Brain scans show that children adopted from China as babies into families that don't speak Chinese still unconsciously recognize Chinese sounds as language more than a decade later.
"It was amazing to see evidence that such an early experience continued to have a lasting effect," said Lara Pierce, lead author of the study published today in the journal Proceedings of the National Academy of Sciences, in an email to CBC News.
The adopted children, who were raised in French-speaking Quebec families, had no conscious memory of hearing Chinese.
"If you actually test these people in Chinese, they don't actually know it," said Denise Klein, a researcher at McGill University's Montreal Neurological Institute who co-authored the paper.
But their brains responded to Chinese language sounds the same way as those of bilingual children raised in Chinese-speaking families.
"In essence, their pattern still looks like people who've been exposed to Chinese all their lives."
Pierce, a PhD candidate in psychology at McGill University, working with Klein and other collaborators, scanned the brains of 48 girls aged nine to 17. Each participant lay inside a functional magnetic resonance imaging machine while she listened to pairs of three-syllable phrases. The phrases contained either:- Sounds and tones from Mandarin, the official Chinese dialect.
- Hummed versions of the same tones but no actual words.
Participants were asked to tell if the last syllables of each pair were the same or different. The imaging machine measured what parts of the brain were active as the participants were thinking.
"Everybody can do the task — it's not a difficult task to do," Klein said. But the sounds are processed differently by people who recognize Chinese words — in that case, they activate the part of the brain that processes language.
Klein said the 21 children adopted from China who participated in the study might have been expected to show patterns similar to those of the 11 monolingual French-speaking children. After all, the adoptees left China at an average age of 12.8 months, an age when most children can only say a few words. On average, those children had not heard Chinese in more than 12 years.
The fact that their brains still recognized Chinese provides some insight into the importance of language learning during the first year of life, Klein suggested.
Effect on 'relearning' language not known
But Klein noted that the study is a preliminary one and the researchers don't yet know what the results mean.
For example, would adopted children exposed to Chinese in infancy have an easier time relearning Chinese later, compared with monolingual French-speaking children who were learning it for the first time?
Pierce said studies trying to figure that out have had mixed results, but she hopes the findings in this study could generate better ways to tackle that question.
She is also interested in whether the traces of the lost language affect how the brain responds to other languages or other kinds of learning. Being able to speak multiple languages has already been shown to have different effects on the way the brain processes languages and other kinds of information.