Time-Varying Synergies in Velocity Profiles of Finger Joints of the Hand during Reach and Grasp

This paper presents time-varying synergies that were observed during reach and grasp experiments in angular velocity profiles of metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints of five fingers of the hand. Five right handed subjects were asked to reach and grasp 28 different objects and during this experiment joint angles were measured by a data glove. Our results showed that the angular velocity profiles for a period of 0.86 seconds of ten joints (two per finger) were accurately reproduced by using only 3 synergies in 28 different tasks. Interestingly, there were correlations between the object size and velocity profiles which lead to unique distinctions in the combinations of these synergies in achieving the natural movements.