Fig. 1

a Kinarm Endpoint Lab b Schematic of the Movement Discrimination Threshold (MDT) task. Subjects were seated and grasped the handles of the robot and the arms were occluded from view. Robot moved dominant hand and subjects used the opposite arm to indicate the direction of movement (right or left) by moving into the corresponding rectangular target (arms were occluded from view, subjects could see the rectangles on the screen and the white hand feedback dot indicating the position of the non-dominant hand). c Example traces of hand displacement (X position) and velocity (X Velocity) of the robot-moved dominant arm. d Example of displacements imposed on the arm during the MDT task. Commanded displacements are displayed in red and the actual displacements of the hand are displayed in black. Displacements began at 2 cm and were reduced by 1 step for each correct answer and increased by 3 steps after an incorrect answer. Discrimination Threshold was determined as the median of all displacements after the first wrong answer