A systematic review and Bayesian meta-analysis of the acoustic features of infant-directed speech

When speaking to infants, adults often produce speech that differs systematically from that directed to other adults. To quantify the acoustic properties of this speech style across a wide variety of languages and cultures, we extracted results from empirical studies on the acoustic features of infant-directed speech. We analysed data from 88 unique studies (734 effect sizes) on the following five acoustic parameters that have been systematically examined in the literature: fundamental frequency (f(0)), f(0) variability, vowel space area, articulation rate and vowel duration. Moderator analyses were conducted in hierarchical Bayesian robust regression models to examine how these features change with infant age and differ across languages, experimental tasks and recording environments. The moderator analyses indicated that f(0), articulation rate and vowel duration became more similar to adult-directed speech over time, whereas f(0) variability and vowel space area exhibited stability throughout development. These results point the way for future research to disentangle different accounts of the functions and learnability of infant-directed speech by conducting theory-driven comparisons among different languages and using computational models to formulate testable predictions. This meta-analysis examines different features of infant-directed speech across languages and infant ages. The results suggest that there are cross-linguistic tendencies and that caregivers adjust the properties of infant-directed speech to suit infants' changing needs.

Automated summary

This study examines the acoustic properties of infant-directed speech across different languages and cultures. The results suggest that some acoustic parameters of infant-directed speech become more similar to adult-directed speech as infants grow older, while other parameters remain stable throughout development. This research provides insights for future studies on the functions and learnability of infant-directed speech by comparing different languages and using computational models.