Auditory Spatial Tuning in Late-onset Blindness in Humans

Blind individuals who lost their sight as older children or adults were compared with normally sighted controls in their ability to focus auditory spatial attention and to localize sounds in a noisy acoustic environment. Event-related potentials (ERPs) were recorded while participants attended to sounds presented in free field from either central or peripheral arrays of speakers with the task of detecting infrequent targets at the attended location. When attending to the central array of speakers, the two groups detected targets equally well, and their spatial tuning curves for both ERPs and target detections were highly similar. By contrast, late blind participants were significantly more accurate than sighted participants at localizing sounds in the periphery. For both groups, the early N1 amplitude to peripheral standard stimuli displayed no significant spatial tuning. In contrast, the amplitude of the later P3 elicited by targets/deviants displayed a more sharply tuned spatial gradient during peripheral attention in the late blind than in the sighted group. These findings were compared with those of a previous study of congenitally blind individuals in the same task [Röder, B., Teder-Sälejärvi, W., Sterr, A., Rösler, F., Hillyard, S. A., & Neville, H. J. Improved auditory spatial tuning in blind humans. Nature, 400, 162–166, 1999]. It was concluded that both late blind and congenitally blind individuals demonstrate an enhanced capability for focusing auditory attention in the periphery, but they do so via different mechanisms: whereas congenitally blind persons demonstrate a more sharply tuned early attentional filtering, manifested in the N1, late blind individuals show superiority in a later stage of target discrimination and recognition, indexed by the P3.