Effects of Delayed Language Exposure on the Language Neural Network

ABSTRACT Deaf individuals are uniquely vulnerable to language deprivation—chronic lack of access to robust and reliable linguistic input during early development—which has wide‐ranging consequences for language, cognition, and neural processing throughout the lifespan. This review synthesizes research on the neural effects of late first language acquisition in deaf signers, focusing on how delayed exposure to sign language affects brain structure and function. Evidence from electrophysiological and neuroimaging studies indicates that late signers attend more to surface‐level visual and phonological features, at the expense of higher‐order lexicosemantic and syntactic processing. Neuroimaging research reveals three primary patterns associated with late sign language acquisition: (1) increased activation in posterior occipital and parietal regions, which may reflect less efficient visual and phonological processing of signs; (2) increased right hemisphere involvement, similar to patterns observed in novice learners and less proficient signers; and (3) attenuated processing in left frontotemporal language regions, though evidence for widespread frontotemporal attenuation is primarily derived from case studies of severely language‐deprived individuals. Structural neuroimaging studies indicate altered gray matter structure in occipital and frontotemporal language regions and decreased connectivity along the arcuate fasciculus. However, the relationship between age of acquisition and language proficiency complicates interpretation of these findings, as both factors may independently contribute to observed neural differences. Future research should utilize more multivariate analyses of functional data with diverse samples of deaf signers, develop more comprehensive measures of early language access beyond age of acquisition alone, and carefully distinguish effects of language deprivation from effects of proficiency.