Doctoral Dissertation Research: Late First Language Acquisition Effects on Phonological Processing in Sign Language

Late first language acquisition is rare for hearing individuals who have automatic access to spoken languages used around them, but it occurs frequently for deaf individuals who are unable to hear any spoken languages and who are not exposed to a sign language as a first language until after early childhood. These late first language deaf signers can experience dramatic effects on all aspects of life including language outcomes. While much of the previous research on this topic has looked at language outcomes at the sentence level, this project aims to better understand the effects of late first language acquisition by looking below the sentence and word levels at how signers process the smallest pieces of language that make up signs/words. This work is necessary for a more complete understanding of the effects of late first language acquisition and better insight into how the human brain processes language more broadly. Practically, this work helps those who work with deaf individuals, like speech language pathologists and educators, to better understand how late first language signers process the linguistic pieces that make up language. In this dissertation, participants are deaf signers who acquired a sign language at a variety of ages, from early in childhood to late in adolescence. Study 1 investigates how the signers produce the smallest pieces of the sign language (manual forms like handshape, movement, and location) through sign repetition and error analysis. Study 2 investigates how the signers perceive the manual forms of sign language through similarity judgments. Study 3 investigates how the signers identify and process the manual forms of sign language through form monitoring and using magnetoencephalography (MEG). Together, these studies provide insight into how late first language signers compared to early first language signers produce, perceive, and process the smallest pieces of sign language, providing a systematic look at the effects of late first language acquisition at the sub-word level. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.