Trajectories and experimental protocol. (a) Planar representation (Y-Z axis, in the robot reference frame) of the ideal (blue) and perturbed (yellow) Cartesian trajectories. The corresponding trajectories in the joint space are depicted in panel (b). (c) The controlled joints of the robot correspond to three rotations: shoulder elevation (Joint 1), humeral rotation (Joint 2), and elbow flex extension (Joint 3). (d) The experimental protocol consists of 5 baseline trials, 20 trials of acquisition, where a load is applied to the robot arm, and 5 trials of extinction, where the additional load is removed.