Reprogramming the Inner Ear: My Bionic Quest for Bolero

The author has been haunted by Ravel’s masterpiece since he lost his hearing. A deaf man’s pursuit of the perfect audio upgrade.

The author spent years tweaking the software on his cochlear implant.
By Michael Chorost, WIRED Magazine, November 2005 Issue 13.11

When technicians activated my cochlear implant in October 2001, they gave me a pager-sized processor that decoded sound and sent it to a headpiece that clung magnetically to the implant underneath my skin. The headpiece contained a radio transmitter, which sent the processor’s data to the implant at roughly 1 megabit per second. Sixteen electrodes curled up inside my cochlea strobed on and off to stimulate my auditory nerves. The processor’s software gave me eight channels of auditory resolution, each representing a frequency range. The more channels the software delivers, the better the user can distinguish between sounds of different pitches.
Eight channels isn’t much compared with the capacity of a normal ear, which has the equivalent of 3,500 channels. Still, eight works well enough for speech, which doesn’t have much pitch variation. Music is another story. The lowest of my eight channels captured everything from 250 hertz (about middle C on the piano) to 494 hertz (close to the B above middle C), making it nearly impossible for me to distinguish among the 11 notes in that range. Every note that fell into a particular channel sounded the same to me.
Music depends on low frequencies for its richness and mellowness. The lowest-pitched string on a guitar vibrates at 83 hertz, but my Hi-Res software, like the eight-channel model, bottoms out at 250 hertz. I do hear something when I pluck a string, but it’s not actually an 83-hertz sound. Even though the string is vibrating at 83 times per second, portions of it are vibrating faster, giving rise to higher-frequency notes called harmonics. The harmonics are what I hear.

Cochlear implants, introduced 20 years ago, have given 83,000 deaf people the ability to hear human speech. Surgeons drill a hole in the skull, embed a sound receiver, and weave an electrode array into the cochlea. Once the hardware is in place, software engineers take over, upgrading the devices as needed so users can enjoy more complex sounds, like music.
1. The earpiece contains a microphone to receive sound and a processor to convert it to digital information.
2. The information travels up to a headpiece that uses a radio transmitter to relay the digitized sound through the skin.
3. The sound is picked up by an implant in the user’s skull. The headpiece clings magnetically to the implant through the scalp.
4. The implant converts the radio signal into electrical pulses, which travel to an array of 16 or 24 electrodes in the inner ear. The electrodes strobe on and off to stimulate the auditory nerves. In time, the user learns to interpret the signals as sound.
5. Users upgrade their hearing by downloading software to the external processor. Early implant users heard just eight channels (compared to 3,000 for normal hearing). The latest software makes 121 channels possible. Tomorrow?
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