We review studies that indicate a dissociation between the perceptual estimate and the resulting cognitive representation of given properties of a seen object, on the one hand, and the motor action exerted on the same object. We propose that there exist multiple levels of organization of sensorimotor loops and that internal models may be made accessible to one level of organization while remaining inaccessible to another level.

We review studies on catching that reveal internalization of physics for action control. In catching free-falling balls, an internal model of gravity is used by the brain to time anticipatory muscle activation, modulation of reflex responses, and tuning of limb impedance. An internal model of the expected momentum of the ball at impact is used to scale the amplitude of anticipatory muscle activity. [Barlow; Hecht; Shepard].

Mechanisms of visual prediction based on spatial extrapolation work only for targets moving at constant speed, but do not easily accommodate accelerating or decelerating motion. We argue that mechanisms based on temporal extrapolation deal with both uniform and non-uniform motion. We provide behavioural examples from interception of falling objects and suggest possible neurophysiological substrates of time extrapolation.

We argue that planning and control may not be separable entities, either at the behavioural level or at the neurophysiological level. We review studies that show the involvement of superior and inferior parietal cortex in both planning and control. We propose an alternative view to the localization theory put forth by Glover.