Open Access
Van der Wel, Robrecht Parsival Reinhard Diederik
Graduate Program:
Doctor of Philosophy
Document Type:
Date of Defense:
January 15, 2009
Committee Members:
  • David A. Rosenbaum, Dissertation Advisor
  • David A. Rosenbaum, Committee Chair
  • Richard Alan Carlson, Committee Member
  • Frank Gerard Hillary, Committee Member
  • Dagmar Sternad, Committee Member
  • motor control
  • action planning
  • object manipulation
  • bimanual coordination
  • reference frames
The degrees of freedom problem refers to the problem of how people select their actions from infinite sets of possible actions. Addressing this question requires identifying which factors are taken into account in action planning. Possibly, the adopted solutions depend on the nature of the task, including factors such as task difficulty and experience. In general, the solution may depend on cognitive as well as biomechanical factors. From a cognitive perspective, solving the degrees of freedom problem requires identifying which reference frame is used for action control. Actors may control physical actions relative to their bodies or relative to the external world. The origin of the adopted reference frames may be task-dependent. To explore these possibilities, I conducted a series of experiments on how people manipulate two objects, one with each hand. I studied the influence of task difficulty and experience on performance through manipulations of start and target locations, timing of object grasps and object transports, number of repetitions that were performed, and object weight. These manipulations allowed me to determine which reference frame people used to plan their grasps. Participants planned object grasps in cognitively efficient ways by adopting similar solutions for the two hands. Grasp selection was consistent with the use of an allocentric reference frame tied to the objects. The adoption of object symmetric grasps did not consistently depend on experience or grasp timing, but did depend on the similarity of the mass distribution of the two objects. In other words, symmetry in the mass distributions for the two objects appeared to drive the preference for symmetry in grasp selection. The results suggested that participants selected similar grasp locations because doing so allowed similar dynamics for the two hands during object transport. Breaking symmetry in allocentric dynamics resulted in changes in grasp selection. The results are consistent with the notion that solving the degrees of freedom problem involves an interplay of representational and biomechanical efficiency.