Bilingualism.

The cognitive and linguistic processes involved in the acquisition and use of two languages are systematically different from those processes engaged in monolingual language use, leading to detectable changes in language and cognitive outcomes for bilinguals. The present article describes these differences and offers speculation on possible mechanisms. Measures of linguistic proficiency and processing are often poorer in bilinguals than in monolinguals: bilingual children have a smaller vocabulary in each language than comparable monolingual children in that language and bilingual adults take longer to retrieve specific words than monolinguals. In contrast, measures of nonverbal executive control, including the ability to selectively attend to relevant information, inhibit distraction, and shift between tasks is generally better in bilinguals than in monolinguals. These two types of outcomes are illustrated and explained through behavioral and neuroimaging evidence. The implications of these effects of bilingualism on cognitive and linguistic processing are considered in terms of both their clinical and theoretical consequences.