Attention, amplitude, and asymmetry in interlimb coordination

*Harjo J. de Poel
Research Institute MOVE, Amsterdam, Faculty of Human Movemen

C. (Lieke) E. Peper
Research Institute MOVE, Amsterdam, Faculty of Human Movement Sciences, VU University Amsterdam, The Netherlands

*Peter J. Beek
Research Institute MOVE, Amsterdam, Faculty of Human Movement Sciences, VU University Amsterdam, The Netherlands

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     Last modified: February 27, 2007

Abstract
In human bimanual behavior, perfect symmetry is the exception rather than the rule. A typical asymmetry during rhythmic bimanual coordination is that the dominant (D) limb leads the non-dominant (ND) limb in time. Interestingly, directing (visual) attention to either limb has been shown to affect the relative phase dynamics in a manner comparable to handedness. From the perspective of coordination dynamics, these effects have been considered to result from an asymmetry in the strength of the interlimb coupling (e.g., the ND limb being influenced more strongly by the D limb than vice versa), which, theoretically, may improve the stability of coordinative performance. Alternatively, on the basis of recent results, we hypothesized that attention-induced relative phase asymmetries may also be engendered by an accompanying difference between the amplitudes (and hence the preferred frequencies) of the limb movements. We conducted three experiments to examine those (not mutually exclusive) potential effects. Controlled manipulations of amplitude disparity and attentional focus, both alone and in conjunction, revealed that variations in amplitude disparity had the expected effects on the relative phasing between the limbs. However, no compelling evidence was obtained for the interpretation that attentional asymmetry affects (the stability of) the relative phasing through an asymmetry in coupling strength. Together these results indicated that, indeed, the effects of asymmetric attentional focus on the interlimb phasing results from (unintended) variations in the movement amplitudes of the individual limbs (with the attended limb?s amplitude being larger than that of the unattended limb). On a more general note, this study demonstrated that the analysis of rhythmic bimanual performance in terms of the compound effects at the level of the relative phasing alone is not always sufficient and may even hamper interpretation of the data, thereby underscoring the importance of complementary analyses of both the coupling and the component dynamics.