Figure 1. Experimental setup. A, Depiction of experimental setup in Experiment 1A with circular obstacles within the workspace (filled circles) and one circular goal. Subjects made reaching movements to a circular end target (open circles, radius = 1 cm); and occasionally, the limb was perturbed rightward or leftward with applied joint torques. τe, Elbow torque; τs, shoulder torque. Thick arrow indicates evoked motion. The black line indicates corrective responses of an exemplar subject without obstacles. B, Schematic of the torques applied to the shoulder and elbow. The background load (Bkg load) was ramped up >100 ms, and step torque perturbations (vertical second dashed line) were applied just after movement onset (vertical solid line). C, Same as in A, depiction of experimental setups of Experiment 1B (top) and Experiment 1C (bottom) with circular obstacles within the workspace (top; filled circles) and either three circular goals (top; solid circles) or a bar target (bottom; dashed line). Similar to A, the limb was occasionally perturbed rightward or leftward with applied joint torques. τe, Elbow torque; τs, shoulder torque. Thick arrow indicates evoked motion. D, Depiction of Experiment 2 setup with either one (solid circle) or three (solid and dashed circles) in the workspace. Subjects made reaching movements in both target conditions (circles, radius = 1 cm); and occasionally, the limb was perturbed rightward or leftward with applied joint torques. τe, Elbow torque; τs, shoulder torque. Thick arrow indicates evoked motion.