Interlimb differences in trajectory and positional control mechanisms

Previous findings suggest that movement trajectory and final position are specified and controlled differentially by the dominant and nondominant limb/hemisphere systems. In the current studies, we examine interlimb differences in trajectory planning and feedback mediated positional control mechanisms. The first study examines load compensation responses, whereas, the second study examines control of movements made to a range of distances. In the first study, the nondominant arm showed substantially better response to load compensation, whereas, the dominant arm over-compensated the effects of the load, producing a large and systematic overshoot of final position. In the second study, dominant arm movement amplitude was well predicted by peak acceleration, reflecting pre-planning of movement distance. However, nondominant arm peak accelerations did not predict movement distance well. Instead, the duration of acceleration varied systematically with peak velocity and movement amplitude. These findings suggest that the nondominant and dominant controllers specify and control movement distance through distinct mechanisms, the former utilizing a pulse-height strategy, and the latter using a pulse-width strategy. Taken together, these findings support the hypothesis that the dominant arm system is specialized for feedforward control of trajectory, and the nondominant system, for feedback mediated control of final limb posture.