Behavior of spontaneous otoacoustic emissions following intense ipsilateral acoustic stimulation.

Following presentation of brief, intense pure tones spontaneous otoacoustic emissions (SOAEs) were reduced in frequency and/or amplitude. The effects were highly tuned with exposures between 1/8 and 5/8 of an octave below the SOAE producing the maximum changes. Exposure frequencies above the SOAE had no effect. The degree of tuning observed depended upon the post-exposure time sampled, with sharpness maximal between 3 and 120 s post-exposure. The effects increased nonlinearly as exposure level and duration were increased. The recovery functions were biphasic, the first phase being rapid and non-monotonic over about 2 min, while the second phase was monotonic and slow, sometimes taking several hours. These data are consistent with changes in outer hair cell (OHC) function and support the hypothesis that OHC changes underlie behavioral temporary threshold shift (TTS).