Spatial hearing and speech intelligibility in bilateral cochlear implant users

Talking in Time: The development of a self-administered conversation analysis based training programme for cochlear implant users

Objectives: Training software to facilitate participation in conversations where overlapping talk is common was to be developed with the involvement of Cochlear implant (CI) users. Methods: Examples of common types of overlap were extracted from a recorded corpus of 3.5 hours of British English conversation. In eight meetings, an expert panel of five CI users tried out ideas for a computer-based training programme addressing difficulties in turn-taking. Results: Based on feedback from the panel, a training programme was devised. The first module consists of introductory videos. The three remaining modules, implemented in interactive software, focus on non-overlapped turn-taking, competitive overlaps and accidental overlaps. Discussion: The development process is considered in light of feedback from panel members and from an end of project dissemination event. Benefits, limitations and challenges of the present approach to user involvement and to the design of self-administered communication training programmes are discussed. Conclusion: The project was characterized by two innovative features: the involvement of service users not only at its outset and conclusion but throughout its course; and the exclusive use of naturally occurring conversational speech in the training programme. While both present practical challenges, the project has demonstrated the potential for ecologically valid speech rehabilitation training.

An Individual With Hearing Preservation and Bimodal Hearing Using a Cochlear Implant and Hearing Aids Has Perturbed Sound Localization but Preserved Speech Perception

This study describes sound localization and speech-recognition-in-noise abilities of a cochlear-implant user with electro-acoustic stimulation (EAS) in one ear, and a hearing aid in the contralateral ear. This listener had low-frequency, up to 250 Hz, residual hearing within the normal range in both ears. The objective was to determine how hearing devices affect spatial hearing for an individual with substantial unaided low-frequency residual hearing. Sound-localization performance was assessed for three sounds with different bandpass characteristics: low center frequency (100-400 Hz), mid center frequency (500-1,500 Hz) and high frequency broad-band (500-20,000 Hz) noise. Speech recognition was assessed with the Dutch Matrix sentence test presented in noise. Tests were performed while the listener used several on-off combinations of the devices. The listener localized low-center frequency sounds well in all hearing conditions, but mid-center frequency and high frequency broadband sounds were localized well almost exclusively in the completely unaided condition (mid-center frequency sounds were also localized well with the EAS device alone). Speech recognition was best in the fully aided condition with speech presented in the front and noise presented at either side. Furthermore, there was no significant improvement in speech recognition with all devices on, compared to when the listener used her cochlear implant only. Hearing aids and cochlear implant impair high frequency spatial hearing due to improper weighing of interaural time and level difference cues. The results reinforce the notion that hearing symmetry is important for sound localization. The symmetry is perturbed by the hearing devices for higher frequencies. Speech recognition depends mainly on hearing through the cochlear implant and is not significantly improved with the added information from hearing aids. A contralateral hearing aid provides benefit when the noise is spatially separated from the speech. However, this benefit is explained by the head shadow in that ear, rather than by an ability to spatially segregate noise from speech, as sound localization was perturbed with all devices in use.

[Processing of interaural time differences in normal-hearing subjects and cochlear implant users with FSP and HDCIS coding strategy]

BACKGROUND

Sound localization is necessary for social interaction and remains challenging for bilateral cochlear implant (CI) users. This study investigated the influence of fine structure processing (FSP) coding strategies on temporal accuracy and source localization. The ability to discriminate between different interaural time differences (ITD) was measured objectively and compared.

MATERIALS AND METHODS

Fifteen normal-hearing subjects and five CI users participated in this study. Electrophysiological recording of mismatch negativity (MMN) and psychoacoustic tests with headphones and loudspeakers were conducted to measure and compare the discrimination of ITDs.

RESULTS

In normal-hearing subjects the discrimination threshold for ITD was 83-117 µs. Localization ability in a free sound field was below the limit of resolution. A significant MMN was measured. CI users showed a mean angle detection error of more than 30° and a discrimination threshold between 1100 and 2100 µs. Due to artifacts, no clear MMN component could be recorded.

CONCLUSION

This study shows that MMN can be used as an objective measure of ITD discrimination in normal-hearing participants. An indication that improvements in directional hearing can be achieved with the transfer of fine structure could not be provided by this study.

Comparison Between Simulated and Actual Unilateral Hearing in Sequentially Implanted Cochlear Implant Users, a Cohort Study

Introduction: Previous studies have proven the effectiveness of bilateral cochlear implantation compared to unilateral cochlear implantation. In many of these studies the unilateral hearing situation was simulated by switching off one of the cochlear implants in bilateral cochlear implant users. In the current study we assess the accuracy of this test method. Does simulated unilateral hearing (switching off one cochlear implant) result in the same outcomes as real life unilateral hearing with one cochlear implant and a non-implanted contralateral ear?

Study design: We assessed the outcomes of one arm of a multicenter randomized controlled trial.

Methods: In the original trial, 38 postlingually deafened adults were randomly allocated to either simultaneous bilateral cochlear implantation or sequential bilateral cochlear implantation. In the current study we used the data of the sequentially implanted group (n = 19). The primary outcome was speech perception-in-noise from straight ahead. Secondary outcomes were speech perception-in-silence, speech intelligibility-in-noise from spatially separated sources and localization capabilities. A within-subjects design was used to compare the results of hearing with one cochlear implant and a non-implanted contralateral ear (1- and 2-year follow-up) with the results of switching off one cochlear implant after sequential bilateral implantation (3-year follow-up).

Results: We found no significant differences on any of the objective outcomes after 1-, 2-, or 3-year follow-up.

Conclusion: This study shows that simulating unilateral hearing by switching off one cochlear implant seems a reliable method to compare unilateral and bilateral hearing in bilaterally implanted patients.

Clinical Trial Registration: Dutch Trial Register NTR1722.

Head Movements Allow Listeners Bilaterally Implanted With Cochlear Implants to Resolve Front-Back Confusions

OBJECTIVES

We report on the ability of patients fit with bilateral cochlear implants (CIs) to distinguish the front-back location of sound sources both with and without head movements. At issue was (i) whether CI patients are more prone to front-back confusions than normal hearing listeners for wideband, high-frequency stimuli; and (ii) if CI patients can utilize dynamic binaural difference cues, in tandem with their own head rotation, to resolve these front-back confusions. Front-back confusions offer a binary metric to gain insight into CI patients' ability to localize sound sources under dynamic conditions not generally measured in laboratory settings where both the sound source and patient are static.

DESIGN

Three-second duration Gaussian noise samples were bandpass filtered to 2 to 8 kHz and presented from one of six loudspeaker locations located 60° apart, surrounding the listener. Perceived sound source localization for seven listeners bilaterally implanted with CIs, was tested under conditions where the patient faced forward and did not move their head and under conditions where they were encouraged to moderately rotate their head. The same conditions were repeated for 5 of the patients with one implant turned off (the implant at the better ear remained on). A control group of normal hearing listeners was also tested for a baseline of comparison.

RESULTS

All seven CI patients demonstrated a high rate of front-back confusions when their head was stationary (41.9%). The proportion of front-back confusions was reduced to 6.7% when these patients were allowed to rotate their head within a range of approximately ± 30°. When only one implant was turned on, listeners' localization acuity suffered greatly. In these conditions, head movement or the lack thereof made little difference to listeners' performance.

CONCLUSIONS

Bilateral implantation can offer CI listeners the ability to track dynamic auditory spatial difference cues and compare these changes to changes in their own head position, resulting in a reduced rate of front-back confusions. This suggests that, for these patients, estimates of auditory acuity based solely on static laboratory settings may underestimate their real-world localization abilities.

Auditory motion tracking ability of adults with normal hearing and with bilateral cochlear implants

Adults with bilateral cochlear implants (BiCIs) receive benefits in localizing stationary sounds when listening with two implants compared with one; however, sound localization ability is significantly poorer when compared to normal hearing (NH) listeners. Little is known about localizing sound sources in motion, which occurs in typical everyday listening situations. The authors considered the possibility that sound motion may improve sound localization in BiCI users by providing multiple places of information. Alternatively, the ability to compare multiple spatial locations may be compromised in BiCI users due to degradation of binaural cues, and thus result in poorer performance relative to NH adults. In this study, the authors assessed listeners' abilities to distinguish between sounds that appear to be moving vs stationary, and track the angular range and direction of moving sounds. Stimuli were bandpass-filtered (150-6000 Hz) noise bursts of different durations, panned over an array of loudspeakers. Overall, the results showed that BiCI users were poorer than NH adults in (i) distinguishing between a moving vs stationary sound, (ii) correctly identifying the direction of movement, and (iii) tracking the range of movement. These findings suggest that conventional cochlear implant processors are not able to fully provide the cues necessary for perceiving auditory motion correctly.

Effects of Cochlear Implantation on Binaural Hearing in Adults With Unilateral Hearing Loss

A FDA clinical trial was carried out to evaluate the potential benefit of cochlear implant (CI) use for adults with unilateral moderate-to-profound sensorineural hearing loss. Subjects were 20 adults with moderate-to-profound unilateral sensorineural hearing loss and normal or near-normal hearing on the other side. A MED-EL standard electrode was implanted in the impaired ear. Outcome measures included: (a) sound localization on the horizontal plane (11 positions, -90° to 90°), (b) word recognition in quiet with the CI alone, and (c) masked sentence recognition with the target at 0° and the masker at -90°, 0°, or 90°. This battery was completed preoperatively and at 1, 3, 6, 9, and 12 months after CI activation. Normative data were also collected for 20 age-matched control subjects with normal or near-normal hearing bilaterally. The CI improved localization accuracy and reduced side bias. Word recognition with the CI alone was similar to performance of traditional CI recipients. The CI improved masked sentence recognition when the masker was presented from the front or from the side of normal or near-normal hearing. The binaural benefits observed with the CI increased between the 1- and 3-month intervals but appeared stable thereafter. In contrast to previous reports on localization and speech perception in patients with unilateral sensorineural hearing loss, CI benefits were consistently observed across individual subjects, and performance was at asymptote by the 3-month test interval. Cochlear implant settings, consistent CI use, and short duration of deafness could play a role in this result.

Assessing the Acoustic Characteristics of Rooms: A Tutorial with Examples

In both practicing audiology and speech language pathology, as well as in speech and hearing science research, the space where the work is done is an integral part of the function. Hence, for all of these endeavors it can be important to measure the acoustics of a room. This article provides a tutorial regarding the measurement of room reverberation and background noise, both of which are important when evaluating a space's strengths and limitations for speech communication. As the privacy of patients and research participants is a primary concern, the tutorial also describes a method for measuring the amount of acoustical insulation provided by a room's barriers. Several room measurement data sets - all obtained from the assessment of clinical and research spaces within our own department - are presented here as examples.

Cochlear Implantation for Single-Sided Deafness: A New Treatment Paradigm

Unilateral severe-to-profound sensorineural hearing loss (SNHL), also known as single sided deafness (SSD), is a problem that affects both children and adults, and can have severe and detrimental effects on multiple aspects of life including music appreciation, speech understanding in noise, speech and language acquisition, performance in the classroom and/or the workplace, and quality of life. Additionally, the loss of binaural hearing in SSD patients affects those processes that rely on two functional ears including sound localization, binaural squelch and summation, and the head shadow effect. Over the last decade, there has been increasing interest in cochlear implantation for SSD to restore binaural hearing. Early data are promising that cochlear implantation for SSD can help to restore binaural functionality, improve quality of life, and may faciliate reversal of neuroplasticity related to auditory deprivation in the pediatric population. Additionally, this new patient population has allowed researchers the opportunity to investigate the age-old question "what does a cochlear implant (CI) sound like?."

Early auditory skills development in Mandarin speaking children after bilateral cochlear implantation

OBJECTIVES

The purpose of the present study was: (1) to investigate the early auditory preverbal behaviors of infants/toddlers with bilateral cochlear implants (BCI), and to compare their performance with that of unilateral cochlear implant (UCI) peers; (2) to investigate effects of age of implantation, education level of caregivers, living environment, and unaided behavioral threshold before operation on early auditory preverbal development.

METHODS

The evaluation material of the present study was the Mandarin version of the LittlEARS^® Auditory Questionnaire (LEAQ). Assessments were administrated at 0, 1, 2, 3, 6, 9, 12 and 24 months after cochlear implants (CIs) were switched on. A one-way ANOVA was used to analyze the differences of early auditory preverbal performance between each two contiguous test intervals. A two-sample t-test was used to analyze the difference of behaviors between infants/toddlers with BCI and UCI. Non-parametric tests were used to analyze the effects of potential affecting factors on auditory preverbal skills.

RESULTS

Nineteen subjects aging from 9 to 54 months (Mean = 22.7, SD = 13.7) were recruited in the study. At each evaluation time, the average scores of LEAQ were 4.58, 9.00, 16.00, 18.56, 22.00, 31.50, 29.67, and 34.35 respectively. The total score and semantic auditory behavior score increased significantly during the second months after CIs activation (the total score: LSD-t = 3.157, p = 0.030; semantic auditory behavior score: LSD-t = 1.972, p = 0.034). The score of BCI group was significantly higher than UCI group after 1, 3 and 6 months of CI use (1 month: t = 3.257, p = 0.002; 3 months: t = 5.042, p = 0.000; 6 months: t = 4.054, p = 0.000). Education level of caregivers had a positive effect on receptive auditory behavior (H = 6.538, p = 0.035) after CIs switched on for 3 months. The LEAQ performance was not significantly correlated with pre-operative behavioral threshold although they showed a trend of negative correlation in the first 3 months after activation.

CONCLUSION

The study indicated that infants and toddlers who underwent BCI had better auditory preverbal skills than their UCI peers. Higher caregivers' education level positively correlated with the early development of auditory preverbal skills. Better pre-operative behavioral threshold might also benefit early auditory preverbal skills development for BCI children.

Sound Localization and Speech Perception in Noise of Pediatric Cochlear Implant Recipients: Bimodal Fitting Versus Bilateral Cochlear Implants

OBJECTIVES

The aim of this study was to compare binaural performance of auditory localization task and speech perception in babble measure between children who use a cochlear implant (CI) in one ear and a hearing aid (HA) in the other (bimodal fitting) and those who use bilateral CIs.

DESIGN

Thirteen children (mean age ± SD = 10 ± 2.9 years) with bilateral CIs and 19 children with bimodal fitting were recruited to participate. Sound localization was assessed using a 13-loudspeaker array in a quiet sound-treated booth. Speakers were placed in an arc from -90° azimuth to +90° azimuth (15° interval) in horizontal plane. To assess the accuracy of sound location identification, we calculated the absolute error in degrees between the target speaker and the response speaker during each trial. The mean absolute error was computed by dividing the sum of absolute errors by the total number of trials. We also calculated the hemifield identification score to reflect the accuracy of right/left discrimination. Speech-in-babble perception was also measured in the sound field using target speech presented from the front speaker. Eight-talker babble was presented in the following four different listening conditions: from the front speaker (0°), from one of the two side speakers (+90° or -90°), from both side speakers (±90°). Speech, spatial, and quality questionnaire was administered.

RESULTS

When the two groups of children were directly compared with each other, there was no significant difference in localization accuracy ability or hemifield identification score under binaural condition. Performance in speech perception test was also similar to each other under most babble conditions. However, when the babble was from the first device side (CI side for children with bimodal stimulation or first CI side for children with bilateral CIs), speech understanding in babble by bilateral CI users was significantly better than that by bimodal listeners. Speech, spatial, and quality scores were comparable with each other between the two groups.

CONCLUSIONS

Overall, the binaural performance was similar to each other between children who are fit with two CIs (CI + CI) and those who use bimodal stimulation (HA + CI) in most conditions. However, the bilateral CI group showed better speech perception than the bimodal CI group when babble was from the first device side (first CI side for bilateral CI users or CI side for bimodal listeners). Therefore, if bimodal performance is significantly below the mean bilateral CI performance on speech perception in babble, these results suggest that a child should be considered to transit from bimodal stimulation to bilateral CIs.

Restoration of spatial hearing in adult cochlear implant users with single-sided deafness

In recent years, cochlear implants (CIs) have been provided in growing numbers to people with not only bilateral deafness but also to people with unilateral hearing loss, at times in order to alleviate tinnitus. This study presents audiological data from 15 adult participants (ages 48 ± 12 years) with single sided deafness. Results are presented from 9/15 adults, who received a CI (SSD-CI) in the deaf ear and were tested in Acoustic or Acoustic + CI hearing modes, and 6/15 adults who are planning to receive a CI, and were tested in the unilateral condition only. Testing included (1) audiometric measures of threshold, (2) speech understanding for CNC words and AzBIO sentences, (3) tinnitus handicap inventory, (4) sound localization with stationary sound sources, and (5) perceived auditory motion. Results showed that when listening to sentences in quiet, performance was excellent in the Acoustic and Acoustic + CI conditions. In noise, performance was similar between Acoustic and Acoustic + CI conditions in 4/6 participants tested, and slightly worse in the Acoustic + CI in 2/6 participants. In some cases, the CI provided reduced tinnitus handicap scores. When testing sound localization ability, the Acoustic + CI condition resulted in improved sound localization RMS error of 29.2° (SD: ±6.7°) compared to 56.6° (SD: ±16.5°) in the Acoustic-only condition. Preliminary results suggest that the perception of motion direction, whereby subjects are required to process and compare directional cues across multiple locations, is impaired when compared with that of normal hearing subjects.

Spatial Release From Masking in Adults With Bilateral Cochlear Implants: Effects of Distracter Azimuth and Microphone Location

PURPOSE

The primary purpose of this study was to derive spatial release from masking (SRM) performance-azimuth functions for bilateral cochlear implant (CI) users to provide a thorough description of SRM as a function of target/distracter spatial configuration. The secondary purpose of this study was to investigate the effect of the microphone location for SRM in a within-subject study design.

METHOD

Speech recognition was measured in 12 adults with bilateral CIs for 11 spatial separations ranging from -90° to +90° in 20° steps using an adaptive block design. Five of the 12 participants were tested with both the behind-the-ear microphones and a T-mic configuration to further investigate the effect of mic location on SRM.

RESULTS

SRM can be significantly affected by the hemifield origin of the distracter stimulus-particularly for listeners with interaural asymmetry in speech understanding. The greatest SRM was observed with a distracter positioned 50° away from the target. There was no effect of mic location on SRM for the current experimental design.

CONCLUSION

Our results demonstrate that the traditional assessment of SRM with a distracter positioned at 90° azimuth may underestimate maximum performance for individuals with bilateral CIs.

Mixed stimulation rates to improve sensitivity of interaural timing differences in bilateral cochlear implant listeners

Normal hearing listeners extract small interaural time differences (ITDs) and interaural level differences (ILDs) to locate sounds and segregate targets from noise. Bilateral cochlear implant listeners show poor sensitivity to ITDs when using clinical processors. This is because common clinical stimulation approaches use high rates [∼1000 pulses per-second (pps)] for each electrode in order to provide good speech representation, but sensitivity to ITDs is best at low rates of stimulation (∼100-300 pps). Mixing rates of stimulation across the array is a potential solution. Here, ITD sensitivity for a number of mixed-rate configurations that were designed to preserve speech envelope cues using high-rate stimulation and spatial hearing using low rate stimulation was examined. Results showed that ITD sensitivity in mixed-rate configurations when only one low rate electrode was included generally yielded ITD thresholds comparable to a configuration with low rates only. Low rate stimulation at basal or middle regions on the electrode array yielded the best sensitivity to ITDs. This work provides critical evidence that supports the use of mixed-rate strategies for improving ITD sensitivity in bilateral cochlear implant users.

Lateralization of Interaural Level Differences with Multiple Electrode Stimulation in Bilateral Cochlear-Implant Listeners

OBJECTIVE

There is currently no accepted method of mapping bilateral cochlear-implant (BiCI) users to maximize binaural performance, but the current approach of mapping one ear at a time could produce spatial perceptions that are not consistent with a sound's physical location in space. The goal of this study was to investigate the perceived intracranial lateralization of bilaterally synchronized electrical stimulation with a range of interaural level differences (ILDs) and to determine a method to produce relatively more centered auditory images when provided multielectrode stimulation.

DESIGN

Using direct stimulation, lateralization curves were measured in nine BiCI listeners using 1000-pulses per second (pps), 500-msec constant-amplitude pulse trains with ILDs that ranged from -20 to +20 clinical current units (CUs). The stimuli were presented bilaterally at 70 to 80% of the dynamic range on single or multiple electrode pairs. For the multielectrode pairs, the ILD was applied consistently across all the pairs. The lateralization response range and the bias magnitude at 0 CU ILD (i.e., the number of CUs needed to produce a centered auditory image) were computed. Then the levels that elicit a centered auditory image with single-electrode stimulation were used with multielectrode stimulation to determine if this produced fewer significant biases at 0 CU ILD. Lastly, a multichannel ILD processing model was used to predict lateralization for the multielectrode stimulation from the single-electrode stimulation.

RESULTS

BiCI listeners often perceived both single- and multielectrode stimulation at 0-CU ILD as not intracranially centered. For single-electrode stimulation, 44% of the lateralization curves had relatively large (≥5 CU) bias magnitudes. For the multielectrode stimulation, 25% of the lateralization curves had large bias magnitudes. After centering the single-electrode pairs, the percentage of multielectrode combinations that produced large biases significantly decreased to only 4% (p < 0.001, McNemar's test). The lateralization with multielectrode stimulation was well predicted by a model that used unweighted or weighted average single-electrode lateralization percepts across electrode pairs (87 or 90%, respectively).

CONCLUSION

Current BiCI mapping procedures can produce an inconsistent association between a physical ILD and the perceived location across electrodes for both single- and multielectrode stimulation. Explicit centering of single-electrode pairs using the perceived centered intracranial location almost entirely corrects this problem and such an approach is supported by our understanding and model of across-frequency ILD processing. Such adjustments might be achieved by clinicians using single-electrode binaural comparisons. Binaural abilities, like sound localization and understanding speech in noise, may be improved if these across-electrode perceptual inconsistencies are removed.

The Relationship Between Intensity Coding and Binaural Sensitivity in Adults With Cochlear Implants

OBJECTIVES

Many bilateral cochlear implant users show sensitivity to binaural information when stimulation is provided using a pair of synchronized electrodes. However, there is large variability in binaural sensitivity between and within participants across stimulation sites in the cochlea. It was hypothesized that within-participant variability in binaural sensitivity is in part affected by limitations and characteristics of the auditory periphery which may be reflected by monaural hearing performance. The objective of this study was to examine the relationship between monaural and binaural hearing performance within participants with bilateral cochlear implants.

DESIGN

Binaural measures included dichotic signal detection and interaural time difference discrimination thresholds. Diotic signal detection thresholds were also measured. Monaural measures included dynamic range and amplitude modulation detection. In addition, loudness growth was compared between ears. Measures were made at three stimulation sites per listener.

RESULTS

Greater binaural sensitivity was found with larger dynamic ranges. Poorer interaural time difference discrimination was found with larger difference between comfortable levels of the two ears. In addition, poorer diotic signal detection thresholds were found with larger differences between the dynamic ranges of the two ears. No relationship was found between amplitude modulation detection thresholds or symmetry of loudness growth and the binaural measures.

CONCLUSIONS

The results suggest that some of the variability in binaural hearing performance within listeners across stimulation sites can be explained by factors nonspecific to binaural processing. The results are consistent with the idea that dynamic range and comfortable levels relate to peripheral neural survival and the width of the excitation pattern which could affect the fidelity with which central binaural nuclei process bilateral inputs.

The Effect of Microphone Placement on Interaural Level Differences and Sound Localization Across the Horizontal Plane in Bilateral Cochlear Implant Users

OBJECTIVE

This study examined the effect of microphone placement on the interaural level differences (ILDs) available to bilateral cochlear implant (BiCI) users, and the subsequent effects on horizontal-plane sound localization.

DESIGN

Virtual acoustic stimuli for sound localization testing were created individually for eight BiCI users by making acoustic transfer function measurements for microphones placed in the ear (ITE), behind the ear (BTE), and on the shoulders (SHD). The ILDs across source locations were calculated for each placement to analyze their effect on sound localization performance. Sound localization was tested using a repeated-measures, within-participant design for the three microphone placements.

RESULTS

The ITE microphone placement provided significantly larger ILDs compared to BTE and SHD placements, which correlated with overall localization errors. However, differences in localization errors across the microphone conditions were small.

CONCLUSIONS

The BTE microphones worn by many BiCI users in everyday life do not capture the full range of acoustic ILDs available, and also reduce the change in cue magnitudes for sound sources across the horizontal plane. Acute testing with an ITE placement reduced sound localization errors along the horizontal plane compared to the other placements in some patients. Larger improvements may be observed if patients had more experience with the new ILD cues provided by an ITE placement.

Having Two Ears Facilitates the Perceptual Separation of Concurrent Talkers for Bilateral and Single-Sided Deaf Cochlear Implantees

OBJECTIVES

Listening to speech with multiple competing talkers requires the perceptual separation of the target voice from the interfering background. Normal-hearing listeners are able to take advantage of perceived differences in the spatial locations of competing sound sources to facilitate this process. Previous research suggests that bilateral (BI) cochlear-implant (CI) listeners cannot do so, and it is unknown whether single-sided deaf (SSD) CI users (one acoustic and one CI ear) have this ability. This study investigated whether providing a second ear via cochlear implantation can facilitate the perceptual separation of targets and interferers in a listening situation involving multiple competing talkers.

DESIGN

BI-CI and SSD-CI listeners were required to identify speech from a target talker mixed with one or two interfering talkers. In the baseline monaural condition, the target speech and the interferers were presented to one of the CIs (for the BI-CI listeners) or to the acoustic ear (for the SSD-CI listeners). In the bilateral condition, the target was still presented to the first ear but the interferers were presented to both the target ear and the listener's second ear (always a CI), thereby testing whether CI listeners could use information about the interferer obtained from a second ear to facilitate perceptual separation of the target and interferer.

RESULTS

Presenting a copy of the interfering signals to the second ear improved performance, up to 4 to 5 dB (12 to 18 percentage points), but the amount of improvement depended on the type of interferer. For BI-CI listeners, the improvement occurred mainly in conditions involving one interfering talker, regardless of gender. For SSD-CI listeners, the improvement occurred in conditions involving one or two interfering talkers of the same gender as the target. This interaction is consistent with the idea that the SSD-CI listeners had access to pitch cues in their normal-hearing ear to separate the opposite-gender target and interferers, while the BI-CI listeners did not.

CONCLUSIONS

These results suggest that a second auditory input via a CI can facilitate the perceptual separation of competing talkers in situations where monaural cues are insufficient to do so, thus partially restoring a key advantage of having two ears that was previously thought to be inaccessible to CI users.

Benefits to Speech Perception in Noise From the Binaural Integration of Electric and Acoustic Signals in Simulated Unilateral Deafness

OBJECTIVES

This study used vocoder simulations with normal-hearing (NH) listeners to (1) measure their ability to integrate speech information from an NH ear and a simulated cochlear implant (CI), and (2) investigate whether binaural integration is disrupted by a mismatch in the delivery of spectral information between the ears arising from a misalignment in the mapping of frequency to place.

DESIGN

Eight NH volunteers participated in the study and listened to sentences embedded in background noise via headphones. Stimuli presented to the left ear were unprocessed. Stimuli presented to the right ear (referred to as the CI-simulation ear) were processed using an eight-channel noise vocoder with one of the three processing strategies. An Ideal strategy simulated a frequency-to-place map across all channels that matched the delivery of spectral information between the ears. A Realistic strategy created a misalignment in the mapping of frequency to place in the CI-simulation ear where the size of the mismatch between the ears varied across channels. Finally, a Shifted strategy imposed a similar degree of misalignment in all channels, resulting in consistent mismatch between the ears across frequency. The ability to report key words in sentences was assessed under monaural and binaural listening conditions and at signal to noise ratios (SNRs) established by estimating speech-reception thresholds in each ear alone. The SNRs ensured that the monaural performance of the left ear never exceeded that of the CI-simulation ear. The advantages of binaural integration were calculated by comparing binaural performance with monaural performance using the CI-simulation ear alone. Thus, these advantages reflected the additional use of the experimentally constrained left ear and were not attributable to better-ear listening.

RESULTS

Binaural performance was as accurate as, or more accurate than, monaural performance with the CI-simulation ear alone. When both ears supported a similar level of monaural performance (50%), binaural integration advantages were found regardless of whether a mismatch was simulated or not. When the CI-simulation ear supported a superior level of monaural performance (71%), evidence of binaural integration was absent when a mismatch was simulated using both the Realistic and the Ideal processing strategies. This absence of integration could not be accounted for by ceiling effects or by changes in SNR.

CONCLUSIONS

If generalizable to unilaterally deaf CI users, the results of the current simulation study would suggest that benefits to speech perception in noise can be obtained by integrating information from an implanted ear and an NH ear. A mismatch in the delivery of spectral information between the ears due to a misalignment in the mapping of frequency to place may disrupt binaural integration in situations where both ears cannot support a similar level of monaural speech understanding. Previous studies that have measured the speech perception of unilaterally deaf individuals after CI but with nonindividualized frequency-to-electrode allocations may therefore have underestimated the potential benefits of providing binaural hearing. However, it remains unclear whether the size and nature of the potential incremental benefits from individualized allocations are sufficient to justify the time and resources required to derive them based on cochlear imaging or pitch-matching tasks.

Perceived improvements and challenges following sequential bilateral cochlear implantation in children and adults

OBJECTIVE

Semi-structured interviews were conducted with sequentially implanted bilateral cochlear-implant (biCI) recipients to examine functional aspects of communication that are affected by listening with one versus two CIs.

DESIGN

Participants were 15 adult biCI recipients and parents of 30 children (categorized into three groups by age) with biCIs. All CI users had sequential placement of biCIs with at least six months' experience with the first CI before activation of the second device, and at least three months' experience with both CIs prior to the interview. The parent/paediatric and adult interviews were all conducted by the same examiner. Electronic transcripts of the interview responses were coded for perceived changes or lack thereof in 23 behaviours following biCI. Extent of reported benefit was quantified for each subject within and across these behaviours and at the group level as a function of age.

RESULTS

Most adults and parents of children reported multiple functional changes following biCI use, and changes often translated to enhanced social communication. Nearly all participants were consistent users of biCIs, and were satisfied with their perceived gains in communicating in everyday settings. Most reported ongoing challenges listening in noisy settings. Although many reports on children paralleled those of adults, developmental differences were apparent. Thirteen percent of adults and twenty percent of parents of children in each of the respective groups reported low levels of change.

CONCLUSIONS

Results suggest that many biCI users experience meaningful functional benefits that may be underestimated by traditional outcome measures. We suggest the need to expand measurement approaches to better quantify the nature of these benefits.

Improving Speech Recognition in Bilateral Cochlear Implant Users by Listening With the Better Ear

For patients with bilateral cochlear implants (BiCIs), understanding a target talker in a noisy situation can be difficult. Current efforts for improving speech-in-noise understanding have focused on improving signal-to-noise ratio by using multiple microphones or signal processing, with only moderate improvements in speech understanding performance. However, BiCI users typically report having a better ear for listening which can lead to an asymmetry in speech unmasking performance. This work proposes a novel listening strategy for improving speech-in-noise understanding by combining (a) a priori knowledge of a better ear and having a BiCI user selectively attend to a target talker in that ear with (b) signal processing that delivers the target talker to the better ear and the noisy background to the opposite ear. This strategy is different from traditional noise reduction strategies because it maintains situational awareness (background sounds are delivered to the ear contralateral to the better ear) while improving speech understanding. Speech recognition performance was evaluated with and without the better ear strategy in a speech-in-noise listening test using a virtual auditory space created from individualized head-related transfer functions. Listeners showed an average improvement of 4.4 dB signal-to-noise ratio in their speech reception threshold when using the better ear strategy with no listener showing a decrement in performance. This implies that the strategy has the potential to boost speech-in-noise recognition in BiCI users and may be useful in other hearing assistance devices such as hearing aids.

Determining the minimum number of electrodes that need to be pitch matched to accurately estimate pitch matches across the array

OBJECTIVE

With bilateral cochlear implant (CI) users there is typically a place mismatch between the locations stimulated by the left and right electrode arrays. This mismatch can affect performance, potentially limiting binaural benefits. One way to address this is by perceptually realigning the arrays such that a given frequency in the input stimulates perceptually matched locations in the two ears. A clinically feasible technique is needed that can determine the appropriate perceptual alignment. A pitch matching task can potentially be used for this, but only if it can be performed in a clinically feasible amount of time. The objective of this study was to determine the minimal number of electrodes that need to be pitch matched to accurately determine pitch matches across the entire array.

DESIGN

A retrospective analysis of pitch matching data was conducted. Subsets of pitch matches were selected and the predicted pitch matching across the array was compared to that predicted by the full dataset.

STUDY SAMPLE

16 bilateral CI users.

RESULTS

The results indicated that nine pitch matches are sufficient, which can typically be obtained in approximately 7 min.

CONCLUSION

The results reveal a clinically feasible method for determining pitch matches across the array.

United Kingdom national paediatric bilateral project: Demographics and results of localization and speech perception testing

OBJECTIVES

To assess longitudinal outcomes in a large and varied population of children receiving bilateral cochlear implants both simultaneously and sequentially.

METHODS

This observational non-randomized service evaluation collected localization and speech recognition in noise data from simultaneously and sequentially implanted children at four time points: before bilateral cochlear implants or before the sequential implant, 1 year, 2 years, and 3 years after bilateral implants. No inclusion criteria were applied, so children with additional difficulties, cochleovestibular anomalies, varying educational placements, 23 different home languages, a full range of outcomes and varying device use were included.

RESULTS

1001 children were included: 465 implanted simultaneously and 536 sequentially, representing just over 50% of children receiving bilateral implants in the UK in this period. In simultaneously implanted children the median age at implant was 2.1 years; 7% were implanted at less than 1 year of age. In sequentially implanted children the interval between implants ranged from 0.1 to 14.5 years. Children with simultaneous bilateral implants localized better than those with one implant. On average children receiving a second (sequential) cochlear implant showed improvement in localization and listening in background noise after 1 year of bilateral listening. The interval between sequential implants had no effect on localization improvement although a smaller interval gave more improvement in speech recognition in noise. Children with sequential implants on average were able to use their second device to obtain spatial release from masking after 2 years of bilateral listening. Although ranges were large, bilateral cochlear implants on average offered an improvement in localization and speech perception in noise over unilateral implants.

CONCLUSION

These data represent the diverse population of children with bilateral cochlear implants in the UK from 2010 to 2012. Predictions of outcomes for individual patients are not possible from these data. However, there are no indications to preclude children with long inter-implant interval having the chance of a second cochlear implant.

Head orientation benefit to speech intelligibility in noise for cochlear implant users and in realistic listening conditions

Cochlear implant (CI) users suffer from elevated speech-reception thresholds and may rely on lip reading. Traditional measures of spatial release from masking quantify speech-reception-threshold improvement with azimuthal separation of target speaker and interferers and with the listener facing the target speaker. Substantial benefits of orienting the head away from the target speaker were predicted by a model of spatial release from masking. Audio-only and audio-visual speech-reception thresholds in normal-hearing (NH) listeners and bilateral and unilateral CI users confirmed model predictions of this head-orientation benefit. The benefit ranged 2-5 dB for a modest 30° orientation that did not affect the lip-reading benefit. NH listeners' and CI users' lip-reading benefit measured 3 and 5 dB, respectively. A head-orientation benefit of ∼2 dB was also both predicted and observed in NH listeners in realistic simulations of a restaurant listening environment. Exploiting the benefit of head orientation is thus a robust hearing tactic that would benefit both NH listeners and CI users in noisy listening conditions.

Benefits of simultaneous bilateral cochlear implantation on verbal reasoning skills in prelingually deaf children

BACKGROUND

Impaired auditory speech perception abilities in deaf children with hearing aids compromised their verbal intelligence enormously. The availability of unilateral cochlear implantation (CI) auditory speech perception and spoken vocabulary enabled them to reach near ageappropriate levels. This holds especially for children in spoken language environments. However, speech perception in complex listening situations and the acquisition of complex verbal skills remains difficult. Bilateral CI was expected to enhance the acquisition of verbal intelligence by improved understanding of speech in noise.

METHODS

This study examined the effect of bilateral CI on verbal intelligence of 49 deaf children (3;5-8;0 years). Relations between speech perception in noise, auditory short-term memory and verbal intelligence were analysed with multiple linear regressions. In addition, the interaction of educational setting, mainstream or special, on these relations was analysed.

RESULTS

Children with bilateral CI obtained higher scores on verbal intelligence. Significant associations were present between speech perception in noise, auditory short-term memory and verbal intelligence.

CONCLUSION

Children with simultaneous bilateral CIs showed better speech perception in noise than children with unilateral CIs, which mediated by the auditory short-term memory capacity, enhanced the ability to acquire more complex verbal skills for BICI children in mainstream education.

Lateralization of interaural timing differences with multi-electrode stimulation in bilateral cochlear-implant users

Bilateral cochlear implant (BiCI) users have shown variability in interaural time difference (ITD) sensitivity at different places along the cochlea. This paper investigates perception of multi-electrode binaural stimulation to determine if auditory object formation (AOF) and lateralization are affected by variability in ITD sensitivity when a complex sound is encoded with multi-channel processing. AOF and ITD lateralization were compared between single- and multi-electrode configurations. Most (7/8) BiCI users perceived a single auditory object with multi-electrode stimulation, and the range of lateralization was comparable to single-electrode stimulation, suggesting that variability in single-electrode ITD sensitivity does not compromise AOF with multi-electrode stimulation.

Five-Year Hearing Outcomes in Bilateral Simultaneously Cochlear-Implanted Adult Patients

Objective: To report the speech performance and sound localization in adult patients 5 years after bilateral simultaneous cochlear implantation and to evaluate the change in speech scores between 1 and 5 years. Design: In this prospective multicenter study, 26 patients were evaluated 5 years after implantation using long straight electrode arrays (MED-EL Combi 40+, standard electrode array, 31 mm). Speech perception was measured using disyllabic words in quiet and noise, with the speech coming from the front and a cocktail party background noise coming from 5 loudspeakers. Speech localization measurements were performed in noise under the same test conditions. These results were compared to those obtained at 1 year reported in a previous study. Results: Five years after implantation, an improvement in speech performance scores compared to 1 year after implantation was found for the poorer ear both in quiet and in noise (+12.1 ± 2.6%, p < 0.001). The lower the speech score of the poorer ear at 1 year, the greater the improvement at 5 years, both in quiet (r = -0.62) and at a signal-to-noise ratio of +15 dB (r = -0.58). The sound localization on the horizontal plane in noise provided by bilateral implantation was better than the unilateral one and remained stable after the results observed at 1 year. Conclusion: In adult patients simultaneously and bilaterally implanted, the poorest speech scores improved between 1 and 5 years after implantation. These findings are an additional element to recommend bilateral implantation in adult patients. The use of both cochlear implants and speech training sessions for patients with poor performance should continue in the period after 1 year following implantation, since the speech scores will improve over time.

Modeling the Test-Retest Statistics of a Localization Experiment in the Full Horizontal Plane

HYPOTHESIS

Two approaches to model the test-retest statistics of a localization experiment basing on Gaussian distribution and on surrogate data are introduced. Their efficiency is investigated using different measures describing directional hearing ability.

BACKGROUND

A localization experiment in the full horizontal plane is a challenging task for hearing impaired patients. In clinical routine, we use this experiment to evaluate the progress of our cochlear implant (CI) recipients. Listening and time effort limit the reproducibility.

METHODS

The localization experiment consists of a 12 loudspeaker circle, placed in an anechoic room, a "camera silens". In darkness, HSM sentences are presented at 65 dB pseudo-erratically from all 12 directions with five repetitions. This experiment is modeled by a set of Gaussian distributions with different standard deviations added to a perfect estimator, as well as by surrogate data. Five repetitions per direction are used to produce surrogate data distributions for the sensation directions. To investigate the statistics, we retrospectively use the data of 33 CI patients with 92 pairs of test-retest-measurements from the same day.

RESULTS

The first model does not take inversions into account, (i.e., permutations of the direction from back to front and vice versa are not considered), although they are common for hearing impaired persons particularly in the rear hemisphere. The second model considers these inversions but does not work with all measures.

CONCLUSION

The introduced models successfully describe test-retest statistics of directional hearing. However, since their applications on the investigated measures perform differently no general recommendation can be provided. The presented test-retest statistics enable pair test comparisons for localization experiments.

A metric for predicting binaural speech intelligibility in stationary noise and competing speech maskers

One criterion in the design of binaural sound scenes in audio production is the extent to which the intended speech message is correctly understood. Object-based audio broadcasting systems have permitted sound editors to gain more access to the metadata (e.g., intensity and location) of each sound source, providing better control over speech intelligibility. The current study describes and evaluates a binaural distortion-weighted glimpse proportion metric-BiDWGP-which is motivated by better-ear glimpsing and binaural masking level differences. BiDWGP predicts intelligibility from two alternative input forms: either binaural recordings or monophonic recordings from each sound source along with their locations. Two listening experiments were performed with stationary noise and competing speech, one in the presence of a single masker, the other with multiple maskers, for a variety of spatial configurations. Overall, BiDWGP with both input forms predicts listener keyword scores with correlations of 0.95 and 0.91 for single- and multi-masker conditions, respectively. When considering masker type separately, correlations rise to 0.95 and above for both types of maskers. Predictions using the two input forms are very similar, suggesting that BiDWGP can be applied to the design of sound scenes where only individual sound sources and their locations are available.

Binaural release from masking with single- and multi-electrode stimulation in children with cochlear implants

Cochlear implants (CIs) provide children with access to speech information from a young age. Despite bilateral cochlear implantation becoming common, use of spatial cues in free field is smaller than in normal-hearing children. Clinically fit CIs are not synchronized across the ears; thus binaural experiments must utilize research processors that can control binaural cues with precision. Research to date has used single pairs of electrodes, which is insufficient for representing speech. Little is known about how children with bilateral CIs process binaural information with multi-electrode stimulation. Toward the goal of improving binaural unmasking of speech, this study evaluated binaural unmasking with multi- and single-electrode stimulation. Results showed that performance with multi-electrode stimulation was similar to the best performance with single-electrode stimulation. This was similar to the pattern of performance shown by normal-hearing adults when presented an acoustic CI simulation. Diotic and dichotic signal detection thresholds of the children with CIs were similar to those of normal-hearing children listening to a CI simulation. The magnitude of binaural unmasking was not related to whether the children with CIs had good interaural time difference sensitivity. Results support the potential for benefits from binaural hearing and speech unmasking in children with bilateral CIs.

Bilateral Loudness Balancing and Distorted Spatial Perception in Recipients of Bilateral Cochlear Implants

OBJECTIVE

To determine whether bilateral loudness balancing during mapping of bilateral cochlear implants (CIs) produces fused, punctate, and centered auditory images that facilitate lateralization with stimulation on single-electrode pairs.

DESIGN

Adopting procedures similar to those that are practiced clinically, direct stimulation was used to obtain most-comfortable levels (C levels) in recipients of bilateral CIs. Three pairs of electrodes, located in the base, middle, and apex of the electrode array, were tested. These electrode pairs were loudness-balanced by playing right-left electrode pairs sequentially. In experiment 1, the authors measured the location, number, and compactness of auditory images in 11 participants in a subjective fusion experiment. In experiment 2, the authors measured the location and number of the auditory images while imposing a range of interaural level differences (ILDs) in 13 participants in a lateralization experiment. Six of these participants repeated the mapping process and lateralization experiment over three separate days to determine the variability in the procedure.

RESULTS

In approximately 80% of instances, bilateral loudness balancing was achieved from relatively small adjustments to the C levels (≤3 clinical current units). More important, however, was the observation that in 4 of 11 participants, simultaneous bilateral stimulation regularly elicited percepts that were not fused into a single auditory object. Across all participants, approximately 23% of percepts were not perceived as fused; this contrasts with the 1 to 2% incidence of diplacusis observed with normal-hearing individuals. In addition to the unfused images, the perceived location was often offset from the physical ILD. On the whole, only 45% of percepts presented with an ILD of 0 clinical current units were perceived as fused and heard in the center of the head. Taken together, these results suggest that distortions to the spatial map remain common in bilateral CI recipients even after careful bilateral loudness balancing.

CONCLUSIONS

The primary conclusion from these experiments is that, even after bilateral loudness balancing, bilateral CI recipients still regularly perceive stimuli that are unfused, offset from the assumed zero ILD, or both. Thus, while current clinical mapping procedures for bilateral CIs are sufficient to enable many of the benefits of bilateral hearing, they may not elicit percepts that are thought to be optimal for sound-source location. As a result, in the absence of new developments in signal processing for CIs, new mapping procedures may need to be developed for bilateral CI recipients to maximize the benefits of bilateral hearing.

Developing an assessment approach for perceptual changes to tinnitus sound characteristics for adult cochlear implant recipients

OBJECTIVE

To investigate the impact of cochlear implantation on tinnitus suppression, characteristics, localization, and duration.

DESIGN

A cochlear implant (CI) recipient-focused postal questionnaire survey.

STUDY SAMPLE

The questionnaire was posted, with consent, to 100 adults who had received a unilateral CI at the RNTNEH between 1988 and 1999. All adults spoke English as their first language and were postlingually deafened. Sixty-eight adults (38 female, 29 male, one unspecified) aged 31-80 years (mean 61 years) completed and returned the questionnaire without interview.

RESULTS

With the processor 'ON', CI recipients experienced total or partial suppression of tinnitus ipsilateral to their CI in 57% of cases, and in 43% where tinnitus was perceived contralateral to the CI. The percentage of CI recipients who experienced high tone tinnitus was reduced from 60% pre-implant to 29% post-implant with the processor 'ON' while pulsatile tinnitus was reduced from 38% pre-implant to 13% post-implant. CIs were also found to reduce the tonal complexity and duration, and change the source localization of tinnitus post-implantation.

CONCLUSIONS

Perceptual changes to tinnitus can take place post-implantation. Changes can occur within the four categories explored: tinnitus suppression, characteristics, localization, and duration of awareness per day.

A Retrospective Multicenter Study Comparing Speech Perception Outcomes for Bilateral Implantation and Bimodal Rehabilitation

OBJECTIVES

To compare speech perception outcomes between bilateral implantation (cochlear implants [CIs]) and bimodal rehabilitation (one CI on one side plus one hearing aid [HA] on the other side) and to explore the clinical factors that may cause asymmetric performances in speech intelligibility between the two ears in case of bilateral implantation.

DESIGN

Retrospective data from 2247 patients implanted since 2003 in 15 international centers were collected. Intelligibility scores, measured in quiet and in noise, were converted into percentile ranks to remove differences between centers. The influence of the listening mode among three independent groups, one CI alone (n = 1572), bimodal listening (CI/HA, n = 589), and bilateral CIs (CI/CI, n = 86), was compared in an analysis taking into account the influence of other factors such as duration of profound hearing loss, age, etiology, and duration of CI experience. No within-subject comparison (i.e., monitoring outcome modifications in CI/HA subjects becoming CI/CI) was possible from this dataset. Further analyses were conducted on the CI/CI subgroup to investigate a number of factors, such as implantation side, duration of hearing loss, amount of residual hearing, and use of HAs that may explain asymmetric performances of this subgroup.

RESULTS

Intelligibility ranked scores in quiet and in noise were significantly greater with both CI/CI and CI/HA than with a CI-alone group, and improvement with CI/CI (+11% and +16% in quiet and in noise, respectively) was significantly better than with CI/HA (+6% and +9% in quiet and in noise, respectively). From the CI/HA group, only subjects with ranked preoperative aided speech scores >60% performed as well as CI/CI participants. Furthermore, CI/CI subjects displayed significantly lower preoperative aided speech scores on average compared with that displayed by CI/HA subjects. Routine clinical data available from the present database did not explain the asymmetrical results of bilateral implantation.

CONCLUSIONS

This retrospective study, based on basic speech audiometry (no lateralization cues), indicates that, on average, a second CI is likely to provide slightly better postoperative speech outcome than an additional HA for people with very low preoperative performance. These results may be taken into consideration to refine surgical indications for CIs.

Analysis of electrically evoked compound action potential of the auditory nerve in children with bilateral cochlear implants

Introduction

The cochlear implant device has the capacity to measure the electrically evoked compound action potential of the auditory nerve. The neural response telemetry is used in order to measure the electrically evoked compound action potential of the auditory nerve.

Objective

To analyze the electrically evoked compound action potential, through the neural response telemetry, in children with bilateral cochlear implants.

Methods

This is an analytical, prospective, longitudinal, historical cohort study. Six children, aged 1–4 years, with bilateral cochlear implant were assessed at five different intervals during their first year of cochlear implant use.

Results

There were significant differences in follow-up time (p = 0.0082) and electrode position (p = 0.0019) in the T-NRT measure. There was a significant difference in the interaction between time of follow-up and electrode position (p = 0.0143) when measuring the N1-P1 wave amplitude between the three electrodes at each time of follow-up.

Conclusion

The electrically evoked compound action potential measurement using neural response telemetry in children with bilateral cochlear implants during the first year of follow-up was effective in demonstrating the synchronized bilateral development of the peripheral auditory pathways in the studied population.

Scanning for Digital Content

The widespread availability of digital media has changed the way that people consume information and has impacted the consumption of auditory information. Despite this recent popularity among sighted people, the use of auditory feedback to access digital information is not new for visually impaired users. However, its sequential nature undermines both blind and sighted people’s ability to efficiently find relevant information in the midst of several potentially useful items. We propose taking advantage of the Cocktail Party Effect , which states that people are able to focus on a single speech source among several conversations, but still identify relevant content in the background. Therefore, in contrast to one sequential speech channel, we hypothesize that people can leverage concurrent speech channels to quickly get the gist of digital information. In this article, we present an experiment with 46 (23 blind, 23 sighted) participants, which aims to understand people’s ability to search for relevant content listening to two, three, or four concurrent speech channels. Our results suggest that both blind and sighted people are able to process concurrent speech in scanning scenarios. In particular, the use of two concurrent sources may be used both to identify and understand the content of the relevant sentence. Moreover, three sources may be used for most people depending on the task intelligibility demands and user characteristics. Contrasting with related work, the use of different voices did not affect the perception of concurrent speech but was highly preferred by participants. To complement the analysis, we propose a set of scenarios that may benefit from the use of concurrent speech sources, for both blind and sighted people, toward a Design for All paradigm.

Monaural Congenital Deafness Affects Aural Dominance and Degrades Binaural Processing

Cortical development extensively depends on sensory experience. Effects of congenital monaural and binaural deafness on cortical aural dominance and representation of binaural cues were investigated in the present study. We used an animal model that precisely mimics the clinical scenario of unilateral cochlear implantation in an individual with single-sided congenital deafness. Multiunit responses in cortical field A1 to cochlear implant stimulation were studied in normal-hearing cats, bilaterally congenitally deaf cats (CDCs), and unilaterally deaf cats (uCDCs). Binaural deafness reduced cortical responsiveness and decreased response thresholds and dynamic range. In contrast to CDCs, in uCDCs, cortical responsiveness was not reduced, but hemispheric-specific reorganization of aural dominance and binaural interactions were observed. Deafness led to a substantial drop in binaural facilitation in CDCs and uCDCs, demonstrating the inevitable role of experience for a binaural benefit. Sensitivity to interaural time differences was more reduced in uCDCs than in CDCs, particularly at the hemisphere ipsilateral to the hearing ear. Compared with binaural deafness, unilateral hearing prevented nonspecific reduction in cortical responsiveness, but extensively reorganized aural dominance and binaural responses. The deaf ear remained coupled with the cortex in uCDCs, demonstrating a significant difference to deprivation amblyopia in the visual system.

Binaural integration abilities in bilateral cochlear implant user

Bilateral Cochlear implants (CIs) improved speech intelligibility, speech perception in background noise, and sound localization in quiet and noisy situations. However, it is unclear whether these advantages essentially result in binaural integration of acoustic stimuli from each ear. In this study, we investigated the effectiveness of binaural integration by bilateral CIs placement using binaural hearing tests and subjective auditory perceptual assessment. A 61-year-old bilateral CIs subject underwent the following four tests: the Japanese Hearing in Noise Test (HINT-J), the dichotic listening test (DLT), the Rapidly Alternating Speech Perception (RASP) test, and subjective auditory perceptual assessment. The HINT-J score was significantly higher for bilateral CIs than for a unilateral CI. However, DLT and the RASP test revealed contradictory results. Subjective auditory perceptual assessment revealed active and bright impressions for bilateral hearing, which were also noisy and strong compared with those for unilateral hearing. The results of this study revealed that bilateral CIs improved speech perception in background noise and an improved auditory impression, although the bilateral integration abilities were not improved. This was probably because the patient was required to combine information from the two ears into a single perception in DLT and the RASP test. More longitudinal data should be collected and analyzed in future studies to evaluate the long-term effects of bilateral CIs.

Effect of multi-electrode configuration on sensitivity to interaural timing differences in bilateral cochlear-implant users

Recent psychophysical studies in bilateral cochlear implant users have shown that interaural timing difference (ITD) sensitivity with electrical stimulation varies depending on the place of stimulation along the cochlear array. While these studies have measured ITD sensitivity at single electrode places separately, it is important to understand how ITD sensitivity is affected when multiple electrodes are stimulated together because multi-electrode stimulation is required for representation of complex sounds. Multi-electrode stimulation may lead to poorer overall performance due to interference from places with poor ITD sensitivity, or from channel interaction due to electrical current spread. Alternatively, multi-electrode stimulation might result in overall good sensitivity if listeners can extract the most reliable ITD cues available. ITD just noticeable differences (JNDs) were measured for different multi-electrode configurations. Results showed that multi-electrode ITD JNDs were poorer than ITD JNDs for the best single-electrode pair. However, presenting ITD information along the whole array appeared to produce better sensitivity compared with restricting stimulation to the ends of the array, where ITD JNDs were comparable to the poorest single-electrode pair. These findings suggest that presenting ITDs in one cochlear region only may not be optimal for maximizing ITD sensitivity in multi-electrode stimulation.

Precedence based speech segregation in bilateral cochlear implant users

The precedence effect (PE) enables the perceptual dominance by a source (lead) over an echo (lag) in reverberant environments. In addition to facilitating sound localization, the PE can play an important role in spatial unmasking of speech. Listeners attending to binaural vocoder simulations with identical channel center frequencies and phase demonstrated PE-based benefits in a closed-set speech segregation task. When presented with the same stimuli, bilateral cochlear implant users did not derive such benefits. These findings suggest that envelope extraction in itself may not lead to a breakdown of the PE benefits, and that other factors may play a role.

Auditory Model-Based Sound Direction Estimation With Bilateral Cochlear Implants

Users of bilateral cochlear implants (CIs) show above-chance performance in localizing the source of a sound in the azimuthal (horizontal) plane; although localization errors are far worse than for normal-hearing listeners, they are considerably better than for CI listeners with only one implant. In most previous studies, subjects had access to interaural level differences and to interaural time differences conveyed in the temporal envelope. Here, we present a binaural model that predicts the azimuthal direction of sound arrival from a two-channel input signal as it is received at the left and right CI processor. The model includes a replication of a clinical speech-coding strategy, a model of the electrode-nerve interface and binaural brainstem neurons, and three different prediction stages that are trained to map the neural response rate to an azimuthal angle. The model is trained and tested with various noise and speech stimuli created by means of virtual acoustics. Localization error patterns of the model match experimental data and are explicable largely in terms of the nonmonotonic relationship between interaural level difference and azimuthal angle.

Comparison of Interaural Electrode Pairing Methods for Bilateral Cochlear Implants

In patients with bilateral cochlear implants (CIs), pairing matched interaural electrodes and stimulating them with the same frequency band is expected to facilitate binaural functions such as binaural fusion, localization, and spatial release from masking. Because clinical procedures typically do not include patient-specific interaural electrode pairing, it remains the case that each electrode is allocated to a generic frequency range, based simply on the electrode number. Two psychoacoustic techniques for determining interaurally paired electrodes have been demonstrated in several studies: interaural pitch comparison and interaural time difference (ITD) sensitivity. However, these two methods are rarely, if ever, compared directly. A third, more objective method is to assess the amplitude of the binaural interaction component (BIC) derived from electrically evoked auditory brainstem responses for different electrode pairings; a method has been demonstrated to be a potential candidate for bilateral CI users. Here, we tested all three measures in the same eight CI users. We found good correspondence between the electrode pair producing the largest BIC and the electrode pair producing the maximum ITD sensitivity. The correspondence between the pairs producing the largest BIC and the pitch-matched electrode pairs was considerably weaker, supporting the previously proposed hypothesis that whilst place pitch might adapt over time to accommodate mismatched inputs, sensitivity to ITDs does not adapt to the same degree.

Melodic Contour Training and Its Effect on Speech in Noise, Consonant Discrimination, and Prosody Perception for Cochlear Implant Recipients

Cochlear implant (CI) recipients generally have good perception of speech in quiet environments but difficulty perceiving speech in noisy conditions, reduced sensitivity to speech prosody, and difficulty appreciating music. Auditory training has been proposed as a method of improving speech perception for CI recipients, and recent efforts have focussed on the potential benefits of music-based training. This study evaluated two melodic contour training programs and their relative efficacy as measured on a number of speech perception tasks. These melodic contours were simple 5-note sequences formed into 9 contour patterns, such as "rising" or "rising-falling." One training program controlled difficulty by manipulating interval sizes, the other by note durations. Sixteen adult CI recipients (aged 26-86 years) and twelve normal hearing (NH) adult listeners (aged 21-42 years) were tested on a speech perception battery at baseline and then after 6 weeks of melodic contour training. Results indicated that there were some benefits for speech perception tasks for CI recipients after melodic contour training. Specifically, consonant perception in quiet and question/statement prosody was improved. In comparison, NH listeners performed at ceiling for these tasks. There was no significant difference between the posttraining results for either training program, suggesting that both conferred benefits for training CI recipients to better perceive speech.

Investigating long-term effects of cochlear implantation in single-sided deafness: a best practice model for longitudinal assessment of spatial hearing abilities and tinnitus handicap

OBJECTIVES

To evaluate methods for measuring long-term benefits of cochlear implantation in a patient with single-sided deafness (SSD) with respect to spatial hearing and to document improved quality of life because of reduced tinnitus.

PATIENT

A single adult male with profound right-sided sensorineural hearing loss and normal hearing in the left ear who underwent right-sided cochlear implantation.

METHODS

The subject was evaluated at 6, 9, 12, and 18 months after implantation on speech intelligibility with specific target-masker configurations, sound localization accuracy, audiologic performance, and tinnitus handicap. Testing conditions involved the acoustic (NH) ear only, the cochlear implant (CI) ear (acoustic ear plugged), and the bilateral condition (CI+NH). Measures of spatial hearing included speech intelligibility improvement because of spatial release from masking (SRM) and sound localization. In addition, traditional measures known as "head shadow," "binaural squelch," and "binaural summation" were evaluated.

RESULTS

The best indicator for improved speech intelligibility was SRM, in which both ears are activated, but the relative locations of target and masker(s) are manipulated. Measures that compare performance with a single ear to performance using bilateral auditory input indicated evidence of the ability to integrate inputs across the ears, possibly reflecting early binaural processing, with 12 months of bilateral input. Sound localization accuracy improved with addition of the implant, and a large improvement with respect to tinnitus handicap was observed.

CONCLUSION

Cochlear implantation resulted in improved sound localization accuracy when compared with performance using only the NH ear, and reduced tinnitus handicap was observed with use of the implant. The use of SRM addresses some of the current limitations of traditional measures of spatial and binaural hearing, as spatial cues related to target and maskers are manipulated, rather than the ear(s) tested. Sound testing methods and calculations described here are therefore recommended for assessing performance of a larger sample size of individuals with SSD who receive a CI.

The history of Cochlear™ Nucleus® sound processor upgrades: 30 years and counting

To review developments in sound processors over the past 30 years that have resulted in significant improvements in outcomes for Nucleus^® recipients.