My father is an avid concertgoer who turned 61 in February, and I’ve been trying for more than two years—since I joined the team at Hearing Health Foundation (HHF)—to convince him to get his hearing tested.
ERG Grantees' Advancements in OAE Hearing Tests, Speech-in-Noise Listening
By Yishane Lee and Inyong Choi, Ph.D.
Support for a Theory Explaining Otoacoustic Emissions: Fangyi Chen, Ph.D.
It’s a remarkable feature of the ear that it not only hears sound but also generates it. These sounds, called otoacoustic emissions (OAEs), were discovered in 1978. Thanks in part to ERG research in outer hair cell motility, measuring OAEs has become a common, noninvasive hearing test, especially among infants too young to respond to sound prompts..
There are two theories about how the ear produces its own sound emanating from the interior of the cochlea out toward its base. The traditional one is the backward traveling wave theory, in which sound emissions travel slowly as a transverse wave along the basilar membrane, which divides the cochlea into two fluid-filled cavities. In a transverse wave, the wave particles move perpendicular to the wave direction. But this theory does not explain some anomalies, leading to a second hypothesis: The fast compression wave theory holds that the emissions travel as a longitudinal wave via lymph fluids around the basilar membrane. In a longitudinal wave, the wave particles travel in the same direction as the wave motion.
Figuring out how the emissions are created will promote greater accuracy of the OAE hearing test and a better understanding of cochlear mechanics. Fangyi Chen, Ph.D., a 2010 Emerging Research Grants (ERG) recipient, started investigating the issue at Oregon Health & Science University and is now at China’s Southern University of Science and Technology. His team’s paper, published in the journal Neural Plasticity in July 2018, for the first time experimentally validates the backward traveling wave theory.
Chen and his coauthors—including Allyn Hubbard, Ph.D., and Alfred Nuttall, Ph.D., who are each 1989–90 ERG recipients—directly measured the basilar membrane vibration in order to determine the wave propagation mechanism of the emissions. The team stimulated the membrane at a specific location, allowing for the vibration source that initiates the backward wave to be pinpointed. Then the resulting vibrations along the membrane were measured at multiple locations in vivo (in guinea pigs), showing a consistent lag as distance increased from the vibration source. The researchers also measured the waves at speeds in the order of tens of meters per second, much slower than would be the speed of a compression wave in water. The results were confirmed using a computer simulation. In addition to the wave propagation study, a mathematical model of the cochlea based on an acoustic electrical analogy was created and simulated. This was used to interpret why no peak frequency-to-place map was observed in the backward traveling wave, explaining some of the previous anomalies associated with this OAE theory.
Speech-in-Noise Understanding Relies on How Well You Combine Information Across Multiple Frequencies: Inyong Choi, Ph.D.
Understanding speech in noisy environments is a crucial ability for communications, although many individuals with or without hearing loss suffer from dysfunctions in that ability. Our study in Hearing Research, published in September 2018, finds that how well you combine information across multiple frequencies, tested by a pitch-fusion task in "hybrid" cochlear implant users who receive both low-frequency acoustic and high-frequency electric stimulation within the same ear, is a critical factor for good speech-in-noise understanding.
In the pitch-fusion task, subjects heard either a tone consisting of many frequencies in a simple mathematical relationship or a tone with more irregular spacing between frequencies. Subjects had to say whether the tone sounded "natural" or "unnatural" to them, given the fact that a tone consisting of frequencies in a simple mathematical relationship sounds much more natural to us. My team and I are now studying how we can improve the sensitivity to this "naturalness" in listeners with hearing loss, expecting to provide individualized therapeutic options to address the difficulties in speech-in-noise understanding.
2017 ERG recipient Inyong Choi, Ph.D., is an assistant professor in the department of communication sciences and disorders at the University of Iowa in Iowa City.
We need your help supporting innovative hearing and balance science through our Emerging Research Grants program. Please make a contribution today.
ReSound HearSay: Be The Voice of Hearing
By Tom Woods
"A journey of a thousand miles begins with a single step.” For many individuals who know—or suspect—they have a hearing loss, the first step in their journey to better hearing can prove difficult.
It took more than two years for Francine Murphy of Peoria, Arizona to take action. She says, “I was in denial and I was concerned that it would not help, especially if the sound quality was poor. Start with acknowledging that there may be an issue and start with your family doctor. The best resource I found was my audiologist.”
ReSound hearing aid user Francine Murphy.
Francine is clearly not alone. For many, the delay is due to uncertainty, apprehension, and lots of questions. In the U.S. alone, more than 25 million people who could benefit from hearing aids have yet to take that first step.
We believe that hearing is fundamental to life. When it starts to decline, it’s imperative that everyone understands, and has access to, the best hearing technology.
That’s why we created ReSound HearSay, an online resource that gives people who are successfully managing their hearing loss an opportunity to lend their voice to educate and inspire others to seek care.
We think that peer-to-peer information sharing is critical in this learning process.
“Get your hearing tested now,” urges John Chynoweth from Orlando, Florida. “Determine exactly what your hearing is like now (get a baseline). Work with a hearing specialist to determine the environments where you struggle to hear. Try different types of hearing aids to find the right ones for you.”
I’m reaching out to readers of this blog to share their hearing journey. Just like Francine and John, you can help those who are just starting to realize hearing loss or considering a hearing aid, and may be hesitant or unsure where to start.
Through posts, you’ll encourage others into action by addressing common concerns and questions, giving them practical advice to help navigate the process, from diagnosis to hearing aids. And you’ll help them understand the important role of the hearing care professional.
Be the “Voice of Hearing” and help others on the path to better hearing. Please take time today to visit ReSoundHearSay.com to share your insights and experience.
Tom Woods is President, ReSound North America.
New Data-Driven Analysis Procedure for Diagnostic Hearing Test
By Carol Stoll
Stimulus frequency otoacoustic emissions (SFOAEs) are sounds generated by the inner ear in response to a pure-tone stimulus. Hearing tests that measure SFOAEs are noninvasive and effective for those who are unable to participate, such as infants and young children. They also give valuable insight into cochlear function and can be used to diagnose specific types and causes of hearing loss. Though interpreting SFOAEs is simpler than other types of emissions, it is difficult to extract the SFOAEs from the same-frequency stimulus and from background noise caused by patient movement and microphone slippage in the ear canal.
2014 Emerging Research Grants (ERG) recipient Srikanta Mishra, Ph.D., and colleagues have addressed SFOAE analysis issues by developing an efficient data-driven analysis procedure. Their new method considers and rejects irrelevant background noise such as breathing, yawning, and subtle movements of the subject and/or microphone cable. The researchers used their new analysis procedure to characterize the standard features of SFOAEs in typical-hearing young adults and published their results in Hearing Research.
Mishra and team chose 50 typical-hearing young adults to participate in their study. Instead of using a discrete-tone procedure that measures SFOAEs one frequency at a time, they used a more efficient method: a single sweep-tone stimulus that seamlessly changes frequencies from 500 to 4,000 Hz, and vice versa, over 16 and 24 seconds. The sweep tones were interspersed with suppressor tones that reduce the response to the previous tone. The tester manually paused and restarted the sweep recording when they detected background noises from the subject’s movements.
The SFOAEs generated were analyzed using a mathematical model called a least square fit (LSF) and a series of algorithms based on statistical analysis of the data. This model objectively minimized the potential error from extraneous noises. Conventional SFOAE features such as level, noise floor, and signal-to-noise ratio (SNR) were described for the typical-hearing subjects.
Overall, the results of this study demonstrate the effectiveness of the automated noise rejection procedure of sweep-tone–evoked SFOAEs in adults. The features of SFOAEs characterized in this study from a large group of typical-hearing young adults should be useful for developing tests for cochlear function that can be useful in the clinic and laboratory.
Srikanta Mishra, Ph.D, was a 2014 Emerging Research Grants scientist and a General Grand Chapter Royal Arch Masons International award recipient. For more, see “Sweep-tone evoked stimulus frequency otoacoustic emissions in humans: Development of a noise-rejection algorithm and normative features” in Hearing Research.
We need your help supporting innovative hearing and balance science through our Emerging Research Grants program. Please make a contribution today.
