Ken Platz (left) presents a thank you gift to Jonathan Siegel, PhD (right). Chicago AES section meeting on April 27, 2016.
Mead Killion, PhD. (founder of Etymotic Reasearch) introduced the evening's presentation with some background information on the hearing system. Otoacoustic emissions (OAEs) are sounds generated in the inner ear spontaneously or in response to acoustic stimuli. In the cochlea (the inner ear), hair cells are responsible for transducing the small motions of the basilar membrane into electrical signals. While the inner hair cells (IHC) provide a path to the brain, the outer hair cells (OHC) actually provide a return path from the brain and serve as motion amplifiers to increase sensitivity. The OHC's can actually generate tones as well, which are detected as otoacoustic emissions.
Jonathan Siegel, PhD. provided the bulk of the evening's presentation, discussing his many years of work on the topic of OAEs and current research efforts. OAEs are typically the cubic distortion product (tone) of a pair of stimulus tones. The strength (weakness) of this tone can be used to detect hearing loss. Clinically, this phenomenon has several uses, especially to identify hearing defects in newborns, where conventional audiometric tests cannot be used. In addition, OAEs may be helpful to identify hearing damage that is not measurable with a conventional audiogram. In studying hearing loss among service personnel in the Navy, for instance. A reduction in the strength of OAEs consistently predicted the onset of hearing loss as measured by a conventional audiogram.
Prior efforts to study OAEs have been frustrated by the acoustics of the ear canal. Specifically, small changes in the insertion depth of a probe can significantly impact the measurements. The key to the success of Siegel and Etymotic Research has been in using a Thevenin methodology to characterize the complex response of both the probe and the ear's acoustics. This, in turn, allows them to decompose measurements into forward and reverse waves. Through this process of forward pressure level calibration they are able to achieve much more consistent measurements than were previously possible.
Robert Cochran concluded the presentation with an overview of Etymotic Research's work in developing systems for measuring OAEs in both clinical and research use. A new research system, the ER-10X, extends the bandwidth well beyond 20 kHz. In addition, Etymotic Research provides technology for hearing aids, hearing protection, and earphones.
Both before and after the meeting, attendees had the opportunity to get a scan of their hearing for OAEs.
A video recording can be viewed at:
https://www.youtube.com/watch?v=mYd37yJ-vQY
