Disorders of the perceptual-motor system.

The study of patients with movement disorders provides insight into both the functional organization and the neural substrates of the perceptual-motor system. By and large, we feel this source of information has been underutilized within the basic science of motor control. To begin to address this shortcoming, this chapter reviews three disorders of the perceptual-motor system (disorders of the body schema, optic ataxia, and ideomotor apraxia) and illustrates how the study of these disorders can inform central issues within the field of motor control. These issues include (1) the need for the perceptual-motor system to maintain a representation of the body's current configuration in order to produce movements, (2) the use of visual information in movement production, (3) the coordinate frame in which movements are controlled, (4) the distinction between movement planning and online correction, and (5) the role of the parietal cortex in action. In the conclusion, we discuss several limitations of studying patients with movement disorders as well as suggest that greater communication is needed between researchers in the basic science of motor control and clinicians developing treatments for movement disorders.