Middle-ear velocity transfer function, cochlear input immittance, and middle-ear efficiency in chinchilla.

Area of Science:

• Bioacoustics
• Auditory Physiology
• Middle Ear Mechanics

Background:

• The transfer function H(V) describes sound transmission through the middle ear (ME).
• Middle ear power transmission efficiency (MEE) quantifies sound energy transfer to the cochlea.
• Previous studies have reported ME input admittance and pressure gain measurements.

Purpose of the Study:

• To compute MEE from transfer function H(V) measurements.
• To analyze cochlear input admittance (Y(C)) and its frequency-dependent characteristics.
• To compare MEE with previous estimates in chinchillas.

Main Methods:

• Measured transfer function H(V) between stapes velocity and tympanic membrane sound pressure in seven chinchilla ears.
• Utilized previously reported ME input admittance (Y(TM)) and ME pressure gain (G(MEP)) data.
• Calculated cochlear input admittance (Y(C)) from H(V) and G(MEP) with an open ME and cochlear pressure sensor.

Main Results:

• Cochlear input admittance (Y(C)) is governed by mass and resistance, behaving as a minimum-phase system up to 27 kHz.
• The real part of Y(C) (Re{Y(C)}) gradually decreased with frequency up to 25 kHz, then decreased more rapidly.
• MEE was approximately 0.5 from 0.1 to 8 kHz, higher than prior estimates, and sharply declined at higher frequencies.

Conclusions:

• The study provides a detailed analysis of middle ear sound transmission efficiency in chinchillas.
• MEE is substantial across a broad frequency range relevant for hearing.
• The findings offer insights into the mechanical properties of the cochlear input impedance.