Graeme M. Clark - US grants

The use of multiple channel cochlear prostheses to improve the communication abilities of profoundly deaf patients is now an established procedure. The central problems of this technique are the provision of a number of perceptually independent information channels and the provision of reliable and usable speech information with these channels. This application aims to provide a versatile and precisely controlled implantable multiple-channel stimulator using custom designed silicon chip technology. The stimulator will simultaneously control the electric currents between three pairs of electrodes chosen from a linear array of 22 electrodes. A voltage monitoring circuit will be switchable to any of the 22 electrodes or to crucial nodes of the circuit to provide in vivo verification of the performance of the device and direct measurement of electrode impedances. The stimulator will be implanted in at least three patients. A psychophysical study will investigate the interactions between simultaneously stimulated groups of electrodes in different positions along the cochlea. The patients' perceptions of spatially complex current distributions will be investigated. A programmable, portable speech processor will be developed concurrently to evaluate the presentation of the frequencies and amplitudes of three peaks derived from the speech signal. The frequencies will be coded as the positions of three simultaneously stimulated electrode pairs in the cochlea. The stimulation waveform will be a biphasic pulse, with the pulse rate derived from the fundamental frequency of the speaker's voice. Speech studies with the patients will compare the performance of this speech processing strategy with the presently used strategy that uses only a single spectral peak. The programmable speech processor will allow optimisation of performance for different patients as well as easy conversion from one speech coding strategy to another. The complete cochlear prosthesis system will provide a powerful tool for the evaluation of further alternative strategies with the aim of providing good speech comprehension for profoundly deaf patients without the use of lipreading.

speech viewer; ear /hearing prosthesis; computer system design /evaluation; clinical biomedical equipment; deaf aid; communication disorders; computer simulation; computer assisted patient care; online computer;

speech; electrostimulus; radio controlled electronic stimulator; cochlear implants; deafness; auditory discrimination; clinical biomedical equipment; psychoacoustics; deaf aid; cochlear microphonic potentials; online computer; human subject;

ear /hearing prosthesis; child (0-11);

ear /hearing prosthesis; child (0-11);

Development of a laboratory-based speech processing system; evaluation of different speech processing techniques in implanted humans; design of wearable speech processors; and fabrication of at least two wearable devices for specific individuals who already have auditory implants. Accomplishment of the tasks setforth in this project would permit recognition of many environmental sounds by the deaf individual and would serve as an aid to lip reading individuals. With further refinement, it is hoped that auditory prostheses would permit the understanding of speech by deaf individuals without the aid of lip reading.

The use of multiple channel cochlear prostheses to improve the communication abilities of profound/totally deaf patients is now an established procedure. Design improvements for these prostheses have been undertaken in the University of Melbourne's Department of Otolaryngology since 1970. The long term goal of the program is to achieve good speech discrimination without lip reading for a wide range of patients including children. The four specific aims of this grant proposal are as follows: (1) The first aim is to conduct psychophysical studies on profound/totally deaf patients who will be implanted with the receiver-stimulator, CI2, in the middle of 1987. CI2 is being developed under NIH Grant NS21027 ("An advanced multi-channel cochlear implant for deafness"; completion date: August 1987). It will produce simultaneous stimulation on three bipolar electrode pairs within a stimulus period (inverse of repetition rate). (2) The second aim is to monitor the changes in electrode impedance in patients following implantation by the telemetry system incorporated in the electronic design of CI2. (3) The third aim of this grant proposal is to develop a new receiver-stimulator, CI3, to enable research into the nature of the hearing sensations produced by electrical stimulation using different pulse rates on different electrode pairs, or alternatively the same rate on a large number (greater than three) of electrode pairs. CI2 and the existing receiver-stimulator, CI1, are not suitable for this research. (4) The fourth aim of this proposal is to undertake psychophysical studies on patients with CI3. The results of the psychophysical studies mentioned in (1) and (4) above will be used to direct the choice of the detailed structure and parameter values of the algorithms to be used in the speech processors for patients who will be implanted with CI2 or CI3. Loudness summation, electrode identification, repetition rate identification and synthetic vowel studies will be conducted. The development of the receiver-stimulator, CI3, will involve the design and layout of a single LSI CMOS integrated circuit to be fabricated under contract to VLSI Technology Ltd., Ca. The integrated circuit will be packaged into an implantable receiver- stimulator under contract to Cochlear Pty. Limited, Sydney.