Feasibility of an auditory prostheses by multiple channel intracochlear stimulation in man

Although single-channel electrode arrays implanted in the scala tympani of deaf patients are useful as an aid to lip reading and to distinguishing some environmental sounds, they do not transmit intelligible speech. Multichannel electrode arrays, which take advantage of the cochleafs tonotopic organization,, may be capable of generating the complex patterns of neural activity necessary for speech discrimination. In this study, multichannel electrodes were implanted in the cochlea of two 61-year-old volunteers, and the connecting wires were brought through the skin via a percutaneous connector. One volunteer had been bilaterally deaf since birth; the other had been unilaterally deaf for approximately 15 years* Experiments with another bilaterally deaf patientj whose tympani was implanted with five electrodes by House in 1969, are also described. Data on pitch and loudness discrimination as well as the effects of stimulation parameters on threshold, impedance, and electrode interaction are presented. Place pitch and periodicity pitch were observed in all volunteers. The results of pitch-matching experiments with the unilaterally deaf volunteer were consistent with tontopic maps of the cochlea, and initial experiments indicated that a pitch continuum can be achieved by combining place and periodicity pitch modulation. The loudness of the sensations elicited by intracochlcar stimulation could be modulated by changing the amplitude, frequency, and pulse durations of the stimulation wave form. An analytic expression for relating stimulation parameters and the loudness of stimuli was derived based on loudness matching experiments conducted with the unilaterally deaf volunteer. Small difference limens of 3 dB SPL indicated that it will be possible to achieve a relatively smooth loudness continuum. These results, coupled with the finding that subjective sensations remain stable over the long-term, support the feasibility of providing artificial hearing with a multichannel cochlear stimulation system.