Of Monkey Calls And Human Sound Processing : Shots - Health News A brain imaging study of grown-ups hints at how children learn that "dog" and "fog" have different meanings, even though they sound so much alike.
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How People Learned To Recognize Monkey Calls Reveals How We All Make Sense Of Sound

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How People Learned To Recognize Monkey Calls Reveals How We All Make Sense Of Sound

ARI SHAPIRO, HOST:

Even though the words dog and fog sound pretty similar, even a little kid knows whether you're talking about a puppy or the weather. NPR's Jon Hamilton reports on new research that helps explain how our brains learn to make sense of what we hear. It involves monkey calls.

JON HAMILTON, BYLINE: Maximilian Riesenhuber is a brain scientist at Georgetown University Medical Center who speaks with a very slight German accent.

MAXIMILIAN RIESENHUBER: You hear my voice, you've probably never heard me before, but you can hopefully recognize what I'm saying.

HAMILTON: Riesenhuber is part of a team that wanted to know how the brain learns to recognize a particular word, no matter who is speaking it.

RIESENHUBER: So what we decided to use was monkey calls.

HAMILTON: Monkey calls were perfect because to people, they don't convey any meaning. The team had 16 volunteers listen to calls from rhesus monkeys.

(SOUNDBITE OF MONKEY CALLS)

HAMILTON: Riesenhuber says these calls mean very different things.

RIESENHUBER: One means, OK, great food. The other one - not so great food. If you had been a monkey, of course, you'd say, oh, wow. This is wonderful to hear this.

HAMILTON: The human volunteers weren't told what any of the calls meant, but after hours of practice, they learned to tell the difference between...

(SOUNDBITE OF MONKEY CALLS)

HAMILTON: ...And...

(SOUNDBITE OF MONKEY CALLS)

HAMILTON: And they learned to sort the calls into two general categories. Next, Riesenhuber's team used brain imaging to search for clues about how people learn to do this.

RIESENHUBER: We looked at people's brains before, when they never heard these calls before, and then after they'd learned it, and then could see which parts of the brain changed and in what way.

HAMILTON: Riesenhuber says the changes indicate a two-step process. First, one area of the brain learns to recognize the new sounds. Then, a separate area learns to categorize each sound. So going back to dog and fog, one area of a child's brain learns to hear the subtle differences between those words. Then, a second area learns to put one sound in the animal category and the other in the weather category.

Riesenhuber says the brain uses a similar approach to categorize things we see, like faces and places.

RIESENHUBER: That's very exciting because it suggests there are general principles at work here of how the brain makes sense of the world.

HAMILTON: The research, which appears in the journal Neuron, also hints at what may be going wrong in the brains of children with dyslexia. Guinevere Eden studies learning disorders at Georgetown University. She says dyslexia is often described as a reading problem, but researchers have found that children with the disorder also tend to have trouble categorizing sounds.

GUINEVERE EDEN: If you take 4-year-olds and you play rhyming games with them - hat, cat, dog, mat - which is the odd one out? Children who struggled with that went on to have difficulty with reading.

HAMILTON: Eden says brain imaging studies, like the one with monkey calls, could show how the brains of children with dyslexia are different. They could also show how tutoring helps kids overcome the problem.

EDEN: Where do we see the change? Is it that their brains look more like children who've never had difficulties in learning to read, or do they reach out to other areas that compensate?

HAMILTON: Eden says research to answer these questions is already underway. Jon Hamilton, NPR News.

(SOUNDBITE OF JON BURR'S "MINOR SWING")

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