Children who grow up learning two languages are better at multi-tasking but slower at building vocabulary than their monolingual peers, two Canadian psychologists have found.

Raluca Barac and Ellen Bialystok tested a total of 104 six-year-old public school children, then compared the results of monolingual anglophones with their Chinese-English, French-English and Spanish-English counterparts.

In a test of their ability to pay attention, plan, organize and strategize, the children were all asked to press a computer button while viewing images of either animals or colors.

They all responded at the same speed when responses were limited to either animals or colors -- but when asked to switch from animals to colors only, and press a different button, the bilinguals proved faster at making the changeover.

“In simplest terms, the switching task is an indicator of the ability to multi-task,” said Peggy McCardle, chief of the child development and behavior branch of the National Institute of Child Health and Human Development.

“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,” she said in a press statement Tuesday.

Testing for verbal ability, Barac and Bialystok found the English monolingual youngsters scored higher for vocabulary, word meaning and grammar than the bilingual children, the institute said.

That was apparently due to the fact that they only had to learn one language, although the Spanish bilinguals -- who attended English-language schools -- came a close second in vocabulary.

In contrast to previous studies, the children who took part in the study came from similar economic and social backgrounds in multi-ethnic Toronto -- minimizing the potential impact of socio-economic differences on the results.

Barac and Bialystok teach at York University in Toronto. Their research was funded by the institute, a branch of the US government‘s Department of Health, and published in the journal Child Development. (AFP)