Age of second-language acquisition: Critical periods and social concerns

A classic topic in research on bilingualism across the lifespan is the relationship between the age at which learners start to acquire a second language (L2) and their ultimate level of proficiency in that language. Learning of an L2 that begins in infancy is typically associated with fluent speech, effortless language processing, and native accent. In contrast, late L2 learners tend to diverge from monolingual natives on measures of grammatical and lexical knowledge, processing speed, and acoustic properties of speech. Various classes of explanations for age effects in L2 acquisition – attitudinal, neurobiological, experiential, psycho-social, and cognitive – have been proposed in the literature. It is not the purpose of this chapter to examine these various accounts; for an overview, see Muñoz and Singleton (2011). Similarly, with the exception of a brief discussion in the section on social concerns, this chapter does not consider research on the efficiency of early foreign language teaching in schools; for an overview, see Lambelet and Berthele (2015). Rather, we are concerned with the hypothesis that L2 learning in naturalistic contexts is constrained by a critical period (CP). With its roots in the seminal works of Penfield and Roberts (1959) and Lenneberg (1967), the Critical Period Hypothesis for L2 acquisition (CPH/L2A) posits that nativelike attainment in the L2 from mere exposure is possible if learning begins within, but not after, a limited developmental span. Several recent overviews comprehensively summarize studies inspired by the CPH/L2A (references below), and we do not intend to rehash these surveys. Instead, we aim to provide readers with a technical toolkit to critically evaluate research on the divisive issue that is the CPH/L2A. To this end, we first discuss the CPH/L2A’s prediction that nativelikeness among learners with post-CP AoAs is impossible and highlight epistemological difficulties with this prediction. We then turn to the nature of the function that relates AoA to L2 attainment. The logic here is that a discontinuous function, but not a straight-line function, properly reflects the workings of a critical period. Here we illustrate how seemingly minor technical (statistical) caveats, which often risk being brushed under the rug as nit-picking, can fundamentally affect the conclusions of a study. In the final section, we expand our scope by considering the relevance of L2 acquisition theory to the social context of L2 learners and users. Specifically, we examine three issues relating to the notion that late L2 acquisition is inferior to L1 acquisition: early instruction of foreign languages in schools, the emphasis on deficits versus capacities, and societal prejudices against non-nativelikeness