Control strategies and topological invariance of human prehension

Control strategies and topological invariance of human prehension are discussed through the analysis and comparison of upper-limb reaching-grasping tasks. Five subjects were asked to perform different reaching-grasping tasks with different indices of difficulty, and the movements were captured using a Vicon 3D motion analysis system. Topological invariance was observed in the trajectories of different task performances. After normalization, the trajectories of the hand had very close patterns for different reaching-grasping tasks. Synergy control in the reaching-grasping movements of the upper limbs was also found among the different joint angles. Despite joint redundancy, the joint angles can be fitted using the same format of functions proposed in this study. The parameters in the function can be taken as a characteristic feature of reaching-grasping movement patterns.