Open Access
Hu, Xiaogang
Graduate Program:
Doctor of Philosophy
Document Type:
Date of Defense:
May 27, 2011
Committee Members:
  • Karl M. Newell, Committee Chair
  • Mark Latash, Committee Member
  • David A. Rosenbaum, Committee Member
  • Jinger S. Gottschall, Committee Member
  • aging
  • motor control
  • isometric force
  • force coordination
  • redundancy
This dissertation used a bimanual asymmetric force coordination task to investigate the interactive influence of multiple categories of constraints on the organization of redundant force coordination. The force asymmetry was manipulated by imposing different coefficients on the finger forces such that the relative contribution of the individual force to the total force could be changed. The amount of visual information of the force output was manipulated in different conditions. Three primary questions were addressed in the dissertation. (1) Whether and how the relative influence of the different categories of constraints are modified and consequently new force coordination patterns are formed when the task asymmetry is changed. (2) Whether the influence of visual information on the force coordination patterns is dependent on the settings of the task asymmetry. (3) How aging processes reorganize the influence of the constraints on force coordination and control patterns. The results revealed that there was a decrement in performance outcome when there was an asymmetric task constraint, less visual information, and with advanced age. The results also showed flexible force coordination patterns in response to the changes in constraints. (1) The young adult participants adapted the force coordination patterns to the task asymmetry flexibly. The models of constraints indicated that a coefficient-dependent efficient strategy rather than a minimum-variance strategy was used. (2) The amount of visual information had a moderate influence on force coordination, which depends on the conditions of task asymmetry. (3) With less visual information, the elderly exhibited reduced adaptability to the task asymmetry; however, they had the same extent of adaptability as the young group when enhanced visual information was provided. The models of constraints reveal that the goal of the system is not to find solutions that lead to a perfect task performance but to find solutions that satisfy the constraints from different categories. Overall, the results support the proposition that redundant force coordination and control patterns are organized by the interactive influence of different categories of constraints.