Fig. 2.

A, Hand path of a typical subject in the null field (the points in all hand paths are 10 msec apart). B, An example of a force field produced by the robot. The field is a linear function of hand velocity, and thex- and y-coordinates refer to that of Figure 1. C, Hand path of an untrained subject in the field. D, Hand path after 300 movements in the field. The trajectory in the field converges to the trajectory observed in the null field. E, Forces produced by a typical trained subject to counter the effect of the force field as a function of hand position for each movement. These forces are the projection of the forces measured at the interaction point between the subject and robot onto a direction perpendicular to the direction of target.F, While training in the field, random targets are presented with null field conditions. The results are after-effects.