Accent-induced Modulation of Neural and Movement Patterns during Spontaneous Synchronization to Auditory Rhythms.

Human rhythmic movements spontaneously synchronize with auditory rhythms at various frequency ratios. The emergence of more complex relationships-for instance, frequency ratios of 1:2 and 1:3-is enhanced by adding a congruent accentuation pattern (binary for 1:2 and ternary for 1:3), resulting in a 1:1 movement-accentuation relationship. However, this benefit of accentuation on movement synchronization appears to be stronger for the ternary pattern than for the binary pattern. Here, we investigated whether this difference in accent-induced movement synchronization may be related to a difference in the neural tracking of these accentuation profiles. Accented and control unaccented auditory sequences were presented to participants who concurrently produced finger taps at their preferred frequency, and spontaneous movement synchronization was measured. EEG was recorded during passive listening to each auditory sequence. The results revealed that enhanced movement synchronization with ternary accentuation was accompanied by enhanced neural tracking of this pattern. Larger EEG responses at the accentuation frequency were found for the ternary pattern compared with the binary pattern. Moreover, the amplitude of accent-induced EEG responses was positively correlated with the magnitude of accent-induced movement synchronization across participants. Altogether, these findings show that the dynamics of spontaneous auditory-motor synchronization is strongly driven by the multi-time-scale sensory processing of auditory rhythms, highlighting the importance of considering neural responses to rhythmic sequences for understanding and enhancing synchronization performance.

Feeling better: Tactile verbs speed up tactile detection.

Embodiment of action-related language into the motor system has been extensively documented. Yet the case of sensory words, especially referring to touch, remains overlooked. We investigated the influence of verbs denoting tactile sensations on tactile perception. In Experiment 1, participants detected tactile stimulations on their forearm, preceded by tactile or non-tactile verbs by one of three delays (170, 350, 500 ms) reflecting different word processing stages. Results revealed shorter reaction times to tactile stimulations following tactile than non-tactile verbs, irrespective of delay. To ensure that priming pertained to tactile, and not motor, verb properties, Experiment 2 compared the impact of tactile verbs to both action and non-tactile verbs, while stimulations were delivered on the index finger. No priming emerged following action verbs, therefore not supporting the motor-grounded interpretation. Facilitation by tactile verbs was however not observed, possibly owing to methodological changes. Experiment 3, identical to Experiment 2 except that stimulation was delivered to participants' forearm, replicated the priming effect. Importantly, tactile stimulations were detected faster after tactile than after both non-tactile and action verbs, indicating that verbs' tactile properties engaged resources shared with sensory perception. Our findings suggest that language conveying tactile information can activate somatosensory representations and subsequently promote tactile detection.

Accent-induced stabilization of spontaneous auditory-motor synchronization.

Humans spontaneously synchronize their movements with external auditory rhythms such as a metronome or music. Although such synchronization preferentially occurs toward a simple 1:1 movement-sound frequency ratio, the parameters facilitating spontaneous synchronization to more complex frequency ratios remain largely unclear. The present study investigates the dynamics of spontaneous auditory-motor synchronization at a range of frequency ratios between movement and sound, and examines the benefit of simple accentuation pattern on synchronization emergence and stability. Participants performed index finger oscillations at their preferred tempo while listening to a metronome presented at either their preferred tempo, or twice or three times faster (frequency ratios of 1:1, 1:2 or 1:3) with different patterns of accentuation (unaccented, binary or ternary accented), and no instruction to synchronize. Participants' movements were spontaneously entrained to the auditory stimuli in the three different frequency ratio conditions. Moreover, the emergence and stability of the modes of coordination were influenced by the interaction between frequency ratio and pattern of accentuation. Coherent patterns, such as a 1:3 frequency ratio supported by a ternary accentuation, facilitated the emergence and stability of the corresponding mode of coordination. Furthermore, ternary accentuation induced a greater gain in stability for the corresponding mode of coordination than was observed with binary accentuation. Together, these findings demonstrate the importance of matching accentuation pattern and movement tempo for enhanced synchronization, opening new perspectives for stabilizing complex rhythmic motor behaviors, such as running.

Single (1:1) vs. double (1:2) metronomes for the spontaneous entrainment and stabilisation of human rhythmic movements.

Rhythmic movements produced by humans become spontaneously entrained to auditory rhythms in the environment. Evidence suggests that synchronisation to external auditory rhythms can contribute to the stabilisation of movements in time and space, opening new perspectives for motor training and rehabilitation. Here we compared the effects of single (1:1) and double (1:2) metronomes (i.e., one or two stimulations per preferred movement cycle) on spontaneous movement entrainment and stabilisation. We examined the spontaneous entrainment of self-paced hand-held pendulum swinging when single or double metronomes were presented either at the participant's preferred tempo or slightly slower or faster (± 10%). The results showed that participants' movements spontaneously entrained to auditory rhythms, and that the strength of this entrainment was the same for single and double metronomes. However, double metronomes decreased movement tempo stability, whereas single metronomes increased movement tempo stability compared to a control condition without a stimulus. These effects preferentially occurred for metronomes presented at participants' preferred movement tempi and especially for participants whose movements were intrinsically more variable. Participants' movement amplitude stability was also modulated in such a way that the stability of participants who were intrinsically less stable increased, whereas the stability of intrinsically more stable participants decreased with auditory rhythms, an effect that was stronger with double than single metronomes. Moreover, movement stabilisation in time and space were positively correlated, suggesting that tempo and amplitude stabilisation depend on similar processes and may be complementary. These findings provide new insight into the processes underlying auditory-motor entrainment and how auditory rhythms can be used to improve movement stability in time and space.

Preferred frequency ratios for spontaneous auditory-motor synchronization: Dynamical stability and hysteresis.

Humans spontaneously synchronize their movements with external auditory rhythms such as a metronome or music. Although such synchronization preferentially occurs toward simple 1:1 movement-stimulus frequency ratio, the extent to which spontaneous synchronization can also occur toward more complex frequency ratios remains largely unclear. The present study investigates the occurrence and dynamical stability of spontaneous auditory-motor synchronization at multiple frequency ratios. Participants performed index finger oscillations at their preferred tempo while listening to auditory metronomes with frequency progressively increasing or decreasing between 1 Hz and 6 Hz. The results demonstrated that participants' movements were not only entrained toward the 1:1 frequency ratio but also toward the 1:2 ratio. The occurrence and stability of these ratios differed as a function of the direction of frequency change. Participants synchronized to the 1:2 ratio and transitioned to a 1:1 ratio in the descending condition. In the ascending condition only the 1:1 ratio was sustained, for a longer extent than in the descending condition. These results show that the initial coordination pattern influenced pattern transition, demonstrating the occurrence of a hysteresis effect that is typical of complex system dynamics. These findings provide new insight into the mechanisms underlying the occurrence and stability of spontaneous movement synchronization to auditory rhythms.