Figure 6.

Grip-type clustering. a, Recorded joint positions of the upper limb were used to drive a 3D musculoskeletal model. Applying the kinematics to the primate-specific model allowed extracting joint angles of the hand and arm (27 DOFs). A selection of features is shown in b. Presented are from top to bottom: thumb and index angles (carpometacarpal adduction/abduction in black, carpometacarpal flexion/extension in red, proximal interphalangeal flexion/extension in blue, and distal interphalangeal flexion/extension in green), wrist angles (deviation in black, flexion/extension in red, and pronation/supination in blue), elbow angle (flexion in black), and shoulder angles (adduction/abduction in black, elevation in red, and rotation in blue). The hold epoch (used for classification) is highlighted in blue for grasping a horizontal bar, ring, and small ball. Subplot c illustrates the joint angles of the hold epoch as principal component (PC) transforms. Each symbol reflects an individual and correctly performed trial within the space of the first three principal components. Different symbols represent different object shapes, whereas their size reflects the object size. Applying hierarchical clustering to the multidimensional kinematic data allowed us to recluster the trials based on the applied grip type (d). The 20 most different hand configurations of the example session are numbered consecutively, and trials from the same grip-type class share the same color.