Transient-Evoked Otoacoustic Emissions as a Measure of Noise-Induced Threshold Shift

Otoacoustic emissions and behavioral hearing thresholds were measured before and after exposure to a 10-min, 105-dB SPL, half-octave band of noise centered at 1.414 kHz. Along a single recovery function, transient-evoked otoacoustic-emission (TEOAE) measurements made with 74-dB pSPL nonlinear click ensembles were alternated with a Bekesy threshold-tracking procedure. Each of the 14 participants with normal hearing underwent 2 hour-long temporary-threshold shift (TTS) sessions as well as 2 pretest sessions and a posttest session. The Bekesy test frequency was fixed at 2.0 kHz, whereas emissions were analyzed in half-octave bandwidths with center frequencies ranging from 0.707 to 5.656 kHz. Results showed that (a) the maximum temporary emission shifts (TES) were half to 1 octave above the exposure frequency; (b) the 4.7-dB average temporary emission shift magnitude at approximately 2 min postexposure was less than half of the 11.7-dB average TTS; (c) the average recovery times for emissions and hearing thresholds were similar (188 vs. 186 min); and (d) the average TTS magnitude along the recovery function was predictable from TES magnitude. It is concluded that both TEOAEs and Bekesy thresholds reveal the same aspects of postexposure inner-ear changes.