Title

Role of haptic information in shaping coordination dynamics

Date of Completion

January 2009

Keywords

Psychology, Experimental

Degree

Ph.D.

Abstract

Current research suggests that non-visual perception of the spatial orientation of body segments is tied to vectors representative of their mass moment distribution and not to geometrical parameters, such as joint angle. This dissertation was designed to investigate whether the relative orientation of the mass moment vectors Vmm of right and left hands (ΔVmm = Vmm left – Vmm right) constitutes information supporting the organization of bimanual coordination patterns. In four experiments, blindfolded participants coordinated the motions of a pair of cross-shaped hand-held pendulums under selective manipulations of ΔVmm. In order to manipulate ΔV mm, Vmm shifts of the right pendulum were introduced by asymmetrically distributing weight on the crosspiece. Coordination performance was indexed by measures of mean relative phase (&phgr;) and its variability. Experiment 1 showed that manipulations of the sign and magnitude of ΔVmm systematically affected the mean &phgr; of inphase coordination. Experiment 2 showed that the shifts in mean &phgr; were related to spatial adjustments to the hand trajectories directed at preserving the symmetry between the inertial and not the geometrical axes of the hands. Experiment 3 demonstrated that the effects of ΔVmm during in-phase, comfort mode coordination generalized to anti-phase and to coupled frequencies lower and higher than the preferred frequency. Finally, Experiment 4 showed that systematic phase shifts observed in Experiments 1-3 were specifically tied to the relative orientation of center of mass vector of right and left hands. As opposed to what occurs with detuning manipulations, the ΔVmm- induced shifts in mean &phgr; were not related to increases in the variability of coordination and were not magnified during the performance of less stable modes of coordination. The results described above indicate that coordination patterns are organized with respect to inertial frames of reference defined by ΔVmm. The observed mean scalar shifts in the steady state patterns of coordination seem to be a function of a directional bias in this frame of reference. These results were discussed in the context of general theories of movement organization.^