L1 attrition, or first language attrition, is governed by two main factors: the increasing use and dominance of the L2, or learned language, and the reduction of exposure to the L1. This attrition tends to make itself evident in the constriction of the speaker’s vocabulary, while knowledge of grammar (structure) and phonology (sound) remains more stable. A speaker’s attitude and motivation toward his or her new and native languages can also have an effect on language attrition.
In children, the phenomenon is somewhat easier to explain since their brains are generally more flexible and adaptable. Until the age of about 12, a person’s language skills are relatively vulnerable to change. Studies on international adoptees have found that even nine-year-olds can almost completely forget their first language when they are removed from their country of birth.
But in adults, the first language is unlikely to disappear entirely except in extreme circumstances.
native fluency is also strongly linked to how we manage the different languages in our brain. “The fundamental difference between a monolingual and bilingual brain is that when you become bilingual, you have to add some kind of control module that allows you to switch”
Knowledge of your native language feels different to other sorts of knowledge. It’s a vital, foundational, a priori knowledge that’s intricately wound up with your notion of identity.
