TNRT profiles with the nucleus research platform 8 system.

This study investigates the effect of the Nucleus CI24RE implant's neural response telemetry (NRT) system, which has less internal noise compared to its predecessor, the CI24M/R implant, on the NRT threshold (TNRT) profile across the array. CI24M/R measurements were simulated by ignoring CI24RE measurements with response amplitudes below 50 uV. Comparisons of the estimated TNRTs from the CI24RE measurements and the CI24M/R simulations suggest that, apart from a constant level difference, the TNRT profiles from the newer implant generally would not have differed very much from those of its predecessor. This view was also reflected by principal component analysis (PCA) results which revealed a 'shift' component similar to that reported by Smoorenburg et al (2002). On the whole, there is no indication that current practices of using the TNRT profiles for assisting with speech processor programming need to be revised for the CI24RE implant.

Performance and preference for ACE stimulation rates obtained with nucleus RP 8 and freedom system.

Cochlear recently released the Nucleus Freedom System which has been based on the Nucleus Research Platform 8. Both systems make use of the same implant, the CI24RE, which includes expanded total stimulation rates up to 32 kHz. In this study the performance of the ACE strategy at 500, 1200 and 3500 pps/channel was investigated using an ABC-CBA design. At the end of each period speech tests were performed. In the CBA phase the patients completed a comparative questionnaire to determine the subjective rate preference. Preliminary results in 13 recipients indicate no differences in for the ACE strategy at rates ranging from 500 pps to 3500 pps/channel.

Normative findings of electrically evoked compound action potential measurements using the neural response telemetry of the Nucleus CI24M cochlear implant system.

One hundred and forty-seven adult recipients of the Nucleus 24 cochlear implant system, from 13 different European countries, were tested using neural response telemetry to measure the electrically evoked compound action potential (ECAP), according to a standardised postoperative measurement procedure. Recordings were obtained in 96% of these subjects with this standardised procedure. The group results are presented in terms of peak amplitude and latency, slope of the amplitude growth function and ECAP threshold. The effects of aetiological factors and the duration of deafness on the ECAP were also studied. While large intersubject variability and intrasubject variability (across electrodes) were found, results fell within a consistent pattern and a normative range of peak amplitudes and latencies was established. The aetiological factors had little effect on the ECAP characteristics. However, age affected ECAP amplitude and slope of the amplitude growth function significantly; i.e., the amplitude is higher in the lowest age category (15-30 years). Principal component analysis of the ECAP thresholds shows that the thresholds across 5 electrodes can be described by two factors accounting for 92% of the total variance. The two factors represent the overall level of the threshold profiles ('shift') and their slopes across the electrode array ('tilt'). Correlation between these two factors and the same factors describing the T- and C-levels appeared to be moderate, in the range of 0.5-0.6.

Multicenter audiometric results with the Vibrant Soundbridge, a semi-implantable hearing device for sensorineural hearing impairment.

The Vibrant Soundbridge, a semi-implantable hearing device for subjects with moderate to severe sensorineural hearing impairment was introduced commercially. First audiologic results are presented on 63 patients from 10 European implant centers. Hearing loss was at 0.5, 1, 2, and 4 kHz varying between 43 and 81 dB HL. The patients used the analogue audio processor, type 302. Measured sound-field gain was compared with NAL-R target values. For most patients an acceptable agreement was found. There was a subgroup of patients, however, with relatively low gain. The results suggest that this was related to the suboptimal positioning and fixation of the transducer to the incus.

Performance of an adaptive beamforming noise reduction scheme for hearing aid applications. I. Prediction of the signal-to-noise-ratio improvement.

Adaptive beamformers have been proposed as noise reduction schemes for conventional hearing aids and cochlear implants. A method to predict the amount of noise reduction that can be achieved by a two-microphone adaptive beamformer is presented. The prediction is based on a model of the acoustic environment in which the presence of one acoustic target-signal source and one acoustic noise source in a reverberant enclosure is assumed. The acoustic field is sampled using two omnidirectional microphones mounted close to the ears of a user. The model takes eleven different parameters into account, including reverberation time and size of the room, directionality of the acoustic sources, and design parameters of the beamformer itself, including length of the adaptive filter and delay in the target signal path. An approximation to predict the achievable signal-to-noise improvement based on the model is presented. Potential applications as well as limitations of the proposed prediction method are discussed and a FORTRAN subroutine to predict the achievable signal-to-noise improvement is provided. Experimental verification of the predictions is provided in a companion paper [J. Acoust. Soc. Am. 109, 1134 (2001)].

Performance of an adaptive beamforming noise reduction scheme for hearing aid applications. II. Experimental verification of the predictions.

A method to predict the amount of noise reduction which can be achieved using a two-microphone adaptive beamforming noise reduction system for hearing aids [J. Acoust. Soc. Am. 109, 1123 (2001)] is verified experimentally. 34 experiments are performed in real environments and 58 in simulated environments and the results are compared to the predictions. In all experiments, one noise source and one target signal source are present. Starting from a setting in a moderately reverberant room (reverberation time 0.42 s, volume 34 m3, distance between listener and either sound source 1 m, length of the adaptive filter 25 ms), eight different parameters of the acoustical environment and three different design parameters of the adaptive beamformer were systematically varied. For those experiments, in which the direct-to-reverberant ratios of the noise signal is +3 dB or less, the difference between the predicted and the measured improvement in signal-to-noise ratio (SNR) is -0.21+/-0.59 dB for real environments and -0.25+/-0.51 dB for simulated environments (average +/- standard deviation). At higher direct-to-reverberant ratios, SNR improvement is systematically underestimated by up to 5.34 dB. The parameters with the greatest influence on the performance of the adaptive beamformer have been found to be the direct-to-reverberant ratio of the noise source, the reverberation time of the acoustic environment, and the length of the adaptive filter.

Evaluation of eardrum laser doppler interferometry as a diagnostic tool.

OBJECTIVES: Laser Doppler interferometry (LDI) of the eardrum allows noncontact optical analysis of its vibrations in response to sound. Although LDI has been widely used in research, it has not yet been introduced into clinical practice as an adjunctive test for otological workup. The aim of this study was to evaluate LDI as a diagnostic tool in the clinical sphere. STUDY DESIGN: Prospective. METHODS: A measurement system was developed based on a commercially available scanning He-Ne laser Doppler interferometer. The study included 129 eardrums of 79 subjects that were divided into 3 groups: 1) normal subjects and 2) patients with sensorineural and 3) conductive hearing loss (HL). All the patients suffering from conductive HL underwent ossiculoplasty, which allowed confirmation of the final diagnosis, and patients were assigned accordingly to the subgroups malleus fixation, incus luxation, and stapes fixation. RESULTS: The modified LDI system allowed bilateral evaluation of a subject within 30 minutes. No significant difference between normal subjects and patients having sensorineural HL were found. However, it was possible to distinguish between normal subjects and patients with conductive HL. Furthermore, the system had the ability to differentiate between various middle ear diseases. These groups differed statistically significantly in terms of manubrium vibration amplitude and resonance frequency. In malleus fixation significant differences in tympanic membrane movement patterns were found. CONCLUSIONS: Our LDI is applicable in clinical otological practice and serves as a valuable addition to the routine audiological investigations for preoperative evaluation of the mobility and integrity of the ossicular chain.

Intraoperative assessment of stapes movement.

A method is described that allows, for the first time, intraoperative vibration modes assessment of the acoustically stimulated stapes by means of scanning laser Doppler interferometry (LDI). The study was designed to answer the following questions: 1) Is LDI practical for taking measurements during surgery? 2) Are the results comparable to the findings in temporal bone preparations? and 3) Do the vibration characteristics of the stapes change after the posterior incudal ligament is detached from the incus? Seven patients with profound bilateral hearing loss who were undergoing cochlear implantation were included in the study. The measurement system was easily applicable for intraoperative measurements and allowed contact-free analysis with very high accuracy. No major differences in the results from the live human subjects and temporal bone preparations were observed. The stapes movement was predominantly pistonlike at the lower frequencies and became complex at higher frequencies. Sacrificing the posterior incudal ligament had no statistically significant effect on stapes vibration.

A simple two-component model of the electrically evoked compound action potential in the human cochlea.

Neural response telemetry (NRT) permits in situ intracochlear recordings of the electrically evoked compound action potential from the auditory nerves using scala tympani electrodes. The recorded NRT waveforms can generally be categorized under either single positive peak or double positive peak waveforms. This is similar to the observations from Stypulkowski and van den Honert, who suggested that the double peak complex arises from two components that could be axonal and dendritic in origin, respectively. Using a simple mathematical model which linearly combines two separate waveforms similar in shape but differing in amplitude and latencies, it was possible to simulate the various NRT waveform categories. The simulation results support the view that the two waveform components originate from dendritic or axonal processes and implies that the shape of the response waveform may provide information about the degree of neural survival in the stimulated cochlea. This information could be useful for determining optimal speech coding parameters for cochlear implant users on an individual basis.

Cochlear implants for adults obtaining marginal benefit from acoustic amplification: a European study.

OBJECTIVE: This study aimed to examine the application of a speech recognition score of 30% on open-set word materials as the upper limit for preoperative performance in determining cochlear implant (CI) candidacy for European non-English-speaking hearing-impaired persons. This study also aimed to determine the effect of implantation on residual pure-tone hearing thresholds and to determine the incidence and benefit of a contralateral hearing aid postimplant. STUDY DESIGN: The single-subject design study, involving 20 postlinguistically deafened subjects, compares preoperative performance with hearing aids to postoperative performance with a CI at 6 months after surgery. Subjects were implanted with either the Nucleus Mini 22 or the Nucleus 24 CI systems implementing the MPEAK and SPEAK coding strategies. Fourteen subjects meeting the selection criteria were accrued consecutively specifically for inclusion in the study, whereas the remaining 6 retrospectively implanted subjects were identified for inclusion via patient records. PATIENTS: The investigation included 8 clinics over 3 countries (France, Germany, and Spain) and involved 20 postlinguistically deafened subjects who obtained marginal benefit from acoustic amplification before surgery. Nineteen subjects were older than 18 years of age with 1 subject being 14 years old included in the data report as well. MAIN OUTCOME MEASURES: Open-set speech recognition was evaluated before and after surgery using recorded word lists and sentence lists in the subject's native language to determine benefit from the treatment. Baseline audiograms were obtained before surgery for frequencies of 0.25-8.0 kHz for both ears and compared to pure-tone hearing thresholds measured at 1 month after surgery to determine the effect of the implantation on residual hearing. Additionally, a questionnaire was administered to determine the incidence and benefit of continued hearing aid use in the contralateral ear postimplant. RESULTS: Nineteen of the 20 study subjects displayed a significant benefit after surgery at 6 months after switch-on for open-set speech recognition. The remaining subject displayed no significant change in performance on objective testing. The implantation resulted in a significant downward shift in hearing thresholds for the implant ear in the majority of subjects. However, 50% of subjects displayed conservation of some residual hearing. For the majority of subjects, hearing aid use in the contralateral ear was discontinued because of lack of perceived benefit after surgery. CONCLUSIONS: The Nucleus Multichannel CI provides a significant benefit for postlinguistically deafened adults who display marginal benefit from acoustic amplification. Therefore, in French-, German-, and Spanish-speaking clinics, a speech recognition score of 30% on open-set word materials is considered an appropriate upper limit for preoperative performance in determining CI candidacy. In view of a significant downward shift in pure-tone thresholds in the implant ear for the majority of subjects, in cases of asymmetry, it is recommended that the poorer ear be implanted. After surgery, the majority of subjects did not perceive an added benefit from continued use of their contralateral hearing aid.

Results from a pilot study using the nucleus CI24M/SP5 cochlear implant system.

OBJECTIVE: To conduct a pilot study in adults with the Nucleus CI24M/SP5 cochlear implant system. PATIENTS AND METHODS: Eight postlingually deafened adults who had received little or no benefit from conventional hearing aids, equipped with the Nucleus CI24M/SP5 cochlear implant system. RESULTS AND CONCLUSIONS: The results indicate that most of the subjects were able to perform well in speech recognition tests. The test performances appeared to be strongly affected by the duration of deafness. The speech processor's four user-selectable program memories have been extremely useful for the subjects to evaluate variations to the speech coding strategies in ordinary surroundings outside of the laboratory. The telemetry functions of the new implant provide a set of useful clinical and research tools for gathering greater insights into the in-situ operation of the implant.

Electrodographic analysis and field evaluation of the Speak coding strategy.

The Speak speech-coding strategy for the Nucleus Minisystem-22 cochlear implant continuously analyzes the speech signal using 20 digitally programmable band-pass filters and presents up to 10 spectral maxima to the implanted electrodes. To analyze the performance of this system for a variety of speech sounds in quiet and noise, the stimulation patterns of the implanted electrode array were reconstructed from the transmitted radio frequency signals by software as electrodograms and compared to electrodograms generated by other speech-coding strategies, as well as to the spectrograms of the input signals. The performance with the Speak strategy relative to that with the Multipeak (Mpeak) speech-processing strategy was also evaluated in a field trial study with 20 native German-speaking cochlear implant users from four European implant centers, involving a variety of auditory perceptual tasks in an ABAB paradigm over a 12-week period. Vowel, consonant, and monosyllable word tests, as well as sentence tests in quiet and noise, were conducted. Significant differences in group mean scores for most speech recognition subtests were obtained for the Speak versus the Mpeak strategy, with the largest overall improvements observed for the sentence tests in noisy conditions.

Glide psychophysics and related Mpeak and Speak speech performance.

Speech test results have indicated that improvements in speech comprehension can be achieved by means of coding strategies with high pulse rates. A possible effect of using high rates to encode speech information is that temporal information such as formant transitions could be better represented in the resulting electrode activity. A psychophysical study involving 4 cochlear implant users was carried out to observe the effect of various carrier pulse rates on the absolute identification of stimuli with a transient electrode trajectory. Also, the duration of the trajectory was varied. The results from this study indicated, first, that the trajectory identification became progressively more difficult as the duration of the trajectory was shortened. The identification score generally deteriorated much faster at a lower rate (100 pulses per second [pps]) than at higher rates (300 and 500 pps) with decreasing transient duration. The higher two pulse rates, 300 pps and 500 pps, yielded results similar to one another for longer (500 and 300 milliseconds) transient durations, but the identification of shorter (100 and 50 milliseconds) transient durations was better at 500 pps than at 300 pps. The implication is that higher carrier pulse rates are likely to be able to transmit short transient information better than lower ones. A comparison with speech test results using the Speak (spectral peak) speech-coding strategy shows that the place of articulation feature is significantly improved when compared to the slower-rate Mpeak (Multipeak) pitch-synchronous strategy.

Multicentric field evaluation of a new speech coding strategy for cochlear implants.

In a multicentric study involving 4 European cochlear implant centers, the speech perception abilities of 20 native German-speaking individuals implanted with the Nucleus 22 Channel Cochlear Implant System when using a new spectral peak (SPEAK) speech coding strategy were investigated. This strategy continuously analyzes the speech signal using 20 digital programmable bandpass filters and presents up to 10 spectral maxima to the 22 implanted electrodes. Each subject's performance on a variety of auditory perceptual tasks was evaluated with the experimental encoder (SPEAK), relative to his or her performance in a reference condition. An ABAB experimental design was used whereby each strategy was reversed and replicated. The reference levels of auditory performance were established using the multipeak (MPEAK) speech-processing strategy of the Nucleus speech processor. Only subjects who achieved open-set monosyllable word recognition in the reference condition were included in this study. Significant differences in group mean scores for most speech recognition subtests were obtained for the SPEAK versus the MPEAK strategy. The largest overall improvements were observed for the sentence tests under noisy conditions.

[Cochlear implants for children: technological prerequisites and practical experiences in audiologic rehabilitation]. / Cochlearimplantate bei Kindern: technologische Voraussetzungen und praktische Erfahrungen bei der audiologischen Rehabilitation.

Prerequisites for the use of cochlear implants in children are technical reliability and safety of the devices as well as their efficacy in providing useful auditory information. The actual state of technology fulfills those requirements which is documented with examples from the literature as well as own practical experiences.

Speech encoding strategies for multielectrode cochlear implants: a digital signal processor approach.

The following processing strategies have been implemented on an experimental laboratory system of a cochlear implant digital speech processor (CIDSP) for the Nucleus 22-channel cochlear prosthesis. The first approach (PES, Pitch Excited Sampler) is based on the maximum peak channel vocoder concept whereby the time-varying spectral energy of a number of frequency bands is transformed into electrical stimulation parameters for up to 22 electrodes. The pulse rate at any electrode is controlled by the voice pitch of the input speech signal. The second approach (CIS, Continuous Interleaved Sampler) uses a stimulation pulse rate which is independent of the input signal. The algorithm continuously scans all specified frequency bands (typically between four and 22) and samples their energy levels. As only one electrode can be stimulated at any instance of time, the maximally achievable rate of stimulation is limited by the required stimulus pulse widths (determined individually for each subject) and some additional constraints and parameters. A number of variations of the CIS approach have, therefore, been implemented which either maximize the number of quasi-simultaneous stimulation channels or the pulse rate on a reduced number of electrodes. Evaluation experiments with five experienced cochlear implant users showed significantly better performance in consonant identification tests with the new processing strategies than with the subjects' own wearable speech processors; improvements in vowel identification tasks were rarely observed. Modifications of the basic PES- and CIS strategies resulted in large variations of identification scores. Information transmission analysis of confusion matrices revealed a rather complex pattern across conditions and speech features. Optimization and fine-tuning of processing parameters for these coding strategies will require more data both from speech identification and discrimination evaluations and from psychophysical experiments.

Digital signal processing (DSP) applications for multiband loudness correction digital hearing aids and cochlear implants.

Single-chip digital signal processors (DSPs) allow the flexible implementation of a large variety of speech analysis, synthesis, and processing algorithms for the hearing impaired. A series of experiments was carried out to optimize parameters of the adaptive beamformer noise reduction algorithm and to evaluate its performance in realistic environments with normal-hearing and hearing-impaired subjects. An experimental DSP system has been used to implement a multiband loudness correction (MLC) algorithm for a digital hearing aid. Speech tests in quiet and noise with 13 users of conventional hearing aids demonstrated significant improvements in discrimination scores with the MLC algorithm. Various speech coding strategies for cochlear implants were implemented in real time on a DSP laboratory speech processor. Improved speech discrimination performance was achieved with high-rate stimulation. Hybrid strategies incorporating speech feature detectors and complex decision algorithms are currently being investigated.