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Brenda L. Lonsbury-Martin
Postal:
Department of Otolaryngology and Head and Neck Surgery Loma Linda University Health, #2584 11234 Anderson Street Loma Linda, California 92354-2804 USA
Email:
blonsbury-martin@llu.edu
Barden B. Stagner
Postal:
Research Service (151) Veterans Affairs Loma Linda Healthcare System 11201 Benton Street Loma Linda, California 92351-0001 USA
Email:
barden.stagner@va.gov
Glen K. Martin
Postal:
Research Service (151) Veterans Affairs Loma Linda Healthcare System 11201 Benton Street Loma Linda, California 92351-0001 USA
Email:
glen.martin2@va.gov
Otoacoustic Emissions:
Can Laboratory Research Improve Their Clinical Utility?
Are research-based otoacoustic emissions clinically useful?
From the Research Bench
The existence of otoacoustic emissions (OAEs), the sounds generated in the co- chlea of the inner ear and measured with an acoustic probe fitted snugly in the outer ear canal, has been known for almost 40 years. The schematic drawing in Figure 1 illustrates the fit of the acoustic probe in the outer ear canal.
Figure 1. Schematic of emissions measurement system. Both the miniature sound source and microphone transducer are sealed into the outer ear canal using a soft disposable foam ear tip in- corporating two sound ports for stimulus delivery and micro- phone pickup of emitted sounds. The acoustic stimulus sets up a traveling wave in the cochlea of the inner ear (right), which is measured in the cochlea as an otoacoustic emission. The middle ear lies between the outer ear (left) and cochlea.
The original descrip- tions of OAEs in hu- mans (Kemp, 1978) described emitted re- sponses that exist ei- ther without external stimulation (naturally occurring in the ab- sence of acoustic stim- ulation) as spontane- ous OAEs (SOAEs) or as evoked OAEs that are elicited using vari- ous types of acoustic stimuli. For example, short-lasting moder- ate sounds like clicks and tone pips elicit transient-evoked OAEs (TEOAEs),whereas
much longer continuous low-level pure tones evoke stimulus-frequency OAEs (SFOAEs). When two longer pure-tone bursts that are related in frequency (f1 low- er frequency and f2 higher frequency) are presented simultaneously, they produce distortion-product OAEs (DPOAEs). Initially, the main appeal of these cochlear- based responses primarily concerned basic-research issues related to the periph- eral auditory nervous system.
Consequently, the existence of OAEs brought about significant modifications to the prevailing mathematical models of inner ear function that needed to acknowl- edge the reality of such active intracochlear processing. Accordingly, as a research tool, it was well appreciated that OAEs provided a noninvasive window on the pre- neural mechanical activities of the cochlea that as a group is known as the cochlear amplifier. Moreover, during the initial years after their discovery, some efforts were made to relate OAEs to parallel neural and psychoacoustical phenomena. Thus, emitted responses were described in several experimental species commonly used
44 | Acoustics Today | Fall 2017 | volume 13, issue 3 ©2017 Acoustical Society of America. All rights reserved.