Summary

There has been an enormous expansion during the early 21st century in psychological research on topics relating to bilingualism, paralleling developments in other fields of psychology that investigate the interface between experience and the mind. These issues reflect the view that brains and minds remain plastic and can be modified by experience throughout life. In the case of bilingualism, a central question is whether bilingual experience modifies cognitive systems in general, and more specifically, if it improves cognitive ability and executive functioning. The research has produced contradictory results, in some cases supporting a beneficial effect on cognition and in some cases indicating no effect. Crucially, there is essentially no research that indicates that bilingualism is associated with poorer cognitive outcomes than found for those who are monolingual. Studies showing a positive role for bilingualism on cognitive outcomes have been reported across the life span. Early research with children in the first half of the 20th century concluded that bilingualism was detrimental to children’s intelligence, a claim that has been thoroughly refuted and replaced with evidence identifying specific cognitive processes that are more advanced in bilingual than in monolingual children. A few studies have even reported better attentional control, the foundation of executive functioning, for infants in the first year of life being raised in bilingual homes than for those in monolingual environments. Young adults frequently show no behavioral differences between language groups when performing executive function tasks, but neuroimaging (electrophysiology or brain imaging) consistently indicates that monolinguals and bilinguals use different brain regions and different degrees of effort to perform these tasks. The clearest language group differences, however, occur in older age where evidence for cognitive reserve from bilingualism is found most clearly in the postponement of symptoms of dementia. Therefore, it is necessary to analyze the factors that mediate these effects, notably, the nature of bilingual experience and the details of the cognitive task being used. The conclusion is that bilingualism is complex but there is evidence for a consistent and systematic impact on cognitive systems.