Really? Really. How Our Brains Figure Out What Words Mean Based On How They're Said

Aug 24, 2017
Originally published on August 24, 2017 6:01 pm

It's not just what you say that matters. It's how you say it.

Take the phrase, "Here's Johnny." When Ed McMahon used it to introduce Johnny Carson on The Tonight Show, the words were an enthusiastic greeting. But in The Shining, Jack Nicholson used the same two words to convey murderous intent.

Now scientists are reporting in the journal Science that they have identified specialized brain cells that help us understand what a speaker really means. These cells do this by keeping track of changes in the pitch of the voice.

"We found that there were groups of neurons that were specialized and dedicated just for the processing of pitch," says Dr. Eddie Chang, a professor of neurological surgery at the University of California, San Francisco.

Chang says these neurons allow the brain to detect "the melody of speech," or intonation, while other specialized brain cells identify vowels and consonants.

"Intonation is about how we say things," Chang says. "It's important because we can change the meaning, even — without actually changing the words themselves."

For example, by raising the pitch of our voice at the end of a sentence, a statement can become a question.

The identification of neurons that detect changes in pitch was largely the work of Claire Tang, a graduate student in Chang's lab and the Science paper's lead author.

Tang and a team of researchers studied the brains of 10 epilepsy patients awaiting surgery. The patients had electrodes placed temporarily on the surface of their brains to help surgeons identify the source of their seizures.

This allowed the team to monitor the activity of cells in each patient's brain as they listened to a series of sentences spoken by a computer.

"What we did was change where the intonation contour — the pitch changes — were happening in each of those sentences," Chang says.

So the volunteers would hear different versions of a sentence like, "Reindeer are a visual animal." Sometimes the computer voice started high and ended low, making the sentence a statement. Other times it started low and ended high, making the sentence a question.

The cells that track pitch didn't care whether they heard a high female voice or a low male voice, Chang says. It was the pattern of pitch changes that mattered.

"To people like musicians this is not a surprise," Chang says, "because you can take a melody and shift all of its notes higher or lower, but it's still recognizable."

The identification of specialized cells that track intonation shows just how much importance the human brain assigns to hearing, says Nina Kraus, a neurobiologist who runs the Auditory Neuroscience Laboratory at Northwestern University.

"Processing sound is one of the most complex jobs that we ask our brain to do," Kraus says. And it's a skill that some brains learn better than others, she says.

Kraus found that out when she did a study that looked at whether musicians were better than people who aren't musicians at recognizing the subtle tonal changes found in Mandarin Chinese.

"The English-speaking musicians were able to process with high precision those contours," she says, "and the nonmusicians didn't."

On the other hand, recognizing intonation is a skill that's often impaired in people with autism, Kraus says.

"A typically developing child will process those pitch contours very precisely," Kraus says. "But some kids on the autism spectrum don't. They understand the words you are saying, but they are not understanding how you mean it."

The new study suggests that may be because the brain cells that usually keep track of pitch aren't working the way they should.

Copyright 2017 NPR. To see more, visit http://www.npr.org/.

ROBERT SIEGEL, HOST:

Communication is about more than just the words we say. It's about how we say them.

(SOUNDBITE OF TV SHOW, "THE TONIGHT SHOW STARRING JOHNNY CARSON")

ED MCMAHON: Here's Johnny.

(CHEERING, APPLAUSE)

SIEGEL: That's how Ed McMahon used to introduce Johnny Carson on "The Tonight Show." And here's Jack Nicholson's version from "The Shining."

(SOUNDBITE OF FILM, "THE SHINING")

JACK NICHOLSON: (As Jack Torrance) Here's Johnny.

SHELLEY DUVALL: (As Wendy Torrance, screaming).

SIEGEL: Not quite the same message. Well, now scientists have identified a group of brain cells that help listeners figure out what a speaker's words actually mean. NPR's Jon Hamilton reports.

JON HAMILTON, BYLINE: When we speak, we do a lot more than produce a stream of vowels and consonants. Our voices rise and fall in a way that adds meaning to every sentence.

EDDIE CHANG: Some people think about this as sort of the melody of speech.

HAMILTON: Eddie Chang is a neurosurgeon at the University of California, San Francisco. He's been studying how the brain keeps track of this melody or intonation.

CHANG: Intonation is about how we say things. It's important because we can actually change the meaning even without actually changing the words themselves.

HAMILTON: It's the difference between really and really. To learn more, Chang's lab monitored the brain activity of ten people as they listened to speech produced by a computer.

CHANG: What we did was change where the intonation contour or where the pitch changes were happening in each of those sentences.

HAMILTON: So the volunteers might hear a statement like...

COMPUTER-GENERATED VOICE: Movies demand minimal energy.

HAMILTON: ...Or a question like...

COMPUTER-GENERATED VOICE: Movies demand minimal energy?

HAMILTON: And Chang says certain brain cells were responding only to intonation.

CHANG: We found that there were groups of neurons that were actually specialized and dedicated just for the processing of pitch.

HAMILTON: The cells didn't care whether they heard a high female voice or a low male voice. Chang says it was the pattern of pitch changes that mattered.

CHANG: To people like musicians, this is not a surprise because you can take a melody and shift all of its notes higher or lower, but it's still recognizable.

HAMILTON: Chang says the cells that recognize intonation work with other specialized cells to help us understand what someone is trying to say. Nina Kraus, a neurobiologist at Northwestern University, says it's remarkable.

NINA KRAUS: Processing sound is one of the most complex jobs that we ask our brain to do.

HAMILTON: And Kraus says it's something some brains learn better than others. She found that out when she studied whether musicians were better at recognizing the subtle tonal changes found in Mandarin Chinese.

KRAUS: The English-speaking musicians were able to process with high precision those contours. And the non-musicians didn't.

HAMILTON: On the other hand, Kraus says, recognizing intonation is a skill that's often impaired in people with autism.

KRAUS: A typically developing child will process those pitch contours very precisely. But some kids on the autism spectrum don't. You know, they understand the words that you're saying, but they are not understanding how you mean it.

HAMILTON: Perhaps because the brain cells that usually keep track of pitch aren't working the way they should. The new research appears in the journal Science. Jon Hamilton, NPR News. Transcript provided by NPR, Copyright NPR.