Middle-ear phenomenology: The view from the three windows

Abstract

To provide a common ground for the comparison between theory and experiment, this paper presents a framework for the phenomenological description of middle-ear mechanics. The framework defines those measurements sufficient to characterize the transduction properties of the middle ear and its components. Phenomenological equations are represented in the form of an equivalent electrical circuit that can be used to deduce testable relations among measurable quantities. Two applications are then discussed. First, the classical concept of the middle-ear transformer ratio is generalized to include any effects of eardrum flexion or nonrotational ossicular motion. Middle-ear models predict that the resulting transformer ratios vary considerably with frequency. Second, the conditions under which the topology of existing circuit analogs satisfactorily approximates middle-ear mechanics are given. Most middle-ear models cannot be used to correctly predict the absolute pressures in the cochlea.

Distortion product otoacoustic emissions measured as vibration on the eardrum of human subjects

“…Thus, in addition to its application to indirectly assessing cochlear mechanics, the vibration DPOAEs could be used to evaluate part of the middle-ear transfer function, because the umbo velocity relative to ear-canal pressure can now be measured directly in both the forward and the reverse directions in vivo. This type of measurement is of considerable interest because the forward and reverse transfer functions are not identical (39,40). By applying parametric changes to the middleear impedances, e.g., by manipulating acoustic reflex or static pressure (e.g., ref.…”

Human middle-ear model with compound eardrum and airway branching in mastoid air cells

“…This approximation was previously used by Shera and Zweig (1992), and is adopted in the present study to model the tympanic cleft using a one-dimensional model. 2 The input impedance Z cav of the middle-ear cleft at this location in the tympanic cavity is related to the volume velocities out of the TM and into each of the oval and round windows by…”

“…If the eardrum were modeled as a rigid piston, then each effective transformer ratio would be equal to N 1 in Eq. (37), i.e.,N P ¼N U ¼ N 1 (Shera and Zweig, 1992).…”

“…As described by Shera and Zweig (1992),N P is an effective transformer ratio for pressure andN U is an effective transformer ratio for volume velocity. The circuit in Fig.…”

“…This circuit topology lacks the property that the oval and round windows are also boundaries of the tympanic cleft with respect to the fluids within the cochlea. To predict intracochlear pressures within cochlear fluid, it is necessary to describe the boundary conditions between the tympanic cleft at each of the eardrum, oval, and round windows (Peake et al, 1992;Shera and Zweig, 1992). A model that adequately represented these boundary conditions was that of Shera and Zweig (1992), which modified the middle-ear model of Kringlebotn (1988).…”