Binaural Advantage Research Articles

Auditory Localization Abilities in Bilateral Cochlear Implant Recipients

To quantify binaural advantage for auditory localization in the horizontal plane by bilateral cochlear implant (CI) recipients. Also, to determine whether the use of dual microphones with one implant improves localization. Twenty subjects from the UK multicenter trial of bilateral cochlear implantation with Nucleus 24 K/M device were recruited. Sound localization was assessed in an anechoic room with an 11-loudspeaker array under four test conditions: right CI, left CI, binaural CI, and dual microphone. Two runs were undertaken for each of five stimuli (speech, tones, noise, transients, and reverberant speech). Order of conditions was counterbalanced across subjects. Mean localization error with bilateral implants was 24 degrees compared with 67 degrees for monaural implant and dual microphone conditions (chance performance is 65 degrees). Normal controls average 2 to 3 degrees in similar conditions. Binaural performance was significantly better than monaural performance for all subjects, for all stimulus types, and for different sound sources. Only small differences in performance with different stimuli were observed. Bilateral cochlear implantation with the Nucleus 24 device provides marked improvement in horizontal plane localization abilities compared with unilateral CI use for a range of stimuli having different spectral and temporal characteristics. Benefit was obtained by all subjects, for all stimulus types, and for all sound directions. However, binaural performance was still worse than that obtained by normal hearing listeners and hearing aid users with the same methodology. Monaural localization performance was at chance. There is no benefit for localization with dual microphones.

Cochlear implantation after translabyrinthine acoustic tumour removal: preliminary results

The insertion depth difference is correlated with the relative pitch offset at the base of the electrode arrays. Symmetrical insertions produce a more usual pattern of bilateral speech results in noise than asymmetrical insertions at the 9-month stage. An asymmetrical insertion can produce greater patient dissatisfaction with their second device than symmetrical insertions. However, an asymmetrical insertion can still produce some binaural advantage. These case studies illustrate the importance of insertion depth in achieving a good outcome. An important surgical goal should be achieving a similar insertion depth as far as possible in cases of bilateral implantation.

Amplitude-Mapping Effects on Speech Intelligibility With Unilateral and Bilateral Cochlear Implants

A study was conducted examining the effects of amplitude-mapping adjustments on speech intelligibility with bilateral cochlear implant users, for both unilateral and bilateral device use. The main motivation for this study was the consideration that bilateral loudness summation may result in sounds becoming too loud if no adjustments are made to standard monaural amplitude-mapping functions (maps) when used bilaterally. In that case, reductions of the stimulation levels may be needed. The objective was to assess the impact of such adjustments on speech intelligibility in noise and in quiet. Four different maps were compared in eight bilateral users of the Nucleus 24 system. Each map variation was taken home for 1 week and used bilaterally. After each week, the map used was tested both unilaterally and bilaterally using an adaptive speech-in-noise test and bilaterally for low-level speech in quiet. For the tests in noise, both speech and noise were presented from the same loudspeaker placed directly in front of the listener (S0N0). One of the maps evaluated was a standard clinical map, fitted as if only one ear were to be used. The three other maps used stimulation levels that were reduced more near the maximal stimulation levels, near thresholds, or else by a similar amount over the entire dynamic range. The data showed a modest but statistically significant decrease in performance when stimulation levels were lowered. This was true both in noise and in quiet. For level reductions corresponding to binaural loudness summation effects, the performance decrease was on the order of 1 to 2 dB. Altering the slope of the map had relatively little effect on performance. Comparison of unilateral with bilateral performance using the same map (i.e., no compensation for bilateral loudness summation) and with speech and noise both presented from in front of the listeners showed a modest but statistically significant improvement in the bilateral condition. Using higher stimulation levels in amplitude-mapping functions can improve both monaural and binaural speech perception performance in quiet and in noise, even when the slope of the acoustic to electrical amplitude-mapping function is held constant (i.e., when the electrical signal-to-noise ratio remains constant). The results in noise can be understood if we assume that the relation between electrical stimulation levels and loudness grows faster at higher stimulation levels. When comparing the monaural better ear with binaural performance in noise (S0N0) by using the same map, that is to say, when no adjustments were made in the bilateral condition for bilateral loudness summation, an average signal-to-noise ratio benefit of 1.4 dB was found in the bilateral condition. These findings indicate that when fitting bilateral devices clinically, although binaural performance may decrease slightly if levels need to be reduced to compensate for binaural loudness summation, the binaural S0N0 advantage over the better ear will offset this. Consequently, performance with both ears after adjustment is likely to remain at least as good as for the better ear alone without level adjustment, even in the S0N0 condition where binaural advantages are minimized.

Benefit of Wearing a Hearing Aid on the Unimplanted Ear in Adult Users of a Cochlear Implant

The purpose of this investigation was to document performance of participants wearing a cochlear implant and hearing aid in opposite ears on speech-perception and localization tests. Twelve individuals who wore a cochlear implant and a hearing aid on contralateral ears were tested on their abilities to understand words in quiet and sentences in noise, and to localize everyday sounds. All speech stimuli were presented from the front, with the noise stimuli presented from the front, the right, or the left at a 90 degrees angle. Binaural summation in quiet and in noise, binaural squelch effects, and localization were studied to determine bilateral advantages. The magnitude of the monaural head shadow effect (the difference in unilateral performance when noise was facing the unilateral device vs. when the noise was opposite the unilateral device) also was studied. The test setup for localization was composed of an 8-speaker array spanning an arc of approximately 108 degrees in front of each participant. Group results yielded a statistically significant combined benefit of wearing a hearing aid in conjunction with a cochlear implant on opposite ears in noise conditions. Those participants who received a binaural advantage in 1 condition did not necessarily show a binaural advantage in another. Only 2 participants out of 12 were able to localize when wearing 2 devices. Further efforts are required to improve the integration of information from combined use of cochlear implant and hearing aid devices for enhancement of speech perception in noise and localization.

The spatial unmasking of speech: evidence for within-channel processing of interaural time delay

Across-frequency processing by common interaural time delay (ITD) in spatial unmasking was investigated by measuring speech reception thresholds (SRTs) for high- and low-frequency bands of target speech presented against concurrent speech or a noise masker. Experiment 1 indicated that presenting one of these target bands with an ITD of +500 micros and the other with zero ITD (like the masker) provided some release from masking, but full binaural advantage was only measured when both target bands were given an ITD of + 500 micros. Experiment 2 showed that full binaural advantage could also be achieved when the high- and low-frequency bands were presented with ITDs of equal but opposite magnitude (+/- 500 micros). In experiment 3, the masker was also split into high- and low-frequency bands with ITDs of equal but opposite magnitude (+/-500 micros). The ITD of the low-frequency target band matched that of the high-frequency masking band and vice versa. SRTs indicated that, as long as the target and masker differed in ITD within each frequency band, full binaural advantage could be achieved. These results suggest that the mechanism underlying spatial unmasking exploits differences in ITD independently within each frequency channel.

Intelligibility and preferred rate of Chinese speaking

This research was conducted to investigate the relationship between the rate of natural speech and intelligibility, and to examine the effects that some subject and task factors may have on Chinese speech perception. Other than the objective measure of speech intelligibility, subjective preferences of listeners towards speech rate and presentation mode were also investigated. Sixty subjects performed a set of intelligibility tests and subjective preference evaluations. The results indicated that at the rate of 4.3 characters per second (231 ms per character) previously established for professional newscasters, subjects perceived information with correctness of up to 99% and a maximum preference level was observed. Speech rates and presentation modes that were preferred by the subjects were also more easily intelligible. There was a binaural advantage over the monaural mode of presentation in speech intelligibility, and subjects generally preferred the binaural presentation to the monaural presentation. An accurate prediction of speech intelligibility was possible based on age of listener, presentation mode, and speech rate. The older subjects perceived speech less accurately and preferred slower speech than the younger subjects. The study demonstrated the importance of considering subject and task factors for compilation of standard speaking time for practical applications. Relevance to industry The results of this study are useful in generating a category of basic Chinese speaking times for standardizing speech performance and prediction of speech intelligibility and preference ratings of listeners under different listening conditions. In the reverse, the speaking rate for a certain intelligibility level can be estimated for practical use if detailed listening conditions are known.

Benefits of Bilateral Electrical Stimulation with the Nucleus Cochlear Implant in Adults: 6-Month Postoperative Results

To evaluate the benefits of bilateral electrical stimulation for hearing-impaired adult subjects using the Nucleus 24 cochlear implant in a multicenter study, and to compare and quantify performance on speech perception measures in quiet and in noise and localization ability for unilateral and bilateral cochlear implant use. : Repeated single subject measures were carried out for each subject, with each subject serving as their own control. Assessment of unilateral and bilateral listening conditions for performance on tests of speech comprehension and sound localization were performed. Speech comprehension measures were performed in quiet at 0 degree azimuth and in the presence of background noise simultaneously presented from the same speaker and spatially separated by 90 degrees, at S+45 degrees N45 degrees and at S-45 degrees N+45 degrees . Test materials included Freiburger monosyllabic words, Oldenburger sentences, and the Hochmair-Schulz-Moser sentences. Tests of localization were performed in the horizontal plane with 12 speaker locations 30 degrees apart using a shortened sentence stimulus from the Hochmair-Schulz-Moser sentences at two possible presentation levels of 55 and 70 dB sound pressure level for assessment of directionality. The binaural advantage provided by bilateral stimulation was calculated with respect to each ear separately, classified as either the better or poorer performing ear for each speech material in quiet and in noise test conditions. For localization of sound, the binaural advantage was compared with left and right ears separately. Paired comparisons for performance data in all conditions were carried out by considering measurements for each subject in different conditions as paired observations and applying the Student's t test to determine the statistical difference between the data sets. Tertiary referral centers with a cochlear implant program. Thirty-seven profoundly hearing-impaired adults were enrolled in the study, 22 simultaneously and 15 sequentially bilaterally implanted. All patients received the Nucleus 24 cochlear implant and used the Nucleus SPrint or ESPrit 3G speech processor, with the vast majority using the ACE speech coding strategy. For spatially separated speech in noise conditions, an interaural performance advantage for the ear closest to the speech source (i.e., with a superior signal to noise ratio) compared with that for the ear closest to the noise source (i.e., with an inferior signal to noise ratio) is consistently demonstrated regardless of whether it is the better or poorer performing ear closest to the speech signal. This is referred to as a significant binaural head-shadow benefit, resulting in a mean improvement between -10 dB and -11.4 dB in the critical signal to noise ratio required for 50% speech comprehension for the Olden-burger sentences and a mean improvement in the maximum score of 42% to 55% for the ear closest to the speech signal over the ear farthest away for the Hochmair-Schulz-Moser sentences. Bilateral stimulation is always observed to provide a performance advantage over the unilateral listening condition for either ear when ipsilateral to the noise source. In addition, as demonstrated by approximately half the subjects tested in noise with the Hochmair-Schulz-Moser sentences, a performance advantage of bilateral stimulation may be observed over the better ear alone when positioned ipsilateral to the speech signal, which is referred to as a binaural squelch effect. On average, for the group, this resulted in a statistically significant improvement in speech comprehension scores of 8% in the bilateral listening condition compared with the scores for the better ear alone. Through assessment of comprehension of coincidental speech in noise and speech in quiet, a significant benefit of binaural redundancy was noted for the group for Oldenburger sentence scores in noise and in quiet compared with unilateral scores for either ear and for the Freiburger monosyllabic words in quiet in comparison with the better ear alone scores. Binaural stimulation also led to a significant improvement in localization ability over either monaural condition, with the root mean square degrees of error reduced by 38 degrees compared with that observed for unilateral stimulation. Similar to what has been observed for bilateral acoustic stimulation in the past, bilateral electrical stimulation provides the foundation for the potential advantages of the head-shadow effect, providing a binaural head-shadow benefit and binaural auditory processing such as binaural redundancy and binaural squelch effects, all of which combine to lead to improved speech comprehension over unilateral listening conditions. The combination of improved speech comprehension and improved localization ability made available through bilateral electrical stimulation provides the necessary foundation to further assist the hearing-impaired listener to better cope with communication in the everyday listening situation both in noise and in quiet.

Monaural and interaural intensity discrimination: level effects and the "binaural advantage".

This study examined whether the level effects seen in monaural intensity discrimination (Weber's law and the "near miss") in a two-interval task are also observed in discrimination of interaural intensity differences (IIDs) in a single-interval task. Both tasks were performed for various standard levels of 4-kHz pure tones and broadband noise. The Weber functions (10 log deltaI/I versus I in dB) in the monaural and binaural conditions were parallel. For noise, the Weber functions had slopes close to zero (Weber's law) while the Weber functions for the tones had a mean slope of -0.089 (near miss). The near miss for the monaural and binaural tasks with tones was eliminated when a high-pass masker was gated with the listening intervals. The near-miss was also observed for 250- and 1000-Hz tones in the binaural task despite overall decreased sensitivity to changes in IID at 1000 Hz. The binaural thresholds showed a small (about 2-dB) advantage over monaural thresholds only in the broadband noise conditions. More important, however, is the fact that the level effects seen monaurally are also seen binaurally. This suggests that the basic mechanisms responsible for Weber's law and the near miss are common to monaural and binaural processing.

Binaural benefits for adults who use hearing aids and cochlear implants in opposite ears.

This study aimed to investigate 1) how a hearing aid needs to be adjusted for an adult who uses a cochlear implant in the contralateral ear; 2) whether the use of a hearing aid with a cochlear implant leads to interference; and 3) whether adults derive binaural benefits from using a hearing aid with a cochlear implant for speech perception, localization, and functional performance in everyday life. Twenty-one adults (11 female and 10 male) who used either a Nucleus CI-22 (N = 3) or a Nucleus CI-24 (N = 18) cochlear implant system in one ear participated in this study. Twelve of the adults were experienced hearing aid and implant users, whereas nine did not use a hearing aid after implantation. The hearing aids were fitted using the NAL-NL1 prescription, and fine-tuned for each individual by using a paired-comparisons test to identify the frequency response that was best for understanding speech, and a loudness balancing test to find the hearing aid gain that gave the same overall loudness as that perceived in the ear with a cochlear implant. Effects from using a hearing aid with a cochlear implant (bimodal hearing) were assessed by three measures. These included speech perception in noise in diotic and dichotic listening conditions, horizontal localization, and functional performance in everyday life. Performance with cochlear implant and hearing aid (CIHA) was compared with that with cochlear implant alone (CI) and hearing aid alone (HA). The NAL-NL1 prescribed appropriate frequency response slope on average, and the mean gain needed for binaural loudness balance was 4 dB lower than the prescribed gain. Individual variations in preferences suggest that it is desirable to fine-tune the hearing aid response slope and gain according to individual needs. The speech test results indicated that the CIHA scores were significantly better than the CI or the HA scores. Localization test results showed that the adults made significantly less error when locating a sound source using CIHA compared with CI or HA. Functional performance questionnaire scores for CIHA were significantly higher than CI scores or HA scores. All adults showed binaural benefits in at least one performance measure. On average, those who derived greater speech benefits also made less localization error and functioned more effectively in real life. The results clearly indicate that binaural advantages can be obtained from using a hearing aid with a cochlear implant in opposite ears. It is recommended that bimodal stimulation be standard practice for rehabilitation of adults who wear unilateral cochlear implants. A hearing aid should be fitted to the nonimplanted ear using the NAL-NL1 prescription as a starting point, and the frequency response slope and gain could be fine-tuned to suit individual needs.

Developmental effects in the masking-level difference.

Adults and children (aged 5 years 1 month to 10 years 8 months) were tested in a masking-level difference (MLD) paradigm in which detection of brief signals was contrasted for signal placement in masker envelope maxima versus masker envelope minima. Maskers were 50-Hz-wide noise bands centered on 500 Hz, and the signals were So or Sp 30-ms, 500-Hz tones. In agreement with previous studies, it was found that MLDs were greater for masker envelope minima placement than for masker envelope maxima placement. Across the age range of the children tested here, the binaural advantage associated with the masker envelope minima increased with the age of the child. One interpretation of the present results is that there is a developmental improvement in binaural temporal resolution over the age range tested here.

The benefit of binaural hearing in a cocktail party: effect of location and type of interferer.

The "cocktail party problem" was studied using virtual stimuli whose spatial locations were generated using anechoic head-related impulse responses from the AUDIS database [Blauert et al., J. Acoust. Soc. Am. 103, 3082 (1998)]. Speech reception thresholds (SRTs) were measured for Harvard IEEE sentences presented from the front in the presence of one, two, or three interfering sources. Four types of interferer were used: (1) other sentences spoken by the same talker, (2) time-reversed sentences of the same talker, (3) speech-spectrum shaped noise, and (4) speech-spectrum shaped noise, modulated by the temporal envelope of the sentences. Each interferer was matched to the spectrum of the target talker. Interferers were placed in several spatial configurations, either coincident with or separated from the target. Binaural advantage was derived by subtracting SRTs from listening with the "better monaural ear" from those for binaural listening. For a single interferer, there was a binaural advantage of 2-4 dB for all interferer types. For two or three interferers, the advantage was 2-4 dB for noise and speech-modulated noise, and 6-7 dB for speech and time-reversed speech. These data suggest that the benefit of binaural hearing for speech intelligibility is especially pronounced when there are multiple voiced interferers at different locations from the target, regardless of spatial configuration; measurements with fewer or with other types of interferers can underestimate this benefit.

Update on bilateral cochlear implantation.

Providing a unilateral cochlear implant in a patient with a profound bilateral hearing loss has now been a standard clinical practice for more than a decade. Although results are often very good, normal hearing has not been restored. One exciting opportunity to improve hearing in this population is to provide a second implant. However, it is not obvious that bilateral electrical stimulation can be integrated by the central nervous system. This article describes binaural hearing and reviews currently published articles on binaural cochlear implants. Controlled laboratory trials have focused on distinguishing different categories of potential binaural advantages. A potential summation effect occurs when the same stimulus is available at two ears. Listening in noise with two ears should be better than listening with one ear when the additional ear is away from the noise. This head shadow benefit results from acoustic effects, not physiologic ones. When the second ear is added near the noise source, a binaural squelch benefit can occur, requiring neural integration from both sides. Finally, two ears may improve sound localization. Binaural implantees generally benefit from head shadow effects. Only some benefit from summation and squelch effects. Most, but not all, show improved horizontal plane localization. It is now appropriate to begin experimental studies of binaural cochlear implants. Preliminary results show promise to improve head shadow, a physical advantage, and sound localization. Some benefits have been observed for improved summation and squelch. These findings have demonstrated that the brain can integrate electrical stimulation from the two ears. Future studies will be required to maximize this binaural hearing.

Binaural advantage on usage of hearing aid together with cochlear implant--examination on speech perception (Japanese monosyllable word list 67-S and Japanese HINT)

Six cochlear implant recipients with hearing aids in the opposite ear were studied to survey binaural advantage. They were examined in separate tests by using a hearing aid alone, cochlear implant alone, and by using both devices (bimodal condition). Test items used were the Japanese monosyllable word list 67--S and Japanese HINT. Statistically significantly results were obtained in the bimodal condition, three out of six subjects were successful in the monosyllable word test and all successful in the Japanese HINT. We conclude that all subjects enjoyed binaural advantage in speech perception in bimodal condition with no conflict at the recognition level; even when different sounds from cochlear implant and contralateral hearing aid were received. The plasticity of the brain is thought to be of importance in the bimodal condition.

Bilateral amplification for the elderly: are two aids better than one?

This paper reviews the advantages and disadvantages of bilateral amplification as opposed to unilateral hearing use for older persons with bilateral symmetric hearing loss. Binaural advantages, such as improved localization and speech recognition in noise, are presented as they pertain to the older population. In addition, contraindications, such as binaural interference, increased costs, cosmetic concerns, decreased manipulation skills, and additional hearing aid management issues, are discussed, A. case study is provided in which unilateral hearing aid fitting was more beneficial to a patient than two hearing aids. It is concluded that bilateral amplification should be attempted for all elderly patients with symmetric hearing loss, unless a contraindication is suspected.

Further investigations on binaural intelligibility of reverberant speech

There is a binaural intelligibility advantage for many subjects when listening to reverberant speech. Two processes offer explanations as to why the binaural advantage exists. First, directional information may identify echoes and remove a portion of the reverberation in a manner similar to the precedence effect. A more likely possibility is that the reverberation behaves as additive noise with a specific time and frequency dependence. In this case, subjects may utilize the coherence of the left and right channels to limit the effects of the incoherent reverberation, similar to binaural masking release. To test the latter hypothesis, subjects listen to diotic (L+R), binaural (L&R), and diotic (L or R) reverberant words. The diotic treatment (L+R) adds two recordings measured at the location of the listener’s ears. Since the listener faces the source, the direct signals are coherent while some cancellation is expected for the reverberation. The presentation will compare diotic (L+R) intelligibility to the binaural (L&R) condition as well as the diotic (L or R) control condition where the left or right signal plays to both ears.

Binaural Cochlear Implants Placed during the Same Operation

To evaluate the binaural listening advantages for speech in quiet and in noise and to localize sound when independently programmed binaural cochlear implants are used, and to determine whether ears with different hearing ability and duration of profound deafness perform differently with cochlear implants as well as to what extent preimplant psychophysical and physiologic assessment could be predictive of performance. Prospective study in which patients were prospectively selected to undergo bilateral implantation during a single surgical procedure at a tertiary referral center. All testing was performed with patients using their right, left, or both cochlear implants. Preimplant and intraoperative measures used electrical stimulation at the round window and stimulation through the cochlear implant. Bilateral implantation during the same operation did not cause any postoperative problems such as severe vertigo or ataxia. At 1 year, results of speech testing in quiet demonstrated a binaural advantage for 2 of 10 subjects. Speech-in-noise testing demonstrated that two implants were beneficial for two individuals. All subjects benefited from a head shadow effect when an ear with a better signal-to-noise ratio was available. The ability to localize sound was improved with binaural implants in all subjects. Preimplant psychophysical or physiologic measures were not predictive of eventual speech perception performance. Binaural cochlear implants can assist in the localization of sounds and have the potential in some individuals to improve speech understanding in quiet and in noise.

The bone-anchored hearing aid in patients with a unilateral air-bone gap.

To study the benefit of the application of a bone-anchored hearing aid in patients with a unilateral air-bone gap. Prospective evaluation in eight patients. Binaural hearing was assessed in the sound field by comparing aided and unaided scores obtained with a sound localization test and a speech recognition in noise test with spatially separated sound and noise sources. Tertiary referral center. The patients had subnormal hearing and unilateral conductive hearing loss. Sound localization improved significantly in the six patients with acquired hearing loss. The binaural advantage, studied with speech-in-noise tests with spatially separated speech and noise sources, proved to be comparable with that in a control group of subjects with normal hearing when they were listening monaurally versus binaurally. For one of the two patients with unilateral congenital conductive hearing loss, the results were ambiguous. This patient's age at the time of surgery was high: 40 years (the other patient was 19 years old at the time of surgery). This might have played a role. If reconstructive surgery is not possible (e.g., in a patient with a chronically draining ear or a severe congenital malformation), a bone-anchored hearing aid is an option to reestablish binaural hearing. The results reported herein suggest that, at least for patients with acquired hearing loss, the bone-anchored hearing aid is an effective treatment of unilateral conductive hearing loss.

Should children who use cochlear implants wear hearing aids in the opposite ear?

The aim of this study was to investigate 1) whether a hearing aid needs to be adjusted differently depending on whether a child wears a cochlear implant or another hearing aid in the contralateral ear; 2) whether the use of a hearing aid and a cochlear implant in opposite ears leads to binaural interference; and 3) whether the use of a hearing aid and a cochlear implant in opposite ears leads to binaural benefits in speech perception, localization, and communicative functioning in real life. Sixteen children participated in this study. All children used a Nucleus 22 or Nucleus 24 cochlear implant system programmed with the SPEAK strategy in one ear. The hearing aid amplification requirements in the nonimplanted ear of these children were determined using two procedures. A paired comparison technique was used to identify the frequency response that was best for speech intelligibility in quiet, and a loudness balancing technique was used to match the loudness of speech in the ear with a hearing aid to that with a cochlear implant. Eleven of the 16 children participated in the investigation of binaural effects. Performance in speech perception, localization, and communicative functioning was assessed under four aided conditions: cochlear implant with hearing aid as worn, cochlear implant alone, hearing aid alone, and cochlear implant with hearing aid adjusted according to individual requirements. Fifteen of the 16 children whose amplification requirements were determined preferred a hearing aid frequency response that was within +/-6 dB/octave of the NAL-RP prescription. On average, the children required 6 dB more gain than prescribed to balance the loudness of the implanted ear for a speech signal presented at 65 dB SPL. For all 11 children whose performance was evaluated for investigating binaural effects, there was no indication of significantly poorer performance under bilaterally aided conditions compared with unilaterally aided conditions. On average, there were significant benefits in speech perception, localization, and aural/oral function when the children used cochlear implants with adjusted hearing aids than when they used cochlear implants alone. All individuals showed benefits in at least one of the measures. Hearing aids for children who also use cochlear implants can be selected using the NAL-RP prescription. Adjustment of hearing aid gain to match loudness in the implanted ear can facilitate integration of signals from both ears, leading to better speech perception. Given that there are binaural advantages from using cochlear implants with hearing aids in opposite ears, clinicians should advise parents and other professionals about these potential advantages, and facilitate bilateral amplification by adjusting hearing aids after stable cochlear implant MAPs are established.

Investigation of Binaural Interference in Normal-Hearing and Hearing-Impaired Adults

When speech recognition testing is performed under diotic conditions, some elderly persons with asymmetric hearing loss exhibit a phenomenon in which the performance of the poorer ear interferes with that of the better ear. This binaural interference phenomenon has been estimated to occur in 8 to 10 percent of elderly hearing aid users. The purpose of the present study was to investigate the prevalence of this phenomenon in groups (n = 12) of young and elderly listeners with normal hearing, plus groups of elderly listeners with hearing loss who were aided or unaided. Of 48 subjects tested, only 2 exhibited significant evidence of binaural interference, a result that is close to that expected by chance. Although both of these subjects were elderly, one had normal hearing and the other was aided binaurally. A third elderly unaided subject exhibited a significant binaural advantage. Further studies are needed to determine the prevalence of binaural interference in normal-hearing or hearing-impaired listeners in any decade of life.

The impact of head angle on monaural and binaural performance with directional and omnidirectional hearing aids.

To evaluate the impact of head turn and monaural and binaural fittings on the sentence reception thresholds of hearing-impaired listeners wearing directional and omnidirectional hearing aids. Sentence reception thresholds were measured for 20 listeners fit monaurally and binaurally with behind-the-ear hearing aids set in both directional and omnidirectional modes. All listeners exhibited symmetrical, sloping, sensorineural hearing loss. The aided performance across these four fittings was evaluated for three different head and body angles. The three angles reflected body turns of 0 degrees, 15 degrees, and 30 degrees as measured relative to the primary sound source, with 0 degrees denoting the listener directly facing the sound source. Listeners were instructed to keep their heads in a fixed horizontal position and turn their heads and bodies to face visual targets at the three test angles. Sentences from the Hearing in Noise Test presented with a background of five, spatially separated, uncorrelated samples of cafeteria noise served as test material. All testing was performed in a moderately reverberant (Rt = 631 msec) "living room" environment. Participants generally performed significantly better when fit with directional versus omnidirectional hearing aids, and when fit binaurally versus monaurally across test conditions. The measured "binaural advantage" was reduced with increasing head angle. Participants performed significantly better with a 30 degree head angle than when directly facing the primary speaker. This "head turn advantage" was most prominent for monaural (versus binaural) conditions. Binaural and head turn advantages were not significantly different across directional and omnidirectional modes. These data provide additional support for the use of directional hearing aids and binaural amplification to improve speech intelligibility in noisy environments. The magnitude of these advantages was similar to that reported in previous investigations. The data also showed that hearing aid wearers achieved significantly better speech intelligibility in noise by turning their heads and bodies to a position in which they were not directly facing the sound source. This head turn advantage was in good agreement with the increase in Directivity Index with head turn and reflected the fact that hearing aids are generally most sensitive to sounds arriving from angles other than directly in front of the hearing aid wearer. Although these data suggest that many monaural hearing aid wearers may significantly improve speech intelligibility in noise through the use of head turn, the interaction between this advantage and the potential loss of visual cues with head turn is unknown.