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Effects of Low-Frequency Bias Tones on Stimulus-Frequency Otoacoustic Emissions

Effects of Low-Frequency Bias Tones on Stimulus-Frequency Otoacoustic Emissions. Eric L. Carmichel Mentors Dr. Michael Dorman Dr. Lin Bian. Committee Members. Dr. Lin Bian (Committee Chair) Dr. Michael Dorman Dr. Andrea Pittman. Otoacoustic Emissions (OAEs).

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Effects of Low-Frequency Bias Tones on Stimulus-Frequency Otoacoustic Emissions

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  1. Effects of Low-Frequency Bias Tones on Stimulus-Frequency Otoacoustic Emissions Eric L. Carmichel Mentors Dr. Michael Dorman Dr. Lin Bian

  2. Committee Members • Dr. Lin Bian (Committee Chair) • Dr. Michael Dorman • Dr. Andrea Pittman

  3. Otoacoustic Emissions (OAEs) • Faint acoustical signals originating from the inner ear but can be detected in ear canal • They can occur spontaneously (SOAEs) • Can occur during and after stimulation of the ear • In general, healthy ears produce OAEs, whereas hearing-impaired ears do not

  4. Otoacoustic Emissions (OAEs) • OAEs are a by-product of the active mechanism of the inner ear (Probst et al., 1991) • When OHCs are damaged, the active mechanism is reduced in effectiveness or lost altogether • Compressive nonlinearity is associated with the active cochlear process

  5. What does “compressive nonlinearity” mean?

  6. Previous studies • Low-frequency biasing technique used to assess the dynamic nonlinearity of the inner ear • The bias tone can shift the cochlear partition. This produced an amplitude modulation of DPOAEs (Bian et al., 2002, 2007; Bian, 2004)

  7. Cochlear partition—Consists of the basilar membrane, tectorial membrane, and the Organ of Corti

  8. Cochlear partition

  9. Biasing the cochlear partition

  10. Question: Can the biasing technique be applied to SFOAEs? • SFOAEs evoked in response to a single external tone • Measuring SFOAEs presents a unique challenge. As the name implies… • The emission is at the same frequency as the stimulus (or probe) tone

  11. DPOAE visible via spectral analysis SFOAE cannot be “seen”

  12. Question: Can the biasing technique be applied to SFOAEs? • Cannot “see” the emission • Separating a minute signal (i.e.,the emission) requires an indirect method • Can we study the effects of amplitude modulating the SFOAE with a bias tone? • More theory (oh boy!) and a hardware model

  13. “OHC” Probe |Bias| Bias tone

  14. Question: Can the biasing technique be applied to SFOAEs? • We have a mathematical foundation • We have a working hardware model • Now all we need… are human ears!

  15. Methods • Nine participants, ages 21 – 48 yrs (M=25) • Ten ears total • Eight normal ears with robust DPOAEs • Two ears with profound hearing loss • Bias tone and probe tone presented simultaneously • Ear canal acoustics recorded

  16. Participants were comfortably seated

  17. Summary • Noninvasive nature of biasing technique—shows potential as a research tool and development of new clinical applications • Normal and impaired ears can be tested—potentially be applied in the differential diagnosis of cochlear pathologies • Just the beginning—present assay can be expanded upon

  18. Acknowledgements • Thanks to committee members Dr. Bian, Dr. Dorman, and Dr. Pittman • Thanks to Tina Stinson for recruiting and screening participants • Thanks to the participants • Many thanks to all of you!

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