Endogenous and social factors influencing infant vocalizations as fitness signals

This dissertation evaluated the role of social and endogenous prelinguistic vocalizations as vocal fitness signals in human development. It consists of three studies. The first investigated the saliency of infant vocal imitation using listener judgments regarding the degree of imitativeness in parent-infant vocal turn pairs. Participating listeners demonstrated moderate to high intra- and inter-rater agreement, suggesting vocal imitation has the potential to be used as a signal of fitness to caregivers in early development. The work also showed that vocal imitation in infancy is rare. The second study sought to quantify the extent to which infants produce vocalizations socially (directed to a caregiver) vs endogenously (not directed to a caregiver) in laboratory settings where parents either attempted to engage them or talked with another adult. The infants produced three times as many vocalizations endogenously as socially in both settings. High rates of endogenously produced sounds may result from evolutionary pressures to signal wellness to caregivers through vocalization. Extensive independent vocal play may offer infants the opportunity to explore sensorimotor characteristics of the vocal system and provide the raw material that parents can use in face-to-face interactions. The third study examined social and endogenous motivations in the emergence of advanced vocal forms. Specifically, it compared canonical babbling ratios of infants at low- and high-risk for autism across high and low levels of both vocal turn-taking and vocal play. Both groups showed a tendency to produce more canonical babbling during high turn-taking and high vocal play. The findings highlight a potentially robust internal social motivation for vocalization, even in the presence of likely social-cognitive differences such as risk for autism. High rates of endogenously produced canonical syllables in high-risk infants support the idea of robust evolutionary pressures for infants to signal fitness through vocalization. Furthermore, differences in vocal production across settings can inform our understanding of the importance of both vocal interaction and independent infant exploration of vocalization. This dissertation offers perspective on the ways in which social and endogenous factors reveal natural selection pressures on fitness signaling in the human infant.

Social and endogenous motivations in the emergence of canonical babbling in infants at low and high risk for autism

There is a growing body of research emphasizing the role of social and endogenous motivations in human development. The present study evaluated canonical babbling across the second-half year of life using all-day recordings of 98 children with typical or elevated likelihoods of autism i.e., at “low risk” or “high risk”, respectively. Canonical babbling ratios (CBRs) were calculated from human coding along with Likert-scale ratings on vocal turn taking and vocal play in each segment. We observed no main effect of risk on CBRs. CBRs were significantly elevated during high vocal play. High turn taking yielded a weaker significant effect. We conclude that both social and endogenous motivations may drive infants’ tendencies to produce their most advanced vocal forms.

Social and endogenous motivations in the emergence of canonical babbling in infants at low and high risk for autism

There is a growing body of research emphasizing the role of social and endogenous motivations in human development. The present study evaluated canonical babbling across the second-half year of life using all-day recordings of 98 children with typical or elevated likelihoods of autism i.e., at “low risk” or “high risk”, respectively. Canonical babbling ratios (CBRs) were calculated from human coding along with Likert-scale ratings on vocal turn taking and vocal play in each segment. We observed no main effect of risk on CBRs. CBRs were significantly elevated during high vocal play. High turn taking yielded a weaker significant effect. We conclude that both social and endogenous motivations may drive infants’ tendencies to produce their most advanced vocal forms.

Early Vocal Development in Tuberous Sclerosis Complex

Objective: To determine whether entry into the canonical stage, canonical babbling ratios (CBR) and the level of volubility (vocal measures) are delayed in infants with Tuberous Sclerosis Complex (TSC), we completed human coding of their vocalizations at 12 months and compared the results to typically developing infants with no clinical features (TD/NCF). Methods: We randomly selected videos from 40 infants with TSC from the TACERN database. All 78 videos were coded in real-time in AACT (Action Analysis, Coding and Training). Results: Entry into the canonical stage was delayed in the great majority of the infants with TSC. The CBR for the TD/NCF infants was significantly higher than for the infants with TSC (TD/NCF mean = .346, SE = .19; TSC mean = .117, SE = .023). Volubility level in infants with TSC was less than half that of TD/NCF infants (TD/NCF mean = 9.82, SE = 5.78; TSC mean = 3.99, SE = 2.16). CBR and volubility were also lower in TSC infants than in TD/NCF infants recorded all-day at home. Conclusions: Entry into the canonical stage was delayed, while canonical babbling ratios and volubility were low in infants with TSC. Assessing prediction of neurodevelopmental outcome using these vocal measures in combination with non-vocal measures will be the focus of planned studies in this high-risk population.

Canonical Babbling and Early Consonant Development Related to Hearing in Children With Otitis Media With Effusion With or Without Cleft Palate

Objective: To investigate and compare babbling, early consonant production and proficiency from 10 to 36 months of age and its relationship with hearing in children with otitis media with effusion (OME) with or without cleft palate. Design: Prospective, longitudinal group comparison study. Setting: University hospital. Participants: Fifteen children born with nonsyndromic cleft palate with or without cleft lip (CP±L) and 15 age-matched children with hearing loss (HL) associated with OME but without cleft palate (noncleft group). Main Outcome Measures: Canonical babbling (CB) and early consonant variables (presence of oral stops, anterior stops, dental/alveolar stops, number of different true consonants) at 10 and 18 months, and percentage of consonants correct proficiency (PCC) at 36 months. Results: A total of 54% of the CP±L group and 77% of the noncleft group had CB. The noncleft group had a significantly higher prevalence of all consonant variables. Percentage of consonants correct was 61.9% in the CP±L group and 81.6% in the noncleft group. All early consonant variables except CB were significantly related to PCC. Hearing sensitivity at 18 and 30 months correlated with PCC and explained 40% of the variation. Conclusions: Mild HL impacted presence of CB at 10 months and was related to consonant proficiency at 36 months in children with HL associated with OME and children with cleft palate. The noncleft group showed results at 36 months similar to children with normal hearing; however, the CP±L group did not. Although the cleft palate may have a bigger impact on the speech development, management of hearing sensitivity would also be beneficial.

Social and endogenous motivations in the emergence of canonical babbling: An autism risk study

There is a growing body of research emphasizing the role of intrinsic motivation and endogenous activity to support the development of cognitive systems alongside the well-established role of social interaction. The present study longitudinally evaluated canonical babbling across the second-half year of life, when canonical babbling becomes well-established. We compared segments rated as having high and low levels of turn taking and independent vocal play in 98 children at low and high risk for autism spectrum disorder. Segments were extracted from all-day home audio recordings to observe infants in naturalistic settings. Canonical babbling ratios (CBR) were determined based on human coding along with Likert-scale ratings on the level of turn taking and vocal play in each segment. We observed highly significant differences in CBRs between risk groups during high and low vocal play, but high and low levels of turn taking yielded a weaker effect. There were also interactions of CBR with age, risk, and vocal function variables. We conclude that social and endogenous/exploratory motivations may drive both high- and low-risk infant tendencies to produce their most speech-like vocalizations.Lay abstractInfants at low and high risk for autism produced similar babbling rates across various levels of social interaction. Infants at high risk for autism produced higher rates of mature, well-formed (canonical) syllables during bouts of independent vocal play. In this study, we compared rates of babbling in infants at low and high risk for autism across different levels of infant vocal turn taking and vocal play. Eight 5-minute segments were selected from each all-day home recording (98 infants, 483 recordings in the second half-year of life). Listeners coded infant syllables as canonical, i.e., “adult-like,” or noncanonical, i.e., “immature,” forms. After coding each segment, listeners rated each segment for its frequency of both infant turn taking and vocal play using a Likert scale. We predicted that low-risk infants would do more canonical babbling during social interaction and high-risk infants would babble more during independent vocal play. But infants at high risk for autism did not differ significantly in babbling rates across levels of social interaction from low-risk infants. Also contrary to our prediction both groups produced higher rates of canonical babbling during periods of high vocal play. Both groups produced similar canonical babbling rates over time. These findings may inform our understanding of internal motivations for canonical babbling and potentially early indicators of differences in the vocal production of infants with autism before they produce their first words.