How a Cochlear Implant Sounds

PBS has a demonstration of what a cochlear implant sounds like to a hearing impaired person wearing one. The sounds were created by a friend of mine at the House Ear Institute, Bob Shannon, who is one of the leading cochlear implant scientists. The demonstration also provides a visual analogy that will be appreciated by those who use digital cameras, showing how the reduction in the "audio pixel" resolution of sound affects quality and intelligibility.

The human cochlea, the snail shell-looking organ, transduces sound from an acoustic wave into electrical nerve impulses that the brain can understand. The frequency resolution at which it does this is approximately 3500 "sound pixels" (the number of inner hair cells, for those of you who know the auditory system's biology). Cochlear implants attempt to replicate this transduction in place of cochleas that no longer function. These implants have a resolution of around 20 "sound pixels" (channels in the implant industry's nomenclature). Imagine how the quality of your digital photos would be reduced and how much detail would be lost if the image resolution were changed from 3000x2000 pixels to 30x20 pixels, and you get some of the idea of the difficulty facing implant design and implant wearers.

I remember when I first heard this demo from Bob at a hearing science conference (Association for Research in Otolaryngology) about 15 years ago. I was eating lunch at Crabby Bills in St. Petersburg, Florida and Bob came by with a portable tape player saying, "Listen to this!" and I heard a demo similar to the one on the PBS site. I, and anyone who heard it, was amazed at how understandable speech was even with only 4 "sound pixels", and the perceived potential for success with cochlear implants grew tremendously at that moment.