Pathophysiology of Facial Nerve Stimulation and Its Implications for Electrical Stimulation in Cochlear Implants.

OBJECTIVES: A small number of cochlear implant (CI) users experience facial nerve stimulation (FNS), which can manifest as facial twitching. In some patients, this can be resolved by adjusting the electrical stimulation parameters. However, for others, facial stimulation can significantly impair CI outcomes or even prevent its use. The exact mechanisms underlying FNS are unclear and may vary among patients. DESIGN: Transimpedance measurements were used to assess lateral and longitudinal spread of current within 15 cochlea of nucleus CI recipients with FNS (13 unilateral recipients and 1 bilateral recipient). We compared the transimpedance measurements with programming parameters from clinical visits and pre- and postoperative temporal bone computed tomography (CT) scans to identify factors that may contribute to FNS in each CI ear. RESULTS: In nine ears, transimpedance curves showed inflection, which suggests a localized current sink within the cochlea. This indicates a low-impedance pathway through which current exits the cochlea and stimulates the labyrinthine segment of the facial nerve canal. Electrodes near this current sink were disabled or underfit to minimize facial stimulation. In the other seven ears, current flow peaked toward the basal end of the cochlea, suggesting that current exits through the round window or other structures near the basal end of the cochlea, stimulating the tympanic segment of the facial nerve. CONCLUSIONS: Objective transimpedance measurements can be used to elucidate the mechanisms of FNS and to develop strategies for optimizing electrical stimulation parameters and speech coding to minimize or eliminate FNS in a small subset of CI users.

The Thomas More Lists: A Phonemically Balanced Dutch Monosyllabic Speech Audiometry Test.

Speech audiometry tests are a crucial tool in clinical care and research. In Dutch, the common practice is to use lists of monosyllabic words with a consonant-vowel-consonant (CVC) structure. However, there are relatively few lists, and they are short. Here, the goal is to develop an adult speech audiometry test for Dutch (Flemish) consisting of phonemically balanced lists of 25 CVC words. The ISO 8253-3:2012 norm was followed. From a pool of 689 well-known words, an initial set of 26 lists was recorded by a female speaker. The lists were optimized for perceptual balance by means of two studies with young normal hearing listeners (N1 = 24, N2 = 32). The final corpus contains 16 phonetically and perceptually balanced lists. In a last study (N3 = 25), the reference speech recognition curves in quiet and in speech-shaped noise were determined. Reference speech recognition threshold and slope values for phoneme scoring are respectively 20.3 dBSPL in quiet (slope 5.2%/dB) and -7.7 dBSNR (7.5%/dB) in noise, similar to existing materials. The lists may be a useful addition to the existing audiometric tests.

Novel Impedance Measures as Biomarker for Intracochlear Fibrosis.

Measurement of the complex electrical impedance of the electrode contacts can provide new insights into the factors playing a role in the preservation of residual hearing with cochlear implants (CIs). However, unraveling the contributions related to the different phenomena from impedance data necessitates more advanced measurement and analysis techniques. The present study explores a new impedance measurement option recently included into the cochlear-implant programming software and aims to contribute to a more solid basis for the clinical use of impedance measures as a biomarker for fibrous tissue formation. Twenty adult CI-recipients were followed from surgery until 1 year after implantation by means of Electrode Voltage Telemetry (EVT), also called Electric Field Imaging or TransImpedance-Matrix measurement, and a 4-point technique for probing the voltage between adjacent electrode contacts. The data were compared to the electrode location derived from computed tomography, and to the device usage log. Using our impedance model for electrical stimulation of the cochlea, the polarization impedance related the electrode-tissue interface was determined, and the bulk impedance (access resistance) was split into a near-field and a far-field component. On average, the polarization impedance increased abruptly after surgery, indicating a strong passivation of the electrode contacts before cochlear-implant initiation. Its initial rise resolved almost completely soon after device switchon (2-4 weeks). The gradual increase of the access resistance mainly happened during the first 40 days on a time scale very similar to that observed in a guinea-pig study correlating impedance changes to fibrous tissue growth. The higher increase towards the round window is consistent with the higher amount of tissue observed in histological animal studies close to the electrode entry point. While the initial changes were due to the near-field resistance, the far-field resistance began to rise only after one month for half of the study group, once the near-field component had reached its critical value. This suggests indeed fibrosis initiating near the electrode contacts and spreading thereafter farther away. The near-field resistance positively correlated to device usage. EVT data allow for a further decomposition of the impedance at a cochlear-implant electrode, yielding a more detailed description of the postoperative intracochlear phenomena, such as fibrosis.

Age-Related Changes in Listening Effort for Children and Teenagers With Normal Hearing and Cochlear Implants.

OBJECTIVES: A clinically viable measure of listening effort is crucial in safeguarding the educational success of hard-of-hearing students enrolled in mainstream schools. To this end, a novel behavioral paradigm of listening effort targeting school-age children has been designed and reported in Hsu et al. (2017). The current article consists of two follow-up experiments investigating the effects of noise, processing depth, and age in a similar paradigm, first in a group of participants with normal hearing (NH) followed by a sample of school-age cochlear implant (CI) users. Research objectives include the construction of normative values of listening effort and comparing outcomes between age-matched NH and CI participants. DESIGN: In Experiment 1, the listening effort dual-task paradigm was evaluated in a group of 90 NH participants with roughly even age distribution between 6 and 26 years. The primary task asked a participant to verbally repeat each of the target words presented in either quiet or noise, while the secondary task consisted of categorization true-or-false questions "animal" and "dangerous," representing two levels of semantic processing depth. Two outcome measures were obtained for each condition: a classic word recognition score (WRS) and an average response time (RT) measured during the secondary task. The RT was defined as the main listening effort metric throughout the study. Each NH participant's long-term memory retrieval speed and working memory capacity were also assessed through standardized tests. It was hypothesized that adding noise would negatively affect both WRS and RT, whereas an increase in age would see significant improvement in both measures. A subsequent Experiment 2 administered a shortened version of the paradigm to 14 school-age CI users between 5 and 14 years old at a university clinic. The patterns of results from the CI group were expected to approximate those of the NH group, except with larger between-subject variability. RESULTS: For NH participants, while WRS was significantly affected by age and noise levels, RT was significantly affected by age, noise levels, and depth of processing. RT was significantly correlated with long-term memory retrieval speed but not with working memory capacity. There was also a significant interaction effect between age and noise levels for both WRS and RT. The RT data set from the NH group served as a basis to establish age-dependent 95% prediction intervals for expected future observations. For CI participants, the effect of age on the two outcome measures was more visible when target words were presented in quiet. Depending on the condition, between 35.7% and 72.7% of the children with CI exhibited higher-than-norms listening effort as measured by categorization processing times. CONCLUSION: Listening effort appears to decrease with age from early school-age years to late teenage years. The effects of background noise and processing depth are comparable with those reported in Hsu et al. (2017). Future studies interested in expanding the paradigm's clinical viability should focus on the reduction of testing time while maintaining or increasing the sensitivity and external validity of its outcome measures.

Cochlear Implant Data Logs Predict Children's Receptive Vocabulary.

OBJECTIVES: The data logs of Cochlear Nucleus cochlear implant (CI) sound processors show large interindividual variation in children's daily CI use and auditory environments. This study explored whether these differences are associated with differences in the receptive vocabulary of young implanted children. DESIGN: Data of 52 prelingually deaf children, who had received a CI before 3 years of age, were obtained from their clinical records. In total, 73 Peabody Picture Vocabulary tests and CI data logs for 1 year preceding each test were collected. The data logs were used to determine the children's average daily amount of CI use and exposure to speech, speech in noise, noise, music, and quiet. In addition, information was collected about other potential predictors of language abilities, namely gender, age, age at implantation, etiology of deafness, educational placement, and implantation mode (unilateral, bilateral). Model selection with Akaike's information criterion was used to determine which data-logging metrics, other variables, and combinations of both best predict receptive vocabulary scores. RESULTS: The data showed a strong positive association between receptive vocabulary and daily CI use, and a negative association between receptive vocabulary and daily exposure to music. Associations with the data logs' speech and noise metrics were less clear. The most important other variable was educational placement. The best model performance was achieved when data logs and other information were combined. CONCLUSIONS: The results emphasize the importance of consistent CI use and a rich auditory environment for the early language development of young CI users. The study also shows that CI data logs capture information about children's environment and CI use that are related to language performance and can help to detect and address problems and improve the auditory rehabilitation after cochlear implantation.

Empowering Senior Cochlear Implant Users at Home via a Tablet Computer Application.

PURPOSE: The introduction of connectivity technologies in hearing implants allows new ways to support cochlear implant (CI) users remotely. Some functionalities and services that are traditionally only available in an in-clinic care model can now also be accessed at home. This study explores the feasibility of a prototype of a tablet computer application (MyHearingApp [MHA]) in a group of senior experienced CI users at home, evaluating usability and user motivation. METHOD: Based on user feedback, a tablet computer application (MHA) for the Cochlear Nucleus 6 CP910 sound processor was designed implementing six different functionalities: (a) My Hearing Tests, (b) My Environment, (c) My Hearing Journey, (d) Tip of the Day, (e) Recipient Portal, and (f) Program Use and Events. The clinical evaluation design was a prospective study of the MHA in 16 senior experienced CI users. During 4 weeks, participants could freely explore the functionalities. At the end, the usability and their motivation for uptake and adherence were measured using a baseline and follow-up questionnaire. RESULTS: Based on the System Usability Score (as part of the follow-up questionnaire), a good level of usability was indicated (M = 75.6, range: 62.5-92.5, SD = 8.6). The ability to perform hearing tests at home is ranked as the most relevant functionality within the MHA. According to the Intrinsic Motivation Inventory (Deci, Eghrari, Patrick, & Leone, 1994) questionnaire (as part of the follow-up questionnaire), participants reported high levels of interest and enjoyment, found themselves competent, and did not experience pressure while working with the app. CONCLUSIONS: This study evaluated a tablet computer application (MHA) for experienced senior CI users by means of a prospective design, which provided novel insights into delivering CI care into the home of the CI user. The user feedback from this small-scale study suggests that the participants are open to take more responsibility for and to become a more active actor in their own hearing care, if only this is facilitated with the right tools. This may foster the evolution from a clinic-led to a more patient-centered care model, where CI users feel more empowered in the self-management of their hearing implant device.

Correlation and agreement between Language ENvironment Analysis (LENA™) and manual transcription for Dutch natural language recordings.

The Language ENvironment Analysis system (LENA™) automatically analyzes the natural sound environments of children. Among other things, it estimates the amounts of adult words (AWC), child vocalizations (CV), conversational turns (CT), and electronic media (TV) that a child is exposed to. To assess LENA's reliability, we compared it to manual transcription. Specifically, we calculated the correlation and agreement between the LENA estimates and manual counts for 48 five-min audio samples. These samples were selected from eight day-long recordings of six Dutch-speaking children (ages 2-5). The correlations were strong for AWC, r = . 87, and CV, r = . 77, and comparatively low for CT, r = . 52, and TV, r = . 50. However, the agreement analysis revealed a constant bias in AWC counts, and proportional biases for CV and CT (i.e., the bias varied with the values for CV and CT). Agreement for detecting electronic media was poor. Moreover, the limits of agreement were wide for all four metrics. That is, the differences between LENA and the manual transcriptions for individual audio samples varied widely around the mean difference. This variation could indicate that LENA was affected by differences between the samples that did not equally affect the human transcribers. The disagreements and biases cast doubt on the comparability of LENA measurements across families and time, which is crucial for using LENA in research. Our sample is too small to conclude within which limits LENA's measurements are comparable, but it seems advisable to be cautious of factors that could systematically bias LENA's performance and thereby create confounds.

The use of cochlear's SCAN and wireless microphones to improve speech understanding in noise with the Nucleus6® CP900 processor.

OBJECTIVES: The newest Nucleus CI processor, the CP900, has two new options to improve speech-in-noise perception: (1) use of an adaptive directional microphone (SCAN mode) and (2) wireless connection to MiniMic1 and MiniMic2 wireless remote microphones. DESIGN: An analysis was made of the absolute and relative benefits of these technologies in a real-world mimicking test situation. Speech perception was tested using an adaptive speech-in-noise test (sentences-in-babble noise). In session A, SRTs were measured in three conditions: (1) Clinical Map, (2) SCAN and (3) MiniMic1. Each was assessed for three distances between speakers and CI recipient: 1 m, 2 m and 3 m. In session B, the benefit of the use of MiniMic2 was compared to benefit of MiniMic1 at 3 m. STUDY SAMPLE: A group of 13 adult CP900 recipients participated. RESULTS: SCAN and MiniMic1 improved performance compared to the standard microphone with a median improvement in SRT of 2.7-3.9 dB for SCAN at 1 m and 3 m, respectively, and 4.7-10.9 dB for the MiniMic1. MiniMic1 improvements were significant. MiniMic2 showed an improvement in SRT of 22.2 dB compared to 10.0 dB for MiniMic1 (3 m). CONCLUSIONS: Digital wireless transmission systems (i.e. MiniMic) offer a statistically and clinically significant improvement in speech perception in challenging, realistic listening conditions.

Listening Effort Through Depth of Processing in School-Age Children.

OBJECTIVES: A reliable and practical measure of listening effort is crucial in the aural rehabilitation of children with communication disorders. In this article, we propose a novel behavioral paradigm designed to measure listening effort in school-age children based on different depths and levels of verbal processing. The paradigm consists of a classic word recognition task performed in quiet and in noise coupled to one of three additional tasks asking the children to judge the color of simple pictures or a certain semantic category of the presented words. The response time (RT) from the categorization tasks is considered the primary indicator of listening effort. DESIGN: The listening effort paradigm was evaluated in a group of 31 normal-hearing, normal-developing children 7 to 12 years of age. A total of 146 Dutch nouns were selected for the experiment after surveying 14 local Dutch-speaking children. Windows-based custom software was developed to administer the behavioral paradigm from a conventional laptop computer. A separate touch screen was used as a response interface to gather the RT data from the participants. Verbal repetition of each presented word was scored by the tester and a percentage-correct word recognition score (WRS) was calculated for each condition. Randomized lists of target words were presented in one of three signal to noise ratios (SNR) to examine the effect of background noise on the two outcome measures of WRS and RT. Three novel categorization tasks, each corresponding to a different depth or elaboration level of semantic processing, were developed to examine the effect of processing level on either WRS or RT. It was hypothesized that, while listening effort as measured by RT would be affected by both noise and processing level, WRS performance would be affected by changes in noise level only. The RT measure was also hypothesized to increase more from an increase in noise level in categorization conditions demanding a deeper or more elaborate form of semantic processing. RESULTS: There was a significant effect of SNR level on school-age children's WRS: their word recognition performance tended to decrease with increasing background noise level. However, depth of processing did not seem to affect WRS. Moreover, a repeated-measure analysis of variance fitted to transformed RT data revealed that this measure of listening effort in normal-hearing school-age children was significantly affected by both SNR level and the depth of semantic processing. There was no significant interaction between noise level and the type of categorization task with regard to RT. CONCLUSIONS: The observed patterns of WRS and RT supported the hypotheses regarding the effects of background noise and depth of processing on word recognition performance and a behavioral measure of listening effort. The magnitude of noise-induced change in RT did not differ between categorization tasks, however. Our findings point to future research directions regarding the potential effects of age, working memory capacity, and cross-modality interaction when measuring listening effort in different levels of semantic processing.

Auditory Environment Across the Life Span of Cochlear Implant Users: Insights From Data Logging.

Purpose: We describe the natural auditory environment of people with cochlear implants (CIs), how it changes across the life span, and how it varies between individuals. Method: We performed a retrospective cross-sectional analysis of Cochlear Nucleus 6 CI sound-processor data logs. The logs were obtained from 1,501 people with CIs (ages 0-96 years). They covered over 2.4 million hr of implant use and indicated how much time the CI users had spent in various acoustical environments. We investigated exposure to spoken language, noise, music, and quiet, and analyzed variation between age groups, users, and countries. Results: CI users spent a substantial part of their daily life in noisy environments. As a consequence, most speech was presented in background noise. We found significant differences between age groups for all auditory scenes. Yet even within the same age group and country, variability between individuals was substantial. Conclusions: Regardless of their age, people with CIs face challenging acoustical environments in their daily life. Our results underline the importance of supporting them with assistive listening technology. Moreover, we found large differences between individuals' auditory diets that might contribute to differences in rehabilitation outcomes. Their causes and effects should be investigated further.

Feasibility of an implanted microphone for cochlear implant listening.

This study aimed at evaluating the feasibility of an implanted microphone for cochlear implants (CI) by comparison of hearing outcomes, sound quality and patient satisfaction of a subcutaneous microphone to a standard external microphone of a behind-the-ear sound processor. In this prospective feasibility study with a within-subject repeated measures design comparing the microphone modalities, ten experienced adult unilateral CI users received an implantable contralateral subcutaneous microphone attached to a percutaneous plug. The signal was pre-processed and fed into their CI sound processor. Subjects compared listening modes at home for a period of up to 4 months. At the end of the study the microphone was explanted. Aided audiometric thresholds, speech understanding in quiet, and sound quality questionnaires were assessed. On average thresholds (250, 500, 750, 1k, 2k, 3k, 4k and 6 kHz) with the subcutaneous microphone were 44.9 dB, compared to 36.4 dB for the external mode. Speech understanding on sentences in quiet was high, within approximately 90% of performance levels compared to hearing with an external microphone. Body sounds were audible but not annoying to almost all subjects. This feasibility study with a research device shows significantly better results than previous studies with implanted microphones. This is attributed to technology enhancements and careful fitting. Listening effort was somewhat increased with an implanted microphone. Under good sound conditions, speech performance is nearly similar to that of external microphones demonstrating that an implanted microphone is feasible in a range of normal listening conditions.

The Development of Remote Speech Recognition Tests for Adult Cochlear Implant Users: The Effect of Presentation Mode of the Noise and a Reliable Method to Deliver Sound in Home Environments.

The number of cochlear implant (CI) users is increasing annually, resulting in an increase in the workload of implant centers in ongoing patient management and evaluation. Remote testing of speech recognition could be time-saving for both the implant centers as well as the patient. This study addresses two methodological challenges we encountered in the development of a remote speech recognition tool for adult CI users. First, we examined whether speech recognition in noise performance differed when the steady-state masking noise was presented throughout the test (i.e. continuous) instead of the standard clinical use for evaluation where the masking noise stops after each stimulus (i.e. discontinuous). A direct coupling between the audio port of a tablet computer to the accessory input of the sound processor with a personal audio cable was used. The setup was calibrated to facilitate presentation of stimuli at a predefined sound level. Finally, differences in frequency response between the audio cable and microphones were investigated.

Hearing Device Manufacturers Call for Interoperability and Standardization of Internet and Audiology.

PURPOSE: This article describes the perspectives of hearing device manufacturers regarding the exciting developments that the Internet makes possible. Specifically, it proposes to join forces toward interoperability and standardization of Internet and audiology. METHOD: A summary of why such a collaborative effort is required is provided from historical and scientific perspectives. A roadmap toward interoperability and standardization is proposed. RESULTS: Information and communication technologies improve the flow of health care data and pave the way to better health care. However, hearing-related products, features, and services are notoriously heterogeneous and incompatible with other health care systems (no interoperability). Standardization is the process of developing and implementing technical standards (e.g., Noah hearing database). All parties involved in interoperability and standardization realize mutual gains by making mutually consistent decisions. De jure (officially endorsed) standards can be developed in collaboration with large national health care systems as well as spokespeople for hearing care professionals and hearing device users. The roadmap covers mutual collaboration; data privacy, security, and ownership; compliance with current regulations; scalability and modularity; and the scope of interoperability and standards. CONCLUSIONS: We propose to join forces to pave the way to the interoperable Internet and audiology products, features, and services that the world needs.

Deactivating Cochlear Implant Electrodes Based on Pitch Information for Users of the ACE Strategy.

There is a wide range in performance for cochlear implant (CI) users and there is some evidence to suggest that implant fitting can be modified to improve performance if electrodes that do not provide distinct pitch information are de-activated. However, improvements in performance may not be the same for users of all CI devices; in particular for those with Cochlear devices using n-of-m strategies (ACE or SPEAK).The goal of this research was to determine for users of Cochlear devices (CP810 or CP900 series processors) if speech perception could be improved when indiscriminable electrodes were de-activated and this was also compared to when the same number of discriminable electrodes were de-activated.A cross-over study was conducted with 13 adult CI users who received experimental maps with de-activated channels for a minimum of 2 months and these were compared to optimised clinical maps.The findings showed that there were no significant benefits of electrode de-activation on speech perception and that there was a significant deterioration in spectro-temporal ripple perception when electrodes were switched off. There were no significant differences between de-activation of discriminable or indiscriminable electrodes.These findings suggest that electrode de-activation with n-of-m strategies may not be beneficial.

Measures of the electrically evoked compound action potential threshold and slope in HiRes 90K(TM) users.

OBJECTIVES: To investigate electrically evoked compound action potentials (eCAPs) measured with the neural response imaging (NRI) 'SmartNRI' algorithm. NRI thresholds and slopes were examined according to three aspects: (1) site along the cochlea, (2) development of responses over time, and (3) influence of age/duration of deafness. METHODS: Thirty-four individuals implanted with the Advanced Bionics HiRes 90K(TM) device were included. The eCAP recordings were made from four electrodes along the array at first fitting and at frequent intervals up to at least 2 years. Slope and threshold (tNRI) of the amplitude growth function were measured and a range of explanatory variables were tested for significant effects on these measures using multi-factorial analysis of variance. RESULTS: Electrode position emerged as a significant effect for the tNRI measure, with lowest thresholds at the apical end of the array. Mean slope was greatest for the most apical electrode, but not significantly. Slope was significantly influenced by onset of deafness, with congenital hearing loss associated with steeper slopes than acquired hearing loss. There was also a highly significant effect of duration of device use, with a gradual increase in slope over the 2 years following device activation. DISCUSSION: The observed effects of electrode position are consistent with a model in which eCAP threshold is governed primarily by an effect of distance between electrode and neural interface (which is shorter towards the apex of the cochlea) and in which slope is governed primarily by density of surviving neural elements.

Restoring speech perception with cochlear implants by spanning defective electrode contacts.

CONCLUSION: Even with six defective contacts, spanning can largely restore speech perception with the HiRes 120 speech processing strategy to the level supported by an intact electrode array. Moreover, the sound quality is not degraded. OBJECTIVES: Previous studies have demonstrated reduced speech perception scores (SPS) with defective contacts in HiRes 120. This study investigated whether replacing defective contacts by spanning, i.e. current steering on non-adjacent contacts, is able to restore speech recognition to the level supported by an intact electrode array. METHODS: Ten adult cochlear implant recipients (HiRes90K, HiFocus1J) with experience with HiRes 120 participated in this study. Three different defective electrode arrays were simulated (six separate defective contacts, three pairs or two triplets). The participants received three take-home strategies and were asked to evaluate the sound quality in five predefined listening conditions. After 3 weeks, SPS were evaluated with monosyllabic words in quiet and in speech-shaped background noise. RESULTS: The participants rated the sound quality equal for all take-home strategies. SPS with background noise were equal for all conditions tested. However, SPS in quiet (85% phonemes correct on average with the full array) decreased significantly with increasing spanning distance, with a 3% decrease for each spanned contact.

Assessing the placement of a cochlear electrode array by multidimensional scaling.

Correct placement of the electrode is crucial for cochlear implantation (CI) surgery. It determines the access to the auditory nerve and subsequent hearing performance. Here, we propose an objective measures tool that can partially verify the electrode position. The intracochlear spread of the electrical fields is measured and analyzed by means of multidimensional scaling resulting in an intuitive visual representation. The user can then detect major issues, such as electrode foldover or ossification. Other implantation issues, such as electrode migration into the scala vestibuli, may not significantly alter the electrical conduction pattern and remain undetected. Still, as the measurement is quick and readily available, it may be a valuable intraoperative verification tool.

Spread of excitation and channel interaction in single- and dual-electrode cochlear implant stimulation.

OBJECTIVES: To determine how simultaneous dual-electrode stimulation (DES) can be optimized for the individual patient to deliver better sound quality and speech recognition. DES was compared with single-electrode stimulation (SES) with respect to the site of stimulation (X) in the cochlea, the spread of excitation (SOE), and channel interaction. Second, it was investigated whether the number of intermediate pitches created with DES can be predicted from SOE, channel interaction measures, current distribution in the cochlea, or distance of the electrode to the medial wall. DESIGN: Twelve users of the HiRes90K cochlear implant with HiFocus1J electrode were randomly selected to participate in this study. Electrode contacts were selected based on their location in the cochlea as determined by multislice computed tomography, viz. 120 degrees (basal), 240 degrees (middle), and 360 degrees (apical) from the round window. The number of intermediate pitches with simultaneous DES was assessed with a three-alternative forced choice pitch discrimination experiment. The channel interactions between two single-electrode contacts and two DES pairs were determined with a threshold detection experiment (three-alternative forced choice). The eCAP-based SOE method with fixed probe and variable masker was used to determine the location of the neurons responding to a single-electrode contact or dual-electrode contact stimulus. Furthermore, the intracochlear electrical fields were determined with the Electrical Field Imaging tool kit. RESULTS: DES was not different from SES in terms of channel interaction and SOE. The X of DES was 0.54 electrode contacts more basal compared with SES stimulation, which was not different from the predicted shift of 0.5. SOE and current distribution were significantly different for the three locations in the cochlea but showed no correlation with the number of perceivable pitches. A correlation was found between channel interaction and the number of intermediate pitches along the array within a patient, not between patients. CONCLUSION: SES and DES are equivalent with regard to SOE and channel interaction. The excitation site of DES has the predicted displacement compared with the excitation region induced by the neighboring single-electrode contact. Unfortunately, no predictor for the number of intermediate pitches was found.

Influence of widening electrode separation on current steering performance.

OBJECTIVES: Current steering between adjacent electrodes makes it possible to create more spectral channels than the number of electrodes in an electrode array. With current steering on nonadjacent electrodes, called "spanning," it could be possible to bridge a defective electrode contact or potentially reduce the number of electrode contacts for the same level of access to the auditory nerve. This study investigates the effectiveness of spanning in terms of the number of intermediate pitches, loudness effects, and linearity of the current weighting coefficient (α) with respect to the perceived pitch. DESIGN: Twelve postlingually deafened users of the HiRes90K cochlear implant with HiFocus1j electrode were randomly selected to participate in this study. Electrode contacts were selected at two locations in the cochlea, as determined on multislice computed tomography: 180° (basal) and 360° (apical) from the round window. For both cochlear locations, three psychophysical experiments were performed using simultaneous stimulation of electrode contacts. An adaptive staircase-based procedure was used. The number of intermediate pitches was assessed with a three-alternative forced choice (3AFC) pitch discrimination task, and the extent of current adjustment required when varying the current weighting coefficient (α) was determined with loudness balancing (2AFC). Finally, the pitch of a spanned channel was matched with the pitch of an intermediate physical electrode in a 2AFC procedure to assess the place of the spanned channel on the electrode array. RESULTS: Spanning required significantly more current compensation to maintain equal loudness than current steering between adjacent electrode contacts. A significant decrease of discriminable intermediate pitches occurred with spanning in comparison with current steering between adjacent electrode contacts. No significant difference was found between the pitch-matched current steering coefficient and the theoretical coefficient corresponding a priori with the intermediate physical electrode. No significant difference was found between the data from the apical and the basal sections of the electrode array. CONCLUSIONS: Spanning over wider electrode distance is feasible. With increasing electrode spanning distance, more current compensation is needed to maintain equal loudness, and a gradual deterioration in the just noticeable difference for pitch is observed. However, the pitch progression is linear. For a spanned signal with equal proportions of current delivered to both electrodes, pitch is equivalent to that produced by an intermediate physical electrode.

Electrical field imaging as a means to predict the loudness of monopolar and tripolar stimuli in cochlear implant patients.

Tripolar and other electrode configurations that use simultaneous stimulation inside the cochlea have been tested to reduce channel interactions compared to the monopolar stimulation conventionally used in cochlear implant systems. However, these "focused" configurations require increased current levels to achieve sufficient loudness. In this study, we investigate whether highly accurate recordings of the intracochlear electrical field set up by monopolar and tripolar configurations correlate to their effect on loudness. We related the intra-scalar potential distribution to behavioral loudness, by introducing a free parameter (α) which parameterizes the degree to which the potential field peak set up inside the scala tympani is still present at the location of the targeted neural tissue. Loudness balancing was performed on four levels between behavioral threshold and the most comfortable loudness level in a group of 10 experienced Advanced Bionics cochlear implant users. The effect of the amount of focusing on loudness was well explained by α per subject location along the basilar membrane. We found that α was unaffected by presentation level. Moreover, the ratios between the monopolar and tripolar currents, balanced for equal loudness, were approximately the same for all presentation levels. This suggests a linear loudness growth with increasing current level and that the equal peak hypothesis may predict the loudness of threshold as well as at supra-threshold levels. These results suggest that advanced electrical field imaging, complemented with limited psychophysical testing, more specifically at only one presentation level, enables estimation of the loudness growth of complex electrode configurations.