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Children who grow up learning to speak two languages are better at switching between tasks than children who speak only one language, according to a study funded in part by the National Institutes of Health (NIH). However, the researchers also found that bilinguals are slower to acquire vocabulary than monolinguals because they must divide their time between two languages while monolinguals can focus on just one (Child Development, online, April 3, 2012).

In the study bilingual and monolingual children were asked to press a computer key as they viewed a series of images depicting animals or colors. When the responses were limited to either of the two categories, the children responded at the same speed. But when the children were asked to switch from animals to a color and press a different button for the new category, bilinguals were faster at making the change than monolinguals.

Researchers often use this switching task to gauge executive functioning. The task engages three mental processes: working memory, inhibition and shifting.

"The switching task is an indicator of the ability to multitask," said Peggy McCardle, PhD, chief of the Child Development and Behavior Branch at the National Institute of Child Health and Human Development (NICHD), which provided funding for the study. "Bilinguals have two sets of language rules in mind, and their brains apparently are wired to toggle back and forth between them depending on the circumstances."

The study was conducted by Raluca Barac and Ellen Bialystok at York University in Toronto, Canada. The researchers tested a total of 104 children. They compared test results of English-speaking monolinguals to those of Chinese-English bilinguals, French-English bilinguals, and Spanish-English bilinguals.

More than one in five U.S. children spoke a language other than English at home in 2009.

Studies of bilingualism in this country often are complicated by the cultural and economic differences between English-speaking monolinguals and immigrant groups of second language learners. As a result, researchers cannot be sure if differences in test scores between the groups is due to bilingualism or economic differences.

Canada has a large French-speaking population with income levels comparable to that of the English-speaking population. This allowed researchers of the current study to rule out economic differences as a potential contributor to the results, at least when comparing English-speaking monolinguals to French-English bilinguals.

The researchers tested the verbal and nonverbal cognitive abilities of 104 6-year-olds from the Toronto area. All were public school students and from similar economic and social backgrounds. In addition to English monolinguals and English-French bilinguals, the study included English-Spanish and English-Chinese bilinguals.

Along with the switching task, the test battery consisted of three English language tests of verbal ability. The verbal tests measured vocabulary and understanding of such linguistic tasks as forming plurals, conjugating verbs, grammatical structure and English pronunciation rules.

While the accuracy scores for the switching task were similar for all of the groups, the bilinguals could switch from one task to another more rapidly than the monolinguals.

Earlier studies had shown that bilinguals could perform the switching task more rapidly, but those studies tended to include only one group of bilinguals. As a result, researchers were not able to rule out whether it was bilingualism itself that conferred the increased ability to make the switch or some aspect of the language they spoke. The fact that all three groups of bilinguals in the current study could make the switch faster than the monolinguals indicates that bilingualism confers the more rapid switching ability.

In tests of verbal ability the English language monolinguals scored highest on a measure of English receptive vocabulary. Because they are learning only one language, they are able to acquire a larger vocabulary than any of the bilingual groups. However, English-Spanish bilinguals scored nearly as well as English monolinguals on the measure of receptive vocabulary.

The monolinguals also scored higher than the other groups on a test measuring knowledge of English grammar and word meaning. The English-Spanish bilinguals scored higher on the grammatical test than the Chinese-English bilinguals, who scored higher than English-French bilinguals. The Spanish bilinguals attended English language schools, which may have provided an advantage in tests of English grammar compared to the French bilinguals, who attended French language schools.

The Spanish bilinguals scored highest on the test of metalinguistic awareness. The monolinguals and the Chinese and French bilinguals received comparable scores on the metalinguistic test. The researchers concluded that the similarity of Spanish and English and the fact that the Spanish bilinguals attended English-speaking schools likely gave the Spanish bilinguals an advantage over all the other groups on the metalinguistic task, as well as an advantage over the bilingual groups in the other language tasks.