Fig. 1.

Experimental setup and task. A: participants performed reaching movements in the horizontal plane while holding onto a robotic manipulandum. B: example nonchannel perturbation trial. Participants reached from a start position to a narrow (blue) or wide (red) reach target while fixating their gaze at a fixation target (gray circle). On a subset of trials, the hand cursor was visually perturbed by displacing it 3 cm to the left or right after it passed under a visual occluder. C: example force channel trial. In one-half of the trials, the participants’ movements were constrained along a straight line from the start to target position, allowing us to measure the forces applied to the virtual walls of the channel (broken lines). In cursor perturbation trials, the cursor automatically moved back to this line 250 ms after the perturbation. D: fixation targets were placed at different distances (12.5 cm, “near”; 22.5 cm, “far”) from the perturbation location and at different angles (0°, ±45°, ±90°) with respect to the movement direction.