An important issue in neuroscience is the effect of visual loss on the rema
ining senses. Two opposing views have been advanced. On the one hand, visua
l loss may lead to compensatory plasticity and sharpening of the remaining
senses. On the other hand, early blindness may also prevent remaining senso
ry modalities from a full development.
In the case of sound localization, it has been reported recently that, unde
r certain conditions, early-blind humans can localize sounds better than si
ghted controls. However, these studies were confined to a single sound sour
ce in the horizontal plane. This study compares sound localization of early
-blind and sighted subjects in both the horizontal and vertical domain, whe
reas background noise was added to test more complex hearing conditions.
The data show that for high signal-to-noise (S/N) ratios, localization by b
lind and sighted subjects is similar for both azimuth and elevation. At dec
reasing S/N ratios, the accuracy of the elevation response components deter
iorated earlier than the accuracy of the azimuth component in both subject
groups. However, although azimuth performance was identical for the two gro
ups, elevation accuracy deteriorated much earlier in the blind subject grou
p. These results indicate that auditory hyper-compensation in early-blind h
umans does not extend to the frontal target domain, where the potential ben
efit of vision is maximal. Moreover, the results demonstrate for the first
time that in this domain the human auditory system may require vision to op
timally calibrate the elevation-related spectral pinna cues. Sensitivity to
azimuth-encoding binaural difference cues, however, may be adequately cali
brated in the absence of vision.