We're often told that people who speak two or more languages have a distinct cognitive advantage over monolingual speakers – but how big is this advantage, really?

In a fantastic piece published in this week's New Yorker, Maria Konnikova considers the evidence that supports what what researchers have come to call "the bilingual advantage":

For the first half of the twentieth century, researchers actually thought that bilingualism put a child at a disadvantage, something that hurt her I.Q. and verbal development. But, in recent years, the notion of a bilingual advantage has emerged from research to the contrary, research that has seemed both far-reaching and compelling, much of it coming from the careful work of the psychologist Ellen Bialystok. For many tasks, including ones that involve working memory, bilingual speakers seem to have an edge. In a 2012 review of the evidence, Bialystok showed that bilinguals did indeed show enhanced executive control, a quality that has been linked, among other things, to better academic performance. And when it comes to qualities like sustained attention and switching between tasks effectively, bilinguals often come out ahead. It seems fairly evident then that, given a choice, you should raise your child to speak more than one language. Indeed, papers touting "Creativity and Bilingualism," "Cognitive Advantages of Bilingual Five-Year-Olds," "A Bilingual Advantage in Task-Switching," "Bilingualism Reduces Native-Language Interference During Novel-Word Learning," and "Good Language-Switchers Are Good Task-Switchers"—and the resulting books with provocative titles such as "The Bilingual Edge" and "Bilingual Is Better"—suggest that raising a bilingual child is, in large part, a recipe for raising a successful child.

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But the evidence in support of bilingual superiority is less one-sided than many of us have been led to believe. In a systematic analysis of abstracts submitted to 169 research conferences, psychologist Angela de Bruin has uncovered in the field a clear bias against the reporting of negative results:

At conferences, about half the presented results provided either complete or partial support for the bilingual advantage on certain tasks, while half provided partial or complete refutation. When it came to the publications that appeared after the preliminary presentation, though, the split was decidedly different. Sixty-eight per cent of the studies that demonstrated a bilingual advantage found a home in a scientific journal, compared to just twenty-nine per cent of those that found either no difference or a monolingual edge. "Our overview," de Bruin concluded, "shows that there is a distorted image of the actual study outcomes on bilingualism, with researchers (and media) believing that the positive effect of bilingualism on nonlinguistic cognitive processes is strong and unchallenged."

It's important to point out that De Bruin does not disagree that there are advantages to being bilingual, only with the oft-repeated notion that this advantage is somehow global or pervasive. In fact, there may be more compelling reasons to continue learning new languages well into adulthood than those usually trumpeted under the banner of a "bilingual advantage." Check out Konnikova's full writeup to find out what they are.

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