Cognitive effects of bilingualism

Bilingualism, a subset of multilingualism, means having proficiency in two or more languages. A bilingual individual is traditionally defined as someone who understands and produces two or more languages on a regular basis. A bilingual individual's initial exposure to both languages may start in early childhood, e.g. before age 3, but exposure may also begin later in life, in monolingual or bilingual education. Equal proficiency in a bilingual individuals' languages is rarely seen as it typically varies by domain. For example, a bilingual individual may have greater proficiency for work-related terms in one language, and family-related terms in another language.

Being bilingual has been linked to a number of cognitive benefits. Research on how a bilingual individual's first language (L1) and second language (L2) interact shows that both languages have an influence on the function of one another and on cognitive function outside of language. Research on executive functions like working memory, perception, and attentional and inhibitory control, suggests that bilinguals can benefit from significant cognitive advantages over monolingual peers in various settings. There are also age-related benefits which seem to protect against cognitive decline in older adults.

Throughout the history of research into the cognitive advantages of bilingualism, views have shifted from a subtractive to an additive perspective: it is now believed that being bilingual adds to an individual's abilities rather than subtracting from it.

There is, however, strong disagreement over how findings on this subject should be interpreted. Systematic reviews and meta-analyses of executive functioning studies have failed to find compelling evidence for cognitive advantages in healthy adults or in participants across a broader age range. Moreover, the distribution of effect sizes in meta-analyses suggest publication bias, or that the reporting of bilingualism effects on executive functioning give a distorted view of the evidence.