By Jill Pease
University of Florida researchers looking for students with "normal" hearing for a study recently made a surprising discovery - a quarter of the students who thought they had normal hearing actually already had hearing loss.
Researchers in UF's College of Public Health and Health Professions were recruiting college students with normal hearing for a study on temporary hearing loss and personal music players.
"You would expect normal hearing in that population," said lead researcher Colleen Le Prell, an associate professor in the Department of Speech, Language and Hearing Sciences. "The criteria for normal hearing we used for the study were, we thought, extremely liberal criteria."
The study identified 56 potential study participants who reported having normal hearing in initial phone interviews. In the next phase those students completed a health survey and a questionnaire about their previous exposure to loud noise, such as playing a musical instrument, listening to personal music players, using lawn equipment or attending sporting events or concerts. Participants then received hearing tests in a sound booth at all of the sound frequencies used in a traditional full clinical hearing test.
In 25 percent of the participants, researchers measured 15 decibels or more of hearing loss at one or more test frequencies, an amount that is not severe enough to require a hearing aid, but could disrupt learning, Le Prell said. Of the participants who demonstrated hearing loss, 7 percent had 25 decibels or more of hearing loss, which is clinically diagnosed as mild hearing loss. Hearing loss occurred in both the range of frequencies identified as "speech frequencies" because of their importance for speech discrimination, as well as higher frequencies.
"With high-frequency hearing loss a person can miss a lot of subtle speech sounds, making it much harder to discriminate different vowels or phonemes," Le Prell said. "It would also be much harder to hear sounds like bird songs or children's voices."
Several experts have speculated that increased rates of hearing loss in young adults may be related to the popularity of personal music players. The UF study did find that the highest levels of high-frequency hearing loss were in male students who reported using personal music players. More research is needed with a larger sample size to determine the role of personal music players and gender in noise-induced hearing loss, Le Prell said.
The UF study and other related studies on hearing loss in young adults point to the need for more thorough hearing tests in school children and better hearing health education for children and adolescents, Le Prell said.
"The implication is that the current screening protocols are potentially missing a lot of hearing loss, based on the kinds of failure rates that we've detected when you broaden the criteria," she said.