Beat Patterns Determine Inter-Hand Differences in Synchronization Error in a Bimanual Coordination Tapping Task

A previous study reported the unique finding that people tapping a beat pattern with the right hand produce larger negative synchronization error than when tapping with the left hand or other effectors, in contrast to previous studies that have shown that the hands tap patterns simultaneously without any synchronization errors. We examined whether the inter-hand difference in synchronization error occurred due to handedness or to a specificity of the beat pattern employed in that study. Two experiments manipulated the hand–beat assignments. A comparison between the identical beat to the pacing signal and a beat with a longer interval excluded the handedness hypothesis and demonstrated that beat patterns with relatively shorter intervals were tapped earlier (Experiment 1). These synchronization errors were not local but occurred consistently throughout the beat patterns. Experiment 2 excluded alternative explanations. These results indicate that the apparent inconsistency in previous studies was due to the specificity of the beat patterns, suggesting that a beat pattern with a relatively shorter interval between hands is tapped earlier than beats with longer intervals. Our finding that the bimanual tapping of different beat patterns produced different synchronization errors suggests that the notion of a central timing system may need to be revised.

Beat patterns determine inter-hand differences in synchronization error in a bimanual coordination tapping task.

A previous study reported the unique finding that people tap a beat pattern with the right hand earlier than with the left hand or other effectors, in contrast to previous studies that have shown that the hands tap patterns simultaneously without any synchronization errors. We examined whether the inter-hand difference in synchronization error occurred due to handedness or to a specificity of the beat pattern employed in that study. Two experiments manipulated the hand–beat assignments. A comparison between the identical beat to the pacing signal and a beat with a longer interval excluded the handedness hypothesis and demonstrated that beat patterns with relatively shorter intervals were tapped earlier (Experiment 1). These synchronization errors were not local but occurred consistently throughout the beat patterns. Experiment 2 excluded alternative explanations. These results indicate that the apparent inconsistency in previous studies was due to the specificity of the beat patterns, suggesting that a beat pattern with a shorter interval is tapped earlier than beats with longer intervals. Our results are consistent with a model of central timing control in bimanual tapping.

Distortions in Reproduction of Two-Interval Rhythms: When the “Attractor Ratio” Is Not Exactly 1:2

when rhythms consisting of two unequal intervals are reproduced cyclically, their interval ratio tends to be distorted in the direction of 1:2 (= 0.5), which thus seems to function as an “attractor ratio” (AR). However, recent results for musicians in a synchronization task (Repp, London, & Keller, 2011) have suggested an upward-shifted AR (USAR) somewhat greater than 0.5. Three new experiments suggest that this shift is not due to synchronization versus continuation tapping, the range of interval ratios employed, unimanual versus bimanual tapping, intensity differences between taps, or mental subdivision of the long interval, although some of these factors may affect its size. The new results also show that the USAR is found more consistently in musicians than in nonmusicians and seems to arise in rhythm production, not in perception. While the exact causes of the USAR remain unclear, the results suggest that the AR is not necessarily the mathematically simplest interval ratio.

Interhemispheric connectivity between distinct motor regions as a window into bimanual coordination

Performing coordinated bimanual movement is a fundamental feature of the human motor system, with imaging techniques revealing the involvement of an extensive network of motor regions in both hemispheres. Using transcranial magnetic stimulation, Liuzzi et al. ( J Neurosci 31: 9111–9117, 2011) recently extended our understanding of the neural correlates of motor actions by showing that the nature of the interhemispheric connectivity between primary and premotor regions may influence motor performance during a bimanual tapping task.