'Side-effects': intrinsic and task-induced asymmetry in bimanual rhythmic coordination.

Multifrequency coordination studies have shown the importance of hand-role in addition to hand-preference in bimanual rhythmic coordination. In these studies, hand-role has been defined by the task of the individual hands (moving fast or slow). In the present study, the hands were coordinated at the same frequency and hand-role was defined by the asymmetry of the coordination pattern. Eleven consistent left-handers and 13 consistent right-handers tapped three patterns (anti-phase, left-gallop, right-gallop) in four visual feedback conditions (no feedback, left-hand feedback, right-hand feedback, full feedback). The analysis focused on phase shifts, phase variability, intertap interval variability, and correlations between intertap intervals. The manipulation of visual feedback had only minor effects. In the anti-phase pattern, a symmetric coupling mechanism was found. The results support the idea that coordination in the gallop pattern is governed by a hierarchical control mechanism. In contrast to the multifrequency studies, however, successful control in the gallop is not dependent on a hand arrangement that accommodates the preferred hand as the leading hand. An adjustment to the model of Summers et al. (1993, J Exp Psychol Hum Percept Perform 19:416-428) is presented for the case of the gallop pattern.