Examining MEG visual mismatch responses to ASL signs by deaf and hearing signers

Project Summary/Abstract: Early perceptual learning is crucial for later language development. A rich, native language environment shapes perceptual development during a critical period, which in turn predicts later language development. To date, most research on the critical period of perceptual development focused on language users who had a rich, early, spoken language environment. Little is known about the perceptual development when the language environment is impoverished, delayed, and visual. Deaf babies often lack a sufficient natural language environment when they do not have signing parents. Such reduced early language experience often results in atypical language and brain development, including reduced perceptual sensitivity. Due to previous methodological constraints, we still know little about the neural mechanisms underlying early perceptual processing in sign languages and how it is affected by lacking sufficient early language. The current study aims to 1) establish a visual mismatch response (vMMR) paradigm in ASL using anatomically constrained MEG, and 2) examine the effect of early language experience on pre-attentive perceptual processing for ASL. We adopt a neural measure widely used with spoken languages, the auditory mismatch responses (aMMR), to the visual domain. We establish the vMMR paradigm by comparing hearing signers and nonsigners’ pre-attentive neural sensitivity to changes between real-signs and fake-signs contrasting only in the handshape in American Sign Language (ASL). We use Magnetoencephalography (MEG) combined with MRI scans to provide better temporal and spatial precision when characterizing the vMMR signals. Once we establish the vMMR paradigm, we will further examine the role of early language experience by testing deaf individuals with varying early language environments: native signers with ASL exposure from birth, early signers with ASL exposure between ages 5 to 7, and severely delayed signers with ASL exposure after age 12. Based on existing literature, we predict increased vMMR, especially when detecting real-signs from fake-signs, by hearing native signers as compared to hearing non-signers, with both modality-specific (parieto-occipital) and modality- general (fronto-temporal) generators. We also predict reduced and/or delayed vMMR by severely delayed signers as compared to deaf native and early signers. We also predict more visual (parieto-occipital) and less language (fronto-temporal) activations by severely delayed signers. This project serves as an important initial step to examine pre-attentive perceptual processing in ASL, furthering our understanding of language development in relation to early language environment and perceptual learning. Findings from the project can also provide guidance to parents and practitioners regarding the early language environment for deaf babies, and also support diagnosis and intervention for deaf children who are at risk of language deprivation.