Joint rushing alters internal timekeeping in non-musicians and musicians

Dance of two brains: Interval subdivision in alternated condition enhances resistance to interference by others

The accomplishment of interpersonal sensorimotor synchronization is a challenging endeavor because it requires the achievement of a balance between accurate temporal control within individuals and smooth communication between them. This raises a critical question: How does the brain comprehend and process the perceptual information of others to guarantee accurate temporal control of action goals in a social context? A joint synchronization - continuation tapping task was conducted together with varying relative phases (0°/180°) and intervals of tempos (400 ms/800 ms/1600 ms) while neural data was collected using fNIRS (functional near-infrared spectroscopy). Individuals showed better behavioral performance and greater interpersonal brain synchronization(IBS) in the left dorsolateral prefrontal cortex at alternated condition (180° relative phase) compared to symmetric condition (0° relative phase), suggesting that the individual can better maintain behavioral performance and show improved IBS when the partner taps between the individual's gaps. Meanwhile, in most levels of alternated condition, IBS is inversely proportional to interference from partner, implying the counteraction of IBS against interference from others. In addition, when the interval of tempo was 1600 ms, behavioral performance showed a sharp decline, accompanied by a decrease in IBS, reflecting that IBS in SMS reflects effective information exchange between individuals rather than ineffective interference with each other. This study provides insight into the mechanisms underlying sensorimotor synchronization between individuals.

Effect of time delay on performance and timing control in dyadic rhythm coordination using finger tapping

In musical ensembles, people synchronise with each other despite the presence of time delays such as those related to sound transmission. However, the ways in which time delays in synchronisation are overcome remain unclear. This study aimed to investigate the basic characteristics and mechanism of synchronisation with time delays using a dyadic synchronisation-continuation finger-tapping task with time delays ranging from 0 to 240 ms. The results reveal that synchronisation performance improved under time delays of 40-160 ms compared with in the other conditions. This tolerance to the time delay could have been because such a delay allowed both participants in each pair to tap before receiving the stimuli from their partner, as seen in synchronisation with a constant-tempo metronome. In addition, the dependency of the timing control on the partner's previous inter-tap interval decreased at a time delay of 80 ms, relating to the fact that the acceleration and deceleration of the tapping tempo reduced under certain time delays, while the synchronisation performance improved. Uncertainty in the timing of the partner's stimulus could induce greater anticipatory responses, making it possible to tolerate longer time delays in dyadic finger-tapping tasks.

Videos posted on the internet provide evidence for joint rushing in naturalistic social interactions

When people engage in rhythmic joint actions, they unintentionally increase their tempo. However, this phenomenon of joint rushing has so far been investigated only under very specific and somewhat artificial conditions. Therefore, it remains unclear whether joint rushing generalizes to other instances of rhythmic joint action. In this study our aim was to investigate whether joint rushing can also be observed in a wider range of naturalistic rhythmic social interactions. To achieve this, we retrieved videos of a wide range of rhythmic interactions from an online video-sharing platform. The data suggest that joint rushing indeed can also be observed in more naturalistic social interactions. Furthermore, we provide evidence that group size matters for how tempo unfolds in social interactions with larger groups showing a stronger tempo increase than smaller groups. Comparing the data from naturalistic interactions with data collected in a lab study further showed that unintended tempo changes in social interactions are reduced in naturalistic interactions compared to interactions in a lab context. It is an open question which factors led to this reduction. One possibility is that humans might have come up with strategies to reduce the effects of joint rushing.

Emergent and planned interpersonal synchronization are both sensitive to 'tempo aftereffect contagion'

Interpersonal synchronization is fundamental for motor coordination during social interactions. Discerning emergent (entrainment) from planned synchronization represents a non-trivial issue in visually bonded individuals acting together, as well as assessing whether inter-individual differences, e.g., in autistic traits, modulate both types of synchronization. In a visuomotor finger-tapping task, two participants replicated a target tempo either synchronizing ('joint' condition) or not ('non-interactive' condition, 'non-int') with each other. One participant was exposed ('induced') to tempo aftereffect (a medium tempo seems faster or slower after exposure to slower or faster inducing tempi), but not the other participant ('not induced'); thus they had different timing perceptions of the same target. We assessed to what degree emergent and/or planned synchronization affected dyads by analyzing inter-tap-intervals, synchronization indexes, and cross-correlation coefficients. Results revealed a 'tempo aftereffect contagion': inter-tap-intervals of both induced and not-induced participants showed aftereffect in both the joint and non-int conditions. Moreover, aftereffects did not correlate across conditions suggesting they might be due to (at least in part) different processes, but the propensity for tempo aftereffect contagion correlated with individuals' autistic traits only in the non-int condition. Finally, participants co-adjusted their tapping more in the joint condition than in the non-int one, as confirmed by higher synchronization indexes and the mutual adaptation pattern of cross-correlation coefficients. Altogether, these results show the subtle interplay between emergent and planned interpersonal synchronization mechanisms that act on a millisecond timescale independently from synching or not with the partner.

Interpersonal synchronization of movement intermittency

Most animal species group together and coordinate their behavior in quite sophisticated manners for mating, hunting, or defense purposes. In humans, coordination at a macroscopic level (the pacing of movements) is evident both in daily life (e.g., walking) and skilled (e.g., music and dance) behaviors. By examining the fine structure of movement, we here show that interpersonal coordination is established also at a microscopic – submovement – level. Natural movements appear as marked by recurrent (2–3 Hz) speed breaks, i.e., submovements, that are traditionally considered the result of intermittency in (visuo)motor feedback-based control. In a series of interpersonal coordination tasks, we show that submovements produced by interacting partners are not independent but alternate tightly over time, reflecting online mutual adaptation. These findings unveil a potential core mechanism for behavioral coordination that is based on between-persons synchronization of the intrinsic dynamics of action-perception cycles.

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Movements show intermittent speed pulses occurring at 2–3 Hz, called submovements

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Submovements are actively coordinated in counter-phase by interacting partners

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Submovements coordination depends on spatial alignment but not movement congruency

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Behavioral coordination occurs both at macro- and microscopic movement scales