Stability and instability in the coordination of multijoint limb movements
The experiment reported focused on the analysis of qualitative changes in the response dynamics in multijoint drawing movements. Stability and instability in end-effector and joint angular dynamics were assessed under unexpected friction changes between stylus and writing surface and examined as a function of the practice level of the limb involved, the perturbation magnitude or the amount of friction change between stylus and writing surface, and the interaction between perturbation magnitude and practice level. Reversal point locations for the stylus (end-effector) and the distal limb angles (wrist joint angle, segmental angles of hand and lowerarm) were affected by increases in friction between the stylus and writing surface. However, there existed a threshold perturbation level, below which reversal point locations were not affected. The reversal point locations for the proximal limb angles (elbow joint, segmental angles of upperarm) did not change with increases in friction level. These findings demonstrated the existence of equifinality in multijoint limb movements. Changes in movement form in relative limb motions in configuration space and joint phase planes, as measured by pattern recognition techniques, showed deviations from nonperturbation patterns at low levels of added friction. Phase plane stability, as measured by deviations in the phase plane from the mean nonperturbation pattern became weaker with increases in friction level. The phase plane stability measures showed also overall higher degrees of stiffness and higher stability in the joints of the nondominant limb compared to the dominant limb, especially for the elbow joint. Joint time-series were highly coupled in the nondominant limb and uncoupled in the dominant limb under nonperturbation conditions. Under perturbation conditions the compensations in the dominant limb were different for all of the degrees of freedom involved. In contrast, the compensations in the nondominant limb were the same in all degrees of freedom. It was concluded that: (a) the equifinality principle holds for multijoint limb movements; (b) this equifinality in multijoint movements is observed for some but not all of the degrees of freedom; (c) movement form in configuration space and phase plane changes under relatively low perturbation levels; (d) practice changes the responses to perturbations from anatomically-specific early in practice to task-specific late in practice; and (e) this shift from anatomical to task specific adjustments is related to the degree of stability in the phase plane dynamics and degree of coupling in the joint degrees of freedom.
Biology, Neuroscience, Education, Physical, Psychology, Experimental
University of Illinois - Urbana-Champaign
Networked Digital Library of Theses and Dissertations
University of Illinois at Urbana-Champaign