Electrical Dynamic Range Research Articles

Experienced Adult Cochlear Implant Users Show Improved Speech Recognition When Target Fitting Parameters Are Applied.

The aim of the present study was to investigate whether prediction models built by de Graaff et al. (2020) can be used to improve speech recognition in experienced adult postlingual implanted Cochlear CI users. de Graaff et al. (2020) found relationships between elevated aided thresholds and a not optimal electrical dynamic range (<50 CL or >60 CL), and poorer speech recognition in quiet and in noise. The primary hypothesis of the present study was that speech recognition improves both in quiet and in noise when the sound processor is refitted to match targets derived from the prediction models from de Graaff et al. (2020). A second hypothesis was that subjectively, most of the CI users would find the new setting too loud because of an increase in C levels, and therefore, prefer the old settings. A within-participant repeated measures design with 18 adult Cochlear CI users was used. T- and C-levels were changed to "optimized settings," as predicted by the model of de Graaff et al. (2020). Aided thresholds, speech recognition in quiet, and speech recognition in noise were measured with the old settings and after a 4-week acclimatization period with the optimized settings. Subjective benefit was measured using the Device Oriented Subjective Outcome Scale questionnaire. The mean electrical dynamic range changed from 41.1 (SD = 6.6) CL to 48.6 (SD = 3.0) CL. No significant change in aided thresholds was measured. Speech recognition improved for 16 out of 18 participants and remained stable for 2 participants. Average speech recognition scores in quiet significantly improved by 4.9% (SD = 3.8%). No significant change for speech recognition in noise was found. A significant improvement in subjective benefit was found for one of the Device Oriented Subjective Outcome subscales (speech cues) between the old and optimized settings. All participants chose to keep the optimized settings at the end of the study. We were able to improve speech recognition in quiet by optimizing the electrical dynamic range of experienced adult CI users, according to the prediction models built by de Graaff et al. (2020). There was no significant change in aided thresholds nor in speech recognition in noise. The findings of the present study suggest that improved performance for speech recognition in quiet in adult Cochlear CI users can be achieved by setting the dynamic range as close as possible to values between 50 and 60 CL when the volume level is at 10.

The relation between cochlear implant programming levels and speech perception performance in post-lingually deafened adults: a data-driven approach

PurposeProgramming a cochlear implant (fitting) is an essential part of a user’s post-implantation journey, defining how sound will be translated into electrical stimulation and aiming to provide optimal speech perception outcomes. Currently, there are no established, evidence-based guidelines for fitting cochlear implant users, leading to a high degree of variability in fitting practices, users’ parameters, and probably outcomes. In this study a data-driven approach is used to retrospectively investigate the relation between cochlear implant fitting parameters and speech perception outcomes in post-lingually deafened adults.Methods298 data points corresponding to fitting parameters and speech audiometry test results for the same number of adult, post-lingually deafened, experienced CI users were analyzed. Correlation analysis was performed, after which parameters from the top-scoring and bottom-scoring tertiles were compared via the Mann–Whitney–Wilcoxon u test.ResultsWeak correlations between dynamic range and speech audiometry outcomes were identified, having p values lower than (albeit close to) 0.05. A significant (p < 0.05) difference in electrical dynamic range (the difference between the minimum and maximum amount of current which may be delivered by each electrode) was found, with top-scoring subjects having on average a wider dynamic range.ConclusionThe association between dynamic range and speech perception outcomes shown in this retrospective study highlights the need for deeper investigation into evidence-driven fitting. It might be a first step in the direction of evidence-based fitting, minimizing variability in outcomes for cochlear implant users and helping mitigate the issue of unexplained low performance.

Machine Learning and Cochlear Implantation: Predicting the Post-Operative Electrode Impedances

Cochlear implantation is the common treatment for severe to profound sensorineural hearing loss if there is no benefit from hearing aids. Measuring the electrode impedance along the electrode array at different time points after surgery is crucial in verifying the electrodes’ status, determining the compliance levels, and helping to identify the electric dynamic range. Increased impedance values without proper reprogramming can affect the patient’s performance. The prediction of acceptable levels of electrode impedance at different time points after the surgery could help clinicians during the fitting sessions through a comparison of the predicted with the measured levels. Accordingly, clinicians can decide if the measured levels are within the predicted normal range or not. In this work, we used a dataset of 80 pediatric patients who had received cochlear implants with the MED-EL FLEX 28 electrode array. We predicted the impedance of the electrode arrays in each channel at different time points: at one month, three months, six months, and one year after the date of surgery. We used different machine learning algorithms such as linear regression, Bayesian linear regression, decision forest regression, boosted decision tree regression, and neural networks. The used features include the patient’s age and the intra-operative electrode impedance at different electrodes. Our results indicated that the best algorithm varies depending on the channel, while the Bayesian linear regression and neural networks provide the best results for 75% of the channels. Furthermore, the accuracy level ranges between 83% and 100% in half of the channels one year after the surgery, when an error range between 0 and 3 KΩ is defined as an acceptable threshold. Moreover, the use of the patient’s age alone can provide the best prediction results for 50% of the channels at six months or one year after surgery. This reflects that the patient’s age could be a predictor of the electrode impedance after the surgery.

Electrical Field Interactions during Adjacent Electrode Stimulations: eABR Evaluation in Cochlear Implant Users.

The present study investigates how electrically evoked Auditory Brainstem Responses (eABRs) can be used to measure local channel interactions along cochlear implant (CI) electrode arrays. eABRs were recorded from 16 experienced CI patients in response to electrical pulse trains delivered using three stimulation configurations: (1) single electrode stimulations (E11 or E13); (2) simultaneous stimulation from two electrodes separated by one (En and En+2, E11 and E13); and (3) stimulations from three consecutive electrodes (E11, E12, and E13). Stimulation level was kept constant at 70% electrical dynamic range (EDR) on the two flanking electrodes (E11 and E13) and was varied from 0 to 100% EDR on the middle electrode (E12). We hypothesized that increasing the middle electrode stimulation level would cause increasing local electrical interactions, reflected in characteristics of the evoked compound eABR. Results show that group averaged eABR wave III and V latency and amplitude were reduced when stimulation level at the middle electrode was increased, in particular when stimulation level on E12 reached 40, 70, and 100% EDR. Compound eABRs can provide a detailed individual quantification of electrical interactions occurring at specific electrodes along the CI electrode array. This approach allows a fine determination of interactions at the single electrode level potentially informing audiological decisions regarding mapping of CI systems.

Effects of number of maxima and electrical dynamic range on speech-in-noise perception with an “n-of-m” cochlear-implant strategy

Cochlear implant (CI) recipients face great challenges in speech-in-noise recognition, partially due to the fact that only temporal envelopes from a limited number of bands are preserved in most CI signal processing strategies. In “n-of-m” strategies (e.g., the Advanced Combinational Encoder, ACE), the number of maxima (nmax) and electrical dynamic range (EDR) are two essential parameters that may affect the envelope representation and further influence speech perception. Speech recognition can be improved by optimizing parameter settings in CI programming. To investigate the effects of nmax and EDR on speech-in-noise perception, Mandarin speech reception thresholds (SRTs) in babble noise were measured in CI recipients using ACE. The nmax was set to 2, 4, 6, 8, and 16. The EDR was set to the base EDR (i.e., participants’ clinical EDR) and 50 % EDR (i.e., 50 %-compressed base EDR). Results showed that: 1) there was no significant interaction effect between nmax and EDR, 2) SRTs with nmax = 2, 4, and 16 were significantly higher (or worse) than those with moderate nmax (6–8), 3) narrower EDRs significantly lead to higher SRTs. Simulation experiments using a Gaussian-Enveloped Tones Vocoder in normal-hearing listeners were also conducted and provided both supportive and additional observations to the CI results. This study suggests that, in CI programming, nmax and EDR are two independent influencing factors. Large nmax (e.g., 16) is not recommended as it may harm speech intelligibility in noisy environments, and inaccurate EDR measurements should be avoided.

Perceptual Loudness Growth in Cochlear Implant Users

Purpose: Despite a growing number of cochlear implant (CI) studies, little attention has been given to loudness perception. The overall purpose of this study is to obtain the perceptual loudness growth from CI users and systematically investigate it with other relevant variables.Methods: Fourteen CI users and 14 normal hearing (NH) adults participated in this study. Loudness growth functions were obtained using three warble tones presented at 500 Hz, 1 kHz, and 4 kHz. Sentence recognition tests were implemented under favorable and adverse noise conditions. Mapping parameters including T-level, C-level, and electrical dynamic range were analyzed in conjunction with outcomes from the loudness growth.Results: The loudness growth curves for CI group were sharper than those for NH group. CI group showed a narrower acoustic dynamic range than NH group. There was no significant relationship between acoustic dynamic range and electrical dynamic range for CI users. Sentence recognition scores in adverse noise conditions were associated with electrical dynamic range in CI users. In NH group, a significant positive relationship was found between sentence recognition scores in adverse condition and acoustic dynamic range.Conclusion: This study showed that the perceptual loudness growth of CI users is not identical to that of NH adults, due to the unique way of signal processing mechanisms. Acoustic dynamic range for CI users seems affected by gain control algorithms. The adjusting mapping parameters associated with loudness may improve speech perception performance regardless of the dynamic range of CIs.

Optical Waveguide Electric Field Sensor Based on Dual Parallel Mach-Zehnder Interferometer

Integrated optical waveguide sensor has characteristics of good insulation, broadband response and small size. A LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (LN) integrated optical waveguide sensor based on a dual parallel asymmetric Mach-Zehnder interferometer (DAMZI) and segmented electrode is designed, fabricated and experimentally demonstrated. By using the DAMZI with segmented electrode fabricated between the two straight waveguide arms, a push-pull modulation is generated, yielding a pair of differential signals are formed at the two outputs of the sensor. Thus based on the differential effect of the balanced photo detection (PD) at the receiving end, the noise is suppressed while the signal is enhanced. The noise floor, minimum detectable electric field, and input/output characteristics of the sensor are measured and compared with those of the sensor with single PD. Experiment results demonstrate that in comparison to the sensor with single PD, the noise floor of the sensor with balanced PD is reduced by about 6 dB while the minimum detectable electric field is reduced by about 18 dB. Besides, in the time domain, the minimum detectable electric field and dynamic range of the sensor are 12.5 V/m and 47 dB respectively. The frequency response variation is within ±1 dB from 9 kHz to 340 MHz, and the temperature stability variation is less than ±0.3 dB with the ambient temperature changed from 18 °C to 28 °C within 19 hours. All these results demonstrate that the sensor has powerful potential capability to be used for measuring the weaker electric field in the electromagnetic compatibility (EMC) area.

Stapedius reflex evoked in free sound field in cochlear implant users compared to normal-hearing listeners

Objective To determine the relation between stapedius reflex thresholds in cochlear implant users evoked once through direct electric stimulation on single channels (ESRT) and once through acoustic stimulation in free sound field. For comparison, stapedius reflex thresholds were obtained in free sound field in a normal-hearing control group. Design For each participant a new ESRT-based fitting was created. Stapedius reflex thresholds were obtained for this new fitting in free sound field for different loudness adjustments. Acoustic stimuli for eliciting the stapedius reflex were narrow band noise signals covering the audiometric frequency range. Study sample N = 29 experienced CI users (34 ears) and N = 10 normal hearing listeners. Results ESRT-based fitting resulted in different stapedius reflex behaviour compared to normal-hearing listeners. A frequency dependence was observed. Stapedius reflex thresholds decreased with increasing centre frequencies of acoustic narrow band noise stimuli. A linear relation between upper stimulation levels on the implant channels and corresponding stapedius reflex thresholds evoked in free sound field was found. Conclusion The found correlation may be a guideline for adjusting the electrical dynamic range during cochlear implant fitting. This allows the implant system to mimic the natural reflex behaviour in the best possible way and potentially avoid overstimulation.

Examining spectral and intensity resolution in web-based vocoder simulations of electric hearing

The poor spectral resolution in current cochlear implants contributes to the difficulty implant users face when trying to listen in noisy backgrounds. Recent work examining measures of spectral resolution and speech perception in normal-hearing and cochlear-implant listeners found that the amount of simulated spectral resolution producing similar speech-in-noise performance between groups resulted in poorer performance for the normal-hearing group on spectral-ripple detection and discrimination tasks. The results suggest that simulating poorer spectral resolution alone is not sufficient to explain implant user performance. Spectral-ripple detection performance likely reflects both spectral- and intensity-resolution, but few vocoder simulations utilize implant-like intensity resolution. In this study, a vocoder processing strategy simulating both electric field spread and dynamic range limitations was used to evaluate performance of normal-hearing and cochlear-implant listeners on speech-in-noise and spectral-resolution tasks. Data were collected using a novel online remote testing platform developed implemented with the MATLAB Web App Server. A comparison of results between groups highlights the implications of including psychophysically measured estimates of cochlear-implant performance in acoustic simulations of electric hearing. [Work supported by NIH grant R01DC012262.]

Influence of systematic variations of the stimulation profile on responses evoked with a vestibular implant prototype in humans

Objective. To explore the impact of different electrical stimulation profiles in human recipients of the Geneva-Maastricht vestibular implant prototypes. Approach. Four implanted patients were recruited for this study. We investigated the relative efficacy of systematic variations of the electrical stimulus profile (phase duration, pulse rate, baseline level, modulation depth) in evoking vestibulo-ocular (eVOR) and perceptual responses. Main results. Shorter phase durations and, to a lesser extent, slower pulse rates allowed maximizing the electrical dynamic range available for eliciting a wider range of intensities of vestibular percepts. When either the phase duration or the pulse rate was held constant, current modulation depth was the factor that had the most significant impact on peak velocity of the eVOR. Significance. Our results identified important parametric variations that influence the measured responses. Furthermore, we observed that not all vestibular pathways seem equally sensitive to the electrical stimulus when the electrodes are placed in the semicircular canals and monopolar stimulation is used. This opens the door to evaluating new stimulation strategies for a vestibular implant, and suggests the possibility of selectively activating one vestibular pathway or the other in order to optimize rehabilitation outcomes.

A Site-Selection Strategy Based on Polarity Sensitivity for Cochlear Implants: Effects on Spectro-Temporal Resolution and Speech Perception

ABSTRACTThresholds of asymmetric pulses presented to cochlear implant (CI) listeners depend on polarity in a way that differs across subjects and electrodes. It has been suggested that lower thresholds for cathodic-dominant compared to anodic-dominant pulses reflect good local neural health. We evaluated the hypothesis that this polarity effect (PE) can be used in a site-selection strategy to improve speech perception and spectro-temporal resolution. Detection thresholds were measured in eight users of Advanced Bionics CIs for 80-pps, triphasic, monopolar pulse trains where the central high-amplitude phase was either anodic or cathodic. Two experimental MAPs were then generated for each subject by deactivating the five electrodes with either the highest or the lowest PE magnitudes (cathodic minus anodic threshold). Performance with the two experimental MAPs was evaluated using two spectro-temporal tests (Spectro-Temporal Ripple for Investigating Processor EffectivenesS (STRIPES; Archer-Boyd et al. in J Acoust Soc Am 144:2983–2997, 2018) and Spectral-Temporally Modulated Ripple Test (SMRT; Aronoff and Landsberger in J Acoust Soc Am 134:EL217–EL222, 2013)) and with speech recognition in quiet and in noise. Performance was also measured with an experimental MAP that used all electrodes, similar to the subjects’ clinical MAP. The PE varied strongly across subjects and electrodes, with substantial magnitudes relative to the electrical dynamic range. There were no significant differences in performance between the three MAPs at group level, but there were significant effects at subject level—not all of which were in the hypothesized direction—consistent with previous reports of a large variability in CI users’ performance and in the potential benefit of site-selection strategies. The STRIPES but not the SMRT test successfully predicted which strategy produced the best speech-in-noise performance on a subject-by-subject basis. The average PE across electrodes correlated significantly with subject age, duration of deafness, and speech perception scores, consistent with a relationship between PE and neural health. These findings motivate further investigations into site-specific measures of neural health and their application to CI processing strategies.

Electrical dynamic range is only weakly associated with auditory performance and speech recognition in long-term users of cochlear implants

ObjectiveThe electrical dynamic range (EDR) has been suggested to be related to auditory performance in cochlear implant (CI) users. However, few reports have evaluated postlingual CI users who have used CIs for long periods in comparison with prelingual CI users. Here, we evaluated auditory perception and speech performance in terms of the EDR in long-term CI users. The EDR, and auditory and speech performances, were compared between pre- and post-lingual CI users. MethodsWe enrolled all patients who received CIs from April 2000 to December 2010 at Seoul National University Hospital, and who had ≥5 years of experience with CIs. The EDRs affording subjective responses at the threshold level (T-level) and comfortable level (C-level) were analyzed in terms of their relationships with pure tone audiometry levels, speech evaluation scores, including those on the Phonetically Balanced (PB) Word List test, vowel and consonant tests, a sentence test, and the Korean version of the Central Institute for the Deaf (K-CID) test; we also calculated Category in Auditory Performance (CAP) scores. ResultsWe found no significant difference in the average EDR, CAP, K-CID, PB word, consonant, or vowel scores between pre- and post-lingual CI users. The EDR was weakly associated with the PB word (P = 0.003, r = 0.462) and consonant scores (P = 0.005, r = 0.438). Other speech evaluations, such as the CAP, K-CID, and vowel scores, were not significantly associated with the EDR T-level. We found no association between pure tone thresholds at 0.5, 1, or 2 kHz, and the speech evaluation scores or EDRs of low-, middle-, or high-frequency channels. ConclusionsThe EDR was only weakly associated with speech performance, such as scores on consonant and PB word tests in long-term CI users, irrespective of pre- or post-lingual deafness status.

Auditory Performance and Electrical Stimulation Measures in Cochlear Implant Recipients With Auditory Neuropathy Compared With Severe to Profound Sensorineural Hearing Loss.

The aim of the study was to compare auditory and speech outcomes and electrical parameters on average 8 years after cochlear implantation between children with isolated auditory neuropathy (AN) and children with sensorineural hearing loss (SNHL). The study was conducted at a tertiary, university-affiliated pediatric medical center. The cohort included 16 patients with isolated AN with current age of 5 to 12.2 years who had been using a cochlear implant for at least 3.4 years and 16 control patients with SNHL matched for duration of deafness, age at implantation, type of implant, and unilateral/bilateral implant placement. All participants had had extensive auditory rehabilitation before and after implantation, including the use of conventional hearing aids. Most patients received Cochlear Nucleus devices, and the remainder either Med-El or Advanced Bionics devices. Unaided pure-tone audiograms were evaluated before and after implantation. Implantation outcomes were assessed by auditory and speech recognition tests in quiet and in noise. Data were also collected on the educational setting at 1 year after implantation and at school age. The electrical stimulation measures were evaluated only in the Cochlear Nucleus implant recipients in the two groups. Similar mapping and electrical measurement techniques were used in the two groups. Electrical thresholds, comfortable level, dynamic range, and objective neural response telemetry threshold were measured across the 22-electrode array in each patient. Main outcome measures were between-group differences in the following parameters: (1) Auditory and speech tests. (2) Residual hearing. (3) Electrical stimulation parameters. (4) Correlations of residual hearing at low frequencies with electrical thresholds at the basal, middle, and apical electrodes. The children with isolated AN performed equally well to the children with SNHL on auditory and speech recognition tests in both quiet and noise. More children in the AN group than the SNHL group were attending mainstream educational settings at school age, but the difference was not statistically significant. Significant between-group differences were noted in electrical measurements: the AN group was characterized by a lower current charge to reach subjective electrical thresholds, lower comfortable level and dynamic range, and lower telemetric neural response threshold. Based on pure-tone audiograms, the children with AN also had more residual hearing before and after implantation. Highly positive coefficients were found on correlation analysis between T levels across the basal and midcochlear electrodes and low-frequency acoustic thresholds. Prelingual children with isolated AN who fail to show expected oral and auditory progress after extensive rehabilitation with conventional hearing aids should be considered for cochlear implantation. Children with isolated AN had similar pattern as children with SNHL on auditory performance tests after cochlear implantation. The lower current charge required to evoke subjective and objective electrical thresholds in children with AN compared with children with SNHL may be attributed to the contribution to electrophonic hearing from the remaining neurons and hair cells. In addition, it is also possible that mechanical stimulation of the basilar membrane, as in acoustic stimulation, is added to the electrical stimulation of the cochlear implant.

Suprathreshold compound action potential amplitude as a measure of auditory function in cochlear implant users

Electrically evoked compound action potential (eCAP) amplitudes elicited at suprathreshold levels were assessed as a measure of the effectiveness of cochlear implant (CI) stimulation. Twenty-one individuals participated; one was excluded due to facial stimulation during eCAP testing. For each participant, eCAPs were elicited with stimulation from seven electrodes near the upper limit of the individual's electrical dynamic range. A reduced-channel CI program was created using those same seven electrodes, and participants performed a vowel discrimination task. Consistent with previous reports, eCAP amplitudes varied across tested electrodes; the profiles were unique to each individual. In 6 subjects (30%), eCAP amplitude variability was partially explained by the impedance of the recording electrode. The remaining amplitude variability within subjects, and the variability observed across subjects could not be explained by recording electrode impedance. This implies that other underlying factors, such as variations in neural status across the array, are responsible. Across-site mean eCAP amplitude was significantly correlated with vowel discrimination scores (r2 = 0.56). A single eCAP amplitude measured from the middle of the array was also significantly correlated with vowel discrimination, but the correlation was weaker (r2 = 0.37), though not statistically different from the across-site mean. Normalizing each eCAP amplitude by its associated recording electrode impedance did not improve the correlation with vowel discrimination (r2 = 0.52). Further work is needed to assess whether combining eCAP amplitude with other measures of the electrode-neural interface and/or with more central measures of auditory function provides a more complete picture of auditory function in CI recipients.

Effects of Threshold Adjustment on Speech Perception in Nucleus Cochlear Implant Recipients.

The objective of this study was to investigate the impact of using smaller and larger electric dynamic ranges on speech perception, aided thresholds, and subjective preference in cochlear implant (CI) subjects with the Nucleus device. Data were collected from 19 adults using the Nucleus CI system. Current levels (CLs) used to set threshold stimulation levels (T-levels) were set above or below the measured hearing thresholds to create smaller or larger electric output dynamic ranges, respectively, whereas the upper stimulation level (C-level) was fixed. The base (unadjusted) condition was compared against two conditions with higher T-levels (compression), by 30% and 60% of the measured hearing dynamic range, and three conditions with lower T-levels (expansion), by 30%, 60%, and 90% of the measured hearing dynamic range. For each subject, the clinical CL units were adjusted on each electrode to achieve these conditions. The slow-acting dynamic acoustic gains of ADRO and Autosensitivity™ were enabled. Consonant-nucleus-consonant (CNC) word scores were measured in quiet at 50 dB and 60 dB SPL presentation levels. The signal-to-noise ratios (SNRs) for 50% understanding of sentences in noise were measured for sentences presented at 55 dB and 65 dB SPL in 4-talker babble noise. Free-field aided thresholds were measured at octave frequencies using frequency-modulated (warble) tones. Thirteen of the 19 subjects had take-home experience with the base and experimental conditions and provided subjective feedback via a questionnaire. There were no significant effects of 30% expansion and 30% compression of the electric dynamic range on scores for words in quiet and SNRs for sentences in noise, at the two presentation levels. There was a significant decrement in scores for words in quiet for 60% and 90% expansion compared with the base condition at the 50 dB and 60 dB SPL presentation levels. The score decrement was much less at 60 dB SPL. For the 50 dB SPL presentation level, the decrements in word scores at 60% and 90% expansion were linearly related to the reduction in CL units required to achieve these experimental conditions, with a greater decrement in scores for a larger CL change. There was a significant increase in SNR for sentences in noise for 60% compression compared with the base condition at the 55 dB and 65 dB SPL presentation levels. There was also a significant increase in SNR for sentences at the 55 dB SPL presentation level for 90% expansion. Aided thresholds were significantly elevated for the three expansion conditions compared with the base condition, although the mean elevation at 30% expansion was only 4 dB. The questionnaire results showed no clear preference for any condition; however, subjects reported a reduced preference for the extreme compression (60%) and expansion (90%) conditions. The results showed that CI subjects using the Nucleus sound processor had no significant change in performance or preference for adjustments in T-levels by ±30% of the hearing dynamic range. In quiet, speech perception scores were reduced for the more marked expansion (60% and 90%) conditions, whereas in noise, performance was poorer for the highest compression (60%) condition. Across subjects, the decrement in scores for words at 50 dB SPL for the 60% and 90% expansion conditions was related to the changes in CL units required for these conditions, with greater decrements for larger changes in levels.

The effect of fluctuating maskers on speech understanding of high-performing cochlear implant users

Objective: The present study evaluated whether the poorer baseline performance of cochlear implant (CI) users or the technical and/or physiological properties of CI stimulation are responsible for the absence of masking release. Design: This study measured speech reception thresholds (SRTs) in continuous and modulated noise as a function of signal to noise ratio (SNR). Study sample: A total of 24 subjects participated: 12 normal-hearing (NH) listeners and 12 subjects provided with recent MED-EL CI systems. Results: The mean SRT of CI users in continuous noise was −3.0 ± 1.5 dB SNR (mean ± SEM), while the normal-hearing group reached −5.9 ± 0.8 dB SNR. In modulated noise, the difference across groups increased considerably. For CI users, the mean SRT worsened to −1.4 ± 2.3 dB SNR, while it improved for normal-hearing listeners to −18.9 ± 3.8 dB SNR. Conclusions: The detrimental effect of fluctuating maskers on SRTs in CI users shown by prior studies was confirmed by the current study. Concluding, the absence of masking release is mainly caused by the technical and/or physiological properties of CI stimulation, not just the poorer baseline performance of many CI users compared to normal-hearing subjects. Speech understanding in modulated noise was more robust in CI users who had a relatively large electrical dynamic range.

Vestibular Implants: 8 Years of Experience with Electrical Stimulation of the Vestibular Nerve in 11 Patients with Bilateral Vestibular Loss

Background: The concept of the vestibular implant is primarily to artificially restore the vestibular function in patients with a bilateral vestibular loss (BVL) by providing the central nervous system with motion information using electrical stimulation of the vestibular nerve. Our group initiated human trials about 10 years ago. Methods: Between 2007 and 2013, 11 patients with a BVL received a vestibular implant prototype providing electrodes to stimulate the ampullary branches of the vestibular nerve. Eye movements were recorded and analyzed to assess the effects of the electrical stimulation. Perception induced by electrical stimulation was documented. Results: Smooth, controlled eye movements were obtained in all patients showing that electrical stimulation successfully activated the vestibulo-ocular pathway. However, both the electrical dynamic range and the amplitude of the eye movements were variable from patient to patient. The axis of the response was consistent with the stimulated nerve branch in 17 out of the 24 tested electrodes. Furthermore, in at least 1 case, the elicited eye movements showed characteristics similar to those of compensatory eye movements observed during natural activities such as walking. Finally, diverse percepts were reported upon electrical stimulation (i.e., rotatory sensations, sound, tickling or pressure) with intensity increasing as the stimulation current increased. Conclusions: These results demonstrate that electrical stimulation is a safe and effective means to activate the vestibular system, even in a heterogeneous patient population with very different etiologies and disease durations. Successful tuning of this information could turn this vestibular implant prototype into a successful artificial balance organ.

Improvement of cochlear implant performance: changes in dynamic range

Abstract Theoretically, a wide input dynamic range (IDR) will capture more of the incoming acoustic signal than a narrow IDR, allowing the cochlear implant (CI) user to hear soft, medium, and loud sound. A narrow IDR may restrict the CI user’s ability to hear soft speech and sound because less of the incoming acoustic signal is being mapped into the CI user′s electrical dynamic range. The overall goal of the study is to provide guidelines for audiologists to efficiently and effectively optimize performance of CI recipients for two difficult listening situations: understanding soft speech and speech in noise. Two variables were studied; the independent variables were IDR and the electric dynamic range of the channels. The dependent variables were six Ling sounds, monosyllabic word test, and speech in noise test. Fourteen patients participated in the study. For each patient, seven programs were created. In each program, dependent variables were assessed in different independent ones. A restricted IDR resulted in poor speech recognition compared with the relatively wide IDR. Subjectively determined T level and most comfortable level (MCL) at the most, not the maximum, comfortable level appears to have a positive effect on both soft sound recognition and speech discrimination. Dynamic range is an important factor -among others- to improve the ability of CI users to understand soft speech as well as speech in noise.

Current focussing in cochlear implants: An analysis of neural recruitment in a computational model

Several multipolar current focussing strategies are examined in a computational model of the implanted human cochlea. The model includes a realistic spatial distribution of cell bodies of the auditory neurons throughout Rosenthal's canal. Simulations are performed of monopolar, (partial) tripolar and phased array stimulation. Excitation patterns, estimated thresholds, electrical dynamic range, excitation density and neural recruitment curves are determined and compared. The main findings are: (I) Current focussing requires electrical field interaction to induce spatially restricted excitation patterns. For perimodiolar electrodes the distance to the neurons is too small to have sufficient electrical field interaction, which results in neural excitation near non-centre contacts. (II) Current focussing only produces spatially restricted excitation patterns when there is little or no excitation occurring in the peripheral processes, either because of geometrical factors or due to neural degeneration. (III) The model predicts that neural recruitment with electrical stimulation is a three-dimensional process; regions of excitation not only expand in apical and basal directions, but also by penetrating deeper into the spiral ganglion. (IV) At equal loudness certain differences between the spatial excitation patterns of various multipoles cannot be simulated in a model containing linearly aligned neurons of identical morphology. Introducing a form of variability in the neurons, such as the spatial distribution of cell bodies in the spiral ganglion used in this study, is therefore essential in the modelling of spread of excitation.This article is part of a Special Issue entitled <Lasker Award>.

A 25-µW All-MOS Potentiostatic Delta-Sigma ADC for Smart Electrochemical Sensors

This paper presents a low-power all-MOS delta-sigma ADC specifically optimized for the potentiostatic biasing and amperometric read-out of electrochemical sensors. The proposed architecture reuses the dynamic properties of the sensor itself to implement a continuous-time mixed electrochemical delta-sigma modulator with minimalist analog circuits fully integrable in purely digital CMOS technologies. A 25-μW smart electrochemical sensor demonstrator integrated in low-cost 1M CMOS technology with Au post-processing is presented. Experimental results show electrical dynamic range values exceeding 10-bit, while electrochemical figures exhibit linearity levels close to R2 = 0.999 combined with RSD <; 15% in terms of reproducibility. A comparative test with commercial potentiostat equipment is also included to qualify the performance of the proposed ADC.