ARI SHAPIRO, HOST:
A song takes words and music and fuses them.
(SOUNDBITE OF SONG, "THE BRIAR AND THE ROSE")
NIAMH PARSONS AND THE LOOSE CONNECTIONS: (Singing) I fell asleep down by a stream, and there I had the strangest dream.
SHAPIRO: Yet the human brain can instantly separate a song's lyrics from its melody. NPR's Jon Hamilton reports on new research that explains how that happens.
JON HAMILTON, BYLINE: The idea came from songbirds. Robert Zatorre of McGill University says their brains analyze sounds using two separate measures. One assesses how quickly a sound fluctuates over time. The other detects the frequencies a sound contains.
ROBERT ZATORRE: So we were sort of inspired by that. And we thought, hey, maybe that's what the human brain does, too.
HAMILTON: To find out, Zatorre and his team got help from a composer and a soprano, and they created lots of acapella recordings like this one.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED PERSON: (Singing) The people thought a coin was hidden there.
HAMILTON: Then they used a computer to alter the recordings. Zatorre says sometimes they removed information about sound frequencies.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED PERSON: (Singing) The people thought a coin was hidden there.
ZATORRE: So the speech is perfectly comprehensible, but all the melody is essentially gone.
HAMILTON: Zatorre says other songs were altered to remove information about changes over time.
(SOUNDBITE OF ARCHIVED RECORDING)
UNIDENTIFIED PERSON: (Singing, unintelligible).
ZATORRE: Then what happens is that you can still perceive the melody, but you can no longer tell what the speech is.
HAMILTON: That set the stage for what Zatorre really wanted to know - how a human brain would process these altered songs. So...
ZATORRE: We had people listen to these strange sounds inside the fMRI scanner, which allows us to look at brain activity.
HAMILTON: And the team found that these 49 people decoded sounds the same way songbirds do. Zatorre says the process involves two circuits on opposite sides of the brain.
ZATORRE: On the left side, you can decode the speech content, but not the melodic content. And on the right side, you can decode the melodic content, but not the speech content.
HAMILTON: So Zatorre says when we hear a song, it engages both hemispheres of the brain in a way that's different than either speech or music alone.
ZATORRE: That might be why it's especially prominent and especially meaningful. And to this day, you know, songs are by far the most common style of music.
HAMILTON: The study appears in the journal Science. And Daniela Sammler from the Max Planck Institute for Human Cognitive and Brain Sciences in Germany says it explains something scientists have known for many decades.
DANIELA SAMMLER: If you have a stroke in the left hemisphere, you're much more likely to have a language impairment than after a stroke in the right hemisphere.
HAMILTON: And if something damages certain areas in the right hemisphere, it can affect the perception of music. But Sammler says it takes both hemispheres to fully experience any type of sound. And she says it's likely that the circuitry connecting areas involved in speech and music has been around for a long time.
SAMMLER: Charles Darwin said that actually the languages that we use today emerged from something that was a song-like proto-language. So you see that he had song in his thinking.
HAMILTON: Sammler says now that there's evidence a song takes two separate paths through the brain, researchers need to figure out how the brain assembles the information into a coherent whole.
SAMMLER: We perceived a song as a song, right? It's one thing. And it's not like a speech stream or a melody stream.
HAMILTON: And the impact can be more powerful than either on its own.
Jon Hamilton, NPR News.
(SOUNDBITE OF SONG, "IT'S ONLY A SONG")
ROB MORSBERGER: (Singing) You might think that every song you hear is a dramatic revelation about the nature of the world you live in or the one you left behind. Transcript provided by NPR, Copyright NPR.
