The Bilingual Advantage: Three Years Later

In a post published three years ago, I stated that the debate on the cognitive advantage of being bilingual had entered troubled waters and that some researchers even doubted its very existence. Findings that had "captured our hearts and minds," as Aneta Pavlenko had so rightly stated, were being questioned or could not be replicated. The list of problems cited by researchers in the field was long, not the least being that it was difficult to prove a direct causal relationship between bilingualism and cognitive advantage. I ended the post by listing some of the solutions that were proposed for future research.

Three years have now gone by and numerous other studies have been undertaken. What better way to understand where things stand than to interview Dr. Mark Antoniou, Research Program Leader at Western Sydney University in Australia. He has just published a review article on the topic, The advantages of bilingualism debate, and he is ideally placed to bring us up to date. We thank him wholeheartedly.

In the first pages of your review, two sentences stand out from the text: "... the field has now reached an impasse", and "...there is no consensus as yet on the relationship between bilingualism and cognitive benefits". Can you say a few introductory words on this?

The debate surrounding the bilingual advantage is very heated and fierce. It is also repetitive. Certain research groups consistently find support for a bilingual advantage, while other groups consistently find none. Those familiar with the literature are able to surmise whether the findings will be for or against the existence of a bilingual advantage simply by peering at the list of authors.

Your review covers three areas of research. The first concerns experimental evidence for a bilingual advantage in executive functions. Could you explain what is meant by "executive functions"?

Executive functions are cognitive processes that are used to control behavior in service of a goal. They include our ability to plan, direct attention, ignore distracting information, withhold habitual responses, be cognitively flexible, and juggle multiple tasks. Executive functions have been linked to success throughout life: academic achievement, positive behaviors, healthy relationships, and occupational success. It is thought by some that bilingual experience changes brain areas responsible for executive functions, and this leads to cognitive improvements in nonlinguistic processing.

Evidence has been found for a bilingual advantage in cognitive abilities, primarily in older adults, but there is also evidence against it. What are the problems that have led to this discrepancy?

There are many problems: differing definitions of bilingualism, misunderstanding the nature of bilingualism, misinterpretation of prior findings, studies plagued by methodological confounds, a publication bias that limited the chances of publishing null findings, and drawing conclusions that are not supported by the data. These problems may be found on both sides of the debate.

The second area of research you deal with concerns cognitive aging and the bilingual advantage. Why might bilingualism delay the onset of neurodegenerative disease such as dementia?

I'll focus on those researchers who have argued that bilingualism may indeed delay the incidence of dementia, but let's keep in mind that some passionately challenge this view. The truth is that we do not yet have a comprehensive theory that is capable of explaining the role of bilingualism.

A popular view is that over the course of a lifetime, a bilingual’s two languages constantly interact and in order to manage this competition, a bilingual’s executive function system, and the brain structures associated with it, will develop in ways that differ from a monolingual who faces no such pressures. Consequently, as we age and experience age-related cognitive decline, the bilingual brain is more resistant to the neurodegeneration that occurs. This is referred to as cognitive reserve, but the way that this works is not agreed upon either.

One possibility is that brain structures stay healthier because they are more resistant to neurodegeneration. Another possibility is that when certain structures or connections between brain regions are damaged and disrupted, the bilingual brain is able to compensate by making use of alternative intact pathways. The challenge facing any theory seeking to reconcile these findings is that there exists evidence for each of these seemingly incompatible views.

In this area too, evidence has been found for and against the bilingual advantage. You state that the cause may be that some studies are prospective whilst others are retrospective. What is meant by this?

Retrospective studies are historical in nature. They involve examination of medical records and attempt to understand the causes of neuropathology after the fact by examining relationships between demographic data, and other data, and diagnosis. Such studies were the first to support the claim that bilingualism may delay the incidence of dementia. They have been criticized by some as being methodologically flawed but not all these criticisms stand up to scrutiny.

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Prospective studies involve recruiting a sample of participants and following them longitudinally over some period of time. Studies on dementia incidence typically involve recruiting a large initial sample, following those individuals over many years, and taking note of which people were later diagnosed with dementia and comparing whether differences can be observed between mono- and bilinguals. They too are limited by methodological confounds.

In the third area of research, brain plasticity resulting from bilingualism, the results are clearer. What are they?

Studies that examine structural changes in the brain resulting from long-term bilingual language use present results that are particularly compelling. Bilingualism unquestionably changes both gray and white matter in numerous brain structures distributed across a wide network, and many of these structures are associated with executive functions. Although we know that bilingual and monolingual brains differ, it is less clear how differences in brain structure relate to performance on experimental tasks.

One message that emerges from your review is that bilingual advantages are unlikely to extend to all bilinguals under all circumstances. Could you explain this?

Recent work has moved away from comparing separate groups of monolinguals and bilinguals, but has instead come to the realization that bilinguals also differ from other bilinguals in terms of their patterns of language learning and use. We are starting to see studies treat bilingualism as a continuum. Such designs allow one to explore bilingual variables that may affect cognitive abilities.

You end by stating that "the bilingual advantage debate is likely to roar on" and you give a few leads as to where this research could go. Please explain.

It is roaring on as we speak and new papers are published regularly. We can already see the direction in which the field is heading. Studies are being conducted with larger sample sizes to make them more solid. There is a move away from using bilingualism as a categorical variable, as we saw above, and towards examining a monolingual-bilingual continuum. Such designs make it possible to ask questions regarding “how much bilingual experience is needed for an advantage to emerge?” The goal would be to predict which types of bilinguals would be more likely to show an advantage in a given domain and which would be less likely.

This said, we still have some way to go before we can reconcile those on opposite sides of the debate concerning the cognitive consequences of bilingualism.

For a full list of "Life as a bilingual" blog posts by content area, see here, or visit François Grosjean's website.