Hybrid Cochlear Implant Research Articles

Spatial release from masking with simulated hybrid cochlear implant speech

Spatial release from masking (SRM) is the improvement in speech intelligibility when the masking signals are spatially separated from the target signal. Cochlear implant (CI) users utilizing electric-only (E-Only) stimulation had poorer speech recognition than CI users utilizing electric-acoustic stimulation (EAS). Previous research investigating SRM on hybrid CI users big spatial separations (±90°) between the target and the maskers which were unrealistic in conversational settings. Here, we present SRM data using natural speech, simulated CI speech, and simulated EAS speech from young, normal hearing listeners for smaller, yet realistic, spatial separations between the target and the maskers. An eight-channel noise-excited vocoder was used to simulate cochlear implant processing and low-frequency filtering was used to simulate residual low-frequency hearing. Five spatial configurations were used: (colocated (target and the two maskers presented from 0° azimuth) and one of four spatially separated conditions (target at 0°, symmetrical maskers at ± 5°, ± 10°, ±15°, or ±30°). Initial analysis of the data revealed that the listeners had significantly poorer speech identification thresholds for the simulated CI speech when compared to EAS speech. The individual variability and the relationship between the speech identification thresholds in the three conditions will be discussed.

Long-Term Hearing Outcomes After Hybrid Cochlear Implantation.

To examine long-term (>5 yr) low-frequency hearing preservation after hybrid cochlear implantation. Retrospective cross-sectional study. Tertiary care center outpatient clinic. All patients older than 21 years implanted with a Cochlear Hybrid L24 device from 2014 to 2021. Changes in low-frequency pure-tone average (LFPTA) were calculated at each of several time points relative to the date of implantation. The proportion of patients with preserved LFPTA at last follow-up and Kaplan-Meier estimates for loss of residual hearing were calculated in addition to hazard ratios for hearing loss according to patient- and surgery-specific factors. Thirty ears in 29 patients underwent hybrid cochlear implantation and were eligible for inclusion (mean age, 59 yr; 65% female). Mean preoperative LFPTA was 31.7 dB. Mean LFPTA across all implanted ears at first follow-up was 45.1 dB; no patient had experienced loss of residual hearing at first follow-up. Six patients had loss of residual hearing during the follow-up period, with Kaplan-Meier probability estimates of preserved hearing of 100% at 1 month, 90% at 12 months, 87% at 24 months, and 80% at 48 months. There was no association between loss of residual hearing and patient age, preoperative LFPTA, surgeon, or use of topical steroids intraoperatively (hazard ratios, 1.05 [0.96-1.15], 0.97 [0.88-1.05], 1.39 [0.20-9.46], 0.93 [0.09-9.74], respectively). Long-term (>5 yr) outcomes after hybrid cochlear implantation demonstrate good preservation of low-frequency hearing, with only modest decline in the long-term postimplantation, and a low proportion of loss of residual low-frequency hearing.

Acoustic Change Complex Recorded in Hybrid Cochlear Implant Users

Introduction: Expanding cochlear implant (CI) candidacy criteria and advances in electrode arrays and soft surgical techniques have increased the number of CI recipients who have residual low-frequency hearing. Objective measures such as obligatory cortical auditory-evoked potentials (CAEPs) may help clinicians make more tailored recommendations to recipients regarding optimal listening mode. As a step toward this goal, this study investigated how CAEPs measured from hybrid CI users differ in two listening modes: acoustic alone (A-alone) versus acoustic plus electric (A + E). Methods: Eight successful hybrid CI users participated in this study. Two CAEPs, the P1-N1-P2 and the acoustic change complex (ACC), were measured simultaneously in response to the onset and change of a series of different and spectrally complex acoustic signals, in each of the two listening modes (A-alone and A + E). We examined the effects of listening mode and stimulus type on the onset and ACC N1-P2 amplitudes and peak latencies. Results: ACC amplitudes in hybrid CI users significantly differed as a function of listening mode and stimulus type. ACC responses in A + E were larger than those in the A-alone mode. This was most evident for stimuli involving a change from low to high frequency. Conclusions: Results of this study showed that the ACC varies as a function of listening mode and stimulus type. This finding suggests that the ACC can be used as a physiologic, objective measure of the benefit of hybrid CIs, potentially supporting clinicians in making clinical recommendations on individualized listening mode, or to document subjective preference for a given listening mode. Further research into this potential clinical application in a range of hybrid recipients and/or long electrode users who have residual low-frequency hearing is warranted.

Chronic cochlear implantation with and without electric stimulation in a mouse model induces robust cochlear influx of CX3CR1+/GFP macrophages

BackgroundCochlear implantation is an effective auditory rehabilitation strategy for those with profound hearing loss, including those with residual low frequency hearing through use of hybrid cochlear implantation techniques. Post-mortem studies demonstrate the nearly ubiquitous presence of intracochlear fibrosis and neo-ossification following cochlear implantation. Current evidence suggests post-implantation intracochlear fibrosis is associated with delayed loss of residual acoustic hearing in hybrid cochlear implant (CI) recipients and may also negatively influence outcomes in traditional CI recipients. This study examined the contributions of surgical trauma, foreign body response and electric stimulation to intracochlear fibrosis and the innate immune response to cochlear implantation and the hierarchy of these contributions. MethodsNormal hearing CX3CR1+/GFP mice underwent either round window opening (sham), acute CI insertion or chronic CI insertion with no, low- or high-level electric stimulation. Electric stimulation levels were based on neural response telemetry (NRT), beginning post-operative day 7 for 5 h per day. Subjects (n=3 per timepoint) were sacrificed at 4 h, 1,4,7,8,11,14 and 21 days. An unoperated group (n=3) served as controls. Cochleae were harvested at each time-point and prepared for immunohistochemistry with confocal imaging. The images were analyzed to obtain CX3CR1+ macrophage cell number and density in the lateral wall (LW), scala tympani (ST) and Rosenthal's canal (RC). ResultsA ST peri-implant cellular infiltrate and fibrosis occurred exclusively in the chronically implanted groups starting on day 7 with a concurrent infiltration of CX3CR1+ macrophages not seen in the other groups. CX3CR1+ macrophage infiltration was seen in the LW and RC in all experimental groups within the first week, being most prominent in the 3 chronically implanted groups during the second and third week. ConclusionsThe cochlear immune response was most prominent in the presence of chronic cochlear implantation, regardless of electric stimulation level. Further, the development of intracochlear ST fibrosis was dependent on the presence of the indwelling CI foreign body. An innate immune response was evoked by surgical trauma alone (sham and acute CI groups) to a lesser degree. These data suggest that cochlear inflammation and intrascalar fibrosis after cochlear implantation are largely dependent on the presence of a chronic indwelling foreign body and are not critically dependent on electrical stimulation. Also, these data support a role for surgical trauma in inciting the initial innate immune response.

The natural progression of low-frequency hearing loss in patients who meet hybrid implant system candidacy criteria.

To investigate the natural progression of hearing loss in patients with high-frequency hearing loss whose audiograms met the criteria for a hybrid cochlear implant (CI). Retrospective database review. We retrospectively identified patients who met the criteria for a hybrid CI from our audiometric database. We also recorded the etiology of hearing loss in each patient and excluded patients with retrocochlear etiologies, those age <6 years, duration of observation <1 year, or those with a mixed or conductive hearing loss. We calculated the pre-CI progression of residual low-frequency (LF) hearing level in decibels per year and investigated the risk factor of the progression of hearing loss. A total of 1,083 ears of 944 patients were included in this study. The average rate of hearing loss progression for all etiologies was 1.70 ± 0.10 dB/yr at an average of 250 Hz, 500 Hz, and 1 kHz in the affected ear(s). The progression of hearing loss was 5.0 ± 0.93 dB/yr in patients with Meniere's disease and 3.5 ± 0.76 dB/yr in those with autoimmune disease, both of which were significantly faster than progression rates in other etiologies. In patients with idiopathic, genetic/hereditary, and congenital hearing loss, the progression of hearing loss was 1.46 ± 0.10 dB/yr. Patients with steeply sloping hearing loss experienced significantly faster progression in the ipsilateral ear compared to patients with another audiometric type. It is suggested that Meniere's disease, autoimmune-mediated inner ear disease, and steeply sloping hearing loss in the ipsilateral ear are risk factors for faster progression of residual LF hearing level. 4 Laryngoscope, 130:1299-1303, 2020.

Hybrid Music Perception Outcomes: Implications for Melody and Timbre Recognition in Cochlear Implant Recipients.

To examine whether or not electric-acoustic music perception outcomes, observed in a recent Hybrid L24 clinical trial, were related to the availability of low-frequency acoustic cues not present in the electric domain. Prospective, repeated-measures, within-subject design. Academic research hospital. Nine normally hearing individuals. Simulated electric-acoustic hearing in normally hearing individuals. Acutely measured melody and timbre recognition scores from the University of Washington Clinical Assessment of Music Perception (CAMP) test. Melody recognition scores were consistently better for listening conditions that included low-frequency acoustic information. Mean scores for both acoustic (73.5%, S.D. = 15.5%) and electric-acoustic (67.9%, S.D. = 21.2%) conditions were significantly better (p < 0.001) than electric alone (39.2%, S.D. = 18.1%). This was not the case for timbre recognition for which scores were more variable across simulated listening modes with no significant differences found in mean scores across electric (36.1%, S.D. = 17.7%), acoustic (38.0%, S.D. = 20.4%), and electric-acoustic (40.7%, S.D. = 19.7%) conditions (p > 0.05). Recipients of hybrid cochlear implants demonstrate music perception abilities superior to those observed in traditional cochlear implant recipients. Results from the present study support the notion that electric-acoustic stimulation confers advantages related to the availability of low-frequency acoustic hearing, most particularly for melody recognition. However, timbre recognition remains more limited for both hybrid and traditional cochlear implant users. Opportunities remain for new coding strategies to improve timbre perception.

An improved method of obtaining electrocochleography recordings from Nucleus Hybrid cochlear implant users

Interest in electrocochleography (ECoG) has recently resurged as a potential tool to assess peripheral auditory function in cochlear implant (CI) users. ECoG recordings can be evoked using acoustic stimulation and recorded from an extra- or intra-cochlear electrode in CI users. Recordings reflect contributions from cochlear hair cells and the auditory nerve. We recently demonstrated the feasibility of using Custom Sound EP (clinically available software) to record ECoG responses in Nucleus Hybrid CI users with preserved acoustic hearing in the implanted ear (Abbas et al, 2017). While successful, the recording procedures were time intensive, limiting clinical applications. The current report describes how we improved data collection efficiency by writing custom software using Python programming language. The software interfaced with Nucleus Implant Communicator (NIC) routines to record responses from an intracochlear electrode. ECoG responses were recorded in eight CI users with preserved acoustic hearing using Custom Sound EP and the Python-based software. Responses were similar across both recording systems, but the recording time decreased significantly using the Python-based software. Seven additional CI users underwent repeated testing using the Python-based software and showed high test-retest reliability. The improved efficiency and high reliability increases the likelihood of translating intracochlear ECoG to clinical practice.

Electric and acoustic harmonic integration predicts speech-in-noise performance in hybrid cochlear implant users

BackgroundPitch perception of complex tones relies on place or temporal fine structure-based mechanisms from resolved harmonics and the temporal envelope of unresolved harmonics. Combining this information is essential for speech-in-noise performance, as it allows segregation of a target speaker from background noise. In hybrid cochlear implant (H-CI) users, low frequency acoustic hearing should provide pitch from resolved harmonics while high frequency electric hearing should provide temporal envelope pitch from unresolved harmonics. How the acoustic and electric auditory inputs interact for H-CI users is largely unknown. Harmonicity and inharmonicity are emergent features of sound in which overtones are concordant or discordant with the fundamental frequency. We hypothesized that some H-CI users would be able to integrate acoustic and electric information for complex tone pitch perception, and that this ability would be correlated with speech-in-noise performance. In this study, we used perception of inharmonicity to demonstrate this integration. MethodsFifteen H-CI users with only acoustic hearing below 500 Hz, only electric hearing above 2 kHz, and more than 6 months CI experience, along with eighteen normal hearing (NH) controls, were presented with harmonic and inharmonic sounds. The stimulus was created with a low frequency component, corresponding with the H-CI user's acoustic hearing (fundamental frequency between 125 and 174 Hz), and a high frequency component, corresponding with electric hearing. Subjects were asked to identify the more inharmonic sound, which requires the perceptual integration of the low and high components. Speech-in-noise performance was tested in both groups using the California Consonant Test (CCT), and perception of Consonant-Nucleus-Consonant (CNC) words in quiet and AzBio sentences in noise were tested for the H-CI users. ResultsEight of the H-CI subjects (53%), and all of the NH subjects, scored significantly above chance level for at least one subset of the inharmonicity detection task. Inharmonicity detection ability, but not age or pure tone average, predicted speech scores in a linear model. These results were significantly correlated with speech scores in both quiet and noise for H-CI users, but not with speech in noise performance for NH listeners. Musical experience predicted inharmonicity detection ability, but did not predict speech performance. ConclusionsWe demonstrate integration of acoustic and electric information in H-CI users for complex pitch sensation. The correlation with speech scores in H-CI users might be associated with the ability to segregate a target speaker from background noise using the speaker's fundamental frequency.

Hybrid Cochlear Implantation Long―Term Outcomes: Insights into the Future

Hybrid Cochlear Implantation Long―Term Outcomes: Insights into the Future

Mechanisms underlying speech masking release in hybrid cochlear implant users

Hybrid cochlear implant (CI) users utilize low-frequency acoustic and high-frequency electric stimulation in the implanted ear, outperform traditional CI users in speech perception in noise (Gantz et al., 2017), and show “masking release,” an improvement in speech recognition in fluctuating noise relative to steady noise (Turner et al., 2004). Improved performance in noise has been attributed (but not proven) to the spectral resolution and temporal fine structure (TFS) provided by acoustic hearing. Spondee recognition in two-talker and ten-talker babble was assessed in Hybrid CI users, and masking release was calculated as the percent difference in performance in two-talker (easy condition) and ten-talker (hard condition) babble. Spectral ripple density discrimination thresholds and fundamental frequency discrimination limens was also assessed, as these psychophysical measures reflect underlying spectral resolution and TFS and correlate with speech perception in noise in traditional CI users (Won et al., 2007; Goldsworthy et al., 2013; Goldsworthy, 2015; Jeon et al., 2015). Preliminary data suggest masking release is possible in Hybrid CI users, and that psychophysical measures and masking release may be correlated, suggesting a role of spectral resolution and TFS in masking release. The extent of residual hearing also appears to correlate with psychophysical and masking release performance.

Hybrid cochlear implantation: quality of life, quality of hearing, and working performance compared to patients with conventional unilateral or bilateral cochlear implantation.

The objective of the present study is to evaluate the effect of hybrid cochlear implantation (hCI) on quality of life (QoL), quality of hearing (QoH), and working performance in adult patients, and to compare the long-term results of patients with hCI to those of patients with conventional unilateral cochlear implantation (CI), bilateral CI, and single-sided deafness (SSD) with CI. Sound localization accuracy and speech-in-noise test were also compared between these groups. Eight patients with high-frequency sensorineural hearing loss of unknown etiology were selected in the study. Patients with hCI had better long-term speech perception in noise than uni- or bilateral CI patients, but the difference was not statistically significant. The sound localization accuracy was equal in the hCI, bilateral CI, and SSD patients. QoH was statistically significantly better in bilateral CI patients than in the others. In hCI patients, residual hearing was preserved in all patients after the surgery. During the 3.6-year follow-up, the mean hearing threshold at 125-500Hz decreased on average by 15dB HL in the implanted ear. QoL and working performance improved significantly in all CI patients. Hearing outcomes with hCI are comparable to the results of bilateral CI or CI with SSD, but hearing in noise and sound localization are statistically significantly better than with unilateral CI. Interestingly, the impact of CI on QoL, QoH, and working performance was similar in all groups.

Using Neural Response Telemetry to Monitor Physiological Responses to Acoustic Stimulation in Hybrid Cochlear Implant Users.

This report describes the results of a series of experiments where we use the neural response telemetry (NRT) system of the Nucleus cochlear implant (CI) to measure the response of the peripheral auditory system to acoustic stimulation in Nucleus Hybrid CI users. The objectives of this study were to determine whether they could separate responses from hair cells and neurons and to evaluate the stability of these measures over time. Forty-four CI users participated. They all had residual acoustic hearing and used a Nucleus Hybrid S8, S12, or L24 CI or the standard lateral wall CI422 implant. The NRT system of the CI was used to trigger an acoustic stimulus (500-Hz tone burst or click), which was presented at a low stimulation rate (10, 15, or 50 per second) to the implanted ear via an insert earphone and to record the cochlear microphonic, the auditory nerve neurophonic and the compound action potential (CAP) from an apical intracochlear electrode. To record acoustically evoked responses, a longer time window than is available with the commercial NRT software is required. This limitation was circumvented by making multiple recordings for each stimulus using different time delays between the onset of stimulation and the onset of averaging. These recordings were then concatenated off-line. Matched recordings elicited using positive and negative polarity stimuli were added off-line to emphasize neural potentials (SUM) and subtracted off-line to emphasize potentials primarily generated by cochlear hair cells (DIF). These assumptions regarding the origin of the SUM and DIF components were tested by comparing the magnitude of these derived responses recorded using various stimulation rates. Magnitudes of the SUM and DIF components were compared with each other and with behavioral thresholds. SUM and DIF components were identified for most subjects, consistent with both hair cell and neural responses to acoustic stimulation. For a subset of the study participants, the DIF components grew as stimulus level was increased, but little or no SUM components were identified. Latency of the CAPs in response to click stimuli was long relative to reports in the literature of recordings obtained using extracochlear electrodes. This difference in response latency and general morphology of the CAPs recorded was likely due to differences across subjects in hearing loss configuration. The use of high stimulation rates tended to decrease SUM and CAP components more than DIF components. We suggest this effect reflects neural adaptation. In some individuals, repeated measures were made over intervals as long as 9 months. Changes over time in DIF, SUM, and CAP thresholds mirrored changes in audiometric threshold for the subjects who experienced loss of acoustic hearing in the implanted ear. The Nucleus NRT software can be used to record peripheral responses to acoustic stimulation at threshold and suprathreshold levels, providing a window into the status of the auditory hair cells and the primary afferent nerve fibers. These acoustically evoked responses are sensitive to changes in hearing status and consequently could be useful in characterizing the specific pathophysiology of the hearing loss experienced by this population of CI users.

Post Hybrid Cochlear Implant Hearing Loss and Endolymphatic Hydrops.

To evaluate for potential causes of delayed loss of residual hearing that variably occurs with hybrid cochlear implants. Histopathological evaluation of 29 human temporal bone (HTB) with cochlear implant (CI). The Neurotology and House HTB Laboratory of UCLA (House-UCLA). HTB from CI patients from the House-UCLA HTB Laboratory (n = 28) and one courtesy of Massachusetts Eye and Ear Infirmary (MEEI). Histopathological analysis to identify the location of cochleostomy, fibrosis, and bone formation in the scala vestibuli and tympani, and endolymphatic hydrops. Spiral ganglion neuron counts were obtained. Statistical analysis compared presence of cochleostomy and location with the histopathological findings. Seventeen of 29 bones with fibrosis in the scala vestibule (SV) and tympani had evidence of a cochleostomy involving the SV containing the ductus reunions, all of which had hydrops. Ten of 11 bones had no SV fibrosis, and a cochleostomy limited to the scala tympani, of which all had no hydrops. One HTB had moderate SV fibrosis not involving the ductus reuniens, and was without hydrops. One HTB had a SV cochleostomy but the electrode ruptured Reissner's membrane, and was without hydrops. Cochleostomy was significantly associated with SV fibrosis and hydrops (p < 0.01), those without hydrops had no SV atrophy (p < 0.01). Round window insertion was associated with no fibrosis and no hydrops. We hypothesize that cochleostomies involving scala vestibuli incite fibrosis, compromising the ductus reuniens, causing hydrops which may cause the delayed loss of residual low frequency hearing in CI.

Performance differences between electroacoustic and electric alone cochlear stimulation using complex tests in noise. A pilot study

Objectives: Hybrid cochlear implants enable very interesting performances in bisyllabic words recognition, mainly in noisy conditions. In this paper, we studied patients with implants performing some very difficult timbric tasks in quiet and noisy conditions.Methods: We studied three adult patients with hybrid implants (group A-hybrid implants) and three adult patients with traditional ones (group B-traditional implants). We made the following tests (in quiet and noise): bisyllabic words recognition; voice kind recognition; common melodies identification and recognition; musical instrument identification and recognition.Results: Mean results in quiet: test 1: 35% A, 47% B; test 2: 92% A, 42% B; test 3: identification scores 88% A, 100% B, recognition scores: 37.5% A, 50% B; test 4 identification scores 50% A, 20% B, recognition scores 30% A, 20% B. As for tests in noise: test 1: 28% A, 46% B; test 2: 75% A, 25% B; test 3: identification 81% A, 87.5% B and recognition 56% A, 50% B; test 4: identification 60% A, 30% B and recognition 50% A, 20% B.Conclusion: Patients with hybrid implants seem to have better results, mainly in noisy timbric tasks. This could be explained by the better quality of low frequency stimulation and could be an encouragement for further studies and a larger diffusion of this kind of implant in the future.

Cortical Auditory Evoked Potentials Recorded From Nucleus Hybrid Cochlear Implant Users.

Nucleus Hybrid Cochlear Implant (CI) users hear low-frequency sounds via acoustic stimulation and high-frequency sounds via electrical stimulation. This within-subject study compares three different methods of coordinating programming of the acoustic and electrical components of the Hybrid device. Speech perception and cortical auditory evoked potentials (CAEP) were used to assess differences in outcome. The goals of this study were to determine whether (1) the evoked potential measures could predict which programming strategy resulted in better outcome on the speech perception task or was preferred by the listener, and (2) CAEPs could be used to predict which subjects benefitted most from having access to the electrical signal provided by the Hybrid implant. CAEPs were recorded from 10 Nucleus Hybrid CI users. Study participants were tested using three different experimental processor programs (MAPs) that differed in terms of how much overlap there was between the range of frequencies processed by the acoustic component of the Hybrid device and range of frequencies processed by the electrical component. The study design included allowing participants to acclimatize for a period of up to 4 weeks with each experimental program prior to speech perception and evoked potential testing. Performance using the experimental MAPs was assessed using both a closed-set consonant recognition task and an adaptive test that measured the signal-to-noise ratio that resulted in 50% correct identification of a set of 12 spondees presented in background noise. Long-duration, synthetic vowels were used to record both the cortical P1-N1-P2 "onset" response and the auditory "change" response (also known as the auditory change complex [ACC]). Correlations between the evoked potential measures and performance on the speech perception tasks are reported. Differences in performance using the three programming strategies were not large. Peak-to-peak amplitude of the ACC was not found to be sensitive enough to accurately predict the programming strategy that resulted in the best performance on either measure of speech perception. All 10 Hybrid CI users had residual low-frequency acoustic hearing. For all 10 subjects, allowing them to use both the acoustic and electrical signals provided by the implant improved performance on the consonant recognition task. For most subjects, it also resulted in slightly larger cortical change responses. However, the impact that listening mode had on the cortical change responses was small, and again, the correlation between the evoked potential and speech perception results was not significant. CAEPs can be successfully measured from Hybrid CI users. The responses that are recorded are similar to those recorded from normal-hearing listeners. The goal of this study was to see if CAEPs might play a role either in identifying the experimental program that resulted in best performance on a consonant recognition task or in documenting benefit from the use of the electrical signal provided by the Hybrid CI. At least for the stimuli and specific methods used in this study, no such predictive relationship was found.

A Retrospective Analysis of the Contribution of Reported Factors in Cochlear Implantation on Hearing Preservation Outcomes.

Preservation of residual hearing is essential to perceive acoustic stimulation from hybrid cochlear implants (CI). Preservation is a good marker of atraumatic surgery and residual hearing may be exploited further or enhanced in future therapies, making complete hearing preservation a desirable goal for all current CI surgeries. There is large variability in the amount of hearing preserved and the timeframe over which it is lost after CI. The increase in numbers of patients with high levels of residual hearing at implantation means that understanding the variables affecting its preservation is more important than ever. An English search term with generic and specific items concerning hearing preservation and cochlear implantation was searched on the Web of Science service. The search timeframe was limited to 2000 to 2014, with no language limitations on results. Hearing preservation, retrospective CI outcome studies which reported pre- and post-surgical pure-tone audiometry (PTA) were identified and selected. PTA thresholds were extracted from audiograms or tables and converted into a low-frequency hearing preservation (LFHP) score. Data for 21 factors associated with hearing preservation were collected from studies. Factors were included in a hearing preservation model if they had both a significant bivariate correlation with LFHP and a significant Kruskal-Wallis H test result (for ordinal data) or a significant multiple regression analysis result (for scale data). Seven factors were found to have a significant effect on hearing preservation: insertion site, progressive versus stable hearing loss, insertion angle of electrode, use of intraoperative topical steroids, use of steroids (via any route/timing), hearing etiology, and electrode array type. The best hearing preservation options are given.

The effects of spectral smearing and elevated thresholds on speech-in-noise recognition in simulated electric-acoustic hearing

Combined electric-acoustic stimulation (EAS) via hybrid cochlear implants is a relatively new treatment for severe-profound sloping high-frequency hearing loss. Residual acoustic hearing at low frequencies is a vital component of EAS, but it cannot be assumed that residual hearing will be normal; thresholds may be elevated, frequency selectivity may have decreased, or both. In this study, the effects of reduced frequency selectivity and elevated low-frequency thresholds on the intelligibility of speech in noise were simulated. Sentences mixed with a babble masker were processed by an eight-channel vocoder. Residual low-frequency hearing was simulated by replacing the first four channels with the unprocessed acoustic stimulus, with a spectrally smeared stimulus, or with a spectrally smeared and attenuated stimulus. These conditions simulated listening by cochlear implant users with no residual hearing, with normal residual hearing, or with various degrees of impaired residual hearing. Simulating normal residual hearing increased intelligibility, compared to the intelligibility of fully vocoded speech. Low-frequency spectral smearing with filters three or six times broader than normal had little effect on intelligibility. A simulated threshold shift of 60 dB, combined with factor-of-three spectral smearing, significantly decreased intelligibility, but 30 dB of simulated threshold shift did not. These results are consistent with previous results demonstrating the effect of good residual low-frequency hearing on intelligibility. They are also consistent with the use of amplification for individuals who use EAS but have poorer residual hearing.

Pitch adaptation patterns in bimodal cochlear implant users: over time and after experience.

Pitch plasticity has been observed in Hybrid cochlear implant (CI) users. Does pitch plasticity also occur in bimodal CI users with traditional long-electrode CIs, and is pitch adaptation pattern associated with electrode discrimination or speech recognition performance? The goals of this study were to characterize pitch adaptation patterns in long-electrode CI users, to correlate these patterns with electrode discrimination and speech perception outcomes, and to analyze which subject factors are associated with the different patterns. Electric-to-acoustic pitch matches were obtained in 19 subjects over time from CI activation to at least 12 months after activation, and in a separate group of 18 subjects in a single visit after at least 24 months of CI experience. Audiometric thresholds, electrode discrimination performance, and speech perception scores were also measured. Subjects measured over time had pitch adaptation patterns that fit one of the following categories: (1) "Pitch-adapting," that is, the mismatch between perceived electrode pitch and the corresponding frequency-to-electrode allocations decreased; (2) "Pitch-dropping," that is, the pitches of multiple electrodes dropped and converged to a similar low-pitch; and (3) "Pitch-unchanging," that is, the electrode pitches did not change. Subjects measured after CI experience had a parallel set of adaptation patterns: (1) "Matched-pitch," that is, the electrode pitch was matched to the frequency allocation; (2) "Low-pitch," that is, the pitches of multiple electrodes were all around the lowest frequency allocation; and (3) "Nonmatched-pitch," that is, the pitch patterns were compressed relative to the frequency allocations and did not fit either the matched-pitch or low-pitch categories. Unlike Hybrid CI users which were mostly in the pitch-adapting or matched-pitch category, the majority of bimodal CI users were in the latter two categories, pitch-dropping/low-pitch or pitch-unchanging/nonmatched-pitch. Subjects with pitch-adapting or matched-pitch patterns tended to have better low-frequency thresholds than subjects in the latter categories. Changes in electrode discrimination over time were not associated with changes in pitch differences between electrodes. Reductions in speech perception scores over time showed a weak but nonsignificant association with dropping-pitch patterns. Bimodal CI users with more residual hearing may have somewhat greater similarity to Hybrid CI users and be more likely to adapt pitch perception to reduce mismatch with the frequencies allocated to the electrodes and the acoustic hearing. In contrast, bimodal CI users with less residual hearing exhibit either no adaptation, or surprisingly, a third pattern in which the pitches of the basal electrodes drop to match the frequency range allocated to the most apical electrode. The lack of association of electrode discrimination changes with pitch changes suggests that electrode discrimination does not depend on perceived pitch differences between electrodes, but rather on some other characteristics such as timbre. In contrast, speech perception may depend more on pitch perception and the ability to distinguish pitch between electrodes, especially since during multielectrode stimulation, cues such as timbre may be less useful for discrimination.

Middle Ear Implant versus Hybrid Cochlear Implant for High‐Frequency Sensorineural Hearing Loss

Objectives:Profound SNHL responds well to a standard cochlear implant (CI) with rewarding results. However, if the individual has residual hearing in the low frequencies there is a reasonable chance that the pure tones will be lost. Hybrid cochlear implants have been suggested as a solution for this problem. Unfortunately, there continues to be a loss of the low frequency pure tones in a large number of these patients.Methods:One solution would be to use a middle ear implant instead of a hybrid CI. The Maxum middle ear implant has the advantage of being a minimally invasive surgical procedure that can be performed under local anesthesia. A small magnet is attached to the stapes through a transcanal approach.Results:After 3 weeks an integrated processor coil (IPC) is inserted into the external auditory canal. The IPC has an electromagnet driver. By driving the stapes directly it is possible to obtain as much as 60 dB of functional gain in the high frequencies without distortion, acoustic feedback, or the sensation of occlusion.Conclusions:For these reasons the author believes a Maxum should be considered in these patients before a Hybrid Cochlear Implant. If the SNHL progresses, then a CI can still be performed at a later date. This sequence of events delays the invasion of the cochlea and in some cases prevents the need for a CI altogether.

Factors associated with hearing loss in a normal-hearing guinea pig model of hybrid cochlear implants

The Hybrid cochlear implant (CI), also known as Electro-Acoustic Stimulation (EAS), is a new type of CI that preserves residual acoustic hearing and enables combined cochlear implant and hearing aid use in the same ear. However, 30–55% of patients experience acoustic hearing loss within days to months after activation, suggesting that both surgical trauma and electrical stimulation may cause hearing loss.The goals of this study were to: 1) determine the contributions of both implantation surgery and EAS to hearing loss in a normal-hearing guinea pig model; 2) determine which cochlear structural changes are associated with hearing loss after surgery and EAS. Two groups of animals were implanted (n = 6 per group), with one group receiving chronic acoustic and electric stimulation for 10 weeks, and the other group receiving no direct acoustic or electric stimulation during this time frame. A third group (n = 6) was not implanted, but received chronic acoustic stimulation. Auditory brainstem response thresholds were followed over time at 1, 2, 6, and 16 kHz. At the end of the study, the following cochlear measures were quantified: hair cells, spiral ganglion neuron density, fibrous tissue density, and stria vascularis blood vessel density; the presence or absence of ossification around the electrode entry was also noted.After surgery, implanted animals experienced a range of 0–55 dB of threshold shifts in the vicinity of the electrode at 6 and 16 kHz. The degree of hearing loss was significantly correlated with reduced stria vascularis vessel density and with the presence of ossification, but not with hair cell counts, spiral ganglion neuron density, or fibrosis area. After 10 weeks of stimulation, 67% of implanted, stimulated animals had more than 10 dB of additional threshold shift at 1 kHz, compared to 17% of implanted, non-stimulated animals and 0% of non-implanted animals. This 1-kHz hearing loss was not associated with changes in any of the cochlear measures quantified in this study. The variation in hearing loss after surgery and electrical stimulation in this animal model is consistent with the variation in human patients. Further, these findings illustrate an advantage of a normal-hearing animal model for quantification of hearing loss and damage to cochlear structures without the confounding effects of chemical- or noise-induced hearing loss. Finally, this study is the first to suggest a role of the stria vascularis and damage to the lateral wall in implantation-induced hearing loss. Further work is needed to determine the mechanisms of implantation- and electrical-stimulation-induced hearing loss.