A team of researchers at the University of Southern California (USC) has applied cutting-edge imaging tools to the study of human speech, capturing the clearest moving images of the rapid vocal movements that turn sound into language (Journal of the Acoustical Society of America, April 2004).

"We're using technological tools to get better data on how the vocal tract moves during speech," said study author Dani Byrd, PhD, director of the USC Phonetics Laboratory in the College of Letters, Arts and Sciences. "Magnetic resonance imaging [MRI] allows us to look at movies of the entire vocal tract in action-something no one's been able to see in real time before now."

The team reported successful development and use of real-time MRI to create high-resolution movies of the vocal system. By helping to clarify ways that humans produce normal speech, the new technique may help people learn a foreign language, teach machines to speak more naturally, and possibly suggest therapy for those with speech problems due to stroke.

The advance is the result of an interdisciplinary collaboration led by Dr. Byrd, an associate professor of linguistics who focuses her research on the production, perception and physical properties of speech sounds, and electrical engineer Shrikanth Narayanan, a USC researcher who interfaces speech, engineering and computer science.

MRI has been used in speech research for more than a decade, stated Dr. Byrd. Until now the technology primarily has recorded still images of the dynamic vocal tract. These data have been useful but limited in telling researchers about the timing of speech.

Analytical software was developed to reconstruct raw MRI data into a moving image at 20 to 24 frames per second-just fast enough to capture the rapid changes in lips, tongue, jaw and the airway that together produce specific vowels, consonants and intonations of speech.

Real-time MRI offers a view of how to pronounce sounds and allows Dr. Byrd to see and confirm the degree of sound overlap in spoken language, a characteristic of human speech she helped reveal in earlier work.

"There are no spaces between words in speech," she said. "People overlap sounds within syllables. With MRI you can actually see two sounds being made at the same time."

Visual cues produced by MRI movies could help foreign language students learn to speak unfamiliar sounds, such as the "th" sound in English, the researchers speculated. Anther potential application is helping people affected by congenital malformations that may make motor control and the articulation of specific sounds difficult.