A COCHLEAR MODEL USING FEEDFORWARD OUTER-HAIR-CELL FORCES

A linear (frequency-domain) model of the cat cochlea (implemented in b oth 1- and 2-dimensional versions) has been developed which uses outer hair cell (OHC) forces in a geometry which includes the longitudinal (base-to-apex) tilt of the outer hair cells (OHCs). When positive (con tractile) real OHC force-constants are used, very large (50 + dB) resp onse peaks along with very rapidly accumulating phase lags (which can reach -50 pi radians) are obtained, The wider the longitudinal segment ation, the broader the peaks and the less the phase accumulation; 71-m u m segmentation produced the most realistic responses. These large re sponse peaks are achieved by a small zone of negative resistance (ca. 1 mm) just basal to the response peak and the virtual 'zeroing' of the basilar membrane's effective impedance over the entire peak region (c a. 2.5 mm). To produce these peaks, the OHCs generate about 25-times t he incoming acoustic power. Inclusion of low-pass filtering in the mod el's OHC representation produces, by contrast, very unrealistic notch- and-peak displacement complexes accompanied by very large phase lags, for all segmentation widths used. However, when phase reversals of OHC forces are also added, achieved by imbedding a resonant system within the tectorial membrane, very realistic peaks and phase functions are produced. More power must, however, be generated by the OHCs (about 70 -times the incoming). The end result is output which mimics quite clos ely the living basilar membrane's responses to low-intensity high-freq uency tones.