IDENTIFICATION OF FEEDFORWARD-LIKE AND FEEDBACK-LIKE CONTROLLERS FOR WRIST MOVEMENTS IN HUMAN

摘要

In this study, we introduce a new method to analyze functional significance of motor commands based on the causal relationship between muscle activities and movement kinematics. We asked four healthy subjects to perform two tasks of the wrist joint; step-tracking movement and smooth pursuit movement. We recorded movement of the wrist joint and EMG signals of the four wrist prime movers. We then identified the causal relationship between the muscle activities and the movement kinematics in terms of the wrist joint torque. For the optimal identification, the ratio of the viscosity coefficient B and the elastic coefficient K for the identification was systematically different for the two tasks. Based on the B/K ratio for each task, we found that the CNS considered mainly the target position for the step-tracking movement, while the CNS considered velocity as well as position of the target for the smooth pursuit movement. In addition, we also found that there are two controllers working in parallel for the smooth pursuit movement. One controller uses both position and velocity of the target and appears to work as a feedforward-like controller, while the other controller primarily uses position of the target and appears to work as a feedback-like controller.