DERIVED NONLINEAR VERSUS LINEAR CLICK-EVOKED OTOACOUSTIC EMISSIONS

Recordings of emissions evoked in response to transient stimuli (TEOAE ) are partially contaminated by the initial stimulus artifact. For thi s reason, a nonlinear estimation method is widely used (derived nonlin ear response, DNLR). The aims of this paper are: (1) to analyse some v ery basic properties of the derived nonlinear emissions such as the sh ort-time input/output relationships; and (2) to show similarities and differences between the classical averaging (linear) and the derived n onlinear recording techniques, in the same ears, both in time and in t he frequency domain. At latencies greater than about 6 ms, responses w hich are recorded using the derived nonlinear technique exhibit no add itional features in comparison with linear recordings, at all stimulus levels. At latencies less than 6 ms, the derived nonlinear technique greatly reduces the linear content of the acoustic artifact, and the r esponse may be considered as the initial part of the emission. However , the derived nonlinear responses tend to be considerably noisier than the linear emissions, thus reducing the effectiveness of the techniqu e. The linear responses show a strikingly similar frequency content wi th respect to the derived nonlinear responses, at least at a high stim ulus level and around the main peaks of the spectrum.