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.

Multisyllabic words constitute a large portion of children's vocabulary. However, the relationship between phonological neighborhood density and English multisyllabic word learning is poorly understood. We examine this link in three, four and six year old children using a corpus-based approach. While we were able to replicate the well-accepted positive association between CVC word acquisition and neighborhood density, no similar relationship was found for multisyllabic words, despite testing multiple novel neighborhood measures. This finding raises the intriguing possibility that phonological organization of the mental lexicon may play a fundamentally different role in the acquisition of more complex words.

Do parents fine-tune the MLU of utterances with a particular word as the word is on the verge of appearing in the child's production? We analyzed a corpus of spontaneous interactions of 30 dyads. The children were in the initial stages of their lexical development, and the parents’ utterances containing the words the children eventually acquired were selected. The main finding is that the MLU of the parental utterances containing the target words gradually decreased up to the point of the children's first production of those words. This suggests that parents fine-tune their utterances to support the children's linguistic development.