Interaction of language and control processes in monolingual and bilingual cognition

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Neuroplasticity is the idea that brain structure and function change in response to experience, offering the possibility for lifelong adaptation of cognitive ability. Such adaptation may be a powerful approach to interventions designed to protect cognitive function with aging. One experience that has been shown to modify cognitive function is bilingualism: across the lifespan, bilinguals outperform monolinguals on various tests of executive control (EC). However, much is unknown about these effects, both for bilingualism in particular and neuroplasticity more generally. The proposed studies will use behavioural and EEG measures to study younger and older adults who are monolingual or bilingual to understand how this experience affects cognitive ability. There are two crucial outstanding issues in this research.***1: Conditions for cognitive effects of bilingualism***Although a large body of research has reported significant bilingual advantages in EC, there is great variability across studies with some finding no group differences. An important question, therefore, is to determine the conditions under which effects of bilingualism are observed. In general, group differences are more likely found with children and older adults than with younger adults, with complex tasks than with simpler tasks, and with neuroimaging studies than with behavioural studies. These and other factors will be investigated to determine conditions under which bilingualism leads to these beneficial outcomes. ***2: Functional changes in processing***The usual explanation for enhanced EC in bilinguals is that bilinguals use EC to control attention to two jointly activated languages so they can select the target language and avoid intrusions from the other language. The joint activation of both languages for bilinguals is well documented, so language selection is a constant problem of bilingual language use. The idea is that the use of the EC network for language selection fortifies that network and makes it more efficient for other purposes. However, it may also be that the EC network is modified to create a network that is used by bilinguals for both verbal and nonverbal processing, a network that is qualitatively different from that used by monolinguals. This possibility that bilingualism creates a new integrated control network would help to explain the finding that bilinguals show signs of dementia later than monolinguals. Because dementia is usually displayed first as a memory problem, it is hard to understand how bilingual EC advantages would protect performance. However, an integrated control network could allow bilinguals to compensate for failure in some domains by relying on more intact ones. Thus, evidence for the nature of the control networks used by bilinguals has implications for understanding an important aspect of neuroplasticity that may have some application to preserving cognitive function in aging. ********