Bilingualism as a Source of Experience-Dependent Plasticity: Mechanisms and Limits

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This research examines bilingualism as a means of investigating the potential for experience-related neuroplasticity to affect cognitive performance across the lifespan. Bilinguals generally outperform monolinguals on executive function (EF) tasks that require avoiding distraction, shifting between goals, and engaging working memory and show differences in brain structure and function. Moreover, bilinguals display symptoms of dementia at a later stage of disease than monolinguals, all else being equal. However, not all studies find these effects so much remains unknown. The proposed studies will use behavioral and neuroimaging methods to examine children, young adults and older adults to address two crucial gaps in this literature. The first gap is identification of the mechanism responsible for the reported effects. The early explanation was based on a componential view of EF and singled out inhibition as most relevant. The idea was that bilingual language use required inhibition to avoid interference from the jointly activated non-target language but new evidence is inconsistent with this view. My hypothesis is that bilingual experience leads to an adaptation in attention networks that follow from navigating a complex linguistic environment. Attention is involved in all aspects of EF but not tied to a single component. Critically, the component and attention views make different predictions about bilingual performance will diverge. From a componential view of EF, bilinguals will outperform monolinguals on tasks that rely on inhibition; from an attention view, bilinguals will outperform monolinguals on tasks that require efficient attention strategies on complex conditions, regardless of the EF component. These studies will manipulate task difficulty across paradigms to compare the effect of component process demands and attention demands for monolingual and bilingual participants. The second gap is identification of the conditions necessary for these adaptations to occur. Individual differences and context clearly interact with these processes to determine outcomes. Fragmentary evidence points to the need for attention systems to be intact for bilingualism to lead to positive outcomes; bilingual adults with ADHD do not show the benefits found for non-ADHD bilinguals, and bilingual older adults with EF deficits do not show any delay of dementia symptoms. The hypothesis is that for individuals with compromised attention systems, bilingualism will exacerbate rather than benefit an already struggling system. Understanding how bilingualism leads to neuroplastic changes in cognition creates the possibility for devising interventions to improve cognition broadly, stimulating essential development in children and mitigating cognitive decline as older adults sit on the threshold between normal aging and dementia. Identifying attention as a relevant bridge between experience and cognition will have clear implications for new directions in intervention.