Evoked otoacoustic emissions: nonlinearities and response interpretation

Evoked otoacoustic emissions (EOAEs) are acoustic signals produced by the inner ear in response to transient acoustic stimuli, and can be recorded in the external auditory canal. Since emissions can be reduced or even abolished by hearing losses of peripheral origin due to trauma and pathology, EOAEs are presently considered as the most sensitive clinical test for assessing the integrity of peripheral hearing. Recordings of emissions evoked in response to transient stimuli are contaminated by an initial artifact which in most clinical environments can be a very serious limitation. For this reason, a nonlinear estimation method called derived nonlinear response (DNLR) is widely used, instead of classical synchronous averaging. The aims of this work are: (i) to justify theoretically the use of the DNLR technique by means of a simple model and (ii) to compare the results obtained from the classical averaging (a linear estimation technique) with those obtained from the DNLR technique. Some suggestions of practical interest are made on the basis of the analysis.