Being bilingual 有很多好處
The other day I found an interesting interview with Professor Laura-Ann Petitto, a cognitive neuroscientist who has spent the past 29 years seeking to uncover the biological and environmental factors that affect how humans acquire language and how language is organized in the brain. The main aim of her research is the find the biological foundations of language.
She found that the language development of children who grow up bilingually or multilingual is not delayed when compared with monolingual children, as a popular belief suggests. That bilingual and multilingual children do mix languages, just as adults do, and that they do so in a highly principled way. Language mixing is mainly a social phenomenon and the amount of language mixing among children reflects mixing behaviour among adults in their community.
She also studied the optimum time to expose children to two or more languages, comparing groups of children who were exposed to multiply languages at different ages. Some were raised bilingually from birth, others from the ages of three, five, etc. She found that up to nine years old, children immersed in a bilingual environment can become equally fluent in both languages. However if such children are only exposed to one of the languages in school, their ability in that language is much reduced.
Other interesting bits from the interview include the finding that “young children who have rich and early exposure to two languages are [...] cognitively more advanced than their monolingual peers on certain highly sophisticated cognitive tasks to do with attention and abstract reasoning.” Also that those children exposed to two languages after the age of nine or so will eventually learn them, but will probably never speak them as well as the early starters.