One of the most puzzling observations for linguists is the difference between learning a language from birth and later in life: while all normally developing children can attain full native language proficiency, there is considerable variability in ultimate attainment among older speakers who attempt to acquire a second language (L2). There is an ongoing controversy in linguistic research on whether this discrepancy is due to a maturationally constrained window of linguistic development making language learning difficult or impossible after puberty, or to general cognitive factors linked to the fact that the later an L2 is established, the stronger the competition it has to overcome from the more deeply entrenched first language (L1).
Studies attempting to resolve this controversy have so far focussed mainly if not exclusively on the development of L2 skills. New insight may be provided by investigating native speakers who are in many ways similar to L2 learners, namely migrants who have become dominant in the L2 (referred to as L1 attriters). On the one hand, such speakers have learned their L1 monolingually during childhood and are therefore not impeded by maturational constraints. On the other, they experience competition between their seldom-used L1 and their highly entrenched L2. A comparison of L2 learners and L1 attriters may therefore be able to shed some light on the question of whether there is indeed a fundamental difference between early- and late-learned languages.