Feeling vibrations: enhanced tactile sensitivity in congenitally deaf humans.

The human nervous system displays remarkable functional plasticity following long-term sensory deprivation. For example, the auditory cortex of congenitally deaf humans may start to process tactile information. To further explore this type of cross-modal plasticity, we examined the tactile accuracy of congenitally deaf and normal hearing subjects in frequency discrimination and in detection of random suprathreshold frequency changes within a monotonous sequence of vibratory stimuli. We found that congenital deafness can enhance the accuracy of suprathreshold tactile change detection while tactile frequency discrimination is not significantly changed, although there is a trend toward reduced thresholds. The enhanced tactile sensitivity in the deaf probably reflects both neural plasticity and increased attention directed to the stimuli. Whatever the underlying neural mechanisms might be, functional compensation following early sensory loss apparently leads the remaining sensory modalities to develop capacities exceeding those of the normal functional systems.