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.
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
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
Spectrum of Sound in Ear Canal Stimulus Tones Emission Frequency Background Noise
Tone Decay: • Loss of audibility for a tone that is on continuously. • Greater decay is indicative of retrocochlear problem. • There are different methods:
Some Tone Decay Tests • Carhart: begin at 0 SL, up in 5 dB steps until tone is heard for a full minute • Olson-Noffsinger: begin at 20 SL, up until heard for full minute.
Tone Decay Results: • Type I: no decay: norm, conduct or cochlear • Type II: heard for longer times as level is increased: cochlear • Type III: No growth with increasing level: retrocochlear
TONE DECAY SUCCESS? • Sensitivity = 75% • Specificity = 91%
Auditory Brainstem Response: • Response within 10 ms of stimulus • waves labeled with Roman numerals • Peaks I, III, and V most useful • Latencies are the key measure • Disorders will produce delays
ABR SUCCESS? • Sensitivity = 97% • Specificity = 88%