A comparison of transiently evoked and distortion-product otoacoustic emissions in humans.

The measurement of transiently evoked otoacoustic emissions (TEOAEs) can identify a hearing loss exceeding 25-30 dB HL with high sensitivity. However, further quantification of the hearing loss is not possible, and the frequency specificity of TEOAEs has been questioned. Distortion-product otoacoustic emission (DPOAE) measurements are being developed for clinical use in the hope that they will be more frequency-specific than are TEOAEs. We have compared TEOAEs and DPOAEs in both normally hearing and hearing-impaired subjects with the purpose of learning more about the frequency specificity of these two types of emissions. In a first investigation, toneburst-evoked OAEs were compared to DPOAEs stimulated at 1, 2 and 4 kHz in ten ears without spontaneous otoacoustic emissions of ten normally hearing subjects. Input/output (I/O) functions of DPOAEs at frequency regions of 1 and 2 kHz were characterized by roll-overs and irregularities that were not present in either DPOAE I/O functions at 4 kHz or in TEOAE I/O functions at 1, 2 and 4 kHz. Mean slopes of the I/O functions increased with increasing frequency for DPOAEs and decreased for TEOAEs. In a second investigation, click-evoked OAEs and DPOAEs (stimulated by pure tones in the frequency range of 0.75-6 kHz) were measured in 42 ears of 21 normally hearing subjects and 128 ears of 64 subjects with varying degrees of sensorineural hearing loss. Results from both investigations revealed that the amplitude ratio between DPOAEs and TEOAEs changed systematically with frequency. DPOAE amplitudes became larger with increasing frequency and TEOAE amplitudes became smaller.(ABSTRACT TRUNCATED AT 250 WORDS)