With immigration and international mobility on the rise, early exposure to two languages has become the norm for many children across Canada, particularly those raised by parents who themselves are bilingual.

How do these bilingual parents use their two languages when interacting with their young children? Until recently, little has been known about how often parents switch between languages when interacting with their toddlers, and whether such exposure to language mixing influences vocabulary size.

To find the answers, Byers-Heinlein, who is also director of the Concordia Infant Research Laboratory and a member of the Centre for Research in Human Development, collaborated with Dr. Janet Werker's Infant Studies Centre in Vancouver. She recruited 181 bilingual parents who spoke English as well as another language, and examined how often and in what situations they mixed languages while speaking with their children. Each parent had a one- or two-year-old child being raised bilingually or trilingually, having heard English and one or two other languages regularly since birth.

Rather than being a rare phenomenon, the results showed that language mixing is common in interactions between bilingual parents and their children. Indeed, 90 per cent of parents reported mixing their languages in interactions with their children. Parents did not mix their languages haphazardly, however, but instead reported principled reasons for mixing. For example, they borrowed words from the other language when there was no adequate translation, when they were not sure of a word, and when the word was hard to pronounce. Parents also reported frequently borrowing words from one language when teaching new words to their children in the other. Thus, bilingual parents might use language mixing as a strategy to make sure their children learn words equally in both languages.

Byers-Heinlein then examined the vocabulary size of 168 children of parents who had responded to the study. All of the children were learning English, but their non-English language varied widely -- from German to Japanese, French to Farsi. As such, she focused on children's English vocabulary size, while statistically controlling for the words that children likely knew in their non-English language.

She found that exposure to parental language mixing predicted significantly smaller comprehension vocabularies (words understood) in the younger children, and marginally smaller production vocabularies (words spoken) in the older children.

Why is that? Byers-Heinlein explains that, "high rates of language mixing make it harder for children to categorize words they hear. That could lead to slower word learning and smaller vocabularies. It also seems that it's more difficult to learn a word from a mixed-language sentence than from a single-language sentence."

But that in no way means that children raised in a bilingual environment are at a disadvantage. Byers-Heinlein cautions that, "even if exposure to language mixing is initially challenging for vocabulary acquisition, it likely has benefits over the long term."

"Studies comparing monolingual and bilingual infants have shown that bilinguals are more adept at switching between strategies and are more able to learn two rules at the same time," she explains. "Infants exposed to frequent language mixing could develop specific strategies for coping with this type of input. That could lead to cognitive advantages that would outweigh any initial difficulties brought about by language mixing."

Byers-Heinlein is now undertaking new research with French-English bilinguals in Montreal to examine whether these findings hold in other bilingual communities, and when children's vocabularies are assessed in both of their languages.

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