Using otoacoustic emissions to measure the transmission matrix of the middle-ear

Abstract

Here we describe an experimental method for measuring the acoustic transmission matrix of the middle-ear using otoacoustic emissions. The experiment builds on previous work that uses distortion product otoacoustic emissions (DPOAEs) as an intracochlear sound source to drive the middle-ear in reverse. This technique eliminates the complications introduced by needing to place an acoustic transducer inside the cochlea. Previous authors have shown how the complete 4x3 system response matrix, with its 12 unknowns, can be simplified to a 2x2 transmission matrix by de-coupling the middle-ear cavity and assuming the cochlear fluids are incompressible. This simplified description of middle-ear mechanics assumes that the input-output response at the tympanic membrane and stapes footplate is linear, one dimensional and time invariant. The technique allows for estimating the acoustic pressure and volume velocity at the tympanic membrane and the volume velocity of the stapes footplate, in both the forward and reverse direction, and under different boundary conditions at the stapes. The technique was applied to deeply anesthetized cats with widely opened middle-ear cavities over a frequency range of 200Hz to 10kHz. Results on three animals are reported and generally agree with previous data and a published middle-ear model.