Wd Byblow

Attention as a mediating variable in the dynamics of bimanual coordination

Abstract The influence of focal attention on the coordination dynamics in a bimanual circle drawing task was investigated. Six right-handed and seven left-handed subjects performed bimanual circling movements, in two modes of coordination, symmetrical or asymmetrical. The frequency of movement was scaled by an auditory metronome from 1.50 Hz to 3.00 Hz in 7 steps. On each trial, subjects were required to attend either to the dominant hand, to a neutral position, or to the nondominant hand. The uniformity of the relative tangential angle was lower in asymmetrical than in symmetrical conditions, but was not influenced by the direction of attention. In the asymmetrical mode, shifts in RTA relations, suggestive of loss of stability, were evident as the movement frequency was increased. Typically, these shifts were mediated by distortions of the trajectory of the nondominant limb. When the nondominant hand was the focus of attention, movements of this hand were more circular, and temporal variability was reduced, at the cost of a greater deviation from the target frequency. Movements of the dominant hand were not affected by the direction of attention. The findings show that although directed attention acts to modify the coordination dynamics, it does so primarily at the level of the individual hands, rather then in terms of the relation between them.

The contribution of inherent and incidental constraints to intentional switching between patterns of bimanual coordination

This article addresses the contribution of inherent (arising from the structure of the neuromuscular-skeletal system) and incidental (arising from specific features of a task or environment) constraints/resources to intentional modifications of coordination dynamics. An experiment was conducted to determine the extent to which the organization of voluntary transitions between locally stable modes of bimanual coordination was influenced by the frequency of movement, and by the provision and phase of external auditory pacing. Subjects performed rhythmic pronation and supination movements of the forearm in four bimanual patterns. In two in-phase patterns, either maximum pronation (inphase pronation) or maximum supination (inphase supination) was synchronised with each beat of an auditory metronome. In two antiphase patterns, either maximum excursion to the left (antiphase left) or to the right (antiphase right) was synchronised with the metronome. In an initial session, mean (spontaneous) transition frequencies (MTF) were established. In a second session pacing was provided at MTF −0.5 Hz, MTF −0.25 Hz, MTF and MTF + 0.25 Hz. A visual signal presented early or late in the trial indicated that subjects were to switch to the opposite mode of coordination. On some trials, metronome pacing was removed following an induction period. Transition durations decreased in a linear fashion with increases in pacing frequency, both when the metronome was present and when it had been removed prior to the imperative signal, suggesting that movement frequency acts as an inherent constraint upon the coordination dynamics. Transitions were of greater mean duration when the metronome was present than when it was absent, indicating that external pacing signals may impose incidental constraints. Transitions from the antiphase to the inphase pattern were generally of shorter duration than those in the reverse direction. These results are discussed with reference to both dynamical and physiological models of multilimb coordination.