New test uncovers early hidden hearing loss
Researchers at the University of Connecticut have developed a new test to identify a specific, potential manifestation of hidden hearing loss in individuals whose standard hearing evaluations reveal normal or close to normal findings. The test, which may one day help hearing healthcare professionals identify early stages of hearing loss, detects deficits in the binaural auditory processing system, a complex system involving both ears and the brain in locating sounds and navigating noisy environments.
This outcome is the first in a series of a larger project focusing on binaural hearing conducted by Leslie R. Bernstein, professor of neuroscience and surgery and Constantine Trahiotis, emeritus professor of neuroscience and surgery at University of Connecticut Health. The two researchers have been colleagues for nearly 40 years and are considered leaders in the field of binaural auditory research. The results of their study were published in the November 2016 online issue of The Journal of the Acoustical Society of America.
Binaural changes are an early window
While there are various reasons for hidden hearing loss -- damage to the inner ear’s hair cells from noise is the most common -- Bernstein and Trahiotis theorized that small neural losses for each individual ear might show only slight or even no measureable changes in some individuals’ audiograms, yet still produce a deficiency in their binaural auditory system. To test their hypothesis, the researchers studied 31 adults ages 30 to 67 with normal or near normal audiograms by measuring binaural changes in sounds at levels of loudness that are close to those experienced in normal conversations.
“The finding we have is that people with normal audiograms and who are fine with monaural or single ear hearing, have a deficit when it comes to binaural hearing,” Bernstein said. “We see it as sort of an early window to what is going on. If you want to catch something early, you might just want to test the binaural system.”
Bernstein explained that in binaural processing, the brain compares what’s going on in the left and right ear from a series of neural connections it receives from both. “Any deficit in the left or right could have a big impact on a system that’s looking for coincident occurrence of neural firing,” he said. “It’s an unbelievable system in terms of what it calculates. If you do anything to diminish its temporal precision, then you’ll see it in tests of the binaural system.”
Trouble understanding conversation is common
One of the chief complaints of people with hearing loss is that while they report that they can “hear” just fine, they have trouble understanding conversation in noisy environments—an ability that relies to a great extent on a normally-functioning binaural system. Bernstein believes his and Trahiotis’s research is another step forward in understanding the complexities of the human auditory system, which is an instrumental part of providing medical professionals with the insight they need to one day restore hearing loss.
“Before you can develop ways to redress hearing deficits, it’s important to understand how the normal system works in great detail," he said. “So by understanding what the deficit might be, one might imagine future prosthetic devices to restore that particular function in a very targeted way.”
The team’s research is funded by a $1.5 million grant from the Office of Naval Research as part of an effort to find ways to protect its workforce from their high risk of developing noise-induced hearing loss. If Bernstein has his way, his team’s research will eventually help detect hearing loss in its early stages across the entire hearing population with testing that is easy to administer.
“One thing we’d like to do is make behavioral tests like these very portable,” Bernstein said. “There’s nothing about the signal generation that couldn’t be done with the computing power of a smartphone. This entire procedure could be run on standard laptop with a sound card and earphones -- nothing more elaborate than that.”
But don’t expect this to be standard testing protocol at your local hearing center anytime soon.
“Under laboratory conditions with standard paradigms, my colleague and I decided to look at people who had no more than any slight hearing loss to see if these kinds of laboratory tests would reveal any types of difference between these groups. And they did. Translating this into a test that people want to use easily and effectively will take some time.”
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