WEBVTT - Why Do Noises Other People Make Seem Louder Than Our Own?

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<v Speaker 1>Welcome to brain Stuff production of I Heart Radio. Hey

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<v Speaker 1>brain Stuff, Lauren Vogelbaum. Here, you're walking down a deserted

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<v Speaker 1>street to all quiet in your thoughts, and suddenly you

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<v Speaker 1>hear footsteps. Of course, your own footfalls. We're making noise too,

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<v Speaker 1>So why is it so easy to ignore our own

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<v Speaker 1>noises and so easy to hear others? Scientists have long

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<v Speaker 1>known that we're capable of tuning out our own personal noises,

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<v Speaker 1>but we're previously in the dark about how the brain

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<v Speaker 1>accomplishes this feat. The results of a new study published

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<v Speaker 1>in the journal Nature aims to amp up our understanding

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<v Speaker 1>of this phenomenon by focusing on footsteps. We spoke with

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<v Speaker 1>lead researcher Dr David Schneider, an assistant professor with the

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<v Speaker 1>Center for Neural Science at New York University. He explained,

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<v Speaker 1>we wanted to understand how the individual cells in our

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<v Speaker 1>brains are neurons, work together to make that happen. To

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<v Speaker 1>do that, we studied mouse brains, and we built an

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<v Speaker 1>augmented reality system so that when mice ran, we could

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<v Speaker 1>experimentally control the sounds they heard. We could give them

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<v Speaker 1>a couple of days with their walking, making one sound

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<v Speaker 1>then we could unexpectedly switch the sound. The research was

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<v Speaker 1>conducted at Duke University's School of Medicine. The scientists soon

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<v Speaker 1>discovered that when the mice expected their walking to sound

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<v Speaker 1>a particular way, the neurons and the auditory cortex, one

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<v Speaker 1>of the main hearing centers of the brain, stopped responding

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<v Speaker 1>to the noise. Schneider said. It was almost like they

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<v Speaker 1>were wearing special headphones that could filter out the sound

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<v Speaker 1>of their own movements. In contrast, when we played an

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<v Speaker 1>unexpected sound, neurons and their auditory cortex had large responses.

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<v Speaker 1>The scientists soon realized that as the mice were becoming

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<v Speaker 1>familiar with the sounds of their own walking, there were

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<v Speaker 1>some important connections being changed between the auditory cortex and

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<v Speaker 1>the motor cortex, which is the part of the brain

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<v Speaker 1>responsible for moving. Schneider said the connections strengthen onto inhibitory

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<v Speaker 1>neurons and the auditory cortex that are active when the

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<v Speaker 1>mouse heard the footsteps sound. The end result was that

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<v Speaker 1>every time the mouse walked, a group of inhibitory neurons

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<v Speaker 1>were active to create a photo negative of the sound

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<v Speaker 1>the mouse expected, which could cancel out the expected sound

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<v Speaker 1>when it was heard. The experience isn't limited to footsteps either.

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<v Speaker 1>Schneider said, the heavy breather rarely knows that they're a

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<v Speaker 1>heavy breather because it doesn't sound as loud to them,

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<v Speaker 1>And I think the same is true of keystrokes as sure.

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<v Speaker 1>I can hear my own keystrokes when I'm typing, but

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<v Speaker 1>I don't usually get annoyed by them. But if someone

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<v Speaker 1>sitting next to me is typing heavily, it drives me batty.

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<v Speaker 1>For any creature accustomed to being hunted, like mice, this

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<v Speaker 1>ability to filter out one's own innocuous noises and focus

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<v Speaker 1>on the more potentially dangerous ones is critical. This is

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<v Speaker 1>also the same phenomenon at play when we sing, speak,

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<v Speaker 1>or play music. Schneider explained, we usually have an idea

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<v Speaker 1>in our head for what sound would like to produce.

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<v Speaker 1>When I sit down at the piano and strike the keys,

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<v Speaker 1>for example, I know what music I want it to make,

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<v Speaker 1>But when we're practicing, we often get it wrong. The

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<v Speaker 1>mechanism that we've described in this paper, the ability to

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<v Speaker 1>ignore the expected consequences of our movement, gives us the

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<v Speaker 1>extra cool ability to detect when we've got it wrong.

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<v Speaker 1>So if I play the piano just right, I hear it, sure,

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<v Speaker 1>but my auditory cortex is pretty silent. But when I

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<v Speaker 1>play it wrong, I get a much larger response. As

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<v Speaker 1>a result, the brain is able to interpret that response

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<v Speaker 1>is hey, that didn't sound right. Maybe I should move

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<v Speaker 1>my fingers a little different next time. That allows us

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<v Speaker 1>to learn from our mistakes. Though the researchers are still

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<v Speaker 1>trying to figure out exactly how such error signals are

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<v Speaker 1>employed by the brain when learning language and music skills,

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<v Speaker 1>they're hoping to use this information to shed light on

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<v Speaker 1>a couple of different areas next. For example, it's possible

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<v Speaker 1>that the same brain circuits involved in ignoring and or

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<v Speaker 1>detecting sounds malfunction in patients with diseases like schizophrenia. Schneider

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<v Speaker 1>said they often vividly experienced phantom voices that aren't actually

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<v Speaker 1>the air. It's been suggested that these hallucinations may be

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<v Speaker 1>due to altered connectivity between motor and hearing centers of

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<v Speaker 1>the brain, and we think the brain circuitry we've identified

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<v Speaker 1>might be involved. So I'd like to study mice who

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<v Speaker 1>have similar genetic mutations to those that are associated with

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<v Speaker 1>schizophrenia in humans. Today's episode was written by Alia Hoyt

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<v Speaker 1>and produced by Tyler Klang. Brain Stuff is a production

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<v Speaker 1>of iHeart Radio's How Stuff Works. For more in this

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<v Speaker 1>and lots of other notable topics, visit our home planet,

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