CONTROL MECHANISIMS OF MULTI-FINGER GRASPING

Open Access
Author:
Niu, Xun
Graduate Program:
Kinesiology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
July 08, 2010
Committee Members:
  • Vladimir M Zatsiorsky, Dissertation Advisor
  • Vladimir M Zatsiorsky, Committee Chair
  • Mark Latash, Committee Member
  • Stephen Jacob Piazza, Committee Member
  • Andris Freivalds, Committee Member
  • James Landis Rosenberger, Committee Member
Keywords:
  • synergy
  • optimization
  • grasping
Abstract:
Object manipulation with the hand is a complicated task for the central nervous system (CNS). In numerous investigations of multi-finger prehension (reviewed in Zatsiorsky and Latash 2004, 2008), it has been found that the CNS simplifies control by employing stable patterns of conjoint changes in finger forces and moments of force, called prehension synergies (PSs). Although PSs have been comprehensively studied in a series of customized experiments, certain aspects of them have not been well-addressed in current literature. To cover this deficiency, we investigate: (1) the effect of transcrainial magnetic stimulation (TMS) on the stability of multi-finger prehension synergies, the relationship between the background magnitude and TMS-induced changes, and the applicability of the principle of superposition under these conditions; (2) the effect of grasping force magnitude on prehension synergies, including a test of the scale invariance hypothesis for multi-finger prehension; (3) the applicability of a newly-developed inverse optimization method (analytical inverse optimization, ANIO) to multi-digit grasping, including a comparison with other optimization methods; and (4) the reproducibility of both multi-finger prehension over time, and the associated optimization cost functions. A series of experiments have been performed, and the following conclusions have been reached: (1) the TMS-induced changes in normal forces, tangential forces and moments of force were proportional to the background force/moment magnitudes; (2) the restoration of prehension patterns after TMS involved two phases: synergy restoration (i.e., the restoration of the correlation between elemental variables) and force magnitude restoration; (3) observations of PS restoration time after TMS supported the principle of superposition in human hand grasping; (4) the scale invariance hypothesis was confirmed only for zero-torque tasks, and rejected for tasks with torque; (5) the inverse optimization problem for force-sharing among fingers could be solved using the Analytical Inverse Optimization (ANIO) method, creating good agreement with the experimental observations; (6) reproducibility of PSs and the reconstructed cost functions over time was confirmed for multi-finger prehension; and (7) the planarity of finger forces in multi-finger prehension was valid for all subjects over time; the 2nd order coefficients of the cost function, Ki, had a linear relationship with finger force averages.