The dual influence of pacer continuity and pacer pattern for visuomotor synchronisation

Spatial and temporal (non)binding of audiovisual rhythms in sensorimotor synchronisation

Human movement synchronisation with moving objects strongly relies on visual input. However, auditory information also plays an important role, since real environments are intrinsically multimodal. We used electroencephalography (EEG) frequency tagging to investigate the selective neural processing and integration of visual and auditory information during motor tracking and tested the effects of spatial and temporal congruency between audiovisual modalities. EEG was recorded while participants tracked with their index finger a red flickering (rate f_V = 15 Hz) dot oscillating horizontally on a screen. The simultaneous auditory stimulus was modulated in pitch (rate f_A = 32 Hz) and lateralised between left and right audio channels to induce perception of a periodic displacement of the sound source. Audiovisual congruency was manipulated in terms of space in Experiment 1 (no motion, same direction or opposite direction), and timing in Experiment 2 (no delay, medium delay or large delay). For both experiments, significant EEG responses were elicited at f_V and f_A tagging frequencies. It was also hypothesised that intermodulation products corresponding to the nonlinear integration of visual and auditory stimuli at frequencies f_V ± f_A would be elicited, due to audiovisual integration, especially in Congruent conditions_. However, these components were not observed. Moreover, synchronisation and EEG results were not influenced by congruency manipulations, which invites further exploration of the conditions which may modulate audiovisual processing and the motor tracking of moving objects.

Neural tracking of visual periodic motion

Periodicity is a fundamental property of biological systems, including human movement systems. Periodic movements support displacements of the body in the environment as well as interactions and communication between individuals. Here, we use electroencephalography (EEG) to investigate the neural tracking of visual periodic motion, and more specifically, the relevance of spatiotemporal information contained at and between their turning points. We compared EEG responses to visual sinusoidal oscillations versus nonlinear Rayleigh oscillations, which are both typical of human movements. These oscillations contain the same spatiotemporal information at their turning points but differ between turning points, with Rayleigh oscillations having an earlier peak velocity, shown to increase an individual's capacity to produce accurately synchronized movements. EEG analyses highlighted the relevance of spatiotemporal information between the turning points by showing that the brain precisely tracks subtle differences in velocity profiles, as indicated by earlier EEG responses for Rayleigh oscillations. The results suggest that the brain is particularly responsive to velocity peaks in visual periodic motion, supporting their role in conveying behaviorally relevant timing information at a neurophysiological level. The results also suggest key functions of neural oscillations in the Alpha and Beta frequency bands, particularly in the right hemisphere. Together, these findings provide insights into the neural mechanisms underpinning the processing of visual periodic motion and the critical role of velocity peaks in enabling proficient visuomotor synchronization.

Dynamic Modulation of Beta Band Cortico-Muscular Coupling Induced by Audio-Visual Rhythms

Human movements often spontaneously fall into synchrony with auditory and visual environmental rhythms. Related behavioral studies have shown that motor responses are automatically and unintentionally coupled with external rhythmic stimuli. However, the neurophysiological processes underlying such motor entrainment remain largely unknown. Here, we investigated with electroencephalography (EEG) and electromyography (EMG) the modulation of neural and muscular activity induced by periodic audio and/or visual sequences. The sequences were presented at either 1 or 2 Hz, while participants maintained constant finger pressure on a force sensor. The results revealed that although there was no change of amplitude in participants' EMG in response to the sequences, the synchronization between EMG and EEG recorded over motor areas in the beta (12-40 Hz) frequency band was dynamically modulated, with maximal coherence occurring about 100 ms before each stimulus. These modulations in beta EEG-EMG motor coherence were found for the 2-Hz audio-visual sequences, confirming at a neurophysiological level the enhancement of motor entrainment with multimodal rhythms that fall within preferred perceptual and movement frequency ranges. Our findings identify beta band cortico-muscular coupling as a potential underlying mechanism of motor entrainment, further elucidating the nature of the link between sensory and motor systems in humans.

Dynamic modulation of cortico-muscular coupling during real and imagined sensorimotor synchronisation

People have a natural and intrinsic ability to coordinate body movements with rhythms surrounding them, known as sensorimotor synchronisation. This can be observed in daily environments, when dancing or singing along with music, or spontaneously walking, talking or applauding in synchrony with one another. However, the neurophysiological mechanisms underlying accurately synchronised movement with selected rhythms in the environment remain unclear. Here we studied real and imagined sensorimotor synchronisation with interleaved auditory and visual rhythms using cortico-muscular coherence (CMC) to better understand the processes underlying the preparation and execution of synchronised movement. Electroencephalography (EEG), electromyography (EMG) from the finger flexors, and continuous force signals were recorded in 20 participants during tapping and imagined tapping with discrete stimulus sequences consisting of alternating auditory beeps and visual flashes. The results show that the synchronisation between cortical and muscular activity in the beta (14-38 Hz) frequency band becomes time-locked to the taps executed in synchrony with the visual and auditory stimuli. Dynamic modulation in CMC also occurred when participants imagined tapping with the visual stimuli, but with lower amplitude and a different temporal profile compared to real tapping. These results suggest that CMC does not only reflect changes related to the production of the synchronised movement, but also to its preparation, which appears heightened under higher attentional demands imposed when synchronising with the visual stimuli. These findings highlight a critical role of beta band neural oscillations in the cortical-muscular coupling underlying sensorimotor synchronisation.

The effect of perceptual-motor continuity compatibility on the temporal control of continuous and discontinuous self-paced rhythmic movements

One of the questions yet to be fully understood is to what extent the properties of the sensory and the movement information interact to facilitate sensorimotor integration. In this study, we examined the relative contribution of the continuity compatibility between motor goals and their sensory outcomes in timing variability. The variability of inter-response intervals was measured in a synchronization-continuation paradigm. Participants performed two repetitive movement tasks whereby they drew circles either using continuous or discontinuous self-paced movements while receiving discrete or continuous auditory feedback. The results demonstrated that the effect of perceptual-motor continuity compatibility may be limited in self-paced auditory-motor synchronization as timing variability was not significantly influenced by the continuity of the feedback or the continuity compatibility between feedback and the movement produced. In addition, results suggested that the presence of salient perceptual events marking the completion of the time intervals elicited a common timing process in both continuous and discontinuous circle drawing, regardless of the continuity of the auditory feedback. These findings open a new line of investigation into the role of the discriminability and reliability of the event-based information in determining the nature of the timing mechanisms engaged in continuous and discontinuous self-paced rhythmic movements.

Advantage of audition over vision in a perceptual timing task but not in a sensorimotor timing task

Timing is essential for various behaviors and relative to vision, audition is considered to be specialized for temporal processing. The present study conducted a sensorimotor timing task that required tapping in synchrony with a temporally regular sequence and a perceptual timing task that required detecting a timing deviation among a temporally regular sequence. The sequence was composed of auditory tones, visual flashes, or a visual bouncing ball. In the sensorimotor task, sensorimotor timing performance (synchronization stability) of the bouncing ball was much greater than that of flashes and was comparable to that of tones. In the perceptual task, where perceptual timing performance of the bouncing ball was greater than that of flashes, it was poorer than that of tones. These results suggest the facilitation of both perceptual and sensorimotor processing of temporal information by the bouncing ball. Given such facilitation of temporal processing, however, audition is still superior over vision in perceptual detection of timing.