Syllable complexity in 24-month-old infants resulting from spontaneous mother–child vocal interactions

Infant Directed Speech (IDS) influences language development via caregiver–child interactions and can promote early speech and language outcomes in some cultures (Golinkoff et al., 2015). IDS is characterized by a higher, more dynamic fundamental frequency (f0) as well as shorter caregiver utterances and simplified phono-lexical structures (Ramirez-Esparza et al., 2014). In line with social feedback theories of early vocal development (Warlaumont et al. 2014), this study proposes that certain acoustic aspects of IDS, when produced contingently with infant speech, will promote infants’ early vocal maturity. N = 84 infant-caregiver dyads were recorded during semi-naturalistic play sessions at 7, 10, 18, and 24 months. Infant vocal maturity was quantified as syllable complexity at 24-months where syllables with consonant-vowel (CV or VC) transitions were more complex than syllables with only a nucleus (V). The complexity of children’s syllables produced within 5 sof contingent caregiver speech will be compared to those produced outside of 5-swindows of caregiver speech. Infants’ syllable production will also be related to acoustic characteristics of IDS including f0 height, modulation, and caregiver speaking rate. Positive correlations between IDS characteristics and infant syllable complexity will provide additional evidence that socially contingent IDS spurs early speech development.