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New study explores how human voice works

BOWLING GREEN, O.--Although the human voice is understood in the most basic of terms, the intricate workings of the larynx and vocal folds--the primary parts used in the making of sound--remain a mystery.

Now a four-year, $1.2 million research project directed by Bowling Green State University professor Ronald Scherer is attempting to explore those mysteries.

One of the country's leading researchers in the study of voice production, Scherer is an associate professor of communication disorders at Bowling Green's College of Health and Human Services.

The grant, funded by the National Institutes of Health, will enable Scherer and a team of scientists and students from BGSU and two other universities, to design, build and test both mechanical and computer models of the voice-making process. Researchers at Purdue University and the University of Toledo are collaborating on the project.

The models will be used to explore the aerodynamic and aeroacoustic properties of voice, measuring things such as airflows, air pressures, and sound, and how those measures change when the shape of the larynx changes.

"We are trying to answer some very basic questions," Scherer said. "How is the air from the lungs converted into sound due to vocal fold vibration? What makes the vocal folds vibrate in the first place? Why do vocal fold problems result in greater difficulties in making voiced sounds and in hoarse voice qualities?"

To find the answers, Scherer's team of researchers will use one of the most sophisticated physical models ever built to simulate the mechanics of speech. Made of Plexiglas and seven-and-one-half times larger than the human voice box, the model has removable inserts which simulate the vocal folds.

Each insert has an array of sensors which can measure minute changes in air pressure. In all, 63 combinations of inserts can be tested simulating various vocal shapes and sizes. It can also mimic the resulting shape and structure of the vocal folds following an injury or other event, such as a surgery.

The physical model, however, is only one of a variety of models, both mechanical and computer, the research team will use to explore voice production.

The larynx, located about half way down the human throat, is a marvel of evolutionary engineering, Scherer said. As people breathe, certain muscles in the larynx are relaxed, allowing the vocal folds to separate, forming a v-shaped opening which enables air to pass freely.

When we speak, those muscles contract and the vocal folds are pulled across the wind pipe narrowing the opening. As air is forced out of the lungs and past the vocal folds, the air pressure causes the vocal folds to vibrate and produce sound.

But claiming to understand the intricate workings of the human voice from this overall perspective is like claiming to understand the workings of the internal combustion engine because you learned to pump your own gas at a service station.

Even a subtle change in the shape of the vocal folds can have a major impact on a person's voice.

"Understanding more about how the folds vibrate through modeling normal and abnormal conditions is critical to helping a person with an abnormally working larynx," said Scherer, who predicts results of this research will assist almost every endeavor associated with speech.

For example, he said the model studies could especially help surgeons who must remove tissue from the larynx during surgery.

About 5 percent of all cancers are found in the throat, Scherer said. After the tumors are removed, the surgeon is faced with the task of reconstructing the area. How to reconstruct the larynx to allow the patient the best chance to regain normal speech is something Scherer said he hopes his research team will help clarify.

The findings should also help speech and language therapists and pathologists develop better methods for working with patients and benefit voice teachers who work with actors and singers. It should also be of interest to telecommunication companies worldwide which collectively spend millions of dollars annually to develop more natural sounding synthetic speech.

"The research could help us to revise our concepts of aerodynamics and aeroacoustics in speech. It could help us create new ways of thinking about the voice," Scherer said.