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Do deaf individuals see better?

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The possibility that, following early auditory deprivation, the remaining senses such as vision are enhanced has been met with much excitement. However, deaf individuals exhibit both better and worse visual skills than hearing controls. We show that, when deafness is considered to the exclusion of other confounds, enhancements in visual cognition are noted. The changes are not, however, widespread but are selective, limited, as we propose, to those aspects of vision that are attentionally demanding and would normally benefit from auditory–visual convergence. The behavioral changes are accompanied by a reorganization of multisensory areas, ranging from higher-order cortex to early cortical areas, highlighting cross-modal interactions as a fundamental feature of brain organization and cognitive processing.

Introduction

Compensatory plasticity holds that the lack of auditory stimulation experienced by deaf individuals is met by enhancements in visual cognition. However, reports in the educational and cochlear implant literature document deficient visual cognition in deaf individuals. This discrepancy is probably due to the complex etiology of deafness. When free from various confounding factors, deafness per se is seen to shift the spatial distribution of attention such that attention to the peripheral visual field, but not the central visual field, is heightened. Associated neural bases reveal a widespread reorganization from higher association cortices to early sensory cortices. A common feature found across reorganized areas is their fundamental multimodal organization, reinforcing recent views on the role of multimodal integration at all stages of cognitive processing [1].

Section snippets

The complex etiology of deafness

The bulk of the literature on deafness reports either no change in or worse performance by deaf individuals on a variety of tasks as compared to hearing 2, 3. Amid this large literature describing deficiencies in deaf individuals, some recent evidence documents enhancement of a few perceptual and cognitive skills following congenital deafness 4, 5. Discrepancies in the literature might be largely explained by the fact that most studies reporting deficient functions typically include deaf

Selective effects of deafness on visual cognition

Changes in visual cognition following congenital deafness are highly specific. Not all aspects of vision are modified. Visual sensory thresholds are comparable in Deaf and hearing individuals, be it for brightness discrimination, visual flicker, different aspects of contrast sensitivity, or direction and velocity of motion 8, 9, 10, 11. Enhanced performance has been reported in some areas, such as processing of the visual periphery or motion processing, but only under conditions of attention.

Deafness alters the spatial distribution of visual attention

Differences between Deaf and hearing individuals are noted mostly under conditions of attention, as when processing in the face of uncertainty and/or selecting a target from among distractors. Could Deaf/hearing differences be better characterized as a generalized attentional difference? This proposal needs qualification as few population differences have been documented on standard attentional paradigms. Studies of attentional orienting, using the Posner-cueing paradigm, report no robust

Neural correlates of cross-modal plasticity

The enhanced peripheral vision noted in Deaf individuals could be mediated by several distinct brain mechanisms. First, the sensory representation of the peripheral field in early visual cortex might be expanded in genetically deaf individuals. In hearing individuals, it is known that a larger part of the visual cortex is dedicated to processing central vision than peripheral vision. A greater amount of visual cortex might be dedicated to the processing of the visual periphery in Deaf

Summary

The study of plastic changes in Deaf individuals, born profoundly deaf within the Deaf community, highlights the impact of auditory deprivation on cognition without the confounds often associated with deafness. Auditory deprivation leads to enhanced peripheral visual attention, an enhancement particularly notable when contrasted with central attention. Such behavioral change could put deaf individuals at risk in academic or clinical settings that typically rely on the use of centrally presented

Acknowledgements

We thank Helen Neville, Elissa Newport and Courtney Stevens for their helpful feedback and stimulating discussions. D.B. acknowledges support from NIH-DC04418, the Charles A. Dana Foundation and the James S. McDonnell Foundation.

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