REMOTE MASKING IN NORMAL-HEARING AND NOISE-EXPOSED CHINCHILLAS

Remote masking (RM), the phenomenon whereby an intense high-frequency masking noise elevates thresholds for low-frequency signals, has been shown to be sensitive to various types of hearing loss in humans. We p erformed two experiments to evaluate the chinchilla as a model of RM a nd to examine changes in RM associated with temporary threshold shifts (TTSs) induced by low-frequency noise exposure. Thresholds for 0.5-, 1- and 2-kHz tones were measured in quiet, then in the presence of a n arrow-band (300-Hz-wide) masking noise centered at 3 kHz. In Experimen t I, effective masking was measured as a function of masker level, fro m 48 to 98 dB sound pressure level (SPL; referenced to 20 mu Pa), to d etermine threshold and rate of growth of RM in the chinchilla. In Expe riment II, RM was measured before, during and after exposure to a low- frequency noise known to produce TTSs in chinchillas (i.e., a 0.5-kHz octave band noise at 90 dB SPL for 6 h/day for 10 days). The results s how that normal-hearing chinchillas have the same pattern of RM as hum ans, and that a noise exposure that produces TTSs also produces rapid and significant changes in RM.