The Extent of Task Specificity for Visual and Tactile Sequences in the Auditory Cortex of the Deaf and Hard of Hearing.

It has been proposed that the auditory cortex in the deaf humans might undergo task-specific reorganization. However, evidence remains scarce as previous experiments used only two very specific tasks (temporal processing and face perception) in visual modality. Here, congenitally deaf/hard of hearing and hearing women and men were enrolled in an fMRI experiment as we sought to fill this evidence gap in two ways. First, we compared activation evoked by a temporal processing task performed in two different modalities, visual and tactile. Second, we contrasted this task with a perceptually similar task that focuses on the spatial dimension. Additional control conditions consisted of passive stimulus observation. In line with the task specificity hypothesis, the auditory cortex in the deaf was activated by temporal processing in both visual and tactile modalities. This effect was selective for temporal processing relative to spatial discrimination. However, spatial processing also led to significant auditory cortex recruitment which, unlike temporal processing, occurred even during passive stimulus observation. We conclude that auditory cortex recruitment in the deaf and hard of hearing might involve interplay between task-selective and pluripotential mechanisms of cross-modal reorganization. Our results open several avenues for the investigation of the full complexity of the cross-modal plasticity phenomenon. Previous studies suggested that the auditory cortex in the deaf may change input modality (sound to vision) while keeping its function (e.g., rhythm processing). We investigated this hypothesis by asking deaf or hard of hearing and hearing adults to discriminate between temporally and spatially complex sequences in visual and tactile modalities. The results show that such function-specific brain reorganization, as has previously been demonstrated in the visual modality, also occurs for tactile processing. On the other hand, they also show that for some stimuli (spatial) the auditory cortex activates automatically, which is suggestive of a take-over by a different kind of cognitive function. The observed differences in processing of sequences might thus result from an interplay of task-specific and pluripotent plasticity.