Acoustic Structure of Early Infant Babble

There is a plethora of information surrounding the stages of infant vocal development, and canonical babble’s predictive power concerning future language outcomes. However, there is less information regarding how the acoustic features of early babble differ between canonical and non-canonical syllable types over the course of development. Furthermore, previous studies rely on small sample sizes which limit their findings’ generalizability. This project examined the pitch range, mean pitch, and syllabic nuclei duration of monosyllabic canonical and non-canonical infant vocalizations over the course of development. 

Audio files of monosyllabic utterances were obtained from 29 infants at low risk for developing a speech or language disorder, aged 10-26 months. The infants were divided into three age bands: 10-12 months (M=11.74, N=10, 5=F), 13-22 months (M=16.08, N=9, 6=F), and 23-26 months (M=24.67, N=9, 2=F). We listened to each utterance and marked syllable nucleus boundaries prior to running scripts to measure acoustic cues. Between 6 and 15 utterances were selected from each participant. The number of canonical utterances was matched to the number of noncanonical utterances (e.g., if 13 canonical utterances were selected for a specific participant, 13 non-canonical utterances were also selected). We then ran a Praat script which yielded the mean pitch, pitch range, and duration of the syllabic nucleus for each audio file. 

We found that there was a significant effect of syllable type on duration, as canonical syllables were shorter in duration than non-canonical syllables (F (1, 618.34) = 10.64, p = .001), and on mean pitch, as canonical syllables were lower in mean pitch than non-canonical syllables (F (1, 618.57) = 7.18, p = .008). We did not find an effect of syllable type on pitch range, age on mean pitch or duration, or any interaction effects between syllable type and age. However, we did find an effect of age on pitch range, because infants in the oldest age bracket (23-26 months) were more likely to have a wider pitch range than younger infants (F (2, 44.77) = 5.05, p = .011). 

This provides preliminary evidence that there are pitch and duration distinctions between canonical and non-canonical syllable types and suggests that as infants age they are more likely to use greater pitch variation within their vocalizations. However, as our study only examined monosyllabic utterances, further research is necessary in order to thoroughly investigate pitch and duration distinctions present in canonical and non-canonical syllables.