Variation in late L1 acquisition?

Abstract

Mayberry and Kluender review evidence that second language (L2) proficiency declines with age of acquisition (regardless of modality), but they also review evidence for variable L2 outcomes for individuals, with factors such as motivation, language aptitude, education, and L2 experience playing a role. They argue that if L2 outcomes were fully under the control of a critical period for language (CPL), these learning variables should not predict L2 outcome, and the outcome of L2 learning would not be consistently observed to be so variable. The questions raised in this commentary are whether there is variation in late L1 proficiency and whether such variation could provide insights into the CPL.