| Summary: | To rise to the challenge of acquiring their native language, infants must deploy tools to support their learning. This thesis compared infants growing up in two very different language environments, monolingual and bilingual, to better understand these tools and how their development and use changes with the context of language acquisition.
The first set of studies − Chapter 2 − showed that infants adapt very early-developing tools to the context of their prenatal experience. Newborns born to bilingual mothers directed their attention to both of their native languages, while monolinguals preferred listening to their single native language. However, prenatal bilingual experience did not result in language confusion, as language discrimination was robustly maintained in both monolinguals and bilinguals. Thus, learning mechanisms allow experience-based listening preferences, while enduring perceptual sensitivities support language discrimination even in challenging language environments.
Chapter 3 investigated a fundamental word learning tool: the ability to associate word and object. Monolinguals and bilinguals showed an identical developmental trajectory, suggesting that, unlike some aspects of word learning, this associative ability is equivalent across different types of early language environments.
Chapters 4 and 5 explored the development of a heuristic for learning novel words. Disambiguation is the strategy of associating a novel word with a novel object, rather than a familiar one. In Chapter 4, disambiguation was robustly demonstrated by 18-month-old monolinguals, but not by age-matched bilinguals and trilinguals. The results supported the “lexicon structure hypothesis”, that disambiguation develops with mounting evidence for a one-to-one mapping between words and their referents, as is typical for monolinguals. For bilinguals, translation equivalents (cross-language synonyms) represent a departure from one-to-one mapping. Chapter 5 directly tested the lexicon structure hypothesis, by comparing subgroups of bilinguals who knew few translation equivalents to bilinguals who knew many. Only the former group showed disambiguation, supporting the lexicon structure hypothesis.
The series of studies presented in this thesis provides a window into language acquisition across all infants. Whether growing up monolingual or bilingual, infants harmonize their development and use of the tools of language acquisition to the particular challenges mounted by their language environment.
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