We tested the hypothesis that our ability to detect fine kinematics variations is tuned to reveal more subtle differences when the motion pattern belongs to the observer compared to another individual. To this purpose, we analyzed the responses of 15 subjects in a same-different task on pairs of movements, which could belong to one or two different subjects. Self vs. Other comparisons were obtained by presenting both the observer’s and another participant’s kinematics. Subjects responded faster and more accurately when they (...) observed their own gestures compared to movements of another participant. In the latter case, slight kinematic differences were more likely to remain undetected. These findings are discussed within an ecological framework: in observing others, we are more concerned with detection of goals and intentions, i.e., outstanding variations in motion patterns. Conversely, in self-observation detection of more subtle differences is required to facilitate learning and optimization of motor acts. (shrink)

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.