Longitudinal relationships between phonology and the lexicon in typically developing toddlers and late talkers : a psycholinguistic perspective.

Background: Research spanning more than two decades has emphasised the lexical deficits of late talkers. However, late talkers have been found to have associated delayed phonological acquisition. Given the close connection between these two linguistic domains, it may be that the late language emergence often observed in these children, arises from deficits in their underlying phonological processing system. This thesis explored the longitudinal relationships between the phonological and lexical development in typically developing toddlers (TD) and those who fit the criteria of late talkers (LT), in light of a psycholinguistic speech processing framework. Methods: The cohort comprised 168 children aged 2;0 (years; months) at intake who were reassessed when they were about 3;6 and 5;0 years, on measures of phonological accuracy and expressive language. Phonological accuracy (expressed in terms of a percentage of consonants correct) was used as the main behavioural indicator of children‘s phonological development and was measured in two conditions; in a test of nonword repetition (NWR), and a standardised picture naming/articulation test. Children‘s lexical development was assessed using standardised tests of language. Relationships between phonology and expressive language were derived based on correlation and regression analyses of groups‘ scores, as well as in the varied clinical profiles characterised by children‘s abilities in one domain of language relative to the other. With the dataset, analysis of concurrent correlations was conducted in order to identify and compare statistical significance between individual measures of phonological accuracy and the lexicon at each time-point for TD children and LTs. Regression analyses were conducted to identify the proportion of variance in expressive language explained by each measure of phonological accuracy in TD children and LTs. Differences between TD and LT groups in mean scores for phonology and expressive language at each time point were analysed to determine statistical significance