What other factors, then, might have caused these problems? While held in captivity, Bergdahl probably had very little occasion to speak or hear English. But how frequently someone uses his or her language plays a far smaller role for the maintenance of this language than one might think. Several studies have attempted to probe this, and all have found a complete absence of any correlation between frequency of use and degree of language loss.
These findings may appear counterintuitive, but they suggest that, for adult speakers, the native language has become so deeply entrenched and so frequently rehearsed that it will remain active in memory despite the fact that it is hardly used at all, sometimes for decades.