Arousal elevation drives the development of oscillatory vocal output

Adult behaviors, such as vocal production, often exhibit temporal regularity. In contrast, their immature forms are more irregular. We ask whether the coupling of motor behaviors with arousal changes give rise to temporal regularity and drive the transition from variable to regular motor output over the course of development. We used marmoset monkey vocal production to explore this putative influence of arousal on the nonlinear changes in their developing vocal output patterns. Based on a detailed analysis of vocal and arousal dynamics in marmosets, we put forth a general model incorporating arousal and auditory-feedback loops for spontaneous vocal production. Using this model, we show that a stable oscillation can emerge as the baseline arousal increases, predicting the transition from stochastic to periodic oscillations occurring in marmoset vocal development. We further provide a solution for how this model can explain vocal development as the joint consequence of energetic growth and social feedback. Together, our model offers a plausible mechanism for the development of arousal-mediated adaptive behavior.

Longitudinal Study of Vocal Development and Language Environments in Infants With Cleft Palate

Objective This study investigated vocalization and language environment longitudinally in infants with cleft palate (CP) based on day-long audio recordings collected in their natural environments. Design Language Environment Analysis (LENA) data from all-day recordings at home were collected at 3-month intervals for infants from 4-6 to 16-18 months of age. The recordings were analyzed using experimentally blinded human coding as well as LENA automated analysis. Participants Ten infants with CP (± cleft lip) and 10 age-matched infants without CP. Main Outcome Measures Several measurements were obtained from the LENA automated analysis software. In addition, human coded measurements of vocalization and language environment, including the true canonical babbling ratio and the infant-directed speech ratio, were analyzed for each time point of data collection for each infant. Statistical analyses were performed to conduct group and age comparisons for each measure of vocalization and language environment. Results No group differences emerged in number of syllables produced. Infants with CP exhibited late onset and fewer productions of canonical syllables compared to infants without CP. Infants with CP did not show significant differences from infants without CP in measures related to language environment across ages. Conclusion This study provides detailed information through naturalistic all-day home recordings about vocal development and early language environments in infants with CP before and after palatal repair. Clinical implications for early intervention are discussed.

A Call to Expand Avian Vocal Development Research

Birds are our best models to understand vocal learning – a vocal production ability guided by auditory feedback, which includes human language. Among all vocal learners, songbirds have the most diverse life histories, and some aspects of their vocal learning ability are well-known, such as the neural substrates and vocal control centers, through vocal development studies. Currently, species are classified as either vocal learners or non-learners, and a key difference between the two is the development period, extended in learners, but short in non-learners. But this clear dichotomy has been challenged by the vocal learning continuum hypothesis. One way to address this challenge is to examine both learners and canonical non-learners and determine whether their vocal development is dichotomous or falls along a continuum. However, when we examined the existing empirical data we found that surprisingly few species have their vocal development periods documented. Furthermore, we identified multiple biases within previous vocal development studies in birds, including an extremely narrow focus on (1) a few model species, (2) oscines, (3) males, and (4) songs. Consequently, these biases may have led to an incomplete and possibly erroneous conclusions regarding the nature of the relationships between vocal development patterns and vocal learning ability. Diversifying vocal development studies to include a broader range of taxa is urgently needed to advance the field of vocal learning and examine how vocal development patterns might inform our understanding of vocal learning.

Cross-species parallels in babbling: animals and algorithms

A key feature of vocal ontogeny in a variety of taxa with extensive vocal repertoires is a developmental pattern in which vocal exploration is followed by a period of category formation that results in a mature species-specific repertoire. Vocal development preceding the adult repertoire is often called ‘babbling’, a term used to describe aspects of vocal development in species of vocal-learning birds, some marine mammals, some New World monkeys, some bats and humans. The paper summarizes the results of research on babbling in examples from five taxa and proposes a unifying definition facilitating their comparison. There are notable similarities across these species in the developmental pattern of vocalizations, suggesting that vocal production learning might require babbling. However, the current state of the literature is insufficient to confirm this suggestion. We suggest directions for future research to elucidate this issue, emphasizing the importance of (i) expanding the descriptive data and seeking species with complex mature repertoires where babbling may not occur or may occur only to a minimal extent; (ii) (quasi-)experimental research to tease apart possible mechanisms of acquisition and/or self-organizing development; and (iii) computational modelling as a methodology to test hypotheses about the origins and functions of babbling. This article is part of the theme issue ‘Vocal learning in animals and humans’.

The vocal development of the pale spear-nosed bat is dependent on auditory feedback

Human vocal development and speech learning require acoustic feedback, and humans who are born deaf do not acquire a normal adult speech capacity. Most other mammals display a largely innate vocal repertoire. Like humans, bats are thought to be one of the few taxa capable of vocal learning as they can acquire new vocalizations by modifying vocalizations according to auditory experiences. We investigated the effect of acoustic deafening on the vocal development of the pale spear-nosed bat. Three juvenile pale spear-nosed bats were deafened, and their vocal development was studied in comparison with an age-matched, hearing control group. The results show that during development the deafened bats increased their vocal activity, and their vocalizations were substantially altered, being much shorter, higher in pitch, and more aperiodic than the vocalizations of the control animals. The pale spear-nosed bat relies on auditory feedback for vocal development and, in the absence of auditory input, species-atypical vocalizations are acquired. This work serves as a basis for further research using the pale spear-nosed bat as a mammalian model for vocal learning, and contributes to comparative studies on hearing impairment across species. This article is part of the theme issue ‘Vocal learning in animals and humans’.

Vocalisations and the Dynamics of Interpersonal Arousal Coupling in Caregiver-Infant dyads

We currently understand little about how autonomic arousal influences early vocal development. To examine this, we used wearable microphones and autonomic sensors to collect multimodal naturalistic datasets from 12-month-olds and their caregivers. We observed that clusters of vocalisations occurred during elevated infant and caregiver arousal, but the relationship is stronger in infants than caregivers. Caregivers show greater functional flexibility, and their vocal production is more influenced by the infant’s arousal than their own. Negative affect vocalisations occur following reduced arousal stability and lead to increased child-caregiver arousal coupling, and decreased infant arousal. Positive vocalisations also occur at elevated arousal, but lead to increases in arousal, and elicit more parental speech. Our results point to important bi-directional associations between vocalisations and arousal regulation across caregiver-infant dyads.

Evaluation of Parent–Researcher Agreement on the Vocal Development Landmarks Interview

Purpose Parent report was compared to judgments made by a trained researcher to determine the utility of the Vocal Development Landmarks Interview (VDLI) for monitoring development of vocal behaviors in very young children. Method Parents of 40 typically developing children, ages 6–21 months, provided full-day naturalistic audio recordings of their children's vocalizations after completing the VDLI. Six 5-min segments of highly voluble periods were selected from each recording and were analyzed, coded, and scored by the researcher. These data were then compared to the parents' VDLI responses. Parent–researcher agreement was examined using two methods and a generalized linear mixed model. Patterns of disagreement were explored descriptively to gain insights regarding potential sources of parent–researcher differences. Finally, developmental patterns in the researcher-observed vocal behaviors were examined as a function of children's age. Results No significant differences in parent–researcher agreement were found for the Canonical and Word subscales of the VDLI; however, significant differences in agreement were found for the Precanonical subscale. Mean percentages of agreement were high overall for both scoring methods evaluated. Additionally, the researcher's categorization and quantification of vocal behaviors for each age group aligned well with developmental trajectories found in the literature. Conclusion Results provide further support for use of parent report to assess early vocal development and use of the VDLI as a clinical measure of vocal development in infants and toddlers ages 6–21 months.

Song preferences predict the quality of vocal learning in zebra finches

In songbirds, learning to sing is a highly social process that likely involves social reward. Here, we hypothesized that the degree to which a juvenile songbird learns a song depends on the degree to which it finds that song rewarding to hear during vocal development. We tested this hypothesis by measuring song preferences in young birds during song learning and then analyzing their adult songs. Song preferences were measured in an operant key-pressing assay. Juvenile male zebra finches (Taeniopygia guttata) had access to two keys, each of which was associated with a higher likelihood of playing the song of their father or that of another familiar adult ("neighbor"). To minimize the effects of exposure on learning, we implemented a reinforcement schedule that allowed us to detect preferences while balancing exposure to each song. On average, the juveniles significantly preferred the father's song early during song learning, before they were themselves singing. At around post-hatch day 60, their preference shifted to the neighbor's song. At the end of the song learning period, we recorded the juveniles' songs and compared them to the father's and the neighbor's song. All of the birds copied father's song. The accuracy with which the father's song was imitated was positively correlated with the peak strength of the preference for the father's song during the sensitive period. Our results show that preference for a social stimulus, in this case a vocalization, predicted social learning during development.