Fig. 1.

Experimental setup and task apparatus. A: subject was instructed to release a centrally located home object and reach toward, grasp, and manipulate 1 of 4 peripheral objects (sphere, mallet, pushbutton, pull handle) arranged in a planar circle. A set of blue LEDs cued which object to reach for, and green LEDs indicated when the object was manipulated. Upper limb kinematics were tracked with 30 optically reflective markers affixed to the monkey's right forearm, hand, and digits. B: drawings from digital video frames are shown adjacent to the reconstructed kinematics from the motion tracking system (stick figures). Grasping each object invoked a unique grasp conformation of the fingers and wrist. C: for monkey X, marker placement included 4 markers on the dorsal aspect of the forearm, 6 markers on the dorsal surface of the hand, 2 markers over the first metacarpal, 2 markers between the metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints for each digit, and 2 markers between the PIP and distal interphalangeal (DIP) joints for digits 2 through 5. For monkey Y, 5 markers were placed on the dorsal surface of the hand and the forearm. Distribution of kinematic data for monkey X is shown in Cartesian space (D; shown separately for x-, y-, and z-dimensions) and joint angle space (E; shown separately for joint angles of the wrist, thumb, and fingers).