Binaural Advantage Research Articles

Bone-Conduction Hearing Aids

Bone-Conduction Hearing Aids

Individual Differences in Behavioral and Electrophysiological Measures of Binaural Processing Across the Adult Life Span.

The purpose of the present study was to examine individual differences in binaural processing across the adult life span. Sixty listeners (aged 23-80 years) with symmetrical hearing were tested. Binaural behavioral processing was measured by the Words-in-Noise Test, the 500-Hz masking level difference, and the Dichotic Digit Test. Electrophysiologic responses were assessed by the auditory middle latency response binaural interaction component. No correlations among binaural measures were found. Age accounted for the greatest amount of variability in speech-in-noise performance. Age was significantly correlated with the Words-in-Noise Test binaural advantage and dichotic ear advantage. Partial correlations, however, revealed that this was an effect of hearing status rather than age per se. Inspection of individual results revealed that 20% of listeners demonstrated reduced binaural performance for at least 2 of the binaural measures. The lack of significant correlations among variables suggests that each is an important measurement of binaural abilities. For some listeners, binaural processing was abnormal, reflecting a binaural processing deficit not identified by monaural audiologic tests. The inclusion of a binaural test battery in the audiologic evaluation is supported given that these listeners may benefit from alternative forms of audiologic rehabilitation.

Binaural Masking Release in Children With Down Syndrome

Binaural hearing results in a number of listening advantages relative to monaural hearing, including enhanced hearing sensitivity and better speech understanding in adverse listening conditions. These advantages are facilitated in part by the ability to detect and use interaural cues within the central auditory system. Binaural hearing for children with Down syndrome could be impacted by multiple factors including, structural anomalies within the peripheral and central auditory system, alterations in synaptic communication, and chronic otitis media with effusion. However, binaural hearing capabilities have not been investigated in these children. This study tested the hypothesis that children with Down syndrome experience less binaural benefit than typically developing peers. Participants included children with Down syndrome aged 6 to 16 years (n = 11), typically developing children aged 3 to 12 years (n = 46), adults with Down syndrome (n = 3), and adults with no known neurological delays (n = 6). Inclusionary criteria included normal to near-normal hearing sensitivity. Two tasks were used to assess binaural ability. Masking level difference (MLD) was calculated by comparing threshold for a 500-Hz pure-tone signal in 300-Hz wide Gaussian noise for N0S0 and N0Sπ signal configurations. Binaural intelligibility level difference was calculated using simulated free-field conditions. Speech recognition threshold was measured for closed-set spondees presented from 0-degree azimuth in speech-shaped noise presented from 0-, 45- and 90-degree azimuth, respectively. The developmental ability of children with Down syndrome was estimated and information regarding history of otitis media was obtained for all child participants via parent survey. Individuals with Down syndrome had higher masked thresholds for pure-tone and speech stimuli than typically developing individuals. Children with Down syndrome had significantly smaller MLDs than typically developing children. Adults with Down syndrome and control adults had similar MLDs. Similarities in simulated spatial release from masking were observed for all groups for the experimental parameters used in this study. No association was observed for any measure of binaural ability and developmental age for children with Down syndrome. Similar group psychometric functions were observed for children with Down syndrome and typically developing children in most instances, suggesting that attentiveness and motivation contributed equally to performance for both groups on most tasks. The binaural advantages afforded to typically developing children, such as enhanced hearing sensitivity in noise, were not as robust for children with Down syndrome in this study. Children with Down syndrome experienced less binaural benefit than typically developing peers for some stimuli, suggesting that they could require more favorable signal-to-noise ratios to achieve optimal performance in some adverse listening conditions. The reduced release from masking observed for children with Down syndrome could represent a delay in ability rather than a deficit that persists into adulthood. This could have implications for the planning of interventions for individuals with Down syndrome.

Erratum: Binaural advantages in users of bimodal and bilateral cochlear implant devices [J. Acoust. Soc. Am. 135, EL47–EL53 (2014)

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Towards a unifying basis of auditory thresholds: binaural summation.

Absolute auditory threshold decreases with increasing sound duration, a phenomenon explainable by the assumptions that the sound evokes neural events whose probabilities of occurrence are proportional to the sound's amplitude raised to an exponent of about 3 and that a constant number of events are required for threshold (Heil and Neubauer, Proc Natl Acad Sci USA 100:6151-6156, 2003). Based on this probabilistic model and on the assumption of perfect binaural summation, an equation is derived here that provides an explicit expression of the binaural threshold as a function of the two monaural thresholds, irrespective of whether they are equal or unequal, and of the exponent in the model. For exponents >0, the predicted binaural advantage is largest when the two monaural thresholds are equal and decreases towards zero as the monaural threshold difference increases. This equation is tested and the exponent derived by comparing binaural thresholds with those predicted on the basis of the two monaural thresholds for different values of the exponent. The thresholds, measured in a large sample of human subjects with equal and unequal monaural thresholds and for stimuli with different temporal envelopes, are compatible only with an exponent close to 3. An exponent of 3 predicts a binaural advantage of 2 dB when the two ears are equally sensitive. Thus, listening with two (equally sensitive) ears rather than one has the same effect on absolute threshold as doubling duration. The data suggest that perfect binaural summation occurs at threshold and that peripheral neural signals are governed by an exponent close to 3. They might also shed new light on mechanisms underlying binaural summation of loudness.

Advantages of binaural amplification to acceptable noise level of directional hearing aid users.

ObjectivesThe goal of the present study was to examine whether Acceptable Noise Levels (ANLs) would be lower (greater acceptance of noise) in binaural listening than in monaural listening condition and also whether meaningfulness of background speech noise would affect ANLs for directional microphone hearing aid users. In addition, any relationships between the individual binaural benefits on ANLs and the individuals' demographic information were investigated.MethodsFourteen hearing aid users (mean age, 64 years) participated for experimental testing. For the ANL calculation, listeners' most comfortable listening levels and background noise level were measured. Using Korean ANL material, ANLs of all participants were evaluated under monaural and binaural amplification with a counterbalanced order. The ANLs were also compared across five types of competing speech noises, consisting of 1- through 8-talker background speech maskers. Seven young normal-hearing listeners (mean age, 27 years) participated for the same measurements as a pilot testing.ResultsThe results demonstrated that directional hearing aid users accepted more noise (lower ANLs) with binaural amplification than with monaural amplification, regardless of the type of competing speech. When the background speech noise became more meaningful, hearing-impaired listeners accepted less amount of noise (higher ANLs), revealing that ANL is dependent on the intelligibility of the competing speech. The individuals' binaural advantages in ANLs were significantly greater for the listeners with longer experience of hearing aids, yet not related to their age or hearing thresholds.ConclusionBinaural directional microphone processing allowed hearing aid users to accept a greater amount of background noise, which may in turn improve listeners' hearing aid success. Informational masking substantially influenced background noise acceptance. Given a significant association between ANLs and duration of hearing aid usage, ANL measurement can be useful for clinical counseling of binaural hearing aid candidates or unsuccessful users.

Binaural advantages in users of bimodal and bilateral cochlear implant devices

This paper investigates to what extent users of bilateral and bimodal fittings should expect to benefit from all three different binaural advantages found to be present in normal-hearing listeners. Head-shadow and binaural squelch are advantages occurring under spatially separated speech and noise, while summation emerges when speech and noise coincide in space. For 14 bilateral or bimodal listeners, speech reception thresholds in the presence of four-talker babble were measured in sound-field under various speech and noise configurations. Statistical analysis revealed significant advantages of head-shadow and summation for both bilateral and bimodal listeners. Squelch was significant only for bimodal listeners.

Binaural speech recognition in continuous and intermittent noises in people with hearing loss

Multiple tests have been developed to quantify speech recognition in noise, but the characteristics of the masking noise vary significantly across tests and can considerably impact performance and clinical interpretation. Using the HINT, speech perception in 24 young adults with normal hearing was assessed using both the standard masker (a continuous speech-spectrum noise) and an intermittent version of the masker at an ON-OFF rate of 16 Hz. Intermittency helps in extracting speech from the “quiet” segments of the noise. Speech recognition thresholds for frontal speech were better in the intermittent than the continuous noise by an amount of 13 and 10 dB for noise maskers located in front or side, respectively, The average difference in thresholds between the noise front and side conditions, called the binaural advantage, was 4.7 and 8.4 dB for the intermittent and continuous noises, respectively. Data collected with people presenting different hearing loss profiles also show binaural and intermittency advantages, but to a lesser degree. Considering that people encounter a wide a range of fluctuating noises in daily life, these results motivate adding an intermittent noise condition to the HINT protocol to better reflect the challenges faced by individuals with hearing loss.

Contralateral Suppression of Transient Otoacoustic Emissions and Sentence Recognition in Noise in Young Adults

One purported role of the medial olivocochlear (MOC) efferent system is to reduce the effects of masking noise. MOC system functioning can be evaluated noninvasively in humans through contralateral suppression of otoacoustic emissions. It has been suggested that the strength of the MOC efferent activity should be positively associated with listening performance in noise. The objective of the study was to further explore this notion by examining contralateral suppression of transient evoked otoacoustic emissions (TEOAEs) and sentence recognition in two noises with normal hearing young adults. A repeated measures multivariate quasi-experimental design was employed. Thirty-two normal hearing young adult females participated. Reception thresholds for sentences (RTSs) were determined monaurally and binaurally in quiet and in competing continuous and interrupted noises. Both noises had an identical power spectrum and differed only in their temporal continuity. "Release from masking" was computed by subtracting RTS signal-to-noise ratios in interrupted from continuous noise. TEOAEs were evoked with 80 dB peSPL click stimuli. To examine contralateral suppression, TEOAEs were evaluated with 60 dB peSPL click stimuli with and without a contralateral 65 dB SPL white noise suppressor. A binaural advantage was observed for RTSs in quiet and noise (p < .0001) while there was no difference between ears (p >.05). In noise, performance was superior in the interrupted noise (i.e., RTSs were lower vs. continuous noise; p < .0001). There were no statistically significant differences in TEOAE levels between ears (p >.05). There was also no significant difference in the amount of suppression between ears (p = .41). There were no significant correlations or predictive linear relations between the amount of TEOAE suppression and any indices of sentence recognition in noise (i.e., RTS signal-to-noise ratios and release from masking; p > .05). The findings are not consistent with the notion that increased medial olivocochlear efferent feedback, as assessed via contralateral suppression of TEOAEs, is associated with improved speech perception in continuous and interrupted noise.

A systematic review of the effectiveness and cost‐effectiveness of bilateral multichannel cochlear implants in adults with severe‐to‐profound hearing loss

In the UK, approximately 10 000 people have cochlear implants, more than 99% with a unilateral implant. Evidence shows that adults implanted bilaterally may benefit from binaural advantages; however, systematic review evidence is limited. To conduct a systematic review to discover the evidence for effectiveness and cost-effectiveness of using bilateral cochlear implants in adults with severe-to-profound hearing loss by comparing their effectiveness with unilateral cochlear implantation or unilateral cochlear implantation and acoustic hearing aid in the contralateral ear. Systematic review. This examined 16 electronic databases, plus bibliographies and references for published and unpublished studies. Abstracts were independently assessed against inclusion criteria by two researchers, and disagreements were resolved. Selected papers were then retrieved and further independently assessed in a similar way. Included studies had their data extracted by one reviewer and checked by another. Searches yielded 2892 abstracts producing 19 includable studies. Heterogeneity between studies precluded meta-analysis. However, all studies reported that bilateral cochlear implants improved hearing and speech perception: one randomised controlled trial found a significant binaural benefit over the first ear alone for speech and noise from the front (12.6 ± 5.4%, P < 0.001) and when noise was ipsilateral to the first ear (21 ± 6%, P < 0.001); and another found a significant benefit for spatial hearing at 3 and 9 months post-implantation compared with pre-implantation [mean difference (sd) scores: 3 months = 1.46 (0.83-2.09), P < 0.01].Quality of life results varied, showing bilateral implantation may improve quality of life in the absence of worsening tinnitus. Limited cost-effectiveness evidence showed that bilateral implantation is probably only cost-effective at a willingness-to-pay threshold above £62 000 per quality adjusted life year. Despite inconsistency in the quality of available evidence, the robustness of systematic review methods gives weight to the positive findings of included studies demonstrating that bilateral implantation is clinically effective in adults but unlikely to be cost-effective.

Cochlear Implant Combined with a Linear Frequency Transposing Hearing Aid

Adults with cochlear implants (CIs) are usually implanted unilaterally. To preserve binaural advantages, a noninvasive method involves maintaining the hearing aid (HA) on the contralateral ear; the choice of HA for this purpose is therefore crucial. In recent years, the use of frequency transposition has gained a renewed interest in clinical practice. This type of processing records information from the high-frequency region and conveys it to a low-frequency region where there is still some residual hearing. To conduct an investigation and examine whether adults with unilateral CI derive benefits from a HA utilizing linear frequency transposition (LFT) on the contralateral ear. A two-period, single-blind, repeated-measures crossover design was conducted to examine the combination of LFT in conjunction with a CI. Speech recognition tests were performed in quiet and in noise with LFT either activated or deactivated. The Speech, Spatial and Qualities of Hearing Questionnaire (SSQ) was used to measure subjective benefit. The participants were nine frequent bimodal users, five males and four females, with a moderate to profound high-frequency sensorineural hearing loss in the nonimplanted ear. The current study was conducted using the Widex Mind440 power (m4-19) behind-the-ear HA. The participants acted as their own control in a total of seven conditions: (1) bimodal with own HA, (2) CI only, (3) own HA alone, (4) bimodal new HA LFT-off, (5) new HA LFT-off, (6) bimodal new HA LFT-on, and (7) new HA LFT-on. Monosyllabic words in quiet and the Swedish version of Hearing in Noise Test (HINT) were used as speech test materials. Stimuli were presented in sound field at a speech level of 65 dB sound pressure level (SPL) via a loudspeaker at a distance of 1 m from the participant in a sound-treated room. The SSQ was administered in each session evaluating the three bimodal conditions. SPSS software was used for statistical analyses. General linear model (GLM) analysis of variance for repeated measures was performed and followed with Bonferroni-adjusted post hoc pairwise comparisons. Participants performed better with CI only than with HA alone, and the bimodal conditions were superior to the CI alone. No significant differences (p > .05) were observed when comparing the LFT-on with LFT-off regardless of whether the use of CI was included in the different listening conditions in objective and subjective measurements. The results suggest an advantage for CI patients with a HA in the opposite ear, and that the LFT neither degraded nor enhanced speech performance in conjunction with a CI in quiet or in noise in comparison to when it was deactivated.

Effects of reverberation and masker fluctuations on binaural unmasking of speech

In daily life, listeners use two ears to understand speech in situations which typically include reverberation and non-stationary noise. In headphone experiments, the binaural benefit for speech in noise is often expressed as the difference in speech reception threshold between diotic (N(0)S(0)) and dichotic (N(0)S(π)) conditions. This binaural advantage (BA), arising from the use of inter-aural phase differences, is about 5-6 dB in stationary noise, but may be lower in everyday conditions. In the current study, BA was measured in various combinations of noise and artificially created diotic reverberation, for normal-hearing and hearing-impaired listeners. Speech-intelligibility models were applied to quantify the combined effects. Results showed that in stationary noise, diotic reverberation did not affect BA. BA was reduced in conditions where the masker fluctuated. With additional reverberation, however, it was restored. Results for both normal-hearing and hearing-impaired listeners were accounted for by assuming that binaural unmasking is only effectively realized at low instantaneous speech-to-noise ratios (SNRs). The observed BA was related to the distribution of SNRs resulting from fluctuations, reverberation, and peripheral processing. It appears that masker fluctuations and reverberation, both relevant for everyday communication, interact in their effects on binaural unmasking and need to be considered together.

Hemispheric Asymmetry of Auditory Steady-State Responses to Monaural and Diotic Stimulation

Amplitude modulations in the speech envelope are crucial elements for speech perception. These modulations comprise the processing rate at which syllabic (~3-7 Hz), and phonemic transitions occur in speech. Theories about speech perception hypothesize that each hemisphere in the auditory cortex is specialized in analyzing modulations at different timescales, and that phonemic-rate modulations of the speech envelope lateralize to the left hemisphere, whereas right lateralization occurs for slow, syllabic-rate modulations. In the present study, neural processing of phonemic- and syllabic-rate modulations was investigated with auditory steady-state responses (ASSRs). ASSRs to speech-weighted noise stimuli, amplitude modulated at 4, 20, and 80 Hz, were recorded in 30 normal-hearing adults. The 80 Hz ASSR is primarily generated by the brainstem, whereas 20 and 4 Hz ASSRs are mainly cortically evoked and relate to speech perception. Stimuli were presented diotically (same signal to both ears) and monaurally (one signal to the left or right ear). For 80 Hz, diotic ASSRs were larger than monaural responses. This binaural advantage decreased with decreasing modulation frequency. For 20 Hz, diotic ASSRs were equal to monaural responses, while for 4 Hz, diotic responses were smaller than monaural responses. Comparison of left and right ear stimulation demonstrated that, with decreasing modulation rate, a gradual change from ipsilateral to right lateralization occurred. Together, these results (1) suggest that ASSR enhancement to binaural stimulation decreases in the ascending auditory system and (2) indicate that right lateralization is more prominent for low-frequency ASSRs. These findings may have important consequences for electrode placement in clinical settings, as well as for the understanding of low-frequency ASSR generation.

The relationship between binaural benefit and difference in unilateral speech recognition performance for bilateral cochlear implant users

Objective: The full benefit of bilateral cochlear implants may depend on the unilateral performance with each device, the speech materials, processing ability of the user, and/or the listening environment. In this study, bilateral and unilateral speech performances were evaluated in terms of recognition of phonemes and sentences presented in quiet or in noise. Design: Speech recognition was measured for unilateral left, unilateral right, and bilateral listening conditions; speech and noise were presented at 0° azimuth. The ‘binaural benefit’ was defined as the difference between bilateral performance and unilateral performance with the better ear. Study sample: Nine adults with bilateral cochlear implants participated. Results: On average, results showed a greater binaural benefit in noise than in quiet for all speech tests. More importantly, the binaural benefit was greater when unilateral performance was similar across ears. As the difference in unilateral performance between ears increased, the binaural advantage decreased; this functional relationship was observed across the different speech materials and noise levels even though there was substantial intra- and inter-subject variability. Conclusions: The results indicate that subjects who show symmetry in speech recognition performance between implanted ears in general show a large binaural benefit.SumarioObjetivo: Se estudiaron los datos audiológicos de investigación epidemiológica basada en una población de adultos mayores. Se buscaron diagnósticos específicos de alteraciones otológicas y audiológicas que pueden ocasionar hipoacusia. Diseño: Estudio retrospectivo de registros. Muestra: Se estudiaron tres cohortes etáreas, 474 individuos de 70 a 75 años (“jóvenes) y 252 individuos de 85 años o mayores (“viejos”). Se utilizaron las audiometrías de tonos puros y de lenguaje. Se incluyeron los datos de sus expedientes médicos. Resultados: Se diagnosticó hipoacusia conductiva en 6.1% del grupo de “jóvenes” y un 10.3% de los “viejos”. Se establecieron diagnósticos especfícos (otitis media crónica y otoesclerosis) en cerca de la mitad de los casos. Se diagnosticó hipoacusia sensorineural no relacionada con la edad ni inducida por ruido en 3.4 y 5.2% de los casos. El 0.4% del grupo de “jóvenes” y el 10% del grupo de “viejos” presentaban un reconocimiento del lenguaje severamente afectado, posiblemente relacionado con neuropatía auditiva por edad. El 3.2% de las personas de 85 años de edad presentaban sordera funcional bilateral, pero ésta no se presentó en el grupo de 70–75 años. Conclusiones: La incidencia de neuropatíaa auditiva probablemente relacionada con la edad aumenta considerablemente de los 70–75 años a los 85. Existen marcadas diferencias en cuando a hipoacusia que afecta severamente la comunicación entre los grupos de “jóvenes” y “viejos” en la población estudiada.

Attentional tracking in real-room reverberation.

A listener can attend to one talker in a mixture of sound sources, and a difference in bearing between “target” and interfering sources is thought to aid this “tracking.” Interaural cues are degraded by reverberation however, raising the question of what cues are actually used to track sources in rooms? Listeners can also use differences in voice characteristics, so this study asks how well cues arising from location compete with talker differences when tracking messages in real-room reverberation. Real room measurements of binaural room impulse responses (BRIRs) were used to spatialize the stimuli and listeners decided which of two simultaneous target words belonged in a target phrase played simultaneously with a “distracter” phrase. Location differences were in competition with talker differences so that listeners’ responses indicated which cue-type they were tracking. Further experiments used processed BRIRs to eliminate temporal cues. Location was dominant over talker difference in dichotic but not diotic conditions, and results with processed BRIRs indicated that this “binaural advantage” is almost entirely due to ILD. Furthermore, an analysis of spectral distances between BRIR channels revealed that the probability of location difference overriding talker difference correlates with the distance between ILD patterns but not with monaural spectral distances.

The relationship between diotic and dichotic word recognition performance in young and older adults.

A left-ear disadvantage for dichotic listening and a deficit in recognition of speech in a competing message have been described for older adults; however, few studies have reported performance on both measures in the same group of listeners. The purpose of the present study was to assess binaural word recognition abilities in competitive listening situations among young and older adults. Young adults (18–30 years) with normal hearing and older adults (60–90 years) with bilateral mild to severe sensorineural hearing loss participated. Word recognition performance was evaluated using NU-6 monosyllabic words presented in multitalker babble and dichotically. Psychometric functions across five signal-to-noise ratios were measured in three conditions: monaural right, monaural left, and diotic. Dichotic word recognition (DWR) was also measured in three conditions: free recall, directed-right, and directed-left. Results for the psychometric functions revealed better recognition performance in the diotic condition than for either monaural condition. Results for DWR indicated a mean right ear advantage for both the free recall and directed-right conditions, and a mean left ear advantage for the directed-left condition. Group data are consistent with a binaural advantage for speech recognition in competing listening conditions for both young and older adults. Individual differences will be discussed.

A computational model of binaural speech recognition: Role of across-frequency vs. within-frequency processing and internal noise

This study describes a model of binaural speech recognition that is tested against psychoacoustic findings on binaural speech intelligibility in noise. It consists of models of the auditory periphery, binaural pathway and recognition of speech from glimpses based on the missing data approach, which allows the speech reception threshold (SRT) of the model and listeners to be compared. The binaural advantage based on differences between the interaural time differences (ITD) of the target and masker is modelled using the equalization–cancellation (EC) mechanism, either independently within each frequency channel or across all channels. The model is tested using a stimulus paradigm in which the target speech and noise interference are split into low- and high-frequency bands, so that the ITD in each band can be varied independently. The match between the model and listener data is quantified by a normalized SRT distance and a correlation metric, which demonstrate a slightly better match for the within-channel model (SRT: 0.5 dB, correlation: 0.94), than for the across-channel model (SRT: 0.7 dB, correlation: 0.90). However, as the differences between the approaches are small and non-significant, our results suggest that listeners exploit ITD via a mechanism that is neither fully frequency-dependent nor fully frequency-independent.

Effects of simulated spectral holes on speech intelligibility and spatial release from masking under binaural and monaural listening

The possibility that "dead regions" or "spectral holes" can account for some differences in performance between bilateral cochlear implant (CI) users and normal-hearing listeners was explored. Using a 20-band noise-excited vocoder to simulate CI processing, this study examined effects of spectral holes on speech reception thresholds (SRTs) and spatial release from masking (SRM) in difficult listening conditions. Prior to processing, stimuli were convolved through head-related transfer-functions to provide listeners with free-field directional cues. Processed stimuli were presented over headphones under binaural or monaural (right ear) conditions. Using Greenwood's [(1990). J. Acoust. Soc. Am. 87, 2592-2605] frequency-position function and assuming a cochlear length of 35 mm, spectral holes were created for variable sizes (6 and 10 mm) and locations (base, middle, and apex). Results show that middle-frequency spectral holes were the most disruptive to SRTs, whereas high-frequency spectral holes were the most disruptive to SRM. Spectral holes generally reduced binaural advantages in difficult listening conditions. These results suggest the importance of measuring dead regions in CI users. It is possible that customized programming for bilateral CI processors based on knowledge about dead regions can enhance performance in adverse listening situations.

人工内耳医療の過去・現在・未来

Cochlear implant (CI) technology, surgical technique, and candidacy criteria continue to rapidly evolve. Although outcomes are steadily advancing, there is still room for improvement. CI patients with residual hearing in the implanted ear can combine both electrical and acoustic stimulation (EAS/Hybrid CI) to improve speech perception, particularly in the presence of background noise. Binaural advantages are found in both adult and pediatric bilateral CI recipients, in terms of improved sound localization and enhanced speech perception under noisy conditions. Instead of widespread implantation in children younger than 12 months, evidence that supports infant implantation, with regard to speech perception and production outcomes, is still limited and of low quality. Long-term, high quality studies concerning both bilateral CI and infants’ CI are needed. While the long-term reports show that many profoundly hearing-impaired children using CI can develop functional levels of speech perception and production, attain age-appropriate oral language, and achieve satisfactory academic performance, cochlear implantation in younger children should be performed by skilled surgeons, provided that the attending pediatric anesthesiologist is considerably experienced and appropriate pediatric perioperative care facilities are readily available. In advanced future CI technology, gene therapy and/or regenerative medicine should be introduced to and combined with CI to preserve both auditory and vestibular function even after CI surgery, which might help it reach to a higher stage as the most successful innovation in the rebirth of artificial sense.

An Attempt to Improve Bilateral Cochlear Implants by Increasing the Distance between Electrodes and Providing Complementary Information to the Two Ears

The purpose of this investigation was to determine if adult bilateral cochlear implant recipients could benefit from using a speech processing strategy in which the input spectrum was interleaved among electrodes across the two implants. Two separate experiments were conducted. In both experiments, subjects were tested using a control speech processing strategy and a strategy in which the full input spectrum was filtered so that only the output of half of the filters was audible to one implant, while the output of the alternative filters was audible to the other implant. The filters were interleaved in a way that created alternate frequency "holes" between the two cochlear implants. In experiment one, four subjects were tested on consonant recognition. Results indicated that one of the four subjects performed better with the interleaved strategy, one subject received a binaural advantage with the interleaved strategy that they did not receive with the control strategy, and two subjects showed no decrement in performance when using the interleaved strategy. In the second experiment, 11 subjects were tested on word recognition, sentences in noise, and localization (it should be noted that not all subjects participated in all tests). Results showed that for speech perception testing one subject achieved significantly better scores with the interleaved strategy on all tests, and seven subjects showed a significant improvement with the interleaved strategy on at least one test. Only one subject showed a decrement in performance on all speech perception tests with the interleaved strategy. Out of nine subjects, one subject preferred the sound quality of the interleaved strategy. No one performed better on localization with the interleaved strategy. Data from this study indicate that some adult bilateral cochlear implant recipients can benefit from using a speech processing strategy in which the input spectrum is interleaved among electrodes across the two implants. It is possible that the subjects in this study who showed a significant improvement with the interleaved strategy did so because of less channel interaction; however, this hypothesis was not directly tested.