The goal of this research is to assess and separate the effect of deafness and of acquisition of a sign language on the organization of the visual system. Visual abilities in hearing individuals will be compared with those of deaf signers. To separately document the role of deafness from that of signing, deaf with minimal exposure to sign and hearing individuals who are native signers will also be included. Indeed, the existing literature indicates that deafness and acquisition of American Sign Language have different and separate effects on the reorganization of visual functions. The aspects of the visual system that have been modified will be first determined by comparing behavioral indices of visual processes in these four populations. Modifications in brain organization that accompany these behavioral differences will be then characterized with functional magnetic resonance imaging (fMRI). The existing literature indicates that congenital auditory deprivation is associated with specific enhancement of behavioral performance and neural activity in response to moving stimuli and visual stimuli in the periphery. Since this type of information is predominantly represented along the dorsal visual pathway, it has been proposed that early deafness affects predominantly the dorsal visual pathway. This work will test the hypothesis that dorsal visual functions are altered after early deafness, by studying and comparing motion processing and spatial localization in deaf and hearing. The contribution of deafness and signing will be separately assessed by looking at deaf with minimal signing experience and hearing who are native signers. The second goal of this work is to test whether plastic changes are indeed specific to the dorsal pathway as has been hypothesized in the literature or if plastic changes can be induced by early dearness or signing in the other main visual pathway, i.e. the ventral pathway. For that purpose, face processing and handshape processing will be compared in deaf and hearing as a function of their signing ability. These experiments will provide new information about which sub-systems within vision are most altered by early auditory deprivation and/or early acquisition of signs, and will help to characterize how these changes are implemented at the cortical level. Since these studies will determine the aspects of visual perception that are most likely to reorganize when the environment is altered early on, these results will also carry implications for the kind of training that would optimize visual and attentional skills in children.
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