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When It Comes to Hearing, Timing Isn't Everything

New study could lead to help for those with severe hearing loss

MONDAY, Jan. 12, 2004 (HealthDayNews) -- Discerning pitch is crucial to understanding language and appreciating music, but scientists still aren't sure if humans detect these differences in sound by the timing of the sound or by the location in the ear that the sound stimulates.

However, new research from the Massachusetts Institute of Technology (MIT) may offer some answers.

The study, which appears in this week's issue of the Proceedings of the National Academy of Sciences, suggests that "place" may be more important than timing. This knowledge may help make cochlear implants -- electronic devices that help people with profound hearing impairment -- more effective in the future, the researchers say.

"These theories have been argued about for 150 years," says study author Andrew Oxenham, a principal research scientist at MIT. "The reason it's still debated is it's very hard to separate these theories."

That's because if you change the timing of a sound, you also change the location it stimulates in the cochlea, a small snail-like structure in the ear that sends sound information to the brain.

Oxenham says high-frequency sounds stimulate one area of the cochlea, while low-frequency sounds stimulate another. When the frequency of a sound changes, its timing also changes. High-frequency sounds occur very rapidly, while low-frequency sounds occur less rapidly, Oxenham explains.

So, if you change the frequency of a sound you not only change its timing, but also the place it stimulates in the cochlea.

To get around this problem, Oxenham and his colleagues had four normal-hearing volunteers listen to a transposed sound. This transposed sound, developed by other researchers, takes timing information from one sound and presents it to an area of the cochlea that normally doesn't receive information from that type of sound.

Oxenham says that since the timing information wasn't changed, if the timing theory was correct, the study subjects should have been able to hear the pitch of the sound with no difficulty. However, they couldn't.

"What we found, is that for these simple stimuli, people do very poorly in these transposed conditions, which suggests that place is important when coding pitch," Oxenham says.

Dr. Timothy Malony, director of otology and neurotology at Ochsner Clinic Foundation Hospital in New Orleans, says, "This study had some valuable things to say in terms of cochlear mechanics. How to best program cochlear implants has been a real issue and this helps point us in a direction."

Dr. Susan Waltzman, co-director of the New York University Cochlear Implant Center, also feels the study has added important knowledge to the understanding of how normal hearing works. But, she adds, these findings may not translate to people with hearing impairments.

"We need to exercise caution when we switch this information to the hearing-impaired population," she says, adding that more research needs to be done before any changes in cochlear implants are made.

More information

To learn more about cochlear implants, visit the National Institute on Deafness and Other Communication Disorders or the American Academy of Otolaryngology - Head and Neck Surgery.

SOURCES: Andrew Oxenham, Ph.D., principal research scientist, Massachusetts Institute of Technology, Cambridge, Mass.; Timothy Malony, M.D., director, otology and neurotology, Ochsner Clinic Foundation Hospital, New Orleans; Susan Waltzman, M.D., co-director, New York University Cochlear Implant Center, and professor, otolaryngology, New York University School of Medicine, New York City; Jan. 12-16, 2004, Proceedings of the National Academy of Sciences
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