Published Online: 03 December 2020This study investigated the effects of hearing loss and hearing experience on the acoustic features of infant-directed speech (IDS) to infants with hearing loss (HL) compared to controls with normal hearing (NH) matched by either chronological or hearing age (experiment 1) and across development in infants with hearing loss as well as the relation between IDS features and infants' developing lexical abilities (experiment 2). Both experiments included detailed acoustic analyses of mothers' productions of the three corner vowels /a, i, u/ and utterance-level pitch in IDS and in adult-directed speech. Experiment 1 demonstrated that IDS to infants with HL was acoustically more variable than IDS to hearing-age matched infants with NH. Experiment 2 yielded no changes in IDS features over development; however, the results did show a positive relationship between formant distances in mothers' speech and infants' concurrent receptive vocabulary size, as well as between vowel hyperarticulation and infants' expressive vocabulary. These findings suggest that despite infants' HL and thus diminished access to speech input, infants with HL are exposed to IDS with generally similar acoustic qualities as are infants with NH. However, some differences persist, indicating that infants with HL might receive less intelligible speech.This research was supported by HEARing Cooperative Research Centre Grant No. 82631, “The Seeds of Language Development,” to D.B. The second author's work is supported by the Basque Government through the BERC 2018-2021 program and by the Spanish Ministry of Science and Innovation through the Ramon y Cajal Research Fellowship PID2019-105528GA-I00. We would like to thank all the parents and infants for participating in the study; “The Shepherd Centre” in Sydney and Wollongong; “Hear and Say” in Brisbane for their help in recruitment of participants with HL; and Benjawan Kasisopa, Maria Christou-Ergos, Hana Zjakic, and Scott O'Loughlin for their assistance with data collection
