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Searching for speech

Researchers work to replicate the human voice

By Paul Voosen
Staff Writer, The Prague Post
June 27th, 2007 issue

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When you lose your larynx — and voice — to throat cancer, there are only a few ways you can return to conversation with the world.
There are the traditional treatments, neither of which has changed much over the past 50 years: the injection method, where air is swallowed and forced back through the mouth via the esophagus — think burping and reciting the alphabet — or the electrolarynx, a vibrator that nestles against the neck’s muscles and produces a stilted, robotic voice.
Now a lone wolf researcher in Brno, south Moravia, is challenging the dominant theories of voice generation, with a limited degree of success.
Vojtěch Mišun, a biomechanical scientist at Brno Technical University, says his team has discovered a new principle governing how breath is expelled through the vocal folds, the mucous membranes stretched across the larynx whose vibrations generate the source voice for human speech.
“We found many imperfections in the current research, and so we decided to study and define another principle of vocal fold function,” he said.
That was six years ago. Since then, Mišun has defined the “compressed air bubble” principle, which says that the lungs rapidly generate pockets of air that expand as they pass through the vocal folds, generating the vibrations and tonal flexibility needed to restore natural speech.
Following this, Mišun has developed what he says is a new, superior model for artificial vocal folds. The physical prototype is bulky and injects compressed air through the nose, meaning it is limited in application. Still, Mišun has tested the prototype and the voice produced, while raspy, is stronger than a voice produced with esophageal speech.
More advances in Mišun’s research will have to wait, however, as the government has turned down Mišun’s request for a new research grant, citing his distance from the mainstream.
“So now I’m writing a book [on my research], which will be finished this summer. Then scientists can compare my model with the dominant theories and see which is better,” he said.
Muted research
Mišun’s research has not been critiqued thoroughly enough to say whether it could have broad implications, researchers say.
“I don’t think there’s anything wrong with his theories,” said Jan Švec, a Czech scientist at the University of Groningen. “[But] there hasn’t been any clear differentiation from other research. He has gone a separate way from other people in this area. He’s going on his own.”
Another common treatment for restoring the voice is making a puncture between the windpipe and esophagus, through which air from the lungs can be forced and shaped into speech. Scientists at Groningen are refining the prosthesis used for this to generate more natural speech, Švec said.
The most promising research is being done in Boston, where scientists have a prototype of an electrolarynx that generates much more natural speech.
“It sounds much better. It’s the most exciting thing I’ve seen in this area in the last two years,” Švec said.
As for Mišun’s research, it remains to be seen if his theories will ever gain wider circulation.
Ingo Titze, director of the U.S.’s National Center for Voice and Speech, is one who would like to see more of Mišun’s work.
“He has some novel ideas,” Titze said. “He needs support to travel and present his ideas in several peer-reviewed journals, so that the work can be more appreciated and scrutinized.”

Paul Voosen can be reached at pvoosen@praguepost.com


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