Relearning to Hear

Editor: Most people who receive cochlear implants report that it takes them a while to get used to the sound from the implant. Voices may initially sound like Donald Duck or the Chipmunks, and gradually come to sound like the recipient remembers. Scientists at the Indiana University School of Medicine are now reporting that people may be able to hasten the adjustment process by being introduced to the CI sound gradually. Here's the scoop!

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SEATTLE -- Cochlear implants can provide a return to the world of sound for some deaf patients, but learning to "hear" with them can require much effort. Scientists at Indiana University School of Medicine are developing ways to speed that process. Mario Svirsky, Ph.D., professor of Otolaryngology -- Head and Neck Surgery, discussed his work at the meeting of the American Association for the Advancement of Science here.

Cochlear implants are surgically implanted devices that stimulate the auditory nerve to enable profoundly deaf persons to sense and understand speech. Adults who have lost their hearing must somehow match the signals provided by the implants to the speech sounds they heard and stored in memory before losing their hearing. To do so, they must overcome two simultaneous forms of distortion introduced by the implants -- the sound has lower frequency resolution and is shifted to a higher pitch.

Svirsky and his Indiana University School of Medicine colleagues tested whether a training regimen that gradually introduced subjects to the frequency shift could improve their ability to comprehend speech. The experiment was done with an "acoustic simulation" of a cochlear implant, which allows listeners who have normal hearing to hear sounds that are degraded and frequency-shifted in a way similar to that found in cochlear implants. They found that subjects introduced to the frequency shift in a gradual way adapted sooner than those who were introduced to the full frequency shift from the beginning.

Brain scans performed by Thomas Talavage, Ph.D., assistant professor of electrical and computer engineering at Purdue University, showed systematic changes in cortical responses in one of the subjects, who was tested before and after several hours of exposure to the degraded speech.

Svirsky and Talavage concluded that human listeners can learn to understand an extremely impoverished and frequency-shifted acoustic signal, and this learning process can be facilitated by gradual exposure.

A multimedia document in Microsoft Word format summarizing Svirsky's presentation is available at the Public and Media Relations web site at http://www.medicine.indiana.edu/.