Observing chartacteristic frequency shifts using chirp-evoked otoacoustic emissions.

Abstract

Otoacoustic emissions (OAEs) are often used to assess the integrity of specific regions of the cochlea. There is, however, evidence that the frequency that causes maximal response for a particular cochlear region shifts toward lower frequencies at high-stimulus levels. Therefore, OAE-based assessments of cochlear activity over a wide range of levels may need to take into account these shifts. The present study employed two experiments in order to confirm and characterize the extent to which this shift in cochlear excitation as a function of level can be observed in OAEs. In the first experiment, chirp-evoked otoacoustic emissions (ChOAEs) were used to track changes in the frequency spectra of each listener. The results showed a shift toward low frequencies in the spectral peak of ChOAE response in a majority of listeners (−9.1% average shift). This shift was then confirmed using a single-listener measurement of tone-burst otoacoustic emission input/output functions measured at three different frequencies. These results support the contention that it may be necessary to vary stimulus frequency to take the cochlear excitation shift into account when making assessments of the cochlear activity at a particular location across a wide range of levels.