Abbreviated abstract: Children learn language more easily than adults, though when and why this ability declines have been obscure for a number of reasons. Studying a very large number of subjects, the authors 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 large size of the dataset also provides novel insight into several other outstanding questions in language acquisition.
Hartshorne JK, Tenenbaum JB and Pinker S: A critical period for second language acquisition: Evidence from 2/3 million English speakers. Cognition 177: 263-277 (2018).