Phrasing in prelinguistic vocalizations

Canonical babbling trajectories across the first year of life in autism and typical development

LAY ABSTRACT

Our study examined how babies develop their ability to talk to help identify early signs of autism. We looked at babies' production of babbling with mature syllables across the first year of life. Babies usually start producing mature babbling at 7 months of age before they say their first words. Some studies have suggested that babies who are later diagnosed with autism produce this kind of babbling less frequently in their first year of life, but other studies have shown complicated outcomes. In this new study, we followed 44 autistic babies and compared them to 127 typically developing babies. We recorded the babies once every month, all day long, from the time that they were born until they were around 13 months old. Then, we studied their mature babbling from segments of these recordings. We found that the rate at which babies used mature babbling was lower in boys with autism, and higher in girls with autism, compared to babies without autism. This research helps us understand how babies with autism learn to talk. It also raises important questions about differences between boys and girls with autism. Our study can help us improve how scientists and clinicians can identify autism earlier, which could lead to better communication supports for autistic children and their families.

Foundations of Vocal Category Development in Autistic Infants

The present study compared the infant's tendency in the first year of life to produce clusters of particular vocal types (squeals, vocants, and growls) in typically developing (TD) and autistic infants. Vocal clustering provides evidence of vocal category formation and may establish a foundation for speech development. Specifically, we compared the extent of vocal clustering across outcome groups and age groups. We also examined the associations between the extent of vocal clustering and later outcomes at 2 years within the autistic group. Randomly selected 5-min segments (27,153 5-min segments total) from 1293 all-day home recordings from 103 TD infants and 44 autistic infants across the first year were humancoded (about 9.75 h of data coded per infant on average) to derive vocal clustering patterns. Fisher's exact tests were used to compare the occurrence of squeals versus vocants, as well as growls versus vocants, across coded segments. Infants in both groups demonstrated clear clustering patterns of squeals and growls across all age groups. The extent of vocal clustering in the autistic group did not correlate significantly with later language, repetitive behavior, or autism severity outcomes. These findings highlight the robustness of the systematic production of vocal categories across the first year of life. The similarity of the clustering patterns in the TD and autistic groups suggests that vocal category formation through active infant vocal exploration is a robust feature of early speech development.

Infant vocal category exploration as a foundation for speech development

Non-random exploration of infant speech-like vocalizations (e.g., squeals, growls, and vowel- like sounds or "vocants") is pivotal in speech development. This type of vocal exploration, often noticed when infants produce particular vocal types in clusters, serves two crucial purposes: it establishes a foundation for speech because speech requires formation of new vocal categories, and it serves as a basis for vocal signaling of wellness and interaction with caregivers. Despite the significance of clustering, existing research has largely relied on subjective descriptions and anecdotal observations regarding early vocal category formation. In this study, we aim to address this gap by presenting the first large-scale empirical evidence of vocal category exploration and clustering throughout the first year of life. We observed infant vocalizations longitudinally using all-day home recordings from 130 typically developing infants across the entire first year of life. To identify clustering patterns, we conducted Fisher's exact tests to compare the occurrence of squeals versus vocants, as well as growls versus vocants. We found that across the first year, infants demonstrated clear clustering patterns of squeals and growls, indicating that these categories were not randomly produced, but rather, it seemed, infants actively engaged in practice of these specific categories. The findings lend support to the concept of infants as manifesting active vocal exploration and category formation, a key foundation for vocal language.

Vocal Characteristics of Infants at Risk for Speech Motor Involvement: A Scoping Review

PURPOSE

The purpose of this scoping review was to (a) summarize methodological characteristics of studies examining vocal characteristics of infants at high risk for neurological speech motor involvement and (b) report the state of the high-quality evidence on vocal characteristic trends of infants diagnosed or at high risk for cerebral palsy (CP).

METHOD

The PRISMA (Preferred Reporting Items of Systematic Reviews and Meta-Analyses) extension for scoping reviews was followed for reporting our review. Studies measured prelinguistic vocal characteristics of infants under 24 months with birth risk or genetic conditions known to commonly present with speech motor involvement. Fifty-five studies met criteria for Part 1. Eleven studies met criteria for synthesis in Part 2.

RESULTS

A smaller percentage of studies examined infants with or at risk for CP compared to studies examining genetic conditions such as Down syndrome. The median year of publication was 1999, with a median sample size of nine participants. Most studies were conducted in laboratory settings and used human coding of vocalizations produced during caregiver-child interactions. Substantial methodological differences were noted across all studies. A small number of high-quality studies of infants with or at risk for CP revealed high rates of marginal babbling, low rates of canonical babbling, and limited consonant diversity under 24 months. Mixed findings were noted across studies of general birth risk factors.

CONCLUSIONS

There is limited evidence available to support the early detection of speech motor involvement. Large methodological differences currently impact the ability to synthesize findings across studies. There is a critical need to conduct longitudinal research with larger sample sizes and advanced, modern technologies to detect vocal precursors of speech impairment to support the accurate diagnosis and prognosis of speech development in infants with CP and other clinical populations.

Sex differences in infant vocalization and the origin of language

Seeking to discern the earliest sex differences in language-related activities, our focus is vocal activity in the first two years of life, following up on recent research that unexpectedly showed boys produced significantly more speech-like vocalizations (protophones) than girls during the first year of life.We now bring a much larger body of data to bear on the comparison of early sex differences in vocalization, data based on automated analysis of all-day recordings of infants in their homes. The new evidence, like that of the prior study, also suggests boys produce more protophones than girls in the first year and offers additional basis for informed speculation about biological reasons for these differences. More broadly, the work offers a basis for informed speculations about foundations of language that we propose to have evolved in our distant hominin ancestors, foundations also required in early vocal development of modern human infants.

Infant vocalizations elicit simplified speech in childcare

Infant babbling has an important social function in promoting early language development by attracting caregiver attention and prompting parents' contingent, simplified speech, which is more learnable for infants. Here, we demonstrate that prelinguistic infant vocalizations also create learning opportunities for infants in childcare settings by eliciting simplified and more learnable linguistic information during teacher-infant interactions. We compared the rates and complexity of contingent and non-contingent verbal interactions of 34 childcare teachers during a one-on-one free play interaction with a familiar infant under their care (M = 12.6 months old). As compared to non-contingent utterances, teachers' contingent utterances included fewer unique words, a higher proportion of single-word responses, and a shorter mean length of utterances. Teachers did not change their response length based on infants' syllable type and were equally likely to respond to vowels and consonant-vowel vocalizations. Sources of individual differences in the simplification effect related to infant behaviors and teacher characteristics are discussed. The results parallel previous findings demonstrating the simplification effect in parent-infant interactions. That teachers also show this simplification effect when responding to infant vocalizations suggests the power of infant prelinguistic vocalizations for organizing caregiver attention in various settings to elicit simplified, learnable language.

A Probe Study on Vocal Development in Two Infants at Risk for Cerebral Palsy

The present work examined canonical babbling ratios longitudinally as a measure of onset and consolidation of canonical babbling in two infants at risk of cerebral palsy (CP) between 5 and 16 months. Ten typically developing infants were included for comparison at 6, 9, 12, and 16-19 months. Canonical babbling ratios (CBRs) were calculated from 5-min segments, and follow-up diagnostic outcomes were collected between 24 and 33 months. The two infants at risk demonstrated low CBR growth trajectories compared to the typical infant group, and slightly different patterns of consolidation. The two infants at risk were later diagnosed with different levels of CP and speech impairment severity. All infants demonstrated greater variability than expected. Studying canonical babbling and other prelinguistic milestones in this population may inform our perspective of the involvement of the motor system in the vocal domain. Additional implications on the analysis of canonical babbling using all-day home recordings are discussed.

Emerging Verbal Functions in Early Infancy: Lessons from Observational and Computational Approaches on Typical Development and Neurodevelopmental Disorders

OBJECTIVES

Research on typically developing (TD) children and those with neurodevelopmental disorders and genetic syndromes was targeted. Specifically, studies on autism spectrum disorder, Down syndrome, Rett syndrome, fragile X syndrome, cerebral palsy, Angelman syndrome, tuberous sclerosis complex, Williams-Beuren syndrome, Cri-du-chat syndrome, Prader-Willi syndrome, and West syndrome were searched. The objectives are to review observational and computational studies on the emergence of (pre-)babbling vocalisations and outline findings on acoustic characteristics of early verbal functions.

METHODS

A comprehensive review of the literature was performed including observational and computational studies focusing on spontaneous infant vocalisations at the pre-babbling age of TD children, individuals with genetic or neurodevelopmental disorders.

RESULTS

While there is substantial knowledge about early vocal development in TD infants, the pre-babbling phase in infants with neurodevelopmental and genetic syndromes is scarcely scrutinised. Related approaches, paradigms, and definitions vary substantially and insights into the onset and characteristics of early verbal functions in most above-mentioned disorders are missing. Most studies focused on acoustic low-level descriptors (e.g. fundamental frequency) which bore limited clinical relevance. This calls for computational approaches to analyse features of infant typical and atypical verbal development.

CONCLUSIONS

Pre-babbling vocalisations as precursor for future speech-language functions may reveal valuable signs for identifying infants at risk for atypical development. Observational studies should be complemented by computational approaches to enable in-depth understanding of the developing speech-language functions. By disentangling features of typical and atypical early verbal development, computational approaches may support clinical screening and evaluation.

Perspectives on the origin of language: Infants vocalize most during independent vocal play but produce their most speech-like vocalizations during turn taking

A growing body of research emphasizes both endogenous and social motivations in human vocal development. Our own efforts seek to establish an evolutionary and developmental perspective on the existence and usage of speech-like vocalizations ("protophones") in the first year of life. We evaluated the relative occurrence of protophones in 40 typically developing infants across the second-half year based on longitudinal all-day recordings. Infants showed strong endogenous motivation to vocalize, producing vastly more protophones during independent vocal exploration and play than during vocal turn taking. Both periods of vocal play and periods of turn-taking corresponded to elevated levels of the most advanced protophones (canonical babbling) relative to periods without vocal play or without turn-taking. Notably, periods of turn taking showed even more canonical babbling than periods of vocal play. We conclude that endogenous motivation drives infants' tendencies to explore and display a great number of speech-like vocalizations, but that social interaction drives the production of the most speech-like forms. The results inform our previously published proposal that the human infant has been naturally selected to explore protophone production and that the exploratory inclination in our hominin ancestors formed a foundation for language.

The maturational gradient of infant vocalizations: Developmental stages and functional modules

Stage models have been influential in characterizing infant vocalizations in the first year of life. These models are basically descriptive and do not explain why certain types of vocal behaviors occur within a particular stage or why successive patterns of vocalization occur. This review paper summarizes and elaborates a theory of Developmental Functional Modules (DFMs) and discusses how maturational gradients in the DFMs explain age typical vocalizations as well as the transitions between successive stages or other static forms. Maturational gradients are based on biological processes that effect the reconfiguration and remodeling of the respiratory, laryngeal, and craniofacial systems during infancy. From a dynamic systems perspective, DFMs are part of a complex system with multiple degrees of freedom that can achieve stable performance with relatively few control variables by relying on principles such as synergies, self-organization, nonlinear performance, and movement variability.

Effects of mother's imitation on speech sounds in infants with Down syndrome

BACKGROUND

The Down syndrome behavioral phenotype includes delays in making speech sounds, production of more non-speech sounds than speech sounds, and contrasting strengths in social development. Within a behavior analytic framework, we conceptualize characteristics of the Down syndrome behavioral phenotype as creating a context for impairments in speech sound development that suggest interventions caregivers can use to improve speech sounds.

AIM AND METHOD

We examined one intervention, the effects of mother's contingent vocal imitation, on rate of speech and non-speech sound production in infants with Down syndrome using an ABAB design.

RESULTS

Mothers responded favorably to learning to imitate their infants' vocalizations and their contingent vocal imitation was associated with increases in infant speech sounds.

CONCLUSIONS

The increases in infant speech sound suggest the promise of this approach and future research examining variations in contingent vocal imitation and additional outcomes.

Protophones, the precursors to speech, dominate the human infant vocal landscape

Human infant vocalization is viewed as a critical foundation for vocal learning and language. All apes share distress sounds (shrieks and cries) and laughter. Another vocal type, speech-like sounds, common in human infants, is rare but not absent in other apes. These three vocal types form a basis for especially informative cross-species comparisons. To make such comparisons possible we need empirical research documenting the frequency of occurrence of all three. The present work provides a comprehensive portrayal of these three vocal types in the human infant from longitudinal research in various circumstances of recording. Recently, the predominant vocalizations of the human infant have been shown to be speech-like sounds, or 'protophones', including both canonical and non-canonical babbling. The research shows that protophones outnumber cries by a factor of at least five based on data from random-sampling of all-day recordings across the first year. The present work expands on the prior reports, showing the protophones vastly outnumber both cry and laughter in both all-day and laboratory recordings in various circumstances. The data provide new evidence of the predominance of protophones in the infant vocal landscape and illuminate their role in human vocal learning and the origin of language. This article is part of the theme issue 'Vocal learning in animals and humans'.

Association Between Symbolic Play and Language: A Comparison Between Typically Developing Children and Children with Down Syndrome

OBJECTIVE

Language and symbolic play require the same underlying symbolic ability and develop parallel to one another. The aim of this study was to determine the association between symbolic play and vocabulary in typically developing children and children with Down syndrome in Malaysia.

METHODS

Twenty-five typically developing children and 25 children with Down syndrome aged between 12 and 36 months were involved in this study. They were recruited from an early intervention center and various kindergartens from the West Coast of Peninsular Malaysia. Their play skills were assessed using the Symbolic Play Test Second Edition, and information about their vocabulary was obtained through the MacArthur Bates Communicative Development Inventories that was filled out by their parents.

RESULTS

There was a significant difference in the vocabulary and symbolic play scores of children with Down syndrome compared with typically developing children. There was also a positive correlation between symbolic play scores and receptive and expressive vocabulary scores for both groups of children.

CONCLUSION

When providing intervention, speech-language pathologists need to promote the development of symbolic play in addition to language, given the association between the two. They should also look into introducing an augmentative and alternative communication system to the children who demonstrate age-appropriate symbolic play skills but have trouble with symbolic language production.

Cross-linguistic comparison of utterance shapes in Korean- and English-learning children: An ambient language effect

This study compared vocal development in Korean- and English-learning infants and examined ambient-language effects focusing on predominant utterance shapes. Vocalization samples were obtained from 14 Korean-learning children and 14 English-learning children, who ranged in age from 9 to 21 months, in monolingual environments using day-long audio recordings. The analyzers, who were blind to participants' demographic information, identified utterance shapes to determine functional vocal repertoires through naturalistic listening simulating the caregiver's natural mode of listening. The results showed no cross-linguistic differences in the amount of vocal output or the proportion of canonical syllables. However, the infants from the two language backgrounds showed differences regarding the predominant canonical utterance shapes. The percentage of VCV utterances in Korean-learning children was higher than in English-learning children while CV syllables predominated in the English-learning children. We speculate that the difference between the predominant utterance shapes of Korean- and English-learning children could be associated with differences in early lexical items typically acquired in the two language groups.

Syllable duration changes during babbling: a longitudinal study of French infant productions

At the babbling stage, the syllable does not have the temporal characteristics of adult syllables because of the infant's limited oro-motor skills. This research aims to further our knowledge of syllable duration and temporal variability and their evolution with age as an indicator of the development of articulatory skills. The possible impact of syllable position, as well as that of type of intrasyllabic associations and intersyllabic articulatory changes on these parameters has also been tested. Oral productions of 22 French infants were recorded monthly from 8 to 14 months. 11 261 Consonant-Vowel (CV) syllables were annotated and temporally analyzed. The mean duration varied according to syllable position, but not to the intrasyllabic or intersyllabic articulatory changes. Moreover, the syllable duration decreased significantly from the age of 10 months onwards, whereas the temporal variability remained the same.

Efficient Collection and Representation of Preverbal Data in Typical and Atypical Development

Human preverbal development refers to the period of steadily increasing vocal capacities until the emergence of a child’s first meaningful words. Over the last decades, research has intensively focused on preverbal behavior in typical development. Preverbal vocal patterns have been phonetically classified and acoustically characterized. More recently, specific preverbal phenomena were discussed to play a role as early indicators of atypical development. Recent advancements in audio signal processing and machine learning have allowed for novel approaches in preverbal behavior analysis including automatic vocalization-based differentiation of typically and atypically developing individuals. In this paper, we give a methodological overview of current strategies for collecting and acoustically representing preverbal data for intelligent audio analysis paradigms. Efficiency in the context of data collection and data representation is discussed. Following current research trends, we set a special focus on challenges that arise when dealing with preverbal data of individuals with late detected developmental disorders, such as autism spectrum disorder or Rett syndrome.

Temporal Coordination in Mother-Infant Vocal Interaction: A Cross-Cultural Comparison

Temporal coordination of vocal exchanges between mothers and their infants emerges from a developmental process that relies on the ability of communication partners to co-coordinate and predict each other's turns. Consequently, the partners engage in communicative niche construction that forms a foundation for language in human infancy. While robust universals in vocal turn-taking have been found, differences in the timing of maternal and infant vocalizations have also been reported across cultures. In this study, we examine the temporal structure of vocal interactions in 38 mother-infant dyads in the first two years across two cultures-American and Lebanese-by studying observed and randomized distributions of vocalizations, focusing on both gaps and overlaps in naturalistic 10-min vocal interactions. We conducted a series of simulations using Kolmogorov-Smirnov (K-S) tests to examine whether the observed responsivity patterns differed from randomly generated simulations of responsivity patterns in both Arabic and English for mothers responding to infants and for infants responding to mothers. Results revealed that both mothers and infants engaged in conversational alternation, with mothers acting similarly across cultures. By contrast, significant differences were observed in the timing of infant responses to maternal utterances, with the Lebanese infants' tendency to cluster their responses in the first half-second after the offset of the Lebanese mothers' utterances to a greater extent than their American counterparts. We speculate that the results may be due to potential phonotactic differences between Arabic and English and/or to differing child-rearing practices across Lebanese and American cultures. The findings may have implications for early identification of developmental disorders such as autism spectrum disorders within and across cultures.

Acoustic properties of early vocalizations in infants with fragile X syndrome

Fragile X syndrome (FXS) is a neurogenetic syndrome characterized by cognitive impairments and high rates of autism spectrum disorder (ASD). FXS is often highlighted as a model for exploring pathways of symptom expression in ASD due to the high prevalence of ASD symptoms in this population and the known single-gene cause of FXS. Early vocalization features-including volubility, complexity, duration, and pitch-have shown promise in detecting ASD in idiopathic ASD populations but have yet to be extensively studied in a population with a known genetic cause for ASD such as FXS. Investigating early trajectories of these features in FXS may inform our limited knowledge of potential mechanisms that predict later social communication outcomes. The present study addresses this need by presenting preliminary findings which (a) characterize early vocalization features in FXS relative to low-risk controls (LRC) and (b) test the specificity of associations between these features and language and ASD outcomes. We coded vocalization features during a standardized child-examiner interaction for 39 nine-month-olds (22 FXS, 17 LRC) whose clinical outcomes were assessed at 24 months. Our results provide preliminary evidence that within FXS, associations between vocalization features and 24-month language outcomes may diverge from those observed in LRC, and that vocalization features may be associated with later ASD symptoms. These findings provide a starting point for more research exploring these features as potential early markers of ASD in FXS, which in turn may lead to improved early identification methods, treatment approaches, and overall well-being of individuals with ASD. Autism Res2019. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Although vocal features of 9-month-olds with FXS did not differ from those of low-risk controls, several features were associated with later language and ASD outcomes at 24 months in FXS. These preliminary results suggest acoustic data may be related to clinical outcomes in FXS and potentially other high-risk populations. Further characterizing these associations may facilitate understanding of biological mechanisms and risk factors associated with social communication development and ASD.

Preterm and full term infant vocalization and the origin of language

How did vocal language originate? Before trying to determine how referential vocabulary or syntax may have arisen, it is critical to explain how ancient hominins began to produce vocalization flexibly, without binding to emotions or functions. A crucial factor in the vocal communicative split of hominins from the ape background may thus have been copious, functionally flexible vocalization, starting in infancy and continuing throughout life, long before there were more advanced linguistic features such as referential vocabulary. 2-3 month-old modern human infants produce "protophones", including at least three types of functionally flexible non-cry precursors to speech rarely reported in other ape infants. But how early in life do protophones actually appear? We report that the most common protophone types emerge abundantly as early as vocalization can be observed in infancy, in preterm infants still in neonatal intensive care. Contrary to the expectation that cries are the predominant vocalizations of infancy, our all-day recordings showed that protophones occurred far more frequently than cries in both preterm and full-term infants. Protophones were not limited to interactive circumstances, but also occurred at high rates when infants were alone, indicating an endogenous inclination to vocalize exploratorily, perhaps the most fundamental capacity underlying vocal language.

Acoustic Correlates and Adult Perceptions of Distress in Infant Speech-Like Vocalizations and Cries

Prior research has not evaluated acoustic features contributing to perception of human infant vocal distress or lack thereof on a continuum. The present research evaluates perception of infant vocalizations along a continuum ranging from the most prototypical intensely distressful cry sounds ("wails") to the most prototypical of infant sounds that typically express no distress (non-distress "vocants"). Wails are deemed little if at all related to speech while vocants are taken to be clear precursors to speech. We selected prototypical exemplars of utterances representing the whole continuum from 0 and 1 month-olds. In this initial study of the continuum, our goals are to determine (1) listener agreement on level of vocal distress across the continuum, (2) acoustic parameters predicting ratings of distress, (3) the extent to which individual listeners maintain or change their acoustic criteria for distress judgments across the study, (4) the extent to which different listeners use similar or different acoustic criteria to make judgments, and (5) the role of short-term experience among the listeners in judgments of infant vocalization distress. Results indicated that (1) both inter-rater and intra-rater listener agreement on degree of vocal distress was high, (2) the best predictors of vocal distress were number of vibratory regimes within utterances, utterance duration, spectral ratio (spectral concentration) in vibratory regimes within utterances, and mean pitch, (3) individual listeners significantly modified their acoustic criteria for distress judgments across the 10 trial blocks, (4) different listeners, while showing overall similarities in ratings of the 42 stimuli, also showed significant differences in acoustic criteria used in assigning the ratings of vocal distress, and (5) listeners who were both experienced and inexperienced in infant vocalizations coding showed high agreement in rating level of distress, but differed in the extent to which they relied on the different acoustic cues in making the ratings. The study provides clearer characterization of vocal distress expression in infants based on acoustic parameters and a new perspective on active adult perception of infant vocalizations. The results also highlight the importance of vibratory regime segmentation and analysis in acoustically based research on infant vocalizations and their perception.

The Structural Effects of Modality on the Rise of Symbolic Language: A Rebuttal of Evolutionary Accounts and a Laboratory Demonstration

Why does symbolic communication in humans develop primarily in an oral medium, and how do theories of language origin explain this? Non-human primates, despite their ability to learn and use symbolic signs, do not develop symbols as in oral language. This partly owes to the lack of a direct cortico-motoneuron control of vocalizations in these species compared to humans. Yet such modality-related factors that can impinge on the rise of symbolic language are interpreted differently in two types of evolutionary storylines. (1) Some theories posit that symbolic language originated in a gestural modality, as in "sign languages." However, this overlooks work on emerging sign and spoken languages showing that gestures and speech shape signs differently. (2) In modality-dependent theories, some emphasize the role of iconic sounds, though these lack the efficiency of arbitrary symbols. Other theorists suggest that ontogenesis serves to identify human-specific mechanisms underlying an evolutionary shift from pitch varying to orally modulated vocalizations (babble). This shift creates numerous oral features that can support efficient symbolic associations. We illustrate this principle using a sound-picture association task with 40 learners who hear words in an unfamiliar language (Mandarin) with and without a filtering of oral features. Symbolic associations arise more rapidly and accurately for sounds containing oral features compared to sounds bearing only pitch features, an effect also reported in experiments with infants. The results imply that, beyond a competence to learn and use symbols, the rise of symbolic language rests on the types of signs that a modality of expression affords.

Typical vs. atypical: Combining auditory Gestalt perception and acoustic analysis of early vocalisations in Rett syndrome

BACKGROUND

Early speech-language development of individuals with Rett syndrome (RTT) has been repeatedly characterised by a co-occurrence of apparently typical and atypical vocalisations.

AIMS

To describe specific features of this intermittent character of typical versus atypical early RTT-associated vocalisations by combining auditory Gestalt perception and acoustic vocalisation analysis.

METHODS AND PROCEDURES

We extracted N = 363 (pre-)linguistic vocalisations from home video recordings of an infant later diagnosed with RTT. In a listening experiment, all vocalisations were assessed for (a)typicality by five experts on early human development. Listeners' auditory concepts of (a)typicality were investigated in context of a comprehensive set of acoustic time-, spectral- and/or energy-related higher-order features extracted from the vocalisations.

OUTCOMES AND RESULTS

More than half of the vocalisations were rated as 'atypical' by at least one listener. Atypicality was mainly related to the auditory attribute 'timbre', and to prosodic, spectral, and voice quality features in the acoustic domain.

CONCLUSIONS AND IMPLICATIONS

Knowledge gained in our study shall contribute to the generation of an objective model of early vocalisation atypicality. Such a model might be used for increasing caregivers' and healthcare professionals' sensitivity to identify atypical vocalisation patterns, or even for a probabilistic approach to automatically detect RTT based on early vocalisations.

The social functions of babbling: acoustic and contextual characteristics that facilitate maternal responsiveness

What is the social function of babbling? An important function of prelinguistic vocalizing may be to elicit parental behavior in ways that facilitate the infant's own learning about speech and language. Infants use parental feedback to their babbling to learn new vocal forms, but the microstructure of parental responses to babbling has not been studied. To enable precise manipulation of the proximal infant cues that may influence maternal behavior, we used a playback paradigm to assess mothers' responsiveness to prerecorded audiovisual clips of unfamiliar infants' noncry prelinguistic vocalizations and actions. Acoustic characteristics and directedness of vocalizations were manipulated to test their efficacy in structuring social interactions. We also compared maternal responsiveness in the playback paradigm and in free play with their own infants. Maternal patterns of reactions to babbling were stable across both tasks. In the playback task, we found specific vocal cues, such as the degree of resonance and the transition timing of consonant-vowel syllables, predicted contingent maternal responding. Vocalizations directed at objects also facilitated increased responsiveness. The responses mothers exhibited, such as sensitive speech and vocal imitation, are known to facilitate vocal learning and development. Infants, by influencing the behavior of their caregivers with their babbling, create social interactions that facilitate their own communicative development.

The Origin of Protoconversation: An Examination of Caregiver Responses to Cry and Speech-Like Vocalizations

Turn-taking is a universal and fundamental feature of human vocal communication. Through protoconversation, caregivers play a key role for infants in helping them learn the turn-taking system. Infants produce both speech-like vocalizations (i.e., protophones) and cries from birth. Prior research has shown that caregivers take turns with infant protophones. However, no prior research has investigated the timing of caregiver responses to cries. The present work is the first to systematically investigate different temporal patterns of caregiver responses to protophones and to cries. Results showed that, even in infants' first 3 months of life, caregivers were more likely to take turns with protophones and to overlap with cries. The study provides evidence that caregivers are intuitively aware that protophones and cries are functionally different: protophones are treated as precursors to speech, whereas cries are treated as expressions of distress.

Development of Velopharyngeal Closure for Vocalization During the First 2 Years of Life

PURPOSE

The vocalizations of young infants often sound nasalized, suggesting that the velopharynx is open during the 1st few months of life. Whereas acoustic and perceptual studies seemed to support the idea that the velopharynx closes for vocalization by about 4 months of age, an aeromechanical study contradicted this (Thom, Hoit, Hixon, & Smith, 2006). Thus, the current large-scale investigation was undertaken to determine when the velopharynx closes for speech production by following infants during their first 2 years of life.

METHOD

This longitudinal study used nasal ram pressure to determine the status of the velopharynx (open or closed) during spontaneous speech production in 92 participants (46 male, 46 female) studied monthly from age 4 to 24 months.

RESULTS

The velopharynx was closed during at least 90% of the utterances by 19 months, though there was substantial variability across participants. When considered by sound category, the velopharynx was closed from most to least often during production of oral obstruents, approximants, vowels (only), and glottal obstruents. No sex effects were observed.

CONCLUSION

Velopharyngeal closure for spontaneous speech production can be considered complete by 19 months, but closure occurs earlier for speech sounds with higher oral pressure demands.

Utterance Duration as It Relates to Communicative Variables in Infant Vocal Development

PURPOSE

We aimed to provide novel information on utterance duration as it relates to vocal type, facial affect, gaze direction, and age in the prelinguistic/early linguistic infant.

METHOD

Infant utterances were analyzed from longitudinal recordings of 15 infants at 8, 10, 12, 14, and 16 months of age. Utterance durations were measured and coded for vocal type (i.e., squeal, growl, raspberry, vowel, cry, laugh), facial affect (i.e., positive, negative, neutral), and gaze direction (i.e., to person, to mirror, or not directed).

RESULTS

Of the 18,236 utterances analyzed, durations were typically shortest at 14 months of age and longest at 16 months of age. Statistically significant changes were observed in utterance durations across age for all variables of interest.

CONCLUSION

Despite variation in duration of infant utterances, developmental patterns were observed. For these infants, utterance durations appear to become more consolidated later in development, after the 1st year of life. Indeed, 12 months is often noted as the typical age of onset for 1st words and might possibly be a point in time when utterance durations begin to show patterns across communicative variables.

Differing Roles of the Face and Voice in Early Human Communication: Roots of Language in Multimodal Expression

Seeking roots of language, we probed infant facial expressions and vocalizations. Both have roles in language, but the voice plays an especially flexible role, expressing a variety of functions and affect conditions with the same vocal categories-a word can be produced with many different affective flavors. This requirement of language is seen in very early infant vocalizations. We examined the extent to which affect is transmitted by early vocal categories termed "protophones" (squeals, vowel-like sounds, and growls) and by their co-occurring facial expressions, and similarly the extent to which vocal type is transmitted by the voice and co-occurring facial expressions. Our coder agreement data suggest infant affect during protophones was most reliably transmitted by the face (judged in video-only), while vocal type was transmitted most reliably by the voice (judged in audio-only). Voice alone transmitted negative affect more reliably than neutral or positive affect, suggesting infant protophones may be used especially to call for attention when the infant is in distress. By contrast, the face alone provided no significant information about protophone categories. Indeed coders in VID could scarcely recognize the difference between silence and voice when coding protophones in VID. The results suggest that partial decoupling of communicative roles for face and voice occurs even in the first months of life. Affect in infancy appears to be transmitted in a way that audio and video aspects are flexibly interwoven, as in mature language.

A Novel Way to Measure and Predict Development: A Heuristic Approach to Facilitate the Early Detection of Neurodevelopmental Disorders

PURPOSE OF REVIEW

Substantial research exists focusing on the various aspects and domains of early human development. However, there is a clear blind spot in early postnatal development when dealing with neurodevelopmental disorders, especially those that manifest themselves clinically only in late infancy or even in childhood.

RECENT FINDINGS

This early developmental period may represent an important timeframe to study these disorders but has historically received far less research attention. We believe that only a comprehensive interdisciplinary approach will enable us to detect and delineate specific parameters for specific neurodevelopmental disorders at a very early age to improve early detection/diagnosis, enable prospective studies and eventually facilitate randomised trials of early intervention. In this article, we propose a dynamic framework for characterising neurofunctional biomarkers associated with specific disorders in the development of infants and children. We have named this automated detection 'Fingerprint Model', suggesting one possible approach to accurately and early identify neurodevelopmental disorders.

Vocalization Rate and Consonant Production in Toddlers at High and Low Risk for Autism

BACKGROUND

Previous work has documented lower vocalization rate and consonant acquisition delays in toddlers with autism spectrum disorder (ASD). We investigated differences in these variables at 12, 18, and 24 months in toddlers at high and low risk for ASD.

METHOD

Vocalization rate and number of different consonants were obtained from speech samples from a prospective study of infant siblings of children with ASD. Three groups were compared: 18 toddlers at low risk for ASD (low-risk control), 18 high-risk siblings without ASD (HRA-), and 10 high-risk siblings with ASD (HRA+).

RESULTS

All groups' mean language scores were within the normal range. HRA+ toddlers showed consistently lower vocalization rate; vocalization rate did not predict number of different consonants at 12 months for HRA+. HRA-, not HRA+, toddlers had the smallest number of different consonants and produced significantly fewer different consonants than predicted by their vocalization rate at 12 months. Consonant-acquisition trajectories differed between groups, with HRA- showing the greatest increase from 12 to 18 months.

CONCLUSION

Lower vocalization rate was not associated with reduced number of different consonants in these toddlers. Between-groups differences in developmental trajectories are discussed in the context of the social feedback loop and differential ability to benefit from adult feedback between groups.

A Retrospective Video Analysis of Canonical Babbling and Volubility in Infants with Fragile X Syndrome at 9-12 Months of Age

An infant's vocal capacity develops significantly during the first year of life. Research suggests early measures of pre-speech development, such as canonical babbling and volubility, can differentiate typical versus disordered development. This study offers a new contribution by comparing early vocal development in 10 infants with Fragile X syndrome and 14 with typical development. Results suggest infants with Fragile X syndrome produce fewer syllables and have significantly lower canonical babbling ratios compared to infants who are typically developing. Furthermore, the particular measures of babbling were strong predictors of group membership, adding evidence regarding the possible utility of these markers in early identification.

Emergence of Functional Flexibility in Infant Vocalizations of the First 3 Months

Functional flexibility, as manifest in the use of any word or sentence to express different affective valences on different occasions, is required in linguistic communication and can be said to be an infrastructural property of language. Early infant vocalizations (protophones), believed to be precursors to speech, occur in the first month and are functionally different from non-speech-like signals (e.g., cries and laughs). Oller et al. (2013) showed that infants by 3 months used three different protophone types with a full range of affect as manifest in facial expression, from positive to neutral to negative. These differences in affect were also shown to correspond to different illocutionary functions, unlike fixed signals, or vegetative sounds, which showed functional rigidity. The present study investigated whether infants show functional flexibility in protophones even earlier than the ages studied by Oller et al. (2013). Data were obtained from 6 infants across the first 3 months. Results showed that as early as the first month, infant protophones were already accompanied by variable facial affect valences and continued to be affectively flexible at the later ages. The present study thus documents the very early emergence of an infrastructural property of human communication.

Multiple Coordination Patterns in Infant and Adult Vocalizations

The study of vocal coordination between infants and adults has led to important insights into the development of social, cognitive, emotional and linguistic abilities. We used an automatic system to identify vocalizations produced by infants and adults over the course of the day for fifteen infants studied longitudinally during the first two years of life. We measured three different types of vocal coordination: coincidence-based, rate-based, and cluster-based. Coincidence-based and rate-based coordination are established measures in the developmental literature. Cluster-based coordination is new and measures the strength of matching in the degree to which vocalization events occur in hierarchically nested clusters. We investigated whether various coordination patterns differ as a function of vocalization type, whether different coordination patterns provide unique information about the dynamics of vocal interaction, and how the various coordination patterns each relate to infant age. All vocal coordination patterns displayed greater coordination for infant speech-related vocalizations, adults adapted the hierarchical clustering of their vocalizations to match that of infants, and each of the three coordination patterns had unique associations with infant age. Altogether, our results indicate that vocal coordination between infants and adults is multifaceted, suggesting a complex relationship between vocal coordination and the development of vocal communication.

Cross-Cultural Register Differences in Infant-Directed Speech: An Initial Study

Infant-directed speech (IDS) provides an environment that appears to play a significant role in the origins of language in the human infant. Differences have been reported in the use of IDS across cultures, suggesting different styles of infant language-learning. Importantly, both cross-cultural and intra-cultural research suggest there may be a positive relationship between the use of IDS and rates of language development, underscoring the need to investigate cultural differences more deeply. The majority of studies, however, have conceptualized IDS monolithically, granting little attention to a potentially key distinction in how IDS manifests across cultures during the first two years. This study examines and quantifies for the first time differences within IDS in the use of baby register (IDS/BR), an acoustically identifiable type of IDS that includes features such as high pitch, long duration, and smooth intonation (the register that is usually assumed to occur in IDS), and adult register (IDS/AR), the type of IDS that does not include such features and thus sounds as if it could have been addressed to an adult. We studied IDS across 19 American and 19 Lebanese mother-infant dyads, with particular focus on the differential use of registers within IDS as mothers interacted with their infants ages 0-24 months. Our results showed considerable usage of IDS/AR (>30% of utterances) and a tendency for Lebanese mothers to use more IDS than American mothers. Implications for future research on IDS and its role in elucidating how language evolves across cultures are explored.

Vocal patterns in infants with autism spectrum disorder: canonical babbling status and vocalization frequency

Canonical babbling is a critical milestone for speech development and is usually well in place by 10 months. The possibility that infants with autism spectrum disorder (ASD) show late onset of canonical babbling has so far eluded evaluation. Rate of vocalization or "volubility" has also been suggested as possibly aberrant in infants with ASD. We conducted a retrospective video study examining vocalizations of 37 infants at 9-12 and 15-18 months. Twenty-three of the 37 infants were later diagnosed with ASD and indeed produced low rates of canonical babbling and low volubility by comparison with the 14 typically developing infants. The study thus supports suggestions that very early vocal patterns may prove to be a useful component of early screening and diagnosis of ASD.

Facial expressions and the evolution of the speech rhythm

In primates, different vocalizations are produced, at least in part, by making different facial expressions. Not surprisingly, humans, apes, and monkeys all recognize the correspondence between vocalizations and the facial postures associated with them. However, one major dissimilarity between monkey vocalizations and human speech is that, in the latter, the acoustic output and associated movements of the mouth are both rhythmic (in the 3- to 8-Hz range) and tightly correlated, whereas monkey vocalizations have a similar acoustic rhythmicity but lack the concommitant rhythmic facial motion. This raises the question of how we evolved from a presumptive ancestral acoustic-only vocal rhythm to the one that is audiovisual with improved perceptual sensitivity. According to one hypothesis, this bisensory speech rhythm evolved through the rhythmic facial expressions of ancestral primates. If this hypothesis has any validity, we expect that the extant nonhuman primates produce at least some facial expressions with a speech-like rhythm in the 3- to 8-Hz frequency range. Lip smacking, an affiliative signal observed in many genera of primates, satisfies this criterion. We review a series of studies using developmental, x-ray cineradiographic, EMG, and perceptual approaches with macaque monkeys producing lip smacks to further investigate this hypothesis. We then explore its putative neural basis and remark on important differences between lip smacking and speech production. Overall, the data support the hypothesis that lip smacking may have been an ancestral expression that was linked to vocal output to produce the original rhythmic audiovisual speech-like utterances in the human lineage.

Beginning to talk like an adult: increases in speech-like utterances in young cochlear implant recipients and typically developing children

PURPOSE

Speech-like utterances containing rapidly combined consonants and vowels eventually dominate the prelinguistic and early word productions of typically developing (TD) toddlers. It seems reasonable to expect a similar phenomenon in young recipients of cochlear implants (CIs). The authors of this study sought to determine the number of months of robust hearing experience needed to achieve a majority of speech-like utterances in both of these groups.

METHOD

Speech samples were recorded from CI recipients at 3-month intervals during the first 2 years of CI experience, and from TD children at time points between 6 and 24 months of age. Speech-like utterances were operationally defined as those belonging to the basic canonical syllables (BCS) or advanced forms (AF) levels of the Consolidated Stark Assessment of Early Vocal Development-Revised ( Ertmer, Young, & Nathani, 2007).

RESULTS

On average, the CI group achieved a majority of speech-like utterances after 12 months of robust hearing experience and the TD group after 18 months. The CI group produced greater percentages of speech-like utterances at each interval until 24 months, when both groups approximated 80%.

CONCLUSION

Auditory deprivation did not limit progress in vocal development as young CI recipients showed more-rapid-than-typical speech development during the first 2 years of device use. Implications for the infraphonological model of speech development are considered.

Speech impairment in Down syndrome: a review

PURPOSE

This review summarizes research on disorders of speech production in Down syndrome (DS) for the purposes of informing clinical services and guiding future research.

METHOD

Review of the literature was based on searches using MEDLINE, Google Scholar, PsycINFO, and HighWire Press, as well as consideration of reference lists in retrieved documents (including online sources). Search terms emphasized functions related to voice, articulation, phonology, prosody, fluency, and intelligibility.

CONCLUSIONS

The following conclusions pertain to four major areas of review: voice, speech sounds, fluency and prosody, and intelligibility. The first major area is voice. Although a number of studies have reported on vocal abnormalities in DS, major questions remain about the nature and frequency of the phonatory disorder. Results of perceptual and acoustic studies have been mixed, making it difficult to draw firm conclusions or even to identify sensitive measures for future study. The second major area is speech sounds. Articulatory and phonological studies show that speech patterns in DS are a combination of delayed development and errors not seen in typical development. Delayed (i.e., developmental) and disordered (i.e., nondevelopmental) patterns are evident by the age of about 3 years, although DS-related abnormalities possibly appear earlier, even in infant babbling. The third major area is fluency and prosody. Stuttering and/or cluttering occur in DS at rates of 10%-45%, compared with about 1% in the general population. Research also points to significant disturbances in prosody. The fourth major area is intelligibility. Studies consistently show marked limitations in this area, but only recently has the research gone beyond simple rating scales.

Monitoring progress in vocal development in young cochlear implant recipients: relationships between speech samples and scores from the Conditioned Assessment of Speech Production (CASP)

PURPOSE

To determine the concurrent validity of the Conditioned Assessment of Speech Production (CASP; Ertmer & Stoel-Gammon, 2008) and data obtained from speech samples recorded at the same intervals.

METHOD

Nineteen children who are deaf who received cochlear implants before their 3rd birthdays participated in the study. Speech samples and CASP scores were gathered at 6, 12, 18, and 24 months postactivation. Correlation analyses were conducted to assess the concurrent validity of CASP scores and data from samples.

RESULTS

CASP scores showed strong concurrent validity with scores from speech samples gathered across all recording sessions (6-24 months).

CONCLUSIONS

The CASP was found to be a valid, reliable, and time-efficient tool for assessing progress in vocal development during young cochlear implant recipients' first 2 years of device experience.

Monkey lipsmacking develops like the human speech rhythm

Across all languages studied to date, audiovisual speech exhibits a consistent rhythmic structure. This rhythm is critical to speech perception. Some have suggested that the speech rhythm evolved de novo in humans. An alternative account--the one we explored here--is that the rhythm of speech evolved through the modification of rhythmic facial expressions. We tested this idea by investigating the structure and development of macaque monkey lipsmacks and found that their developmental trajectory is strikingly similar to the one that leads from human infant babbling to adult speech. Specifically, we show that: (1) younger monkeys produce slower, more variable mouth movements and as they get older, these movements become faster and less variable; and (2) this developmental pattern does not occur for another cyclical mouth movement--chewing. These patterns parallel human developmental patterns for speech and chewing. They suggest that, in both species, the two types of rhythmic mouth movements use different underlying neural circuits that develop in different ways. Ultimately, both lipsmacking and speech converge on a ~5 Hz rhythm that represents the frequency that characterizes the speech rhythm of human adults. We conclude that monkey lipsmacking and human speech share a homologous developmental mechanism, lending strong empirical support to the idea that the human speech rhythm evolved from the rhythmic facial expressions of our primate ancestors.

Prelinguistic vocal development in young cochlear implant recipients and typically developing infants: year 1 of robust hearing experience

This investigation examined the time course and sequence of prelinguistic vocal development during the first year of cochlear implant (CI) experience. Thirteen children who were implanted between 8 and 35 months and 11 typically developing (TD) infants participated in this longitudinal study. Adult-child play interactions were video- and audio-recorded at trimonthly intervals for each group, and child utterances were classified into categories representing progressively more mature productions: Precanonical Vocalizations, Basic Canonical Syllables, and Advanced Form vocalizations. Young CI recipients met the 20% criterion for establishment of the Basic Canonical Syllables and Advanced Forms levels with fewer months of robust hearing experience than the TD infants. Most CI recipients followed the sequence of development predicted by the Stark Assessment of Early Vocal Development-Revised. The relatively rapid progress of the CI children suggests that an earlier period of auditory deprivation did not have negative consequences for prelinguistic vocal development. It also supports the notion that young CI recipients comparatively advanced maturity facilitated expeditious auditory-guided speech development.

The lithic technology of Cebus apella and its implications for brain evolution and the preconditions of language in Homo habilis

Wilkins & Wakefield (1995) provide a thoughtful contribution to our understanding of language origins. In this commentary I attempt to define the relationship between object-manipulation and primate brain function further by reviewing research on aimed throwing and the production and use of stone tools by tufted capuchin monkeys (Cebtis apella). I propose that examining the relation between brain function and object-manipulation in Cebus will provide insight into the preconditions of language in our hominid ancestors.

The dating of linguistic beginnings

The problem of how certain structure–function composites of high complexity could have evolved gradually and by natural selection has been with us at least since Charles Darwin admitted how difficult it was to explain, “his” theory, the origins of “organs of extreme perfection and complication” – such as the eyes of higher animals. Human language capacity is another evolutionary achievement of extraordinary perfection and complexity. Like other skilled human activities, it involves both central (neural) and peripheral (vocal and respiratory) complexes. The reduction of these to simpler building stones to which evolutionary principles may be applied is staggeringly difficult.

And what of human musicality?

The hypothesized brain evolution and preconditions for language may have allowed for the emergence of musicality either simultaneously with or before the emergence of language. Music and language are parallel in their hierarchical, temporally organized structure, and the evolution of hierarchical representation in hominids may have provided the basis for musical representation. Because music could have been produced manually or vocally before the production of spoken language, it remains possible that language emerged from music and that music thus served as a communicative precursor to language.

Further issues in neurolinguistic preconditions

This response to continuing commentary addresses brain-hand relationships in Cebus apella (as introduced in West-ergaard's commentary), the evolutionary and acquisition parallels between music and language (suggested by Lynch), and the potential behavioral linguistic consequences of the evolutionary neurobiology in Australopithecus africanus and Homo habilis (discussed by Tobias). Finally, we reiterate the importance of well informed, multidisciplinary approaches to the study of the emergence of human species-specific cognition, especially linguistic capacity.

Mean Length of Utterance before words and grammar: longitudinal trends and developmental implications of infant vocalizations

This study measured longitudinal change in six parameters of infant utterances (i.e. number of sounds, CV syllables, supraglottal consonants, and repetitions per utterance, temporal duration, and seconds per sound), investigated previously unexplored characteristics of repetition (i.e. number of vowel and CV syllable repetitions per utterance) and analyzed change in vocalizations in relation to age and developmental milestones using multilevel models. Infants (N=18) were videotaped bimonthly during naturalistic and semi-structured activities between 0 ; 3 and the onset of word use (M=11.8 months). Results showed that infant utterances changed in predictable ways both in relation to age and in relation to language milestones (i.e. reduplicated babble onset, word comprehension and word production). Looking at change in relation to the milestones of language development led to new views of babbling, the transition from babbling to first words, and processes that may underlie these transitions.

Fundamental frequency development in typically developing infants and infants with severe-to-profound hearing loss

Little research has been conducted on the development of suprasegmental characteristics of vocalizations in typically developing infants (TDI) and the role of audition in the development of these characteristics. The purpose of the present study was to examine the longitudinal development of fundamental frequency (F(0)) in eight TDI and eight infants with severe-to-profound hearing loss matched for level of vocal development. Results revealed no significant changes in F(0) with advances in pre-language vocal development for TDI. Infants with hearing loss, however, showed a statistically reliable higher variability of F(0) than TDI, when age was accounted for as a covariate. The results suggest development of F(0) may be strongly influenced by audition.

Characteristics of the rhythmic organization of vocal babbling: implications for an amodal linguistic rhythm

Vocal babbling involves production of rhythmic sequences of a mouth close-open alternation giving the perceptual impression of a sequence of consonant-vowel syllables. Petitto and co-workers have argued vocal babbling rhythm is the same as manual syllabic babbling rhythm, in that it has a frequency of 1 cycle per second. They also assert that adult speech and sign language display the same frequency. However, available evidence suggests that the vocal babbling frequency approximates 3 cycles per second. Both adult spoken language and sign language show higher frequencies than babbling in their respective modalities. No information is currently available on the basic rhythmic parameter of intercyclical variability in either modality. A study of reduplicative babbling by 4 infants and 4 adults producing reduplicated syllables confirms the 3 per second vocal babbling rate, as well as a faster rate in adults, and provides new information on intercyclical variability.