Patterns of impulse noise‐induced TTS during a work‐week exposure

Five monaural chinchillas were exposed to a repetitive and reverberant impulse noise for a period of five days, eight h/day at a rate of 1 impulse/sec. The average peak over pressure within the holding cage was 113 dB SPL and the B duration was 160 msec. Auditory thresholds were estimated before and after each exposure using the AER technique. Thresholds were followed for 30 days following the last exposure; the animals were then sacrificed for the surface preparation histology. A clear oscillation in the animal's threshold emerged; high frequencies (4, 8 kHz) were shifted 40 dB after the 8‐h exposure and recovered 25 dB following 16 h of quiet. Low frequencies (0.25, 0.5 kHz) were shifted 22 dB after the 8‐h exposure and recovered 25 dB following 16 h Paradoxically, the low frequencies took longer to recover from an initially lower level of TTS. In general, there was no evidence of any accumulation of TTS over the four‐day period. The final audiograms will be correlated with the cochlear histology.