The impact of metrical structure on performance stability in bimanual 1:3 tapping

Participants performed a three-beat (strong-weak-weak) finger-tapping pattern with one hand while synchronizing taps of the other hand with either the strong tap (metrically congruous rhythm) or one of the weak taps (metrically incongruous rhythms). We tested the hypothesis that performance would be less stable during the production of the incongruous rhythms. The tapping sequences were performed at two different tempi (Experiment 1) and under two different cognitive descriptions of the task (Experiment 2). Metrically incongruous rhythms showed greater force differentiation between strong and weak taps, increases in the variability of the timing within and between hands, and frequent breakdowns of the between-hand coordination. Tempo variations and the different cognitive descriptions of the task did not influence performance. We suggest that the difficulty in producing incongruous rhythms arises from interference between the required incongruous metric pattern and a spontaneously available pattern in which the potential boundary-markers of the metric units systematically coincide.