Master of Science
Butler, Blake E.
Deaf signers exhibit superior visual perception compared to hearing controls in several domains, including the perception of faces and peripheral motion. These visual enhancements are thought to compensate for an absence of auditory input. However, it is also possible that they reflect experience using a visual-manual language, where signers must process complex moving hand signs and facial cues simultaneously. Thus, the current study sought to isolate the effects of sign language experience by examining how visual perception is altered as a function of American Sign Language (ASL) proficiency in hearing individuals. Hearing signers completed an online test of ASL proficiency and were compared to hearing non-signers on online behavioural measures of face perception and biological motion perception. No group-level differences in performance were observed, suggesting that the visual enhancements found in Deaf signers result from hearing loss itself rather than sign language. Potential neurodevelopmental mechanisms for these findings are discussed.
Summary for Lay Audience
Deaf sign language users are better at some visual tasks compared to hearing individuals with no sign language experience, especially recognizing faces and detecting motion in the visual periphery. In the absence of auditory input, these enhancements are thought to reflect the increased importance of visual information when D/deaf individuals monitor their surrounding environment. However, compared to spoken language, using a visual-manual language such as American Sign Language (ASL) also provides a drastically different visual experience. Therefore, it remains difficult to determine whether the visual enhancements observed in Deaf signers are the result of sign language experience or a direct consequence of hearing loss.
The aim of the current study was to disentangle the effect of sign language experience from the effect of hearing loss by examining visual abilities in sign language users with typical hearing. Hearing signers and non-signers completed online assessments of their face matching and motion discrimination abilities in the central and peripheral visual fields. Additionally, hearing signers in the current study completed an online ASL proficiency test, which allowed us to examine the relationship between performance on the visual tasks and sign language skill.
Hearing signers and non-signers performed similarly on the visual tasks, suggesting that the visual enhancements previously observed in Deaf signers likely reflect the role of hearing loss itself rather than sign language experience. We propose that differences in auditory experience from a young age can result in distinct developmental paths and outcomes for Deaf and hearing signers and that exploring different aspects of sign language experience is important to understanding how it interacts with hearing loss. Overall, the current study contributes to a growing field of research on deafness and sign language that provides critical insights into the effects of hearing and language experience on the brain unique from the study of typical hearing, spoken-language users.
Lammert, Jessica M., "Visual Perception in Hearing Sign Language Users" (2021). Electronic Thesis and Dissertation Repository. 7947.
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