AILSA CHANG, HOST:
For people with hearing aids or a cochlear implant, a crowded room can be really overwhelming.
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CHANG: Lots of voices, but none of them distinct. NPR's Jon Hamilton reports on new research that could lead to hearing aids with the ability to select one voice among many.
JON HAMILTON, BYLINE: It's called the cocktail party effect. In a room full of speakers, the brain can focus on just one and largely filter out the others. But Nima Mesgarani of Columbia University says that filtering is a lot harder for people who use a hearing device.
NIMA MESGARANI: When they go to very crowded places, they usually end up not using them because they just simply amplify everybody.
HAMILTON: Mesgarani and a team thought they might be able to solve this problem by harnessing the brain's neck for identifying a particular sound source. He'd shown in a previous study that the key is special brain waves coming from the auditory cortex, which processes sounds.
MESGARANI: And when you look at the brain of a listener at the cocktail party, what you see is that these brain waves are tracking only the sound that they are focusing on and not the other sources.
HAMILTON: Mesgarani thought the discovery might offer a way to improve hearing aids, cochlear implants and other hearing devices.
MESGARANI: That gives us a signature that we can look at someone's brain, and then they can decide, oh, yeah, this is the source that they want to listen to.
HAMILTON: So his team did an experiment with four people who were in the hospital for epilepsy treatment. The participants already had electrodes in their brains. That allowed the team to monitor signals coming from their auditory cortex. Mesgarani says the next step was to simulate a cocktail party at the bedside.
MESGARANI: They have two loudspeakers in front of them. Each one of those loudspeakers is playing a different conversation.
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HAMILTON: At first, the competing conversations were played at the same volume. That left the participants struggling to focus on either one. Then Mesgarani says the team switched on a system that automatically adjusted the volume based on the person's brain waves.
MESGARANI: If the person wants to hear Conversation 1, we make that louder. We make everything else softer.
UNIDENTIFIED AI-GENERATED VOICE #1: My brothers even recommended him. My brothers simply do not hire bad workmen.
HAMILTON: When their attention switches to Conversation 2, so does the system.
UNIDENTIFIED AI-GENERATED VOICE #2: Bad for my diet. But I can tell, this is just the thing that...
HAMILTON: Mesgarani says the participants had a strong preference for brain control.
MESGARANI: They said this is better. I prefer to keep this on. Their comprehension went up, and their listening effort goes down.
HAMILTON: The study appears in the journal Nature Neuroscience, and Josh McDermott of MIT says it offers strong evidence that the approach works. But he notes that this study was done in people with typical hearing.
JOSH MCDERMOTT: If instead, you have somebody who has hearing loss, could you still actually decode the target of attention successfully? And that is still kind of an open question.
HAMILTON: Because in people with hearing loss, the signal isn't as strong. But McDermott says, if it's still detectable, hearing aids might get better. Right now, he says, their ability to filter sounds is pretty limited.
MCDERMOTT: They have some pretty good algorithms for reducing background noise. So in situations where the noise is pretty clearly a different signal from the speech you're trying to listen to, you can attenuate the noise.
HAMILTON: But with multiple voices, hearing aids don't know which one to amplify. McDermott says a brain-controlled hearing aid may be one solution. Another approach is using artificial intelligence to learn which sound you probably want to amplify. Either way, he says, hearing devices badly need to solve the cocktail party problem.
MCDERMOTT: If you live long enough, you start to go deaf, and nowadays most people live long enough. And it's a really important problem to be doing basic scientific research on.
HAMILTON: In the U.S., disabling hearing loss affects more than half of people 75 and older. Jon Hamilton, NPR News.
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