Current status of multichannel cochlear protheses.

Multichannel cochlear prostheses are being developed and evaluated with emphasis on providing sensory deaf individuals enough information about their acoustic environment to permit communication by ordinary speech. Studies of the safety of the electrode arrays and stimulus values indicate that the remaining nerve fibers will not be damaged at the levels that will be typically used in human prostheses, but that a narrow safety range exists for suprathreshold stimuli. Early multichannel human implants have demonstrated that place pitch can be utilized with scali tympani implants, but this has not been demonstrated with modiolar electrode arrays. With both approaches, information about pitch can be conveyed by the frequency of stimulation. Research questions remain on the long-term viability of the eighth nerve with stimulated implants, on the interactions of closely spaced electrodes, on optimal methods of encoding the acoustic signal for multichannel nerve stimulation and on the ability of deaf individuals to utilize this information.