Tuned in when out of sight

Abstract

It has been reported previously that blind humans show improved auditory discrimination, as if to compensate for the sensory lack in the visual modality (e.g. 1 Lessard N. et al. Early-blind human subjects localize sound sources better than sighted subjects. Nature. 1998; 395: 278-280 Crossref PubMed Scopus (478) Google Scholar ). However, it is unclear how this sensory enhancement relates to altered cortical activation patterns found in these blind individuals. A recent study by Röder et al. makes an important contribution to the investigation of this phenomenon by comparing behavioural and electrophysiological measures of auditory spatial tuning in congenitally blind individuals and normally sighted but blindfolded control subjects 2 Röder B. et al. Improved auditory spatial tuning in blind humans. Nature. 1999; 400: 162-166 Crossref PubMed Scopus (510) Google Scholar . In an attentional paradigm, brief noise bursts were presented in random sequence with equal probability from one of four central and four peripheral speakers. Subjects were instructed to attend either to a central or to a peripheral loudspeaker and to detect infrequent higher-pitched sounds when they came from the target speaker, but to ignore sounds from all other speakers. The results showed that the blind subjects had better localization abilities than those of the control subjects, but only when they attended to peripheral auditory space. ERP recordings measured at the same time revealed sharper tuning curves for the component of the ERP related to early spatial attention in the blind subjects, and differences in the scalp topography of the ERP responses strongly suggest that there is a reorganization of the neural substrates for early auditory processing in the congenitally blind. This study adds support to the notion that when the brain is faced with the loss of one sensory modality, it reacts with compensatory changes in the remaining modalities.