Child first language and adult second language are both tied to general-purpose learning systems

Abstract

<p id="d7422784e189">It has long been debated whether the mechanisms that underlie language are dedicated to this uniquely human capacity or whether in fact they serve more general-purpose functions. Our study provides strong evidence that language—indeed both first and second language—is learned, in specific ways, by general-purpose neurocognitive mechanisms that preexist <i>Homo sapiens</i>. The results have broad implications. They elucidate both the ontogeny (development) and phylogeny (evolution) of language. Moreover, they suggest that our substantial knowledge of the general-purpose mechanisms, from both animal and human studies, may also apply to language. The study may thus lead to a research program that can generate a wide range of predictions about this critical domain. </p><p class="first" id="d7422784e195">Do the mechanisms underlying language in fact serve general-purpose functions that preexist this uniquely human capacity? To address this contentious and empirically challenging issue, we systematically tested the predictions of a well-studied neurocognitive theory of language motivated by evolutionary principles. Multiple metaanalyses were performed to examine predicted links between language and two general-purpose learning systems, declarative and procedural memory. The results tied lexical abilities to learning only in declarative memory, while grammar was linked to learning in both systems in both child first language and adult second language, in specific ways. In second language learners, grammar was associated with only declarative memory at lower language experience, but with only procedural memory at higher experience. The findings yielded large effect sizes and held consistently across languages, language families, linguistic structures, and tasks, underscoring their reliability and validity. The results, which met the predicted pattern, provide comprehensive evidence that language is tied to general-purpose systems both in children acquiring their native language and adults learning an additional language. Crucially, if language learning relies on these systems, then our extensive knowledge of the systems from animal and human studies may also apply to this domain, leading to predictions that might be unwarranted in the more circumscribed study of language. Thus, by demonstrating a role for these systems in language, the findings simultaneously lay a foundation for potentially important advances in the study of this critical domain. </p>