Possible role of peripheral vision in individuals with Retinitis Pigmentosa and those with Usher syndrome

Abstract

It has been speculated that the lack of auditory experience in Deaf individuals may lead to changes in their ability to perceive visual stimuli. In particular Deaf subjects have found to perform better for motion stimuli tasks appearing in the periphery than in the central of the Visual Field. Retinitis Pigmentosa (RP) is a progressive retinal disease that leads to restriction in the peripheral Visual Field. People with Usher Syndrome (US) Type 1 are born deaf and communicate with Sign Language; they develop RP during their teens. We speculate that rearrangement of peripheral visual function occurs with the progression of RP. Indeed, it has been empirically observed that signers with US reduce the space within which they sign (signing space) as RP reduces their visual field. Two explanations have been suggested: some role of visual feedback in sign production (in addition to proprioceptive feedback); or an attempt to induce the conversational partner to adapt the size of his signing space to fall into the reduced cone of vision of the person with US. We used infra-red cameras to measure the positions of markers placed on the hands of subjects while they described pictures representing arrangements of dolls' house furniture. Four groups were studied: signers with US, normally sighted deaf signers, normally hearing people with RP, and normally hearing/sighted people. We also measured each participant's visual field using a standard Visual Field test (Goldmann perimeter). This was compared to participant's signing or gesturing space. Results indicate a correlation between the size of the visual field and the size of signing and gesturing in the presence of visual impairments for both the Usher and RP groups. These findings support the hypothesis of a role for visual feedback in calibration of the size of sign and gesture space.