Insights into linear and nonlinear cochlear transduction: Application of anew system-identification procedure on transient-evoked otoacoustic emissions data

Transient-evoked otoacoustic emissions (TEOAE) were used to characterize li near and nonlinear cochlear transduction using a new system-identification procedure. In this technique, a computational model of the system is first developed. From the measured stimulus and response records, spectral-densit y functions and multiple coherence functions are calculated, The coherence functions allow the characterization of linear/nonlinear processes as a fun ction of frequency. Summations of linear and nonlinear coherences provide a goodness-of-fit of the chosen model. Finite impulse response pulses with a bandwidth of 1-8 kHz were used to evoke otoacoustic emissions. Eleven adul ts with normal hearing served as subjects. Third- and fifth-order polynomia l models were used to model the data, and the results indicate that the fif th-order model is a better fit to the TEOAE data. The results of this study suggest that this system-identification procedure can be successfully appl ied to model cochlear transduction using a broadband stimulus. Most importa ntly, coherence functions provide useful insights into linear and nonlinear cochlear processes and have the potential to be developed as a clinical me asure for monitoring changes in cochlear status. (C) 1999 Acoustical Societ y of America.[S0001-4966(99)0301-X].