Do deaf individuals see better?

Abstract

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.

Figure 1

The proposal that Deaf individuals have greater attentional resources in the visual periphery predicts that peripheral distractors should be more distracting to Deaf than to hearing individuals. (a) The spatial distribution of attention as a function of eccentricity was measured by comparing the extent to which peripheral and central distractors interfere with target performance in Deaf and hearing individuals. (b) Hearing individuals exhibit greater distractability from central than from peripheral distractors, in line with the view of heightened central attention in the hearing population. By contrast, Deaf individuals exhibit greater distractability from peripheral distractors, supporting the view that Deaf individuals have enhanced peripheral attention.

Figure 2

(a) The extent to which central versus peripheral distractors interfere with the target task can be computed as a difference ratio: (central — peripheral)/(central + peripheral). Both hearing non-signers and hearing signers demonstrate positive ratios, indicating more interference from central than peripheral distractors. Deaf subjects, however, demonstrate negative ratios, indicating more interference from peripheral distractors. This suggests that deafness, not sign language use, is the driving factor behind enhanced distribution of attention to the periphery in adults with early deafness. (b) The same ratio can be calculated using MT/MST activation data from an fMRI task. Again, positive values are observed for hearing non-signers and hearing signers, indicating greater activation when attention is directed towards the center of the visual field. A negative value for Deaf subjects indicates the reverse pattern, reflecting the greater sensitivity to peripheral events in the Deaf population at the level of neural organization.

Figure 3

Brain imaging studies indicate cortical changes associated with cross-modal plasticity in Deaf individuals in three main multisensory areas – the secondary auditory cortex, the posterior superior temporal sulcus (STS) and the posterior parietal cortex (PPC) – as well as in MT/MST when using moving stimuli under conditions of attention. Numbers correspond to cited references; those references reporting Tailarach coordinates are represented with black numbers, whereas those providing only approximate brain locations (as well as ERP and MEG studies) are represented by red numbers.