Listen closely in Kusköy, a mountainous region of northeast Turkey, and you might hear something like this whistled phrase trill across a steep valley. What you hear is not birdsong, but a version of the Turkish language that is whistled instead of spoken, a method that can convey messages across distances of up to 5 kilometers. In kuş dili, or “bird language,” the phrase means “thank you very much” (çok teşekkür ederim in spoken Turkish). Now, a new study shows that the brain processes kuş dili very differently from spoken Turkish, a finding that challenges conventional wisdom about how language works in the brain. The research could also have implications for stroke victims suffering from language loss.

One of a handful of whistled languages throughout the world, whistled Turkish is still Turkish—it has the same words and the same grammatical structure—but it has a different physical form. A whistle replaces the voice, just as written words replace speech in languages around the world, “but a whistle also imitates essential acoustic cues of the voice,” says bioacoustician and linguist Julien Meyer of France's National Center for Scientific Research in Bron, France, who was not involved in the new study. People who use kuş dili speak ordinary Turkish as well; the whistled version probably arose as a way for villagers to stay in touch when they were far apart.

In general, the brain’s left hemisphere plays a far more active role than the right in processing language, whether spoken, written, or signed, says study author and biopsychologist Onur Güntürkün of the Institut of Cognitive Neuroscience in Bochum, Germany. Because whistled languages use melody to convey their meaning, however, Güntürkün and others wondered whether the right hemisphere, which processes melodic tones, might play a larger role than normal.

To explore that hypothesis, Güntürkün and colleagues put a new twist on a classic test, they report today in Current Biology. In the original experiment, researchers feed two slightly different syllables, such as “ba,” and “da,” into subjects’ right and left ears at precisely the same time, using headphones. Then, they ask the participants to say which syllable they’re hearing.

If “ba” is being piped into the right ear, most people will hear “ba” instead of “da,” Güntürkün says. That’s because auditory nerves in the right ear shuttle signals to the left side of the brain and its language-processing centers, whereas nerves in the left ear carry signals to the right side of the brain before relaying them back to the left hemisphere. When a signal from the left ear finally arrives at its final destination, the left hemisphere is already busy processing the right ear’s speech sound, Güntürkün says. Throughout the experiment, participants are “completely unaware” that they are hearing different signals, he adds.

To see whether the brain processes whistled language in a similar fashion, the team repeated the experiment by playing syllables of kuş dili for native whistlers. All showed left-hemisphere dominance for spoken Turkish. But when the team fed whistled Turkish syllables into the headphones, the two hemispheres became “balanced,” with subjects identifying syllables from the left and right ears with roughly equal frequency. That suggests that the right hemisphere plays a larger role in comprehending whistled languages than in spoken ones, Güntürkün says.

Precisely why the asymmetry normally seen in language processing seems to vanish is “still open to debate,” Meyer says. But the results, he says, are convincing.

The findings could inform treatments for people who have suffered from language loss after a stroke, Güntürkün says. People who lose their speech after a left hemispheric stroke can sometimes learn to sing their words. Similarly, Güntürkün says, “I would expect that people with a left hemispheric stroke could still use whistled Turkish.”

But that will require further studies of kuş dili users, whose numbers—now at roughly 10,000—are dwindling rapidly as cell phones oust whistling as the main method of long-distance communication. One reason whistled Turkish is disappearing? “You can gossip with a mobile phone, but you can’t do that with whistling because the whole valley hears,” Güntürkün says.

Additional phrases in whistled Turkish: