Critical period for first language acquisition may be shorter in autistic children than in typical children

Abstract

Typical children demonstrate nearly constant syntactic language learning-rate, as measured by a parent-reported Mental Synthesis Evaluation Checklist (MSEC), from 2 to 6 years of age and reach the ceiling MSEC score around 8 years of age ¹. In this study we report syntactic language learning-rate (measured as MSEC score change per year) in 15,183 autistic individuals of 2 to 22 years of age. Of these, 98.5% participants did not reach the ceiling MSEC score. Computational models used to estimate the trajectory of underlying learning-rate showed that unlike a constant syntactic language learning-rate in typical children, which is observed until at least 6 years of age, learning-rate in autistic individuals declined exponentially starting from 2.3 years of age. Furthermore, this decline started earlier in more severe forms of autism. One possible explanation for this difference is a shorter critical period for syntactic language acquisition in autistic children compared to typical controls. This early closing of the critical period may explain lifelong syntactic language deficits in some autistic individuals.