Middle latency auditory evoked potentials in congenitally blind and normal sighted subjects.

Middle latency auditory evoked potentials were recorded in two groups of ten subjects each, viz, congenitally blind (CB) and age-matched subjects with normal vision (NV). The age range for both groups was 13 to 16 years. The CB group subjects had peripheral deficits, with absence of visual evoked responses. The peak latency of the Nb wave (the maximum negativity between 38 and 48 ms) was significantly lower in the CB group compared to NV group (p < .05, one-tailed, two factor ANOVA, Tukey test). In addition to these recordings from the vertex, recordings were also made from occipital areas, to test whether the visual cortex contributes to information processing at primary auditory cortical levels in the blind, as was reported in earlier studies on the generation of potentials during auditory selective attention. No such effect was observed. Hence, it appears that in blind subjects changes in generators of auditory middle latency evoked potentials are mainly related to latency, rather than to scalp distribution of these components.