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Human interaction often requires simultaneous precision and flexibility in the coordination of rhythmic behaviour between individuals engaged in joint activity, for example, playing a musical duet or dancing with a partner. This review article addresses the psychological processes and brain mechanisms that enable such rhythmic interpersonal coordination. First, an overview is given of research on the cognitive-motor processes that enable individuals to represent joint action goals and to anticipate, attend and adapt to other's actions in real time. Second, the neurophysiological mechanisms that underpin rhythmic interpersonal coordination are sought in studies of sensorimotor and cognitive processes that play a role in the representation and integration of self- and other-related actions within and between individuals' brains. Finally, relationships between social–psychological factors and rhythmic interpersonal coordination are considered from two perspectives, one concerning how social-cognitive tendencies (e.g. empathy) affect coordination, and the other concerning how coordination affects interpersonal affiliation, trust and prosocial behaviour. Our review highlights musical ensemble performance as an ecologically valid yet readily controlled domain for investigating rhythm in joint action.

Parkinson's disease (PD) and basal ganglia dysfunction impair movement timing, which leads to gait instability and falls. Parkinsonian gait consists of random, disconnected stride times--rather than the 1/f structure observed in healthy gait--and this randomness of stride times (low fractal scaling) predicts falling. Walking with fixed-tempo Rhythmic Auditory Stimulation (RAS) can improve many aspects of gait timing; however, it lowers fractal scaling (away from healthy 1/f structure) and requires attention. Here we show that interactive rhythmic auditory stimulation reestablishes healthy gait dynamics in PD patients. In the experiment, PD patients and healthy participants walked with a) no auditory stimulation, b) fixed-tempo RAS, and c) interactive rhythmic auditory stimulation. The interactive system used foot sensors and nonlinear oscillators to track and mutually entrain with the human's step timing. Patients consistently synchronized with the interactive system, their fractal scaling returned to levels of healthy participants, and their gait felt more stable to them. Patients and healthy participants rarely synchronized with fixed-tempo RAS, and when they did synchronize their fractal scaling declined from healthy 1/f levels. Five minutes after removing the interactive rhythmic stimulation, the PD patients' gait retained high fractal scaling, suggesting that the interaction stabilized the internal rhythm generating system and reintegrated timing networks. The experiment demonstrates that complex interaction is important in the (re)emergence of 1/f structure in human behavior and that interactive rhythmic auditory stimulation is a promising therapeutic tool for improving gait of PD patients.

The tendency to mimic and synchronize with others is well established. Although mimicry has been shown to lead to affiliation between co-actors, the effect of interpersonal synchrony on affiliation remains an open question. The authors investigated the relationship by having participants match finger movements with a visual moving metronome. In Experiment 1, affiliation ratings were examined based on the extent to which participants tapped in synchrony with the experimenter. In Experiment 2, synchrony was manipulated. Affiliation ratings were compared for an experimenter who either (a) tapped to a metronome that was synchronous to the participant's metronome, (b) tapped to a metronome that was asynchronous, or (c) did not tap. As hypothesized, in both studies, the degree of synchrony predicted subsequent affiliation ratings. Experiment 3 found that the affiliative effects were unique to interpersonal synchrony. [PUBLICATION ABSTRACT]

The experience of groove is associated with the urge to move to a musical rhythm. Here we focus on the relevance of audio features, obtained using music information retrieval (MIR) tools, for explaining the perception of groove and music-related movement. In Study 1 we extracted audio features from clips of real music previously rated on perceived groove. Measures of variability, such as the variance of the audio signal’s RMS curve and spectral flux (particularly in low frequencies), predicted groove ratings. Additionally, we dissociated two forms of event density, showing that an algorithm that emphasizes variability between beats predicted groove ratings better. In Study 2 we manipulated RMS levels and groove category (low, mid, and high groove) to confirm that perceived groove is not a function of loudness. In Study 3 we utilized novel music clips that manipulated the frequency of bass and bass drum (low vs. high) and attack time (short vs. long). Groove ratings and tapping velocities tended to be higher and tapping variability tended to be lower when the bass instruments had lower frequencies. The present findings emphasize the multifaceted nature of groove by linking audio and musical qualities to subjective experience and motor behavior.

The auditory environment typically contains several sound sources that overlap in time, and the auditory system parses the complex sound wave into streams or voices that represent the various sound sources. Music is also often polyphonic. Interestingly, the main melody (spectral/pitch information) is most often carried by the highest-pitched voice, and the rhythm (temporal foundation) is most often laid down by the lowest-pitched voice. Previous work using electroencephalography (EEG) demonstrated that the auditory cortex encodes pitch more robustly in the higher of two simultaneous tones or melodies, and modeling work indicated that this high-voice superiority for pitch originates in the sensory periphery. Here, we investigated the neural basis of carrying rhythmic timing information in lower-pitched voices. We presented simultaneous high-pitched and low-pitched tones in an isochronous stream and occasionally presented either the higher or the lower tone 50 ms earlier than expected, while leaving the other tone at the expected time. EEG recordings revealed that mismatch negativity responses were larger for timing deviants of the lower tones, indicating better timing encoding for lower-pitched compared with higher-pitch tones at the level of auditory cortex. A behavioral motor task revealed that tapping synchronization was more influenced by the lower-pitched stream. Results from a biologically plausible model of the auditory periphery suggest that nonlinear cochlear dynamics contribute to the observed effect. The low-voice superiority effect for encoding timing explains the widespread musical practice of carrying rhythm in bass-ranged instruments and complements previously established high-voice superiority effects for pitch and melody.

It has long been known that the auditory system is better suited to guide temporally precise behaviors like sensorimotor synchronization (SMS) than the visual system. Although this phenomenon has been studied for many years, the underlying neural and computational mechanisms remain unclear. Growing consensus suggests the existence of multiple, interacting, context-dependent systems, and that reduced precision in visuo-motor timing might be due to the way experimental tasks have been conceived. Indeed, the appropriateness of the stimulus for a given task greatly influences timing performance. In this review, we examine timing differences for sensorimotor synchronization and error correction with auditory and visual sequences, to inspect the underlying neural mechanisms that contribute to modality differences in timing. The disparity between auditory and visual timing likely relates to differences in the processing specialization between auditory and visual modalities (temporal vs. spatial). We propose this difference could offer potential explanation for the differing temporal abilities between modalities. We also offer suggestions as to how these sensory systems interface with motor and timing systems.

The capacity to entrain motor action to rhythmic auditory stimulation is highly developed in humans and extremely limited in our closest relatives. An important aspect of auditory-motor entrainment is that not all forms of rhythmic stimulation motivate movement to the same degree. This variation is captured by the concept of musical groove: high-groove music stimulates a strong desire for movement, whereas low-groove music does not. Here, we utilize this difference to investigate the neurophysiological basis of our capacity for auditory-motor entrainment. In a series of three experiments we examine pupillary responses to musical stimuli varying in groove. Our results show stronger pupil dilation in response to (1) high- vs. low-groove music, (2) high vs. low spectral content, and (3) syncopated vs. straight drum patterns. We additionally report evidence for consistent sex differences in music-induced pupillary responses, with males exhibiting larger differences between responses, but females exhibiting stronger responses overall. These results imply that the biological link between movement and auditory rhythms in our species is supported by the capacity of high-groove music to stimulate arousal in the central and peripheral nervous system, presumably via highly conserved noradrenergic mechanisms.

The shared circuits model (SCM) is a useful explanatory framework that can be applied to interpersonal synchrony by incorporating temporal dynamics. Temporally precise predictive simulations and mirroring enable interpersonal synchrony. When partners' movements are highly synchronous, the self/other distinction can be blurred.

This work investigates how spatial and temporalaspects of rhythmic movements are affected by spatial and temporal components of a visual pacing sequence. Participants synchronized finger taps with three visual pacing sequences (Flash,High Finger, andLow Finger) at two tempi (500 ms and 400 ms interonset interval). The Flash sequence contained only temporal information, whereas the two Finger sequences contained apparent motion of different amplitudes. Participants' finger movements were recorded with a motion capture system, and movement trajectories and timing accuracy were analyzed. Results indicated that apparent motion facilitates visuomotor synchronization accuracy, which likely stems from tight perception-action links. Stimulus amplitude modulated tap amplitudes in the same direction, but this spatial assimilation did not adversely affect timing accuracy. Flexion times toward the target were significantly shorter than extension or dwell times, and could indicate a relatively ballistic movement trajectory. Local deviations of tap timing correlated with the movement trajectories from the preceding and following movement cycle. For example, after a late tap, the following movement cycle had lower amplitude and shorter extension and dwell times. This could signify the workings of error correction mechanisms that ensure stable synchronization.

Synchronizing movements with auditory beats, compared to visual flashes, yields divergent activation in timing-related brain areas as well as more stable tapping synchronization. The differences in timing-related brain activation could reflect differences in tapping synchronization stability, rather than differences between modality (i.e., audio-motor vs. visuo-motor integration). In the current fMRI study, participants synchronized their finger taps with four types of visual and auditory pacing sequences: flashes and a moving bar, as well as beeps and a frequency-modulated ‘siren’. Behavioral tapping results showed that visuo-motor synchronization improved with moving targets, whereas audio-motor synchronization degraded with frequency-modulated sirens. Consequently, a modality difference in synchronization occurred between the discrete beeps and flashes, but not between the novel continuous siren and moving bar. Imaging results showed that activation in the putamen, a key timing area, paralleled the behavioral results: putamen activation was highest for beeps, intermediate for the continuous siren and moving bar, and was lowest for the flashes. Putamen activation differed between modalities for beeps and flashes, but not for the novel moving bar and siren. By dissociating synchronization performance from modality, we show that activation in the basal ganglia is associated with sensorimotor synchronization stability rather than modality-specificity in this task. Synchronization stability is apparently contingent upon the modality's processing affinity: discrete auditory and moving visual signals are modality appropriate, and can be encoded reliably for integration with the motor system. ► fMRI study of finger tapping with visual flashes, moving bar, auditory beeps, siren. ► Visuo-motor synchrony improved with moving bar; audio-motor degraded with siren. ► Putamen activation reflected stability of sensorimotor synchrony, not modality. ► No modality difference in tapping or timing circuit with modality-appropriate stimuli.