Discrimination and identification of finger joint-angle position using active motion

Abstract

The authors report six experiments on the human ability to discriminate and identify finger joint-angle positions using active motion. The PIP (proximal interphalangeal) joint of the index finger was examined in Exps. 1--3 and the MCP (metacarpophalangeal) joint in Exps. 4--6. In Exp. 1, the just noticeable difference (JND) of PIP joint-angle position was measured when the MCP joint was either fully extended or halfway bent. In Exp. 2, the JND of PIP joint-angle position as a function of PIP joint-angle reference position was measured when the PIP joint was almost fully extended, halfway bent, or almost fully flexed. In Exp. 3, the information transfer of PIP joint-angle position was estimated with the MCP joint in a fully extended position. In Exps. 4--6, the JND and the information transfer of MCP joint-angle position were studied with a similar experimental design. The results show that the JNDs of the PIP joint-angle position were roughly constant (2.5°−2.7°) independent of the PIP joint-angle reference position or the MCP joint-angle position used (Exps. 1 and 2). The JNDs of the MCP joint-angle position, however, increased with the flexion of both the PIP and MCP joints and ranged from 1.7° to 2.7° (Exps. 4 and 5). The information transfer of the PIP and MCP joint-angle position were similar, indicating 3--4 perfectly identifiable joint-angle positions for both joints (Exps. 3 and 6). The results provide the basic data needed for estimating, for example, the resolution of fingertip position during active free motion. They are compared to the results from previous studies on joint position, length, and thickness perception.