A critical period for second language acquisition: Evidence from 2/3 million English speakers

Abstract

Children learn language more easily than adults, though when and why this ability declines have been obscure for both empirical reasons (underpowered studies) and conceptual reasons (measuring the ultimate attainment of learners who started at different ages cannot by itself reveal changes in underlying learning ability). We address both limitations with a dataset of unprecedented size (669,498 native and non-native English speakers) and a computational model that estimates the trajectory of underlying learning ability by disentangling current age, age at first exposure, and years of experience. This allows us to provide the first direct estimate of how grammar-learning ability changes with age, finding that it is preserved almost to the crux of adulthood (17.4 years old) and then declines steadily. This finding held not only for "difficult" syntactic phenomena but also for "easy" syntactic phenomena that are normally mastered early in acquisition. The results support the existence of a sharply-defined critical period for language acquisition, but the age of offset is much later than previously speculated. The size of the dataset also provides novel insight into several other outstanding questions in language acquisition.

More Is More in Language Learning: Reconsidering the Less‐Is‐More Hypothesis

“…For example, an influential study involving native Korean and Chinese learners of English demonstrated that accuracy in judging the grammaticality of a wide range of English constructions declined steadily as a function of learners' age of first L2 exposure up to puberty, even when other experiential and attitudinal variables such as overall years of L2 exposure, amount of classroom instruction, identification with social values of the host country, degree of self-consciousness, and motivation to learn the L2 and to speak it well were taken into account (Johnson & Newport, 1989). Although these and similar studies have been shown to be severely underpowered (Hartshorne, Tenenbaum, & Pinker, 2018;Vanhove, 2013), recent evidence from an extraordinarily large sample exceeding half a million L1 and L2 speakers of English confirmed that ultimate grammatical proficiency declines with age of first L2 exposure, even if the estimated offset of the critical period between 17 and 18 years appears to be much later than previously estimated (Hartshorne et al, 2018).…”

“…Factors such as the presence of school-age siblings and the tendency to engage in conversational code switching (e.g., using English to answer questions posed in Spanish) impede acquisition of Spanish, despite substantial daily exposure to the language from birth (Ribot, Hoff, & Burridge, 2018). Thus, substantial evidence suggests that the link between age of L2 exposure and ultimate attainment may arise from a host of factors unrelated to gains in cognitive capacity (Hartshorne et al, 2018;Mayberry & Kluender, 2017).…”

A sensitive period in the neural phenotype of language in blind individuals

“…Analogously, second language speakers who aquire a language as adults show a reduced ability to acquire aspects of grammatical structure in their second language, while having less trouble with vocabulary acquisition and basic word order (Johnson & Newport, 1989;Newport, 1990;Patkowski, 1980;Weber-Fox & Neville, 1996). A recent large-scale study with over half a million participants has confirmed age-of-acqusition effects on sentence-level syntax in second language learners, although it also suggests that in this particular case, the cortical learning rate may not fall off until the late teens (Hartshorne, Tenenbaum, & Pinker, 2018). There is also evidence of different neural signatures for syntax in first and second languages speakers matched for proficiency (Neville et al, 1998;Pakulak & Neville, 2011;Weber-Fox & Neville, 2001).…”

Age of acquisition impacts the brain differently depending on neuroanatomical metric

“…Given that there is a sensitive period for processing of sensations such as vision and sound (Brainard & Knudsen, 1998;Harrison, Gordon, & Mount, 2005), it follows that the neural substrates recruited to support L2 acquisition may differ depending on the developmental stage of the individual (Hartshorne, Tenenbaum, & Pinker, 2018). For instance, native-like accent production, phonemic perception, and implicit knowledge of syntax are thought to have an early sensitive period (i.e., before age 7; Johnson & Newport, 1989;Tokowicz & MacWhinney, 2005) due to higher plasticity of certain brain structures (e.g., motor/speech pathways) early in development (Hernandez & Li, 2007).…”