Some practical considerations in development of multichannel scala tympani prostheses.

There are several basic issues regarding the safety and feasibility of implanting multichannel scala tympani cochlear prostheses in humans. Physiological and technical studies have been designed to resolve some of these questions. Results of physiological investigations demonstrate that (1) nerve viability is not affected by the presence (without activation) of a multichannel array; (2) use of a highly specified bipolar electrode configuration permits discrete and predictable stimulation of sectors of the auditory nerve array, and (3) some deleterious effects (i.e., nerve damage and calcification products) may result when stimulus parameters (intensity, duration and waveform symmetry) are not well controlled over long periods of stimulation. Results of technical investigations regarding the specifications (materials and design) of multi-electrode arrays and engineering studies regarding hardware and software for safe and efficient stimulators for humans have provided devices with which 2 patients could be implanted and tested psychophysically. Some preliminary results of testing with these provide data regarding threshold, loudness discrimination and pitch perception.