Background noises don’t just cover up conversation, they may actually scramble brain activity, a discovery that helps explain why even perfectly loud speech can be hard to understand in a noisy room, say University of Florida researchers writing in the current Proceedings of the National Academy of Sciences.
The insight from experiments with rats could influence the design of hearing devices, MP3 music players and virtually any audio transmission technology, say the scientists.
“Some people have a tremendously difficult time understanding speech in a noisy environment and we’ve all had the experience of hearing someone tell us something, but we can’t tell what it is they are saying,” said Purvis Bedenbaugh, an assistant professor of neuroscience with the UF College of Medicine and a member of UF’s McKnight Brain Institute. “This research is a first step toward looking at why that would be.”
Scientists examined how brain cells in alert rats responded to specific sounds while one of three standardized noises played in the background. They discovered that brain activity actually decreased in the presence of background noise. Furthermore, background noise didn’t simply cover up sounds, it interfered with the brain’s ability to process or interpret information about a sound, even though the sound was heard. Essentially, the brain couldn’t understand what the ear told it.
The phenomenon may play a role in auditory processing disorder, a problem first noticed in children in the 1970s. The lack of coordination between the ear and brain that characterizes the disorder is expected to be widespread, although it is difficult to diagnose, according to the American Academy of Audiology.
“Some people have a lot of trouble hearing in background noise,” said Eugene Martin, a doctoral associate in the neuroscience department who participated in the research. “Now we know a little bit more about why. The design of hearing aid devices and cochlear implants — any device that involves auditory perception — will benefit from deeper understanding of the organ which serves that perception, which is the brain.”