ADAPTATION AND TRAJECTORY PLANNING IN KINEMATIC
ALTERATION OF JOINT ANGLES.
H. Imamizu*, Y. Uno and M. Kawato
ATR Human Information Processing Research Labs, Kyoto, Japan
The purpose is to investigate whether the trajectory is planned solely in extrinsic (kinematic) space or both in the intrinsic (dynamic) and extrinsic spaces. We virtually minified (1/2) elbow angle and magnified (5/4) shoulder angle while normal human subjects were aiming at targets. A marker of a position measurement system was attached to the subject's hand and its current altered position was displayed as a cursor on the CRT screen. This linear transformation in joint angles corresponds to nonlinear one between the hand plane and the CRT screen. The trajectory on the CRT distorted by the kinematic alteration will be corrected to those under no alteration as adaptation occurs if the trajectory is planned solely in extrinsic space (Wolpert et al. 1993, MIT Computational Cognitive Science Technical Report, 9309). On the other hand, it will not if it is planned in the intrinsic (dynamic) and extrinsic spaces. Task for the subjects was to move the cursor to the target within a short time period (900 ms). Positional error was measured by distance between the target and the end point of the first ballistic movement. It was reduced to less than 60% after 320 trials of training and suggest that substantial adaptation occurred. However, there was not significant correction of trajectories on the CRT screen even in the last stage of training. The result supports the hypothesis that trajectory is planned both in intrinsic and extrinsic spaces. We also investigated whether the subjects adapted to the linear transformation in joint angles or non linear one between the hand plane and the CRT screen.