Transiently evoked and distortion-product otoacoustic emissions. Comparison of results from normally hearing and hearing-impaired human ears

R. Probst and F. P. Harris
Department of Otorhinolaryngology, Kantonsspital, Basel, Switzerland.

Evoked otoacoustic emissions can be measured after a transient stimulus or as distortion products of two pure tones. Measurements of both emission types are being used more frequently as the techniques become easier to implement and the clinical benefits are realized. In addition, comparisons between the two types of emissions from the same ear provide information about cochlear mechanisms. We have measured transiently evoked otoacoustic emissions (TEOAEs) stimulated with clicks and distortion-product otoacoustic emissions (DPOAEs) from 166 ears of individuals with and without hearing impairment. The TEOAE and DPOAE amplitudes were compared with each other and with corresponding audiometric thresholds by frequency. Results revealed a high correspondence between the two emission types (r = .78) and between the distribution of the energy for each emission and audiometric threshold levels at corresponding frequencies (DPOAE, Spearman p = -.84; TEOAE, p = -.77). The DPOAEs were present more often than were TEOAEs when hearing levels across frequency were greater than 30-dB hearing level. The results suggest that both TEOAEs and DPOAEs are derived largely from similar mechanisms. The differences between the occurrence of the two emissions by audiometric threshold level would suggest that TEOAEs may be preferable for screening purposes, whereas DPOAEs may be more valuable for monitoring cochlear changes clinically.