Effects of periodic rest on physiological measures of auditory sensitivity following exposure to noise.

Whole nerve action potential (AP) and single auditory-nerve fiber thresholds were measured in chinchillas exposed to noise. The exposure stimulus was a 500-Hz octave band of noise presented at 95 dB SPL for 15 min/h, for 4 or 40 days. The AP thresholds were elevated by about 40 dB on day 4, between 0.5 kHz and approximately 8 kHz. On day 40, AP thresholds at the same frequencies were lower by 10-25 dB, even though the noise exposure had continued. Single fiber threshold tuning curves exhibited pathologies similar to those previously observed following noise exposure. Tuning curves measured on day 40 were more normal in appearance. These results confirm that similar recovery of threshold observed in psychophysical experiments [Clark et al., J. Acoust. Soc. Am. 82, 1253-1264 (1987)] can be understood in terms of the sensitivity of the peripheral auditory system.