Abstract
An important step to describe the effects of inner-ear impedance and pathologies on middle- and inner-ear mechanics is to quantify middle- and inner-ear function in the normal ear. We present middle-ear pressure gain GMEP and trans-cochlear-partition differential sound pressure ΔPCP in chinchilla from 100Hz to 30kHz derived from measurements of intracochlear sound pressures in scala vestibuli PSV and scala tympani PST and ear-canal sound pressure near the tympanic membrane PTM. These measurements span the chinchilla’s auditory range. GMEP had constant magnitude of about 20dB between 300Hz and 20kHz and phase that implies a 40-μs delay, values with some similarities to previous measurements in chinchilla and other species. ΔPCP was similar to GMEP below about 10kHz and lower in magnitude at higher frequencies, decreasing to 0dB at 20kHz. The high-frequency rolloff correlates with the audiogram and supports the idea that middle-ear transmission limits high-frequency hearing, providing a stronger link between inner-ear macromechanics and hearing. We estimate the cochlear partition impedance ZCP from these and previous data. The chinchilla may be a useful animal model for exploring the effects of non-acoustic inner-ear stimulation such as “bone conduction” on cochlear mechanics.
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