LDV measurement of bird ear vibrations to determine inner ear impedance and middle ear power flow

The mechanical behavior of the middle ear structures in birds and mammals is affected by the fluids in the inner ear (IE) that are present behind the oval window. In this study, the aim was to gather knowledge of the acoustic impedance of the IE in the ostrich, to be able to determine the effect on vibrations and power flow in the single-ossicle bird middle ear for future studies. To determine the IE impedance, vibrations of the ossicle were measured for both the quasi-static and acoustic stimulus frequencies. In the acoustic regime, vibrations were measured with a laser Doppler vibrometer and electromagnetic stimulation of the ossicle. The impedance of the inner ear could be determined by means of a simple RLC model in series, which resulted in a stiffness reactance of K_IE = 0.20·10¹² Pa/m³, an inertial impedance of M_IE = 0.652·10⁶ Pa s²/m³, and a resistance of R_IE = 1.57·10⁹ Pa s/m. The measured impedance is found to be considerably smaller than what is found for the human IE.