Cochlear Implant: Analysis of the Frequency-to-Place Mismatch with the Table-Based Software OTOPLAN® and Its Influence on Hearing Performance.

OBJECTIVE: The purpose of this study was to compare the originally applied frequency allocation of cochlear implant electrodes assigned by default at the time of activation with a more recent frequency allocation that is anatomy-based by a software called OTOPLAN®. Based on a computed tomography scan of the temporal bone, this software calculates the position of each electrode in the cochlea and its corresponding tonotopic frequency. We also evaluated whether patients with a significant mismatch between these two allocations present poorer speech intelligibility. MATERIALS AND METHODS: Patients who underwent cochlear implantation from 2016 to 2021 at the University Hospital of Liege were included in this retrospective study. We used OTOPLAN® to calculate the tonotopic frequency allocation of each electrode according to its exact position in the cochlear duct. This anatomical frequency mapping was compared with the default frequency mapping at the time of cochlear implant activation. Finally, we compared the mismatch with the patients' auditory performance, represented by the Auditory Capacity Index (ACI). RESULTS: Thirteen patients were included in the study. All patients had a mismatch between the two frequency maps, to a variable extent (200 Hz-1,100 Hz). Frequency shift was significantly inversely correlated with ACI and with the time needed to improve speech intelligibility. CONCLUSION: Our primary results show that patients with a larger mismatch between default frequency mapping and anatomically assigned frequency mapping experience poorer hearing performance and slower adaptation to a cochlear implant.

A state-of-the-art implementation of a binaural cochlear-implant sound coding strategy inspired by the medial olivocochlear reflex.

Cochlear implant (CI) users find it hard and effortful to understand speech in noise with current devices. Binaural CI sound processing inspired by the contralateral medial olivocochlear (MOC) reflex (an approach termed the 'MOC strategy') can improve speech-in-noise recognition for CI users. All reported evaluations of this strategy, however, disregarded automatic gain control (AGC) and fine-structure (FS) processing, two standard features in some current CI devices. To better assess the potential of implementing the MOC strategy in contemporary CIs, here, we compare intelligibility with and without MOC processing in combination with linked AGC and FS processing. Speech reception thresholds (SRTs) were compared for an FS and a MOC-FS strategy for sentences in steady and fluctuating noises, for various speech levels, in bilateral and unilateral listening modes, and for multiple spatial configurations of the speech and noise sources. Word recall scores and verbal response times in a word recognition test (two proxies for listening effort) were also compared for the two strategies in quiet and in steady noise at 5 dB signal-to-noise ratio (SNR) and the individual SRT. In steady noise, mean SRTs were always equal or better with the MOC-FS than with the standard FS strategy, both in bilateral (the mean and largest improvement across spatial configurations and speech levels were 0.8 and 2.2 dB, respectively) and unilateral listening (mean and largest improvement of 1.7 and 2.1 dB, respectively). In fluctuating noise and in bilateral listening, SRTs were equal for the two strategies. Word recall scores and verbal response times were not significantly affected by the test SNR or the processing strategy. Results show that MOC processing can be combined with linked AGC and FS processing. Compared to using FS processing alone, combined MOC-FS processing can improve speech intelligibility in noise without affecting word recall scores or verbal response times.

Speech-in-Noise Recognition With More Realistic Implementations of a Binaural Cochlear-Implant Sound Coding Strategy Inspired by the Medial Olivocochlear Reflex.

OBJECTIVES: Cochlear implant (CI) users continue to struggle understanding speech in noisy environments with current clinical devices. We have previously shown that this outcome can be improved by using binaural sound processors inspired by the medial olivocochlear (MOC) reflex, which involve dynamic (contralaterally controlled) rather than fixed compressive acoustic-to-electric maps. The present study aimed at investigating the potential additional benefits of using more realistic implementations of MOC processing. DESIGN: Eight users of bilateral CIs and two users of unilateral CIs participated in the study. Speech reception thresholds (SRTs) for sentences in competition with steady state noise were measured in unilateral and bilateral listening modes. Stimuli were processed through two independently functioning sound processors (one per ear) with fixed compression, the current clinical standard (STD); the originally proposed MOC strategy with fast contralateral control of compression (MOC1); a MOC strategy with slower control of compression (MOC2); and a slower MOC strategy with comparatively greater contralateral inhibition in the lower-frequency than in the higher-frequency channels (MOC3). Performance with the four strategies was compared for multiple simulated spatial configurations of the speech and noise sources. Based on a previously published technical evaluation of these strategies, we hypothesized that SRTs would be overall better (lower) with the MOC3 strategy than with any of the other tested strategies. In addition, we hypothesized that the MOC3 strategy would be advantageous over the STD strategy in listening conditions and spatial configurations where the MOC1 strategy was not. RESULTS: In unilateral listening and when the implant ear had the worse acoustic signal-to-noise ratio, the mean SRT was 4 dB worse for the MOC1 than for the STD strategy (as expected), but it became equal or better for the MOC2 or MOC3 strategies than for the STD strategy. In bilateral listening, mean SRTs were 1.6 dB better for the MOC3 strategy than for the STD strategy across all spatial configurations tested, including a condition with speech and noise sources colocated at front where the MOC1 strategy was slightly disadvantageous relative to the STD strategy. All strategies produced significantly better SRTs for spatially separated than for colocated speech and noise sources. A statistically significant binaural advantage (i.e., better mean SRTs across spatial configurations and participants in bilateral than in unilateral listening) was found for the MOC2 and MOC3 strategies but not for the STD or MOC1 strategies. CONCLUSIONS: Overall, performance was best with the MOC3 strategy, which maintained the benefits of the originally proposed MOC1 strategy over the STD strategy for spatially separated speech and noise sources and extended those benefits to additional spatial configurations. In addition, the MOC3 strategy provided a significant binaural advantage, which did not occur with the STD or the original MOC1 strategies.

Microphone directionality and wind noise reduction enhance speech perception in users of the MED-EL SONNET audio processor.

Objectives: Speech understanding in noise remains a challenge for many cochlear implant users. To improve this, the SONNET audio processor features three microphone directionality (MD) settings and three wind noise reduction (WNR) settings. The primary aim of this study was to assess if speech understanding in noise and hearing in real life was superior with the SONNET or with the OPUS 2, which does not feature MD or WNR.Methods: 31 of 33 participants completed the study. Speech understanding was assessed in two types of acoustic noise, in wind noise, and in quiet. A 4-speaker setup was used and speech was presented from 0° and noise from 90°, 180°, and 270°. Wind noise was simulated with a fan. Sound quality and hearing-related abilities were assessed via two subjective questionnaires.Results: Speech understanding in acoustic noise with the SONNET was significantly better or equal to than with the OPUS 2. Speech understanding in wind with the OPUS 2 was significantly better than with the SONNET in some settings. Sound quality and hearing-related abilities were both significantly better with the SONNET.Conclusions: The SONNET provides the same or significantly improved speech understanding than the OPUS 2 in quiet and in noise. While OPUS 2 was superior in wind than the SONNET in some settings, this was offset by SONNET's superiority in real-life listening situations. We therefore conclude that the front-end processing of the SONNET provides users with better hearing than does the OPUS 2.

Speech polar plots for different directionality settings of SONNET cochlear implant processor.

Objectives: The newest CI processor from MED-EL company, the SONNET, has two new directional microphone settings. Besides the Omnidirectional microphone mode, it has the possibility to switch to Natural or Adaptive directionality. Both new modes favour perception of sound coming from a front-facing direction compared to sounds from sources at alternate azimuths. Natural directionality mimics the pinna effect of the normal external ear. Design: We undertook to verify the effect of these options in vivo by means of clinical audiological tests. Speech reception thresholds were successively measured for a variety of speech presentation azimuths while keeping the noise azimuths constant. Complete 'Speech Reception Threshold (SRT)-Polar-Plots' were obtained from these data for the Omnidirectional and Natural directionality modes of the SONNET. In addition, one 'SRT-point' was also measured in the 'Adaptive' mode for speech coming from 45° azimuth. Study sample: A group of 13 adult CI recipients participated. Only one of these subjects had previous experience with the SONNET processor. Results: Complete 'SRT-Polar-Plots' could be measured in Natural and Omnidirectional modes in CI recipients within an acceptable timeframe. The pinna-following directionality for Natural mode could be confirmed. Median SRT in noise for speech coming from the 45° azimuth speaker was -5.6 dB SNR for Omnidirectional, -9.1 dB SNR for Natural and -12.8 dB SNR for Adaptive microphone. Natural and Adaptive significantly improved performance compared to Omnidirectional mode at this optimal azimuth of 45° with a median improvement in SRT of 3.5 and 7.2 dB respectively. Conclusions: A novel audiological method, 'SRT-Polar-Plot', was developed and described. Significant directionality benefits for Natural and Adaptive mode were confirmed in vivo using this technique.

Lateralization of virtual sound sources with a binaural cochlear-implant sound coding strategy inspired by the medial olivocochlear reflex.

Many users of bilateral cochlear implants (BiCIs) localize sound sources less accurately than do people with normal hearing. This may be partly due to using two independently functioning CIs with fixed compression, which distorts and/or reduces interaural level differences (ILDs). Here, we investigate the potential benefits of using binaurally coupled, dynamic compression inspired by the medial olivocochlear reflex; an approach termed "the MOC strategy" (Lopez-Poveda et al., 2016, Ear Hear 37:e138-e148). Twelve BiCI users were asked to localize wideband (125-6000 Hz) noise tokens in a virtual horizontal plane. Stimuli were processed through a standard (STD) sound processing strategy (i.e., involving two independently functioning sound processors with fixed compression) and three different implementations of the MOC strategy: one with fast (MOC1) and two with slower contralateral control of compression (MOC2 and MOC3). The MOC1 and MOC2 strategies had effectively greater inhibition in the higher than in the lower frequency channels, while the MOC3 strategy had slightly greater inhibition in the lower than in the higher frequency channels. Localization was most accurate with the MOC1 strategy, presumably because it provided the largest and less ambiguous ILDs. The angle error improved slightly from 25.3° with the STD strategy to 22.7° with the MOC1 strategy. The improvement in localization ability over the STD strategy disappeared when the contralateral control of compression was made slower, presumably because stimuli were too short (200 ms) for the slower contralateral inhibition to enhance ILDs. Results suggest that some MOC implementations hold promise for improving not only speech-in-noise intelligibility, as shown elsewhere, but also sound source lateralization.

Introducing real-life listening features into the clinical test environment: Part I: Measuring the hearing performance and evaluating the listening effort of individuals with normal hearing.

OBJECTIVE: Controlled clinical test environments are very different from real-life listening situations in which speaker and background noise level variations can hinder a person's ability to hear and follow conversations. This study was performed to evaluate the ability of people with normal hearing to follow a single speaker in the presence of background noise, and to explore relations between those measures and the listeners' subjective assessments, listening effort, and sound quality judgements. METHODS: A group of adults with normal hearing were evaluated using the following battery of tests: (i) Roving Level Test, (ii) the Just Understanding Speech Test, (iii) Performance Perceptual Test, (iv) the Visual Analogue Scale to evaluate listening effort, and (iv) with a sound quality questionnaire. RESULTS: The results show that people with normal hearing tend to accurately estimate their hearing abilities, and both the listening effort required and speech recognition thresholds tend to increase with increasing background noise. DISCUSSION: Implementing a battery of tests that evaluate speech-in-noise listening abilities, listening effort, and subjective hearing perception might provide greater insight into hearing performance than traditional measures. Additionally, the data generated in this study can be used for comparison with measures obtained from hearing impaired and hearing device listeners, and as such, has the potential to guide counselling and rehabilitation to a range of clinical populations. CONCLUSION: The examination of both the self-estimated and verified performance measurements in simulated real-life listening situations can provide audiologists with a comprehensive and realistic profile of a person's hearing performance.

Deep electrode insertion and sound coding in cochlear implants.

Present-day cochlear implants demonstrate remarkable speech understanding performance despite the use of non-optimized coding strategies concerning the transmission of tonal information. Most systems rely on place pitch information despite possibly large deviations from correct tonotopic placement of stimulation sites. Low frequency information is limited as well because of the constant pulse rate stimulation generally used and, being even more restrictive, of the limited insertion depth of the electrodes. This results in a compromised perception of music and tonal languages. Newly available flexible long straight electrodes permit deep insertion reaching the apical region with little or no insertion trauma. This article discusses the potential benefits of deep insertion which are obtained using pitch-locked temporal stimulation patterns. Besides the access to low frequency information, further advantages of deeply inserted long electrodes are the possibility to better approximate the correct tonotopic location of contacts, the coverage of a wider range of cochlear locations, and the somewhat reduced channel interaction due to the wider contact separation for a given number of channels. A newly developed set of strategies has been shown to improve speech understanding in noise and to enhance sound quality by providing a more "natural" impression, which especially becomes obvious when listening to music. The benefits of deep insertion should not, however, be compromised by structural damage during insertion. The small cross section and the high flexibility of the new electrodes can help to ensure less traumatic insertions as demonstrated by patients' hearing preservation rate. This article is part of a Special Issue entitled .

A uniform graphical representation of intensity coding in current-generation cochlear implant systems.

OBJECTIVES: Understanding and predicting the impact of MAP changes on the electrical current delivered at the level of cochlear implant (CI) electrodes is challenging. However, it is an important prerequisite for effectively programming these devices in clinical practice. This article describes a graphical representation to illustrate the intensity-coding behavior of four CI systems (Cochlear, MED-EL, Advanced Bionics, and Neurelec). DESIGN: For this the authors have broken down the intensity coding into two separate transformations: (1) from broadband acoustical input to band limited channel amplitude and (2) the mapping function within a single channel. These functions have been synthesized and presented in a uniform plot across brands. RESULTS: The plot describes the output of a CI channel in response to different input signals. This has been incorporated in an interactive software application that illustrates the different stages of intensity coding and the impact of the relevant fitting parameters for each CI brand. CONCLUSIONS: The plot provides the clinician with an assistive tool to better understand and predict the behavior of CIs, which may lead to more knowledgeable interpretation and CI programming.

Clinical trial results with the MED-EL fine structure processing coding strategy in experienced cochlear implant users.

OBJECTIVES: To assess the subjective and objective performance of the new fine structure processing strategy (FSP) compared to the previous generation coding strategies CIS+ and HDCIS. METHODS: Forty-six adults with a minimum of 6 months of cochlear implant experience were included. CIS+, HDCIS and FSP were compared in speech perception tests in noise, pitch scaling and questionnaires. The randomized tests were performed acutely (interval 1) and again after 3 months of FSP experience (interval 3). The subjective evaluation included questionnaire 1 at intervals 1 and 3, and questionnaire 2 at interval 2, 1 month after interval 1. RESULTS: Comparison between FSP and CIS+ showed that FSP performed at least as well as CIS+ in all speech perception tests, and outperformed CIS+ in vowel and monosyllabic word discrimination. Comparison between FSP and HDCIS showed that both performed equally well in all speech perception tests. Pitch scaling showed that FSP performed at least as well as HDCIS. With FSP, sound quality was at least as good and often better than with HDCIS. CONCLUSIONS: Results indicate that FSP performs better than CIS+ in vowel and monosyllabic word understanding. Subjective evaluation demonstrates strong user preferences for FSP when listening to speech and music.

From electric acoustic stimulation to improved sound coding in cochlear implants.

Research into electric acoustic stimulation (EAS) indicates that performance improves when acoustic stimulation is added to electric stimulation in subjects with residual low-frequency acoustic hearing. Research further indicates that information from the voice fundamental frequency (F(0)) region accounts for the majority of the added speech perception benefit with EAS. This implies that improved frequency coding in the low frequencies could hold great potential for improving performance with cochlear implants (CIs). Results with new speech coding strategies such as fine structure processing indeed indicate that with improved low-frequency coding, at least some of the benefits of EAS can be translated to regular CI users.

Site of cochlear stimulation and its effect on electrically evoked compound action potentials using the MED-EL standard electrode array.

BACKGROUND: The standard electrode array for the MED-EL MAESTRO cochlear implant system is 31 mm in length which allows an insertion angle of approximately 720 degrees . When fully inserted, this long electrode array is capable of stimulating the most apical region of the cochlea. No investigation has explored Electrically Evoked Compound Action Potential (ECAP) recordings in this region with a large number of subjects using a commercially available cochlear implant system. The aim of this study is to determine if certain properties of ECAP recordings vary, depending on the stimulation site in the cochlea. METHODS: Recordings of auditory nerve responses were conducted in 67 subjects to demonstrate the feasibility of ECAP recordings using the Auditory Nerve Response Telemetry (ART) feature of the MED-EL MAESTRO system software. These recordings were then analyzed based on the site of cochlear stimulation defined as basal, middle and apical to determine if the amplitude, threshold and slope of the amplitude growth function and the refractory time differs depending on the region of stimulation. RESULTS: Findings show significant differences in the ECAP recordings depending on the stimulation site. Comparing the apical with the basal region, on average higher amplitudes, lower thresholds and steeper slopes of the amplitude growth function have been observed. The refractory time shows an overall dependence on cochlear region; however post-hoc tests showed no significant effect between individual regions. CONCLUSIONS: Obtaining ECAP recordings is also possible in the most apical region of the cochlea. However, differences can be observed depending on the region of the cochlea stimulated. Specifically, significant higher ECAP amplitude, lower thresholds and steeper amplitude growth function slopes have been observed in the apical region. These differences could be explained by the location of the stimulating electrode with respect to the neural tissue in the cochlea, a higher density, or an increased neural survival rate of neural tissue in the apex. TRIAL REGISTRATION: The Clinical Investigation has the Competent Authority registration number DE/CA126/AP4/3332/18/05.

Incapacitating unilateral tinnitus in single-sided deafness treated by cochlear implantation.

OBJECTIVES: Tinnitus is a well-known, difficult-to-treat symptom of hearing loss. Users of cochlear implants (CIs) have reported a reduction in tinnitus following implantation for bilateral severe-to-profound deafness. This study assessed the effect of electrical stimulation via a CI on tinnitus in subjects with unilateral deafness and ipsilateral tinnitus who underwent implantation in an attempt to treat tinnitus with the CI. METHODS: Twenty-one subjects who complained of severe intractable tinnitus that was unresponsive to treatment received a CI. Tinnitus loudness was measured with a Visual Analog Scale; loudness percepts were recorded with the device activated and deactivated. Tinnitus distress was measured with the Tinnitus Questionnaire before and after implantation. RESULTS: Electrical stimulation via a CI resulted in a significant reduction in tinnitus loudness (mean +/- SD; 1 year after implantation, 2.4 +/- 1.8; 2 years after implantation, 2.5 +/- 1.9; before implantation, 8.5 +/- 1.3). With the device deactivated, tinnitus loudness was still reduced to between 6.1 and 7.0 over 24 months. The Tinnitus Questionnaire revealed a significant positive effect of CI stimulation. CONCLUSIONS: Unilateral tinnitus resulting from single-sided deafness can be treated with electrical stimulation via a CI. The outcomes of this pilot study demonstrate a new method for treatment of tinnitus in select subjects, perhaps an important new indication for cochlear implantation.

Neural tonotopy in cochlear implants: an evaluation in unilateral cochlear implant patients with unilateral deafness and tinnitus.

In cochlear implants, the signal is filtered into different frequency bands and transmitted to electrodes along the cochlea. In this study the frequency-place function for electric hearing was investigated as a means to possibly improve speech coding by delivering information to the appropriate cochlear place. Fourteen subjects with functional hearing in the contralateral ear have been provided with a MED-EL cochlear implant in the deaf ear in order to reduce intractable tinnitus. Pitch scaling experiments were performed using single-electrode, constant-amplitude, constant-rate stimuli in the implanted ear, and acoustic sinusoids in the contralateral ear. The frequency-place function was calculated using the electrode position in the cochlea as obtained from postoperative skull radiographs. Individual frequency-place functions were compared to Greenwood's function in normal hearing. Electric stimulation elicited a low pitch in the apical region of the cochlea, and shifting the stimulating electrode towards the basal region elicited increasingly higher pitch. The frequency-place function did not show a significant shift relative to Greenwood's function. In cochlear implant patients with functional hearing in the non-implanted ear, electrical stimulation produced a frequency-place function that on average resembles Greenwood's function. These results differ from previously derived data.

Frequency discrimination with sequential or simultaneous stimulation in MED-EL cochlear implants.

CONCLUSION: Amplitude weighting using the bell-shaped filter design within the OPUS speech processors allows the creation of pitches intermediate to those of two adjacent electrodes. This mechanism can be used for both sequential and simultaneous stimulation. OBJECTIVES: This paper describes frequency discrimination experiments which are based on amplitude weighting of two adjacent electrodes. The effects of sequential versus simultaneous stimulation of the electrode pair were investigated. MATERIALS AND METHODS: The experiment was performed using a laboratory system emulating the signal processing using bell-shaped filters in the MED-EL speech processors. The system transformed input files (wav-files) into the stimulation data stream which was transmitted to the implant via the OPUS processor coil. Pitch discrimination was assessed for up to three electrode pairs in each subject, using an adaptive test method. Results for sequential stimulation were collected in eight subjects, a comparison between sequential and simultaneous stimulation was made in five subjects. RESULTS: Results show an average frequency discrimination of 8.8% for sequential stimulation and 11.2% for simultaneous stimulation, of the nominal test frequency. Frequency discrimination ability varied across subjects and test electrode pairs. The difference in performance between sequential and simultaneous stimulation was not statistically significant.

MED-EL Cochlear implants: state of the art and a glimpse into the future.

Cochlear implantation is an accepted treatment method for adults and children with severe to profound hearing loss. Confidence in technology has led to changes in individuals who can receive a cochlear implant and changes in expected benefit with a cochlear implant. This article describes the research and development activities at MED-EL, which make possible the implementation of new speech-coding strategies as well as the application of acoustic and electric stimulation via a combined speech processor in MED-EL devices. Research on benefits from bilateral cochlear implantation and electric-acoustic stimulation are also reviewed. Finally, the potential of drug delivery systems is considered as a way to improve cochlear implant outcomes, and results from preliminary evaluations of a hybrid cochlear implant system with drug delivery capabilities are reported.

Investigations into electrically evoked stapedius reflex measures and subjective loudness percepts in the MED-EL COMBI 40+ cochlear implant.

For several years there has been interest in using objective measures to set channel-specific upper programming limits when programming the speech processor of cochlear implant users. The present study aims to add to previous reports by examining correlations between electrically evoked stapedius reflex threshold (ESRT) and a range of psychophysical loudness estimates in a group of 22 adult users of the MED-EL COMBI 40+ system. Thirteen of the 15 subjects (87%) had recordable stapedius reflexes. Psychophysical measures of threshold, maximum comfort level (MCL) and maximum acceptable loudness (MAL) were recorded. Results showed that mean ESRT was closest to the MCL using 500 ms burst ('MCL500'), with MCL50 (MCL using 50 ms burst) and MAL500 some 2dB and MAL50 3dB higher. Correlations between ESRT and the behavioural loudness judgements were highest for MCL500 (R = 0.69, p < 0.001) and slightly less for MAL500. These results confirm the ease of measuring ESRT in a clinical setting and that a high level of confidence can be placed on the use of these measures for setting processor maps in the absence of behavioural data.

Deep electrode insertion in cochlear implants: apical morphology, electrodes and speech perception results.

Morphological examination of the human temporal bone in the apical region supports the benefits of deep electrode insertion. Initiation of spikes on peripheral processes close to the basilar membrane would provide improved channel selectivity during electrical stimulation but recruiting of nerve fibres requires a higher current. A clinical study was performed on 10 users of the MED-EL COMBI 40 + implant to evaluate the effect of the insertion depth of the cochlear implant electrode on speech perception. All subjects were implanted with the standard COMBI 40 + electrode with an insertion depth of > 30 mm. Acute speech tests were carried out in which stimulation was restricted to the apical, middle and basal regions of the cochlea in turn, and using electrode arrangements in which contacts were either distributed over the whole length of the cochlea or concentrated at the basal end, thus mimicking an insertion depth of approximately 20 mm only. The results showed that stimulation of the apical region of the cochlea supports a significant degree of speech understanding, and that distributing the contacts over the whole length of the cochlea improves speech perception in quiet and in noise.