Altered auditory-tactile interactions in congenitally blind humans: an event-related potential study

It has been shown that stimuli of a task-irrelevant modality receive enhanced processing when they are presented at an attended location in space (crossmodal attention). The present study investigated the effects of visual deprivation on the interaction of the intact sensory systems. Random streams of tactile and auditory stimuli were presented at the left or right index finger of congenitally blind participants. They had to attend to one modality (auditory or tactile) of one side (left or right) and had to respond to deviant stimuli of the attended modality and side. While in a group of sighted participants, early event-related potentials (ERPs) were negatively displaced to stimuli presented at the attended position, compared to the unattended, for both the task-relevant and the task-irrelevant modality, starting as early as 80 ms after stimulus onset (unimodal and crossmodal spatial attention effects, respectively), corresponding crossmodal effects could not be detected in the blind. In the sighted, spatial attention effects after 200 ms were only significant for the task-relevant modality, whereas a crossmodal effect for this late time window was observed in the blind. This positive rather than negative effect possibly indicates an active suppression of task-irrelevant stimuli at an attended location in space. The present data suggest that developmental visual input is essential for the use of space to integrate input of the non-visual modalities, possibly because of its high spatial resolution. Alternatively, enhanced perceptual skills of the blind within the intact modalities may result in reduced multisensory interactions ("inverse effectiveness of multisensory integration").