Kinesthetic and visual control of a bimanual task: specification of direction and amplitude.

Kinesthetic information about a perturbation can quickly modify motor activity by producing reflexive compensation. The purpose of the present study was to determine how quickly kinesthetic information about target movement can modify motor activity. Visual information about target movement is known to guide motor activity both quickly and accurately. Therefore, we compared the speed and accuracy of responses to kinesthetically and visually presented targets. Human subjects produced changes in elbow torque as quickly and accurately as possible after the random presentation of 1 of 8 target torques. Information about the direction and amplitude of the target torque was provided either kinesthetically or visually. Responses to kinesthetic targets started at an average latency of 150 msec, and after an additional 159 msec, these responses became accurately graded according to target amplitude. Responses to visual targets started at an average latency of 250 msec, and after an additional 208 msec, these responses became accurately graded according to target amplitude. The accuracy of responses to kinesthetic targets was very similar to the accuracy of responses to visual targets. We conclude that the neural processing of kinesthetic information about target movement is sufficiently fast and accurate to guide typical motor activities.