Interactions between language experience and cognitive abilities in word learning and word recognition

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There has been much recent interest in the finding of a "bilingual advantage". That is, bilingualism confers benefits on various non-linguistic cognitive measures, particularly executive control. Yet bilingual children often face a different situation when it comes to language: their profile often negatively diverges from that of monolinguals, potentially leading to classification as language-disordered. This, in turn, contributes to public policies that discourage bilingualism. Most studies have examined ways in which bilinguals are better or worse than monolinguals. However, it is possible that bilinguals simply approach tasks differently, or weight information sources differently. This leads to advantages in some tasks and disadvantages in others. This dissertation seeks a principled understanding of this conflict by testing the hypothesis that differences in linguistic exposure and age alter how individuals approach the problem space for learning and comprehending language. To become proficient in a language, learners must process complex acoustic information, while relying on cognition to accomplish higher thought processes like working memory and attention. Over the course of development, individuals rely on these skills to acquire an impressive vocabulary, and to recognize words even in adverse listening conditions (e.g., when speech is heard in the presence of noise).

I present findings from four experiments with monolingual and bilingual adults and toddlers. In adulthood, despite showing advantages in cognitive control, bilinguals appear to be less accurate than monolinguals at identifying familiar words in the presence of white noise. However, the bilingual "disadvantage" identified during word recognition was not present when listeners were asked to acquire novel word-object relations that were trained either in noise or in quiet. Similar group differences were identified with 30-month-olds during word recognition. Bilingual children performed significantly worse than monolinguals, particularly when asked to identify words that were accompanied by white noise. Unlike the pattern shown by adults, when presented with a word-learning task, monolingual but not bilingual toddlers were able to acquire novel word-object associations. Data from this work thus suggest that age, linguistic experience, and the demands associated with the type of task all play a role in the ability of listeners to process speech in noise.