The Role of Language Similarity in the Development of the Infant Bilingual Lexicon

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How do infants growing up in bilingual homes learn words and how are these words represented in the infant bilingual mind? We propose that answers to these questions are heavily influenced by the similarity of the languages involved. For instance, Dutch and English are close languages, while Chinese and English are distant. At the word level, language similarity is reflected in the percentage of 'cognate' words that two languages share. Cognates are word translations that share the same etymological origin and sound similar (such as father and vader in English and Dutch). Evidence for the importance of cognates in bilinguals comes from naming studies with adults. For example, adult bilinguals can name pictures faster when they correspond to cognates (father/vader) than pictures corresponding to non-cognates (bicycle/fiets). A critical property of adult bilingualism is that of non-selective access to the words in both languages. Bilinguals activate all potential word candidates from either language consistent with what they hear or want to say, even in fully monolingual situations. Such findings point to important interactions between the two languages in the bilingual mind. Such interactions are likely to be even more important in the case of infants raised bilingually. Such infants often know only one word in one of their languages to refer to a concept. In this situation, cross-language lexical similarity may facilitate word recognition, but it may hinder the establishment of language-specific lexicons. We propose to conduct a series of experimental studies to uncover the structure of the mental lexicon in bilingual infants, and to construct brain-inspired models to explore theoretical accounts of the structure of their lexicon(s). We will exploit the availability of bilingual learning environments in Oxford and Barcelona. In Barcelona, there is ready access to bilingual infants learning both Spanish and Catalan (two Romance languages sharing many cognates). In Oxford, there is a sufficiently large number of bilingual Spanish and English families. Spanish and English have fewer cognates and offers a critical contrast to the Barcelona context.Experiments: We will use new experimental paradigms, pioneered on monolingual infants in the Oxford BabyLab, that employ well-understood eye-tracking and neuro-imaging techniques. The methods developed with monolingual infants are ideally suited to exploring our research questions. The tasks involve infants looking at pictures at the same time as they hear speech. By monitoring their eye-movements and recording their brain activity, we hope to discover important clues as to how their two languages influence their reaction to the pictures they see. An important methodological advantage of this project is that it will follow infants' performance in a longitudinal manner - at 18, 24 and 30 months of age. A longitudinal design allows us to consider the substantial individual differences observed between infants in their vocabulary development and to apply sophisticated and powerful statistical analyses to the data collected on the project. We will also test monolingual infants on exactly the same set of studies as our bilingual population, thereby providing the appropriate baseline against which to assess the bilingual infants.Modelling: The purpose in constructing a neural model is to understand the mechanism that underlies observed behaviour. Current bilingual computational models only consider adult (large and stable) vocabularies. We will develop the first computational model of early bilingual learning. Recently, we have shown how developmental changes in the self-organising processes in neural network models of word learning can capture important aspects of infant behaviour. We will translate these modelling insights from monolingual infant word learning and recognition to infant bilingual development, in a manner that honours the results of our experiments.