Implications of deep electrode insertion on cochlear implant fitting

Effects of selective stimulation of apical electrodes on temporal pitch perception by cochlear implant recipients

This study investigated whether selective apical stimulation improves temporal pitch perception in eight MED-EL cochlear implant recipients and whether any such improvement relates to auditory-nerve survival. Three stimulation conditions differing in the place and width of excitation were evaluated: single-electrode stimulation of (i) the most apical, (ii) a mid-array electrode, and (iii) multi-electrode stimulation of the four most apical electrodes. Stimulation-current-induced non-stimulating electrode voltages were recorded to identify extracochlear electrodes and gauge insertion depth. The pitches of the four most apical electrodes were compared using place-pitch ranking. Rate-pitch ranking was assessed between 80 and 981 pulses per second for the three stimulation conditions, to estimate the "upper limit" of temporal pitch. Single-electrode apical stimulation did not increase the upper limit relative to other conditions. The polarity effect (PE), defined as the difference between thresholds obtained for triphasic pulse trains with their central high-amplitude phase either anodic or cathodic, was obtained to evaluate peripheral neural health. The PE did not differ between apical and mid-array stimulation or correlate with the upper limit. In conclusion, we found no improvement of temporal pitch perception with single-electrode apical stimulation, and discuss possible explanations for this observation.

Preoperative Imaging in Cochlear Implants

OBJECTIVE

To determine the utility of computed tomography (CT) and magnetic resonance imaging (MRI) in cochlear implant candidates.

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral hospital.

PATIENTS

A total of 207 cochlear implanted patients with CT and/or MRI.

INTERVENTIONS

N/A.

MAIN OUTCOME MEASURES

Age versus abnormal radiologic findings, imaging abnormality versus postoperative outcomes, postoperative outcomes versus electrode design, Cambridge Cochlear Implant Protocol (CCIP) status for imaging abnormalities, sensitivity and specificity of CT and MRI for round-window/cochlear occlusion, and MRI for incomplete partitions.

RESULTS

A total of 207 patients with CT, MRI, or both were reviewed retrospectively. Less than half (15.5%) of CT scans had findings that might affect surgical intervention compared with 5.9% of MRI. No significant difference was found between children and adults for relevant imaging abnormalities (grade 4 or higher) with either CT (p = 0.931) or MRI (p = 0.606). CCIP status correlated with cochlear abnormalities (p = 0.040); however, only 46.2% of radiographic abnormalities on CT would be identified by these criteria. For detecting cochlear occlusion requiring surgical intervention, the sensitivity and specificity for CT were 40% (4 of 10; 95% confidence interval [CI], 12.16-73.76) and 95.73% (95% CI, 91.40-98.27), respectively. For MRI, the sensitivity and specificity were 33.33% (1 of 3; 95% CI, 0.84-90.57) and 96.97% (63 of 65; 95% CI, 89.32-99.63), respectively. There was no difference for postoperative AzBio scores for higher-grade imaging abnormalities (p = 0.6012) or for electrode designs (p = 0.3699).

CONCLUSIONS

Significant radiographic abnormalities were relatively uncommon in cochlear implant patients on either CT or MRI at our single-center institution. If present, abnormal imaging findings rarely translated to management changes. CCIP status does not reliably predict which patients are likely to have abnormalities. Both MRI and CT have low sensitivity for round-window or cochlear occlusion, but detection likely leads to changes in surgical management.

Comparing linear and non-linear models to estimate the appropriate cochlear implant electrode array length-are current methods precise enough?

PURPOSE

In cochlear implantation with flexible lateral wall electrode arrays, a cochlear coverage (CC) range between 70% and 80% is considered ideal for optimal speech perception. To achieve this CC, the cochlear implant (CI) electrode array has to be chosen according to the individual cochlear duct length (CDL). Here, we mathematically analyzed the suitability of different flexible lateral wall electrode array lengths covering between 70% and 80% of the CDL.

METHODS

In a retrospective cross-sectional study preoperative high-resolution computed tomography (HRCT) from patients undergoing cochlear implantation was investigated. The CDL was estimated using an otosurgical planning software and the CI electrode array lengths covering 70-80% of the CDL was calculated using (i) linear and (ii) non-linear models.

RESULTS

The analysis of 120 HRCT data sets showed significantly different model-dependent CDL. Significant differences between the CC of 70% assessed from linear and non-linear models (mean difference: 2.5 mm, p < 0.001) and the CC of 80% assessed from linear and non-linear models (mean difference: 1.5 mm, p < 0.001) were found. In up to 25% of the patients none of the existing flexible lateral wall electrode arrays fit into this range. In 59 cases (49,2%) the models did not agree on the suitable electrode arrays.

CONCLUSIONS

The CC varies depending on the underlying CDL approximation, which critically influences electrode array choice. Based on the literature, we hypothesize that the non-linear method systematically overestimates the CC and may lead to rather too short electrode array choices. Future studies need to assess the accuracy of the individual mathematical models.

Comparison of Tonotopic and Default Frequency Fitting for Speech Understanding in Noise in New Cochlear Implantees: A Prospective, Randomized, Double-Blind, Cross-Over Study

OBJECTIVES

While cochlear implants (CIs) have provided benefits for speech recognition in quiet for subjects with severe-to-profound hearing loss, speech recognition in noise remains challenging. A body of evidence suggests that reducing frequency-to-place mismatch may positively affect speech perception. Thus, a fitting method based on a tonotopic map may improve speech perception results in quiet and noise. The aim of our study was to assess the impact of a tonotopic map on speech perception in noise and quiet in new CI users.

DESIGN

A prospective, randomized, double-blind, two-period cross-over study in 26 new CI users was performed over a 6-month period. New CI users older than 18 years with bilateral severe-to-profound sensorineural hearing loss or complete hearing loss for less than 5 years were selected in the University Hospital Centre of Rennes in France. An anatomical tonotopic map was created using postoperative flat-panel computed tomography and a reconstruction software based on the Greenwood function. Each participant was randomized to receive a conventional map followed by a tonotopic map or vice versa. Each setting was maintained for 6 weeks, at the end of which participants performed speech perception tasks. The primary outcome measure was speech recognition in noise. Participants were allocated to sequences by block randomization of size two with a ratio 1:1 (CONSORT Guidelines). Participants and those assessing the outcomes were blinded to the intervention.

RESULTS

Thirteen participants were randomized to each sequence. Two of the 26 participants recruited (one in each sequence) had to be excluded due to the COVID-19 pandemic. Twenty-four participants were analyzed. Speech recognition in noise was significantly better with the tonotopic fitting at all signal-to-noise ratio (SNR) levels tested [SNR = +9 dB, p = 0.002, mean effect (ME) = 12.1%, 95% confidence interval (95% CI) = 4.9 to 19.2, standardized effect size (SES) = 0.71; SNR = +6 dB, p < 0.001, ME = 16.3%, 95% CI = 9.8 to 22.7, SES = 1.07; SNR = +3 dB, p < 0.001 ME = 13.8%, 95% CI = 6.9 to 20.6, SES = 0.84; SNR = 0 dB, p = 0.003, ME = 10.8%, 95% CI = 4.1 to 17.6, SES = 0.68]. Neither period nor interaction effects were observed for any signal level. Speech recognition in quiet ( p = 0.66) and tonal audiometry ( p = 0.203) did not significantly differ between the two settings. 92% of the participants kept the tonotopy-based map after the study period. No correlation was found between speech-in-noise perception and age, duration of hearing deprivation, angular insertion depth, or position or width of the frequency filters allocated to the electrodes.

CONCLUSION

For new CI users, tonotopic fitting appears to be more efficient than the default frequency fitting because it allows for better speech recognition in noise without compromising understanding in quiet.

Effect of Cochlear Implant Electrode Insertion Depth on Speech Perception Outcomes: A Systematic Review

Objective

The suitable electrode array choice is broadly discussed in cochlear implantation surgery. Whether to use a shorter electrode length under the aim of structure preservation versus choosing a longer array to achieve a greater cochlear coverage is a matter of debate. The aim of this review is to identify the impact of the insertion depth of a cochlear implant (CI) electrode array on CI users' speech perception outcomes.

Databases Reviewed

PubMed was searched for English-language articles that were published in a peer-reviewed journal from 1997 to 2022.

Methods

A systematic electronic search of the literature was carried out using PubMed to find relevant literature on the impact of insertion depth on speech perception. The review was conducted according to the preferred reporting items for systematic reviews and meta-analyses guidelines of reporting. Studies in both, children and adults with pre- or postlingual hearing loss, implanted with a CI were included in this study. Articles written in languages other than English, literature reviews, meta-analyses, animal studies, histopathological studies, or studies pertaining exclusively to imaging modalities without reporting correlations between insertion depth and speech outcomes were excluded. The risk of bias was determined using the "Risk of Bias in Nonrandomized Studies of Interventions" tool. Articles were extracted by 2 authors independently using predefined search terms. The titles and abstracts were screened manually to identify studies that potentially meet the inclusion criteria. The extracted information included: the study population, type of hearing loss, outcomes reported, devices used, speech perception outcomes, insertion depth (linear insertion depth and/or the angular insertion depth), and correlation between insertion depth and the speech perception outcomes.

Results

A total of 215 relevant studies were assessed for eligibility. Twenty-three studies met the inclusion criteria and were analyzed further. Seven studies found no significant correlation between insertion depth and speech perception outcomes. Fifteen found either a significant positive correlation or a positive effect between insertion depth and speech perception. Only 1 study found a significant negative correlation between insertion depth and speech perception outcomes.

Conclusion

Although most studies reported a positive effect of insertion depth on speech perception outcomes, one-third of the identified studies reported no correlation. Thus, the insertion depth must be considered as a contributing factor to speech perception rather than as a major decisive criterion.

Registration

This review has been registered in PROSPERO, the international prospective register of systematic reviews (CRD42021257547), available at https://www.crd.york.ac.uk/PROSPERO/.

Cochlear coverage with lateral wall cochlear implant electrode arrays affects post-operative speech recognition

OBJECTIVES

The goal was to investigate the relationship between the insertion angle/cochlear coverage of cochlear implant electrode arrays and post-operative speech recognition scores in a large cohort of patients implanted with lateral wall electrode arrays.

METHODS

Pre- and post-operative cone beam computed tomography scans of 154 ears implanted with lateral wall electrode arrays were evaluated. Traces of lateral wall and electrode arrays were combined into a virtual reconstruction of the implanted cochlea. This reconstruction was used to measure insertion angles and proportional cochlear coverage. Word recognition scores and sentence recognition scores measured 12 months after implantation using electric-only stimulation were used to examine the relationship between cochlear coverage/insertion angle and implantation outcomes.

RESULTS

Post-operative word recognition scores and the difference between post- and pre-operative word recognition scores were positively correlated with both cochlear coverage and insertion angle, however sentence recognition scores were not. A group-wise comparison of word recognition scores revealed that patients with cochlear coverage below 70% performed significantly worse than patients with coverage between 79%-82% (p = 0.003). Performance of patients with coverage above 82% was on average poorer than between 79%-82, although this finding was not statistically significant (p = 0.84). Dividing the cohort into groups based on insertion angle quadrants revealed that word recognition scores were highest above 450° insertion angle, sentence recognition scores were highest between 450° and 630° and the difference between pre- and post-operative word recognition scores was largest between 540° and 630°, however none of these differences reached statistical significance.

CONCLUSIONS

The results of this study show that cochlear coverage has an effect on post-operative word recognition abilities and the benefit patients receive from their implant. Generally, higher coverage led to better outcomes, however there were results indicating that insertion past 82% cochlear coverage may not provide an additional benefit for word recognition. These findings can be useful for choosing the optimal electrode array and thereby improving cochlear implantation outcomes on a patient-individual basis.

Cochlear Implantation in Pediatrics: The Effect of Cochlear Coverage

The effect of insertion depth and position of cochlear implant (CI) electrode arrays on speech perception remains unclear. This study aimed to determine the relationship between cochlear coverage and speech performance in children with prelingual hearing loss with CI. Pure tone audiometry (PTA) and speech audiometry, including speech reception threshold (SRT) using spondee words and speech discrimination score (SDS) using phonetically balanced monosyllabic words, were tested. The Categories of Auditory Performance (CAP) and Speech Intelligibility Rating (SIR) scales were also used. Thirty-one ears were implanted with the FLEX 28 electrode array, and 54 with the FORM 24 were included in the current study. For the studied ear, the mean cochlear duct length was 30.82 ± 2.24 mm; the mean cochlear coverage was 82.78 ± 7.49%. Cochlear coverage was a significant negative predictor for the mean pure tone threshold across frequecnies of 0.5, 1, 2, and 4 kHz (PTA4) (p = 0.019). Cochlear coverage was a significant positive predictor of SDS (p = 0.009). In children with cochlear coverage ≥ 82.78%, SDS was significantly better than in those with coverage < 82.78% (p = 0.04). Cochlear coverage was not a significant predictor of the SRT, CAP, or SIR. In conclusion, the cochlear coverage of the CI electrode array has an impact on the users' SDS. Further long-term studies with larger sample sizes should be conducted to address the most critical factors affecting CI recipients' outcomes.

Association between lateral wall electrode array insertion parameters and audiological outcomes in bilateral cochlear implantation

Purpose

The aims of this study were to compare speech recognition at different postoperative times for both ears in bilaterally implanted patients and to assess the influence of the time of deafness, frequency-to-place mismatch, angular insertion depth (AID) and angular separation between neighbouring electrode contacts on audiometric outcomes.

Methods

This study was performed at an academic tertiary referral centre. A total of 19 adult patients (6 men, 13 women), who received sequential bilateral implantation with lateral wall electrode arrays, were analysed in retrospective. Statistical analysis was performed using two-sided t test, Wilcoxon test, median test, and Spearman’s correlation.

Results

Postlingually deafened patients (deafness after the age of 10) had a significantly better speech perception (WRS65[CI]) than the perilingually deafened subjects (deafness at the age of 1–10 years) (p < 0.001). Comparison of cochlear duct length between peri- and postlingually deafened subjects showed a slightly significantly smaller cochleae in perilingual patients (p = 0.045). No association between frequency-to-place mismatch as well as angular separation and speech perception could be detected. There was even no significant difference between the both ears in the intraindividual comparison, even if insertion parameters differed.

Conclusion

The exact electrode position seems to have less influence on the speech comprehension of CI patients than already established parameters as preoperative speech recognition or duration of deafness.

Effect of Electrode Insertion Angle on Cochlear Implantation Outcomes in Adult and Children Patients with Sensorineural Hearing Loss

Purpose

To determine the role played by electrode insertion angle in cochlear implantation (CI) outcomes in adult and children patients with sensorineural hearing loss (SNHL).

Methods

Adults (n = 10) and children (n = 19) with SNHL undergoing CI in a tertiary specialized hospital were retrospectively enrolled. The measurements were evaluated before and after CI surgery using sound field audiometry and speech recognition tests. Questionnaires were used to assess subjective benefits. Electrode insertion angles were determined using postoperative X-rays.

Results

Both adult and children patients showed significant improvements in hearing, speech performance, and audiology and speech-related quality of life after CI. The angular insertion depths of adult and children group were 323.70 ± 43.57° and 341.53 ± 57.07°, respectively, showing no significant difference. In the adult group, deeper insertion depths were found to be strongly linked to lower postoperative pure tone thresholds at 12 months and higher postoperative disyllabic Word Recognition and Sentence Recognition Scores at 6 months (all P < 0.05). In the children group, deeper insertion depth had a positive correlation with postoperative monosyllabic Word Recognition Scores 6 and 12 months after CI surgery (both P < 0.05). Multiple linear regression models were constructed to predict disyllabic Word Recognition Scores at 6 and 12 months postoperatively in the children group, in which insertion angle, duration of hearing loss, and preoperative questionnaire result were identified as dependent variables.

Conclusions

Greater angular insertion depths resulted in improved hearing and speech performances after CI. The benefits of greater angular insertion depths can be found in both adult and children patients and last for at least 12 months. Clinicians are expected to determine the optimal implantation direction during CI and ensure the insertion depth to improve the speech rehabilitation of patients.

Effects of Degrees of Degeneration on the Electrical Excitation of Human Spiral Ganglion Neurons Based on a High-Resolution Computer Model

After hearing loss retrograde degeneration of spiral ganglion neurons (SGNs) has been described. Studies modeling the effects of degeneration mostly omitted peripheral processes (dendrites). Recent experimental observations indicated that degenerating SGNs manifested also a reduced diameter of their dendrites. We simulated populations of 400 SGNs inside a high resolution cochlear model with a cochlear implant, based on μCT scans of a human temporal bone. Cochlear implant stimuli were delivered as biphasic pulses in a monopolar configuration. Three SGN situations were simulated, based on our previous measurements of human SGN dendrites: (A) SGNs with intact dendrites (before degeneration), (B) degenerating SGNs, dendrites with a smaller diameter but original length, (C) degenerating SGNs, dendrites omitted. SGN fibers were mapped to characteristic frequency, and place pitch was estimated from excitation profiles. Results from degenerating SGNs (B, C) were similar. Most action potentials were initiated in the somatic area for all cases (A, B, C), except for areas near stimulating electrodes in the apex with intact SGNs (A), where action potentials were initiated in the distal dendrite. In most cases, degenerating SGNs had lower thresholds than intact SGNs (A) (down to -2 dB). Excitation profiles showed increased ectopic activation, i.e., activation of unintended neuronal regions, as well as similar neuronal regions excited by different apical electrodes, for degenerating SGNs (B, C). The estimated pitch showed cases of pitch reversals in apical electrodes for intact SGNs (A), as well as mostly identical pitches evoked by the four most apical electrodes for degenerating SGNs (B, C). In conclusion, neuronal excitation profiles to electrical stimulation exhibited similar traits in both ways of modeling SGN degeneration. Models showed degeneration of dendrites caused increased ectopic activation, as well as similar excitation profiles and pitch evoked by different apical electrodes. Therefore, insertion of electrodes beyond approximately 450° may not provide any benefit if SGN dendrites are degenerated.

Anatomy-Based Frequency Allocation in Cochlear Implantation: The Importance of Cochlear Coverage

OBJECTIVES/HYPOTHESIS

This study aimed to compare the predicted anatomy-based frequency allocation of cochlear implant electrodes with the default standard frequencies.

STUDY DESIGN

Retrospective study.

METHODS

A retrospective analysis was performed using computed tomography (CT) images of patients who received cochlear implants at a tertiary referral center. Patients were excluded if they had any congenital or acquired cochlear anatomical anomalies. The CT images of the patients were uploaded to the surgical planning software. Two independent reviewers allocated the anatomical parameters of the cochlea. The software then used these parameters to calculate the frequency allocation for each electrode according to the type of electrode and the length of the organ of Corti (OC) in each patient. These anatomy-based frequency allocations were compared with the default frequency settings.

MAIN OUTCOME MEASURE

Frequency-to-place mismatch in semitones.

RESULTS

A total of 169 implanted ears in 102 patients were included in this study. The readings of the two reviewers were homogenous, with a Cronbach's alpha of 0.98. The mean anatomy-based frequency allocation was 487.3 ± 202.9 Hz in electrode 1; 9,298.6 ± 490.6 Hz in electrode 12. The anatomy-based frequency allocations were found to be significantly higher than the frequencies of the default frequencies for each corresponding electrode (one-sample t-test, P < .001). The frequency-to-place mismatch was negatively correlated with cochlear coverage and positively correlated with the cochlear duct length (Pearson correlation > 0.65, P < .003).

CONCLUSIONS

The anatomy-based frequency allocation of each electrode is significantly different from the default frequency setting. This frequency-to-place mismatch was affected mainly by the cochlear coverage.

LEVEL OF EVIDENCE

3 Laryngoscope, 2021.

Influence of electrode to cochlear duct length ratio on post-operative speech understanding outcomes

OBJECTIVE

To assess whether the pre-operative electrode to cochlear duct length ratio (ECDLR), is associated with post-operative speech recognition outcomes.

STUDY DESIGN

A retrospective chart review study.

SETTING

Tertiary referral center.

PATIENTS

The study included sixty-one adult CI recipients with a pre-operative computed tomography scan and a speech recognition test 12 months after implantation.

INTERVENTIONS

The average of two raters' cochlear duct length (CDL) measurements and the length of the recipient's cochlear implant electrode array formed the basis for the electrode-to-cochlear duct length ratio (ECLDR). Speech recognition tests were compared as a function of ECDLR and electrode array length itself.

MAIN OUTCOME MEASURES

The relationship between ECDLR and percent correct on speech recognition tests.

RESULTS

A second order polynomial regression relating ECDLR to percent correct on the CNC words speech recognition test was statistically significant, as was a fourth order polynomial regression for the AzBio Quiet test. In contrast, there was no statistically significant relationship between speech recognition scores and electrode array length.

CONCLUSIONS

ECDLR values can be statistically associated to speech-recognition outcomes. However, these ECDLR values cannot be predicted by the electrode length alone, and must include a measure of CDL.

Fully Automated Measurement of Cochlear Duct Length From Clinical Temporal Bone Computed Tomography

OBJECTIVES/HYPOTHESIS

To present and validate a novel fully automated method to measure cochlear dimensions, including cochlear duct length (CDL).

STUDY DESIGN

Cross-sectional study.

METHODS

The computational method combined 1) a deep learning (DL) algorithm to segment the cochlea and otic capsule and 2) geometric analysis to measure anti-modiolar distances from the round window to the apex. The algorithm was trained using 165 manually segmented clinical computed tomography (CT). A Testing group of 159 CTs were then measured for cochlear diameter and width (A- and B-values) and CDL using the automated system and compared against manual measurements. The results were also compared with existing approaches and historical data. In addition, pre- and post-implantation scans from 27 cochlear implant recipients were studied to compare predicted versus actual array insertion depth.

RESULTS

Measurements were successfully obtained in 98.1% of scans. The mean CDL to 900° was 35.52 mm (SD, 2.06; range, [30.91-40.50]), the mean A-value was 8.88 mm (0.47; [7.67-10.49]), and mean B-value was 6.38 mm (0.42; [5.16-7.38]). The R² fit of the automated to manual measurements was 0.87 for A-value, 0.70 for B-value, and 0.71 for CDL. For anti-modiolar arrays, the distance between the imaged and predicted array tip location was 0.57 mm (1.25; [0.13-5.28]).

CONCLUSION

Our method provides a fully automated means of cochlear analysis from clinical CTs. The distribution of CDL, dimensions, and cochlear quadrant lengths is similar to those from historical data. This approach requires no radiographic experience and is free from user-related variation.

LEVEL OF EVIDENCE

3 Laryngoscope, 2021.

Frequency-to-Place Mismatch: Characterizing Variability and the Influence on Speech Perception Outcomes in Cochlear Implant Recipients

OBJECTIVES

The spatial position of a cochlear implant (CI) electrode array affects the spectral cues provided to the recipient. Differences in cochlear size and array length lead to substantial variability in angular insertion depth (AID) across and within array types. For CI-alone users, the variability in AID results in varying degrees of frequency-to-place mismatch between the default electric frequency filters and cochlear place of stimulation. For electric-acoustic stimulation (EAS) users, default electric frequency filters also vary as a function of residual acoustic hearing in the implanted ear. The present study aimed to (1) investigate variability in AID associated with lateral wall arrays, (2) determine the subsequent frequency-to-place mismatch for CI-alone and EAS users mapped with default frequency filters, and (3) examine the relationship between early speech perception for CI-alone users and two aspects of electrode position: frequency-to-place mismatch and angular separation between neighboring contacts, a metric associated with spectral selectivity at the periphery.

DESIGN

One hundred one adult CI recipients (111 ears) with MED-EL Flex24 (24 mm), Flex28 (28 mm), and FlexSOFT/Standard (31.5 mm) arrays underwent postoperative computed tomography to determine AID. A subsequent comparison was made between AID, predicted spiral ganglion place frequencies, and the default frequency filters for CI-alone (n = 84) and EAS users (n = 27). For CI-alone users with complete insertions who listened with maps fit with the default frequency filters (n = 48), frequency-to-place mismatch was quantified at 1500 Hz and angular separation between neighboring contacts was determined for electrodes in the 1 to 2 kHz region. Multiple linear regression was used to examine how frequency-to-place mismatch and angular separation of contacts influence consonant-nucleus-consonant (CNC) scores through 6 months postactivation.

RESULTS

For CI recipients with complete insertions (n = 106, 95.5%), the AID (mean ± standard deviation) of the most apical contact was 428° ± 34.3° for Flex24 (n = 11), 558° ± 65.4° for Flex28 (n = 48), and 636° ± 42.9° for FlexSOFT/Standard (n = 47) arrays. For CI-alone users, default frequency filters aligned closely with the spiral ganglion map for deeply inserted lateral wall arrays. For EAS users, default frequency filters produced a range of mismatches; absolute deviations of ≤ 6 semitones occurred in only 37% of cases. Participants with shallow insertions and minimal or no residual hearing experienced the greatest mismatch. For CI-alone users, both smaller frequency-to-place mismatch and greater angular separation between contacts were associated with better CNC scores during the initial 6 months of device use.

CONCLUSIONS

There is significant variability in frequency-to-place mismatch among CI-alone and EAS users with default frequency filters, even between individuals implanted with the same array. When using default frequency filters, mismatch can be minimized with longer lateral wall arrays and insertion depths that meet the edge frequency associated with residual hearing for CI-alone and EAS users, respectively. Smaller degrees of frequency-to-place mismatch and decreased peripheral masking due to more widely spaced contacts may independently support better speech perception with longer lateral wall arrays in CI-alone users.

Assessment of Inter- and Intra-Rater Reliability of Tablet-Based Software to Measure Cochlear Duct Length

OBJECTIVE

The objective of this study is to build upon previous work validating a tablet-based software to measure cochlear duct length (CDL). Here, we do so by greatly expanding the number of cochleae (n = 166) analyzed, and examined whether computed tomography (CT) slice thickness influences reliability of CDL measurements.

STUDY DESIGN

Retrospective chart review study.

SETTING

Tertiary referral center.

PATIENTS

Eighty-three adult cochlear implant recipients were included in the study. Both cochleae were measured for each patient (n = 166).

INTERVENTIONS

Three raters analyzed the scans of 166 cochleae at 2 different time points. Each rater individually identified anatomical landmarks that delineated the basal turn diameter and width. These coordinates were applied to the elliptic approximation method (ECA) to estimate CDL. The effect of CT scan slice thickness on the measurements was explored.

MAIN OUTCOME MEASURES

The primary outcome measure is the strength of the inter- and intra-rater reliability.

RESULTS

The mean CDL measured was 32.84 ± 2.03 mm, with a range of 29.03 to 38.07 mm. We observed no significant relationship between slice thickness and CDL measurement (F1,164 = 3.04; p = 0.08). The mean absolute difference in CDL estimations between raters was 1.76 ± 1.24 mm and within raters was 0.263 ± 0.200 mm. The intra-class correlation coefficient (ICC) between raters was 0.54 and ranged from 0.63 to 0.83 within raters.

CONCLUSIONS

This software produces reliable measurements of CDL between and within raters, regardless of CT scan thickness.

Incidence of Complete Insertion in Cochlear Implant Recipients of Long Lateral Wall Arrays

OBJECTIVE

High rates of partial insertion have been reported for cochlear implant (CI) recipients of long lateral wall electrode arrays, presumably caused by resistance encountered during insertion due to cochlear morphology. With recent advances in long-electrode array design, we sought to investigate (1) the incidence of complete insertions among patients implanted with 31.5-mm flexible arrays and (2) whether complete insertion is limited by cochlear duct length (CDL).

STUDY DESIGN

Retrospective review.

SETTING

Tertiary referral center.

METHODS

Fifty-one adult CI recipients implanted with 31.5-mm flexible lateral wall arrays underwent postoperative computed tomography to determine the rate of complete insertion, defined as all contacts being intracochlear. CDL and angular insertion depth (AID) were compared between complete and partial insertion cohorts.

RESULTS

Most cases had a complete insertion (96.1%, n = 49). Among the complete insertion cohort, the median CDL was 33.6 mm (range, 30.3-37.9 mm), and median AID was 641° (range, 533-751°). Two cases of partial insertion had relatively short CDL (31.8 mm and 32.3 mm) and shallow AID (542° and 575°). Relatively shallow AID for the 2 cases of partial insertion fails to support the idea that CDL alone prevents a complete insertion.

CONCLUSION

Complete insertion of a 31.5-mm flexible array is feasible in most cases and does not appear to be limited by the range of CDL observed in this cohort. Future studies are needed to estimate other variations in cochlear morphology that could predict resistance and failure to achieve complete insertion with long arrays.

Long-Term Influence of Electrode Array Length on Speech Recognition in Cochlear Implant Users

OBJECTIVES/HYPOTHESIS

Results from a prospective trial demonstrated better speech recognition for cochlear implant (CI) recipients implanted with a long lateral wall electrode array compared to subjects with a short array after 1 year of listening experience. As short array recipients may require an extended adaptation period, this study investigated whether differences in speech recognition continued through 4 years of CI use.

STUDY DESIGN

Long-term follow-up of a prospective randomized trial.

METHODS

Subjects were randomized to receive a MED-EL medium (24 mm) or standard (31.5 mm) array. Linear mixed models compared speech recognition between cohorts with word recognition in quiet and sentence recognition in noise at 1, 3, 6, 12, 24, and 48 months postactivation. Postoperative imaging and electric frequency filters were reviewed to assess the influence of frequency-to-place mismatch and angular separation between neighboring contacts, a metric associated with peripheral spectral selectivity.

RESULTS

Long (31.5 mm) array recipients demonstrated superior speech recognition out to 4 years postactivation. There was a significant effect of angular separation between contacts, with more closely spaced contacts associated with poorer speech recognition. There was no significant effect of mismatch, yet this may have been obscured by changes in frequency filters over time.

CONCLUSIONS

Conventional MED-EL CI recipients implanted with 31.5-mm arrays experience better speech recognition than 24-mm array recipients, initially and with long-term listening experience. The benefit conferred by longer arrays in the present cohort can be partially attributed to more widely spaced electrode contacts, presumably a result of reduced channel interaction.

LEVEL OF EVIDENCE

2 Laryngoscope, 131:892-897, 2021.

Angular Electrode Insertion Depth and Speech Perception in Adults With a Cochlear Implant: A Systematic Review

Objective:

By discussing the design, findings, strengths, and weaknesses of available studies investigating the influence of angular insertion depth on speech perception, we intend to summarize the current status of evidence; and using evidence based conclusions, possibly contribute to the determination of the optimal cochlear implant (CI) electrode position.

Data Sources:

Our search strategy yielded 10,877 papers. PubMed, Ovid EMBASE, Web of Science, and the Cochrane Library were searched up to June 1, 2018. Both keywords and free-text terms, related to patient population, predictive factor, and outcome measurements were used. There were no restrictions in languages or year of publication.

Study Selection:

Seven articles were included in this systematic review. Articles eligible for inclusion: (a) investigated cochlear implantation of any CI system in adults with post-lingual onset of deafness and normal cochlear anatomy; (b) investigated the relationship between angular insertion depth and speech perception; (c) measured angular insertion depth on imaging; and (d) measured speech perception at, or beyond 1-year post-activation.

Data Extraction and Synthesis:

In included studies; quality was judged low-to-moderate and risk of bias, evaluated using a Quality-in-Prognostic-Studies-tool (QUIPS), was high. Included studies were too heterogeneous to perform meta-analyses, therefore, effect estimates of the individual studies are presented. Six out of seven included studies found no effect of angular insertion depth on speech perception.

Conclusion:

All included studies are characterized by methodological flaws, and therefore, evidence-based conclusions regarding the influence of angular insertion depth cannot be drawn to date.

The Effect of Cochlear Coverage on Auditory and Speech Performance in Cochlear Implant Patients

OBJECTIVE

To determine the effect of cochlear coverage on audiological and speech parameters in patients with cochlear implants. Previous work has investigated the effect of tailoring electrode size to a cochlear implant recipient's individual cochlear duct length (CDL). However, no clear relationship has been found between speech development and the extent of electrode insertion, and the benefits of apical stimulation are not yet clear.

METHODOLOGY

In this retrospective study, we assessed the effect of cochlear coverage on audiological and speech performance. Participants were prelingually deaf children who received cochlear implants between June 2013 and December 2014 under the care of a single cochlear implant surgeon. Cochlear coverage was estimated for each ear according to electrode type, depth of insertion, and the number of active electrodes. Electrode type and length were determined by the individual's CDL, measured by computed tomography (CT), and full insertion was documented intraoperatively. The number of active electrodes was recorded using intraoperative audiological response telemetry. Audiological assessments were obtained 6 months and 1 year postoperatively. Results of the categories of auditory performance-II and speech intelligibility rating scales were obtained after 3 years. Patients were divided into two groups based on their cochlear coverage and their audiological and speech outcomes were compared.

RESULTS

Of the 97 children recruited, 47 were girls. Temporal bone CT scans showed the right and left mean CDLs among girls were 27.7 and 27.9 mm, respectively, and 29.2 mm for both ears in boys. For each sex, the right and left CDLs did not differ significantly (p = 0.07). Twenty patients were lost to follow-up, leaving 77 patients (120 ears), which were divided into groups according to cochlear coverage (complete vs. incomplete). Significant between-group differences were not found in assessments of audiology, categories of auditory performances, or speech intelligibility ratings after 3 years.

CONCLUSION

Audiological parameters do not differ according to the degree of cochlear coverage, specifically for low-frequency tones. Speech parameters are also comparable. Therefore, complete cochlear coverage does not appear to provide significant benefit over incomplete coverage for prelingually deaf cochlear implant recipients.

Dynamic current steering with phantom electrode in cochlear implants

Phantom electrode (PE) stimulation can extend the lower limit of pitch perception with cochlear implants (CIs) by using simultaneous out-of-phase stimulation of the most apical primary electrode and the adjacent basal compensating electrode. The total electrical field may push the excitation pattern beyond the most apical electrode to elicit a lower pitch, depending on the ratio of current between the compensating and primary electrodes (i.e., the compensation coefficient σ). This study tested the hypothesis that dynamic current steering of PE stimuli can be implemented by varying σ over time to encode spectral details in low frequencies. To determine the range of σ for current steering and the corresponding current levels, Experiment 1 tested CI users' loudness balance and pitch ranking of static PE stimuli with σ from 0 to 0.6 in steps of 0.2. It was found that the equal-loudness most comfortable level significantly increased with σ and can be modeled by a piecewise linear function of σ. Consistent with the previous findings, higher σ elicited either lower or similar pitches without salient pitch reversals than lower σ. Based on the results of Experiment 1, Experiment 2 created flat, rising, and falling pitch contours of 300-1000 ms using dynamic PE stimuli with time-varying σ from 0 to 0.6 and equal-loudness current levels. In a pitch contour identification (PCI) task, CI users scored 80% and above on average. Increasing the stimulus duration from 300 to 1000 ms slightly but did not significantly improve the PCI scores. Across subjects, the 1000-ms PCI scores in Experiment 2 were significantly correlated with the cumulative pitch-ranking sensitivity in Experiment 1. It is thus feasible to use dynamic current steering with PE to encode low-frequency pitch cues for CI users.

Effectiveness of Phantom Stimulation in Shifting the Pitch Percept in Cochlear Implant Users

OBJECTIVES

Phantom electrode stimulation was developed for cochlear implant (CI) systems to provide a lower pitch percept by stimulating more apical regions of the cochlea, without inserting the electrode array deeper into the cochlea. Phantom stimulation involves simultaneously stimulating a primary and a compensating electrode with opposite polarity, thereby shifting the electrical field toward the apex and eliciting a lower pitch percept. The current study compared the effect sizes (in shifts of place of excitation) of multiple phantom configurations by matching the perceived pitch with phantom stimulation to that perceived with monopolar stimulation. Additionally, the effects of electrode location, type of electrode array, and stimulus level on the perceived pitch were investigated.

DESIGN

Fifteen adult advanced bionics CI users participated in this study, which included four experiments to eventually measure the shifts in place of excitation with five different phantom configurations. The proportions of current delivered to the compensating electrode, expressed as σ, were 0.5, 0.6, 0.7, and 0.8 for the symmetrical biphasic pulses (SBC0.5, SBC0.6, SBC0.7, and SBC0.8) and 0.75 for the pseudomonophasic pulse shape (PSA0.75). A pitch discrimination experiment was first completed to determine which basal and apical electrode contacts should be used for the subsequent experiments. An extensive loudness balancing experiment followed where both the threshold level (T-level) and most comfortable level (M-level) were determined to enable testing at multiple levels of the dynamic range. A pitch matching experiment was then performed to estimate the shift in place of excitation at the chosen electrode contacts. These rough shifts were then used in the subsequent experiment, where the shifts in place of excitation were determined more accurately.

RESULTS

Reliable data were obtained from 20 electrode contacts. The average shifts were 0.39, 0.53, 0.64, 0.76, and 0.53 electrode contacts toward the apex for SBC0.5, SBC0.6, SBC0.7, SBC0.8, and PSA0.75, respectively. When only the best configurations per electrode contact were included, the average shift in place of excitation was 0.92 electrode contacts (range: 0.25 to 2.0). While PSA0.75 leads to equal results as the SBC configurations in the apex, it did not result in a significant shift at the base. The shift in place of excitation was significantly larger at the apex and with lateral wall electrode contacts. The stimulus level did not affect the shift.

CONCLUSIONS

Phantom stimulation results in significant shifts in place of excitation, especially at the apical part of the electrode array. The phantom configuration that leads to the largest shift in place of excitation differs between subjects. Therefore, the settings of the phantom electrode should be individualized so that the phantom stimulation is optimized for each CI user. The real added value to the sound quality needs to be established in a take-home trial.

Pitch Matching in Cochlear Implant Users With Single-Sided Deafness: Effects of Electrode Position and Acoustic Stimulus Type

Previous studies in patients with single-sided deafness (SSD) have reported results of pitch comparisons between electric stimulation of their cochlear implant (CI) and acoustic stimulation presented to their near-normal hearing contralateral ear. These comparisons typically used sinusoids, although the percept elicited by electric stimulation may be closer to a wideband stimulus. Furthermore, it has been shown that pitch comparisons between sounds with different timbres is a difficult task and subjected to various types of range biases. The present study aims to introduce a method to minimize non-sensory biases, and to investigate the effect of different acoustic stimulus types on the frequency and variability of the electric-acoustic pitch matches. Pitch matches were collected from 13 CI users with SSD using the binary search procedure. Electric stimulation was presented at either an apical or a middle electrode position, at a rate of 800 pps. Acoustic stimulus types were sinusoids (SINE), 1/3-octave wide narrow bands of Gaussian noises (NBN), or 1/3-octave wide pulse spreading harmonic complexes (PSHC). On the one hand, NBN and PSHC are presumed to better mimic the spread of excitation produced by a single-electrode stimulation than SINE. On the other hand, SINE and PSHC contain less inherent fluctuations than NBN and may therefore provide a temporal pattern closer to that produced by a constant-amplitude electric pulse train. Analysis of mean pitch match variance showed no differences between stimulus types. However, mean pitch matches showed effects of electrode position and stimulus type, with the middle electrode always matched to a higher frequency than the apical one (p < 0.001), and significantly higher across-subject pitch matches for PSHC compared with SINE (p = 0.017). Mean pitch matches for all stimulus types were better predicted by place-dependent characteristic frequencies (CFs) based on an organ of Corti map compared with a spiral ganglion map. CF predictions were closest to pitch matches with SINE for the apical electrode position, and conversely with NBN or PSHC for the middle electrode position. These results provide evidence that the choice of acoustic stimulus type can have a significant effect on electric-acoustic pitch matching.

Low-Frequency Pitch Perception in Cochlear Implant Recipients With Normal Hearing in the Contralateral Ear

Purpose Three experiments were carried out to evaluate the low-frequency pitch perception of adults with unilateral hearing loss who received a cochlear implant (CI). Method Participants were recruited from a cohort of CI users with unilateral hearing loss and normal hearing in the contralateral ear. First, low-frequency pitch perception was assessed for the 5 most apical electrodes at 1, 3, 6, and 12 months after CI activation using an adaptive pitch-matching task. Participants listened with a coding strategy that presents low-frequency temporal fine structure (TFS) and compared the pitch to that of an acoustic target presented to the normal hearing ear. Next, participants listened with an envelope-only, continuous interleaved sampling strategy. Pitch perception was compared between coding strategies to assess the influence of TFS cues on low-frequency pitch perception. Finally, participants completed a vocal pitch-matching task to corroborate the results obtained with the adaptive pitch-matching task. Results Pitch matches roughly corresponded to electrode center frequencies (CFs) in the CI map. Adaptive pitch matches exceeded the CF for the most apical electrode, an effect that was larger for continuous interleaved sampling than TFS. Vocal pitch matches were variable but correlated with the CF of the 3 most apical electrodes. There was no evidence that pitch matches changed between the 1- and 12-month intervals. Conclusions Relatively accurate and asymptotic pitch perception was observed at the 1-month interval, indicating either very rapid acclimatization or the provision of familiar place and rate cues. Early availability of appropriate pitch cues could have played a role in the early improvements in localization and masked speech recognition previously observed in this cohort. Supplemental Material https://doi.org/10.23641/asha.8862389.

Electrode Designs for Protection of the Delicate Cochlear Structures

The most recent electrode introductions from Advanced Bionics, the HiFocus™ Mid-Scala and the HiFocus SlimJ arrays, have common design goals intended to provide sufficient access to the necessary frequency range while avoiding intracochlear trauma. The electrode choice, either a pre-curved (mid-scala) array or straight (lateral) array, can be made by the surgeon based on anatomical considerations and/or their preferred surgical approach. Both arrays offer ease of handling, suitability for a round window and cochleostomy based insertion and control of the insertion speed.

Measurement of pitch perception as a function of cochlear implant electrode and its effect on speech perception with different frequency allocations

OBJECTIVE

An experiment was conducted to investigate the possibility that speech perception could be improved for some cochlear implant (CI) users by adjustment of the frequency allocation to the electrodes, following assessment of pitch perception along the electrode array.

STUDY SAMPLE

Thirteen adult CI users with MED-EL devices participated in the study.

DESIGN

Pitch perception was assessed for individual CI electrode pairs using the Pitch Contour Test (PCT), giving information on pitch discrimination and pitch ranking for adjacent electrodes. Sentence perception in noise was also assessed with ten different frequency allocations, including the default.

RESULTS

Pitch perception was found to be poorer for both discrimination and ranking scores at either end of the electrode array. A significant effect of frequency allocation was found for sentence scores [F(4.24,38.2) = 7.14, p < 0.001] and a significant interaction between sentence score and PCT ranking score for basal electrodes was found [F(4.24,38.2) = 2.95, p = 0.03]. Participants with poorer pitch perception at the basal end had poorer scores for some allocations with greater basal shift.

CONCLUSIONS

The results suggest that speech perception could be improved for CI users by assessment of pitch perception using the PCT and subsequent adjustment of pitch-related stimulation parameters.

A Smartphone Application for Customized Frequency Table Selection in Cochlear Implants

HYPOTHESIS

A novel smartphone-based software application can facilitate self-selection of frequency allocation tables (FAT) in postlingually deaf cochlear implant (CI) users.

BACKGROUND

CIs use FATs to represent the tonotopic organization of a normal cochlea. Current CI fitting methods typically use a standard FAT for all patients regardless of individual differences in cochlear size and electrode location. In postlingually deaf patients, different amounts of mismatch can result between the frequency-place function they experienced when they had normal hearing and the frequency-place function that results from the standard FAT. For some CI users, an alternative FAT may enhance sound quality or speech perception. Currently, no widely available tools exist to aid real-time selection of different FATs. This study aims to develop a new smartphone tool for this purpose and to evaluate speech perception and sound quality measures in a pilot study of CI subjects using this application.

METHODS

A smartphone application for a widely available mobile platform (iOS) was developed to serve as a preprocessor of auditory input to a clinical CI speech processor and enable interactive real-time selection of FATs. The application's output was validated by measuring electrodograms for various inputs. A pilot study was conducted in six CI subjects. Speech perception was evaluated using word recognition tests.

RESULTS

All subjects successfully used the portable application with their clinical speech processors to experience different FATs while listening to running speech. The users were all able to select one table that they judged provided the best sound quality. All subjects chose a FAT different from the standard FAT in their everyday clinical processor. Using the smartphone application, the mean consonant-nucleus-consonant score with the default FAT selection was 28.5% (SD 16.8) and 29.5% (SD 16.4) when using a self-selected FAT.

CONCLUSION

A portable smartphone application enables CI users to self-select frequency allocation tables in real time. Even though the self-selected FATs that were deemed to have better sound quality were only tested acutely (i.e., without long-term experience with them), speech perception scores were not inferior to those obtained with the clinical FATs. This software application may be a valuable tool for improving future methods of CI fitting.

Consonant and Vowel Identification in Cochlear Implant Users Measured by Nonsense Words: A Systematic Review and Meta-Analysis

PURPOSE

The purpose of this systematic review and meta-analysis was to establish a baseline of the vowel and consonant identification scores in prelingually and postlingually deaf users of multichannel cochlear implants (CIs) tested with consonant-vowel-consonant and vowel-consonant-vowel nonsense syllables.

METHOD

Six electronic databases were searched for peer-reviewed articles reporting consonant and vowel identification scores in CI users measured by nonsense words. Relevant studies were independently assessed and screened by 2 reviewers. Consonant and vowel identification scores were presented in forest plots and compared between studies in a meta-analysis.

RESULTS

Forty-seven articles with 50 studies, including 647 participants, thereof 581 postlingually deaf and 66 prelingually deaf, met the inclusion criteria of this study. The mean performance on vowel identification tasks for the postlingually deaf CI users was 76.8% (N = 5), which was higher than the mean performance for the prelingually deaf CI users (67.7%; N = 1). The mean performance on consonant identification tasks for the postlingually deaf CI users was higher (58.4%; N = 44) than for the prelingually deaf CI users (46.7%; N = 6). The most common consonant confusions were found between those with same manner of articulation (/k/ as /t/, /m/ as /n/, and /p/ as /t/).

CONCLUSIONS

The mean performance on consonant identification tasks for the prelingually and postlingually deaf CI users was found. There were no statistically significant differences between the scores for prelingually and postlingually deaf CI users. The consonants that were incorrectly identified were typically confused with other consonants with the same acoustic properties, namely, voicing, duration, nasality, and silent gaps. A univariate metaregression model, although not statistically significant, indicated that duration of implant use in postlingually deaf adults predict a substantial portion of their consonant identification ability. As there is no ceiling effect, a nonsense syllable identification test may be a useful addition to the standard test battery in audiology clinics when assessing the speech perception of CI users.

Qualities of Single Electrode Stimulation as a Function of Rate and Place of Stimulation with a Cochlear Implant

OBJECTIVES

Although it has been shown previously that changes in temporal coding produce changes in pitch in all cochlear regions, research has suggested that temporal coding might be best encoded in relatively apical locations. The authors hypothesized that although temporal coding may provide useable information at any cochlear location, low rates of stimulation might provide better sound quality in apical regions that are more likely to encode temporal information in the normal ear. In the present study, sound qualities of single electrode pulse trains were scaled to provide insight into the combined effects of cochlear location and stimulation rate on sound quality.

DESIGN

Ten long-term users of MED-EL cochlear implants with 31-mm electrode arrays (Standard or FLEX) were asked to scale the sound quality of single electrode pulse trains in terms of how "Clean," "Noisy," "High," and "Annoying" they sounded. Pulse trains were presented on most electrodes between 1 and 12 representing the entire range of the long electrode array at stimulation rates of 100, 150, 200, 400, or 1500 pulses per second.

RESULTS

Although high rates of stimulation are scaled as having a Clean sound quality across the entire array, only the most apical electrodes (typically 1 through 3) were considered Clean at low rates. Low rates on electrodes 6 through 12 were not rated as Clean, whereas the low-rate quality of electrodes 4 and 5 were typically in between. Scaling of Noisy responses provided an approximately inverse pattern as Clean responses. High responses show the trade-off between rate and place of stimulation on pitch. Because High responses did not correlate with Clean responses, subjects were not rating sound quality based on pitch.

CONCLUSIONS

If explicit temporal coding is to be provided in a cochlear implant, it is likely to sound better when provided apically. In addition, the finding that low rates sound clean only at apical places of stimulation is consistent with previous findings that a change in rate of stimulation corresponds to an equivalent change in perceived pitch at apical locations. Collectively, the data strongly suggest that temporal coding with a cochlear implant is optimally provided by electrodes placed well into the second cochlear turn.

Possibility of differentiation of cochlear electrodes in radiological measurements of the intracochlear and chorda-facial angle position

Due to an increasing number of cochlear implantations, quality control has become more important. In addition to intraoperative biophysical measurements, radiological imaging is another possibility. An upcoming technique regarding this is Cone Beam CT (CBCT). Sixty-five data sets (35 Nucleus Contour Advance–Cochlear; 30 Flex Soft–MedEl) of postoperative imaging by CBCT (Accu-I-tomo F17, Morita, Kyoto, Japan) underwent further evaluation. Insertion angle, height of the cochlea, distance of the electrode to the medial or lateral wall, angle between chorda tympani and facial nerve and the precise position of the electrode cable in the facial-chordal angle were determined. The typical difference between the perimodiolar and lateral course of the electrodes could also be shown in radiological measurements. This demonstrates the accuracy and advantage of CBCT in visualisation of small structures with fewer metal artifacts. Furthermore, in 75% of patients, the angle of the chorda and facial nerve could be visualised. Significant differences in dependence of the electrode type for the relation of them to the facial nerve could be seen. In conclusion, CBCT achieves reliable visualisation and detailed imaging-based measurements of the intracochlear position of different cochlea electrodes. Additionally, clinically known differences can be reproduced. Even visualisation of the position of the electrode in the chorda-facial angle is possible. Therefore, CBCT is a useful tool in intra- and postoperative control of cochlear implants.

Investigation of the effect of cochlear implant electrode length on speech comprehension in quiet and noise compared with the results with users of electro-acoustic-stimulation, a retrospective analysis

Objectives

This investigation evaluated the effect of cochlear implant (CI) electrode length on speech comprehension in quiet and noise and compare the results with those of EAS users.

Methodes

91 adults with some degree of residual hearing were implanted with a FLEX²⁰, FLEX²⁴, or FLEX²⁸ electrode. Some subjects were postoperative electric-acoustic-stimulation (EAS) users; the other subjects were in the groups of electric stimulation-only (ES-only).

Speech perception was tested in quiet and noise at 3 and 6 months of ES or EAS use. Speech comprehension results were analyzed and correlated to electrode length.

Results

While the FLEX²⁰ ES and FLEX²⁴ ES groups were still in their learning phase between the 3 to 6 months interval, the FLEX²⁸ ES group was already reaching a performance plateau at the three months appointment yielding remarkably high test scores. EAS subjects using FLEX²⁰ or FLEX²⁴ electrodes outscored ES-only subjects with the same short electrodes on all 3 tests at each interval, reaching significance with FLEX²⁰ ES and FLEX²⁴ ES subjects on all 3 tests at the 3-months interval and on 2 tests at the 6- months interval. Amongst ES-only subjects at the 3- months interval, FLEX²⁸ ES subjects significantly outscored FLEX²⁰ ES subjects on all 3 tests and the FLEX²⁴ ES subjects on 2 tests. At the-6 months interval, FLEX²⁸ ES subjects still exceeded the other ES-only subjects although the difference did not reach significance.

Conclusions

Among ES-only users, the FLEX²⁸ ES users had the best speech comprehension scores, at the 3- months appointment and tendentially at the 6 months appointment. EAS users showed significantly better speech comprehension results compared to ES-only users with the same short electrodes.

Encoding a Melody Using Only Temporal Information for Cochlear-Implant and Normal-Hearing Listeners

One way to provide pitch information to cochlear implant users is through amplitude-modulation rate. It is currently unknown whether amplitude-modulation rate can provide cochlear implant users with pitch information adequate for perceiving melodic information. In the present study, the notes of a song were encoded via amplitude-modulation rate of pulse trains on single electrodes at the apex or middle of long electrode arrays. The melody of the song was either physically correct or modified by compression or expansion. Nine cochlear implant users rated the extent to which the song was out of tune in the different conditions. Cochlear implant users on average did not show sensitivity to melody compression or expansion regardless of place of stimulation. These results were found despite the fact that three of the cochlear implant users showed the expected sensitivity to melody compression and expansion with the same task using acoustic pure tones in a contralateral acoustic ear. Normal-hearing listeners showed an inconsistent and weak effect of melody compression and expansion when the notes of the song were encoded with acoustic pulse rate. The results suggest that amplitude-modulation rate provides insufficient access to melodic information for cochlear-implant and normal-hearing listeners.

Comparison of the HiFocus Mid-Scala and HiFocus 1J Electrode Array: Angular Insertion Depths and Speech Perception Outcomes

The HiFocus Mid-Scala (MS) electrode array has recently been introduced onto the market. This precurved design with a targeted mid-scalar intracochlear position pursues an atraumatic insertion and optimal distance for neural stimulation. In this study we prospectively examined the angular insertion depth achieved and speech perception outcomes resulting from the HiFocus MS electrode array for 6 months after implantation, and retrospectively compared these with the HiFocus 1J lateral wall electrode array. The mean angular insertion depth within the MS population (n = 96) was found at 470°. This was 50° shallower but more consistent than the 1J electrode array (n = 110). Audiological evaluation within a subgroup, including only postlingual, unilaterally implanted, adult cochlear implant recipients who were matched on preoperative speech perception scores and the duration of deafness (MS = 32, 1J = 32), showed no difference in speech perception outcomes between the MS and 1J groups. Furthermore, speech perception outcome was not affected by the angular insertion depth or frequency mismatch.

The Role of Electrode Placement in Bilateral Simultaneously Cochlear-Implanted Adult Patients

Objective

To evaluate the influence of the electrode placement on hearing performance in adult patients who were simultaneously and bilaterally cochlear implanted.

Study Design

Case series with planned data collection.

Setting

Tertiary referral university centers.

Subjects and Methods

The postoperative computed tomography scan was studied for 19 patients who were simultaneously and bilaterally implanted with a long straight electrode array. The size of the cochlea was measured in consideration of the major cochlear diameter and cochlear height. The electrode-to-modiolus distance for the electrodes positioned at 180 and 360 degrees and the angular depth of insertion of the array were also measured. Speech perception was assessed at 1 and 5 years postimplantation with disyllabic word lists in quiet and in noise, with the speech coming from the front and a background noise (cocktail party) coming from 5 loudspeakers.

Results

At 1 year postimplantation, the electrode-to-modiolus distance at 180 degrees was correlated with the speech perception scores in both quiet and noise. In patients with a full electrode insertion, no correlation was found between the angular depth of insertion and hearing performance. The speech perception scores in noise gradually declined as a function of the number of inserted and active electrodes. No relationship between electrode position and speech perception scores was found at 5 years postimplantation.

Conclusion

In adult patients who were simultaneously and bilaterally implanted, the use of a long straight array, the full electrode array insertion, and the proximity to the modiolus might be determining factors to obtain the best speech performance at 1 year, without influence on the speech perception scores after long-term use.

Depth of Cochlear Implant Array Within the Cochlea and Performance Outcome

OBJECTIVE

To evaluate whether the depth of cochlear implant array within the cochlea affects performance outcomes 1 year following cochlear implantation.

METHODS

A retrospective case review of 120 patients who were implanted with the Advanced Bionics HiFocus 1J. Post-implantation plain-radiographs were retrospectively reviewed, and the depth of insertion was measured in degrees from the round window to the electrode tip. Correlation between the depth of insertion and 1-year post-activation Hearing in Noise Test (HINT) scores was analyzed. Intrascala position was not assessed.

RESULTS

Depth of electrode insertion ranged from 180° to 720°, and HINT scores ranged from 0% to 100%. A Mann-Whitney U test demonstrated significantly improved 1-year post-activation HINT scores in patients with an insertion depth of 360° or more in comparison with patients with insertion depth of less than 360° (81% vs 61%, P = .048). Patients with 13 to 15 contacts within cochlear turns performed as well as patients with full insertion of all 16 contacts, while patients with only 12 contacts performed poorly.

CONCLUSIONS

Insertion depth of the AB HiFocus 1J electrode of less than 360° is associated with reduced 1-year post-activation HINT scores when compared with deeper insertions. Partial insertion of 13 active contacts or more led to similar results as full insertion.

The Relationship Between Insertion Angles, Default Frequency Allocations, and Spiral Ganglion Place Pitch in Cochlear Implants

OBJECTIVES

Commercially available cochlear implant systems attempt to deliver frequency information going down to a few hundred Hertz, but the electrode arrays are not designed to reach the most apical regions of the cochlea, which correspond to these low frequencies. This may cause a mismatch between the frequencies presented by a cochlear implant electrode array and the frequencies represented at the corresponding location in a normal-hearing cochlea. In the following study, the mismatch between the frequency presented at a given cochlear angle and the frequency expected by an acoustic hearing ear at the corresponding angle is examined for the cochlear implant systems that are most commonly used in the United States.

DESIGN

The angular insertion of each of the electrodes on four different electrode arrays (MED-EL Standard, MED-EL Flex28, Advanced Bionics HiFocus 1J, and Cochlear Contour Advance) was estimated from X-ray. For the angular location of each electrode on each electrode array, the predicted spiral ganglion frequency was estimated. The predicted spiral ganglion frequency was compared with the center frequency provided by the corresponding electrode using the manufacturer's default frequency-to-electrode allocation.

RESULTS

Differences across devices were observed for the place of stimulation for frequencies below 650 Hz. Longer electrode arrays (i.e., the MED-EL Standard and Flex28) demonstrated smaller deviations from the spiral ganglion map than the other electrode arrays. For insertion angles up to approximately 270°, the frequencies presented at a given location were typically approximately an octave below what would be expected by a spiral ganglion frequency map, while the deviations were larger for angles deeper than 270°. For frequencies above 650 Hz, the frequency to angle relationship was consistent across all four electrode models.

CONCLUSIONS

A mismatch was observed between the predicted frequency and the default frequency provided by every electrode on all electrode arrays. The mismatch can be reduced by changing the default frequency allocations, inserting electrodes deeper into the cochlea, or allowing cochlear implant users to adapt to the mismatch. Further studies are required to fully assess the clinical significance of the frequency mismatch.

Pitch Discrimination: An Independent Factor in Cochlear Implant Performance Outcomes

Objective:

To assess differences in pitch-ranking ability across a range of speech understanding performance levels and as a function of electrode position.

Study Design:

An observational study of a cross-section of cochlear implantees.

Setting:

Tertiary referral center for cochlear implantation.

Patients:

A total of 22 patients were recruited. All three manufacturers’ devices were included (MED-EL, Innsbruck, Austria, n = 10; Advanced Bionics, California, USA, n = 8; and Cochlear, Sydney, Australia, n = 4) and all patients were long-term users (more than 18 months). Twelve of these were poor performers (scores on BKB sentence lists <60%) and 10 were excellent performers (BKB >90%).

Intervention:

After measurement of threshold and comfort levels, and loudness balancing across the array, all patients underwent thorough pitch-ranking assessments at 80% of comfort levels.

Main Outcome Measure:

Ability to discriminate pitch across the electrode array, measured by consistency in discrimination of adjacent pairs of electrodes, as well as an assessment of the pitch order across the array using the midpoint comparison task.

Results:

Within the poor performing group there was wide variability in ability to pitch rank, from no errors, to a complete inability to reliably and consistently differentiate pitch change across the electrode array. Good performers were overall significantly more accurate at pitch ranking (p = 0.026). Consistent pitch ranking was found to be a significant independent predictor of BKB score, even after adjusting for age. Users of the MED-EL implant experienced significantly more pitch confusions at the apex than at more basal parts of the electrode array.

Conclusions:

Many cochlear implant users struggle to discriminate pitch effectively. Accurate pitch ranking appears to be an independent predictor of overall outcome. Future work will concentrate on manipulating maps based upon pitch discrimination findings in an attempt to improve speech understanding.

Rate discrimination at low pulse rates in normal-hearing and cochlear implant listeners: Influence of intracochlear stimulation site

Temporal pitch perception in cochlear implantees remains weaker than in normal hearing listeners and is usually limited to rates below about 300 pulses per second (pps). Recent studies have suggested that stimulating the apical part of the cochlea may improve the temporal coding of pitch by cochlear implants (CIs), compared to stimulating other sites. The present study focuses on rate discrimination at low pulse rates (ranging from 20 to 104 pps). Two experiments measured and compared pulse rate difference limens (DLs) at four fundamental frequencies (ranging from 20 to 104 Hz) in both CI and normal-hearing (NH) listeners. Experiment 1 measured DLs in users of the (Med-El CI, Innsbruck, Austria) device for two electrodes (one apical and one basal). In experiment 2, DLs for NH listeners were compared for unresolved harmonic complex tones filtered in two frequency regions (lower cut-off frequencies of 1200 and 3600 Hz, respectively) and for different bandwidths. Pulse rate discrimination performance was significantly better when stimulation was provided by the apical electrode in CI users and by the lower-frequency tone complexes in NH listeners. This set of data appears consistent with better temporal coding when stimulation originates from apical regions of the cochlea.

Computational Models for Predicting Outcomes of Neuroprosthesis Implantation: the Case of Cochlear Implants

Electrical stimulation of the brain has resulted in the most successful neuroprosthetic techniques to date: deep brain stimulation (DBS) and cochlear implants (CI). In both cases, there is a lack of pre-operative measures to predict the outcomes after implantation. We argue that highly detailed computational models that are specifically tailored for a patient can provide useful information to improve the precision of the nervous system electrode interface. We apply our framework to the case of CI, showing how we can predict nerve response for patients with both intact and degenerated nerve fibers. Then, using the predicted response, we calculate a metric for the usefulness of the stimulation protocol and use this information to rerun the simulations with better parameters.

The Influence of Cochlear Implant Electrode Position on Performance

Objectives: To study the relation between variables related to cochlear implant electrode position and speech perception performance scores in a large patient population. Design: The study sample consisted of 203 patients implanted with a CII or HiRes90K implant with a HiFocus 1 or 1J electrode of Advanced Bionics. Phoneme and word score averages for the 1- and 2-year follow-up were calculated for 41 prelingually deaf and 162 postlingually deaf patients. Analyses to reveal correlations between these performance outcomes and 6 position-related variables (angle of most basal electrode contact, surgical insertion angle, surgical insertion, wrapping factor, angular insertion depth, linear insertion depth) were executed. The scalar location, as an indication for the presence of intracochlear trauma, and modiolus proximity beyond the basal turn were not evaluated in this study. In addition, different patient-specific variables (age at implantation, age at onset of hearing loss, duration of deafness, preoperative phoneme and word scores) were tested for correlation with performance. Results: The performance scores of prelingual patients were correlated with age at onset of hearing loss, duration of deafness and preoperative scores. For the postlingual patients, performance showed correlations with all 5 patient-specific variables. None of the 6 position-related variables influenced speech perception in cochlear implant patients. Conclusions: Although several patient-specific variables showed correlations with speech perception outcomes, not one of the studied angular and linear position-related variables turned out to have a demonstrable influence on performance.

Effects of Electrode Array Length on Frequency-Place Mismatch and Speech Perception with Cochlear Implants

Frequency-place mismatch often occurs after cochlear implantation, yet its effect on speech perception outcome remains unclear. In this article, we propose a method, based on cochlea imaging, to determine the cochlear place-frequency map. We evaluated the effect of frequency-place mismatch on speech perception outcome in subjects implanted with 3 different lengths of electrode arrays. A deeper insertion was responsible for a larger frequency-place mismatch and a decreased and delayed speech perception improvement by comparison with a shallower insertion, for which a similar but slighter effect was noticed. Our results support the notion that selecting an electrode array length adapted to each individual's cochlear anatomy may reduce frequency-place mismatch and thus improve speech perception outcome.

Optimizing frequency-to-electrode allocation for individual cochlear implant users

Individual adjustment of frequency-to-electrode assignment in cochlear implants (CIs) may potentially improve speech perception outcomes. Twelve adult CI users were recruited for an experiment, in which frequency maps were adjusted using insertion angles estimated from post-operative x rays; results were analyzed for ten participants with good quality x rays. The allocations were a mapping to the Greenwood function, a compressed map limited to the area containing spiral ganglion (SG) cells, a reduced frequency range map (RFR), and participants' clinical maps. A trial period of at least six weeks was given for the clinical, Greenwood, and SG maps although participants could return to their clinical map if they wished. Performance with the Greenwood map was poor for both sentence and vowel perception and correlated with insertion angle; performance with the SG map was poorer than for the clinical map. The RFR map was significantly better than the clinical map for three participants, for sentence perception, but worse for three others. Those with improved performance had relatively deep insertions and poor electrode discrimination ability for apical electrodes. The results suggest that CI performance could be improved by adjustment of the frequency allocation, based on a measure of insertion angle and/or electrode discrimination ability.

Gradual adaptation to auditory frequency mismatch

What is the best way to help humans adapt to a distorted sensory input? Interest in this question is more than academic. The answer may help facilitate auditory learning by people who became deaf after learning language and later received a cochlear implant (a neural prosthesis that restores hearing through direct electrical stimulation of the auditory nerve). There is evidence that some cochlear implants (which provide information that is spectrally degraded to begin with) stimulate neurons with higher characteristic frequency than the acoustic frequency of the original stimulus. In other words, the stimulus is shifted in frequency with respect to what the listener expects to hear. This frequency misalignment may have a negative influence on speech perception by CI users. However, a perfect frequency-place alignment may result in the loss of important low frequency speech information. A trade-off may involve a gradual approach: start with correct frequency-place alignment to allow listeners to adapt to the spectrally degraded signal first, and then gradually increase the frequency shift to allow them to adapt to it over time. We used an acoustic model of a cochlear implant to measure adaptation to a frequency-shifted signal, using either the gradual approach or the "standard" approach (sudden imposition of the frequency shift). Listeners in both groups showed substantial auditory learning, as measured by increases in speech perception scores over the course of fifteen one-hour training sessions. However, the learning process was faster for listeners who were exposed to the gradual approach. These results suggest that gradual rather than sudden exposure may facilitate perceptual learning in the face of a spectrally degraded, frequency-shifted input. This article is part of a Special Issue entitled <Lasker Award>.

Place pitch versus electrode location in a realistic computational model of the implanted human cochlea

Place pitch was investigated in a computational model of the implanted human cochlea containing nerve fibres with realistic trajectories that take the variable distance between the organ of Corti and spiral ganglion into account. The model was further updated from previous studies by including fluid compartments in the modiolus and updating the electrical conductivity values of (temporal) bone and the modiolus, based on clinical data. Four different cochlear geometries are used, modelled with both lateral and perimodiolar implants, and their neural excitation patterns were examined for nerve fibres modelled with and without peripheral processes. Additionally, equations were derived from the model geometries that describe Greenwood's frequency map as a function of cochlear angle at the basilar membrane as well as at the spiral ganglion. The main findings are: (I) in the first (basal) turn of the cochlea, cochlear implant induced pitch can be predicted fairly well using the Greenwood function. (II) Beyond the first turn this pitch becomes increasingly unpredictable, greatly dependent on stimulus level, state of the cochlear neurons and the electrode's distance from the modiolus. (III) After the first turn cochlear implant induced pitch decreases as stimulus level increases, but the pitch does not reach values expected from direct spiral ganglion stimulation unless the peripheral processes are missing. (IV) Electrode contacts near the end of the spiral ganglion or deeper elicit very unpredictable pitch, with broad frequency ranges that strongly overlap with those of neighbouring contacts. (V) The characteristic place pitch for stimulation at either the organ of Corti or the spiral ganglion can be described as a function of cochlear angle by the equations presented in this paper.