Human Cochlear Function: A Continuum of Maturation and Aging.
This project studies changes in cochlear function throughout the human lifespan, defining the timeline for these age-related shifts and the mechanisms driving the changes. We use primarily otoacaoustic emissions, a noninvasive ear canal probe of cochlear mechanics to learn about the human peripheral system. We apply both distortion- (DPOAE) and reflection-source (stimulus frequency OAEs and the reflection-component of the DPOAE) emissions using custom-algorithms, innovative swept-tone methodology and advanced analysis schemes. We disentangle the origin of age-related effects by separating distortion product OAEs into their dual components, distortion and reflection; and studying how each component’s phase and amplitude is impacted throughout the human lifespan. In our lab it is important to study both apical and basal halves of the cochlea to yield a more comprehensive understanding of how the cochlea codes low and high-frequency sounds. The apex has been minimally studied in humans, and wholly unexplored during maturation. Yet, we have recently reported striking immaturities in DPOAE phase for low-frequency signals coded in the apex of neonates. Our exploration of human cochlear function from base to apex using multiple OAE sources establishes a normative framework, provides detailed information about newborn cochlear maturation, and probes how the elderly cochlea ages into senescence. These findings contribute to more comprehensive cochlear models and toward the development of more innovative probes of cochlear function for human application. This project is funded by the NIH-NIDCD.

Exploiting Dual OAE Sources to Study the Normal and Impaired Human Cochlea.
This project attempts to exploit the distinct information embedded in reflection- and distortion-source OAEs to create a more comprehensive and descriptive joint test of cochlear function. At present, OAEs are used in a categorical sense, simply to detect hearing loss. However, once hearing loss is detected, we wish to learn about the underlying deficit and etiology. The ample information provided by the two OAE types (i.e. linear reflection and nonlinear distortion) can offer distinct clues about different aspects of cochlear function. We wish to exploit this distinct information to describe (not just detect) sensorineural hearing loss (SNHL). At present, SNHL is a catch-all term, defined by degree of loss and audiometric configuration. However, two hearing losses with identical audiograms can produce varying perceptual difficulties and varied success with hearing aids. By recording a combined reflection and distortion OAE profile over broad level and frequency ranges, we may be able to learn more about the underlying deficits that comprise the broad and vague category of SNHL. When used in combination, the properties embodied by each OAE can be considered in one joint metric. We are currently developing and testing this joint OAE protocol by recording stimulus frequency OAEs and the distortion component of DPOAEs in ears with normal and impaired hearing. This project is conducted in collaboration with fellow USC faculty member Dr. Christopher Shera.

https://sites.usc.edu/abdalab/