Spatial auditory compensation in early-blind humans: involvement of eye movements and/or attention orienting?

Several studies have reported that the early-blind displays higher auditory spatial abilities than the sighted. Although many studies have attempted to delineate the cortical structures that undergo functional reorganization in blind people, few have tried to determine which auditory or non-auditory processes mediate these increased auditory spatial abilities. The aim of this paper is to investigate the role of eye movements and orientation of attention in auditory localization in blind humans. Although we found, in a first experiment, that the influence of eye movements on auditory spatial localization is preserved in spite of congenital visual deprivation, the saccade influence on spatial hearing is not more pronounced in the blind than in the sighted. In a second experiment, early-blind and sighted subjects undertook a task involving discrimination of sound elevation in which auditory targets followed uninformative auditory cues on either side with an intermediate elevation. When sounds were emitted from the frontal hemifield, both groups showed similar auditory localization performance. Although the auditory cue did not affect discrimination accuracy in both groups, early-blind subjects exhibited shorter reaction times than sighted subjects when sound sources were placed at far-lateral locations. Attentional cues, however, had similar effects on both groups of subjects, suggesting that improved auditory spatial abilities are not mediated by attention orienting mechanisms.