Figure 2

Experimental setup. Subjects held the handle of a 1-D manipulandum while seated in front of a computer display. The position of a cursor (red ring) was manipulated by rotating the manipulandum handle about the elbow joint. The cursor (or arm) was continuously perturbed (upper right inset) with a zero-mean, band-limited disturbance, and the subject was asked to compensate by bringing the cursor to a target (black circle) presented in the center of the display. The arm was occluded by an opaque screen (shaded region) so that the cursor provided the only visual cue of arm movement.