Bilateral cochlear implants controlled by a single speech processor.

OBJECTIVE: This study aimed to assess, in one profoundly hearing impaired subject, potential benefits and limitations in placing bilaterally implanted scala tympani electrode arrays under control of a single speech processor. STUDY DESIGN: All available stimulation sites in both ears were compared in studies of pitch discrimination and pitch ranking, identifying three bilateral pairs capable of supporting interaural comparisons with no perceptible difference in pitch. Using those pairs, the subject's ability to lateralize sound was studied as a function of interaural time delay and interaural amplitude difference. Consonant identification scores were obtained for continuous interleaved sampling processors using various unilateral and bilateral combinations of electrodes. RESULTS: For loudness-matched stimuli composed of 50-msec bursts of 80-microsec/phase pulses at 480 pulses/sec, the subject was able to identify the ear receiving the earlier onset for interaural delays at least as brief as 150 microsec for all three matched pairs. For similar simultaneous stimuli, the subject could identify the ear receiving the louder signal for the smallest deviations from loudness-matched amplitudes available from the implanted electronics. The consonant studies found no evidence that bilateral stimulation per se degrades speech processor performance, even for arbitrary divisions of information between the two ears. Additional contralateral as well as ipsilateral channels were observed to improve speech processor performance. CONCLUSIONS: The ability of this subject to lateralize sounds on the basis of interaural delay or loudness difference, combined with the consonant identification results, supports further use of coordinated binaural stimulation to improve cochlear implant users' ability to understand speech, especially in the presence of competing speech noise.

Design for an inexpensive but effective cochlear implant.

Widespread application of cochlear implants is limited by cost, especially in developing countries. In this article we present a design for a low-cost but effective cochlear implant system. The system includes a speech processor, four pairs of transmitting and receiving coils, and an electrode array with four monopolar electrodes. All implanted components are passive, reducing to a minimum the complexity of manufacture and allowing high reliability. A four-channel continuous interleaved sampling strategy is used for the speech processor. The processor and transmission link have been evaluated in tests with a subject previously implanted with the Ineraid electrode array and percutaneous connector. A prototype of the link, consisting of four pairs of transmitting and external receiving coils, was used, with the outputs of the receiving coils directed to four intracochlear electrodes through the percutaneous connector. The subject achieved speech reception scores with the prototype system that were equivalent to those achieved with a standard laboratory implementation of a continuous interleaved sampling processor with current-controlled stimuli.

Temporal representations with cochlear implants.

OBJECTIVE: To record and characterize intracochlear evoked potentials (EPs) for a variety of electrical stimuli in studies with cochlear implant patients. METHODS: Recordings were made with patients having direct percutaneous access to their implanted electrodes. Intracochlear voltages were recorded via unstimulated electrodes. The stimuli included trains of identical pulses, with pulse rates ranging from 100 to 4065/s, and a modulated pulse train produced by a single-channel speech processor, with the pulse rate of 824/s. RESULTS: Magnitudes of EPs for each pulse in trains of identical pulses were uniform for pulse rates below about 200/s. For rates between about 400 and 1000/s, an alternating pattern of EP magnitudes was observed, with relatively large EPs following the odd-numbered pulses. For rates between about 1000 and 3000/s, more complex patterns were observed. After the first millisecond of each train at even higher rates, uniform EPs again were observed across pulses, although the absolute magnitude of the EPs was much lower than that observed for low rates of stimulation. The approximate rates corresponding to boundaries between these different regions varied among subjects and among electrodes within subjects. EP magnitudes for the modulated pulse train reflected the gross periodicity of the modulation waveform but did not reflect temporal details within the periods. CONCLUSIONS: Population responses of the human auditory nerve, as indicated by EP magnitudes, reflect the amplitudes of electrical pulses for pulse rates below about 200/s and above about 3000/s. Use of intermediate rates may introduce distortions in the transmission of stimulus information with cochlear implants.

Cochlear implant studies at Research Triangle Institute and Duke University Medical Center.

Examples from several areas of cochlear implant research are presented, with emphasis on the continuous interleaved sampling (CIS) approach to speech processor design. Within-subject comparisons of such processors with the compressed analog (CA) approach of the clinical Ineraid device are reviewed, and ongoing similar comparisons with the clinical Nucleus spectral peak (SPEAK) strategy are outlined. Correlations between chronic performance levels with clinical CA processors and initial performance levels with CIS, data on further improvements in performance with chronic use of CIS, and instances of substantial benefit from custom fitting of CIS parameters are presented as examples of findings with immediate clinical implications. New studies are described, involving the measurement of intracochlear evoked potentials in response to cochlear implant stimulation, and the integration of such work with computer modeling studies.

New processing strategies in cochlear implantation.

New strategies for representing acoustic information with multichannel cochlear implants have produced substantial improvements in speech recognition for implant users. This report reviews within-subject comparison of a new continuous interleaved sampling (CIS) strategy with a compressed analog (CA) strategy used in a standard clinical device. In general, the comparison show higher levels of open-set speech recognition with CIS for each of the 11 subjects studied. Data on the importance of the patients variable in determining outcomes with cochlear implants are presented. A brief description of another new strategy, the spectral maxima sound processor (SMSP) strategy is given as well as information on the availability of CIS in various implant systems.

Importance of patient and processor variables in determining outcomes with cochlear implants.

Within-subjects comparisons of processing strategies for cochlear implants are reviewed. Compressed analog strategies were compared to interleaved pulses strategies in tests with one group of 8 subjects, and to continuous interleaved sampling strategies in tests with another group of 11 subjects. The tests included open-set recognition of words and sentences. The results show that, while different strategies may produce quite different outcomes across subjects, individual performances with one processing strategy are significantly correlated with those of alternative strategies. These findings emphasize the importance of patient variables in determining outcomes across a variety of prosthesis designs.

Design and evaluation of a continuous interleaved sampling (CIS) processing strategy for multichannel cochlear implants.

Two approaches for representing speech information with multichannel cochlear prostheses are being compared in tests with implant patients. Included in these studies are the compressed analog (CA) approach of a standard clinical device and research processors utilizing continuous interleaved sampling (CIS). Initial studies have been completed with nine subjects, seven of whom were selected on the basis of excellent performance with the Ineraid clinical processor, and the remaining two for their relatively poor performance with the same device. The tests include open-set recognition of words and sentences. Every subject has obtained a higher score--or repeated a score of 100% correct--on every test when using a CIS processor. These results are discussed in terms of their implications for processor design.

New processing strategies for multichannel cochlear prostheses.

Various strategies for representing speech information with multichannel cochlear prostheses were compared in tests with implant patients. The strategies included the compressed analog (CA) approach of a standard clinical device, and alternative interleaved pulses (IP) and continuous interleaved sampling (CIS) strategies. CA and IP strategies had been compared in previous studies with a wide range of subjects. The present studies compared all three types in tests with one subject and CA and CIS strategies in tests with six additional subjects. Subjects for the present studies were selected for their excellent performance with the clinical CA processor, and the tests included closed-set identification of consonants and open-set recognition of words and sentences. For every test, every subject obtained his or her highest score, or repeated a score of 100% correct, using a CIS strategy. In the comparisons of all three approaches, IP processor scores were between those obtained with CA and CIS processors. The results are discussed in terms of their implications for processor design.

Better speech recognition with cochlear implants.

HIGH levels of speech recognition have been achieved with a new sound processing strategy for multielectrode cochlear implants. A cochlear implant system consists of one or more implanted electrodes for direct electrical activation of the auditory nerve, an external speech processor that transforms a microphone input into stimuli for each electrode, and a transcutaneous (rf-link) or percutaneous (direct) connection between the processor and the electrodes. We report here the comparison of the new strategy and a standard clinical processor. The standard compressed analogue (CA) processor presented analogue waveforms simultaneously to all electrodes, whereas the new continuous interleaved sampling (CIS) strategy presented brief pulses to each electrode in a nonoverlapping sequence. Seven experienced implant users, selected for their excellent performance with the CA processor, participated as subjects. The new strategy produced large improvements in the scores of speech reception tests for all subjects. These results have important implications for the treatment of deafness and for minimal representations of speech at the auditory periphery.

Coding strategies for multichannel cochlear prostheses.

Comparisons of analog and pulsatile coding strategies for multichannel cochlear prostheses are reviewed. The results are related to design considerations for pediatric implants, including efficacy, safety, ease of fitting, and access to future improvements.

Comparative studies of speech processing strategies for cochlear implants.

A wide variety of speech processing strategies for multichannel auditory prostheses were compared in studies of two patients implanted with the UCSF electrode array. Each strategy was evaluated using tests of vowel and consonant confusions, with and without lipreading. Included among the strategies were the compressed analog processor of the present UCSF/Storz prosthesis and a group of interleaved pulses processors in which the amplitudes of nonsimultaneous pulses code the spectral variations of speech. For these patients, each with indications of poor nerve survival, test scores were significantly higher with the interleaved pulses processors. We believe this superior performance was a result of 1. the substantial release from channel interactions provided by nonsimultaneous stimuli and 2. a fast enough rotation among the channels to support adequate temporal and spectral resolution of perceived speech sounds.