Otoacoustic Emissions Low-level sounds produced by the cochlea and recordable in the external ear canal. Spontaneous Click-evoked Distortion Product Stimulus Frequency

History First described by Kemp (1977 & 1978), But predicted by Gold (1948!) Supported by almost simultaneous discovery of OHC motility Movement into Clinical Use: Screening for hearing loss Role in Audiologic Battery

Anatomy and Physiology Generators = Outer Hair Cells “Pre-neural” Low-level event//High level stimuli produce their own distortions Reduction/Loss of emission in NITTS SOAEs correlated to number of rows of OHCs

Energy Path: “Reverse Traveling Wave” is debated Through Middle Ear: Filtering and attenuation Into ear canal Note: requirement of healthy middle ear and clear outer ear.

Clinical Utility -- Neonatal Hearing Screening Transient and Distortion-Product OAEs Rationale: quick, relatively inexpensive, possibly catching losses in a broader frequency range than ABR NIH (1994) recommended two-stage protocol combining OAEs and ABR

Clinical Utility-- in the Audiologic Battery Assessment of cochlear health in site-of lesion testing Objective info on peripheral auditory functioning Correlation to audiogram Assessment of Auditory Efferents through Contralateral Suppression

Recording OAEs

Spectrum of Sound in Ear Canal Stimulus Tones Emission Frequency Background Noise

OAE as Measure of Cochlear Health

Caveats--Remember: there is more to “Hearing” than a healthy cochlea what lies between your equipment and the source? high level stimuli evoke response from inanimate cavities (e.g. in cadavers)