Language is inherently social; thus, language learning must be facilitated by social means. Infant-adult interactions are crucial for language development. However, one cannot view communication as an independent entity; rather, communication is simply one developmental domain within the dynamical scope of infant development. Specifically, language co-exists and develops in conjunction with the motor, cognitive, social, and emotional developmental domains. This dissertation will investigate the interdependent roles of all these developmental domains as they pertain to speech and language development.

The first investigation explores how infant-adult social interactions relate to the speech-relatedness of infant vocalizations. This study, which was recently accepted for publication in Infant Behavior and Development, examined two-event vocal sequences within the context of ultra-naturalistic home interactions captured via the LENA system. We found that the dynamics of infant-adult interactions were dependent upon the type of infant vocalization, the directedness of adult utterances, and the time lags between vocal events.

The second investigation builds upon the first by adding a locomotion dimension: How do these infant-adult interactions look in walking vs crawling infants? This question was previously explored with a smaller, unbalanced sample, but will be re-assessed with a larger, more equal sample of walking and crawling infants. We found differential responses to types of infant vocalizations between walking and crawling infants. We also found a marginally significant association between infant-directed speech and productive vocabulary.

The final component to this dissertation is an exploration of how milestone acquisition across a range of developmental domains (e.g., gross motor, fine motor, problem solving, social/emotional) relates to observable language behaviors within naturalistic daylong home audio recordings (e.g., infant vocalization count, turn count, and adult words heard). We found significant relations between infant vocalization types and adult utterance directions dependent upon age. Additionally, we found that Fine Motor, Social-Emotional, and Communication scores were predictive of vocabulary size. These three studies demonstrate evidence that supports the idea that language development is an active participant, along with the other developmental domains, within the dynamical system that is infant development.

This dissertation, Multi-Domain Synchrony Within Vocal Development, is submitted by Gina Marie Pretzer in 2019 in partial fulfillment of the degree Doctor of Philosophy in Cognitive and Information Sciences at the University of California, Merced, under the guidance of dissertation committee chair, Teenie Matlock.

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