Prosodic and lexical aspects of maternal linguistic input to late-talking toddlers

Background: Children who have reached the age of 2 years without having acquired a 50-word vocabulary and/or who use no word combinations are referred to in the literature as 'Late Talkers'. Research has not yet identified the factors that cause slow development of expressive language; in particular, relatively little research has been carried out on the characteristics of the maternal linguistic input received by Late Talkers. In fact, the majority of studies in this area have focused principally on the mothers' semantic, pragmatic and interactive verbal behaviour. Aims: The objective was to verify whether the input addressed to a group of Late Talkers differs to that addressed to a group of typically developing peers. It was expected that there would be differences in the prosodic and structural/ lexical properties of the input, which by creating a 'less than optimal environment' for language acquisition processes, could affect the children's rate of linguistic development. Methods & Procedures: The spontaneous maternal speech of nine Italian-speaking mothers of late-talking toddlers (LT) at 20 months of age was examined and compared with that of nine mothers of age-matched children with typical language development (Late Starters). Data were collected during video-recorded play sessions, which were transcribed and coded based on the structural-lexical and acoustical characteristics of the mothers' speech. Group differences were tested for the following variables: number of utterances per minute, mean number of words per utterance (MLUw), number of nouns per minute, number of different nouns per minute, common nouns as a percentage of overall words, type/token ratio for common nouns, one-word utterances as a percentage of the total number of utterances, one-word utterances formed by a common noun as a percentage of the total number of utterances, mean syllable duration, duration of the final syllable of the utterance, F-0 maximum (the highest F-0 in the utterance), F-0 minimum (the lowest F-0 in the utterance) and F-0 range (by subtracting F-0 (min) from F-0 max). Outcomes & Results: The mothers of LT produced common nouns and mark nouns by a pitch peak with a significantly lower frequency than the mothers of the children with typical language development. The mothers of LT also used flat pitch contours more often than the mothers of the typically developing peers. Conclusions: The study provides evidence that maternal input addressed to Late Talkers can contribute to slowing the process of language acquisition. Based on these findings, additional investigations that examine the contribution of maternal verbal behaviour to the development of language delay are warranted.