Many people who are considering a cochlear implant (CI) are concerned about the possibility that they could be worse off after the procedure than before it. While very unlikely, it is possible because the procedure can destroy all residual hearing. If a person is one of the few for whom the CI procedure is ineffective, and if his residual hearing is destroyed, he will be worse off following the procedure.

A complicating circumstance is the variation of hearing loss with frequency. Most people with hearing loss have a greater loss at high frequency than at low frequency. Indeed, some people who are profoundly deaf at high frequencies have normal or near-normal hearing at the lower frequencies. The low frequency hearing is effective for environmental noise and for some speech sounds.

But the loss of high frequency hearing makes understanding speech difficult, because many of the consonent sounds are produced at high frequencies. A system that effectively amplifies high frequency sounds without affecting low frequencies can be very effective in these cases. Modern digital hearing aids can be adjusted to provide this type of response, and may be more effective than the traditional analog aids in these cases.

Another emerging technology that may be very effective in these situations is a type of cochlear implant that can restore high frequency reception without destroying the residual low frequency hearing. This device is possible because of the structure of the cochlea.

The cochlea is a spiral shaped device that looks something like a snail shell. Different areas are sensitive to different frequencies; high frequencies stimulate the area near the opening of the spiral, and low frequencies stimulate the area deep within the spiral. With a normal CI, an electrode array is threaded as far into the cochlea as possible. As it is inserted near the opening, it can destroy high frequency residual hearing; as the depth of insertion increases, residual hearing at lower frequencies is affected.

An electrode array that is inserted only a short distance could provide high frequency stimulation without affecting residual low frequency hearing. Furthermore, the insertion depth could be adjusted on an individual basis to match the person's frequency response.

Dr. Bruce Gantz of the University of Iowa has developed such a device and has implanted three subjects. As expected, the early recipients report an increased ability to understand consonants, but no negative affect on their residual low frequency hearing. If the experimental procedure continues to provide positive results, full clinical trials can be expected in a year or two.