Comparison of Place-versus-Pitch Mismatch between a Perimodiolar and Lateral Wall Cochlear Implant Electrode Array in Patients with Single-Sided Deafness and a Cochlear Implant

Factors Affecting Performance in Adults With Cochlear Implants: A Role for Cognition and Residual Cochlear Function

OBJECTIVE

To evaluate the impact of preoperative and perioperative factors on postlinguistic adult cochlear implant (CI) performance and design a multivariate prediction model.

STUDY DESIGN

Prospective cohort study.

SETTING

Tertiary referral center.

PATIENTS AND INTERVENTIONS

Two hundred thirty-nine postlinguistic adult CI recipients.

MAIN OUTCOME MEASURES

Speech-perception testing (consonant-nucleus-consonant [CNC], AzBio in noise +10-dB signal-to-noise ratio) at 3, 6, and 12 months postoperatively; electrocochleography-total response (ECochG-TR) at the round window before electrode insertion.

RESULTS

ECochG-TR strongly correlated with CNC word score at 6 months ( r = 0.71, p < 0.0001). A multivariable linear regression model including age, duration of hearing loss, angular insertion depth, and ECochG-TR did not perform significantly better than ECochG-TR alone in explaining the variability in CNC. AzBio in noise at 6 months had moderate linear correlations with Montreal Cognitive Assessment (MoCA; r = 0.38, p < 0.0001) and ECochG-TR ( r = 0.42, p < 0.0001). ECochG-TR and MoCA and their interaction explained 45.1% of the variability in AzBio in noise scores.

CONCLUSIONS

This study uses the most comprehensive data set to date to validate ECochG-TR as a measure of cochlear health as it relates to suitability for CI stimulation, and it further underlies the importance of the cochlear neural substrate as the main driver in speech perception performance. Performance in noise is more complex and requires both good residual cochlear function (ECochG-TR) and cognition (MoCA). Other demographic, audiologic, and surgical variables are poorly correlated with CI performance suggesting that these are poor surrogates for the integrity of the auditory substrate.

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/.

One-Year Hearing Preservation and Speech Outcomes Comparing Slim Modiolar and Lateral Wall Arrays

OBJECTIVE

Compare postoperative speech outcomes in hearing preservation (HP) cochlear implantation (CI) patients with a low-frequency pure-tone average (LFPTA) ≤ 60 dB using 2 electrode array designs.

STUDY DESIGN

Retrospective cohort study.

SETTING

Large academic cochlear implant referral center.

METHODS

We reviewed adult HP CI cases using either the slim modiolar electrode (SME) (CI 532/CI 632) or th slim lateral wall electrode (SLWE) (CI 624). One-year speech outcomes and HP status were the primary outcomes.

RESULTS

A total of 132 implanted ears were analyzed (mean age 73.1 years, standard deviation [SD] 12.6), with 72% (N = 95) with CI 532/632 and 28% (N = 37) with CI 624. The mean preoperative LFPTA was 44.8 dB, SD 11.8. One-year functional HP was 27.2% (mean LFPTA shift 46.1 dB, SD 22.1) and was as follows: SME 23.9% and SLWE 36.4%, p = .168. The mean age at implantation was significantly younger only in SLWE patients with preserved hearing (66.9 vs 80.3 years, p = .008). At 6 months, speech measures were significantly better in all outcomes in HP patients with an SLWE than nonpreserved SLWE patients; this effect abated at 1 year as performance among nonpreserved SLWE patients became equivalent to the remaining cohort. Speech outcomes in SME patients were similar regardless of HP status. Age at implantation and datalogging was correlated with speech outcomes.

CONCLUSION

In this cohort of HP patients, a 1-year functional HP rate of 23.9% (SME) and 36.4% (SLWE) was observed (p = 0.168). This was initially 57.1% (SME) and 70.3% (SLWE) at activation, p = .172. Datalogging and age at implantation were correlated with postoperative speech outcomes.

Place Coding in the Human Cochlea

The cochlea's capacity to decode sound frequencies is enhanced by a unique structural arrangement along its longitudinal axis, a feature termed 'tonotopy' or place coding. Auditory hair cells at the cochlea's base are activated by high-frequency sounds, while those at the apex respond to lower frequencies. Presently, our understanding of tonotopy primarily hinges on electrophysiological, mechanical, and anatomical studies conducted in animals or human cadavers. However, direct in vivo measurements of tonotopy in humans have been elusive due to the invasive nature of these procedures. This absence of live human data has posed an obstacle in establishing an accurate tonotopic map for patients, potentially limiting advancements in cochlear implant and hearing enhancement technologies. In this study, we conducted acoustically-evoked intracochlear recordings in 50 human subjects using a longitudinal multi-electrode array. These electrophysiological measures, combined with postoperative imaging to accurately locate the electrode contacts allow us to create the first in vivo tonotopic map of the human cochlea. Furthermore, we examined the influences of sound intensity, electrode array presence, and the creation of an artificial third window on the tonotopic map. Our findings reveal a significant disparity between the tonotopic map at daily speech conversational levels and the conventional (i.e., Greenwood) map derived at close-to-threshold levels. Our findings have implications for advancing cochlear implant and hearing augmentation technologies, but also offer novel insights into future investigations into auditory disorders, speech processing, language development, age-related hearing loss, and could potentially inform more effective educational and communication strategies for those with hearing impairments.

Significance Statement

The ability to discriminate sound frequencies, or pitch, is vital for communication and facilitated by a unique arrangement of cells along the cochlear spiral (tonotopic place). While earlier studies have provided insight into frequency selectivity based on animal and human cadaver studies, our understanding of the in vivo human cochlea remains limited. Our research offers, for the first time, in vivo electrophysiological evidence from humans, detailing the tonotopic organization of the human cochlea. We demonstrate that the functional arrangement in humans significantly deviates from the conventional Greenwood function, with the operating point of the in vivo tonotopic map showing a basal (or frequency downward) shift. This pivotal finding could have far-reaching implications for the study and treatment of auditory disorders.

Valid Acoustic Models of Cochlear Implants: One Size Does Not Fit All

HYPOTHESIS

This study tests the hypothesis that it is possible to find tone or noise vocoders that sound similar and result in similar speech perception scores to a cochlear implant (CI). This would validate the use of such vocoders as acoustic models of CIs. We further hypothesize that those valid acoustic models will require a personalized amount of frequency mismatch between input filters and output tones or noise bands.

BACKGROUND

Noise or tone vocoders have been used as acoustic models of CIs in hundreds of publications but have never been convincingly validated.

METHODS

Acoustic models were evaluated by single-sided deaf CI users who compared what they heard with the CI in one ear to what they heard with the acoustic model in the other ear. We evaluated frequency-matched models (both all-channel and 6-channel models, both tone and noise vocoders) as well as self-selected models that included an individualized level of frequency mismatch.

RESULTS

Self-selected acoustic models resulted in similar levels of speech perception and similar perceptual quality as the CI. These models also matched the CI in terms of perceived intelligibility, harshness, and pleasantness.

CONCLUSION

Valid acoustic models of CIs exist, but they are different from the models most widely used in the literature. Individual amounts of frequency mismatch may be required to optimize the validity of the model. This may be related to the basalward frequency mismatch experienced by postlingually deaf patients after cochlear implantation.

Three-Dimensional Modeling and Measurement of the Human Cochlear Hook Region: Considerations for Tonotopic Mapping

HYPOTHESIS

Measuring the length of the basilar membrane (BM) in the cochlear hook region will result in improved accuracy of cochlear duct length (CDL) measurements.

BACKGROUND

Cochlear implant pitch mapping is generally performed in a patient independent approach, which has been shown to result in place-pitch mismatches. In order to customize cochlear implant pitch maps, accurate CDL measurements must be obtained. CDL measurements generally begin at the center of the round window (RW) and ignore the basal-most portion of the BM in the hook region. Measuring the size and morphology of the BM in the hook region can improve CDL measurements and our understanding of cochlear tonotopy.

METHODS

Ten cadaveric human cochleae underwent synchrotron radiation phase-contrast imaging. The length of the BM through the hook region and CDL were measured. Two different CDL measurements were obtained for each sample, with starting points at the center of the RW (CDLRW) and the basal-most tip of the BM (CDLHR). Regression analysis was performed to relate CDLRW to CDLHR. A three-dimensional polynomial model was determined to describe the average BM hook region morphology.

RESULTS

The mean CDLRW value was 33.03 ± 1.62 mm, and the mean CDLHR value was 34.68 ± 1.72 mm. The following relationship was determined between CDLRW and CDLHR: CDLHR  = 1.06(CDLRW)-0.26 (R2  = 0.99).

CONCLUSION

The length and morphology of the hook region was determined. Current measurements underestimate CDL in the hook region and can be corrected using the results herein.

An Approach for Individualized Cochlear Frequency Mapping Determined from 3D Synchrotron Radiation Phase-Contrast Imaging

OBJECTIVE

Cochlear implants are traditionally programmed to stimulate according to a generalized frequency map, where individual anatomic variability is not considered when selecting the centre frequency of stimulation of each implant electrode. However, high variability in cochlear size and spatial frequency distributions exist among individuals. Generalized cochlear implant frequency maps can result in large pitch perception errors and reduced hearing outcomes for cochlear implant recipients. The objective of this work was to develop an individualized frequency mapping technique for the human cochlea to allow for patient-specific cochlear implant stimulation.

METHODS

Ten cadaveric human cochleae were scanned using synchrotron radiation phase-contrast imaging (SR-PCI) combined with computed tomography (CT). For each cochlea, ground truth angle-frequency measurements were obtained in three-dimensions using the SR-PCI CT data. Using an approach designed to minimize perceptual error in frequency estimation, an individualized frequency function was determined to relate angular depth to frequency within the cochlea.

RESULTS

The individualized frequency mapping function significantly reduced pitch errors in comparison to the current gold standard generalized approach.

CONCLUSION AND SIGNIFICANCE

This paper presents for the first time a cochlear frequency map which can be individualized using only the angular length of cochleae. This approach can be applied in the clinical setting and has the potential to revolutionize cochlear implant programming for patients worldwide.

Comparison of Speech Recognition and Localization Ability in Single-sided Deaf Patients Implanted With Different Cochlear Implant Electrode Array Designs

OBJECTIVE

Choice of electrode array (EA) design and differences in outcome are major concerns both to patients with single-sided deafness (SSD) and to surgeons before cochlear implant (CI) surgery. The present work investigates the effects of EA design on 1) insertion depths, and 2) audiological outcomes of SSD CI recipients.

STUDY DESIGN

Retrospective study.

SETTING

Tertiary academic center.

PATIENTS

Forty patients with acquired SSD matched according to duration of deafness MAIN OUTCOME MEASURES:: Fourteen CI recipients were implanted with a perimodiolar electrode (cochlear perimodiolar [CPM]), 12 with a shorter lateral wall electrode (cochlear lateral wall [CLW]), and 14 with a longer lateral wall electrode array (medEl lateral wall [MLW]). Postoperative rotational tomography was evaluated to determine cochlear size and EA angle of insertion depth (AID). Binaural speech comprehension in noise (in three configuration presentations) and localization ability were assessed 12 months postoperatively with CI.

RESULTS

AID was significantly deeper in MLW (mean 527.94 degrees) compared with the CPM (mean 366.35 degrees) and CLW groups (mean 367.01 degrees). No significant difference in AID was seen between the CPM and CLW groups (difference 0.66 degrees). Cochlear sizes revealed no significant differences between any groups. All three groups showed significant improvement in head shadow effect (difference on average CPM: 6.3 dB SPL, CLW 5 dB SPL, and MLW 4.05 dB SPL) and localization ability at 12 months postoperatively (difference on average CPM: 19.72 degrees, CLW: 24 degrees, and MLW: 12.9 degrees). No significant difference in the extent of audiological benefit was observed between any groups.

CONCLUSION

No effect on binaural benefit was apparent from the selection of the three EA designs in SSD CI recipients. Further studies focusing on subjective results, sound quality, and music perception depending on EA design in SSD CI recipients are needed.

Is the spread of excitation width correlated to the speech recognition in cochlear implant users?

PURPOSE

To assess whether there is an interference of the spread of excitation (SOE) on speech recognition.

METHODS

Retrospective cross-sectional study, approved by the institution's ethics committee (CAAE03409212.8.0000.0068). Adult patients with intraoperative neural response telemetry (NRT) performed on electrodes 6, 11 and 16 implanted with Cochlear Ltd (Sydney, Australia) devices were selected. Patients with partial array insertion, pre-lingual hearing loss, deafness etiology due to and CI experience less than 12 months were excluded. SOE was recorded at 10 current units above the NRT threshold (tNRT) and its width in millimeters was collected at point 0.75 of the function. Speech recognition test was 25-recorded monosyllables list, presented at 65 dBHL at 0° azimuth in a sound treated booth. The analysis was divided into groups by electrode array type, regarding the tNRT, SOE width, SOE's peak amplitude and electrode peak.

RESULTS

A 126 SOE measurements of the 3 tested electrodes were obtained from 43 patients. Patients with straight array had significantly wider SOE, greater peak amplitude at electrode 6 and higher tNRTs. In the perimodiolar array, there was a negative correlation between SOE and monosyllables recognition at electrodes 6 and 11, and in the combined average of the three electrodes, with a significant difference in electrode 11. Sixty-six percent of the SOE measurements had their peak shifted to adjacent electrodes.

CONCLUSION

It was observed, in perimodiolar array, the greater the dispersion of electrical current, the worse the speech recognition, especially in the medial electrode.

Characterization of the human helicotrema: implications for cochlear duct length and frequency mapping

Background

Despite significant anatomical variation amongst patients, cochlear implant frequency-mapping has traditionally followed a patient-independent approach. Basilar membrane (BM) length is required for patient-specific frequency-mapping, however cochlear duct length (CDL) measurements generally extend to the apical tip of the entire cochlea or have no clearly defined end-point. By characterizing the length between the end of the BM and the apical tip of the entire cochlea (helicotrema length), current CDL models can be corrected to obtain the appropriate BM length. Synchrotron radiation phase-contrast imaging has made this analysis possible due to the soft-tissue contrast through the entire cochlear apex.

Methods

Helicotrema linear length and helicotrema angular length measurements were performed on synchrotron radiation phase-contrast imaging data of 14 cadaveric human cochleae. On a sub-set of six samples, the CDL to the apical tip of the entire cochlea (CDL_TIP) and the BM length (CDL_BM) were determined. Regression analysis was performed to assess the relationship between CDL_TIP and CDL_BM.

Results

The mean helicotrema linear length and helicotrema angular length values were 1.6 ± 0.9 mm and 67.8 ± 37.9 degrees, respectively. Regression analysis revealed the following relationship between CDL_TIP and CDL_BM: CDL_BM = 0.88(CDL_TIP) + 3.71 (R² = 0.995).

Conclusion

This is the first known study to characterize the length of the helicotrema in the context of CDL measurements. It was determined that the distance between the end of the BM and the tip of the entire cochlea is clinically consequential. A relationship was determined that can predict the BM length of an individual patient based on their respective CDL measured to the apical tip of the cochlea.