Musical Meter Induces Interbrain Synchronization during Interpersonal Coordination

Abstract

Music induces people to coordinate with one another. Here, we conduct two experiments to examine the underlying mechanism of the interbrain synchronization (IBS) that is induced by interpersonal coordination when people are exposed to musical beat and meter. In experiment 1, brain signals at the frontal cortex were recorded simultaneously from two participants of a dyad by using functional near-infrared spectroscopy (fNIRS) hyperscanning, while each tapped their fingers to aural feedback from their partner (coordination task) or from themselves (independence task) with and without the musical meter. The results showed enhanced IBS at the left-middle frontal cortex in case of the coordination task with musical beat and meter. The IBS was significantly correlated with the participants performance in terms of coordination. In experiment 2, we further examined the IBS while the participants coordinated their behaviors in various metrical contexts, such as strong and weak meters (i.e., high/low loudness of acoustically accenting beats). The results showed that strong meters elicited higher IBS at the middle frontal cortex than weak meters. These findings reveal that the musical beat and meter can affect brain-to-brain coupling in action coordination between people, and provide insights into the interbrain mechanism underlying the effects of music on cooperation.

Keywords: fNIRS hyperscanning; interbrain synchronization; interpersonal coordination; musical meter.

Figure 1.

Experimental design. A, Experimental stimulus. B, Experimental procedure and task (P1, participant #1; P2, participant #2). C, Probe configuration in experiment 1. D, Probe configuration of a second patch in experiment 2.

Figure 2.

Behavioral performance on the coordination task between the meter and no-meter conditions in experiment 1. A, Mean interpersonal time lag (Mean lag). Shorter mean interpersonal time lag in the meter condition compared with that in the no-meter condition. B, Hurst exponent H of the detrended fluctuation analysis. There was no significant difference in H between the meter and the no-meter conditions. C, The linear regression of interpersonal time lags across taps in the meter and no-meter conditions. The interpersonal time lags significantly decreased across taps in the meter condition. Colored lines indicate behavioral measures for each dyad. Black lines indicate the averaged values across dyads. Error bars represent SEMs.

Figure 3.

Interbrain synchronization (IBS) during the coordination task. The heat maps of the IBS in (A) experiment 1 and (D) experiment 2. Enhanced IBS was observed at channel 6 in the range of frequencies of 0.026–0.030 Hz in the meter condition compared with the no-meter condition. In experiment 2, the IBS in channels 5 and 10 (frequencies: 0.060–0.065 Hz) was greater in case of strong meters than weak meters. The distributions of the cluster statistic of the permutated data in (B) experiment 1 and (E) experiment 2. The black dashed lines indicate the positions of the cluster statistic of the pairs. The enhanced IBS in (C) experiment 1 and (F) experiment 2. Data were plotted through boxplots, in which the horizontal lines indicate median values, the boxes indicate the 25% and 75% quartiles, and the error bars represent the minimum/maximum values. The diamond dots represent the extreme values.

Figure 4.

Correlation between interbrain synchronization (IBS) and behavioral coordination in experiment 1. The IBS at channel 6 during the coordination task was negatively associated with the mean interpersonal time lag in the meter condition. Each black point depicts a dyad of the mean interpersonal time lag of the participants (y-coordinate) and IBS at channel 6 (x-coordinate). The solid line represents the least-squares fit. The shaded area indicates the 95% confidence interval.

Figure 5.

Behavioral coordination in experiment 2. A shorter mean interpersonal time lag (Mean lag) was observed in strong meters relative to weak meters. Boxplots are presented, with the horizontal lines indicating the median values, boxes indicating the 25% and 75% quartiles, and error bars representing the minimum/maximum values. The diamond dots represent the extreme values; *p < 0.05.

Figure 6.

Correlation between interbrain synchronization (IBS) and behavioral coordination in experiment 2. The average IBS at channels 5 and 10 was negatively associated with the mean interpersonal time lag in case of strong meters. The values in duple and triple meters were averaged. Each black point depicts a dyad of the mean interpersonal time lag of participants (y-coordinate) and the average IBS in channels 5 and 10 (x-coordinate). The solid line represents the least-squares fit. The shaded area indicates the 95% confidence interval.