Bilingualism may protect the mind from deterioration in old age

It is certainly useful to be able to speak more than one language. But, according to a paper by Ellen Bialystok, of York University in Canada, and her colleagues, in this month's issue of Psychology and Aging, it is useful not just for the obvious reason that it makes it possible to talk to more people. Dr Bialystok found that “bilinguals”—individuals who grew up speaking two languages and continue to do so—performed significantly better on a variety of simple cognitive tasks than people who speak only one. Furthermore, the differences between the two groups increased with age, leading her to hypothesise that knowing and using two languages inhibits the mind's decline.
The tests she used rely on a phenomenon known as the Simon effect, in which cognitive clashes cause a person's reaction time to slow down. Dr Bialystok's Simon-effect task involved a computer that displayed either a red or a blue square on either the left-hand or the right-hand side of its screen. She asked her subjects to press the left “shift” key on the keyboard if the square was blue, and the right one if the square was red. The cognitive clash here is between the location of the square and that of the key. It takes longer to hit the left key if the blue square appears on the right-hand side than if it, too, appears on the left—and mutatis mutandis for the red square and the right key.
Initially, Dr Bialystok exposed her subjects to four trial runs, each consisting of a random sequence of 24 squares. Despite the fact that the two groups, bilingual and monoglot, had comparable socio-economic backgrounds and general intelligence scores, Dr Bialystok found that the bilinguals responded faster than the monoglots. That was true both when the squares were on the “correct” side of the screen, so to speak, and—even more so—when they were not.
Her first thought was that this might be because someone who speaks two languages is able to suppress the activity of parts of the brain—in particular, the part that speaks whichever language is not in use at a given moment. This, she speculated, might allow a bilingual individual to suppress information about the spatial position of a square and thus concentrate on the colour.
To test her hypothesis, she gave her subjects a second task. This involved four colours instead of two, but placed the squares squarely, as it were, in the centre of the screen. That made the task more complicated, but eliminated the Simon effect and thus any possible need for suppression.
The result was the same. Bilinguals did better than monoglots. This shows that the effect of bilingualism on space-related reaction time must be caused by more than mere inhibition—though Dr Bialystok has no idea what. On the other hand, when the subjects were exposed to ten, rather than four, runs of squares, the performance of monoglots caught up with that of bilinguals in the last few sets. This, Dr Bialystok says, suggests that the advantages of bilingualism are reduced once a task has become so well learned that it can be performed automatically.
In all cases, however, the performance gap between monoglots and bilinguals increased with age—something that Dr Bialystok is not yet sure how to explain, but which suggests that bilingualism protects the mind against decline. It may never be possible to prove W.H. Auden's dictum that “time...worships language”. But, for the present, it seems that reaction times depend heavily on it.

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