The vocabulary of babies who are bilingual remains¹ flexible as they grow up and boosts their speaking ability as toddlers, a university study has found.

一项大学研究发现，接受双语教育的宝宝在成长过程中可以灵活地掌握两门语言的词汇，而且学步时期的口语表达能力也能有所提高。

Babies and children have a great ability to learn a second language but that begins to fade as early as their first birthdays.

Now researchers at the University of Washington's Institute for Learning & Brain Sciences are investigating the brain mechanisms² that contribute to infants' prowess（英勇，超凡技术） at learning languages, with the hope that the findings could boost bilingualism in adults, too.

In the research, the scientists report that the brains of babies raised in bilingual households show a longer period of being flexible to different languages, especially if they hear a lot of language at home.

The researchers also show that the relative amount of each language - English and Spanish - babies were exposed to affected³ their vocabulary as toddlers（初学走路的孩子） .

The study, published in Journal of Phonetics, is the first to measure brain activity throughout infancy⁴ and relate it to language exposure and speaking ability.

'The bilingual brain is fascinating because it reflects humans' abilities for flexible thinking - bilingual babies learn that objects and events in the world have two names, and flexibly switch between these labels, giving the brain lots of good exercise,' said Patricia Kuhl, co-author of the study and co-director of the UW's Institute for Learning & Brain Sciences.

Kuhl's previous studies show that between 8 and 10 months of age, monolingual babies become increasingly able to distinguish speech sounds of their native language, while at the same time their ability to distinguish sounds from a foreign language declines.

For instance, between 8 and 10 months of age babies exposed to English become better at detecting the difference between 'r' and 'l' sounds, which are prevalent in the English language.

This is the same age when Japanese babies, who are not exposed to as many 'r' and 'l' sounds, decline in their ability to detect them.