Individual Differences in Rhythm Skills: Links with Neural Consistency and Linguistic Ability

The role of acoustic features of maternal infant-directed singing in enhancing infant sensorimotor, language and socioemotional development

The quality of infant-directed speech (IDS) and infant-directed singing (IDSi) are considered vital to children, but empirical studies on protomusical qualities of the IDSi influencing infant development are rare. The current prospective study examines the role of IDSi acoustic features, such as pitch variability, shape and movement, and vocal amplitude vibration, timbre, and resonance, in associating with infant sensorimotor, language, and socioemotional development at six and 18 months. The sample consists of 236 Palestinian mothers from Gaza Strip singing to their six-month-olds a song by their own choice. Maternal IDSi was recorded and analyzed by the OpenSMILE- tool to depict main acoustic features of pitch frequencies, variations, and contours, vocal intensity, resonance formants, and power. The results are based on completed 219 maternal IDSi. Mothers reported about their infants' sensorimotor, language-vocalization, and socioemotional skills at six months, and psychologists tested these skills by Bayley Scales for Infant Development at 18 months. Results show that maternal IDSi characterized by wide pitch variability and rich and high vocal amplitude and vibration were associated with infants' optimal sensorimotor, language vocalization, and socioemotional skills at six months, and rich and high vocal amplitude and vibration predicted these optimal developmental skills also at 18 months. High resonance and rhythmicity formants were associated with optimal language and vocalization skills at six months. To conclude, the IDSi is considered important in enhancing newborn and risk infants' wellbeing, and the current findings argue that favorable acoustic singing qualities are crucial for optimal multidomain development across infancy.

Unravelling individual rhythmic abilities using machine learning

Humans can easily extract the rhythm of a complex sound, like music, and move to its regular beat, like in dance. These abilities are modulated by musical training and vary significantly in untrained individuals. The causes of this variability are multidimensional and typically hard to grasp in single tasks. To date we lack a comprehensive model capturing the rhythmic fingerprints of both musicians and non-musicians. Here we harnessed machine learning to extract a parsimonious model of rhythmic abilities, based on behavioral testing (with perceptual and motor tasks) of individuals with and without formal musical training (n = 79). We demonstrate that variability in rhythmic abilities and their link with formal and informal music experience can be successfully captured by profiles including a minimal set of behavioral measures. These findings highlight that machine learning techniques can be employed successfully to distill profiles of rhythmic abilities, and ultimately shed light on individual variability and its relationship with both formal musical training and informal musical experiences.

Can rhythm-mediated reward boost learning, memory, and social connection? Perspectives for future research

Studies of rhythm processing and of reward have progressed separately, with little connection between the two. However, consistent links between rhythm and reward are beginning to surface, with research suggesting that synchronization to rhythm is rewarding, and that this rewarding element may in turn also boost this synchronization. The current mini review shows that the combined study of rhythm and reward can be beneficial to better understand their independent and combined roles across two central aspects of cognition: 1) learning and memory, and 2) social connection and interpersonal synchronization; which have so far been studied largely independently. From this basis, it is discussed how connections between rhythm and reward can be applied to learning and memory and social connection across different populations, taking into account individual differences, clinical populations, human development, and animal research. Future research will need to consider the rewarding nature of rhythm, and that rhythm can in turn boost reward, potentially enhancing other cognitive and social processes.

Sensorimotor and working memory systems jointly support development of perceptual rhythm processing

We studied the role of sensorimotor and working memory systems in supporting development of perceptual rhythm processing with 119 participants aged 7-12 years. Children were assessed for their abilities in sensorimotor synchronization (SMS; beat tapping), auditory working memory (AWM; digit span), and rhythm discrimination (RD; same/different judgment on a pair of musical rhythm sequences). Multiple regression analysis revealed that children's RD performance was independently predicted by higher beat tapping consistency and greater digit span score, with all other demographic variables (age, sex, socioeconomic status, music training) controlled. The association between RD and SMS was more robust in the slower tempos (60 and 100 beats-per-minute (BPM)) than faster ones (120 and 180 BPM). Critically, the relation of SMS to RD was moderated by age in that RD performance was predicted by beat tapping consistency in younger children (age: 7-9 years), but not in older children (age: 10-12 years). AWM was the only predictor of RD in older children. Together, the current findings demonstrate that the sensorimotor and working memory systems jointly support RD processing during middle-to-late childhood and that the degree of association between the two systems and perceptual rhythm processing is shifted before entering into early adolescence.

The Musical Abilities, Pleiotropy, Language, and Environment (MAPLE) Framework for Understanding Musicality-Language Links Across the Lifespan

Using individual differences approaches, a growing body of literature finds positive associations between musicality and language-related abilities, complementing prior findings of links between musical training and language skills. Despite these associations, musicality has been often overlooked in mainstream models of individual differences in language acquisition and development. To better understand the biological basis of these individual differences, we propose the Musical Abilities, Pleiotropy, Language, and Environment (MAPLE) framework. This novel integrative framework posits that musical and language-related abilities likely share some common genetic architecture (i.e., genetic pleiotropy) in addition to some degree of overlapping neural endophenotypes, and genetic influences on musically and linguistically enriched environments. Drawing upon recent advances in genomic methodologies for unraveling pleiotropy, we outline testable predictions for future research on language development and how its underlying neurobiological substrates may be supported by genetic pleiotropy with musicality. In support of the MAPLE framework, we review and discuss findings from over seventy behavioral and neural studies, highlighting that musicality is robustly associated with individual differences in a range of speech-language skills required for communication and development. These include speech perception-in-noise, prosodic perception, morphosyntactic skills, phonological skills, reading skills, and aspects of second/foreign language learning. Overall, the current work provides a clear agenda and framework for studying musicality-language links using individual differences approaches, with an emphasis on leveraging advances in the genomics of complex musicality and language traits.

You got rhythm, or more: The multidimensionality of rhythmic abilities

Humans have a remarkable capacity for perceiving and producing rhythm. Rhythmic competence is often viewed as a single concept, with participants who perform more or less accurately on a single rhythm task. However, research is revealing numerous sub-processes and competencies involved in rhythm perception and production, which can be selectively impaired or enhanced. To investigate whether different patterns of performance emerge across tasks and individuals, we measured performance across a range of rhythm tasks from different test batteries. Distinct performance patterns could potentially reveal separable rhythmic competencies that may draw on distinct neural mechanisms. Participants completed nine rhythm perception and production tasks selected from the Battery for the Assessment of Auditory Sensorimotor and Timing Abilities (BAASTA), the Beat Alignment Test (BAT), the Beat-Based Advantage task (BBA), and two tasks from the Burgundy best Musical Aptitude Test (BbMAT). Principal component analyses revealed clear separation of task performance along three main dimensions: production, beat-based rhythm perception, and sequence memory-based rhythm perception. Hierarchical cluster analyses supported these results, revealing clusters of participants who performed selectively more or less accurately along different dimensions. The current results support the hypothesis of divergence of rhythmic skills. Based on these results, we provide guidelines towards a comprehensive testing of rhythm abilities, including at least three short tasks measuring: (1) rhythm production (e.g., tapping to metronome/music), (2) beat-based rhythm perception (e.g., BAT), and (3) sequence memory-based rhythm processing (e.g., BBA). Implications for underlying neural mechanisms, future research, and potential directions for rehabilitation and training programs are discussed.

Short-Term Memory for Auditory Temporal Patterns and Meaningless Sentences Predicts Learning of Foreign Word Forms

The ability to accurately repeat meaningless nonwords or lists of spoken digits in correct order have been associated with vocabulary acquisition in both first and second language. Individual differences in these tasks are thought to depend on the phonological loop component of working memory. However, phonological working memory may itself depend on more elementary processes. We asked whether auditory non-verbal short-term memory (STM) for patterns in time supports immediate recall of speech-based sequences. Participants tapped temporal sequences consisting of short and long beeps and repeated nonsense sentences sounding like their native language or an unfamiliar language. As a language learning task, they also memorized familiar-word–foreign-word pairs. Word learning was directly predicted by nonsense sentence repetition accuracy. It was also predicted by temporal pattern STM. However, this association was mediated by performance on the repetition measure. We propose that STM for temporal patterns may reflect a component skill that provides the context signal necessary to encode order in phonological STM. It would be needed to support representation of the prosodic profile of language material, which allows syllables in words and words in sentences to be ordered and temporally grouped for short-term representation and long-term learning.

Memory-Paced Tapping to Auditory Rhythms: Effects of Rate, Speech, and Motor Engagement

PURPOSE

Humans have a near-automatic tendency to entrain their motor actions to rhythms in the environment. Entrainment has been hypothesized to play an important role in processing naturalistic stimuli, such as speech and music, which have intrinsically rhythmic properties. Here, we studied two facets of entraining one's rhythmic motor actions to an external stimulus: (a) synchronized finger tapping to auditory rhythmic stimuli and (b) memory-paced reproduction of a previously heard rhythm.

METHOD

Using modifications of the Synchronization-Continuation tapping paradigm, we studied how these two rhythmic behaviors were affected by different stimulus and task features. We tested synchronization and memory-paced tapping for a broad range of rates, from stimulus onset asynchrony of subsecond to suprasecond, both for strictly isochronous tone sequences and for rhythmic speech stimuli (counting from 1 to 10), which are more ecological yet less isochronous. We also asked what role motor engagement plays in forming a stable internal representation for rhythms and guiding memory-paced tapping.

RESULTS AND CONCLUSIONS

Our results show that individuals can flexibly synchronize their motor actions to a very broad range of rhythms. However, this flexibility does not extend to memory-paced tapping, which is accurate only in a narrower range of rates, around ~1.5 Hz. This pattern suggests that intrinsic rhythmic defaults in the auditory and/or motor system influence the internal representation of rhythms, in the absence of an external pacemaker. Interestingly, memory-paced tapping for speech rhythms and simple tone sequences shared similar "optimal rates," although with reduced accuracy, suggesting that internal constraints on rhythmic entrainment generalize to more ecological stimuli. Last, we found that actively synchronizing to tones versus passively listening to them led to more accurate memory-paced tapping performance, which emphasizes the importance of action-perception interactions in forming stable entrainment to external rhythms.

Rhythmic subvocalization: An eye-tracking study on silent poetry reading

The present study investigates effects of conventionally metered and rhymed poetry on eyemovements in silent reading. Readers saw MRRL poems (i.e., metrically regular, rhymed language) in two layouts. In poem layout, verse endings coincided with line breaks. In prose layout verse endings could be mid-line. We also added metrical and rhyme anomalies. We hypothesized that silently reading MRRL results in building up auditive expectations that are based on a rhythmic “audible gestalt” and propose that rhythmicity is generated through subvocalization. Our results revealed that readers were sensitive to rhythmic-gestalt-anomalies but showed differential effects in poem and prose layouts. Metrical anomalies in particular resulted in robust reading disruptions across a variety of eye-movement measures in the poem layout and caused re-reading of the local context. Rhyme anomalies elicited stronger effects in prose layout and resulted in systematic re-reading of pre-rhymes. The presence or absence of rhythmic-gestalt-anomalies, as well as the layout manipulation, also affected reading in general. Effects of syllable number indicated a high degree of subvocalization. The overall pattern of results suggests that eye-movements reflect, and are closely aligned with, the rhythmic subvocalization of MRRL.

This study introduces a two-stage approach to the analysis of long MRRL stimuli and contributes to the discussion of how the processing of rhythm in music and speech may overlap.

Rhythm and timing as vulnerabilities in neurodevelopmental disorders

Millions of children are impacted by neurodevelopmental disorders (NDDs), which unfold early in life, have varying genetic etiologies and can involve a variety of specific or generalized impairments in social, cognitive and motor functioning requiring potentially lifelong specialized supports. While specific disorders vary in their domain of primary deficit (e.g. autism spectrum disorder (social), attention-deficit/hyperactivity disorder (attention), developmental coordination disorder (motor) and developmental language disorder (language)), comorbidities between NDDs are common. Intriguingly, many NDDs are associated with difficulties in skills related to rhythm, timing and synchrony though specific profiles of rhythm/timing impairments vary across disorders. Impairments in rhythm/timing may instantiate vulnerabilities for a variety of NDDs and may contribute to both the primary symptoms of each disorder as well as the high levels of comorbidities across disorders. Drawing upon genetic, neural, behavioural and interpersonal constructs across disorders, we consider how disrupted rhythm and timing skills early in life may contribute to atypical developmental cascades that involve overlapping symptoms within the context of a disorder's primary deficits. Consideration of the developmental context, as well as common and unique aspects of the phenotypes of different NDDs, will inform experimental designs to test this hypothesis including via potential mechanistic intervention approaches. This article is part of the theme issue 'Synchrony and rhythm interaction: from the brain to behavioural ecology'.

The effect of therapeutic instrumental music performance method on upper extremity functions in adolescent cerebral palsy

The aim of the study is to investigate the improvement of upper extremity functions with piano training of adolescent cerebral palsy. Nine adolescent cerebral palsy patients admitted to the Pediatric Disability Clinic between 2018 and 2020 and 9 healthy adolescent volunteers as control group were included. Therapeutic Instrumental Music Performance method was applied 2 days a week, 3 months in 40-min sessions. Before/after intervention, MACS, Box Block Test, Nine-Hole Peg Test, Jamar hand dynamometer and key pressing force of fingers were evaluated with Cubase MIDI program. Five of our patients included in the study were spastic hemiplegic and 4 were spastic diplegic cerebral palsy. All measurements made after intervention were found to be statistically significant compared to the measurements made before piano training (p < 0.05). The fingers that improved the most in the key pressing force of the fingers were found as the right hand 4th, left hand the 4th and 5th fingers (p < 0.01). A significant strong negative relationship was detected between the Box Block Test and the Nine-Hole Peg Test (p < 0.001). With therapeutic instrumental music performance method, functional gains can be achieved in the grip strength, strengths of the fingers, gross and fine motor skills of adolescent cerebral palsy patients. Further studies are needed to establish a piano training protocol in neurological music therapy.

Rhythm, reading, and sound processing in the brain in preschool children

A child's success in school relies on their ability to quickly grasp language and reading skills, the foundations of which are acquired even before entering a formal classroom setting. Previous studies in preschoolers have begun to establish relationships linking beat synchronization, preliteracy skills, and auditory processing. Beat synchronization involves the integration of sensorimotor systems with auditory and cognitive circuits and, therefore calls on many of the same neural networks as language. Using a drumming task, we analyzed the relationship between children's ability to maintain an isochronous beat with preliteracy skills and frequency following responses (FFRs) in over 150 preschoolers. We show that preschoolers who performed well on the beat synchronization task outscored their peers on all preliteracy measures and had more robust FFRs. Furthermore, the good synchronizers experienced less degradation of certain FFR measures when listening in noise. Together, our results are consistent with the view that rhythm, preliteracy, and auditory processing are interconnected during early childhood.

Reading ability in children relates to rhythm perception across modalities

The onset of reading ability is rife with individual differences, with some children termed "early readers" and some falling behind from the very beginning. Reading skill in children has been linked to an ability to remember nonverbal rhythms, specifically in the auditory modality. It has been hypothesized that the link between rhythm skills and reading reflects a shared reliance on the ability to extract temporal structure from sound. Here we tested this hypothesis by investigating whether the link between rhythm memory and reading depends on the modality in which rhythms are presented. We tested 75 primary school-aged children aged 7-11 years on a within-participants battery of reading and rhythm tasks. Participants received a reading efficiency task followed by three rhythm tasks (auditory, visual, and audiovisual). Results showed that children who performed poorly on the reading task also performed poorly on the tasks that required them to remember and repeat back nonverbal rhythms. In addition, these children showed a rhythmic deficit not just in the auditory domain but also in the visual domain. However, auditory rhythm memory explained additional variance in reading ability even after controlling for visual memory. These results suggest that reading ability and rhythm memory rely both on shared modality-general cognitive processes and on the ability to perceive the temporal structure of sound.

Clapping in Time With Feedback Relates Pervasively With Other Rhythmic Skills of Adolescents and Young Adults

Rhythmic expertise is a multidimensional skill set with clusters of distinct rhythmic abilities. For example, the ability to clap in time with feedback relates extensively to distinct beat- and pattern-based rhythmic skills in school-age children. In this study we aimed to determine whether clapping in time would relate to both beat- and pattern- based rhythmic tasks among adolescents and young adults. We assessed our participants on seven tasks: two beat-based tasks (Metronome and Tempo adaptation), two pattern-based tasks (Reproducing rhythmic patterns and Remembering rhythmic patterns), a self-paced drumming task, a task of drumming to a music beat, and a clapping in time task. We found that clapping in time correlated with all other rhythmic tasks, even though some were not mutually related to one another. These results provide insight into the taxonomy of rhythmic skills and support the practice of clapping in time with feedback as a means of developing broad spectrum rhythmic abilities.

Attentional modulation of neural entrainment to sound streams in children with and without ADHD

To extract meaningful information from complex auditory scenes like a noisy playground, rock concert, or classroom, children can direct attention to different sound streams. One means of accomplishing this might be to align neural activity with the temporal structure of a target stream, such as a specific talker or melody. However, this may be more difficult for children with ADHD, who can struggle with accurately perceiving and producing temporal intervals. In this EEG study, we found that school-aged children's attention to one of two temporally-interleaved isochronous tone 'melodies' was linked to an increase in phase-locking at the melody's rate, and a shift in neural phase that aligned the neural responses with the attended tone stream. Children's attention task performance and neural phase alignment with the attended melody were linked to performance on temporal production tasks, suggesting that children with more robust control over motor timing were better able to direct attention to the time points associated with the target melody. Finally, we found that although children with ADHD performed less accurately on the tonal attention task than typically developing children, they showed the same degree of attentional modulation of phase locking and neural phase shifts, suggesting that children with ADHD may have difficulty with attentional engagement rather than attentional selection.

Distinct rhythmic abilities align with phonological awareness and rapid naming in school-age children

Difficulty in performing rhythmic tasks often co-occurs with literacy difficulties. Motivated by evidence showing that people can vary in their performance across different rhythmic tasks, we asked whether two rhythmic skills identified as distinct in school-age children and young adults would reveal similar or different relationships with two literacy skills known to be important for successful reading development. We addressed our question by focusing on 55 typically developing children (ages 5-8). Results show that drumming to a beat predicted the variability of rapid naming but not of phonological awareness, whereas tapping rhythmic patterns predicted phonological awareness, but not rapid naming. Our finding suggests that rhythmic interventions can be tailored to address PA and RAN deficits specifically in reading disabled children.

Active and Passive Rhythmic Music Therapy Interventions Differentially Modulate Sympathetic Autonomic Nervous System Activity

Dysregulation of the autonomic nervous system (ANS) and the hypothalamic-pituitary-adrenal (HPA) axis has been implicated in psychiatric disorders. Music therapy (MT) has been shown to modulate heart-rate variability (HRV) and salivary stress markers, physiological markers of the ANS and HPA axes, respectively. Given the prominent role of arousal and stress physiology in many psychiatric disorders, MT has the potential to provide therapeutic benefits in psychiatry. Active MT requires patients to engage rhythmically with music; in contrast, passive MT requires patients to listen to music, eliminating the rhythmic movement seen in active MT. Yet, it remains unknown whether active or passive MT differentially modulates arousal and stress physiology. We contrasted the effects of active and passive MT experiences to examine the differential impact of rhythmic movement on the ANS and HPA axes in healthy participants. Individuals (N = 16) participated in a crossover study of 40 min of an active MT and a passive MT intervention. HRV recordings and saliva samples were collected both before and after each intervention. The high-frequency component (HF) and the ratio of low-frequency to high-frequency components (LF/HF) were calculated as cardiac markers of parasympathetic and sympathetic ANS activation, respectively. Saliva samples were analyzed for alpha-amylase and cortisol, markers of the sympathetic ANS and HPA axes, respectively. Active MT and passive MT interventions differentially modulated LF/HF, where active MT decreased LF/HF and passive MT increased LF/HF. These results indicate that MT affects the ANS and suggests that differences in engagement between active MT and passive MT lead to a differential modulation of the sympathetic ANS.

Successful second language learning is tied to robust domain-general auditory processing and stable neural representation of sound

There is a great deal of individual variability in outcome in second language learning, the sources of which are still poorly understood. We hypothesized that individual differences in auditory processing may account for some variability in second language learning. We tested this hypothesis by examining psychoacoustic thresholds, auditory-motor temporal integration, and auditory neural encoding in adult native Polish speakers living in the UK. We found that precise English vowel perception and accurate English grammatical judgment were linked to lower psychoacoustic thresholds, better auditory-motor integration, and more consistent frequency-following responses to sound. Psychoacoustic thresholds and neural sound encoding explained independent variance in vowel perception, suggesting that they are dissociable indexes of sound processing. These results suggest that individual differences in second language acquisition success stem at least in part from domain-general difficulties with auditory perception, and that auditory training could help facilitate language learning in some individuals with specific auditory impairments.

Intrinsic Rhythmicity Predicts Synchronization-Continuation Entrainment Performance

Rhythmic entrainment-defined as a stable temporal relationship between external periodic signals and endogenous rhythmic processes-allows individuals to coordinate with environmental rhythms. However, the impact of inter-individual differences on entrainment processes as a function of the tempo of external periodic signals remain poorly understood. To better understand the effects of endogenous differences and varying tempos on rhythmic entrainment, 20 young healthy adults participated in a spontaneous motor tempo (SMT) task and synchronization-continuation tasks at three experimental tempos (50, 70, and 128 bpm; 1200, 857, and 469 ms inter onset interval (IOI)). We hypothesized that SMT task performance and tempo would influence externally paced synchronization-continuation task behavior. Indeed, intrinsic rhythmicity assessed through the SMT task predicted performance in the externally paced task, allowing us to characterize differences in entrainment behavior between participants with low and high endogenous rhythmicity. High rhythmicity individuals, defined by better SMT performance, deviated from externally paced pulses sooner than individuals with low rhythmicity, who were able to maintain externally paced pulses for longer. The magnitude of these behavioral differences depended on the experimental tempo of the synchronization-continuation task. Our results indicate that differences in intrinsic rhythmicity vary between individuals and relate to tempo-dependent entrainment performance.

Clapping in time parallels literacy and calls upon overlapping neural mechanisms in early readers

The auditory system is extremely precise in processing the temporal information of perceptual events and using these cues to coordinate action. Synchronizing movement to a steady beat relies on this bidirectional connection between sensory and motor systems, and activates many of the auditory and cognitive processes used when reading. Here, we use Interactive Metronome, a clinical intervention technology requiring an individual to clap her hands in time with a steady beat, to investigate whether the links between literacy and synchronization skills, previously established in older children, are also evident in children who are learning to read. We tested 64 typically developing children (ages 5-7 years) on their synchronization abilities, neurophysiological responses to speech in noise, and literacy skills. We found that children who have lower variability in synchronizing have higher phase consistency, higher stability, and more accurate envelope encoding-all neurophysiological response components linked to language skills. Moreover, performing the same task with visual feedback reveals links with literacy skills, notably processing speed, phonological processing, word reading, spelling, morphology, and syntax. These results suggest that rhythm skills and literacy call on overlapping neural mechanisms, supporting the idea that rhythm training may boost literacy in part by engaging sensory-motor systems.

Predictive rhythmic tapping to isochronous and tempo changing metronomes in the nonhuman primate

Beat entrainment is the ability to entrain one's movements to a perceived periodic stimulus, such as a metronome or a pulse in music. Humans have a capacity to predictively respond to a periodic pulse and to dynamically adjust their movement timing to match the varying music tempos. Previous studies have shown that monkeys share some of the human capabilities for rhythmic entrainment, such as tapping regularly at the period of isochronous stimuli. However, it is still unknown whether monkeys can predictively entrain to dynamic tempo changes like humans. To address this question, we trained monkeys in three tapping tasks and compared their rhythmic entrainment abilities with those of humans. We found that, when immediate feedback about the timing of each movement is provided, monkeys can predictively entrain to an isochronous beat, generating tapping movements in anticipation of the metronome pulse. This ability also generalized to a novel untrained tempo. Notably, macaques can modify their tapping tempo by predicting the beat changes of accelerating and decelerating visual metronomes in a manner similar to humans. Our findings support the notion that nonhuman primates share with humans the ability of temporal anticipation during tapping to isochronous and smoothly changing sequences of stimuli.

Monkeys share the neurophysiological basis for encoding sound periodicities captured by the frequency-following response with humans

The extraction and encoding of acoustical temporal regularities are fundamental for human cognitive auditory abilities such as speech or beat entrainment. Because the comparison of the neural sensitivity to temporal regularities between human and animals is fundamental to relate non-invasive measures of auditory processing to their neuronal basis, here we compared the neural representation of auditory periodicities between human and non-human primates by measuring scalp-recorded frequency-following response (FFR). We found that rhesus monkeys can resolve the spectrotemporal structure of periodic stimuli to a similar extent as humans by exhibiting a homologous FFR potential to the speech syllable /da/. The FFR in both species is robust and phase-locked to the fundamental frequency of the sound, reflecting an effective neural processing of the fast-periodic information of subsyllabic cues. Our results thus reveal a conserved neural ability to track acoustical regularities within the primate order. These findings open the possibility to study the neurophysiology of complex sound temporal processing in the macaque subcortical and cortical areas, as well as the associated experience-dependent plasticity across the auditory pathway in behaving monkeys.

The Paradox of Isochrony in the Evolution of Human Rhythm

Isochrony is crucial to the rhythm of human music. Some neural, behavioral and anatomical traits underlying rhythm perception and production are shared with a broad range of species. These may either have a common evolutionary origin, or have evolved into similar traits under different evolutionary pressures. Other traits underlying rhythm are rare across species, only found in humans and few other animals. Isochrony, or stable periodicity, is common to most human music, but isochronous behaviors are also found in many species. It appears paradoxical that humans are particularly good at producing and perceiving isochronous patterns, although this ability does not conceivably confer any evolutionary advantage to modern humans. This article will attempt to solve this conundrum. To this end, we define the concept of isochrony from the present functional perspective of physiology, cognitive neuroscience, signal processing, and interactive behavior, and review available evidence on isochrony in the signals of humans and other animals. We then attempt to resolve the paradox of isochrony by expanding an evolutionary hypothesis about the function that isochronous behavior may have had in early hominids. Finally, we propose avenues for empirical research to examine this hypothesis and to understand the evolutionary origin of isochrony in general.