Parents tune their vowels to the emergence of children’s words

Abstract

The aim of this study was to investigate the acoustic vowel space area in infant directed speech (IDS). The research question is whether the vowel space is expanded or remains constant in IDS. A corpus of spontaneous interactions of 9 dyads followed monthly from the age of 6 to 24 months was analyzed. The occurrences in the parents’ speech of each word that the children eventually acquired were extracted. The surface of the vowel triangle and the convex hull of all vowels were computed. The main result is that the development of the vowel space in IDS follows an inverted U-shaped curve: the vowel space starts relatively small, gradually increases as the child’s first word use approaches, and decreases again afterwards. These findings show that parents adapt their articulation to the evolving linguistic abilities of their child, and this adaptation can be detected at the level of individual lexical items.

Children steer the inflectional diversity of their parents: The role of word births and growing vocabulary

“…However, they differed in utterance length: On the whole, parents of children with CI used shorter utterances than parents of NH children but the pattern of development of MLU was strikingly similar. On the other hand, fine lexical tuning was not found for the vowel space in IDS directed to children with CI (Odijk & Gillis, 2022). Parents of children with CI did not adapt their vowel space relative to the word knowledge of their children, unlike parents of NH children.…”

“…It was shown that the stressed vowels in those words were pronounced more clearly, as represented by acoustic measures such as the surface of the vowel triangle and the vowel convex hull. Speech clarity also increased as word births approached and decreased again afterward (Odijk & Gillis, 2022). Also, the length of the utterances in which those words occurred showed a similar U-shaped curve: a decrease in MLU as word birth approached and an increase after word birth (Odijk & Gillis, 2021a; Roy et al, 2009).…”

“…Thus, the average length of the parents' utterances with a particular word follows a U-curve with at its lowest point the actual word birth, the child's own first use of that word. Fine lexical tuning also turns up when the acoustic characteristics of the vowels are analyzed in the period leading up to word birth (Odijk & Gillis, 2022). The vowel space expanded suggesting that the vowels were acoustically more contrastive or more clearly pronounced.…”

“…The adaptations in IDS are related not only to the child’s developing language skills but also to other characteristics, such as the child’s hearing status. Parents have been shown to speak more clearly when addressing hearing-impaired (HI) children as opposed to children with normal hearing (NH) as evidenced by a larger vowel space (Odijk & Gillis, 2022). Mothers have been shown to talk less and produce less complex utterances when talking to their hearing-impaired child, compared to when talking to normally hearing children; instead, they use more gestures (Goldin-Meadow & Saltzman, 2000; Koester et al, 1998; Vanormelingen et al, 2016).…”