EFFECT OF HIGH-FREQUENCY INTERRUPTED NOISE EXPOSURES ON EVOKED-POTENTIAL THRESHOLDS, DISTORTION-PRODUCT OTOACOUSTIC EMISSIONS, AND OUTER HAIR CELL LOSS

The effect of high-frequency interrupted noise exposures on evoked pot ential (EP) thresholds, distortion-product otoacoustic emissions (DPOA Es), and status of the outer hair cells was studied with the aim of un derstanding the correspondence among the three measures. Animal subjec ts were exposed to an octave band noise centered at 4 kHz at 85 dB SPL for 6 hr/day for 10 days. EP and DPOAE recordings were made before th e exposure and on days 1, 2, 4, 6, 8, and 10 of exposure. A final set of measurements were made 5 days after the last exposure, following wh ich the animals were sacrificed and their cochleas were examined using scanning electron microscopy. Both EPs and DPOAEs showed a worsening of auditory function after the first exposure and then showed a progre ssive recovery toward baseline. However, there was no consistent relat ionship between changes in EP thresholds and changes in DPOAEs nor wer e there any systematic changes in outer Flair cells that corresponded with the changes in DPOAEs. Furthermore, EP thresholds often revealed considerable deficits in function while DPOAEs were normal.