'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 this reason, a nonlinear estimation method is widely used (derived nonlinear response, DNLR). The aims of this paper are: (1) to analyse some very basic properties of the derived nonlinear emissions such as the short-time input/output relationships; and (2) to show similarities and differences between the classical averaging (linear) and the derived nonlinear recording techniques, in the same ears, both in time and in the frequency domain. At latencies greater than about 6 ms, responses which are recorded using the derived nonlinear technique exhibit no additional 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 response 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 technique. The linear responses show a strikingly similar frequency content with respect to the derived nonlinear responses, at least at a high stimulus level and around the main peaks of the spectrum.