By JOE SCHULZENBERG | UPI Staff WriterIn an interview with the Washington Post’s Wonkblog, neuroscientist Dr. David S. Freedman, professor of neurosurgery at the University of Pennsylvania, explains how deaf people can be affected by hearing loss.
Dr. Freedmans lab is part of the Department of Neurosurgery of Johns Hopkins Medicine, where he has been studying how the brain processes sound.
He has been looking at the neural mechanisms that control the auditory pathways in the human auditory cortex.
In one study, published in the Journal of the Acoustical Society of America, Dr. Freedmann and his colleagues found that people who have severe hearing loss are more likely to have a very low threshold for sound, and to have difficulty in detecting the frequency range of sounds.
“Our results show that there are more low frequency sounds in the left auditory cortex than in the right,” said Dr. Freeman, who is also a senior author of the study.
“This finding suggests that our left-right asymmetry is related to hearing loss, because people who are left-handed, as we are, are more sensitive to lower frequency sounds.”
Dr. Freemans findings are based on a study he conducted on over 50 deaf and hard-of-hearing patients, who had experienced at least one hearing loss in the last 20 years.
“They were all at least partially blind and had had severe hearing damage,” he said.
“They had no visual perception of sounds at all, so they couldn’t see the frequency of the sound.
And they had to be trained to hear the tone of the sounds.”
The study found that the patients were able to perceive the frequency ranges of the various sounds they heard.
But they were also unable to distinguish between the frequency tones of sounds from different sources.
Dr Freeman’s research also revealed that people with severe hearing impairment were more likely than others to have low thresholds for sound.
“For people with hearing loss who have low threshold, they don’t hear the same sounds that they would if they were hearing the sounds that their hearing was intact,” he explained.
“So it is not that they don, as a general rule, notice the frequency differences between different sounds, but it is that they’re not sensitive enough to hear them.”
Dr Freedmans team also found that hearing loss is not the only way that hearing is affected by disability.
“In a study that I did a couple of years ago, we found that, when we compared deaf people with normal hearing, they had better hearing with no hearing loss than deaf people who had had hearing loss for more than five years,” Dr. S.J. Freedland, the senior author, said.
The research is important because it shows that hearing, and hearing loss specifically, are not solely due to the loss of a particular auditory pathway.
“There are other things that contribute to hearing impairment,” Dr Freedman said.
“There are things that the body does to help you hear, including the regulation of the blood vessels in your brain, and other things,” he added.
“It’s just the body doesn’t like to lose a whole range of things that are vital to hearing.”