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)

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

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

What does “compressive nonlinearity” mean?

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)

Cochlear partition—Consists of the basilar membrane, tectorial membrane, and the

Organ of Corti

Cochlear partition

Biasing the cochlear partition

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

DPOAE visiblevia spectral

analysis

SFOAEcannot be

“seen”

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

“OHC”

Probe

|Bias|

Bias tone

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!

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

Participants were

comfortably seated

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

Acknowledgements

Thanks to committee members Dr. Bian, Dr. Dorman, and Dr. Pittman

Thanks to Tina Stinson for recruiting and screening participants

Thanks to the participantsMany thanks to all of you!