Modeling Reverse Middle Ear Transmission of Acoustic Distortion Signals

In modeling the propagation of signals produced in the cochlea, the effects of the middle ear must be included. We present a linear two-port network model of the middle ear of cat with air cavities open. Effects of the eardrum, ossicular chain, oval and round windows, and fluid in the vestibule are included. The two ports represented are: 1) the ear canal; and 2) the basal end of the cochlear spiral. The model parameters were selected to fit experimental data measuring various aspects of forward transmission only. However, we have used the model to reproduce acoustic distortion signals observed in the ear canal. Three significant findings are that: 1) The design of an acoustic coupler can have a large effect on signals measured in the ear canal; 2) The middle ear and acoustic coupler affect the reflection of distortion signals back into the cochlea and therefore affect distortion signals observed within the cochlea as well as in the ear canal; 3) The reverse transmission properties of the middle ear circuit model are highly frequency dependent.