computation. In this hierarchy, patterns of activation and inhibition work in a manner of interactive activation. This is a term used to describe the pattern of network activity generated by excitatory and inhibitory interactions of feature detectors and object representations (e.g: when one unit of the schema is activated, the other units at the same level are inhibited).

The frontal cortex is responsible for action planning. Apraxia is a neurological condition typically resulting from brain damage where a person loses the ability to perform activities that they are physically able and willing to do. Ideomotor apraxia is the inability to pantomime tool use and gesture when verbally instructed to do so.

The term cognitive sandwich describes the view that perception and action are like slices of bread that surround cognition. The ideomotor theory relates how thinking about the results of action can give rise to producing the action. Common coding is a theory of perception and action production which holds that both production and perception share certain representations of actions in the world. Planning of action happens automatically when you see something. This is common coding. The perception is tied closely to action planning.

There are several consequences of common coding.

1. Interference when production and perception use the same resources.
2. 1/3 power law of drawing
   We perceive things the same as movement changes.
3. People are quicker to recognize themselves perform actions than others.

Mirror neurons are neurons with the special property that they represent both the sensory aspects of perceiving actions as well as motor aspects of how to produce the actions. Mirror neurons exist in the frontal and parietal parts of the brain in monkeys. In humans, it is unclear where the mirror neurons exist, besides the parts homologous to the monkeys. One possible function of mirror neurons could be providing access to the goal of the movement. Another possible function of mirror neurons is imitation and learning motor actions from visual models. Motor primitives are the basic set of elemental movements that serve as building blocks for an animal’s repertoire of movements.

In the embodied view of cognition, perception and action are intimately connected. One consequence of embodied cognition is that we organize our environment in such a way to decrease the cognitive load. Gestures can convey a message, even without words. Gestures can be seen as a simulated action or simulated speech. One theory states that gestures result because ideas are being simulated in terms of perceptual and motor properties, regardless of whether the idea is about something physically spatial or only metaphorically spatial.