The human brain's remarkable flexibility to understand a variety of signals as language extends to an unusual whistle language used by shepherds on one of the Canary Islands off the northwest coast of Africa.
And the way the brain processes these whistles is similar to the way it goes about deciphering English, Spanish or other spoken languages, according to research being published in tomorrow's issue of the journal Nature.
"Science has developed the idea of brain areas that are dedicated to language and we are starting to understand the scope of signals that can be recognized as language," said David Corina, a University of Washington associate professor of psychology and co-author of the study.
"But how far can you stretch this idea? Sign language studies have shown we can stretch the envelope and here we are expanding it in another way to a whistle language. The brain is adaptable, or plastic, in understanding a variety of forms of communication."
The language studied by Corina and his colleague, Manuel Carreiras, a psychology professor at the University of La Laguna, on the island of Tenerife in the Canaries, is Silbo Gomero, or Silbo. It is primarily used by shepherds to communicate with each other over long distances of rugged terrain on the island of La Gomera, another island in the Spanish owned Canaries.
To see how the brain processes Silbo, the researchers recruited five silbadors, or speakers of Silbo, who also were fluent in Spanish and five Spanish speakers who did not understand Silbo. The word silbador comes from the Spanish verb silbar, which means to whistle.
Functional magnetic resonance imaging was used to measure brain activation, or activity, during two tasks. The two groups first were given a passive listening task in which they listened to recorded sentences in Spanish and Silbo and were to keep track of what had been said. In the second task, the subjects listened to blocks of Spanish words for colors or animals and the equivalent "words" in Silbo. Individual recorded words were played once every three seconds. While having their brains scanned, the subjects were asked to keep track of how many times a target word or whistle appeared during a trial.
When the silbadores listened to the Silbo sentences, several regions were activated in the left hemisphere of their brains including ones in the posterior temporal-parietal region and the frontal premotor cortex. Research has shown these regions are involved in the comprehension and production of language. In addition, there was activation in the right hemisphere temporal lobe, an area believed to be involved in linguistic processing.
Both the silbadores and the Spanish speakers showed this pattern of bilateral activation when they listed to Spanish sentences. However, the results were different when the Spanish speakers listened to the Silbo sentences. Several brain regions were activated, but none has been specifically implicated in language processing, indicating they did not recognize Silbo as a language, Corina said.
The researchers found a similar pattern during the second tasks. While both subjects groups were able to detect the target whistle sound, only the silbadores showed bilateral brain activity in language center. Data from both tasks showed a common focus of brain activity near the temporal-parietal junction among the silbadores.
"Our results provide more evidence about the flexibility of human capacity for language in a variety of forms," said Corina. "These data suggest that left hemisphere language regions are uniquely adapted for communicative purposes, independent of the modality of signal. The non-Silbo speakers were not recognizing Silbo as a language. They had nothing to grab onto so multiple areas of their brains were activated. But the Silbadores were analyzing differently, as a language, and engaging those areas associated with language."
Silbo is believed to have been brought to the island by Berbers from North Africa and today is a surrogate language for Spanish. It condenses Spanish into two vowels and four consonants.
"You wouldn't call Silbo a full-fledged language. Children are not born whistling it," Corina said. "In general, anything in Spanish can be translated into Silbo, but context is very important."
Silbo is an occupation-centered language and is used to say such things as "open the gate" or "there is a stray sheep." It is not the world's only whistle language. There are others in Greece, Turkey, China and Mexico, according to Corina.
The research was funded by Cabildo de La Gomera, the Spanish Ministry of Education and the Spanish Ministry of Science and Technology. Co-authors of the paper were Jorge Lopez of IMETISA, Hospital Universitario de Canarias in Tenerife, and Francisco Rivero of the University of La Laguna.
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