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 cords. 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 cord 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 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 reported for 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 cords 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.