An Explanation for the Predection of a Hand Trajectory Generated by an Imperfect Internal Model Representation

Abstract

In multi-joint planar reaching movement, hand trajectories tend to be gently curved depending on the hand position in extracorporal space. Following two explanations are possible for the observed curvature; (i) planned trajectories themselves are curved, (ii) planned trajectories are straight but realized trajectories are curved because of the reasons other than planning. We examined one of the possible reasons that belongs to the second explanation. That is, the realized trajectories are curved because the internal model in the central nervous system is imperfect. We represented imperfect internal model by (1) parametoric method, (2) neural metwork method (3) table look up method, and compared the trajectory predicted by imperfect internal model with the measured trajectories. The results suggest that the imperfect internal model cannot explain the observed curvature better than the minimum commanded torque change model that plans curved trajectories.