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February 16, 2004

Relearning to Hear: Gradual Adaptation System May Improve Cochlear Implant Success

From: AScribe - USA - Feb 16, 2004

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

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