Social and endogenous infant vocalizations

Abstract

Research on infant vocal development has provided notable insights into vocal interaction with caregivers, elucidating growth in foundations for language through parental elicitation and reaction to vocalizations. A role for infant vocalizations produced endogenously, potentially providing raw material for interaction and a basis for growth in the vocal capacity itself, has received less attention. We report that in laboratory recordings of infants and their parents, the bulk of infant speech-like vocalizations, or "protophones", were directed toward no one and instead appeared to be generated endogenously, mostly in exploration of vocal abilities. The tendency to predominantly produce protophones without directing them to others occurred both during periods when parents were instructed to interact with their infants and during periods when parents were occupied with an interviewer, with the infants in the room. The results emphasize the infant as an agent in vocal learning, even when not interacting socially and suggest an enhanced perspective on foundations for vocal language.

Canonical babbling during vocal turn taking and independent vocal play

“…Infants produce more speech-like vocalizations, or "protophones," (including both canonical and precanonical babbling) without person-directed gaze (both when alone and in the presence of caregivers) than they produce socially-directed sounds (Harold & Barlow, 2013;Oller et al, 2013). More recently, several authors of the present study found that approximately 75% of all infant protophones in laboratory recordings were endogenously produced (Long et al, 2020). We know that social interaction influences infant babbling, phonological learning, and complex language skills (Albert et al, 2018;Elmlinger et al, 2019;Goldstein et al, 2003;Goldstein & Schwade, 2008;Kuhl, 2007), but social and endogenous motivations for infant vocal activity require additional research to elucidate their relative roles.…”

“…We and others have hypothesized selection pressures on the production of endogenously produced protophones. Baby sounds can be seen as fitness signals selected to elicit longterm investment from caregivers, required across the lengthy period of relative helplessness, or altriciality, of infant humans (Locke, 2017;Long et al, 2020;Oller et al, 2016Oller et al, , 2019. In accord with the fitness signaling hypothesis, the quality of infant vocalizations can be considered a salient and reliable signal of fitness.…”

“…We are influenced by the literature-based hypothesis that infants at low autism risk should be expected to produce more canonical syllables during social interaction, while high-risk infants should not be expected to do so, but recent evidence suggests a contrasting possibility. Research by Long et al (2020) has shown that typically developing infants produce protophones (both canonical and precanonical) predominantly endogenously. Even in laboratory recordings, during periods when parents seek social interaction with infants, most protophones (~60%) appear not to be directed to parents, and this predominance of endogenous vocalization is even stronger (~80%) when parents are present with infants but not attempting to engage them.…”

“…Following syllable coding of each 5-minute segment, coders answered a 17-item questionnaire regarding how often infants used vocalizations for various functions based on the audible context of the infant's environment in each segment. See Long et al (2020) for theoretical perspectives on making intuitive judgments of infant vocal functions. We used two items from the questionnaire to measure frequencies of naturalistic infant vocalizations that were judged to be inherently social and exploratory within each segment.…”

“…This subjective measure, obtained immediately after coding for CBR for each segment, can be portrayed as a blunt instrument, subject to only fair interobserver agreement, but it is founded in the notion that human judgments are the gold standard for any such measure, and our method of obtaining the judgments was convenient and workable. A perhaps more reliable measure would require labeling the social or exploratory function of each utterance individually with repeat-observation (and especially with both audio and video), a measure that requires at least tenfold more time to obtain (see Long et al (2020) for an analysis using this method). Future studies using this more expensive measure of the role of TT in infant vocalization are planned.…”