Maturational Constraints on Language Development

TLDR

The article reviews age‑related differences in second language acquisition and identifies the need for first‑language research to clarify findings. The authors conduct a comprehensive literature review of second‑language studies that examine age effects and related first‑language work. The review concludes that acquisition rates and ultimate proficiency depend on age, that sensitive periods exist for different linguistic abilities, that decline is cumulative and can begin as early as age six, that existing explanations are inadequate, and that maturational constraints on neural plasticity underlie the progressive loss of language ability.

Abstract

This article reviews the second language research on age-related differences, as well as first language work needed to disambiguate some of the findings. Five conclusions are drawn, (a) Both the initial rate of acquisition and the ultimate level of attainment depend in part on the age at which learning begins. (b) There are sensitive periods governing language development, first or second, during which the acquisition of different linguistic abilities is successful and after which it is irregular and incomplete. (c) The age-related loss in ability is cumulative (not a catastrophic one-time event), affecting first one linguistic domain and then another, and is not limited to phonology, (d) The deterioration in some individuals begins as early as age 6—not at puberty as is often claimed. (e) Affective, input, and current cognitive explanations for the reduced ability are inadequate. The capacity for language development is maturationally constrained, and its decline probably reflects a progressive loss of neural plasticity, itself possibly associated with increasing myelination.