FIG. 3.

Kinematic data for one of the four subjects. The left column displays cup velocity versus cup position for the three different blocks of the experiment. The right column plots ball angular velocity versus cup position. The vertical line indicates the position of the perturbation. The solid line represents the average of the first $10$ and last $10$ trials of the respective block; the shaded band shows one standard deviation. The different average trajectories and the reduced variability in the late trials indicate learning. The markedly different trajectories in the resistive and assistive perturbations show that subjects developed different strategies for the two perturbations.