Building an auditory lexicon

Abstract

The ability to form mental representations of word sounds is central to language comprehension and production, and provides the basis of grammatical development and literacy. However, this process remains poorly understood. The five empirical studies presented in this thesis address open questions related to the formation and use of word sound memories. Chapter four presents a meta-analysis of studies using the auditory lexical decision task to measure the quality of word sound representations in typically developing children and children with DLD (developmental language disorder). This chapter also provides baseline data and recommendations of use to both researchers and clinicians. The study presented in chapter five uses Bayesian multi-level regression to model large-scale parental report data from CDI’s (communicative development inventories). This study provides insight into the role that high phonological neighbourhood density plays in early word production, though not comprehension, relative to factors including word length, frequency, concreteness, and relevance to infants. The study in chapter six uses the same methodology to evaluate individual differences in the importance of neighbourhood density as a predictor of word production, and presents results with implications for the development of clinical interventions. The study in chapter seven presents a quantitative corpus analysis examining spoken word accuracy and variability rates in typically developing children recorded over a three-year period. I report the effects of age, frequency, and neighbourhood density on accuracy and variability rates, and argue against the view that such rates may provide a reliable marker of speech sound disorder. Finally, in chapter eight, I present a neural network simulation of the high neighbourhood density learning advantage reported in studies two, three, and four, and present an account of network performance that can also accommodate contradictory behavioural evidence of low-density word learning advantages. All studies are integrated within an exemplar-based framework of auditory-lexical development emphasising the mechanism of analogous generalisation. In the interests of transparency this thesis is accompanied by an online repository containing pre-registration protocols and the data and code required to reproduce each analysis: osf.io/u3qsc.