Being raised bilingual is good for you. It can boost your language attainment, enhance overall academic performance and perhaps even protect you against Alzheimer's disease in later life.
That is the good news for Hong Kong from one of the world's leading experts on the biological foundations of language learning.
Cognitive neuroscientist Dr Laura-Ann Petitto shared the latest scientific findings on bilingualism - including her own discoveries - in a lecture to mark the launch of University of Hong Kong's Science of Learning research centre.
Trilingualism and full literacy in two languages is the goal for all students in Hong Kong's public education system. English and Chinese are taught at primary school and the city has at least 28 international kindergartens that teach in English and Putonghua - that's more than 70 per cent of preschools listed in the SCMP Good Schools Guide, reflecting strong demand for bilingual education among parents.
Such kindergartens are absolutely going in the right direction, says Petitto, who just spent a month at University of Hong Kong as Sin Wai-Kin Distinguished Professor in the Humanities, in recognition of her outstanding research record. Early learning is crucial to success in learning two or more languages, she says.
"When you learn two languages early in life, the human brain sets up two powerful distinct representations. The earlier you expose a child to two languages, the stronger the representations of the two languages are," Petitto says, adding that the brain also uses the specialised language tissue and systems in the left hemisphere at this stage.
But with later exposure, aspects of the neural tissue in the brain's language centre have stabilised, so it has to look to other sites to buttress the task of working in two languages. "That's when it draws on the right hemisphere and the neural linkages, and that's when it becomes a very complex neurological process," she says.
The optimal age to expose a child to two or more languages is from three to six years old, says Petitto. "You can even go to seven or eight, but once you get past eight, you are getting past the really major periods of brain development," she says. "You will learn the language but you won't learn it optimally."
As well as starting early, it is essential that children have stable users of the target language - such as a parent or grandparent - with whom they can speak it. There should also be multiple experiences of the language in a variety of different contexts beyond the classroom and these should include speaking it with other children.
"You must have a social group of other children who are Chinese speakers, or French speakers or Thai or Japanese, or whatever your target language is," says Petitto.
"There is a very strong reason for that, and it's fascinating. Our species didn't evolve in these beautiful, nice middle-class homes, where there are parents who are educated and who give children books and talk to them all day. Instead, our species evolved where children were left in packs as the adults went off to search for resources."
The make-up of humans today includes "evolutionary junk": mechanisms that are not needed in modern societies but are retained. One such mechanism, known as the social cohort effect, is that children learn from other children.
So the "magic bullet" for language learning is to make sure the child is interacting with other children who are native speakers of the target language.
You will see "miracles" of the child "switching into the other language and staying in the other language and learning in the other language", she says.
Bilingual children outperform their age-matched monolingual children on every task we could give them
Petitto is scientific director of the Brain and Language Laboratory for Neuroimaging at Gallaudet University in Washington, which is equipped with functional near-infrared spectroscopy, the latest brain imaging technology.
Her cutting-edge research into the brain and behaviour helped to overturn the prevailing view in cognitive psychology from the 1960s to '80s that bilingualism is a taxing, computationally difficult process because the brain has to share and switch between two languages - and monolinguals therefore have a cognitive advantage.
Back then, there was no equipment to test it with. "Now, with the beginning of neuro-imaging, we were able to test these hypotheses," she says.
"If bilingualism is a more computationally taxing state - more demanding - bilinguals would have more frontal lobe activity than a monolingual. But when we did these studies that wasn't the case."
The research revealed that there was no difference between frontal lobe activity levels in bilingual and monolingual people's brains, thereby debunking the theory.
But it also uncovered another startling difference - bilingual people have a bigger language area in the left brain than monolingual people do.
So the team went on to examine whether the larger area of neural tissue for language had any behavioural consequences and found a big, positive impact on overall academic aptitude.
"Bilingual children outperform their age-matched monolingual children on every task we could give them," says Petitto. These included reading tasks, language processing tasks, text comprehension, visual spatial tasks and working memory tasks.
"We also saw spillover into other content areas: better mathematical processing, better on tasks that required complex relations," she says. "So this big language area has a spillover effect into giving the child higher cognitive advantages. These advantages are preserved across the lifespan."
Another team's research is now finding that bilingual brains are better protected from Alzheimer's disease, she adds.
Petitto urges Hongkongers to celebrate their bilingualism and stresses that there is no danger of confusing young children by teaching them Putonghua, Cantonese and English.
"The human brain will drink it up," she says. "You can give five languages to a young baby and it won't hurt the baby at all."
Nor does code-switching by bilingual parents between English and Chinese have a negative impact on their children's language learning.
"We have also studied this," she says. "Children are not confused by adult mixing. If you have parents who are high mixers, you get a high-mixing child.
"If you have parents that are low mixers, you get a low-mixing child. But it has no impact on language competence. Both groups of children have equal competence and mixing is good - it strengthens translational agility," Petitto says.
life@scmp.com