The Bilingual Cognitive Advantage: No Smoke without Fire?

In a commentary on a review article by Paap and colleagues [1], and a response to that review by Saidi and Ansaldo [2], I examine the key arguments for and against the existence of a 'bilingual advantage' in cognitive functions, including the effects of small samples, and of confounding variables in studies on both sides of the debate. While accepting that the behavioural evidence here is inconclusive, I argue that the evidence for wide-ranging, plastic change in the bilingual brain would seem to predict that bilingualism may have similarly wide-ranging effects on behaviour. Finally, I note that bilingual cognitive advantages - if any exist - are inherently longitudinal phenomena, in the sense that they are thought to emerge as a function of the transfer of practice effects from linguistic to non-linguistic cognitive control skills. In that context, the most direct way to characterise those advantages, and the mechanisms that make them possible, may be with longitudinal studies, which also naturally control for many of the factors that may confound the cross-sectional studies which have dominated the field so far.