The influence of external and internal motor processes on human auditory rhythm perception

Musical rhythm is composed of organized temporal patterns, and the processes underlying rhythm perception are found to engage both auditory and motor systems. Despite behavioral and neuroscience evidence converging to this audio-motor interaction, relatively little is known about the effect of specific motor processes on auditory rhythm perception. This doctoral thesis was devoted to investigating the influence of both external and internal motor processes on the way we perceive an auditory rhythm. The first half of the thesis intended to establish whether overt body movement had a facilitatory effect on our ability to perceive the auditory rhythmic structure, and whether this effect was modulated by musical training. To this end, musicians and non-musicians performed a pulse-finding task either using natural body movement or through listening only, and produced their identified pulse by finger tapping. The results showed that overt movement benefited rhythm (pulse) perception especially for non-musicians, confirming the facilitatory role of external motor activities in hearing the rhythm, as well as its interaction with musical training. The second half of the thesis tested the idea that indirect, covert motor input, such as that transformed from the visual stimuli, could influence our perceived structure of an auditory rhythm. Three experiments examined the subjectively perceived tempo of an auditory sequence under different visual motion stimulations, while the auditory and visual streams were presented independently of each other. The results revealed that the perceived auditory tempo was accordingly influenced by the concurrent visual motion conditions, and the effect was related to the increment or decrement of visual motion speed. This supported the hypothesis that the internal motor information extracted from the visuomotor stimulation could be incorporated into the percept of an auditory rhythm. Taken together, the present thesis concludes that, rather than as a mere reaction to the given auditory input, our motor system plays an important role in contributing to the perceptual process of the auditory rhythm. This can occur via both external and internal motor activities, and may not only influence how we hear a rhythm but also under some circumstances improve our ability to hear the rhythm.Musikalische Rhythmen bestehen aus zeitlich strukturierten Mustern akustischer Stimuli. Es konnte gezeigt werden, dass die Prozesse, welche der Rhythmuswahrnehmung zugrunde liegen, sowohl motorische als auch auditive Systeme nutzen. Obwohl sich für diese auditiv-motorischen Interaktionen sowohl in den Verhaltenswissenschaften als auch Neurowissenschaften übereinstimmende Belege finden, weiß man bislang relativ wenig über die Auswirkungen spezifischer motorischer Prozesse auf die auditive Rhythmuswahrnehmung. Diese Doktorarbeit untersucht den Einfluss externaler und internaler motorischer Prozesse auf die Art und Weise, wie auditive Rhythmen wahrgenommen werden. Der erste Teil der Arbeit diente dem Ziel herauszufinden, ob körperliche Bewegungen es dem Gehirn erleichtern können, die Struktur von auditiven Rhythmen zu erkennen, und, wenn ja, ob dieser Effekt durch ein musikalisches Training beeinflusst wird. Um dies herauszufinden wurde Musikern und Nichtmusikern die Aufgabe gegeben, innerhalb von präsentierten auditiven Stimuli den Puls zu finden, wobei ein Teil der Probanden währenddessen Körperbewegungen ausführen sollte und der andere Teil nur zuhören sollte. Anschließend sollten die Probanden den gefundenen Puls durch Finger-Tapping ausführen, wobei die Reizgaben sowie die Reaktionen mittels eines computerisierten Systems kontrolliert wurden. Die Ergebnisse zeigen, dass offen ausgeführte Bewegungen die Wahrnehmung des Pulses vor allem bei Nichtmusikern verbesserten. Diese Ergebnisse bestätigen, dass Bewegungen beim Hören von Rhythmen unterstützend wirken. Außerdem zeigte sich, dass hier eine Wechselwirkung mit dem musikalischen Training besteht. Der zweite Teil der Doktorarbeit überprüfte die Idee, dass indirekte, verdeckte Bewegungsinformationen, wie sie z.B. in visuellen Stimuli enthalten sind, die wahrgenommene Struktur von auditiven Rhythmen beeinflussen können. Drei Experimente untersuchten, inwiefern das subjektiv wahrgenommene Tempo einer akustischen Sequenz durch die Präsentation unterschiedlicher visueller Bewegungsreize beeinflusst wird, wobei die akustischen und optischen Stimuli unabhängig voneinander präsentiert wurden. Die Ergebnisse zeigten, dass das wahrgenommene auditive Tempo durch die visuellen Bewegungsinformationen beeinflusst wird, und dass der Effekt in Verbindung mit der Zunahme oder Abnahme der visuellen Geschwindigkeit steht. Dies unterstützt die Hypothese, dass internale Bewegungsinformationen, welche aus visuomotorischen Reizen extrahiert werden, in die Wahrnehmung eines auditiven Rhythmus integriert werden können. Zusammen genommen, 5 zeigt die vorgestellte Arbeit, dass unser motorisches System eine wichtige Rolle im Wahrnehmungsprozess von auditiven Rhythmen spielt. Dies kann sowohl durch äußere als auch durch internale motorische Aktivitäten geschehen, und beeinflusst nicht nur die Art, wie wir Rhythmen hören, sondern verbessert unter bestimmten Bedingungen auch unsere Fähigkeit Rhythmen zu identifizieren

Impairment of Auditory-Motor Timing and Compensatory Reorganization after Ventral Premotor Cortex Stimulation

Integrating auditory and motor information often requires precise timing as in speech and music. In humans, the position of the ventral premotor cortex (PMv) in the dorsal auditory stream renders this area a node for auditory-motor integration. Yet, it remains unknown whether the PMv is critical for auditory-motor timing and which activity increases help to preserve task performance following its disruption. 16 healthy volunteers participated in two sessions with fMRI measured at baseline and following rTMS (rTMS) of either the left PMv or a control region. Subjects synchronized left or right finger tapping to sub-second beat rates of auditory rhythms in the experimental task, and produced self-paced tapping during spectrally matched auditory stimuli in the control task. Left PMv rTMS impaired auditory-motor synchronization accuracy in the first sub-block following stimulation (p<0.01, Bonferroni corrected), but spared motor timing and attention to task. Task-related activity increased in the homologue right PMv, but did not predict the behavioral effect of rTMS. In contrast, anterior midline cerebellum revealed most pronounced activity increase in less impaired subjects. The present findings suggest a critical role of the left PMv in feed-forward computations enabling accurate auditory-motor timing, which can be compensated by activity modulations in the cerebellum, but not in the homologue region contralateral to stimulation

Neural Responses to Complex Auditory Rhythms: The Role of Attending

The aim of this study was to explore the role of attention in pulse and meter perception using complex rhythms. We used a selective attention paradigm in which participants attended to either a complex auditory rhythm or a visually presented word list. Performance on a reproduction task was used to gauge whether participants were attending to the appropriate stimulus. We hypothesized that attention to complex rhythms – which contain no energy at the pulse frequency – would lead to activations in motor areas involved in pulse perception. Moreover, because multiple repetitions of a complex rhythm are needed to perceive a pulse, activations in pulse-related areas would be seen only after sufficient time had elapsed for pulse perception to develop. Selective attention was also expected to modulate activity in sensory areas specific to the modality. We found that selective attention to rhythms led to increased BOLD responses in basal ganglia, and basal ganglia activity was observed only after the rhythms had cycled enough times for a stable pulse percept to develop. These observations suggest that attention is needed to recruit motor activations associated with the perception of pulse in complex rhythms. Moreover, attention to the auditory stimulus enhanced activity in an attentional sensory network including primary auditory cortex, insula, anterior cingulate, and prefrontal cortex, and suppressed activity in sensory areas associated with attending to the visual stimulus

Transcranial Magnetic Stimulation to assess Motor System Excitability Fluctuations during Auditory Anticipation and Beat Perception

Humans tend to spontaneously move to the regular beat of musical rhythm. Beat perception is the tendency to sense and anticipate the regular time positions (beats) that movements synchronize with. The neural motor system plays an important role in beat perception, but the dynamics of excitability in the motor system associated with beat perception have not been characterized. This project investigated motor system excitability fluctuations using transcranial magnetic stimulation and electromyography during perception of beat-based and non-beat-based rhythms. We applied single-pulse TMS over the left primary motor cortex of healthy participants as they listened to three types of rhythms that varied in the degree to which they induced beat perception. TMS elicited motor evoked potentials (MEPs) from the first dorsal interosseous muscle. MEP amplitude serves as a proxy for real-time motor system excitability. We hypothesized that during beat perception, motor system excitability may fluctuate at the rate of the perceived beat. We found that beat perception was not associated with anticipatory increases in motor system excitability, or with ongoing fluctuations in excitability at multiple rates associated with the beat. These results inform our understanding of the neural mechanisms of beat perception, as well as potential therapeutic uses of music, for example in Parkinson’s disease

Extracting the Beat: An Experience-dependent Complex Integration of Multisensory Information Involving Multiple Levels of the Nervous System

In a series of studies we have shown that movement (or vestibular stimulation) that is synchronized to every second or every third beat of a metrically ambiguous rhythm pattern biases people to perceive the meter as a march or as a waltz, respectively. Riggle (this volume) claims that we postulate an "innate", "specialized brain unit" for beat perception that is "directly" influenced by vestibular input. In fact, to the contrary, we argue that experience likely plays a large role in the development of rhythmic auditory-movement interactions, and that rhythmic processing in the brain is widely distributed and includes subcortical and cortical areas involved in sound processing and movement. Further, we argue that vestibular and auditory information are integrated at various subcortical and cortical levels along with input from other sensory modalities, and it is not clear which levels are most important for rhythm processing or, indeed, what a "direct" influence of vestibular input would mean. Finally, we argue that vestibular input to sound location mechanisms may be involved, but likely cannot explain the influence of vestibular input on the perception of auditory rhythm. This remains an empirical question for future research

Function of the ventral premotor cortex in auditory-motor integration of musical rhythm

Die Tendenz, sich mit einem musikalischen Puls zu synchronisieren wird als kulturübergreifende Universalie betrachtet. Dennoch ist bisher unklar geblieben, welche neuronalen Mechanismen den Drang und die Fähigkeit zur zeitlich akkuraten audio-motorischen Kopplung verursachen. Die vorliegende Arbeit demonstriert mittels funktioneller Bildgebung und nicht-invasiver Stimulation eine kausale Rolle des ventralen prämotorischen Kortex (PMv), einer motorischen Hirnregion mit ausgeprägten Verbindungen zu auditorischen Arealen, bei der audio-motorischen Integration von Rhythmus. Die Ergebnisse legen nahe, dass der PMv sowohl bei perzeptueller Präferenz, als auch bei motorischer Kopplung an einen Rhythmus kritisch beteiligt ist. Hierbei werden weitere unterstützende neuronale Mechanismen identifiziert und ein neuroanatomisch grundiertes Modell der audio-motorischen Integration von Rhythmus vorgestellt, das die Ergebnisse in den Kontext sensomotorischer Kontrolle und Kognition einordnet. The tendency to move in synchrony with an auditory rhythmical pulse is considered a human universal. Nevertheless, it remains unknown, which neural mechanisms give rise to the urge and ability to accurately couple one's own movements to an auditory rhythm. Using functional magnetic resonance imaging (fMRI) and transcranial magnetic stimulation (TMS), the present thesis demonstrates a causal contribution of a motor-related brain region with prominent connections to auditory areas - the ventral premotor cortex (PMv) - to auditory-motor integration of musical rhythm. The current findings suggest a critical role of the PMv in both perceptual preference of and motor coupling to a musical rhythm and reveal additional neural mechanisms that support auditory-motor timing. The thesis provides a neuroanatomically grounded model for auditory-motor integration of rhythm which incorporates the present experimental findings into a framework of sensorimotor control and cognition

Identifying a brain network for musical rhythm: A functional neuroimaging meta-analysis and systematic review

We conducted a systematic review and meta-analysis of 30 functional magnetic resonance imaging studies investigating processing of musical rhythms in neurotypical adults. First, we identified a general network for musical rhythm, encompassing all relevant sensory and motor processes (Beat-based, rest baseline, 12 contrasts) which revealed a large network involving auditory and motor regions. This network included the bilateral superior temporal cortices, supplementary motor area (SMA), putamen, and cerebellum. Second, we identified more precise loci for beat-based musical rhythms (Beat-based, audio-motor control, 8 contrasts) in the bilateral putamen. Third, we identified regions modulated by beat based rhythmic complexity (Complexity, 16 contrasts) which included the bilateral SMA-proper/pre-SMA, cerebellum, inferior parietal regions, and right temporal areas. This meta-analysis suggests that musical rhythm is largely represented in a bilateral cortico-subcortical network. Our findings align with existing theoretical frameworks about auditory-motor coupling to a musical beat and provide a foundation for studying how the neural bases of musical rhythm may overlap with other cognitive domains

Finding rhythm through auditory imagery: an approach to Parkinson’s Disease treatment

The following research article explores music therapy in the treatment of Parkinson’s Disease (PD). The general interaction between the rhythmic properties of music and motor associated brain areas is discussed at length. These interactions provide a basis for understanding how music therapy can address the rhythmic impairments of the disease. Dance therapy, Musical Sonification, Rhythmic Auditory Stimulation (RAS) are three types of music-based therapies that have been found to be effective in treating the motor symptoms of PD. These therapies may be particularly effective for the PD population because they draw upon musical rhythm as an external pacing cue.While external pacing cues have been found to help PD patients entrain to rhythm, research has not yet explored how rhythm can be internalized over time. The current article proposes that the experience of Involuntary Musical Imagery (INMI) may offer patients a means of creating an internalized representation of rhythm that can be maintained beyond the therapeutic setting. Strategies to increase the occurrence of INMI are explored, accounting for individual differences and certain musical characteristics. In addition to advocating for music-based therapies in the treatment of PD, there also calls for increased research on how INMI may be incorporated into these therapies

The Effects Of Transcranial Direct Current Stimulation On Beat Perception And Motor Performance

Humans have an intrinsic tendency to move to music. However, our understanding of the neural mechanisms underlying the music-movement connection remains limited, and most studies have used correlational methods. Here, we used transcranial direct current stimulation (tDCS) to causally investigate the role of four motor brain regions involved in movement timing and beat perception: the supplementary motor area (SMA), left and right premotor cortices (PMC), and cerebellum. Subjects were randomly assigned to a brain region to be stimulated and received anodal, cathodal, or sham stimulation on three different days while they reproduced rhythmic sequences. The sequences had either a strong beat percept, weak beat percept, or no beat percept. We predicted that SMA stimulation would affect reproduction of strong beat rhythms, whereas PMC and cerebellar stimulation would affect reproduction of weak or non-beat rhythms. No difference in reproduction accuracy was found based on brain region or type of stimulation