A curious vocal pattern has crept into the speech of young adult women who speak American English: low, creaky vibrations, also called vocal fry. Pop singers, such as Britney Spears, slip vocal fry into their music as a way to reach low notes and add style. Now, a new study of young women in New York state shows that the same guttural vibration—once considered a speech disorder—has become a language fad.

Vocal fry, or glottalization, is a low, staccato vibration during speech, produced by a slow fluttering of the vocal chords (listen here). Since the 1960s, vocal fry has been recognized as the lowest of the three vocal registers, which also include falsetto and modal—the usual speaking register. Speakers creak differently according to their gender, although whether it is more common in males or females varies among languages. In American English, anecdotal reports suggest that the behavior is much more common in women. (In British English, the pattern is the opposite.) Historically, continual use of vocal fry was classified as part of a voice disorder that was believed to lead to vocal chord damage. However, in recent years, researchers have noted occasional use of the creak in speakers with normal voice quality.

In the new study, scientists at Long Island University (LIU) in Brookville, New York, investigated the prevalence of vocal fry in college-age women. The team recorded sentences read by 34 female speakers. Two speech-language pathologists trained to identify voice disorders evaluated the speech samples. They marked the presence or absence of vocal fry by listening to each speaker's pitch and two qualities called jitter and shimmer—variation in pitch and volume, respectively.

More than two-thirds of the research subjects used vocal fry during their readings, the researchers will report in a future issue of the Journal of Voice. The distinct vibrations weren't continuous. Rather, they arose most often at the ends of sentences. The patterns were "normal" variations, says co-author and speech scientist Nassima Abdelli-Beruh of LIU, because the women rarely slipped into vocal fry during sustained vowel tests—prolonged holding of vowels such as 'aaa' and 'ooo'—a classic way to assess voice quality and probe for possible disorders. Abdelli-Beruh says the creak is unlikely to damage vocal chords because speakers didn't creak continuously or even at the end of every sentence.

The study is the first to quantify the prevalence of vocal fry in normal speech, although other researchers have noted the pattern. The group is also the first to verify that American women are much more likely to exhibit the behavior than men, as its yet-unpublished data show that male college-age students don't use the creaky voice. The team's next steps will attempt to find out when this habit started—and if it is indeed a budding trend.

The researchers also plan to test students in high schools and middle schools to learn why young women creak when they speak. "Young students tend to use it when they get together," Abdelli-Beruh says. "Maybe this is a social link between members of a group."

Abdelli-Beruh also wants to compare the prevalence of vocal fry on radio stations. For example, she says that the popular-music station on her teenage son's dial features creaky announcers, but she does not hear vocal fry on National Public Radio, which targets an older audience.

Linguist Patricia Keating of the University of California, Los Angeles, agrees with Abdelli-Beruh's statement that creaking at the end of a sentence is normal for many speakers. "There are languages that use creak as part of the phonemic system," she says. "The chances of it leading to vocal damage are very minimal."

The small number of subjects and the limited geographic focus of the study make these findings very specific, Keating says. But she notes that speech researchers suspect the vibrational trend is widespread in the United States. "I think there are generational differences," she says. "But it is common to mark the end of sentences [with vocal fry]. If the pitch falls, you get creak."

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