Compound action potential tuning curves (APTC’s) were developed in a series of normal and acoustically traumatized cats. Probe frequency was set to 4 kHz and probe level was set to 15–20 dB SL re: AP threshold for both normal and impaired ears. In addition, normal ears received the probe tone at a level of 70–75 dB SPL. Probe-elicited AP amplitude was measured in a forward-masking paradigm as a function of both masker level and frequency. Results indicated that the sharpness of the APTC’s (defined by Q10) was unaffected by acoustic trauma. The relative difference between required masker level on the tail and at the tip was reduced for the noise-damaged ears. Thus sharpness around the tip was essentially normal yet low-frequency energy was more effective at masking high-frequency regions in these impaired ears. When slope of the decrement in normalized, probe-elicited AP amplitude-versus-masker level functions are calculated for different frequency maskers, normal ears showed a frequency dependence such that low-frequency maskers resulted in the steepest slopes with progressively less steep slopes as masker frequency increased. Some of the noise-damaged ears did not show this same frequency dependence. Specifically, the slopes of these functions were not as different for low-and high-frequency maskers. These slope data may suggest that nonlinearities, present in the normal system, may be reduced as a consequence of this cochlear insult.
ASJC Scopus subject areas
- Arts and Humanities (miscellaneous)
- Acoustics and Ultrasonics