Are the extrinsic muscles better suited for signaling joint angles or finger tip location?

We used a biomechanical model of the human long finger to determine whether the extrinsic muscles are better suited for estimating the finger's joint angles or for estimating location of the finger tip. We found that two of the extrinsic muscles together could provide information sufficient to directly determine the location of the finger tip relative to Metacarpophalangeal (MCP) joint, without having to determine any of the finger's joint angles. We also found that for some finger positions the extrinsic muscles provide ambiguous information about the finger's joint angles. These results suggest that the biomechanics of the finger and the extrinsic muscles lend themselves more readily to a determination of finger tip location than to a determination of joint angles. In light of these results it seems possible that human proprioception in the hand may reflect a sense of finger tip location, not joint angles.