Visual Processing in Deaf Subjects: Effects of Auditory Deprivation and Experience with a Visual Language

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This project investigates the perceptual consequences of altered sensory input early in development, by studying visual perception in deaf adults who have been auditorily deprived since birth and who have acquired a visual language (American Sign Language, ASL) for communication. It has long been thought (mostly through anecdotal evidence) that the deaf `see` better (and that the blind `hear` better); however, only a handful of studies have attempted to characterize systematically the visual capacity of deaf signers. To investigate this issue, deaf and hearing subjects will be tested on a variety of visual tasks. In particular, visual motion processing will be assessed for several reasons. One, motion is a fundamental aspect of visual processing and much is known about its neural basis. Two, results from animal studies suggest that the motion system may be especially susceptible to changes following altered sensory input. Three, motion of the hands is an integral part of the acquisition and comprehension of ASL, and thus there is reason to believe that the increased reliance on such motion cues may enhance and/or alter motion perception in the deaf. Visual perceptual experiments will involve testing various dimensions of motion (and other visual) processing capabilities, in order to elucidate which specific aspects of visual processing are altered in the deaf. Once the types of visual stimuli/tasks yielding the greatest perceptual differences between hearing and deaf subjects have been determined, human brain imaging techniques (such as functional Magnetic Resonance Imaging or Magnetic Source Imaging) will be employed to localize neural areas or structures underlying the perceptual differences. In addition, brain imaging studies may reveal differences across specific brain areas in susceptibility to, and ability to compensate for, early sensory deprivation. These experiments will advance our knowledge regarding the degree to which developing sensory areas of the brain can reorganize themselves in response to altered sensory input, with implications for principles of visual development in general. Moreover, the experiments should shed light on the processing levels at which neural responsivity and connectivity are influenced by input from the sensory environment. The results may also be useful in designing compensatory programs for sensory-deprived persons, who could be trained to exploit those aspects of sensory processing that are most adaptive in response to altered early sensory input.