Stabilisation of bimanual coordination through visual coupling

Eight right-handed participants performed a bilateral circle tracing task in symmetric or asymmetric patterns. Circle tracing was performed in synchrony with an auditory metronome and a visual display at, or comfortably below, each participant's transition frequency. The visual display consisted of a row of five light-emitting diodes (LEDs) arranged between the two circles (hands), Bimanual pattern stability was examined under conditions where the direction of illumination of the visual stimuli was compatible or incompatible with the hand direction. Symmetric patterns maintained stability for both movement rates whereas asymmetric patterns exhibited loss of stability at the transition frequency. Spontaneous reversals in circling direction occurred predominantly (94%) through the nondominant hand. Laterality effects were also evident in the aspect ratio (circularity of trajectories) and limb frequency variation, particularly in asymmetric patterns at the transition frequency. Compatibility between the stimulus direction and circling direction served to: stabilise symmetric patterns; stabilise asymmetric patterns by delaying the onset of transition; and stabilise the individual limb dynamics when the direction of the dominant side was compatible with the visual stimulus. The data from this multisegmental task lend support to a model of coupled oscillators whereby the coupling strength is anisotropic between the dominant and nondominant side, and lend further support for an account of manual asymmetries by way of a preferential perception-action coupling through the dominant limb. (C) 1999 Elsevier Science B.V. All rights reserved.