Prolonged exposure to loud noise alters how the brain processes speech, potentially increasing the difficulty in distinguishing speech sounds, according to neuroscientists at The University of Texas at Dallas.
In a paper published this week in Ear and Hearing, researchers demonstrated for the first time how noise-induced hearing loss affects the brain's recognition of speech sounds.
Noise-induced hearing loss (NIHL) reaches all corners of the population, affecting an estimated 15 percent of Americans between the ages of 20 and 69, according to the National Institute of Deafness and Other Communication Disorders (NIDCD).
Exposure to intensely loud sounds leads to permanent damage of the hair cells, which act as sound receivers in the ear. Once damaged, the hair cells do not grow back, leading to NIHL.
"As we have made machines and electronic devices more powerful, the potential to cause permanent damage has grown tremendously," said Dr. Michael Kilgard, co-author and Margaret Fonde Jonsson Professor in the School of Behavioral and Brain Sciences. "Even the smaller MP3 players can reach volume levels that are highly damaging to the ear in a matter of minutes."
Before the study, scientists had not clearly understood the direct effects of NIHL on how the brain responds to speech.
To simulate two types of noise trauma that clinical populations face, UT Dallas scientists exposed rats to moderate or intense levels of noise for an hour. One group heard a high-frequency noise at 115 decibels inducing moderate hearing loss, and a second group heard a low-frequency noise at 124 decibels causing severe hearing loss.
For comparison, the American Speech-Language-Hearing Association lists the maximum output of an MP3 player or the sound of a chain saw at about 110 decibels and the siren on an emergency vehicle at 120 decibels. Regular exposure to sounds greater than 100 decibels for more than a minute a
|Contact: Ben Porter|
University of Texas at Dallas