Lexicon development in bilingual toddler

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Bilingualism, not monolingualism, is the global norm (UNESCO, 2003). We have a good understanding of how the minds of adult bilinguals store words in their two languages: for example, we know that a proficient French-English bilingual, when hearing the English word 'dog', unconsciously inhibits its French equivalent, 'chien'. However, there is little known about how the words are organised in the mind of a young bilingual. This is not a trivial problem as even monolingual children's mental processing of words is different from that of adults. Understanding how bilingual children deal with words has important implications for assessment of their language learning abilities. Bilinguals tend to have delays in critical stages of language development, which can lead to over-referral for Speech and Language Therapy. The opposite problem is also prevalent, under-referral on the basis that some delay, relative to monolinguals, is expected. Such failings in the assessment system are costly for society in the short-term and the long-term, as a child with undetected language problems will struggle academically and socially.The absence of bilingual-specific tools for language assessment can be attributed to (1) lack of knowledge about the architecture of the developing bilingual lexicon (2) the multiple social and linguistic influences on bilingual language development, which are poorly understood, particularly in combination. For example, we know that the linguistic distance between the languages being learnt is very important, but we don't have tools to measure linguistic distance in children.Here we propose to produce a new computer-based model of the developing bilingual lexicon, based on experimental data, that will provide (1) significant advances in our theoretical understanding of bilingualism, and (2) pave the road for the development of a universal tool for the assessment of young bilinguals' language development.This project is organised in three streams: two three-year data-collection streams and a final-year modelling stream. Children will be aged 18 months, which usually marks the onset of a sharp increase in vocabulary development.In the first data-collection stream, we will run a series of experiments examining the organisation of words in bilingual infants. In collaboration with the Oxford Babylab, pairs of spoken words related or unrelated in meaning ('chien'-'pig' or 'chien'-'boat') will be presented accompanied by appropriate pictures. Children's looking times for pictures associated with related versus unrelated pairs will inform us about the strength of connections between words.In the second data-collection stream, we aim to measure the interactions between the external factors influencing vocabulary development in bilinguals. Two hundred and fifty bilingual toddlers will be assessed in five different sites in the UK (Plymouth, Bangor, Birmingham, Kent and Liverpool) to get a large range of specifics in terms of language background and socioeconomic status. Infants' amount and mode of exposure to their two languages will be checked through appropriate questionnaires. Their level of vocabulary in English and the additional language will be evaluated through language-specific MacArthur-Bates Communicative Development Inventories (CDI), vocabulary questionnaires with versions for 60 languages. The data from the CDIs will help us to design child-adjusted metrics of distance between the two languages being learned. In the final, modelling stream, the findings from the previous data-collection streams will be used to create a computational model of bilingual lexicon development, which will be able to predict language development in toddlers in different social and linguistic environments.This project will considerably advance our understanding of language processing in young bilinguals, and prepare the ground for the design of a universal language assessment tool for this currently overlooked population.