Ingeborg J. Hochmair-Desoyer

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.

Reimplantation of a Molded Scala Tympani Electrode: Impact on Psychophysical and Speech Discrimination Abilities

Revision surgery was successfully performed on two Vienna cochlear implant patients. Twenty months and 40 months, respectively, after initial insertion into the cochleas of two bilaterally deaf patients, electrodes were removed from the scala tympanis and replaced by electrodes of the same design. Psychophysical and speech data gathered before and after the revision surgery were compared. These were thresholds, loudness scalings, amplitude difference limens, pitch scalings, frequency difference limens, and speech tests in the “stimulation only” modality. No negative changes were found. The data available demonstrate a continuous improvement in performance over many months of practice with the sound processor. This development was not impeded by the revision surgery. Thus, it was demonstrated that the removal and replacement of a molded scala tympani electrode is feasible.

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.

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.

Psychoelectrical and speech comprehension results obtained through electrical stimulation of the auditory nerve

For five completely deaf humans equipped with an implanted cochlear prosthesis based on electrical stimulation of the auditory nerve, phoneme and word discrimination and recognition have been determined (optimum recognition results of 70% for an open list of words have been achieved). These results are contrasted to psychoelectrical measurements like amplitude and frequency scaling and masking experiments. Both single channel and multichannel experiments with up to four channels have been performed leading to the result that in most cases single channel stimulation is sufficient to reach up to 80% comprehension of unknown sentences. The influence of the configuration of the stimulating field was also investigated. Bipolar stimulation leads to a steeper increase in subjective loudness as compared to stimulation against a common distributed intracochlear ground. Field extension concepts have been confirmed by masking experiments. Using a suitable compensation for the different slopes in the loudness scaling...

Relationships between speech understanding and temporal processing abilities in cochlear implant patients

A battery of tests has been used with the 20 postlingually deafened patients who have received a Vienna Cochlear Implant in Vienna and have had their implant for at least 3 months. The battery included tests determining the temporal difference limen for a 250–1000‐Hz and a 2000–4000‐Hz noise signal, gap detection tests using the same two signals and a periodic/aperiodic discrimination test. The speech tests were open set one‐syllable‐word understanding, open set sentence understanding, a 16‐consonant identification, and an eight‐vowel identification. The four speech tests were performed without lipreading. For all temporal processing ability tests, limits could be found which separated those 75% of the patients who were able to understand single‐syllable words and sentences to a varying degree and those who were not. Correlations between the speech tests, except the vowel test, and the tests for temporal processing abilities could be found. These correlations demonstrate that cochlear implant patients wea...