Erwin S. Hochmair

System Optimization for Improved Accuracy in Transcutaneous Signal and Power Transmission

A stable transcutaneous transmission of power and signal via two coupled coils with minimized dependence on the relative spacing of external and implanted coil is possible by employing critical coupling between implanted and external circuits. Optimizing coil geometries and preventing the RF output amplifier from saturating is necessary to approximately maintain critical coupling despite placement tolerances within a reasonable range. Based on these considerations a transcutaneous signal transmission system for an auditory prosthesis has been designed. This transmission system can also be used for several other stimulation purposes needing accurate control of stimulation parameters.

Multi-frequency system and method for enhancing auditory stimulation and the like

A plurality of carrier signals are modulated by pulses corresponding to signals in audio frequency bands. The carrier signals are transmitted to a receiver having independent channels for receiving and demodulating the transmitted signals. The detected pulses are applied to electrodes on a prosthetic device implanted in the cochlea with the electrodes selectively positioned in the cochlea to stimulate regions having a desired frequency response. The pulses have a frequency which corresponds to the frequency of signals in an audio band and a pulse width which corresponds to the amplitude of signals in the audio band.

PERCEPTS FROM THE VIENNA COCHLEAR PROSTHESISa

This report includes psychophysical data on some of the 13 patients who have been equipped with intracochlear electrodes and the 6 patients who have received an extracochlear electrode. Thresholds and uncomfortable listening levels versus frequency, amplitude difference limens, and gap detection in noise and frequency difference limens have been determined and represent some essential characteristics of prosthetic hearing.

An Eight Channel Scala Tympani Electrode for Auditory Prostheses

An eight channel stimulation electrode has been developed which can be inserted into the human scala tympani via the round window. This electrode is part of a neuroprosthesis aiming at the restoration of some hearing in cases of sensorineural deafness by electrical stimulation of the auditory nerve.

Method of fitting hearing prosthesis to a patient having impaired hearing

Disclosed is a process of fitting a hearing prosthesis to a deaf or severely hearing impaired patient. The prosthesis is connected to the patient, and a signal is then applied to the prosthesis across an audioband. The frequency response of the prosthesis is adjusted so that the patient detects a desired response to the signal. In one application the prosthesis may include a sound processor driving a transmitter, a transcutaneous receiver, and an implanted electrode. A constant amplitude signal is applied to the sound processor, and the frequency response of the sound processor is adjusted so that the patient detects a generally uniform response to the signal. Other signals can be applied, such as bursts of a sine wave or other periodic wave, and band-filtered noise can be employed with the band center frequency being swept either step-wise or continuously. The transmitter and receiver are first adjusted for normal operating coupling and then a constant amplitude continuous sinusoidal signal, for example, is applied. In a multiple channel system, the signal is applied sequentially to each channel. For each channel, the signal is varied in discrete frequency steps across an audio band, and the frequency response of the transmitter is adjusted so that the patient detects a generally uniform response. The dynamic range is identified at each such frequency step between a threshold level and a discomfort level to establish desired aided thresholds and discomfort levels.

Percepts elicited by different speech-coding strategies.

A number of remarkably different speech-coding strategies exist that were developed or suggested for the electrical stimulation of the auditory nerve. The considerable differences among those strategies may reflect both (1) the relative importance attached by the various groups to the place and periodicity principle, and, to a certain degree, ( 2 ) the varying abilities and limitations of the different implants used. The second point may need some explanation: Without doubt, a percutaneous plug is the most advantageous from the point of view of coding, but many groups do not use it for good reason. The implanted receiver circuits necessary for the transcutaneous transmission are severely restricted in size, power consumption, and complexity. This limits the number and bandwidth of independent stimulation channels. Often some low-power digital circuits are used., Their incompatibility with analog stimulation waveforms may explain the preponderance of pulsatile stimulation schemes. Fortunately, speech seems to be so redundant that even a considerable degree of processing leaves some cues sufficiently intact to enable the listener to partly reconstruct the information. This may explain why widely differing coding schemes may achieve similar results. There is no agreement on the number of independent stimulation channels necessary or feasible. Existing devices feature from one to fifteen channel^.^ The stimulation sites used include the scala tympani, the modiolus, the cochlear nucleus, the round window and the promontory, and sites along, but external to, the cochlea. The stimulation signals themselves span the range from fixedfrequency, variable-duration pulses & to modulated carriers and to completely analog waveforms.6 There are schemes using varying amounts of feature extraction from voiced/unvoiced-coding only, to heavily coded signals on several channels.? In this paper the speech processing used with the Vienna auditory prosthesis is described and results are presented. In addition, some results of our ongoing investigations of further singleand multichannel strategies are given.

Designing of and experience with multichannel cochlear implants.

The technology of two different multichannel cochlear prosthetic devices is described. The clinical results after electrical stimulation in five implanted patients are discussed.

DESIGN AND FABRICATION OF MULTIWIRE SCALA TYMPANI ELECTRODESa

A suitable stimulation electrode is a crucial part of an auditory prosthesis for the deaf. A number of different sites for the placement of such electrodes have been suggested and are being investigated. At present, the optimum site for electrode placement is still being discussd. As yet no results have been found that could scientifically demonstrate an advantage of multichannel stimulation versus single-channel stimulation. It will take some time and more experience with both types of systems before this question can be answered. This report deals with multichannel electrodes that are designed to be inserted into the scala tympani via the round window. Other sites for multichannel electrodes that have been tried or are being used, as well as other approaches into the cochlea, will not be discussed. The majority of researchers working on multichannel implants prefer the access into the scala tympani via the round window. The main reason for this is the short duration and comparatively small risk of the implant surgery required as compared to methods in which wires are put into the cochlea or close to it from outside its outer wall. The requirements that a suitable scala tympani electrode must fulfill are similar to the requirements for electrodes of other neuroprostheses. They have to achieve an unknown degree of neuronal selectivity. This task involves adequate geometry of the electrode body and the stimulating areas and the possibility of sufficiently atraumatic placement in close-enough proximity to the excitable structures. If the number of channels exceeds ten and the spacing between electrode contacts has to be less than 1 mm, then thinor thick-film techniques seem to offer an especially adequate tool for the realization of multichannel stimulation electrodes. Investigators at a number of centers have worked or are working on the design of thin-film electrodes for cochlear prostheses. Several problems have to be overcome before it will be possible to use modern thin-film techniques for the realization of scala tympani electrodes and to be able to eventually benefit from their lower production costs.

An Implantable Current Source for Electrical Nerve Stimulation

A CMOS bipolar voltage controlled current source is described which due to its low part count lends itself very well to integration in a thin film hybrid circuit. The standby power consumption is less than 400 ¿W.

Preliminary Speech Perception Results through a Cochlear Prosthesis

Psychophysical as well as speech comprehension tests have been used in bilaterally deaf patients implanted with a four-channel cochlear prosthesis. The best open speech comprehension without lip-reading was obtained in a 24-year-old patient C. K. with progressive total hereditary deafness. This speech perception was achieved using a small portable stimulator activating only one of the four channels of the implant in a bipolar scala tympani electrode configuration.