Abstract
Visual processing might be altered in deaf people for two reasons. One, they lack auditory input, compelling them to rely more on their intact visual modality. Two, many deaf people have extensive experience using a visual signed language (American Sign Language, ASL), which may alter certain aspects of visual perception that are important for processing of ASL. While some deaf people have ASL exposure since birth, by virtue of having deaf parents, many others are born to hearing parents, with no signing knowledge, and have delayed visual language exposure. In this study, we asked if deafness and/or sign language experience impact visual perception in 40 Deaf signers and 40 Hearing nonsigners, for psychophysical tests of motion, form, shape, and face discrimination, while controlling for contrast detection, age, visuospatial IQ, and gender makeup. The Deaf signers were separated into two groups, Deaf native signers who were exposed to ASL between ages 0 to 2 years and Deaf late-exposed signers who were exposed to ASL after the age of 3 years. Results indicated that enhanced face processing was found in Deaf native signers who have early visual language exposure, but not in Deaf late-exposed signers. Moreover, Deaf late-exposed signers actually have impoverished motion processing, compared to Deaf native signers and Hearing nonsigners. Together, these provide evidence that language exposure to sign or language deprivation in the first 2 years of life does have a lasting impact on visual perception in adults.