Joshua Hartshorne
Assistant Professor, Boston College
A critical period for second language acquisition: A study of 700,000 English speakers
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). I 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. These reveal that grammar-learning ability is preserved almost to the crux of adulthood (17.4 years-old) and then declines steadily. The results support the existence of a critical period for language acquisition, but the age of offset is much later than previous estimates. We show that the results are nonetheless consistent with published data, and consider possible explanations and experimental paths forward.
Date: Thursday October 6th
Time: 1:00-2:00pm
Location: Tobin 423