Factors affecting open-set word recognition in adults with cochlear implants

Relationship Between Psychophysical Tuning Curves and Vowel Identification in Noise in Children and Adults With Cochlear Implants

PURPOSE

Perceptual outcomes in cochlear implant (CI) listeners are influenced by the quality of the interface between individual CI electrodes and their target auditory neurons (i.e., electrode-neuron interface [ENI]). Poor ENI increases the likelihood of CI channel interaction, which may lead to the smearing of sound frequency information, reduced spectral resolution, and, thus, errors in identifying speech sounds, particularly when there is background noise. This research note aims to present preliminary data on whether psychophysical tuning curves (PTCs), as a measure of channel interaction and an indirect measure of ENI, relate to vowel identification in noise in children and adults with CIs.

METHOD

PTCs and medial vowel identification in four-talker babble noise were obtained for eight children (12 ears) and eight adults (eight ears) with CIs. PTCs were measured for one electrode in the middle of the array using direct stimulation and a standard two-interval, two-alternative forced choice procedure.

RESULTS

Adults and children with sharper PTCs performed better on vowel identification in noise (F = 6.63, p = .02), demonstrating an association between less channel interaction and better vowel identification in noise in CI listeners irrespective of age. Although no statistically significant difference was found between children and adults in their PTC sharpness, children performed better than adults on vowel identification in noise (F = 5.38, p = .034).

CONCLUSIONS

The findings provide evidence that the sharpness of the PTC on a mid-array electrode is related to vowel identification in noise for CI listeners. Vowel identification in noise and PTC sharpness could be further investigated for use in developing personalized programming strategies that enhance the transmission of spectral cues crucial for recognizing vowel sounds.

Cochlear-implant simulated spectral degradation attenuates emotional responses to environmental sounds

OBJECTIVE

Cochlear implants (CI) provide users with a spectrally degraded acoustic signal that could impact their auditory emotional experiences. This study evaluated the effects of CI-simulated spectral degradation on emotional valence and arousal elicited by environmental sounds.

DESIGN

Thirty emotionally evocative sounds were filtered through a noise-band vocoder. Participants rated the perceived valence and arousal elicited by each of the full-spectrum and vocoded stimuli. These ratings were compared across acoustic conditions (full-spectrum, vocoded) and as a function of stimulus type (unpleasant, neutral, pleasant).

STUDY SAMPLE

Twenty-five young adults (age 19 to 34 years) with normal hearing.

RESULTS

Emotional responses were less extreme for spectrally degraded (i.e., vocoded) sounds than for full-spectrum sounds. Specifically, spectrally degraded stimuli were perceived as more negative and less arousing than full-spectrum stimuli.

CONCLUSION

By meticulously replicating CI spectral degradation while controlling for variables that are confounded within CI users, these findings indicate that CI spectral degradation can compress the range of sound-induced emotion independent of hearing loss and other idiosyncratic device- or person-level variables. Future work will characterize emotional reactions to sound in CI users via objective, psychoacoustic, and subjective measures.

The influence of electrode array design, scalar dislocation and insertion technique on postoperative vertigo in CI surgery - a prospective study

OBJECTIVES

This study aimed to examine the effect of electrode array design, insertion angle, scalar position, and insertion technique on the occurrence of postoperative subjective vertigo following cochlear implant (CI) surgery using questionnaires in conjunction with objective vestibular functional measurements.

MATERIALS AND METHODS

We prospectively evaluated subjective vertigo using the Dizziness Handicap Inventory (DHI). Additionally, we performed videonystagmography, video head-impulse tests, and vestibular-evoked myogenic potentials to assess the objective vestibular function preoperatively, at four weeks and 12 months after CI. These results were compared with those of postoperative imaging using digital volume tomography.

RESULTS

Postoperative vertigo was observed in 2 out of 62 patients (3%). Cochleostomy (n = 8) did not lead to an increase in postoperative vertigo. Functional diagnostics revealed abnormalities in up to 23% of patients without subjective dizziness. In our patient cohort, neither electrode array dislocation nor increasing insertion depth was associated with an increase in postoperative vertigo.

CONCLUSION

Both postoperative vertigo occurrence and electrode array dislocation rates have significantly decreased due to the optimized atraumatic electrode array design and improved surgical insertion techniques. Neither dislocation nor cochleostomy appeared to induce vertigo but the sample size was too small to draw definitive conclusions.

Severe-to-Profound Hearing Loss and Mental Health: Initial Evidence That Cochlear Implantation Helps Alleviate Symptoms of Anxiety and Stress

OBJECTIVES

Mental-health issues accounted for 418 million disability-adjusted life years in 2019, costing the world economy approximately $5 trillion. Untreated hearing loss is a well-known modifiable risk factor for mental-health issues, with severe-to-profound hearing loss having the largest impact. Therefore, treatment of severe-to-profound hearing loss, namely with cochlear implantation, could help to alleviate psychological distress. However, previous studies have failed to include comprehensive measures of mental health or adequate controls. The current study thus aimed to conduct a controlled, longitudinal investigation of how cochlear implantation affects depression, anxiety and stress levels.

PARTICIPANTS

Participants were 87 adults assigned to conditions based on hearing status: normal hearing (n = 44), received cochlear implant (n = 26) or untreated hearing loss (n = 17).

MAIN OUTCOME MEASURES

The short-form Depression Anxiety Stress Scale was given at four timepoints (baseline, 3 months, 6 months, 12 months). Data were analysed using linear mixed-effects modelling.

RESULTS

Results showed that cochlear implants helped to stabilise anxiety and stress symptoms, while depression symptoms were observed to worsen over time despite treatment.

CONCLUSION

Our findings suggest that treatment of severe-to-profound hearing loss with cochlear implantation was associated with a lessening of anxiety and stress scores, although the clinical significance of such changes remains uncertain. Due to the current study's non-randomised treatment allocation, future randomised controlled trials are required for confirmation. The present findings help inform clinical and societal interventions for mental-health issues associated with hearing loss.

Cochlear Implantation Outcomes in Genotyped Subjects with Sensorineural Hearing Loss

PURPOSE

Cochlear implants (CIs) are an effective rehabilitation option for individuals with severe-to-profound sensorineural hearing loss (SNHL). While genetic factors play a significant role in SNHL, the variability in CI outcomes remains unclear. This study evaluated short- and long-term CI outcomes in a large genotyped cohort and investigated correlations with genetic defects and their cochlear site-of-lesion.

METHODS

This retrospective, single-center, cohort study included 220 subjects (127 females; 299 ears) with pathogenic variants identified in 31 different nuclear genes and in mitochondrial genes. Audiological outcomes were measured pre- and post-implantation. Cochlear site-of-lesion was categorized as pre-synaptic, post-synaptic, or mitochondrial, based on gene function or expression. Multiple regression analysis assessed factors influencing outcomes, including age at implantation, SNHL duration, hearing aid (HA) use, and cochlear site-of-lesion.

RESULTS

Results showed a median phoneme score of 90%, with better outcomes in early implantation (≤ 6 years). Variability in outcomes was not linked to cochlear site-of-lesion, but to subject-specific factors, such as age at implantation, duration of SNHL, pre-implantation HA use, and CI experience. A model incorporating these subject-specific factors explained 19% of the total variance in outcomes. Poorer outcomes (phoneme scores < 70%) were more common in individuals with prolonged auditory deprivation or older age at implantation.

CONCLUSION

Genotyped CI recipients demonstrated excellent outcomes, with variability largely attributed to non-genetic factors. These findings show that cochlear implantation is a beneficial type of rehabilitation for most individuals with hereditary SNHL and underscore the importance of early implantation.

On the Difficulty of Defining Duration of Deafness for Adults With Cochlear Implants

The amount of time that a person with a cochlear implant experiences severe-to-profound hearing loss before implantation is thought to impact the underlying neural survival, health, and function of the auditory system, thus likely being closely related to post-implantation performance in auditory tasks. The reporting of this number in the research literature is ubiquitous. Although it is most commonly called "duration of deafness," our point of view is that the term is imprecise and the calculation of this number can be nontrivial, particularly for cases of adult onset of hearing loss. We provide suggestions on changing the terminology to "duration of severe-to-profound hearing loss." We also propose a method of determining this number through a series of questions that leads a participant/patient through their progression of hearing loss. We encourage research methodology that requires researchers to explicitly report the process used to determine the duration of severe-to-profound hearing loss with the overall goals of (1) improving rigor and reproducibility in cochlear-implant research and (2) improving the translation between research findings and clinical recommendations.

Contributions of Auditory Nerve Density and Synchrony to Speech Understanding in Older Cochlear Implant Users

PURPOSE

The majority of adult cochlear implant (CI) recipients are over the age of 65, and previous research in non-implanted older adults shows that auditory nerve (AN) pathophysiology contributes to senescent declines in speech understanding. However, age-related changes to AN structure and function have not yet been explored as a contributory factor to poorer speech understanding outcomes in older CI users. Here, we explore how estimates of AN disengagement (i.e., AN density) and dyssynchrony in CI users contribute to poorer speech recognition performance observed in older CI users.

METHODS

We examined electrically evoked compound action potentials (ECAPs) in 47 adult (Male = 25) CI recipients. We measured the interphase gap (IPG) effect for the amplitude-growth function (AGF) slope and the N1-P2 interpeak latency as independent metrics of AN density and dyssynchrony, respectively.

RESULTS

Estimates of AN density and dyssynchrony worsen with increasing age in older CI listeners. These measures were not significantly correlated with one another, but were independently related to speech recognition in noise performance. Lower ECAP IPG effect values (lower density of AN fibers) are observed in older CI users. Longer N1-P2 interpeak latency values (poorer neural synchrony) are also observed in older CI users. When controlling for listener age, poorer AN dyssynchrony contributes to declines in speech-recognition-in-noise performance in CI users.

CONCLUSION

These results suggest that AN dyssynchrony rather than density is the primary contributing factor to age-related declines in speech understanding in CI users. These results have important implications for better understanding neural contributions to speech understanding in adult CI users.

Machine Learning Feasibility in Cochlear Implant Speech Perception Outcomes-Moving Beyond Single Biomarkers for Cochlear Implant Performance Prediction

OBJECTIVES

Machine learning (ML) is an emerging discipline centered around complex pattern matching and large data-based prediction modeling and can improve precision medicine healthcare. Cochlear implants (CI) are highly effective, however, outcomes vary widely, and accurately predicting speech perception performance outcomes between patients remains a challenge. This study aims to evaluate the ability of ML to predict speech perception performance among CI recipients at 6-month post-implantation using only preoperative variables on one of the largest CI datasets to date, with an emphasis placed on identification of poor performers.

DESIGN

All patients enrolled in the national CI outcome tracking database, HERMES, and the institutional CI registry. Data were split 90/10 training/testing with hyperparameter tuning designed to optimize AUPRC performed during 10-fold cross-validation within 100 iterations. Multiple models were developed to predict final and delta (Δ) in consonant-nucleus-consonant (CNC) words and AzBio sentences at 6-month post-implantation. Two metrics, (1) final performance scores and (2) equally distributed 20th percentile performance ranking were used as primary outcomes. All models were compared with currently used "gold standard," defined as linear or logistic regression models leveraging Lazard features (LF). Final metrics for comparison included mean absolute error (MAE), calibration curves, heat accuracy maps, area under the receiver operating curve (AUROC), and F1 score.

RESULTS

A total of 1877 patients were assessed through an ML pipeline. (1) XGBoost (XGB) predicted CNC with MAE of 17.4% (95% confidence interval [CI]: 17.34 to 17.53%) and AzBio with MAE of 20.39% (95% CI: 20.28 to 20.50%) and consistently outperformed linear regression with LF (CNC MAE 18.36% [95% CI: 18.25 to 18.47]; AzBio 21.62 [95% CI: 21.49 to 21.74]). Although statistically significant, the 1 to 2% boost of performance is clinically insignificant. (2) Predicting quintiles/20th percentile categories for CI performance, XGB outperformed logistic regression (Log-LF) across all metrics. XGB demonstrated superior calibration compared with Log-LF and provided a larger proportion of predicted probabilities predictions at the extremes (e.g., 0.1 or 0.9). XGB outperformed Log-LF predicting ≤40th percentile for CNC (AUROC: 0.708 versus 0.594; precision: 0.708 versus 0.596; F1 score: 0.708 versus 0.592) and AzBio (AUROC: 0.709 versus 0.572; precision: 0.710 versus 0.572; F1 score: 0.709 versus 0.572). This was consistent for ΔCNC and ΔAzBio. Last, accuracy heat maps demonstrated superior performance of XGB in stratifying sub-phenotypes/categories of CI performance compared with Log-LF.

CONCLUSIONS

This study demonstrates how ML models can offer superior performance in CI speech perception outcomes prediction modeling compared with current gold standard (Lazard-linear or logistic regression). ML offers novel insights capable of capturing nonlinear complex relationships and can identify novel sub-phenotypes at the extremes of CI performance using preoperative clinical variables alone. This is the first study to our knowledge to offer any type of meaningful preoperative stratification for CI speech perception outcomes and may have significant implications that need to be carefully explored when it comes to patient counseling, auditory rehabilitation, and future CI clinical trials. While prospective validation is a necessary next step and performance is still limited based on current traditional CI variables, these results highlight the potential of artificial intelligence (AI) in CI care, the critical need to integrate novel variables that better account for CI performance, and the need for improved data collaboration and standardized registries moving forward.

Model-Based Inference of Electrode Distance and Neuronal Density from Measured Detection Thresholds in Cochlear Implant Listeners

PURPOSE

Cochlear implants (CI) are a highly successful neural prosthesis that can restore hearing in individuals with sensorineural hearing loss. However, the extent of hearing restoration varies widely. Two major factors likely contribute to poor performance: (1) the distances between electrodes and surviving spiral ganglion neurons and (2) the density of those neurons. Reprogramming the CI at a poor electrode-neuron interface, using focused tripolar stimulation or remapping the electrodes, would benefit from understanding the cause of the poor interface.

METHODS

We used a cochlear model with simplified geometry and neuronal composition to investigate how the interface affects stimulation thresholds. We then inverted the model to infer electrode distance and neuronal density from monopolar and tripolar threshold values obtained behaviorally. We validated this inverted model for known scenarios of electrode distance and neuronal density. Finally, we assessed the model using data from 18 CI users whose electrode distances were measured from CT imaging.

RESULTS

The inverted model accurately inferred electrode distance and neuronal density for known scenarios. It also reliably reproduced behavioral monopolar and tripolar threshold profiles for CI users, with mean prediction errors within 1 dB for 17/18 subjects. Fits of electrode distance were more variable; accuracy depended on the assumed value of temporal bone resistivity. Twelve subjects had minimum distance error (0.31 mm) using low resistivity (70 Ω-cm) while the others had better fits (0.30 mm) with higher resistivity (250 Ω-cm).

CONCLUSION

This inverted model shows promise as a simple, practical tool to better assess and understand the electrode-neuron interface.

Cochlear-implant dichotic listening performance and effort are disrupted with functional ear asymmetry

When speech understanding abilities differ across the ears, auditory attention and listening effort could be impacted. Twenty listeners with bilateral cochlear implants (CIs) completed this experiment. Fourteen listeners had symmetric and six listeners had asymmetric functional hearing. Listeners completed monotic and dichotic digit recall with digit string lengths of four and six digits and attention directed to each ear. Pupil size was monitored as an index of listening effort. Individual differences in working memory and inhibition abilities were measured. It was hypothesized that ear asymmetry would lead to poorer listening performance and higher listening effort, and that cognitive abilities would predict both performance and listening effort. Greater differences in performance across ears were observed with asymmetry. Lower listening effort was observed with asymmetry, regardless of which ear was attended. Poorer working memory abilities predicted higher listening effort. These results suggest that asymmetric listeners may experience reduced perception of a poorer ear, and that individuals with poorer working memory abilities are at risk to experience higher listening effort in complex listening environments with CIs. More broadly, these results suggest that the salience of sensory inputs contributes to auditory attention ability and use of cognitive resources.

Speech Outcomes of Cochlear Implantation, from 1983 to Present: A Systematic Review

OBJECTIVE

We sought to assess whether the totality of advancements seen in cochlear implant (CI) design and implementation have translated to significant improvements in speech perception scores.

DATABASES REVIEWED

EMBASE, PubMed/MEDLINE, and the Cochrane Central Register of Controlled Trials.

METHODS

A systematic review of all English-language studies in peer-reviewed journals from 1946 to August 2022 was performed based on the Cochrane Handbook and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Eligible studies were of adult patients who underwent cochlear implantation with Cochlear®, Med-EL, or Advanced Bionics devices with 12 months postoperative sentence recognition testing results. Meta-regression was performed to assess the relationship between speech recognition score and year of implantation. Preimplantation score and unilateral versus bilateral implantation were adjusted for. Subgroup analysis was performed by restricting to studies of <5 years duration and in which outcomes were measured ≤12 months postoperatively to reduce the likelihood of patients with remotely implanted devices having undergone upgrades to more contemporary coding software.

RESULTS

A total of 37 studies met criteria for inclusion, representing CIs implanted between 1983 and 2019. No significant association was identified between median study year and scores on 12-month postoperative sentence recognition testing on any of AzBio in quiet, CNC words, or HINT sentences in quiet. Subgroup analysis showed no difference in outcomes across 15 studies including patients implanted from 2007 to 2019.

CONCLUSION

In the absence of improved CI coding strategies since 2007, speech recognition outcomes in quiet have also not improved significantly since this time.

Intraoperative Assessment of Cochlear Nerve Function During Cochlear Implantation Using the Auditory Nerve Test Stimulator

BACKGROUND/OBJECTIVES

A crucial factor for a successful cochlear implant (CI) outcome is an intact auditory nerve (AN). The integrity of the AN can be tested during implantation by measuring electrical auditory brainstem responses (eABR) via the CI. A method that does not require a CI is the use of the auditory nerve test stimulator (ANTS) from MED-EL (Innsbruck, Austria). The aim of the current study was to investigate the cases tested with the ANTS at our clinic and to describe the hearing results following CI for the cases who were implanted with a CI.

METHODS

All patients underwent preoperative magnetic resonance imaging (MRI) and high-resolution computed tomography (HRCT) to rule out cochlear malformation or retrocochlear pathology. In this study, we described all cases from when we began using the ANTS in 2011.

RESULTS

Five patients were tested intraoperatively: three adults with long-term deafness prior to CI and two children with no detectable AN. Three of the five patients were implanted with a CI. All implanted patients in this study could hear with their CIs, even though the speech perception results were limited.

CONCLUSIONS

The ANTS can be used as a method to assess cochlear nerve function during implantation. The eABR results from the ANTS and the implanted CI were comparable for all cases in our study. Minor changes in waveform latencies were found between ANTS and CI stimulation and may be explained by the insertion depth of the electrode used for stimulation.

Impact of cochlear detailed morphology on insertion results and intracochlear trauma of a slim pre-curved electrode array: a micro-CT study

OBJECTIVE

This study aimed to evaluate the impact of detailed cochlear dimensions, assessed using micro-CT (µCT) imaging, on insertion outcomes and associated trauma with a new slim, precurved electrode array.

MATERIALS AND METHODS

Eleven temporal bone specimens underwent implantation of a 22-electrode slim precurved array via the round window. High-resolution µCT scans post-implantation enabled visualization of cochlear structures and electrode positioning. Combination with subsequent scans taken after electrodes removal, we analyzed angular insertion depth (AID), insertion length, number of electrodes inserted, cochlear dimensions (specifically cochlear duct length (CDL), basal turn diameter, scala tympani dimension), and intracochlear trauma of fine structures. Statistical analyses were performed to correlate cochlear detailed dimensions and morphology with insertion outcomes and trauma.

RESULTS

The mean AID was 351.82°, and the mean insertion length was 21.07 mm. CDL showed positive correlations with AID and insertion length. Basal turn diameter (value B) positively correlated with AID and insertion length, unlike value A. Middle-basal turn (M/B) relationships (angle and height) significantly influenced insertion depth. The cochleae with smaller M/B heights and specific angles were more susceptible to insertion trauma. Larger basal turn diameters correlated with increased trauma and electrode translocation into the scala vestibuli.

CONCLUSION

This study highlights the importance of precise cochlear measurements in predicting and optimizing cochlear implant outcomes. Specific cochlear dimensions and anatomical shapes were identified as critical factors affecting insertion depth, trauma risk, and electrode positioning. Utilizing micro-CT provided detailed insights into cochlear anatomy and insertion outcomes, offering valuable data for advancing cochlear implant technology and surgical practices.

Cochlear Implantation Outcomes in Older Adults, Ages 80-90

OBJECTIVE

To assess whether postoperative speech recognition after cochlear implantation (CI) differ between age groups of 80 to 89 and 90+.

STUDY DESIGN

Retrospective cohort study.

SETTING

Tertiary academic referral center.

PATIENTS

Older adult (80+ years old) bilateral sensorineural hearing loss patients undergoing CI.

INTERVENTIONS

Therapeutic, CI.

MAIN OUTCOME MEASURES

Speech testing battery at 3, 6, and 12 months postoperatively. Self-reported balance and vertigo symptoms were also assessed.

RESULTS

A total of 221 patients were included in this study, with 171 cases ages 80 to 89 and 50 cases ≥90 years old. A total of 60.3% had an abnormal preoperative cognitive screen based on either Montreal Cognitive Assessment or Mini Mental State Examination. No major demographic or clinical variables were noted across age groups. Mean 1 year postoperative speech scores were as follows for ages 80 to 89 versus 90+, respectively: CNC 50% (±21%) versus 47% (±18%), AzBio Quiet 54% (±26%) versus 50% (±25%), and AzBio +10SNR 28% (±21%) versus 21% (±17%). Age, abnormal cognitive screen, duration of hearing loss, and comorbidity measures such as BMI, Adult Comorbidity Evaluation-27, and American Society of Anesthesiology physical status class were not correlated with any speech measure. Overall rates of persistent self-reported balance symptoms at activation were 22.7%, decreasing to 7.5% at 1 year. Datalogging was >11 hours use on average for both age groups.

CONCLUSIONS

CI speech recognition in the 80 to 89 and 90+ age range significantly improved from preoperative scores. No major speech recognition differences were identified between age groups. Age at implantation, abnormal cognitive screening, and comorbidity status did not influence speech perception, which suggests that candidacy in older adult CI patients should not be withheld strictly due to these parameters.

Management of Audiological Disorders in Cochlear Implants: Outcomes in Demanding Listening Situations and Future Perspectives

Severe to profound sensorineural hearing loss can nowadays successfully be treated by cochlear implantation [...].

Effects of Insertion Depth and Modiolar Proximity on Cochlear Implant Speech Recognition Outcomes With a Precurved Electrode Array

OBJECTIVES

To examine the relationship between angular insertion depth (AID), modiolar proximity, and speech recognition outcomes for cochlear implant (CI) recipients of a precurved electrode array.

STUDY DESIGN

Retrospective review.

SETTING

Tertiary academic referral center.

PATIENTS

Thirty-five adult CI recipients (n = 40 ears) of precurved electrode arrays listening with a CI-alone device.

INTERVENTIONS

Cochlear implantation with postoperative computed tomography.

MAIN OUTCOME MEASURES

Consonant-nucleus-consonant (CNC) word recognition at 6 months post-activation.

RESULTS

A multivariate regression model demonstrated that both deeper apical AID and closer modiolar proximity in the basal turn were independently associated with better CNC word scores at 6 months (F2,37 = 7.264, p = 0.002). A deeper basal insertion depth was positively correlated with apical AID (r = 0.754, p < 0.001) but negatively correlated with modiolar proximity in the basal turn (r = -0.766, p < 0.001).

CONCLUSIONS

These data suggest that both apical cochlear coverage and modiolar proximity independently confer speech recognition benefit with a precurved array. However, these benefits are mutually exclusive for current precurved array designs as a deeper basal insertion depth results in greater apical coverage but lateralization of electrodes away from the modiolus in the basal turn. Future work is needed to elucidate mechanisms behind these findings that may motivate electrode array design modifications to further optimize outcomes for CI users.

A Level-Adjusted Cochlear Frequency-to-Place Map for Estimating Tonotopic Frequency Mismatch With a Cochlear Implant

OBJECTIVES

To provide a level-adjusted correction to the current standard relating anatomical cochlear place to characteristic frequency (CF) in humans, and to re-evaluate anatomical frequency mismatch in cochlear implant (CI recipients considering this correction. It is proposed that a level-adjusted place-frequency function may represent a more relevant tonotopic benchmark for CIs in comparison to the current standard.

DESIGN

The present analytical study compiled data from 15 previous animal studies that reported isointensity responses from cochlear structures at different stimulation levels. Extracted outcome measures were CFs and centroid-based best frequencies at 70 dB SPL input from 47 specimens spanning a broad range of cochlear locations. A simple relationship was used to transform these measures to human estimates of characteristic and best frequencies, and nonlinear regression was applied to these estimates to determine how the standard human place-frequency function should be adjusted to reflect best frequency rather than CF. The proposed level-adjusted correction was then compared with average place-frequency positions of commonly used CI devices when programmed with clinical settings.

RESULTS

The present study showed that the best frequency at 70 dB SPL (BF70) tends to shift away from CF. The amount of shift was statistically significant (signed-rank test z = 5.143, p < 0.001), but the amount and direction of shift depended on cochlear location. At cochlear locations up to 600° from the base, BF70 shifted downward in frequency relative to CF by about 4 semitones on average. Beyond 600° from the base, BF70 shifted upward in frequency relative to CF by about 6 semitones on average. In terms of spread (90% prediction interval), the amount of shift between CF and BF70 varied from relatively no shift to nearly an octave of shift. With the new level-adjusted place-frequency function, the amount of anatomical frequency mismatch for devices programmed with standard-of-care settings is less extreme than originally thought and may be nonexistent for all but the most apical electrodes.

CONCLUSIONS

The present study validates the current standard for relating cochlear place to CF, and introduces a level-adjusted correction for how best frequency shifts away from CF at moderately loud stimulation levels. This correction may represent a more relevant tonotopic reference for CIs. To the extent that it does, its implementation may potentially enhance perceptual accommodation and speech understanding in CI users, thereby improving CI outcomes and contributing to advancements in the programming and clinical management of CIs.

Frequency-to-Place Mismatch and Cochlear Implant Outcomes by Electrode Type

Importance

Speech recognition outcomes with a cochlear implant (CI) are highly variable. One factor suggested to correlate with CI-aided speech recognition is frequency-to-place mismatch, or the discrepancy between the natural tonotopic organization of the cochlea and the electric frequency allocation of the CI electrodes within the patient's cochlea.

Objective

To evaluate the association between frequency-to-place mismatch and speech recognition outcomes in a large cohort of postlingually deafened adult CI users, while controlling for various clinical factors known to be associated with those outcomes.

Design, Setting, and Participants

This retrospective cohort study used data from a CI program at a tertiary medical center and included CIs from postlingually deafened adult CI users. After excluding patients whose data were not logged, patients with implantations occurring between 2016 and 2023 were included in the analysis. The data were extracted in November 2023.

Main Outcomes and Measures

Results of the Consonant-Nucleus-Consonant (CNC) monosyllabic word recognition test measured in the CI-aided alone condition 1 month, 3 months, 6 months, and 12 months after activation served as the main outcome. The independent variables included frequency-to-place mismatch, electrode array type, mean modiolar distance, electrode position, age at implantation, biological sex, contralateral hearing abilities, time since CI activation (test interval), and daily device use.

Results

In 498 CIs from 447 postlingually deafened adults (mean [SD] age, 63.1 [17.1] years; 271 [54.4%] CIs with male users), frequency-to-place mismatch was negatively correlated with CI-aided speech recognition outcomes, but the association was only significant for precurved electrode arrays and not straight electrode arrays. In the linear mixed effects model for straight electrode arrays, only test interval (β = 1.14 [95% CI, 0.90-1.38]) and daily device use (β = 0.90 [95% CI, 0.42-1.38]) were correlated with the improvement of word recognition over the first year of device use. In the model for precurved electrode arrays, mismatch at 1500 Hz (β = -0.011 [95% CI, -0.011 to -0.006]), scalar location (β = 16.37 [95% CI, 9.01 to 23.74]), test interval (β = 1.18 [95% CI, 1.18-1.41]) and daily device use (β = 1.65 [95% CI, 1.15-2.14]) all were significantly associated with the improvement of word recognition over the first year of device use.

Conclusions and Relevance

In this cohort study of postlingually deafened adult CI users, including both straight and precurved electrode arrays, daily device use and time since CI activation were found to be significantly associated with improved CI-aided speech recognition outcomes. Frequency-to-place mismatch at 1500 Hz and scalar location were associated with word recognition only for precurved arrays. These findings suggest that, for patients with straight arrays, any interference produced by frequency-to-place mismatch may be overcome by adaptation, which could be supported by daily device use. However, for patients with precurved arrays, daily device use may not be sufficient to completely overcome electrode placement factors, including scalar location and mismatch.

Auditory working memory in noise in cochlear implant users: Insights from behavioural and neuronal measures

OBJECTIVE

We investigated auditory working-memory using behavioural measures and electroencephalography (EEG) in adult Cochlear Implant (CI) users with varying degrees of CI performance.

METHODS

24 adult CI listeners (age: M = 61.38, SD = 12.45) performed the Sternberg auditory-digit-in-working-memory task during which EEG, accuracy, and promptness were captured. Participants were presented with 2, 4, or 6 digits at Signal-to-Noise Ratios (SNR) of 0, +5 and +10dB. They had to identify a probe stimulus as present in the preceding sequence. ANOVA models were used to compare conditions.

RESULTS

ANOVA revealed that increasing memory load (ML) led to decreased task performance and CI performance interacted with ML and SNR. Centro-parietal alpha power increased during memory encoding but did not differ between conditions. Frontal alpha power was positively correlated with accuracy in conditions most affected by SNR (r = 0.57, r = 0.52) and theta power in conditions most affected by ML (r = 0.55, r = 0.57).

CONCLUSIONS

While parietal alpha power is modulated by the task, it is frontal alpha that relates quantitatively to sensory aspects of processing (noise) and frontal theta to memory load in this group of CI listeners.

SIGNIFICANCE

These results suggest that alpha and theta show distinct relationships to behaviour, providing additional insight into neurocognitive (auditory working-memory) processes in CI users.

Transimpedance Matrix Measurement (TIM) Parameters Evaluation for the Assessment of Cochlear Implant Electrode Placement and Modiolar Proximity in Children

Introduction: Transimpedance matrix measurement (TIM) is an electrophysiological measurement protocol of the impedance patterns of electrode contacts within the cochlea. Several studies have reported that TIM is an effective tool for the identification of abnormal electrode array placement. However, the normative values for properly inserted electrodes, as well as correlation of the TIM patterns with the electrode position, are not completely determined. Objectives: The first aim of this study is to establish normative values of TIM measurements obtained in children with proper electrode array insertion and tip fold-over, with proper inner ear anatomy and in congenital anomalies. The second aim of this study is to compare TIM measurements in Slim Modiolar (SM) and in Contour Advance (CA) electrodes, as their position is different according to the modiolus proximity. Methods: A total of 55 pediatric patients were included in the study and underwent cochlear implantation. 62 intraoperative measurements were conducted in this group-50 in children with normal inner ear anatomy and 12 in children with inner ear malformations. After each implantation, a plain x-ray was obtained. Results: There were clear statistically significant differences in TIM patterns in patients where electrode fold-over was confirmed and between SM and CA electrodes. Conclusions: TIM is a promising technique for intraoperative analysis of electrode placement. TIM patterns differ and correlate consistently with the different models of array implanted. This study is the first to report TIM patterns observed in children with normal inner ear anatomy and in inner ear malformations.

Machine-Learning Predictions of Cochlear Implant Functional Outcomes: A Systematic Review

OBJECTIVES

Cochlear implant (CI) user functional outcomes are challenging to predict because of the variability in individual anatomy, neural health, CI device characteristics, and linguistic and listening experience. Machine learning (ML) techniques are uniquely poised for this predictive challenge because they can analyze nonlinear interactions using large amounts of multidimensional data. The objective of this article is to systematically review the literature regarding ML models that predict functional CI outcomes, defined as sound perception and production. We analyze the potential strengths and weaknesses of various ML models, identify important features for favorable outcomes, and suggest potential future directions of ML applications for CI-related clinical and research purposes.

DESIGN

We conducted a systematic literature search with Web of Science, Scopus, MEDLINE, EMBASE, CENTRAL, and CINAHL from the date of inception through September 2024. We included studies with ML models predicting a CI functional outcome, defined as those pertaining to sound perception and production, and excluded simulation studies and those involving patients without CIs. Using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, we extracted participant population, CI characteristics, ML model, and performance data. Sixteen studies examining 5058 pediatric and adult CI users (range: 4 to 2489) were included from an initial 1442 publications.

RESULTS

Studies predicted heterogeneous outcome measures pertaining to sound production (5 studies), sound perception (12 studies), and language (2 studies). ML models use a variety of prediction features, including demographic, audiological, imaging, and subjective measures. Some studies highlighted predictors beyond traditional CI audiometric outcomes, such as anatomical and imaging characteristics (e.g., vestibulocochlear nerve area, brain regions unaffected by auditory deprivation), health system factors (e.g., wait time to referral), and patient-reported measures (e.g., dizziness and tinnitus questionnaires). Used ML models were tree-based, kernel-based, instance-based, probabilistic, or neural networks, with validation and test methods most commonly being k-fold cross-validation and train-test split. Various statistical measures were used to evaluate model performance, however, for studies reporting accuracy, the best-performing models for each study ranged from 71.0% to 98.83%.

CONCLUSIONS

ML models demonstrate high predictive performance and illuminate factors that contribute to CI user functional outcomes. While many models showed favorable evaluation statistics, the majority were not adequately reported with regard to dataset characteristics, model creation, and validation. Furthermore, the extent of overfitting in these models is unclear and will likely result in poor generalization to new data. This suggests the need for more robust validation procedures and standardization in reporting, with the ultimate hope that the iterative improvement of these models will allow for their adoption as a future clinical tool.

Evaluation of Replacement Hearing Aids in Cochlear Implant Candidates Using the Hearing in Noise Test (HINT) and Pupillometry

BACKGROUND/OBJECTIVES

Advances in cochlear implant (CI) technology have led to the expansion of the implantation criteria. As a result, more CI candidates may have greater residual hearing in one or two ears. Many of these candidates will perform better with a CI in one ear and a hearing aid (HA) in the other ear, the so-called bimodal solution. The bimodal solution often requires patients to switch to HAs that are compatible with the CI. However, this can be a challenging decision, not least because it remains unclear whether this impacts hearing performance. Our aim is to determine whether speech perception in noise remains unchanged or improves with new replacement HAs compared to original HAs in CI candidates with residual hearing.

METHODS

Fifty bilateral HA users (mean age 63.4; range 23-82) referred for CI were recruited. All participants received new replacement HAs. The new HAs were optimally fitted and verified using Real Ear Measurement (REM). Participants were tested with the Hearing in Noise Test (HINT), which aimed at determining the signal-to-noise ratio (SNR) required for a 70% correct word recognition score at a speech sound pressure level (SPL) of 65 dB. HINT testing was performed with both their original and new replacement HAs. During HINT, pupillometry was used to control for task engagement.

RESULTS

Replacing the original HAs with new replacement HAs after one month was not statistically significant with a mean change of SRT70 by -1.90 (95% CI: -4.69;0.89, p = 0.182) dB SNR.

CONCLUSIONS

New replacement HAs do not impact speech perception scores in CI candidates prior to the decision of cochlear implantation.

Utilization of the Spanish Bisyllable Word Recognition Test to Assess Cochlear Implant Performance Trajectory

Objectives: The aims of this study were to compare pre- and post-operative word recognition scores (WRSs) for the adult Spanish-speaking population and to describe their cochlear implant (CI) performance trajectory. Methods: A retrospective chart review (n = 115) was completed for Spanish-speaking post-lingually deafened adults who underwent a traditional CI evaluation and subsequent surgery between 2018 and 2023. Pre- and post-CI (3, 6, 12-month) Spanish Bisyllable WRSs and CI datalogging (hours per day) were collected for 66 subjects who met inclusion. Patients were, on average, 61.4 years of age (SD = 14.9) at the time of their first CI, and all were Hispanic and White (100%). Results: The outcomes of the 66 subjects who met the inclusion criteria were analyzed. Spanish Bisyllable WRSs improved at all post-CI test intervals, though the mean change between intervals showed a decreasing trend over time, with a plateau in WRSs occurring by 6 months post-CI. Time was a significant predictor of increased post-CI WRSs at 6 months (p = 0.004) and 12 months (p < 0.001). Sex, the implanted ear, electrode type, CI manufacturer, and datalogging hours did not significantly predict Bisyllable WRSs. Conclusions: This study used the largest cohort dataset to date to describe pre-and post-CI WRSs for Spanish-speaking adults. The post-CI performance trajectory is similar in Spanish-speaking CI recipients compared to English-speaking cohorts. This study is fundamental in providing evidence-based outcomes for Spanish-speaking CI recipients and will assist clinicians with pre-CI counseling based on realistic expectations.

Electrocochleography-Guided Pull-Back Technique of Perimodiolar Electrode for Improved Hearing Preservation

OBJECTIVE

To evaluate whether electrocochleography (ECochG)-guided pull-back of the perimodiolar electrode improves perimodiolar proximity, hearing preservation (HP), and cochlear implant performance.

STUDY DESIGN

Prospective cohort study.

SETTING

Tertiary referral center.

PATIENTS

77 adult CI recipients with residual acoustic hearing (low-frequency pure-tone average of 125, 250, 500 Hz; LFPTA ≤80 dB HL).

INTERVENTION

Unilateral implantation, comparing conventional insertion (N = 31) with ECochG-guided electrode pull-back (N = 46). The guided method uses active ECochG from the apical electrode during adjustment and post-insertion electrode sweep to identify "tonotopic response" (defined as maximum response for 250 Hz at most apical electrode on electrode sweep).

MAIN OUTCOME MEASURES

Perimodiolar proximity (wrapping factor on postoperative CT); speech-perception testing (CNC, AzBio in noise +10 dB SNR); and HP at 3 and 6 months post-activation (defined as LFPTA ≤80 dB HL).

RESULTS

Of the subjects undergoing ECochG-guided insertion, 36 required pull-back based on lack of tonotopic responses, whereas the remaining 10 exhibited "optimal responses" post-insertion, needing no adjustment. Improved perimodiolar proximity was achieved with the ECochG-guided method (mean wrapping factor difference, 6.4; 95% CI, 3.0-9.9). The LFPTA shift was smaller using ECochG-guided pull-back when compared with conventional insertion by 17.0 dB HL (95% CI, 8.3-25.7) and 14.8 dB HL (95% CI, 6.5-23.2) at 3 and 6 months, respectively. Forty percent achieved HP using ECochG-guided pull-back versus 27.5% without. There was no difference in CNC scores among both cohorts, but AzBio in noise scores at 6 months was improved in the ECochG-guided pull-back cohort (mean difference, 19.1%; 95% CI, 5.8-32.4).

CONCLUSIONS

ECochG-guided pull-back increased perimodiolar proximity and HP rates. Although there was no difference in speech perception performance in quiet, a significant improvement was noted in noisy conditions, potentially attributable to HP and the utilization of hybrid stimulation.

Vocal and musical emotion perception, voice cue discrimination, and quality of life in cochlear implant users with and without acoustic hearing

This study aims to provide a comprehensive picture of auditory emotion perception in cochlear implant (CI) users by (1) investigating emotion categorisation in both vocal (pseudo-speech) and musical domains and (2) how individual differences in residual acoustic hearing, sensitivity to voice cues (voice pitch, vocal tract length), and quality of life (QoL) might be associated with vocal emotion perception and, going a step further, also with musical emotion perception. In 28 adult CI users, with or without self-reported acoustic hearing, we showed that sensitivity (d') scores for emotion categorisation varied largely across the participants, in line with previous research. However, within participants, the d' scores for vocal and musical emotion categorisation were significantly correlated, indicating both similar processing of auditory emotional cues across the pseudo-speech and music domains as well as robustness of the tests. Only for musical emotion perception, emotion d' scores were higher in implant users with residual acoustic hearing compared to no acoustic hearing. The voice pitch perception did not significantly correlate with emotion categorisation in either domain, while the vocal tract length significantly correlated in both domains. For QoL, only the sub-domain of Speech production ability, but not the overall QoL scores, correlated with vocal emotion categorisation, partially supporting previous findings. Taken together, results indicate that auditory emotion perception is challenging for some CI users, possibly a consequence of how available the emotion-related cues are via electric hearing. Improving these cues, either via rehabilitation or training, may also help auditory emotion perception in CI users.

Does cochlear implant electrode array design affect audiologic outcomes? A systematic review and meta-analysis

BACKGROUND

There is conflicting literature regarding whether cochlear implants (CI) electrode array (EA) selection impacts audiologic outcomes.

OBJECTIVE

To compare outcomes for the two EA designs, precurved and straight.

METHODS

A systematic search of CINAHL, Cochrane Library, PubMed, and SCOPUS was conducted according to PRISMA guidelines. Included studies reported word recognition scores, sentence recognition scores in quiet or noise, or hearing preservation (HP) rates for patients with post-lingual hearing loss who underwent CI with either EA type. Primary outcome measures included mean difference (baseline vs. post-surgery) and proportions (%) with 95% confidence intervals (CI).

RESULTS

Of 4134 unique abstracts screened, 92 studies (N = 5365 patients, 5658 ears) were included. Mean improvement of overall word recognition scores for patients with precurved EAs (46.5%, 95% CI: 43.13-49.88%) was significantly (p = 0.0009) superior to that of patients with straight EAs (36.33%; 95% CI, 31.4-41.27%). There was no significant difference between mean improvement of Azbio Quiet scores, mean improvement of overall sentences in noise scores, or HP or pure-tone averages between patients with precurved EAs and those with straight EAs.

CONCLUSIONS

Precurved EAs were superior in mean word recognition score improvement, but there was no superior EA design regarding sentence recognition or hearing preservation.

Curvature analysis of CI electrode arrays: a novel approach to categorize perimodiolar positions without anatomical landmarks

PURPOSE

Perimodiolar electrode arrays may be positioned regular, over-inserted or under-inserted into the cochlea depending on the cochlear size and shape. The study aimed to examine whether there are differences between these groups in the local curvature along the intracochlear array. Individual curvature variables were developed to categorize the groups and the relationship between the curvature and the angular insertion depth at the electrode tip was analyzed.

METHODS

The curvature along the intracochlear array was measured in the CBCT image of 85 perimodiolar electrodes of a single type. The mean curvature and the ratio of the mean curvature at contacts E14-16 to the mean curvature at E7-8 (bowing ratio) were calculated across the array, and its true positive rate (TPR) and false positive rate (FPR) were calculated to establish optimal threshold values to categorize the groups.

RESULTS

68.2% of the cases were categorized as regular positioned, 22.4% had an over-insertion and 9.4% had an under-insertion. The mean curvature was significantly weaker with under-insertion (< 342°) than with normal insertion depth (≥ 342°). With an over-insertion, the bowing ratio was < 1 and otherwise > 1. Both the mean curvature and bowing ratio were found to have an optimal threshold value with high TPR (= 1.00) and low FPR (≤ 0.06) for categorizing under-insertion and over-insertion, respectively.

CONCLUSION

Curvature analysis is a useful tool to assess if a perimodiolar electrode array has been inserted deep enough into the cochlea. Independent of critical anatomical landmarks, over-inserted arrays and under-inserted arrays could be well categorized by using individual curvature variables. The results need to be validated using additional data sets.

Comparison of Performance for Cochlear-Implant Listeners Using Audio Processing Strategies Based on Short-Time Fast Fourier Transform or Spectral Feature Extraction

OBJECTIVES

We compared sound quality and performance for a conventional cochlear-implant (CI) audio processing strategy based on short-time fast-Fourier transform (Crystalis) and an experimental strategy based on spectral feature extraction (SFE). In the latter, the more salient spectral features (acoustic events) were extracted and mapped into the CI stimulation electrodes. We hypothesized that (1) SFE would be superior to Crystalis because it can encode acoustic spectral features without the constraints imposed by the short-time fast-Fourier transform bin width, and (2) the potential benefit of SFE would be greater for CI users who have less neural cross-channel interactions.

DESIGN

To examine the first hypothesis, 6 users of Oticon Medical Digisonic SP CIs were tested in a double-blind design with the SFE and Crystalis strategies on various aspects: word recognition in quiet, speech-in-noise reception threshold (SRT), consonant discrimination in quiet, listening effort, melody contour identification (MCI), and subjective sound quality. Word recognition and SRTs were measured on the first and last day of testing (4 to 5 days apart) to assess potential learning and/or acclimatization effects. Other tests were run once between the first and last testing day. Listening effort was assessed by measuring pupil dilation. MCI involved identifying a five-tone contour among five possible contours. Sound quality was assessed subjectively using the multiple stimulus with hidden reference and anchor (MUSHRA) paradigm for sentences, music, and ambient sounds. To examine the second hypothesis, cross-channel interaction was assessed behaviorally using forward masking.

RESULTS

Word recognition was similar for the two strategies on the first day of testing and improved for both strategies on the last day of testing, with Crystalis improving significantly more. SRTs were worse with SFE than Crystalis on the first day of testing but became comparable on the last day of testing. Consonant discrimination scores were higher for Crystalis than for the SFE strategy. MCI scores and listening effort were not substantially different across strategies. Subjective sound quality scores were lower for the SFE than for the Crystalis strategy. The difference in performance with SFE and Crystalis was greater for CI users with higher channel interaction.

CONCLUSIONS

CI-user performance was similar with the SFE and Crystalis strategies. Longer acclimatization times may be required to reveal the full potential of the SFE strategy.

Evaluating cochlear implant outcomes in DFNA9 subjects: a comprehensive study on cerebral white matter lesions and vestibular abnormalities

PURPOSE

This study assessed whether the Fazekas score could account for the variability in cochlear implantation (CI) outcomes among individuals with DFNA9 and evaluated signal loss in the semicircular canals (SCCs) on magnetic resonance imaging (MRI) among individuals with DFNA9.

METHOD

This retrospective cross-sectional study included CI recipients with DFNA9. Pre-implantation MRI-scans were reviewed to determine the Fazekas score, localizing and grading cerebral white matter lesions (WML), and identify abnormalities in the SCCs. CI performance was assessed by evaluating phoneme scores one year post-implantation. The function of the SCCs was evaluated using rotatory chair testing with electronystagmography (ENG) and the video Head Impulse Test (vHIT).

RESULTS

Forty-five subjects (49 ears) were enrolled. The phoneme scores significantly improved from 35% (IQR 11-50) pre-implantation to 84% (IQR 76-90) one year post-implantation. No correlation was observed between the Fazekas score and the one-year post-implantation phoneme score (rsp=0.003, p = 0.986). Signal loss in at least one SCCs was detected in 97.7% of subjects and 77.8% of ears. There was no correlation between vestibular test results and fluid signal loss in the SCCs on MRI.

CONCLUSION

Most individuals with DFNA9 show improved speech recognition with CI. The observed variability in CI outcomes was not linked to the Fazekas score. Additionally, our study confirms a high prevalence of focal sclerosis in DFNA9. Recognizing the limitations of this study, further research is needed to explore the predictive role of the Fazekas score on CI outcomes and its relationship with vestibular function.

Validating an Evoked Potential Platform for Electrocochleography During Cochlear Implantation

OBJECTIVE

To validate electrocochleography (ECochG) between an auditory evoked potential (AEP) machine and an established cochlear implant (CI) manufacturer ECochG system.

METHODS

Intraoperative validation study at a tertiary referral center. Patients included adults and children undergoing cochlear implantation. Intraoperative ECochG was measured with both the Intelligent Hearing Systems (IHS) Duet AEP machine and Cochlear Corporation (CC) ECochG platform. Recording electrodes captured extracochlear measurements through a standard facial recess. Tone-bursts were presented from 250 Hz to 2 kHz (~110 dB SPL). A fast Fourier transform (FFT) of ECochG waveforms at key frequencies was summed into a total response (ECochG-TR). Pearson's correlation was utilized to evaluate the relationship between IHS-ECochG-TR and CC-ECochG-TR after confirming normality.

RESULTS

Thirty patients were enrolled with an average age of 67 years (SD 18.8). In the ear that was implanted, mean preoperative pure-tone average (PTA; 0.5, 1, 2, and 4 kHz) was 87.4 dB HL (SD 19.3) and mean preoperative word-recognition scores (WRS) was 17.0% correct (SD 19.1). There was strong correlation (r = 0.905, 95% confidence interval: 0.809 to 0.954) between IHS-ECochG-TR (median 2.30 μV, range 0.1-148.26) and CC-ECochG-TR (median 3.00 μV, range 0.1-239.63). Four patients underwent transtympanic ECochG with the IHS system for feasibility evaluation and achieved similar responses.

CONCLUSION

Extracochlear ECochG has been predictive of CI speech perception performance. The IHS duet system is a valid measure of extracochlear ECochG for the CI population. Future work will utilize this system for measuring transtympanic ECochG to improve preoperative estimation of CI performance.

LEVEL OF EVIDENCE

3 Laryngoscope, 135:308-315, 2025.

The Inter-Phase Gap Offset Effect as a Measure of Neural Health in Cochlear Implant Users With Residual Acoustic Hearing

OBJECTIVES

The inter-phase gap (IPG) offset effect is defined as the dB offset between the linear parts of electrically evoked compound action potential (ECAP) amplitude growth functions for two stimuli differing only in IPG. The method was recently suggested to represent neural health in cochlear implant (CI) users while being unaffected by CI electrode impedances. Hereby, a larger IPG offset effect should reflect better neural health. The aims of the present study were to (1) examine whether the IPG offset effect negatively correlates with the ECAP threshold and the preoperative pure-tone average (PTA) in CI recipients with residual acoustic hearing and (2) investigate the dependency of the IPG offset effect on hair cell survival and intracochlear electrode impedances.

DESIGN

Seventeen adult study participants with residual acoustic hearing at 500 Hz undergoing CI surgery at the University Hospital of Zurich were prospectively enrolled. ECAP thresholds, IPG offset effects, electrocochleography (ECochG) responses to 500 Hz tone bursts, and monopolar electrical impedances were obtained at an apical, middle, and basal electrode set during and between 4 and 12 weeks after CI surgery. Pure-tone audiometry was conducted within 3 weeks before surgery and approximately 6 weeks after surgery. Linear mixed regression analyses and t tests were performed to assess relationships between (changes in) ECAP threshold, IPG offset, impedance, PTA, and ECochG amplitude.

RESULTS

The IPG offset effect positively correlated with the ECAP threshold in intraoperative recordings ( p < 0.001) and did not significantly correlate with the preoperative PTA ( p = 0.999). The IPG offset showed a postoperative decrease for electrode sets that showed an ECochG amplitude drop. This IPG offset decrease was significantly larger than for electrode sets that showed no ECochG amplitude decrease, t (17) = 2.76, p = 0.014. Linear mixed regression analysis showed no systematic effect of electrode impedance changes on the IPG offset effect ( p = 0.263) but suggested a participant-dependent effect of electrode impedance on IPG offset.

CONCLUSIONS

The present study results did not reveal the expected relationships between the IPG offset effect and ECAP threshold values or between the IPG offset effect and preoperative acoustic hearing. Changes in electrode impedance did not exhibit a direct impact on the IPG offset effect, although this impact might be individualized among CI recipients. Overall, our findings suggest that the interpretation and application of the IPG offset effect in clinical settings should be approached with caution considering its complex relationships with other cochlear and neural health metrics.

Barriers to Early Progress in Adult Cochlear Implant Outcomes

OBJECTIVES

Adult cochlear implant (CI) recipients obtain varying levels of speech perception from their device. Adult CI users adapt quickly to their CI if they have no peripheral "bottom-up" or neurocognitive "top-down" limiting factors. Our objective here was to understand the influence of limiting factors on the progression of sentence understanding in quiet and in noise, initially and over time. We hypothesized that the presence of limiting factors, detected using a short test battery, would predictably influence sentence recognition with practical consequences. We aimed to validate the test battery by comparing the presence of limiting factors and the success criteria of >90% sentence understanding in quiet 1 month after activation.

DESIGN

The study was a single-clinic, cross-sectional, retrospective design incorporating 32 adult unilateral Nucleus CI users aged 27 to 90 years (mean = 70, SD = 13.5). Postoperative outcome was assessed through sentence recognition scores in quiet and in varying signal to noise ratios at 1 day, 1 to 2 months, and up to 2 years. Our clinic's standard test battery comprises physiological and neurocognitive measures. Physiological measures included electrically evoked compound action potentials for recovery function, spread of excitation, and polarity effect. To evaluate general cognitive function, inhibition, and phonological awareness, the Montreal Cognitive Assessment screening test, the Stroop Color-Word Test, and tests 3 and 4 of the French Assessment of Reading Skills in Adults over 16 years of age, respectively were performed. Physiological scores were considered abnormal, and therefore limiting, when total neural recovery periods and polarity effects, for both apical and basal electrode positions, were >1.65 SDs from the population mean. A spread of excitation of >6 electrode units was also considered limiting. For the neurocognitive tests, scores poorer than 1.65 SDs from published normal population means were considered limiting.

RESULTS

At 1 month, 13 out of 32 CI users scored ≥90% sentence recognition in quiet with no significant dependence on age. Subjects with no limiting peripheral or neurocognitive factors were 8.5 times more likely to achieve ≥90% score in quiet at 1 month after CI switch-on ( p = 0.010). In our sample, we detected 4 out of 32 cases with peripheral limiting factors that related to neural health or poor electrode-neural interface at both apical and basal positions. In contrast, neurocognitive limiting factors were identified in 14 out of 32 subjects. Early sentence recognition scores were predictive of long-term sentence recognition thresholds in noise such that limiting factors appeared to be of continuous influence.

CONCLUSIONS

Both peripheral and neurocognitive processing factors affect early sentence recognition after CI activation. Peripheral limiting factors may have been detected less often than neurocognitive limiting factors because they were defined using sample-based criteria versus normal population-based criteria. Early performance was generally predictive of long-term performance. Understanding the measurable covariables that limit CI performance may inform follow-up and improve counseling. A score of ≥90% for sentence recognition in quiet at 1 month may be used to define successful progress; whereas, lower scores indicate the need for diagnostic testing and ongoing rehabilitation. Our findings suggest that sentence test scores as early as 1 day after activation can provide vital information for the new CI user and indicate the need for rehabilitation follow-up.

Angular Insertion Depth in Inner Ear Malformations, Relationship to Cochlear Size, and Implications for Electrode Selection

OBJECTIVE

The objectives were to determine the interrater agreement of the Skull AP X-ray in measuring angular insertion depth (AID), to provide descriptive information about the insertion depths of different electrodes used in inner ear malformations (IEMs), to investigate the effect of cochlear size and electrode length on AID, and to guide clinicians in electrode selection in IEMs.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center.

PATIENTS

A total of 198 IEMs (n = 169 patients) and 60 cochleae with normal anatomy (n = 60 patients) were selected from patients with severe mixed or sensorineural hearing loss who presented to our clinic and underwent cochlear implantation (CI) between January 2010 and December 2022.

INTERVENTIONS

Three neurotologists independently measured AID on Skull AP X-rays. Basal turn length of the cochlea was measured in axial and coronal oblique reformatted sections on HRCT images.

MAIN OUTCOME MEASURES

Interrater reliability (ICC) of the AID measurements on Skull AP X-ray, determining the impact of cochlea size and electrode length on AID measurements.

RESULTS

The interrater reliability (ICC) test showed a high level of consistency in measuring AID in the Skull AP X-ray ( R = 0.906, p < 0.001). In the control group, a negative correlation was observed between the AID and the basal turn length of the cochlea, while a positive correlation was found between electrode length and AID ( R = 0.947, p < 0.001).

CONCLUSIONS

The Skull AP X-ray appears to be a dependable tool for measuring AID. In cases of IEMs, it is important to select an electrode of appropriate length, considering the dimensions of the cochlea.

Electrocochleography-Based Tonotopic Map: I. Place Coding of the Human Cochlea With Hearing Loss

OBJECTIVES

Due to the challenges of direct in vivo measurements in humans, previous studies of cochlear tonotopy primarily utilized human cadavers and animal models. This study uses cochlear implant electrodes as a tool for intracochlear recordings of acoustically evoked responses to achieve two primary goals: (1) to map the in vivo tonotopy of the human cochlea, and (2) to assess the impact of sound intensity and the creation of an artificial "third window" on this tonotopic map.

DESIGN

Fifty patients with hearing loss received cochlear implant electrode arrays. Postimplantation, pure-tone acoustic stimuli (0.25 to 4 kHz) were delivered, and electrophysiological responses were recorded from all 22 electrode contacts. The analysis included fast Fourier transformation to determine the amplitude of the first harmonic, indicative of predominantly outer hair cell activity, and tuning curves to identify the best frequency (BF) electrode. These measures, coupled with postoperative imaging for precise electrode localization, facilitated the construction of an in vivo frequency-position function. The study included a specific examination of 2 patients with auditory neuropathy spectrum disorder (ANSD), with preserved cochlear function as assessed by present distortion-product otoacoustic emissions, to determine the impact of sound intensity on the frequency-position map. In addition, the electrophysiological map was recorded in a patient undergoing a translabyrinthine craniotomy for vestibular schwannoma removal, before and after creating an artificial third window, to explore whether an experimental artifact conducted in cadaveric experiments, as was performed in von Békésy landmark experiments, would produce a shift in the frequency-position map.

RESULTS

A significant deviation from the Greenwood model was observed in the electrophysiological frequency-position function, particularly at high-intensity stimulations. In subjects with hearing loss, frequency tuning, and BF location remained consistent across sound intensities. In contrast, ANSD patients exhibited Greenwood-like place coding at low intensities (~40 dB SPL) and a basal shift in BF location at higher intensities (~70 dB SPL or greater). Notably, creating an artificial "third-window" did not alter the frequency-position map.

CONCLUSIONS

This study successfully maps in vivo tonotopy of human cochleae with hearing loss, demonstrating a near-octave shift from traditional frequency-position maps. In patients with ANSD, representing more typical cochlear function, intermediate intensity levels (~70 to 80 dB SPL) produced results similar to high-intensity stimulation. These findings highlight the influence of stimulus intensity on the cochlear operational point in subjects with hearing loss. This knowledge could enhance cochlear implant programming and improve auditory rehabilitation by more accurately aligning electrode stimulation with natural cochlear responses.

Individualized post-operative prediction of cochlear implantation outcomes in children with prelingual deafness using functional near-infrared spectroscopy

Objective

The goal of this study was to develop an objective measure and predictor of cochlear implantation (CI) outcomes using functional near-infrared spectroscopy (fNIRS) for young children with prelingual deafness.

Methods

Sound-evoked hemodynamic responses were recorded from auditory and language-related cortical regions of 47 child CI recipients (35.47 ± 17.24 months of age) using fNIRS shortly after CI activation (0.26 ± 0.30 months). There were four sound conditions (natural speech, instrumental music, multi-speaker babble noise, and speech-in-noise). Post-CI auditory and verbal communication performance was evaluated using clinical questionnaires with caretakers. Both classification and individualized regression models were constructed to predict post-CI behavioral improvement from fNIRS data using support vector machine (SVM) learning algorithms.

Results

Auditory cortical responses shortly after CI hearing onset yielded highly accurate prediction of behavioral development in young CI children. For classification models, optimal prediction was achieved using cortical responses to two or more sound conditions, with the highest accuracy of 98.20% (precision = 98.17%, sensitivity = 98.96%, area under the curve of the receiver operating characteristic curve = 99.61%) obtained with the combination of speech, noise, and music stimuli. Similarly, for regression models, best prediction of individual development was achieved using three (highest r = 0.919) or four (r = 0.966) sound conditions. The predictability of cortical responses far outperformed (Cohen's d: 18.56) that of the collection of audiological and demographic parameters (classification accuracy: 0.62) under the same SVM algorithms and could not benefit from the inclusion of the latter.

Conclusion

Machine learning models using auditory cortical hemodynamic responses shortly after CI activation were able to predict individualized post-CI behavioral improvement in children with prelingual deafness.

Level of Evidence

Level 5.

The Relationship Between eSRTs and Upper Stimulation Levels in a Large Cohort of Adult Cochlear Implant Recipients

OBJECTIVE

To compare electrically evoked stapedial reflex thresholds (eSRTs) measured at 1 month post-activation to upper stimulation levels used for programming adult cochlear implant (CI) recipients over time in a large clinical population.

STUDY DESIGN

Review of prospectively collected clinical database.

SETTING

Large CI program at an academic medical center.

PATIENTS

Postlingually deafened adult CI recipients (n = 439).

MAIN OUTCOME MEASURES

eSRTs recorded in the medical record and upper stimulation levels derived from the programming software at 1 and 6 months post-activation.

RESULTS

The correlation between eSRTs and upper stimulation levels was strong for all three manufacturers (r = 0.80-0.86). On average, upper stimulation levels were set 15.4 clinical levels below eSRT for Cochlear using a pulse width of 25 microseconds, 13.4 clinical levels below eSRT for Cochlear using a pulse width of 37 microseconds, 11.3 clinical units below eSRT for Advanced Bionics, and 0.1 charge unit above eSRT for MED-EL. eSRTs were found to be elicited at similar levels for different electrodes/frequencies across the array. After upper stimulation levels were set based on eSRT at 1 month post-activation, there was no significant change in upper stimulation levels between 1 and 6 months post-activation.

CONCLUSIONS

eSRTs and upper stimulation levels are highly correlated. Average differences between eSRTs and upper stimulation levels reported herein can be used to guide programming in the clinic. Further, when eSRTs are used to program upper stimulation levels, upper stimulation levels should be relatively similar across channels and stable over time.

Investigating the effect of cochlear implant usage metrics on cortical auditory-evoked potential responses in adult recipients post-implantation

Introduction

This study examines the effect of cochlear implant (CI) device usage metrics on post-operative outcomes in unilateral CI recipients. The primary objective is to investigate the relationship between CI usage frequency (average daily CI use) and duration (total years of CI use) on electrically evoked cortical auditory-evoked potential (eCAEP) response peak latency (ms) and amplitude (μV).

Methods

Adult CI users (n = 41) who previously exhibited absent acoustically evoked CAEP responses participated in the study. The peak latency and amplitude of eCAEP P1-N1-P2 responses were recorded, when present for the apical, medial, and basal test electrode contacts. CI duration was defined as the number of years between the date of CI activation and date that eCAEP testing was performed. CI usage frequency was defined as the average number of hours per day of audio processor use, which was recorded using the CI programming software.

Results

Overall, 27 participants (65.85%) exhibited detectable eCAEP responses across one or more electrode contacts. Among these, 18 participants (43.9%) elicited eCAEP responses at all three electrode contacts, while 7 (17.07%) showed responses at two contacts, and 2 (4.88%) at one contact. For the remaining 14 participants (34.15%), eCAEP responses were either absent or undetectable. CI usage frequency (average daily CI use [hours/day]) was captured for 32 (78%) of the participants (median 10.35 h/day, range 0.2-16 h/day). Participants with present eCAEP responses for the basal electrode (n = 14) showed significantly higher CI usage frequency (11.8 h/day, p = 0.026) compared to those with non-detectable responses (6.25 h/day). An association was found between higher CI usage frequency and reduced N1 (p = 0.002), P2 (p = 0.0037) and P1-N1 inter-peak (p = 0.015) response latency (ms). While CI duration (total CI use [years]) did not differ significantly between groups based on the presence of eCAEP responses, an association was found between greater CI duration and increased eCAEP response amplitude (μV) for the P2 (p = 0.008) and N1-P2 peak-peak (p = 0.009) response components.

Discussion

Additionally, most (65.85%) participants who previously exhibited absent acoustic CAEP responses developed eCAEP responses after consistent CI use and increased CI experience. These findings may suggest a potential for cortical plasticity and adaptation with consistent CI use over time. Recognizing the impact of device usage metrics on neural responses post-implantation enhances our understanding of the importance of consistent daily CI use. Overall, these findings contribute to addressing the variability among CI users, improving post-operative outcomes and advancing the standard of personalized care in auditory rehabilitation.

Speech Perception Ability and Subjective Satisfaction After Upgrade of Speech Processor in Cochlear Implantation

Objective: Cochlear implant (CI) users face the decision of whether to upgrade to a new sound processor (SP) with technological advances. We wanted to assess the changes of speech perception ability and aided hearing thresholds as well as subjective satisfaction after upgrade to a new SP. Methods: Fifty-five patients who have used CI for 10 years or more and upgraded to a new SP were enrolled. Word recognition scores were assessed before the upgrade and compared to those assessed 1 year after the upgrade to the Nucleus 7 SP. Changes of aided hearing thresholds and C- and T-levels were analyzed. Results: Previous SPs were 3G in 5, Freedom in 40, N5 in 24, and N6 in 6. Speech perception remained relatively unaffected by SP upgrade. The C- and T-levels increased after SP upgrading and the aided thresholds with previous generation SPs were higher than those 1 year after SP upgrading at all frequencies. In questionnaires, subjects felt that there was a definite subjective benefit to upgrading while most (60%) felt no difference regarding the communication in noise. Conclusions: Speech perception remained similar, but there were improved hearing sensitivity and better satisfaction after SP upgrade.

The rise of cochlear gene therapy

Recent evidence provides strong support for the safe and effective use of gene therapy in humans with hearing loss. By means of a single local injection of a set of adeno-associated virus (AAV) vectors, hearing was partially restored in several children with neurosensory nonsyndromic autosomal recessive deafness 9 (DFNB9), harboring variants in the OTOF gene. Current research focuses on refining endoscopic and transmastoid injection procedures to reduce risks of side effects, as emerging evidence suggests bidirectional fluid exchanges between the ear and the brain. Moreover, gene editing approaches and novel AAV capsids are successfully tested in animal models and will likely lead to enhanced targeting of the cochlea. Here, we cover the recent advances in cochlear gene therapy, provide an overview of the translational potential of these new approaches for existing and future clinical trials, and highlight the translational implications that remain to be determined for their application in humans.

Task-Specific Rapid Auditory Perceptual Learning in Adult Cochlear Implant Recipients: What Could It Mean for Speech Recognition

OBJECTIVES

Speech recognition in cochlear implant (CI) recipients is quite variable, particularly in challenging listening conditions. Demographic, audiological, and cognitive factors explain some, but not all, of this variance. The literature suggests that rapid auditory perceptual learning explains unique variance in speech recognition in listeners with normal hearing and those with hearing loss. The present study focuses on the early adaptation phase of task-specific rapid auditory perceptual learning. It investigates whether adult CI recipients exhibit this learning and, if so, whether it accounts for portions of the variance in their recognition of fast speech and speech in noise.

DESIGN

Thirty-six adult CI recipients (ages = 35 to 77, M = 55) completed a battery of general speech recognition tests (sentences in speech-shaped noise, four-talker babble noise, and natural-fast speech), cognitive measures (vocabulary, working memory, attention, and verbal processing speed), and a rapid auditory perceptual learning task with time-compressed speech. Accuracy in the general speech recognition tasks was modeled with a series of generalized mixed models that accounted for demographic, audiological, and cognitive factors before accounting for the contribution of task-specific rapid auditory perceptual learning of time-compressed speech.

RESULTS

Most CI recipients exhibited early task-specific rapid auditory perceptual learning of time-compressed speech within the course of the first 20 sentences. This early task-specific rapid auditory perceptual learning had unique contribution to the recognition of natural-fast speech in quiet and speech in noise, although the contribution to natural-fast speech may reflect the rapid learning that occurred in this task. When accounting for demographic and cognitive characteristics, an increase of 1 SD in the early task-specific rapid auditory perceptual learning rate was associated with ~52% increase in the odds of correctly recognizing natural-fast speech in quiet, and ~19% to 28% in the odds of correctly recognizing the different types of speech in noise. Age, vocabulary, attention, and verbal processing speed also had unique contributions to general speech recognition. However, their contribution varied between the different general speech recognition tests.

CONCLUSIONS

Consistent with previous findings in other populations, in CI recipients, early task-specific rapid auditory perceptual, learning also accounts for some of the individual differences in the recognition of speech in noise and natural-fast speech in quiet. Thus, across populations, the early rapid adaptation phase of task-specific rapid auditory perceptual learning might serve as a skill that supports speech recognition in various adverse conditions. In CI users, the ability to rapidly adapt to ongoing acoustical challenges may be one of the factors associated with good CI outcomes. Overall, CI recipients with higher cognitive resources and faster rapid learning rates had better speech recognition.

Speech-evoked cortical activities and speech recognition in adult cochlear implant listeners: a review of functional near-infrared spectroscopy studies

Cochlear implants (CIs) are the most successful neural prostheses, enabling individuals with severe to profound hearing loss to access sounds and understand speech. While CI has demonstrated success, speech perception outcomes vary largely among CI listeners, with significantly reduced performance in noise. This review paper summarizes prior findings on speech-evoked cortical activities in adult CI listeners using functional near-infrared spectroscopy (fNIRS) to understand (a) speech-evoked cortical processing in CI listeners compared to normal-hearing (NH) individuals, (b) the relationship between these activities and behavioral speech recognition scores, (c) the extent to which current fNIRS-measured speech-evoked cortical activities in CI listeners account for their differences in speech perception, and (d) challenges in using fNIRS for CI research. Compared to NH listeners, CI listeners had diminished speech-evoked activation in the middle temporal gyrus (MTG) and in the superior temporal gyrus (STG), except one study reporting an opposite pattern for STG. NH listeners exhibited higher inferior frontal gyrus (IFG) activity when listening to CI-simulated speech compared to natural speech. Among CI listeners, higher speech recognition scores correlated with lower speech-evoked activation in the STG, higher activation in the left IFG and left fusiform gyrus, with mixed findings in the MTG. fNIRS shows promise for enhancing our understanding of cortical processing of speech in CI listeners, though findings are mixed. Challenges include test-retest reliability, managing noise, replicating natural conditions, optimizing montage design, and standardizing methods to establish a strong predictive relationship between fNIRS-based cortical activities and speech perception in CI listeners.

Long-Term Outcomes of Cochlear Implantation in Usher Syndrome

OBJECTIVES

Usher syndrome (USH), characterized by bilateral sensorineural hearing loss (SNHL) and retinitis pigmentosa (RP), prompts increased reliance on hearing due to progressive visual deterioration. It can be categorized into three subtypes: USH type 1 (USH1), characterized by severe to profound congenital SNHL, childhood-onset RP, and vestibular areflexia; USH type 2 (USH2), presenting with moderate to severe progressive SNHL and RP onset in the second decade, with or without vestibular dysfunction; and USH type 3 (USH3), featuring variable progressive SNHL beginning in childhood, variable RP onset, and diverse vestibular function. Previous studies evaluating cochlear implant (CI) outcomes in individuals with USH used varying or short follow-up durations, while others did not evaluate outcomes for each subtype separately. This study evaluates long-term CI performance in subjects with USH, at both short-term and long-term, considering each subtype separately.

DESIGN

This retrospective, observational cohort study identified 36 CI recipients (53 ears) who were categorized into four different groups: early-implanted USH1 (first CI at ≤7 years of age), late-implanted USH1 (first CI at ≥8 years of age), USH2 and USH3. Phoneme scores at 65 dB SPL with CI were evaluated at 1 year, ≥2 years (mid-term), and ≥5 years postimplantation (long-term). Each subtype was analyzed separately due to the significant variability in phenotype observed among the three subtypes.

RESULTS

Early-implanted USH1-subjects (N = 23 ears) achieved excellent long-term phoneme scores (100% [interquartile ranges {IQR} = 95 to 100]), with younger age at implantation significantly correlating with better CI outcomes. Simultaneously implanted subjects had significantly better outcomes than sequentially implanted subjects ( p = 0.028). Late-implanted USH1 subjects (N = 3 ears) used CI solely for sound detection and showed a mean phoneme discrimination score of 12% (IQR = 0 to 12), while still expressing satisfaction with ambient sound detection. In the USH2 group (N = 23 ears), a long-term mean phoneme score of 85% (IQR = 81 to 95) was found. Better outcomes were associated with younger age at implantation and higher preimplantation speech perception scores. USH3-subjects (N = 7 ears) achieved a mean postimplantation phoneme score of 71% (IQR = 45 to 91).

CONCLUSIONS

This study is currently one of the largest and most comprehensive studies evaluating CI outcomes in individuals with USH, demonstrating that overall, individuals with USH benefit from CI at both short- and long-term follow-up. Due to the considerable variability in phenotype observed among the three subtypes, each subtype was analyzed separately, resulting in smaller sample sizes. For USH1 subjects, optimal CI outcomes are expected with early simultaneous bilateral implantation. Late implantation in USH1 provides signaling function, but achieved speech recognition is insufficient for oral communication. In USH2 and USH3, favorable CI outcomes are expected, especially if individuals exhibit sufficient speech recognition with hearing aids and receive ample auditory stimulation preimplantation. Early implantation is recommended for USH2, given the progressive nature of hearing loss and concomitant severe visual impairment. In comparison with USH2, predicting outcomes in USH3 remains challenging due to the variability found. Counseling for USH2 and USH3 should highlight early implantation benefits and encourage hearing aid use.

Electrocochleography-Based Tonotopic Map: II. Frequency-to-Place Mismatch Impacts Speech-Perception Outcomes in Cochlear Implant Recipients

OBJECTIVES

Modern cochlear implants (CIs) use varying-length electrode arrays inserted at varying insertion angles within variably sized cochleae. Thus, there exists an opportunity to enhance CI performance, particularly in postlinguistic adults, by optimizing the frequency-to-place allocation for electrical stimulation, thereby minimizing the need for central adaptation and plasticity. There has been interest in applying Greenwood or Stakhovskaya et al. function (describing the tonotopic map) to postoperative imaging of electrodes to improve frequency allocation and place coding. Acoustically-evoked electrocochleography (ECochG) allows for electrophysiologic best-frequency (BF) determination of CI electrodes and the potential for creating a personalized frequency allocation function. The objective of this study was to investigate the correlation between early speech-perception performance and frequency-to-place mismatch.

DESIGN

This retrospective study included 50 patients who received a slim perimodiolar electrode array. Following electrode insertion, five acoustic pure-tone stimuli ranging from 0.25 to 2 kHz were presented, and electrophysiological measurements were collected across all 22 electrode contacts. Cochlear microphonic tuning curves were subsequently generated for each stimulus frequency to ascertain the BF electrode or the location corresponding to the maximum response amplitude. Subsequently, we calculated the difference between the stimulus frequency and the patient's CI map's actual frequency allocation at each BF electrode, reflecting the frequency-to-place mismatch. BF electrocochleography-total response (BF-ECochG-TR), a measure of cochlear health, was also evaluated for each subject to control for the known impact of this measure on performance.

RESULTS

Our findings showed a moderate correlation ( r = 0.51; 95% confidence interval: 0.23 to 0.76) between the cumulative frequency-to-place mismatch, as determined using the ECochG-derived BF map (utilizing 500, 1000, and 2000 Hz), and 3-month performance on consonant-nucleus-consonant words (N = 38). Larger positive mismatches, shifted basal from the BF map, led to enhanced speech perception. Incorporating BF-ECochG-TR, total mismatch, and their interaction in a multivariate model explained 62% of the variance in consonant-nucleus-consonant word scores at 3 months. BF-ECochG-TR as a standalone predictor tended to overestimate performance for subjects with larger negative total mismatches and underestimated the performance for those with larger positive total mismatches. Neither cochlear diameter, number of cochlear turns, nor apical insertion angle accounted for the variability in total mismatch.

CONCLUSIONS

Comparison of ECochG-BF derived tonotopic electrode maps to the frequency allocation tables reveals substantial mismatch, explaining 26.0% of the variability in CI performance in quiet. Closer examination of the mismatch shows that basally shifted maps at high frequencies demonstrate superior performance at 3 months compared with those with apically shifted maps (toward Greenwood and Stakhovskaya et al.). The implications of these results suggest that electrophysiological-based frequency reallocation might lead to enhanced speech-perception performance, especially when compared with conventional manufacturer maps or anatomic-based mapping strategies. Future research, exploring the prospective use of ECochG-based mapping techniques for frequency allocation is underway.

Are tinnitus burden and tinnitus exacerbation after cochlear implantation influenced by insertion technique, array dislocation, and intracochlear trauma?

Introduction

Although numerous studies suggest that cochlear implantation (CI) generally alleviates the overall burden of tinnitus, certain patients experience tinnitus exacerbation following CI. The exact cause of this exacerbation is still uncertain. This prospective study aimed to investigate whether cochlear trauma, resulting from scalar dislocation of the electrode array, affected postoperative tinnitus intensity, tinnitus burden, and speech perception. Additionally, the influence of CI insertion technique, insertion depth, insertion angle, and cochlear morphology on postoperative tinnitus was assessed.

Methods

We evaluated 66 CI recipients preoperatively at 2 days, 4 weeks, and 12- and 24-months following surgery. Digital volume tomography was employed to document scalar position, insertion depth, and cochlear morphology postoperatively. Speech perception was analyzed using Freiburg monosyllables. The tinnitus burden was evaluated using the tinnitus questionnaire, while the tinnitus intensity was quantified using a visual analog scale.

Results

Study results pertaining to tinnitus intensity and burden did not reveal a significant difference in elevation regarding scalar position and dislocation after CI surgery compared to preoperative tinnitus levels. However, dislocation was only identified in four patients, and scala vestibuli insertions were observed in two patients. Comparing preoperative and 1-year postoperative outcomes, CI was noted to substantially reduce the tinnitus burden. When the speech processor was worn, the tinnitus intensity was significantly diminished. In comparison to round window (RW) insertion, the insertion technique cochleostomy (CS) did not exhibit a significant difference or a trend toward increased tinnitus intensity.

Conclusion

This study demonstrates that CI significantly decreases the tinnitus burden. The observation implies that the electrical stimulation of the auditory pathway, facilitated by wearing the speech processor, significantly reduced the tinnitus intensity. The incidence of dislocations and scala vestibuli insertions has declined to the extent that it is no longer feasible to formulate statistically significant conclusions.

A Novel Algorithm to Analyze Multi-Frequency Electrocochleography Measurements to Monitor Electrode Placement During Cochlear Implant Surgery

OBJECTIVES

During cochlear implant (CI) electrode placement, single low-frequency (e.g., 500 Hz) cochlear microphonics (CM) measurements are used to monitor hair-cell function and provide feedback to avert insertion trauma. However, it can be difficult to differentiate between trauma and the electrode's progression through the cochlea when monitored with a single frequency. Multi-frequency CM measurements, while more complex to analyze, can provide more accurate feedback by measuring CM from various locations along the basilar membrane.

METHODS

A new algorithm was developed to analyze multi-frequency CM tracings by comparing amplitude and phase changes across different test frequencies. The new algorithm was evaluated as to its ability to identify drop-alarm instances with the multi-frequency approach, as compared to single-frequency 500 Hz tracings.

RESULTS

The algorithm presented in this manuscript uses the relationship between CM amplitude and phase changes across frequencies to provide real-time feedback during CI electrode placement. The results show that multi-frequency CM tracings raised an alarm only 0.5 times, as compared to 2.8 instances of alarm raised for the single-frequency 500 Hz CM measurements.

CONCLUSIONS

Multi-frequency CM tracings can help reduce the number of alarms which may be false positives prompting unnecessary electrode manipulations, thereby minimizing the risk of insertion trauma.

Lessons learned in delayed identification of a misplaced electrode array in the vestibule

To report a case of cochlear implantation with a misplaced electrode array in the vestibule and the causes for the delay in identification. A 23-year-old male with left single-sided deafness underwent cochlear implantation. The intraoperative assessment did not reveal any major red flags of electrode array misplacement. He did not display any vestibular symptoms postoperatively but showed poor speech performance, even though the aided tone audiometry revealed good sound detection thresholds. High-resolution computed tomography (HRCT) showed that the entire perimodiolar electrode array was situated within the vestibule, and a revision surgery was conducted. Retrospective analysis of the neural response telemetry (NRT) revealed subtle differences in responses between the misplaced and correctly placed electrode arrays. Unlike previously reported cases, the patient did not display vestibular symptoms despite the misplacement of the electrode in the vestibule due to existing weakness in otolithic function. Further investigation is warranted when a motivated patient with normal inner ear anatomy does not show benefit with the cochlear implant post-operatively.

When to Start Computer-Based Auditory Training After Cochlear Implantation: Effects on Quality of Life and Speech Recognition

OBJECTIVE

Computer-based auditory training (CBAT) has been shown to improve outcomes in adult cochlear implant (CI) users. This study evaluates in new CI users whether starting CBAT within 3 months of activation or later impacts CI outcomes.

STUDY DESIGN

Prospective natural experiment.

SETTING

Tertiary academic medical center.

PATIENTS

Sixty-five new adult CI users.

INTERVENTIONS

CBAT use over the first-year postactivation.

MAIN OUTCOME MEASURES

Speech recognition scores and CIQOL-35 Profile score improvements between CI recipients who started CBAT resources early (<3 mo) and late (3-12 mo) postactivation.

RESULTS

A total of 43 CI recipients started using CBAT within 3 months postactivation (early) and 22 after 3 months (late). Patients who used CBAT within 3 months postactivation showed significantly greater improvement in consonant-nucleus-consonant words (CNCw) (48.3 ± 24.2% vs 27.8 ± 24.9%; d = 0.84), AzBio Sentences in quiet (55.1 ± 28.0% vs 35.7 ± 36.5%; d = 0.62), and CIQOL-35 listening domain scores (18.2 ± 16.3 vs 6.9 ± 12.9, d = 0.73 [0.023, 1.43]), at 3 months postactivation, compared to those who had not yet initiated CBAT. However, by 12 months postactivation, after which all CI recipients had started CBAT, there were no differences observed between patients who started CBAT early or late in speech recognition scores (CNCw: d = 0.26 [-0.35, 0.88]; AzBio: d = 0.37 [-0.23, 0.97]) or in any CIQOL global or domain score (d-range = 0.014-0.47).

CONCLUSIONS

Auditory training with self-directed computer software (CBAT) may yield speech recognition and quality-of-life benefits for new adult CI recipients. While early users showed greater improvement in outcomes at 3 months postactivation than users who started later, both groups achieved similar benefits by 12 months postactivation.

Advances in Evaluation of Electrode Insertion Trauma Induced Residual Hearing loss in Cochlear Implant Recipients and its significance- A Narrative Review

Cochlear implant surgery has revolutionized the management of profound hearing loss, with a growing focus on preserving residual hearing, particularly low-frequency hearing. This review synthesizes existing literature on cochlear implantation techniques, surgical principles, and emerging therapies aimed at reducing post-implantation hearing loss. Methodologically, a comprehensive narrative literature review was conducted, encompassing various study designs and participant demographics. The search strategy involved major biomedical databases, focusing on articles in English. Surgical techniques such as "soft surgery" emphasize minimizing mechanical stress on the cochlea, while advancements in pharmacological agents explore the use of corticosteroids, neurotrophins, and growth factors to enhance hearing preservation. Electrode design and insertion strategies are evolving to minimize trauma and optimize hearing outcomes, including consideration of insertion forces and electrode array designs. Evaluating residual hearing loss involves sophisticated techniques like electrocochleography and radiological imaging. The impact of residual hearing on auditory verbal outcomes is variable, with studies indicating positive correlations with language development, particularly in speech production. Emerging strategies in electrode design, surgical techniques, and drug delivery hold promise for improving outcomes in cochlear implantation. However, challenges such as the lack of standardized guidelines and the need for further clinical trials remain. Future directions include the exploration of nanotechnologies, gene therapies, and stem cells for constructing bionic ears, although ethical and technical hurdles persist. This review underscores the ongoing efforts to enhance cochlear implant functionality and the need for continued research to optimize outcomes for patients with hearing loss.

[Audiological outcome of bimodal CI users over time and depending on different influencing factors]

BACKGROUND

Hearing-impaired persons with asymmetric hearing loss and a unilateral indication for a cochlear implant (CI) generally benefit from a bimodal hearing solution. The influence of bimodal fitting on speech comprehension (SC) over time has not yet been sufficiently investigated. The present study examines the influence of bimodal fitting on SC in bimodally fitted CI users with postlingual deafness at least 36 months after implantation and analyzes possible influencing factors.

METHODS

Included in this retrospective longitudinal study were 54 bimodally fitted speech-competent CI users with at least 36 months of CI experience. Audiometric data of these CI users at predefined timepoints were compared.

RESULTS

The change in the results of the Freiburg monosyllabic test (FT) over 36 months was significant (p < 5%) for the deafness group at <10 years for both the 65 dB sound pressure level (SPL) and at 80 dB SPL and also significant for the deafness group ≥10 years for 65 dB SPL. In the Oldenburg sentence test (OlSa) there was a highly significant change (p < 0.1%) for S0, S0N0, and S0NCI configurations and a very significant change (p < 1%) for S0NHA (HA: hearing aid). Age at implantation as a possible influencing factor could not be confirmed in the FT. In contrast, the duration of deafness was a negative influencing factor for SC with CI in the FT, whereas a longer duration of deafness was associated with worse results in the FT. The degree of hearing loss in the ear fitted with an HA did not influence SC. The median bimodal benefit (here: difference in SC with bimodal fitting compared to unilateral HA fitting for FT at 65 dB SPL) was 10% over the total study period. For a median of 79% of the test subjects, the bimodal benefit was found over the entire period of 36 months.

CONCLUSION

Over time, SC improves significantly with a CI for the bimodal test subjects. The investigated influencing factors (age, duration of deafness, and degree of hearing loss in the contralateral ear) support the indication for bimodal provision in accordance with the guideline in Germany for cochlear implantation-regardless of age, duration of deafness, and hearing ability of the contralateral ear.

Pupillometry reveals effects of pitch manipulation within and across words on listening effort and short-term memory

For individuals with hearing loss, even successful speech communication comes at a cost. Cochlear implants transmit degraded information, specifically for voice pitch, which demands extra and sustained listening effort. The current study hypothesized that abnormal pitch patterns contribute to the additional listening effort, even in non-tonal language native speaking normally hearing listeners. We manipulated the fundamental frequency (F0) within and across words, while participants listen and repeat (simple intelligibility task), or listen, repeat, and later recall (concurrent encoding task) the words. In both experiments, the F0 manipulations resulted in small changes in intelligibility but no difference in free recall or subjective effort ratings. Pupillary metrics were yet sensitive to these manipulations: pupil dilations were larger when words were monotonized (flat contour) or inverted (the natural contour flipped upside-down), and larger when successive words were organized into a melodic pattern. The most likely interpretation is that the natural or expected F0 contour of a word contributes to its identity and facilitate its matching and retrieval from the phonological representation stored in long-term memory. Consequently, degrading words' F0 contour can result in extra listening effort. Our results call for solutions to improve pitch saliency and naturalness in future development of cochlear implants' signal processing strategies, even for non-tonal languages.