Distinguishing the noise and attractor strength of rhythmic and coordinated limb movements using recurrence analysis

Date of Completion

January 2005


Psychology, Experimental




The variability of single and coupled rhythmic limb movements is assumed to be a consequence of the strength of a movement's attractor dynamic and a constant stochastic noise process that continuously perturbs the movement system away from this dynamic. Very little research, however, has examined whether the magnitude of stochastic perturbations or noise remains constant across different patterns of stable movement. One reason for this lack of research is that there are very few methods available to distinguish whether a change in movement variability is due to change in attractor strength or noise---standard measures of movement variability (e.g. SD&phis;) confound noise and attractor strength. Recently, however, it has been suggested that the nonlinear technique of recurrence analysis can be used to index the effects of noise and attractor strength on movement variability. To test this, five experiments were conducted in which the attractor strength of unimanual and bimanual wrist-pendulum movements and the magnitude of stochastic perturbations affecting the variability of these movements (using a temporally fluctuating visual metronome) were manipulated. The results of Experiments 1--3 demonstrate that recurrence analysis can index parametric changes in the attractor strength of coupled rhythmic limb movements and the magnitude of metronome induced stochastic perturbations independently. In contrast, the results of Experiments 4 and 5 found no evidence to suggest that recurrence analysis can also be used to index the attractor strength and noise of single rhythmic limb movements. With the use of simulations, potential reasons for this discrepancy are discussed, including the nature of the experimental manipulations employed and possible differences between the recurrence quantification of unitary and dual movement trajectories. To further highlight how recurrence analysis can be used to distinguish the attractor strength and noise of coupled rhythmic limb movements, the difference in the variability of intra- and interpersonal coordination was examined in a final experiment (Experiment 6). The results of this experiment indicate that the difference in variability between intra- and interpersonal interlimb coordination is due to a difference in the magnitude of noise, as well as attractor strength. ^