search
Donate

News

Older woman with a hearing problem takes test.
[Kzenon | Adobe Stock]

An Ohio University researcher looks at how hearing loss affects our ability to isolate and locate sounds

By:
Posted on:

< < Back to

ATHENS, Ohio (WOUB) — Creatures with two ears, such as ourselves, can isolate sounds and pinpoint their location with a high degree of accuracy, even in an environment filled with competing noises.

Mitch Day is an associate professor of biological sciences and head of the Auditory Neurophysiology Laboratory at Ohio University. His research focuses on how the brain actually processes sound and how hearing loss affects this ability.

Day sat down to speak with WOUB’s David Forster for “Modern Science.”

This interview has been edited for brevity and clarity.

On how we process sound

“When it comes to sound, the only thing that the neurons in our brains have access to is just the vibrating of two membranes, the ear drums in our ear. Ultimately, that sound that’s waggling the ear drums back and forth first gets transformed into a pattern of spikes of electrical activity. That’s the input to the brain. Then the brain takes those spikes and converts them into all the different characteristics of sound that we know.

“That’s the really complex part neuroscientists like me are trying to figure out, how that happens. We think of it as trying to crack a code, the neural code of sound.”

The brain can isolate different sounds processed at the same time

“It’s not only doing that, but it’s also segregating sound sources apart from each other. You could have that cricket chirping and the Beethoven Symphony playing at the same time, and you could easily tell the two apart and understand that there’s two separate sound sources that are being presented, and you can distinguish between those two.”

On why having two ears, and their design, is important to our hearing abilities

“We know now the specific cues that are used to localize sound have to do with comparisons between what’s happening at the two ears. There’s two cues that we use to try to pinpoint whether a

Mitch Day smiles for a portrait
Mitch Day [Ohio University]
sound is coming from, say, more of a left direction or a right direction or in front of you. Those have to do with time differences between the arrival of sound to the two ears and differences in the intensity of the sound to the two ears.

“If a sound is coming from my right, well, then it hits my right ear. A split second, then it hits my left ear. That actually ends up being a really potent cue to tell us that the sound is coming from my right-hand side.

“Another thing is that when that sound is coming from the right, it’s more intense in your right ear than it is in your left ear because your head acts as an object that acoustically shadows some of that sound that’s able to reach your left ear. There ends up being what we call a level difference between the two ears. If a sound is coming from straight in front of us, there would be no time difference and there would be no level difference.

“Whether something’s coming from above you or from straight in front of you or from behind you ends up being kind of complex. It actually has to do with the shape of your ears. What happens is that the sound ricochets off of these different ridges within your your outer ear. It’s different for sound straight ahead, as opposed to sounds that are right above you, as opposed to sounds that are behind you.”

On how hearing loss affects our ability to pinpoint the location of sounds

“It’s been shown that individuals that have hearing loss, say, due to age or due to overexposure to loud noises over time, that they are less able to pinpoint the exact location of a sound as compared to normal hearing individuals. It’s even more exacerbated in these more cluttered acoustic environments that we were discussing before. Say, for instance, trying to understand a conversation of a dining partner at a restaurant when there’s a lot of other clatter going on around you. It seems to be that individuals with hearing loss have much worse ability to localize in those situations.
“That likely goes along with reported difficulty in segregating sound sources from each other, as we talked about before. Part of isolating a sound source is isolating it by its location and focusing in on it. If you have a degraded ability to pinpoint the location of a sound, sometimes when there are multiple sound sources occurring at the same time, then you have a difficult ability to focus in on one person’s speech as compared to another.”

The clinical audiology community is recognizing this type of hearing loss more

“It’s increasingly called hidden hearing loss. You may go into the audiologist and you have all the appropriate hearing thresholds at different frequencies that a normal hearing person would. But you might have these difficulties in trying to segregate sound sources apart from each other, particularly in cluttered acoustic environments.”

On how researchers are addressing hidden hearing loss

“Part of what neuroscientists like me are just trying to figure out at the neural level, what is happening to neurons in the auditory parts of our brain that might be causing this kind of degradation of information about segregating sound sources.
“Part of my research is basically trying to compare the function of neurons of normal hearing animals to the function of neurons in animals that have hearing loss and see if I can detect differences between them. And if, perhaps, those differences might explain some of the the changes that we see in the ability to localize.”

The first draft of the transcripts used for this story was created in Adobe Podcast, which includes an AI transcription tool. A WOUB news editor then reviewed, corrected and reformatted the transcript before publication.