To test the possibility that visual cues might help to boost auditory plasticity, the authors compared the earplugs' behavioral effects on two groups of ferrets: one blind since infancy, and another with normal vision. Both groups could localize about the same without earplugs, made more errors after receiving the plug, and then steadily improved with the periodic retesting. These results show not only that the ferrets could be trained to reprocess abnormal localization cues but also that they could do so without visual cues. Then, by training another group of ferrets to localize both auditory and visual stimuli before inserting the earplug, the authors show that sound localization depends "exclusively on auditory training" and does not involve "a visual recalibration of auditory space." Furthermore, adaptation did not depend on error feedback, since rewards were not based on performance.
After removal of the earplugs, ferrets made errors reflecting a small bias toward the previously plugged ear: they initially processed the cues as if the ear was still plugged. This aftereffect, though transient, indicates that the adaptive response relies in part on reinterpreting the relationship between binaural cues and location. However, compensation for the earplug-disrupted binaural cues mainly involved the animals' learning to make use of other cues that were les
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