Sgt Bowe Bergdahl spoke English for 23 years until he was captured by Taliban fighters in Afghanistan five years ago. But since his release, he has trouble speaking it, says his father. How can you lose your native language, asks Taylor Kate Brown.
Some people have gone decades without speaking or hearing their first language but they retain the ability to speak it easily, says Dr Monika Schmid, a linguistics professor at the University of Essex in the UK. But others begin losing fluency within a few years of not speaking it.
It's rare to totally lose command of a first language, she says. Instead people have "language attrition" - trouble recalling certain words or they use odd grammar structures. Age is a factor. Once past puberty, Dr Schmid says, your first language is stable and the effects of attrition can reverse themselves if you are re-immersed. But children as old as 10 don't necessarily retain the language they were born into. In a study of French adoptees who left South Korea in childhood, when asked in their early 30s to identify Korean, they did no better than native French speakers with no exposure to the language.
The difficulties in recalling your first language are greater the more immersed you are in a second language, says Dr Aneta Pavlenko at Temple University in Philadelphia, because cognitive resources are limited. Despite teaching Russian at university in the US, she herself returned to her Russian-speaking community in Kiev to realise she had forgotten how to start a conversation at the post office.
It's well known that brain injuries can have an impact on language loss, but emotional trauma can also affect it. Among German Jews who fled the country during the Holocaust, Dr Schmid says the loss of language was far more dramatic the greater their trauma.
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