The Involvement of Occipital Cortex in the Early Blind in Auditory and Tactile Duration Discrimination Tasks

Early blind participants outperform controls on several spatially oriented perceptual tasks such as sound localization and tactile orientation discrimination. Previous studies have suggested that the recruitment of occipital cortex in the blind is responsible for this improvement. For example, electroencephalographic studies showed an enlarged posterior negativity for the blind in these tasks compared to controls. In our study, the question was raised whether the early blind are also better at tasks in which the duration of auditory and tactile stimuli must be discriminated. The answer was affirmative. Our electroencephalographic data revealed an enlarged posterior negativity for the blind relative to controls. Source analyses showed comparable solutions in the case of auditory and tactile targets for the blind. These findings support the interpretation of these negativities in terms of a supramodal rather than a modality-specific process, although confirmation with more spatially sensitive methods seems necessary. We additionally examined whether the early blind are less affected by irrelevant tactile or auditory exogenous cues preceding auditory or tactile targets than controls. No differences in alerting and orienting effects of these cues were found between the blind and the controls. Together, our results support the view that major differences between early blind participants and sighted controls on auditory and tactile duration discrimination tasks relate to a late and likely supramodal process that takes place in occipital areas.