Abstract
The total sound pressure measured in the ear canal may be decomposed into a forward- and a reverse-propagating component. Most of the reverse-propagating component is due to reflection at the eardrum. However, a measurable contribution to the reverse-propagating component comes from the cochlea. Otoacoustic emissions (OAEs) are associated with this component and have been shown to be important noninvasive probes of cochlear function. Total ear-canal reflectance (ECR) is the transfer function between forward and reverse propagating components measured in the ear canal. Cochlear reflectance (CR) is the inner-ear contribution to the total ECR, which is the measured OAE normalized by the stimulus. Methods are described for measuring CR with a wide-band noise stimulus. These measurements offer wider bandwidth and minimize the influence of the measurement system while still maintaining features of other OAEs (i.e., frequency- and level-dependent latency). CR magnitude decreases as stimulus level increases. Envelopes of individual band-limited components of the time-domain CR have multiple peaks with latencies that persist across stimulus level, despite a shift in group delay. CR has the potential to infer cochlear function and status, similar to other OAE measurements.
Highlights
Sound pressure measured in the ear canal may be regarded as being composed of two components: (1) a forward-propagating component that transports acoustic energy into the inner ear for the purpose of hearing and (2) a reverse-propagating component that is produced in response to the forward component
We refer to the inner-ear contribution to this reflectance, which is equivalent to a measurement of otoacoustic emission (OAE) normalized by the stimulus, as cochlear reflectance (CR)
The levels of rCR,L (t) are presented as an indicator of the single test condition noise ratio (SNR) of our data and not as an indicator of the level of the OAE that would be obtained if rCR,L (t) was convolved by the stimulus, since rCR,L (t) include residual contributions from the middle-ear and measurement system
Summary
Sound pressure measured in the ear canal may be regarded as being composed of two components: (1) a forward-propagating component that transports acoustic energy into the inner ear for the purpose of hearing and (2) a reverse-propagating component that is produced in response to the forward component. Much of the reverse-propagating component comes from the eardrum. A small but measurable contribution to the reversepropagating component comes from the cochlea, the primary sensory organ for hearing, which is located within the inner ear. We refer to the transfer function between forward- and reverse-propagating components measured in the ear canal as ear-canal reflectance (ECR). We refer to the inner-ear contribution to this reflectance, which is equivalent to a measurement of otoacoustic emission (OAE) normalized by the stimulus, as cochlear reflectance (CR). Methods to extract CR from measurements of ECR are described. The objective is to obtain a cochlear response that has the least possible influence of the middle-ear and measurement system and that can be interpreted in terms of a linear model.
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