Relearning to hear

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.

Mario 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 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. These findings will be presented at the meeting of the American Association for the Advancement of Science.

To speak with Svirksy, contact Eric Schoch at 317-274-8205 or eschoch@iupui.edu.

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