New evidence suggests a drop-off in results after the age of 17

The Economist
May 10, 2018

Excerpt: Those who want to learn a foreign language, or want their children to, often feel they are racing against the clock. People seem to get worse at languages as they age. Children often learn their first without any instruction, and can easily become multilingual with the right exposure. But the older people get, the harder it seems to be. Witness the rough edges on the grammar of many immigrants even after many years in their new countries.

Scientists mostly agree that children are better language learners, but do not know why. Some posit biological factors. Is it because young brains have an extreme kind of plasticity? Or, as Steven Pinker, a Harvard psychologist, argues, an instinct for language-learning specifically, which fades as the brain ages and (in evolutionary terms) is no longer needed? Others think children have special environments and incentives, not more conducive brains. They have a strong motivation to communicate with caregivers and imitate peers, and are not afraid of making mistakes in the way adults are.

Some believe any “critical period” may only apply to the sounds of a foreign tongue. Adults struggle with accents: eight decades after immigrating to America and four after serving as secretary of state, Henry Kissinger still sounds fresh off the boat from Fürth—in what is nevertheless elaborately accurate English. (An alternative explanation, runs a joke about Mr Kissinger, is that he never listens.)

But grammar is different, and some researchers have reckoned that adults, with their greater reasoning powers, are not really at a disadvantage relative to children. One study found that when adults and children are exposed to the same teaching materials for a new language for several months, the adults actually do better. Most such research has had to rely on small numbers of subjects, given the difficulty of recruiting them; it is hard to know how meaningful the results are.

Now a large new study led by Joshua Hartshorne of Boston College (with Mr Pinker and Joshua Tenenbaum as co-authors) has buttressed the critical-period hypothesis. The study ingeniously recruited 670,000 online test-takers by framing the exercise as a quiz that would guess the participants’ native language or dialect. This made it a viral hit. The real point was to test English-learners’ knowledge of tricky bits of grammar, and to see how this correlates with the age at which their studies began.  ...

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