The role of third windows on human sound transmission of forward and reverse stimulations: A lumped-parameter approach.

The vestibular and cochlear aqueducts serve as additional sound transmission paths and produce different degrees of volume velocity shunt flow in cochlear sound transmission. To investigate its effect on forward and reverse stimulations, a lumped-parameter model of the human ear, which incorporates the third windows, was developed. The model combines a transmission-line ear-canal model, a middle-ear model, and an inner-ear model, which were developed previously by different investigators. The model is verified by comparison with experiments. The intracochlear differential-pressure transfer functions, which reflect the input force to the organ of Corti, were calculated. The results show that middle-ear gain for forward sound transmission is greater than the gain for reverse sound transmission. Changes in the cochlear aqueduct impedance have little effect on forward and reverse stimulations. The vestibular aqueduct has little effect on forward stimulation, but increasing its impedance causes deterioration on reverse stimulation below 300 Hz. Decreasing its impedance increases the excitation effect during reverse stimulation over the entire frequency, especially below 1000 Hz. Moreover, compared with the case without the third windows, the presence of the third windows has little effect on forward stimulation. Whereas, it boosts the reverse stimulation's performance below 300 Hz.