Adaptation rate and persistence across multiple sets of spectral cues for sound localization.

The adult auditory system adapts to changes in spectral cues for sound localization. This plasticity was demonstrated by modifying the shape of the pinnae with molds. Previous studies investigating this adaptation process have focused on the effects of learning one additional set of spectral cues. However, adaptation to multiple pinna shapes could reveal limitations in the auditory system's ability to encode discrete spectral-to-spatial mappings without interference and thus help determine the mechanism underlying spectral cue relearning. In the present study, listeners learned to localize sounds with two different sets of earmolds within consecutive adaptation periods. To establish both representations in quick succession, participants underwent daily sessions of sensory-motor training. Both pinna modifications severely disrupted vertical sound localization, but participants recovered within each 5-day adaptation period. After the second adaptation, listeners were able to access three different sets of spectral cues for sound localization. Participants adapted to both sets of earmolds with equal success, and learning a second set of modified cues did not interfere with the previous adaptation. We found no indication of meta-adaptation as the rate of adaptation to the second molds was not increased.