Effects of practicing accurate force production tasks on multi-digit coordination: Performance, synergies, and transfer

Open Access
Wu, Yen-hsun
Graduate Program:
Doctor of Philosophy
Document Type:
Date of Defense:
June 10, 2014
Committee Members:
  • Mark Latash, Dissertation Advisor
  • Vladimir M Zatsiorsky, Committee Member
  • Karl Maxim Newell, Committee Member
  • Joseph Paul Cusumano, Committee Member
  • practice
  • coordination
  • finger
  • variance
  • uncontrolled manifold
Humans become less susceptible to environmental or intrinsic perturbations with practicing a motor task, not only because they are better at correcting the task-relevant errors, but also due to the improvement of flexible involvement of their body to channel parts of the perturbations into the changes of task-irrelevant body configuration. The four studies in this dissertation explored the effects of practice of a finger force production task with adjustable instability encouraging involvement of elements (fingers) on multi-finger coordination quantified within the uncontrolled manifold (UCM) hypothesis in which variance is decomposed into two components: VUCM that had no effect on total force, and VORT that affected total force. The first study showed that practicing a redundant set of fingers (R-task) and practicing each finger separately (non-redundant, NR-task) may lead to similar changes in performance accompanied by dramatically different changes in the total variance in the space of commands to fingers. Practicing R-task led to higher variability in the system with lower variability in task performance. In the second study, the elderly population demonstrated ability comparable to the younger persons to improve task performance by combining high variability with high precision. However, the effects of practice partially transferred to a simpler task on the performance improvement with no transfer of the effects on the structure of variance. The third study explored the effects of practice of a more natural four-finger force production task, and revealed that the short practice of the four-finger task with adjustable task instability also led to a change in the structure of variance characterized by a decrease in VORT and an increase in VUCM. Discouragingly, the effects did not transfer to a more functionally relevant prehensile task. The last study investigated transfer of the effects of practice on the structure of variance using a pressing task that combine accurate force and moment of force production. The strong retention in the series of studies with little transfer makes us optimistic but cautious about possible future developments of the method for motor rehabilitation on improving coordination.