Fig. 1

Center-out reaching experiment setup for a subject with left-side amputation. a Subject holds their arm in a relaxed posture at their side. Attached to the subject’s residual limb, a goniometer (green) measures elbow angle, and EMG sensors (blue) measure EMG amplitude. b Subjects perform center-out reaches with a virtual limb (black); goniometer angle controls the angle of the proximal link (or elbow, green), and the EMG amplitude controls the speed of the distal link (or wrist, blue). Subjects started with the limb endpoint in the home circle and one of four targets would appear. A grey ball would appear above the target; each target could only be reached with a single limb configuration (dashed grey, not shown on the screen). When the limb endpoint left the home circle, the ball began to drop, centering on the target after 0.5 s, signifying the end of the trial. The virtual task was mirrored for subjects with right-side amputation. c Wrist-driven distal link speed is used for frequency-modulated audio feedback, with higher speed corresponding to higher frequency. This audio feedback was played through headphones worn by the subject, providing wrist speed feedback