For several decades now, research on the acquisition of ASL and other signed languages has contributed to our understanding of language acquisition and of age effects in particular. A strong decline in learning capacity with age has been shown in numerous studies with ASL as L1, and the age range for this critical period phenomenon appears to be very similar to what has been observed in even more studies in L2 (for both spoken and signed languages). Mayberry and Kluender (Mayberry & Kluender) argue that the two phenomena are quite different, however, to such an extent that the concept of a critical period is not applicable to L2. Their two main arguments are that L2 learners are less affected by late acquisition than L1 learners and that some L2 studies have not shown the kind of discontinuity in the age-proficiency function that is predicted by the concept of a critical period. As space is very limited, I will limit my comments to these two issues.
The Critical Period Hypothesis Revisited: The Implications for Current Foreign Language Teaching to Young Learners
