ON THE HAND TRANSPORT COMPONENT OF PREHENSILE MOVEMENTS

Jeannerod (1981) proposed that prehensile movements involve two indepe ndent visuomotor channels that are responsible for hand transport and hand aperture. In many studies, the movement of a marker placed on the wrist has been used as an index of hand transport because wrist movem ent is unaffected by the movements of the digits responsible for hand aperture. In the present study, the spatial paths of the wrist, index finger, and thumb of 5 adults, each performing 50 reaching movements, were measured with a WATSMART movement tracking system, and their vari ability was analyzed. The measures of movement variability suggest tha t the motor system is more concerned with thumb position than with wri st position during hand transport. Although the wrist is a technically convenient index of hand transport, the thumb may be a more appropria te index from the point of view of motor control.