Bilingualism gives children a distinct cognitive advantage over their monolingual peers, says a study by York psychology Professor Ellen Bialystok.
The study, published in the journal Developmental Psychology, finds that bilingual children outperform monolingual students on tasks involving executive control – the cognitive processes that allow for abstract thinking, planning, initiating and inhibiting actions. Three separate experiments on six-year-old students demonstrated that children who routinely speak more than one language can 
better focus on pertinent information and suppress their attention to distracting or irrelevant items.
Right: Ellen Bialystok
“This ability to selectively focus on wanted information and ignore distracting elements is a central feature of all higher thought," says study author Bialystok, a Distinguished Research Professor of Psychology in York’s Faculty of Health. "These results have implications for our overall understanding of how bilingualism influences cognitive development in its early stages," she says.
Researchers evaluated bilingual and monolingual children attending the same public school in a middle-class neighbourhood of Toronto. Bilingual students spoke a language other than English at home, including Cantonese, French, Russian, Mandarin, Urdu, Hindi and Spanish. Six-year-olds were selected as they are at a critical stage in their cognitive development: previous studies have established this as the age at which measurable differences in the brains of bilingual children appear.
Participants were tested using standardized neuropsychological tests, including the global-local task and the trail-making test (TMT). The latter is widely used to assess brain functioning in both children and adults, and to diagnose learning disabilities.
The TMT requires subjects to create a sequence, either by connecting scattered numbers in a continuous order, or alternating numbers with corresponding letters of the alphabet. During this test, children need to hold in mind the current place in the sequence while searching for the next element through a distracting space filled with other digits.
“The surprising finding on the TMT was that bilingual children not only performed better than monolingual children on the difficult condition that involved alternating between letters and numbers but also on the simple condition in which they just connected consecutive numbers,” says Bialystok.
The global-local task investigates the ability to perceptually zoom in and out, successfully delineating a system from its parts. Usually, global information is processed faster and interferes with the identification of local elements.
To complete both these tasks, participants must employ critical executive functions, including inhibition (ignoring misleading cues), updating (monitoring a display in the context of current instructions) and switching (adjusting one’s response according to instructions).
Results show that bilingual children develop executive control over a broad range of processes, not only via inhibition and conflict resolution, as suggested by previous research.
Monolingual and bilingual children also performed similarly on tests of vocabulary, digit span, verbal fluency and box completion; where there were differences, it was the monolinguals who achieved slightly higher scores. Bilinguals obtained slightly lower scores on vocabulary and forward digit span but performed significantly better in all aspects of the TMT and global-local tasks. They completed the tasks more rapidly and more accurately than the monolinguals.
“This doesn’t mean that bilinguals are simply faster responders,” says Bialystok. “Both groups completed the control conditions for these tests at the same speed, which rules out basic response speed as the sole explanation for group differences.”
Bialystok also emphasizes the diagnostic implications of her research. Since the TMT is used to establish the presence of learning disabilities such as attention deficit hyperactivity disorder (ADHD), it may not be valid for bilingual students.
“Diagnostic tools may need to be adjusted somewhat if bilingualism – which is so common – can modify children’s performance, and perhaps confuse results,” she says.
The study, “Global-Local and Trail-Making Tasks by Monolingual and Bilingual Children: Beyond Inhibition,” was published in January 2010.