The impact of child age and sentence-type on the acoustics of infant-directed speech

Research has demonstrated differences in the characteristics of infant-directed speech (IDS) based on age (Stern et al., 1983) and sentence-type (Geffen and Mintz, 2017) but has not examined the two factors together. The current study evaluates whether the acoustics of IDS differ as a function of child's age and sentence-type. The study combines two corpora of native-English adult speakers. Both Corpus1(9mo) (described in Geffen and Mintz, 2017), from the Brent corpus of the CHILDES database (Brent and Siskind, 2001) and Corpus2 (12mo) (described in Thompson, 2019), from naturalistic home-recordings, included statements, yes/no and wh-questions, and were acoustically coded in Praat. Three 2-way mixed ANOVAs with Age (9 and 12 months; between-subjects factor) and Sentence-Type (S, WH, YN; within-subjects factor) on OverallF0range, FinalVowelDuration, and FinalVowelF0range found main effects of Age, and Age X Sentence-Type interaction for OverallF0range. There was also a significant effect of Age on FinalVowelDuration. Results demonstrated a developmental shift in acoustic characteristics of IDS, with more exaggerated prosody to younger infants, supporting Stern et al. (1983) and suggests that IDS to older children no longer privileges prosody as strongly. Future studies should investigate whether similar developmental adjustments in IDS occur in languages other than English.