The "inverse problem" solved for a three-dimensional model of the cochlea.III. Brushing-up the solution method

In two earlier papers [de Beer, J. Acoust. Sec. Am. 98, 896-903 and 904-910 (1995)] the inherent problems of the inverse-solution method in cochlear m echanics were described. The present paper shows results obtained with a mo re universal solution method. With the new method it is possible to constru ct a three-dimensional model of the cochlea producing a response that accur ately simulates a measured mechanical basilar-membrane response. With earli er methods this could not be done. The inverse solution invariably yields t hat, with low stimulus levels, the model simulating a viable cochlea must b e locally active. For the response of a dead animal a passive model is suff icient. Once more the :inherent intricacies and problems of the inverse-sol ution method are discussed. Conservation of fluid volume leads to the conce pt of the "virtual stapes velocity." For best results, the input signal to the inverse-solution procedure should be acquired in the form of a "composi te cross-correlation spectrum." Inverse analysis can, under certain circums tances, produce aberrant results. In this paper it is shown why the resulti ng impedance function is the most accurate in the region of the response pe ak. Therefore, it is unlikely that a passive model would exist of which the response simulates the data obtained from a healthy animal. (C) 1999 Acous tical Society of America. [S0001-4966(99)05406-5].