If you want to learn a foreign language, should you begin before a certain age in order to fully master it? Popular opinion holds that young children find it easier than adults because childhood is a “critical period” for language learning.
It has been difficult to prove this, but new research published by my colleagues and me, using brainscans and innovative statistical methods, does indeed suggest that our capacity to learn a language diminishes gradually over our lives.
The familiar mantra that children immersed in a language “soak it up like a sponge”, while adults apparently do not, is not in itself proof of the existence of a critical period for language learning. But it is both easier and more important for children to quickly become good in a second language they hear spoken around them.
There are many reasons for this. Children can spend more time and effort on learning than adults who have many competing demands; the motivation for children to fit in is much higher, and the habits of pronunciation and grammar of their first language are less deeply ingrained and thus easier to overcome. And, of course, all learning gets harder with age.
None of these factors have anything to do with a specific critical period for learning languages, but all of them do make younger learners of a new language eventually outperform older ones.
In addition to this overall and gradual advantage for younger learners, there is one notable qualitative difference: even very good older language learners differ from younger ones when it comes to using grammar correctly and consistently. Every time I mark a run of scripts from my adult students, most of whom are from non-English-speaking backgrounds, I find that while they are amazingly good at using a wide range of vocabulary, appropriate style and complex grammar, they often struggle with some simple grammatical rules.
For example, many adult learners never fully master the distinction between “he walks” and “they walk”. They also often fail to grasp that “I have lived in Colchester for two years” means that I still live there, while “I lived in Colchester for two years” means that I do not. Why are simple and highly frequent rules apparently impossible to master, while words that have been encountered only a few times sink in easily?