Fig. 5.

Control analysis to confirm that passive subjects were not actively moving along with the robot handle. In each trial, forces on the handle were measured and compared with the force exerted by the motor to move the subject. A: time course of the motor force (red) and the measured force on the handle (blue) shows a strong negative correlation, as would be expected if the subject is not moving along with the handle. B: the distribution of correlations of all trials. C: a strong negative correlation was observed for all subjects and was not different between the passive groups. D: no relationship was observed between the motor versus observed force correlation and the amount of learning of the subject. E: to exclude that subjects actively moved along with the handle, we compared the programmed motor force (red arrow in inlay) and the measured force at the handle (blue arrow). The resulting net force (black arrow) was able to explain the observed displacement of a mass corresponding to roughly the weight of the subject arm, thus without needing to appeal to additional forces produced by the subject.