Long-term adaptation in hearing impaired ears

Recovery from adaptation was measured in acoustically-traumatized ears for pure-tone adapters 2-15 min in duration at levels of 70-110 dB SPL. The whole-nerve potential was recorded in cats. The decrease in response to a probe stimulus (normalized decrement) was used as a measure of adaptation and, for a particular adapter, was assessed at different probe frequencies. Impaired animals showed generally less effect of the adapting stimuli at a given adapter level (in dB SPL) and faster recovery than in normal ears. The form of the normalized decrement vs probe frequency functions were generally normal. We interpret these observations to mean that while the effectiveness of the adapter is reduced the spread of adaptation to different frequency regions is relatively normal.