Binaural speech intelligibility in noise for hearing-impaired listeners

Individual differences in selective attention predict speech identification at a cocktail party

Listeners with normal hearing show considerable individual differences in speech understanding when competing speakers are present, as in a crowded restaurant. Here, we show that one source of this variance are individual differences in the ability to focus selective attention on a target stimulus in the presence of distractors. In 50 young normal-hearing listeners, the performance in tasks measuring auditory and visual selective attention was associated with sentence identification in the presence of spatially separated competing speakers. Together, the measures of selective attention explained a similar proportion of variance as the binaural sensitivity for the acoustic temporal fine structure. Working memory span, age, and audiometric thresholds showed no significant association with speech understanding. These results suggest that a reduced ability to focus attention on a target is one reason why some listeners with normal hearing sensitivity have difficulty communicating in situations with background noise.

Selecting Appropriate Tests to Assess the Benefits of Bilateral Amplification With Hearing Aids

The aim of this study was to investigate the effect of bilateral hearing aids (HA) in subjects with mild and moderate-to-severe hearing loss. This study was designed as a within-subject feasibility study. Bilateral HA use was assessed using different laboratory tests on speech reception, listening effort, noise tolerance, and localization. All data were evaluated with bilateral and unilateral HA fittings. Forty experienced bilateral HA users were included with hearing impairment ranging from mild to moderate-to-severe. Subjects were stratified into two groups based on the degree of hearing loss. Speech reception in noise, listening effort, and localization tests showed a bilateral benefit for the moderate-to-severely hearing-impaired subjects. A bilateral benefit was also observed for listening effort in the mildly hearing-impaired group. The assessment of listening effort shows promise as a measure of bilateral HA benefit for mild hearing impairment. Localization and speech reception in noise tests provide additional value for larger losses. The next step is to compare experienced unilateral with bilateral HA users.

Effects of insertion depth on spatial speech perception in noise for simulations of cochlear implants and single-sided deafness

OBJECTIVE

This study evaluated the effects of insertion depth on spatial speech perception in noise for simulations of cochlear implants (CI) and single-sided deafness (SSD).

DESIGN

Mandarin speech recognition thresholds were adaptively measured in five listening conditions and four spatial configurations. The original signal was delivered to the left ear. The right ear received either no input, one of three CI simulations in which the insertion depth was varied, or the original signal. Speech and noise were presented at either front, left, or right.

STUDY SAMPLE

Ten Mandarin-speaking NH listeners with pure-tone thresholds less than 20 dB HL.

RESULTS

Relative to no input in the right ear, the CI simulations provided significant improvements in head shadow benefit for all insertion depths, as well as better spatial release of masking (SRM) for the deepest simulated insertion. There were no significant improvements in summation or squelch for any of the CI simulations.

CONCLUSIONS

The benefits of cochlear implantation were largely limited to head shadow, with some benefit for SRM. The greatest benefits were observed for the deepest simulated CI insertion, suggesting that reducing mismatch between acoustic and electric hearing may increase the benefit of cochlear implantation.

Unilateral cochlear implantation in children with a potentially useable contralateral ear

Increasingly, children are considered for a unilateral CI, even if the contralateral ear falls outside current audiological guidelines, especially if they are not considered to be reaching their educational potential. The primary aim was to investigate the benefit of unilateral CI in children currently outside UK [National Institute for Health and Care Excellence Technology Appraisal Guidance. 2009. Cochlear implants for children and adults with severe to profound deafness. NICE technology appraisal guidance [TAG166]. Available January 29, 2016 from http://www.nice.org.uk/ta166 ] audiological guidelines in the contralateral ear. The secondary aim was to measure compliance. A retrospective case review with standard demographic data was performed. Forty-seven children were identified as having received a unilateral CI with the contralateral ear falling outside of current UK audiological criteria. These children were allocated to two groups; with hearing between 50 and 70 dB, and 70 and 90 dB at 2 and 4 kHz in the contralateral ear, respectively. Categories of auditory performance (CAP) were assessed. Pre- and post-operative CAP scores demonstrated a statistically significant improvement in auditory perception. We would suggest that assessing candidacy in individual ears and subsequent unilateral CI, has given these children a benefit they may not otherwise have acquired if they only had bilateral hearing aid.

Comparison of the CAM2A and NAL-NL2 hearing-aid fitting methods for participants with a wide range of hearing losses

OBJECTIVE

To compare preferences for sounds processed via a simulated five-channel compression hearing aid fitted using CAM2A and NAL-NL2.

DESIGN

Within a trial, the same segment of sound was presented twice, once with CAM2A settings and once with NAL-NL2 settings, in random order. The participant indicated which one was preferred and by how much. Stimuli included female and male speech in quiet and four types of music. The compression speed was slow or fast and the input sound level was 50, 65, or 80 dB SPL.

STUDY SAMPLE

Sixteen experienced hearing-aid users with a wide range of sensorineural hearing losses.

RESULTS

For both compression speeds, CAM2A was slightly preferred over NAL-NL2 for input levels of 65 and 80 dB, but NAL-NL2 was slightly preferred at 50 dB SPL.

CONCLUSIONS

Preferences for CAM2A relative to NAL-NL2 vary with input level. The results suggest that preferences for CAM2A might be increased by using lower gains for high frequencies and low input levels.

Characteristics and international comparability of the Finnish matrix sentence test in cochlear implant recipients

OBJECTIVES

The first Finnish sentence-based speech test in noise--the Finnish matrix sentence test--was recently developed. The aim of this study was to determine the characteristics of the new test with respect to test-retest reliability, speech recognition curve, and international comparability in Finnish cochlear implant (CI) recipients.

DESIGN

The speech reception thresholds (SRT) were measured by means of an adaptive test procedure and compared with the results of the traditional Finnish word test. Additional measurements for concurrent slope and SRT estimation were conducted to determine the speech recognition curve and to check the test-retest reliability.

STUDY SAMPLE

The measurements were performed on 78 Finnish CI recipients. In a subset of 25 patients, additional measurements for test-retest reliability and slope determination were performed.

RESULTS

The mean SRT was -3.5 ± 1.7 dB SNR, with only a weak correlation with the Finnish word test. Test-retest reliability was within ± 1 dB and the mean slope of the speech recognition curve was 14.6 ± 3.6 %/dB. The rehabilitation results were similar to the results published for the German matrix test.

CONCLUSIONS

The Finnish matrix test was found to be suitable and efficient in CI recipients with similar characteristics as the German matrix test.

Cochlear implantation for patients with single-sided deafness or asymmetrical hearing loss: a systematic review of the evidence

OBJECTIVE

A systematic review of the literature to evaluate the clinical outcome of cochlear implantation for patients with single-sided deafness (SSD) or asymmetrical hearing loss (AHL).

DATA SOURCES

We searched the PubMed, Embase, Cochrane Library, and CINAHL databases from their inception up to December 10, 2013 for SSD or AHL and cochlear implantation or their synonyms.

STUDY SELECTION

In total, 781 articles were retrieved, of which 15 satisfied the eligibility criteria. Our outcomes of interest were speech perception in noise, sound localization, quality of life (QoL), and tinnitus.

DATA EXTRACTION

Critical appraisal showed that six studies reported on less than five patients or that they carried a low directness of evidence or a high risk of bias. Therefore, we extracted the data of nine studies (n = 112). Patient numbers, age, duration of deafness, classification of deafness, pure tone audiometry, follow-up duration, and outcome measurements were extracted from all nine articles.

DATA SYNTHESIS

Because of large heterogeneity between studies, we were not able to pool data in a meta-analysis. We therefore summarized the results of the studies specified per outcome.

CONCLUSION

There are no high-level-of-evidence studies concerning cochlear implantation in patients with SSD or AHL. Current literature suggests important benefits of cochlear implantation regarding sound localization, QoL, and tinnitus. Varying results were reported for speech perception in noise, possibly caused by the large clinical heterogeneity between studies. Larger and high-quality studies are certainly warranted.

Temporal Resolution of the Normal Ear in Listeners with Unilateral Hearing Impairment

Unilateral hearing loss (UHL) leads to an imbalanced input to the brain and results in cortical reorganization. In listeners with unilateral impairments, while the perceptual deficits associated with the impaired ear are well documented, less is known regarding the auditory processing in the unimpaired, clinically normal ear. It is commonly accepted that perceptual consequences are unlikely to occur in the normal ear for listeners with UHL. This study investigated whether the temporal resolution in the normal-hearing (NH) ear of listeners with long-standing UHL is similar to those in listeners with NH. Temporal resolution was assayed via measuring gap detection thresholds (GDTs) in within- and between-channel paradigms. GDTs were assessed in the normal ear of adults with long-standing, severe-to-profound UHL (N = 13) and age-matched, NH listeners (N = 22) at two presentation levels (30 and 55 dB sensation level). Analysis indicated that within-channel GDTs for listeners with UHL were not significantly different than those for the NH subject group, but the between-channel GDTs for listeners with UHL were poorer (by greater than a factor of 2) than those for the listeners with NH. The hearing thresholds in the normal or impaired ears were not associated with the elevated between-channel GDTs for listeners with UHL. Contrary to the common assumption that auditory processing capabilities are preserved for the normal ear in listeners with UHL, the current study demonstrated that a long-standing unilateral hearing impairment may adversely affect auditory perception--temporal resolution--in the clinically normal ear. From a translational perspective, these findings imply that the temporal processing deficits in the unimpaired ear of listeners with unilateral hearing impairments may contribute to their overall auditory perceptual difficulties.

Quality of Life and Auditory Performance in Adults with Asymmetric Hearing Loss

We evaluated the relationship between binaural hearing deficits and quality of life. The study included 49 adults with asymmetric hearing loss (AHL), and 11 adult normal-hearing listeners (NHL) served as controls. Speech reception thresholds (SRT) were assessed with the French Matrix Test. Quality of life was evaluated with the Speech, Spatial and Qualities of Hearing Scale (SSQ) and the Glasgow Health Status Inventory. Speech recognition in noise was significantly poorer for AHL subjects [-0.12 dB signal-to-noise ratio (SNR) in dichotic (with speech presented to the poorer ear and noise to the better ear), -1.72 dB in diotic and -6.84 dB in reverse-dichotic conditions] compared to NHL (-4.98 dB in diotic and -9.58 dB in dichotic conditions). Scores for quality-of-life questionnaires were significantly below norms. Significant correlations were found between the SRT for the dichotic condition and the SSQ total score (r = -0.38, p = 0.01), and pure-tone average thresholds for both groups.

Deafness in cochlear and auditory nerve disorders

Sensorineural hearing loss is the most common type of hearing impairment worldwide. It arises as a consequence of damage to the cochlea or auditory nerve, and several structures are often affected simultaneously. There are many causes, including genetic mutations affecting the structures of the inner ear, and environmental insults such as noise, ototoxic substances, and hypoxia. The prevalence increases dramatically with age. Clinical diagnosis is most commonly accomplished by measuring detection thresholds and comparing these to normative values to determine the degree of hearing loss. In addition to causing insensitivity to weak sounds, sensorineural hearing loss has a number of adverse perceptual consequences, including loudness recruitment, poor perception of pitch and auditory space, and difficulty understanding speech, particularly in the presence of background noise. The condition is usually incurable; treatment focuses on restoring the audibility of sounds made inaudible by hearing loss using either hearing aids or cochlear implants.

Effects of unilateral input and mode of hearing in the better ear: self-reported performance using the speech, spatial and qualities of hearing scale

OBJECTIVE

To evaluate effects of hearing mode (normal hearing, cochlear implant, or hearing aid) on everyday communication among adult unilateral listeners using the Speech, Spatial and Qualities of Hearing Scale (SSQ). Individuals with one good, naturally hearing ear were expected to have higher overall ratings than unilateral listeners dependent on a cochlear implant or hearing aid. The authors anticipated that listening environments reliant on binaural processing for successful communication would be rated most disabling by all unilateral listeners. Regardless of hearing mode, all hearing-impaired participants were expected to have lower ratings than individuals with normal hearing bilaterally. A secondary objective was to compare post-treatment SSQ results of participants who subsequently obtained a cochlear implant for the poorer hearing ear with those of participants with a single normal-hearing ear.

DESIGN

Participants were 87 adults recruited as part of ongoing research investigating asymmetric hearing effects. Sixty-six participants were unilateral listeners who had one unaided/nonimplanted severe to profound hearing-loss ear and were grouped based on hearing mode of the better ear: 30 had one normal-hearing ear (i.e., unilateral hearing-loss participants); 20 had a unilateral cochlear implant; and 16 had a unilateral hearing aid. Data were also collected from 21 normal-hearing individuals, as well as a subset of participants who subsequently received a cochlear implant in the poorer ear and thus became bilateral listeners. Data analysis was completed at the domain and subscale levels.

RESULTS

A significant mode-of-hearing group effect for the hearing-impaired participants (i.e., with unilateral hearing loss, unilateral cochlear implant, or unilateral hearing aid) was identified for two domains (Speech and Qualities) and six subscales (Speech in Quiet, Speech in Noise, Speech in Speech Contexts, Multiple Speech Stream Processing and Switching, Identification of Sound and Objects, and Sound Quality and Naturalness). There was no significant mode-of-hearing group effect for the Spatial domain or the other four subscales (Localization, Distance and Movement, Segregation of Sounds, and Listening Effort). Follow-up analysis indicated the unilateral normal-hearing ear group had significantly higher ratings than the unilateral cochlear implant or hearing aid groups for the Speech domain and four of the ten subscales; neither the cochlear implant nor hearing aid group had subscale ratings significantly higher than each other or the unilateral hearing loss group. Audibility and sound quality imparted by hearing mode were identified as factors related to subjective listening experience. After cochlear implantation to restore bilateral hearing, SSQ ratings for bilateral cochlear implant or cochlear implant plus hearing aid participants were significantly higher than those of the unilateral hearing-loss group for Speech in Quiet, Speech in Noise, Localization, Distance and Movement, Listening Effort, and the Spatial domain. Hearing-impaired individuals had significantly poorer ratings in all areas compared with those with bilateral normal hearing.

CONCLUSIONS

Adults reliant on a single ear, irrespective of better ear hearing mode, including those with one normal hearing ear, are at a disadvantage in all aspects of everyday listening and communication. Audibility and hearing mode were shown to differentially contribute to listening experience.

Localization and interaural time difference (ITD) thresholds for cochlear implant recipients with preserved acoustic hearing in the implanted ear

The purpose of this study was to investigate horizontal plane localization and interaural time difference (ITD) thresholds for 14 adult cochlear implant recipients with hearing preservation in the implanted ear. Localization to broadband noise was assessed in an anechoic chamber with a 33-loudspeaker array extending from -90 to +90°. Three listening conditions were tested including bilateral hearing aids, bimodal (implant + contralateral hearing aid) and best aided (implant + bilateral hearing aids). ITD thresholds were assessed, under headphones, for low-frequency stimuli including a 250-Hz tone and bandpass noise (100-900 Hz). Localization, in overall rms error, was significantly poorer in the bimodal condition (mean: 60.2°) as compared to both bilateral hearing aids (mean: 46.1°) and the best-aided condition (mean: 43.4°). ITD thresholds were assessed for the same 14 adult implant recipients as well as 5 normal-hearing adults. ITD thresholds were highly variable across the implant recipients ranging from the range of normal to ITDs not present in real-world listening environments (range: 43 to over 1600 μs). ITD thresholds were significantly correlated with localization, the degree of interaural asymmetry in low-frequency hearing, and the degree of hearing preservation related benefit in the speech reception threshold (SRT). These data suggest that implant recipients with hearing preservation in the implanted ear have access to binaural cues and that the sensitivity to ITDs is significantly correlated with localization and degree of preserved hearing in the implanted ear.

Effects of interferer facing orientation on speech perception by normal-hearing and hearing-impaired listeners

There exist perceptible differences between sound emanating from a talker who faces and a talker who does not face a listener: Sound from a non-facing talker is attenuated and acquires a spectral tilt. The present study assessed the role that these facing-orientation cues play for speech perception. Digit identification for a frontal target talker in the presence of two spatially separated interfering talkers was measured for 10 normal-hearing (NH) and 11 hearing-impaired (HI) listeners. Overall-level differences and spectral tilts were reproduced by means of digital filtering and playback via loudspeakers. Both NH and HI listeners performed significantly better when the interfering talkers were simulated not to be facing them. Spectral tilts and level differences across talkers reduced target-interferer confusions. They enabled the NH listeners to sequentially stream the digits. This was not the case for the HI listeners, who showed smaller benefits, irrespective of whether they were aided by their own hearing aids or not. While hearing-aid amplification increased audibility, it may not have aided target-interferer segregation or target selection. The present results suggest that facing orientation cannot be neglected in the exploration of speech perception in multitalker situations.

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.

The contribution of matched envelope dynamic range to the binaural benefits in simulated bilateral electric hearing

PURPOSE

This study examined the effects of envelope dynamic-range mismatch on the intelligibility of Mandarin speech in noise by simulated bilateral electric hearing.

METHOD

Noise-vocoded Mandarin speech, corrupted by speech-shaped noise at 5 and 0 dB signal-to-noise ratios, was presented unilaterally or bilaterally to 10 normal-hearing listeners for recognition. For unilateral conditions, the right ear was presented with the 8-channel noise-vocoded stimuli generated using a 15-dB envelope dynamic range (DR). To simulate the envelope DR mismatch between the 2 ears, the left ear was presented with the 8-channel noise-vocoded stimuli generated using a 5-, 10-, or 15-dB envelope DR, respectively.

RESULTS

Significant binaural summation benefits for Mandarin speech recognition were observed only with matched envelope DR between the 2 ears. With reduced DR, the performance of tone identification was more consistent in the steady-state speech-shaped noise than that of sentence recognition.

CONCLUSIONS

Consistent with previous findings, the present results suggest that Mandarin speech-perception performance of bilateral electric listening in noise is affected by the difference of envelope DR between the 2 implanted ears, and the binaural summation benefits are maximized when DR mismatch is minimized between the 2 implanted ears.

Advantages from bilateral hearing in speech perception in noise with simulated cochlear implants and residual acoustic hearing

Acoustic simulations were used to study the contributions of spatial hearing that may arise from combining a cochlear implant with either a second implant or contralateral residual low-frequency acoustic hearing. Speech reception thresholds (SRTs) were measured in twenty-talker babble. Spatial separation of speech and noise was simulated using a spherical head model. While low-frequency acoustic information contralateral to the implant simulation produced substantially better SRTs there was no effect of spatial cues on SRT, even when interaural differences were artificially enhanced. Simulated bilateral implants showed a significant head shadow effect, but no binaural unmasking based on interaural time differences, and weak, inconsistent overall spatial release from masking. There was also a small but significant non-spatial summation effect. It appears that typical cochlear implant speech processing strategies may substantially reduce the utility of spatial cues, even in the absence of degraded neural processing arising from auditory deprivation.

Cochlear implantation in adults with asymmetric hearing loss

OBJECTIVE

Bilateral severe to profound sensorineural hearing loss is a standard criterion for cochlear implantation. Increasingly, patients are implanted in one ear and continue to use a hearing aid in the nonimplanted ear to improve abilities such as sound localization and speech understanding in noise. Patients with severe to profound hearing loss in one ear and a more moderate hearing loss in the other ear (i.e., asymmetric hearing) are not typically considered candidates for cochlear implantation. Amplification in the poorer ear is often unsuccessful because of limited benefit, restricting the patient to unilateral listening from the better ear alone. The purpose of this study was to determine whether patients with asymmetric hearing loss could benefit from cochlear implantation in the poorer ear with continued use of a hearing aid in the better ear.

DESIGN

Ten adults with asymmetric hearing between ears participated. In the poorer ear, all participants met cochlear implant candidacy guidelines; seven had postlingual onset, and three had pre/perilingual onset of severe to profound hearing loss. All had open-set speech recognition in the better-hearing ear. Assessment measures included word and sentence recognition in quiet, sentence recognition in fixed noise (four-talker babble) and in diffuse restaurant noise using an adaptive procedure, localization of word stimuli, and a hearing handicap scale. Participants were evaluated preimplant with hearing aids and postimplant with the implant alone, the hearing aid alone in the better ear, and bimodally (the implant and hearing aid in combination). Postlingual participants were evaluated at 6 mo postimplant, and pre/perilingual participants were evaluated at 6 and 12 mo postimplant. Data analysis compared the following results: (1) the poorer-hearing ear preimplant (with hearing aid) and postimplant (with cochlear implant); (2) the device(s) used for everyday listening pre- and postimplant; and (3) the hearing aid-alone and bimodal listening conditions postimplant.

RESULTS

The postlingual participants showed significant improvements in speech recognition after 6 mo cochlear implant use in the poorer ear. Five postlingual participants had a bimodal advantage over the hearing aid-alone condition on at least one test measure. On average, the postlingual participants had significantly improved localization with bimodal input compared with the hearing aid-alone. Only one pre/perilingual participant had open-set speech recognition with the cochlear implant. This participant had better hearing than the other two pre/perilingual participants in both the poorer and better ear. Localization abilities were not significantly different between the bimodal and hearing aid-alone conditions for the pre/perilingual participants. Mean hearing handicap ratings improved postimplant for all participants indicating perceived benefit in everyday life with the addition of the cochlear implant.

CONCLUSIONS

Patients with asymmetric hearing loss who are not typical cochlear implant candidates can benefit from using a cochlear implant in the poorer ear with continued use of a hearing aid in the better ear. For this group of 10, the 7 postlingually deafened participants showed greater benefits with the cochlear implant than the pre/perilingual participants; however, further study is needed to determine maximum benefit for those with early onset of hearing loss.

Contralateral hearing aid use in cochlear implanted patients: multicenter study of bimodal benefit

CONCLUSION

The use of a hearing aid (HA) in combination with a cochlear implant (CI) significantly improved performance for speech perception in quiet, in noise, and for localization compared with monaural conditions. No significant differences in functional performance were observed following optimization of HA fitting.

OBJECTIVES

To evaluate the binaural benefits derived from using a contralateral HA in conjunction with a CI in subjects with significant functional hearing in the nonimplanted ear and the effects of HA fitting optimization.

METHODS

Fifteen adult CI users, intra-subject controls, were enrolled in a prospective repeated-measure multicenter study. Evaluation of performance for speech understanding, localization, and subjective impressions was conducted before and following HA fitting optimization for CI alone, HA alone, and CI + HA.

RESULTS

For speech testing in quiet, bimodal scores were significantly better than for HA alone and CI alone conditions (p < 0.01). For speech and noise (S0N0) at 0° azimuth the scores were significantly better in the bimodal condition than for CI alone (p = 0.01), indicating binaural summation. When noise was presented to the HA side (S0NHA) bimodal scores were significantly better than for CI alone (p < 0.01 and p < 0.05, respectively), suggesting a significant binaural squelch effect. Sound localization ability was significantly improved in the bimodal condition compared with the CI alone condition (p = 0.002).

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.

Informational masking and spatial hearing in listeners with and without unilateral hearing loss

PURPOSE

This study assessed selective listening for speech in individuals with and without unilateral hearing loss (UHL) and the potential relationship between spatial release from informational masking and localization ability in listeners with UHL.

METHOD

Twelve adults with UHL and 12 normal-hearing controls completed a series of monaural and binaural speech tasks that were designed to measure informational masking. They also completed a horizontal localization task.

RESULTS

Monaural performance by participants with UHL was comparable to that of normal-hearing participants. Unlike the normal-hearing participants, the participants with UHL did not exhibit a true spatial release from informational masking. Rather, their performance could be predicted by head shadow effects. Performance among participants with UHL in the localization task was quite variable, with some showing near-normal abilities and others demonstrating no localization ability.

CONCLUSION

Individuals with UHL did not show deficits in all listening situations but were at a significant disadvantage when listening to speech in environments where normal-hearing listeners benefit from spatial separation between target and masker. This inability to capitalize on spatial cues for selective listening does not appear to be related to localization ability.

The influence of non-spatial factors on measures of spatial release from masking

This study tested the hypothesis that the reduction in spatial release from masking (SRM) resulting from sensorineural hearing loss in competing speech mixtures is influenced by the characteristics of the interfering speech. A frontal speech target was presented simultaneously with two intelligible or two time-reversed (unintelligible) speech maskers that were either colocated with the target or were symmetrically separated from the target in the horizontal plane. The difference in SRM between listeners with hearing impairment and listeners with normal hearing was substantially larger for the forward maskers (deficit of 5.8 dB) than for the reversed maskers (deficit of 1.6 dB). This was driven by the fact that all listeners, regardless of hearing abilities, performed similarly (and poorly) in the colocated condition with intelligible maskers. The same conditions were then tested in listeners with normal hearing using headphone stimuli that were degraded by noise vocoding. Reducing the number of available spectral channels systematically reduced the measured SRM, and again, more so for forward (reduction of 3.8 dB) than for reversed speech maskers (reduction of 1.8 dB). The results suggest that non-spatial factors can strongly influence both the magnitude of SRM and the apparent deficit in SRM for listeners with impaired hearing.

Functional benefit of the bone-anchored hearing aid with different auditory profiles: objective and subjective measures

OBJECTIVES

To examine sentence recognition and self-report outcomes in hearing-impaired persons with different auditory profiles and who were fitted unilaterally with a bone-anchored hearing aid.

STUDY-DESIGN

Prospective cohort study.

SETTING

Tertiary referral unit.

PATIENTS

Data were collected of six patients with single-sided deafness (SSD), seven with a mild to severe hearing loss at the bone-anchored hearing aid side and (near-)normal hearing at the other side and six with a severe bilateral hearing loss.

MAIN OUTCOME MEASUREMENTS

Sound field thresholds, and sentence recognition in noise (presented from different angles) with bone-anchored hearing aid, without bone-anchored hearing aid and with bone-anchored hearing aid and other ear occluded. In addition, the Speech, Spatial and Qualities of hearing scale and the Abbreviated Profile of Hearing Aid Benefit questionnaire were administered as self-report measures.

RESULTS

Patients with single-sided deafness listened mainly with their non-bone-anchored hearing aid ear, although the bone-anchored hearing aid lifted the head shadow effect. Patients with mild to severe hearing loss at the bone-anchored hearing aid side and (near-)normal hearing at the other side performed significantly differently in aided and unaided conditions and even regained limited binaural sensitivity with the device. The latter was also true for the patients with severe bilateral hearing loss. However, their hearing loss at the non-bone-anchored hearing aid side was too great to contribute to hearing and they listened predominantly with their bone-anchored hearing aid. Self-report outcomes provided useful information on hearing disability, although this information was not significantly differently for the 3 groups of patients.

CONCLUSIONS

The bone-anchored hearing aid enhanced performance in different hearing configurations, albeit to different extents.

Spectrum Resolving Power of Hearing: Measurements, Baselines, and Influence of Maskers

Contemporary methods of measurement of frequency resolving power in the auditory system are reviewed. Majority of classical methods are based on the frequency-selective masking paradigm and require multi-point measurements (a number of masked thresholds should be measured to obtain a single frequency-tuning estimate). Therefore, they are rarely used for practical needs. As an alternative approach, frequency-selective properties of the auditory system may be investigated using probes with complex frequency spectrum patterns, in particular, rippled noise that is characterized by a spectrum with periodically alternating maxima and minima. The maximal ripple density discriminated by the auditory system is a convenient measure of the spectrum resolving power (SRP). To find the highest resolvable ripple density, a phase-reversal test has been suggested. Using this technique, normal SRP, its dependence on probe center frequency, spectrum contrast, and probe level were measured. The results were not entirely predictable by frequency-tuning data obtained by masking methods. SRP is influenced by maskers, with on- and off-frequency maskers influencing SRP very differently. Dichotic separation of the probe and masker results in almost complete release of SRP from influence of maskers.

Evaluation of different signal processing options in unilateral and bilateral cochlear freedom implant recipients using R-Space background noise

BACKGROUND

Difficulty understanding in background noise is a common complaint of cochlear implant (CI) recipients. Programming options are available to improve speech recognition in noise for CI users including automatic dynamic range optimization (ADRO), autosensitivity control (ASC), and a two-stage adaptive beamforming algorithm (BEAM). However, the processing option that results in the best speech recognition in noise is unknown. In addition, laboratory measures of these processing options often show greater degrees of improvement than reported by participants in everyday listening situations. To address this issue, Compton-Conley and colleagues developed a test system to replicate a restaurant environment. The R-SPACE™ consists of eight loudspeakers positioned in a 360 degree arc and utilizes a recording made at a restaurant of background noise.

PURPOSE

The present study measured speech recognition in the R-SPACE with four processing options: standard dual-port directional (STD), ADRO, ASC, and BEAM.

RESEARCH DESIGN

A repeated-measures, within-subject design was used to evaluate the four different processing options at two noise levels.

STUDY SAMPLE

Twenty-seven unilateral and three bilateral adult Nucleus Freedom CI recipients.

INTERVENTION

The participants' everyday program (with no additional processing) was used as the STD program. ADRO, ASC, and BEAM were added individually to the STD program to create a total of four programs.

DATA COLLECTION AND ANALYSIS

Participants repeated Hearing in Noise Test sentences presented at 0 degrees azimuth with R-SPACE restaurant noise at two noise levels, 60 and 70 dB SPL. The reception threshold for sentences (RTS) was obtained for each processing condition and noise level.

RESULTS

In 60 dB SPL noise, BEAM processing resulted in the best RTS, with a significant improvement over STD and ADRO processing. In 70 dB SPL noise, ASC and BEAM processing had significantly better mean RTSs compared to STD and ADRO processing. Comparison of noise levels showed that STD and BEAM processing resulted in significantly poorer RTSs in 70 dB SPL noise compared to the performance with these processing conditions in 60 dB SPL noise. Bilateral participants demonstrated a bilateral improvement compared to the better monaural condition for both noise levels and all processing conditions, except ASC in 60 dB SPL noise.

CONCLUSIONS

The results of this study suggest that the use of processing options that utilize noise reduction, like those available in ASC and BEAM, improve a CI recipient's ability to understand speech in noise in listening situations similar to those experienced in the real world. The choice of the best processing option is dependent on the noise level, with BEAM best at moderate noise levels and ASC best at loud noise levels for unilateral CI recipients. Therefore, multiple noise programs or a combination of processing options may be necessary to provide CI users with the best performance in a variety of listening situations.

Localization in speech mixtures by listeners with hearing loss

The ability of listeners with bilateral sensorineural hearing loss to localize a speech source in a multitalker mixture was measured. Five simultaneous words spoken by different talkers were presented over loudspeakers in a small room, and listeners localized one target word. Errors were significantly larger in this group compared to a control group with normal hearing. Localization of the target presented alone was not different between groups. The results suggest that hearing loss does not impair spatial hearing per se, but degrades the spatial representation of multiple simultaneous sounds.

Sound source localization using hearing aids with microphones placed behind-the-ear, in-the-canal, and in-the-pinna

OBJECTIVE

The effect of different commercial hearing aids on the ability to resolve front-back confusions and on sound localization in the frontal horizontal and vertical plane was studied.

DESIGN

Commercial hearing aids with a microphone placed in-the-ear-canal (ITC), behind-the-ear (BTE), and in-the-pinna (ITP) were evaluated in the frontal and full horizontal plane, and in the frontal vertical plane.

STUDY SAMPLE

A group of 13 hearing-impaired subjects evaluated the hearing aids. Nine normal-hearing listeners were used as a reference group.

RESULTS AND CONCLUSIONS

Differences in sound localization in the front-back dimension were found for different hearing aids. A large inter-subject variability was found during the front-back and elevation experiments. With ITP or ITC microphones, almost all natural spectral information was preserved. One of the BTE hearing aids, which is equipped with a directional microphone configuration, generated a sufficient amount of spectral cues to allow front-back discrimination. No significant effect of hearing aids on elevation performance in the frontal vertical plane was observed. Hearing-impaired subjects reached the same performance with and without the different hearing aids. In the unaided condition, a frequency-specific audibility correction was applied. Some of the hearing-impaired listeners reached normal hearing performance with this correction.

Spatial release from masking in normal-hearing children and children who use hearing aids

Listening to speech in competing sounds poses a major difficulty for children with impaired hearing. This study aimed to determine the ability of children (3-12 yr of age) to use spatial separation between target speech and competing babble to improve speech intelligibility. Fifty-eight children (31 with normal hearing and 27 with impaired hearing who use bilateral hearing aids) were assessed by word and sentence material. Speech reception thresholds (SRTs) were measured with speech presented from 0° azimuth, and competing babble from either 0° or ±90° azimuth. Spatial release from masking (SRM) was defined as the difference between SRTs measured with co-located speech and babble and SRTs measured with spatially separated speech and babble. On average, hearing-impaired children attained near-normal performance when speech and babble originated from the frontal source, but performed poorer than their normal-hearing peers when babble was spatially separated from target speech. On average, normal-hearing children obtained an SRM of 3 dB whereas children with hearing loss did not demonstrate SRM. Results suggest that hearing-impaired children may need enhancement in signal-to-noise ratio to hear speech in difficult listening conditions as well as normal-hearing children.

Benefit from bimodal hearing in a group of prelingually deafened adult cochlear implant users

PURPOSE

People who receive a unilateral cochlear implant find speech perception in acoustically complex situations very challenging, in part because they do not have access to binaural hearing. For cochlear implant patients with some residual hearing in the nonimplanted ear, bilateral auditory input can be obtained by the use of a cochlear implant and a contralateral conventional hearing aid. This condition is referred to as "bimodal hearing."

MATERIALS AND METHODS

We evaluated the benefits from bimodal stimulation in a group of 10 prelingually deafened adult cochlear implant users, submitted to unilateral cochlear implantation at the ENT Unit of the University of Pisa.

RESULTS

Of 10 patients, 9 decided to continue using bimodal stimulation and demonstrated improvements in speech perception both in quiet and in noise condition from bimodal hearing, in comparison to the cochlear implant alone condition.

CONCLUSIONS

Our results show that bimodal hearing offers some advantages in speech understanding in quiet and noise conditions also in prelingually deafened adults. Moreover, most of our patients reported advantages from bimodal hearing in localizing sound and in perceiving a more natural sound.

Effect of spatial separation, extended bandwidth, and compression speed on intelligibility in a competing-speech task

The benefit for speech intelligibility of extending the bandwidth of hearing aids was assessed when the target speech (sentences) and background (two talkers) were co-located or spatially separated. Also, the relative benefits of slow and fast compression were assessed. Sixteen hearing-impaired (HI) subjects with mild-to-moderate high-frequency hearing loss and eight normal-hearing (NH) subjects were tested. The target and interfering sounds were recorded using a KEMAR manikin and were located at +/-60 degrees azimuth, either co-located or spatially separated. Simulated binaural hearing-aid processing using five-channel slow or fast compression was performed offline, with gains set individually for each HI subject. Upper cutoff frequencies were 5, 7.5, or 10 kHz. Processed stimuli were presented via headphones. For both NH (unaided) and HI subjects, there was no significant effect of cutoff frequency for the co-located condition, but a small but significant benefit from increasing the cutoff frequency from 5 to 7.5 kHz for the spatially separated condition. For the HI subjects, slow compression gave slightly but significantly higher scores than fast compression for the spatially separated but not for the co-located condition. There were marked individual differences both in the benefit from extended bandwidth and in the relative benefit of slow and fast compression.

The binaural intelligibility level difference in hearing-impaired listeners: the role of supra-threshold deficits

Reduced binaural performance of hearing-impaired listeners may not only be caused by raised hearing thresholds (reduced audibility), but also by supra-threshold coding deficits in signal cues. This question was investigated in the present study using binaural intelligibility level difference (BILD) comparisons: the improvement of speech-reception threshold scores for N(0)S(π) relative to N(0)S(0) presentation conditions. Investigated was what types of supra-threshold deficits play a role in reducing BILDs in hearing-impaired subjects. BILDs were investigated for 25 mild to moderate sensorineural hearing-impaired listeners, under conditions where optimal audibility was assured. All stimuli were bandpass filtered (250-4000 Hz). A distortion-sensitivity approach was used to investigate the sensitivity of subjects BILDs to external stimulus perturbations in the phase, frequency, time, and intensity domains. The underlying assumption of this approach was that an auditory coding deficit occurring in a signal cue in a particular domain will result in a low sensitivity to external perturbations applied in that domain. Compared to reference data for listeners with normal BILDs, distortion-sensitivity data for a subgroup of eight listeners with reduced BILDs suggests that these reductions in BILD were caused by coding deficits in the phase and time domains.

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.

Masking of rippled-spectrum-pattern resolution in diotic and dichotic presentations

Using rippled noise probes, spectrum-pattern resolution was measured with and without a narrow-band noise masker. Diotic presentation of both the probe and masker (S(0)N(0) mode) resulted in decreased spectrum resolution as compared to the control (no masker) conditions. The effects of the low- and on-frequency maskers differed quantitatively, however in both cases the ability to discriminate the probe spectrum pattern was suppressed completely when the masker/probe level ratio exceeded 10dB (on-frequency masker) or 10-25dB, depending on the probe level (low-frequency masker). The effect of the high-frequency masker was negligible. Slight but noticeable releasing of the spectrum-pattern resolution was found when the probe was presented to both ears in-phase and the masker counter-phase (S(0)N(pi) mode). In conditions of the probe delivered to one ear and the masker to the other ear (S(L)N(R) mode), the effect on the spectrum-pattern resolution was slight or negligible within a wide range of the noise/probe ratio.

Role of binaural hearing in speech intelligibility and spatial release from masking using vocoded speech

A cochlear implant vocoder was used to evaluate relative contributions of spectral and binaural temporal fine-structure cues to speech intelligibility. In Study I, stimuli were vocoded, and then convolved through head related transfer functions (HRTFs) to remove speech temporal fine structure but preserve the binaural temporal fine-structure cues. In Study II, the order of processing was reversed to remove both speech and binaural temporal fine-structure cues. Speech reception thresholds (SRTs) were measured adaptively in quiet, and with interfering speech, for unprocessed and vocoded speech (16, 8, and 4 frequency bands), under binaural or monaural (right-ear) conditions. Under binaural conditions, as the number of bands decreased, SRTs increased. With decreasing number of frequency bands, greater benefit from spatial separation of target and interferer was observed, especially in the 8-band condition. The present results demonstrate a strong role of the binaural cues in spectrally degraded speech, when the target and interfering speech are more likely to be confused. The nearly normal binaural benefits under present simulation conditions and the lack of order of processing effect further suggest that preservation of binaural cues is likely to improve performance in bilaterally implanted recipients.

Potential benefits of across-aid communication for bilaterally aided people: Listening in a car

We explored whether transferring signals between two hearing aids could improve speech intelligibility in noise. This was evaluated using a simulated conversation in a car; speech was presented to the right ear and car noise was presented either to the right or both ears. In three cross-aid communication conditions, the noise in the right ear was scaled and subtracted from the noise in the left ear. Speech intelligibility was determined for a group of normally hearing listeners and a group with bilateral hearing loss. The hearing-impaired group had relatively higher intelligibility scores when the car noise was diotic, whereas the normal-hearing group had relatively higher intelligibility scores in the binaural (dichotic) conditions. The cross-aid conditions led to improved intelligibility compared to the reference conditions. The results indicate that the transfer of signals between hearing aids may be of benefit when listening to speech in a car.

Binaural redundancy and inter-aural time difference cues for patients wearing a cochlear implant and a hearing aid in opposite ears

We investigated speech perception advantages arising from the use of inter-aural time difference cues, and from the provision of redundant information by the use of a hearing aid contralateral to a cochlear implant (bimodal hearing devices). Thirty-eight subjects (14 normally hearing and 23 hearing-impaired) participated in this study. The effect of binaural redundancy was assessed by comparing the signal-to-noise ratio (SNR) required for 50% correct identification of sentences in noise when listening monaurally to that when listening binaurally. The use of inter-aural time difference cues was determined by comparing the binaural SNRs obtained with or without a noise delay of 700 micros between ears. Results indicated adults who used bimodal hearing devices benefited from binaural redundancy, but children did not. Whereas normally hearing subjects used inter-aural time difference cues to improve speech perception in noise, neither adults nor children who used bimodal hearing devices were able to do so.

Spectro-temporal characteristics of speech at high frequencies, and the potential for restoration of audibility to people with mild-to-moderate hearing loss

OBJECTIVES

It is possible for auditory prostheses to provide amplification for frequencies above 6 kHz. However, most current hearing-aid fitting procedures do not give recommended gains for such high frequencies. This study was intended to provide information that could be useful in quantifying appropriate high-frequency gains, and in establishing the population of hearing-impaired people who might benefit from such amplification.

DESIGN

The study had two parts. In the first part, wide-bandwidth recordings of normal conversational speech were obtained from a sample of male and female talkers. The recordings were used to determine the mean spectral shape over a wide frequency range, and to determine the distribution of levels (the speech dynamic range) as a function of center frequency. In the second part, audiometric thresholds were measured for frequencies of 0.125, 0.25, 0.5, 1, 2, 3, 4, 6, 8, 10, and 12.5 kHz for both ears of 31 people selected to have mild or moderate cochlear hearing loss. The hearing loss was never greater than 70 dB for any frequency up to 4 kHz.

RESULTS

The mean spectrum level of the speech fell progressively with increasing center frequency above about 0.5 kHz. For speech with an overall level of 65 dB SPL, the mean 1/3-octave level was 49 and 37 dB SPL for center frequencies of 1 and 10 kHz, respectively. The dynamic range of the speech was similar for center frequencies of 1 and 10 kHz. The part of the dynamic range below the root-mean-square level was larger than reported in previous studies. The mean audiometric thresholds at high frequencies (10 and 12.5 kHz) were relatively high (69 and 77 dB HL, respectively), even though the mean thresholds for frequencies below 4 kHz were 41 dB HL or better.

CONCLUSIONS

To partially restore audibility for a hearing loss of 65 dB at 10 kHz would require an effective insertion gain of about 36 dB at 10 kHz. With this gain, audibility could be (partly) restored for 25 of the 62 ears assessed.

Candidacy for bilateral hearing aids: a retrospective multicenter study

PURPOSE

The goal of this study was to find factors for refining candidacy criteria for bilateral hearing aid fittings. Clinical files of 1,000 consecutive hearing aid fittings were analyzed.

METHOD

Case history, audiometric, and rehabilitation data were collected from clinical files, and an extensive questionnaire on long-term outcome measures was conducted. After at least 2 years of hearing aid use, 505 questionnaires were returned. In order to compare differences in benefits between unilateral and bilateral fittings, two subgroups were composed in which most relevant variables (age, degree of hearing loss, and audiometric asymmetry) were matched for unilateral fittings (n=212) and bilateral fittings (n=477).

RESULTS

The bilateral group had significantly higher benefit scores than the unilateral group for detection, speech intelligibility in reverberation, and localization, but poorer scores for comfort of loud sounds. The benefit of bilateral hearing aids was not significantly related to the level of technology of the hearing aids.

CONCLUSION

The analysis of the relation between objective parameters and the subjective outcome measures showed that candidacy for a successful bilateral fitting could not be predicted from age, maximum speech intelligibility, employment, exposure to background noise, or social activities.

Effects of sensorineural hearing loss on visually guided attention in a multitalker environment

This study asked whether or not listeners with sensorineural hearing loss have an impaired ability to use top-down attention to enhance speech intelligibility in the presence of interfering talkers. Listeners were presented with a target string of spoken digits embedded in a mixture of five spatially separated speech streams. The benefit of providing simple visual cues indicating when and/or where the target would occur was measured in listeners with hearing loss, listeners with normal hearing, and a control group of listeners with normal hearing who were tested at a lower target-to-masker ratio to equate their baseline (no cue) performance with the hearing-loss group. All groups received robust benefits from the visual cues. The magnitude of the spatial-cue benefit, however, was significantly smaller in listeners with hearing loss. Results suggest that reduced utility of selective attention for resolving competition between simultaneous sounds contributes to the communication difficulties experienced by listeners with hearing loss in everyday listening situations.

The effects of hearing loss and age on the benefit of spatial separation between multiple talkers in reverberant rooms

This study investigated the interaction between hearing loss, reverberation, and age on the benefit of spatially separating multiple masking talkers from a target talker. Four listener groups were tested based on hearing status and age. On every trial listeners heard three different sentences spoken simultaneously by different female talkers. Listeners reported keywords from the target sentence, which was presented at a fixed and known location. Maskers were colocated with the target or presented from spatially separated and symmetrically placed loudspeakers, creating a situation with no simple "better-ear." Reverberation was also varied. The target-to-masker ratio at threshold for identification of the fixed-level target was measured by adapting the level of the maskers. On average, listeners with hearing loss showed less spatial release from masking than normal-hearing listeners. Age was a significant factor although small differences in hearing sensitivity across age groups may have contributed to this effect. Spatial release was reduced in the more reverberant room condition but in most cases a significant advantage remained. These results provide evidence for a large benefit of spatial separation in a multitalker situation that is likely due to perceptual factors. However, this benefit is significantly reduced by both hearing loss and reverberation.

The effect of age on auditory spatial attention in conditions of real and simulated spatial separation

The contributions of auditory and cognitive factors to age-dependent differences in auditory spatial attention were investigated. In conditions of real spatial separation, the target sentence was presented from a central location and competing sentences were presented from left and right locations. In conditions of simulated spatial separation, different apparent spatial locations of the target and competitors were induced using the precedence effect. The identity of the target was cued by a callsign presented either prior to or following each target sentence, and the probability that the target would be presented at the three locations was specified at the beginning of each block. Younger and older adults with normal hearing sensitivity below 4 kHz completed all 16 conditions (2-spatial separation method X 2-callsign conditions X 4-probability conditions). Overall, younger adults performed better than older adults. For both age groups, performance improved with target location certainty, with a priori target cueing, and when location differences were real rather than simulated. For both age groups, the contributions of natural spatial cues were most pronounced when the target occurred at "unlikely" spatial listening locations. This suggests that both age groups benefit similarly from richer acoustical cues and a priori information in difficult listening environments.