Ultrasound to study human sounds

Dec 6, 2010 by

Gone are the days when linguists simply listened to speakers of exotic languages, trying to figure out what it is they’re hearing. Today, new technologies are being used to study and document human speech sounds. From digital dictophones to speech analyzing software, from X-rays to electronic probes. Most recently, portable ultrasound machines have been used to study human speech.

My former colleague from Cornell University (now a visiting assistant professor at Ohio State University) Amanda Miller is one of about 40 linguists worldwide who uses ultrasound. She has long been working on African languages and her special interest is Khoisan languages, such as N|uu, which have some of the fastest speech sounds — the clicks. To pronounce a click, one creates not just one but two closures (points of contact) in the mouth, one forward (at the lips, teeth, alveolar ridge, hard palate or one side of the tongue) and one at the back. The pocket of air enclosed between the two points of contact is rarefied by a sucking action of the tongue. The forward closure is then released, producing a characteristic popping, clicking or smacking sound. However, many languages that use clicks don’t stop at the variation created by the different location of the forward closure: click sounds may be voiced or voiceless, aspirated or unaspirated, and so on. So to identify each click precisely is not as easy as it may seem.

And that’s where the use of ultrasound is particularly handy. It allows researchers to see the tongue as it moves in real time. It is thus the only medical scanning device that can keep up with speech; for instance, MRI (itself a big helper in understanding how language works in the brain) is to slow for analyzing speech. And ultrasound is less clunky or invasive than other technologies such as x-rays and glue-on electronic probes, which linguists had to rely on before ultrasound became affordable to linguists around 2000. The x-rays could not be used extensively because of the harmful radiation they expose subjects to. Probes, on the other hand, were just terribly inconvenient, especially when it comes to working with speakers of such languages as N|uu. In the words of Diana Archangeli, a linguistics professor at the University of Arizona who has worked with ultrasound since 2004:

“You can imagine if you walk into a village and say, ‘Look, people, all I want to do is blow-dry your tongue and glue things to it,’ people might be a little nervous”

Thus, the use of ultrasound allows Miller, Archangeli and their colleagues to shed new light on how sounds are perceived, articulated and organized in different languages.

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