Rethinking the critical period for language: New insights into an old question from American Sign Language

Abstract

The hypothesis that children surpass adults in long-term second-language proficiency is accepted as evidence for a critical period for language. However, the scope and nature of a critical period for language has been the subject of considerable debate. The controversy centers on whether the age-related decline in ultimate second-language proficiency is evidence for a critical period or something else. Here we argue that age-onset effects for first vs. second language outcome are largely different. We show this by examining psycholinguistic studies of ultimate attainment in L2 vs. L1 learners, longitudinal studies of adolescent L1 acquisition, and neurolinguistic studies of late L2 and L1 learners. This research indicates that L1 acquisition arises from post-natal brain development interacting with environmental linguistic experience. By contrast, L2 learning after early childhood is scaffolded by prior childhood L1 acquisition, both linguistically and neurally, making it a less clear test of the critical period for language.

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

“…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).…”

“…The first set of findings comes from congenitally deaf individuals deprived of early language input because of lack of access to a sign language and/or societal insistence on oral communication (e.g., Grimshaw, Adelstein, Bryden, & MacKinnon, 1998;Mayberry, Lock, & Kazmi, 2002). Compared to native signers (i.e., hearing or deaf individuals exposed to sign from birth, typically by deaf parents), late signers (i.e., deaf individuals exposed to sign language at school age or later) demonstrate measurable deficits in the quality of their signing over the lifespan: They exhibit difficulties acquiring the complex morphological and grammatical constructions of American Sign Language (ASL), are less sensitive to grammatical errors (Emmorey, Bellugi, Friederici, & Horn, 1995;Mayberry & Eichen, 1991;Newport, 1988), and are also at a disadvantage in acquiring an oral language as a L2 for literacy purposes (Mayberry, 2007;Mayberry & Lock, 2003). Such age-of-acquisition effects are corroborated by studies of congenitally deaf recipients of cochlear implants who fare markedly better when implantation is done at a young age (Connor, Craig, Raudenbush, Heavner, & Zwolan, 2006;Robbins, Koch, Osberger, Zimmerman-Phillips, & Kishon-Rabin, 2004).…”

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

“…There is also evidence that the neural systems that support language are particularly plastic early in life (MacSweeney, Capek, Campbell, & Woll, 2008;MacSweeney, Waters, Brammer, Woll, & Goswami, 2008; Mayberry et al, 2011). Delays in language acquisition modify the neural basis of language processing (Neville et al, 1998;Allen, Emmorey, Bruss, & Damasio, 2013;MacSweeney, Waters, et al, 2008;Mayberry & Kluender, 2018). Furthermore, unlike adults, children suffering from early damage to left hemisphere language networks have language processing abilities in the normal range, and recruit right-hemisphere homologues of left-hemisphere fronto-temporal language regions during language tasks (Dronkers, Wilkins, Van Valin, Redfern, & Jaeger, 2004, Rasmussen & Milner, 1977Zevin, Datta, & Skipper, 2012;Newport et al, 2017;Kempler, Van Lancker, Marchman, & Bates, 1999;Rosen et al, 2000;Tivarus, Starling, Newport, & Langfitt, 2012).…”

Deaf Children as ‘English Learners’: The Psycholinguistic Turn in Deaf Education

“…The results of these studies suggest that post-childhood L1 learners of ASL achieve many of the same linguistic milestones associated with infant L1 acquisition-relatively rapid acquisition of nouns and verbs combined in two-word utterances [75]-but that development seems to slow after this stage, with no evidence that the language of post-childhood L1 learners develops to the level of complex sentence structure [76,77]. As Mayberry and Kluender [68] note, these findings are in line with those of Curtiss [78], who noticed that Genie-a hearing child virtually deprived of language until the age of thirteen-could acquire new vocabulary and achieve basic word order patterns, but never succeeded in producing complex morphology or syntax. They explain:…”

“…For decades, linguists have been interested in post-childhood L2 acquisition, but deaf children offer a unique opportunity for linguists to study post-childhood L1 acquisition because deafness blocks the infants' exposure to the language of their environment [67]. If deaf children of hearing parents are exposed to sign language, it tends to be well past infancy [68].…”