Coordination of the two hands and effects of attentional manipulation in the production of a bimanual 2:3 polyrhythm

Right-handed subjects were tested on a bimanual task that required the concurrent production of two different isochronous sequences. The direction of attention was manipulated by having subjects count out loud either one or the other of the sequences. Attention interacted with task performance; subjects performed very much better when attending to the faster of the two sequences. Handedness effects were seen in preference but not in performance. A fine-grained analysis of the succession of movements suggests that subjects do not perform the two sequences independently; the initiation of movement in one hand is more clearly dependent on the preceding movement in the other hand than on preceding movement by the same hand. The findings are compatible with a unitary scheduler that provides movement initiations for both hands.