UC Irvine

An aim of research on bilingualism is to understand how the brain adapts to the use of more than one language. Although several important discoveries and insights about the consequences of bilingualism have been generated over the last several decades, concerns about replicability have narrowed the scope of inquiry and discussion to the application of prescriptions about sample size and method. In this dissertation, I critique this approach and reformulate its value by placing it in the broader context of science as a discovery process, in which incremental understanding, methodological and analytical diversification, the framing of our questions, and even underpowered studies, are essential to advance. I propose that this necessitates research practices and tools that: 1) focus on examining variation in the relation between language processing and cognitive functioning; 2) allow us to identify meaningful interactions rather than main effects only; and 3) provide a rich characterization of the participant sample to identify bilingual phenotypes: the adaptive variety induced by the interplay between biology and culture. In seeking to apply this framework, I then present two empirical studies investigating the cognitive mechanisms that enable fluent language use, and examine the hypothesis that proficient bilingualism is characterized by the active engagement of a regulatory mechanism that adapts to the demands of the language environment. To test this, I examine individual differences in language production and cognitive control across four groups of proficient bilingual phenotypes who differ with respect to the interactional contexts of language use. In Study 1, the results suggest that lexical access is mediated by a systematic interaction between regulation of the dominant language and cognitive control, but that the manifestation of this interaction depends on whether bilinguals are immersed in a second-language environment, a context in which active regulation is required. In Study 2, the results further confirm that dominant-language regulation is not analogous to proficiency per se; rather, it may more adequately reflect the coordination of language-related and domain-general resources that interactively contribute to the accessibility of information in the language network. Together, these studies suggest that language regulation is a fundamental feature of bilingual brains that engages a combination of language-related and domain-general cognitive resources to enable proficient language use.