Measurements of wide-band cochlear reflectance in humans

The total sound pressure measured in the ear canal may be decomposed into a forward- and a reversepropagating component. Most of the reverse-propagating component is due to reflection at the eardrum. However, a measurable contribution to the reversepropagating 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 earcanal 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.