Open Access
Gao, Fan
Graduate Program:
Doctor of Philosophy
Document Type:
Date of Defense:
May 12, 2005
Committee Members:
  • Vladimir M Zatsiorsky, Committee Chair
  • Mark Latash, Committee Member
  • Stephen Jacob Piazza, Committee Member
  • Henry Joseph Sommer Iii, Committee Member
  • prehension
  • finger
  • grip force
  • load force
  • synergy
  • chain effects
  • internal force
  • motor control
  • biomechanics
The human hand is an amazing and delicate device; its beauty of dexterity deserves extensive study. However, the redundant nature poses challenge to the study of hand function. Recently, a concept of prehension synergy was proposed and applied to the study of multi-finger prehension task. Prehension synergy is defined as the conjoint changes of finger forces and moments (Zatsiorsky and Latash 2004). In this dissertation, customized manipulandums were used to explore the prehension synergy. The existence of prehension synergy was tested and examined in both static and dynamic tasks. The specific purposes of the investigation of static tasks were: (1) to examine digital force coordination when both external torques and object geometry are varied; (2) to develop and test an artificial neural network model to explore the theory on hierarchical control of prehension; (3) to examine a hypothesis on the principle of superposition in human prehension; (4) to examine if there is a multi-finger synergy stabilizing the direction of the total force. The specific purposes of the investigation of dynamic tasks were: (1) to examine the differential effects of inertia and gravity forces on the grip force-load force relation under voluntary object manipulation; (2) to examine the internal forces acting on the object when the object is manipulated in different directions ¨C vertical, horizontal or diagonal; (3) to examine the control of finger forces and rotational equilibrium during object manipulation with prescribed torques The following aspects associated with prehension synergy had been revealed: (a) prehension was organized in a hierarchical fashion; (b) changes of task parameters result in chain effects; (c) principle of superposition was valid in both static and dynamic tasks; (d) grip force was adjusted to the gravity and load forces differently; (e) internal force was coupled with manipulation force; (f) mechanical advantage hypothesis was supported in both static and dynamic tasks; (g) anticipation is a major characteristic feature of human prehension in self-generated actions. In summary, this dissertation combined the examinations of both static and dynamic tasks and suggested a line of research for the future study on prehension synergy.