We investigate trajectory planning for a time minimizing task in human reaching movements. Using computer simulation, we found that the minimum movement-time trajectory is considerably concave toward a body and its velocity profile has two peaks. In psychophysical experiments, we observed that the subjects generated roughly straight hand paths with bell-shaped velocity profiles in the time-minimizing task. These features can be reproduced by the minimum commanded torque change criterion that requires the smoothness of motor command. We confirmed that the subjects could generate minimum movement-time trajectories when given a via-point and some instructions. The experimental results suggest that the brain cannot calculate the optimal trajectory according to the performance index except for the smoothness.
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