Cognitive processing in multilinguals explained by individual variability in language switching proficiency

Research on the cognitive advantages of bilingualism has triggered much discussion over the last decade. Some researchers have repeatedly given proof of better performance for multilingual participants across the lifespan (Bialystok et al., 2004). Other researchers have not been able to replicate the advantage found in multilingual populations. Reasons for these contradictory results include differences in the tasks employed, in sample selection (for instance, confounding variables such as participants' ethnicity or socio-economic status), or in sociolinguistic background (Morton & Harper, 2007; Costa et al., 2009).

However, little attention has been given to individual variability within a group of multilinguals in order to explain differences in performance on cognitive control tasks. If the hypothesis is true that better language switching leads to improved cognitive control, individual scores on language switching ability need to be accounted for in an all-encompassing research on the cognitive advantages to bilingualism.

This paper presents one part of an ongoing research program carried out in the Dutch-French bilingual city of Brussels, Belgium. We have used functional magnetic resonance imaging (fMRI) to study the effects of variability in language switching on cognitive control. In addition to a Simon task, which is a well-known and reported conflict task, we gave them a language switching lexical decision task. We have compared scores on both tasks for all individuals to trace the interaction between individual variability in language switching ability and cognitive processing in multilinguals.