Humans show a variety of motor behavior which enables us to interact with many different objects under different environments. Considering the number of objects and environments which influence the dynamics of the arm, the corresponding motor control system must be capable of providing appropriate motor commands for the multitude of distinct contexts that are likely to be experienced. In the experiments, we showed a virtual ball moving vertically downward on a 50 inch plasma display with three different force timing from -60 msec to 60 msec at intervals of 60 msec. The ball catching was simulated by a force-feedback system, provided by the SPIDAR. The subject was asked to catch the virtual ball at an initial hand position. The hand position and Electromyographic (EMG) signals of flexor carpi radialis were recorded. At the beginning, subjects caught the ball at the same timing as gravitational acceleration for all condition. The subjects came to receive the ball of any timing gradually as training advanced by force feedback. We found that subjects learned new environments in which the ball was falling by a different timing even though the visual information was same. These results suggest that humans can learn different timing by force feedback.
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