Spatial release from masking in children with normal hearing and with bilateral cochlear implants: effect of interferer asymmetry

Speech Recognition and Spatial Hearing in Young Adults With Down Syndrome: Relationships With Hearing Thresholds and Auditory Working Memory

OBJECTIVES

Individuals with Down syndrome (DS) have a higher incidence of hearing loss (HL) compared with their peers without developmental disabilities. Little is known about the associations between HL and functional hearing for individuals with DS. This study investigated two aspects of auditory functions, "what" (understanding the content of sound) and "where" (localizing the source of sound), in young adults with DS. Speech reception thresholds in quiet and in the presence of interferers provided insight into speech recognition, that is, the "what" aspect of auditory maturation. Insights into "where" aspect of auditory maturation were gained from evaluating speech reception thresholds in colocated versus separated conditions (quantifying spatial release from masking) as well as right versus left discrimination and sound location identification. Auditory functions in the "where" domain develop during earlier stages of cognitive development in contrast with the later developing "what" functions. We hypothesized that young adults with DS would exhibit stronger "where" than "what" auditory functioning, albeit with the potential impact of HL. Considering the importance of auditory working memory and receptive vocabulary for speech recognition, we hypothesized that better speech recognition in young adults with DS, in quiet and with speech interferers, would be associated with better auditory working memory ability and receptive vocabulary.

DESIGN

Nineteen young adults with DS (aged 19 to 24 years) participated in the study and completed assessments on pure-tone audiometry, right versus left discrimination, sound location identification, and speech recognition in quiet and with speech interferers that were colocated or spatially separated. Results were compared with published data from children and adults without DS and HL, tested using similar protocols and stimuli. Digit Span tests assessed auditory working memory. Receptive vocabulary was examined using the Peabody Picture Vocabulary Test Fifth Edition.

RESULTS

Seven participants (37%) had HL in at least 1 ear; 4 individuals had mild HL, and 3 had moderate HL or worse. Participants with mild or no HL had ≥75% correct at 5° separation on the discrimination task and sound localization root mean square errors (mean ± SD: 8.73° ± 2.63°) within the range of adults in the comparison group. Speech reception thresholds in young adults with DS were higher than all comparison groups. However, spatial release from masking did not differ between young adults with DS and comparison groups. Better (lower) speech reception thresholds were associated with better hearing and better auditory working memory ability. Receptive vocabulary did not predict speech recognition.

CONCLUSIONS

In the absence of HL, young adults with DS exhibited higher accuracy during spatial hearing tasks as compared with speech recognition tasks. Thus, auditory processes associated with the "where" pathways appear to be a relative strength than those associated with "what" pathways in young adults with DS. Further, both HL and auditory working memory impairments contributed to difficulties in speech recognition in the presence of speech interferers. Future larger-sized samples are needed to replicate and extend our findings.

Children's use of spatial and visual cues for release from perceptual masking

This study examined the role of visual speech in providing release from perceptual masking in children by comparing visual speech benefit across conditions with and without a spatial separation cue. Auditory-only and audiovisual speech recognition thresholds in a two-talker speech masker were obtained from 21 children with typical hearing (7-9 years of age) using a color-number identification task. The target was presented from a loudspeaker at 0° azimuth. Masker source location varied across conditions. In the spatially collocated condition, the masker was also presented from the loudspeaker at 0° azimuth. In the spatially separated condition, the masker was presented from the loudspeaker at 0° azimuth and a loudspeaker at -90° azimuth, with the signal from the -90° loudspeaker leading the signal from the 0° loudspeaker by 4 ms. The visual stimulus (static image or video of the target talker) was presented at 0° azimuth. Children achieved better thresholds when the spatial cue was provided and when the visual cue was provided. Visual and spatial cue benefit did not differ significantly depending on the presence of the other cue. Additional studies are needed to characterize how children's preferential use of visual and spatial cues varies depending on the strength of each cue.

A longitudinal study of cortical auditory maturation and implications of the short inter-implant delay in children with bilateral sequential cochlear implants

OBJECTIVE

This longitudinal study aimed to investigate the maturational development of P1 latency and the effects of a short inter-implant delay in children who received bilateral sequential cochlear implants.

MATERIALS AND METHODS

Fourteen children (first CI mean age: 1.4 ± 0.4 years and Second CI mean age: 3.3 ± 0.5 years) who had received sequential bilateral cochlear implants during the sensitive period for auditory maturation participated in our study. The speech-evoked cortical P1 response was recorded after the activation of the second CI at four intervals (implant activation, 3 months, 6 months, 12 months) under three listening conditions (first CI, second CI, binaural).

RESULTS

Our results showed that the P1 latencies of the second CI reached normative values within 3 months, but did not reach the P1 latency of the first CI until 12 months. We found a strong negative correlation between the inter-implant delay and the P1 latencies of the second CI when the second CI was activated.

CONCLUSION

Changes in cortical auditory responses over time resulted in normal auditory maturation in children with sequential bilateral cochlear implants during the sensitive period. The results also provide evidence that the timing of auditory experience in the first ear during the sensitive period may influence the speed of compensation in children receiving sequential cochlear implants.

Differential Effects of Binaural Pitch Fusion Range on the Benefits of Voice Gender Differences in a "Cocktail Party" Environment for Bimodal and Bilateral Cochlear Implant Users

OBJECTIVES

Some cochlear implant (CI) users are fitted with a CI in each ear ("bilateral"), while others have a CI in one ear and a hearing aid in the other ("bimodal"). Presently, evaluation of the benefits of bilateral or bimodal CI fitting does not take into account the integration of frequency information across the ears. This study tests the hypothesis that CI listeners, especially bimodal CI users, with a more precise integration of frequency information across ears ("sharp binaural pitch fusion") will derive greater benefit from voice gender differences in a multi-talker listening environment.

DESIGN

Twelve bimodal CI users and twelve bilateral CI users participated. First, binaural pitch fusion ranges were measured using the simultaneous, dichotic presentation of reference and comparison stimuli (electric pulse trains for CI ears and acoustic tones for HA ears) in opposite ears, with reference stimuli fixed and comparison stimuli varied in frequency/electrode to find the range perceived as a single sound. Direct electrical stimulation was used in implanted ears through the research interface, which allowed selective stimulation of one electrode at a time, and acoustic stimulation was used in the non-implanted ears through the headphone. Second, speech-on-speech masking performance was measured to estimate masking release by voice gender difference between target and maskers (VGRM). The VGRM was calculated as the difference in speech recognition thresholds of target sounds in the presence of same-gender or different-gender maskers.

RESULTS

Voice gender differences between target and masker talkers improved speech recognition performance for the bimodal CI group, but not the bilateral CI group. The bimodal CI users who benefited the most from voice gender differences were those who had the narrowest range of acoustic frequencies that fused into a single sound with stimulation from a single electrode from the CI in the opposite ear. There was no similar voice gender difference benefit of narrow binaural fusion range for the bilateral CI users.

CONCLUSIONS

The findings suggest that broad binaural fusion reduces the acoustical information available for differentiating individual talkers in bimodal CI users, but not for bilateral CI users. In addition, for bimodal CI users with narrow binaural fusion who benefit from voice gender differences, bilateral implantation could lead to a loss of that benefit and impair their ability to selectively attend to one talker in the presence of multiple competing talkers. The results suggest that binaural pitch fusion, along with an assessment of residual hearing and other factors, could be important for assessing bimodal and bilateral CI users.

Hearing Preservation and Spatial Hearing Outcomes After Cochlear Implantation in Children With TMPRSS3 Mutations

OBJECTIVE

Investigate hearing preservation and spatial hearing outcomes in children with TMPRSS3 mutations who received bilateral cochlear implantation.

STUDY DESIGN AND METHODS

Longitudinal case series report. Two siblings (ages, 7 and 4 yr) with TMPRSS3 mutations with down-sloping audiograms received sequential bilateral cochlear implantation with hearing preservation with low-frequency acoustic amplification and high-frequency electrical stimulation. Spatial hearing, including speech perception and localization, was assessed at three time points: preoperative, postoperative of first and second cochlear implant (CI).

RESULTS

Both children showed low-frequency hearing preservation in unaided, acoustic-only audiograms. Both children demonstrated improvements in speech perception in both quiet and noise after CI activations. The emergence of spatial hearing was observed. Each child's overall speech perception and spatial hearing when listening with bilateral CIs were within the range or better than published group data from children with bilateral CIs of other etiology.

CONCLUSION

Bilateral cochlear implantation with hearing preservation is a viable option for managing hearing loss for pediatric patients with TMPRSS3 mutations.

Spatial release of masking in children and adults in non-individualized virtual environments

The spatial release of masking (SRM) is often measured in virtual auditory environments created from head-related transfer functions (HRTFs) of a standardized adult head. Adults and children, however, differ in head dimensions and mismatched HRTFs are known to affect some aspects of binaural hearing. So far, there has been little research on HRTFs in children and it is unclear whether a large mismatch of spatial cues can degrade speech perception in complex environments. In two studies, the effect of non-individualized virtual environments on SRM accuracy in adults and children was examined. The SRMs were measured in virtual environments created from individual and non-individualized HRTFs and the equivalent real anechoic environment. Speech reception thresholds (SRTs) were measured for frontal target sentences and symmetrical speech maskers at 0° or ±90° azimuth. No significant difference between environments was observed for adults. In 7 to 12-year-old children, SRTs and SRMs improved with age, with SRMs approaching adult levels. SRTs differed slightly between environments and were significantly worse in a virtual environment based on HRTFs from a spherical head. Adult HRTFs seem sufficient to accurately measure SRTs in children even in complex listening conditions.

The Impact of Synchronized Cochlear Implant Sampling and Stimulation on Free-Field Spatial Hearing Outcomes: Comparing the ciPDA Research Processor to Clinical Processors

OBJECTIVES

Bilateral cochlear implant (BiCI) listeners use independent processors in each ear. This independence and lack of shared hardware prevents control of the timing of sampling and stimulation across ears, which precludes the development of bilaterally-coordinated signal processing strategies. As a result, these devices potentially reduce access to binaural cues and introduce disruptive artifacts. For example, measurements from two clinical processors demonstrate that independently-running processors introduce interaural incoherence. These issues are typically avoided in the laboratory by using research processors with bilaterally-synchronized hardware. However, these research processors do not typically run in real-time and are difficult to take out into the real-world due to their benchtop nature. Hence, the question of whether just applying hardware synchronization to reduce bilateral stimulation artifacts (and thereby potentially improve functional spatial hearing performance) has been difficult to answer. The CI personal digital assistant (ciPDA) research processor, which uses one clock to drive two processors, presented an opportunity to examine whether synchronization of hardware can have an impact on spatial hearing performance.

DESIGN

Free-field sound localization and spatial release from masking (SRM) were assessed in 10 BiCI listeners using both their clinical processors and the synchronized ciPDA processor. For sound localization, localization accuracy was compared within-subject for the two processor types. For SRM, speech reception thresholds were compared for spatially separated and co-located configurations, and the amount of unmasking was compared for synchronized and unsynchronized hardware. There were no deliberate changes of the sound processing strategy on the ciPDA to restore or improve binaural cues.

RESULTS

There was no significant difference in localization accuracy between unsynchronized and synchronized hardware (p = 0.62). Speech reception thresholds were higher with the ciPDA. In addition, although five of eight participants demonstrated improved SRM with synchronized hardware, there was no significant difference in the amount of unmasking due to spatial separation between synchronized and unsynchronized hardware (p = 0.21).

CONCLUSIONS

Using processors with synchronized hardware did not yield an improvement in sound localization or SRM for all individuals, suggesting that mere synchronization of hardware is not sufficient for improving spatial hearing outcomes. Further work is needed to improve sound coding strategies to facilitate access to spatial hearing cues. This study provides a benchmark for spatial hearing performance with real-time, bilaterally-synchronized research processors.

Novel Approaches to Measure Spatial Release From Masking in Children With Bilateral Cochlear Implants

OBJECTIVES

To investigate the role of auditory cues for spatial release from masking (SRM) in children with bilateral cochlear implants (BiCIs) and compare their performance with children with normal hearing (NH). To quantify the contribution to speech intelligibility benefits from individual auditory cues: head shadow, binaural redundancy, and interaural differences; as well as from multiple cues: SRM and binaural squelch. To assess SRM using a novel approach of adaptive target-masker angular separation, which provides a more functionally relevant assessment in realistic complex auditory environments.

DESIGN

Children fitted with BiCIs (N = 11) and with NH (N = 18) were tested in virtual acoustic space that was simulated using head-related transfer functions measured from individual children with BiCIs behind the ear and from a standard head and torso simulator for all NH children. In experiment I, by comparing speech reception thresholds across 4 test conditions that varied in target-masker spatial separation (colocated versus separated at 180°) and listening conditions (monaural versus binaural/bilateral listening), intelligibility benefits were derived for individual auditory cues for SRM. In experiment II, SRM was quantified using a novel measure to find the minimum angular separation (MAS) between the target and masker to achieve a fixed 20% intelligibility improvement. Target speech was fixed at either +90 or -90° azimuth on the side closer to the better ear (+90° for all NH children) and masker locations were adaptively varied.

RESULTS

In experiment I, children with BiCIs as a group had smaller intelligibility benefits from head shadow than NH children. No group difference was observed in benefits from binaural redundancy or interaural difference cues. In both groups of children, individuals who gained a larger benefit from interaural differences relied less on monaural head shadow, and vice versa. In experiment II, all children with BiCIs demonstrated measurable MAS thresholds <180° and on average larger than that from NH children. Eight of 11 children with BiCIs and all NH children had a MAS threshold <90°, requiring interaural differences only to gain the target intelligibility benefit; whereas the other 3 children with BiCIs had a MAS between 120° and 137°, requiring monaural head shadow for SRM.

CONCLUSIONS

When target and maskers were separated at 180° on opposing hemifields, children with BiCIs demonstrated greater intelligibility benefits from head shadow and interaural differences than previous literature showed with a smaller separation. Children with BiCIs demonstrated individual differences in using auditory cues for SRM. From the MAS thresholds, more than half of the children with BiCIs demonstrated robust access to interaural differences without needing additional monaural head shadow for SRM. Both experiments led to the conclusion that individualized fitting strategies in the bilateral devices may be warranted to maximize spatial hearing for children with BiCIs in complex auditory environments.

Factors underlying masking release by voice-gender differences and spatial separation cues in multi-talker listening environments in listeners with and without hearing loss

Voice-gender differences and spatial separation are important cues for auditory object segregation. The goal of this study was to investigate the relationship of voice-gender difference benefit to the breadth of binaural pitch fusion, the perceptual integration of dichotic stimuli that evoke different pitches across ears, and the relationship of spatial separation benefit to localization acuity, the ability to identify the direction of a sound source. Twelve bilateral hearing aid (HA) users (age from 30 to 75 years) and eleven normal hearing (NH) listeners (age from 36 to 67 years) were tested in the following three experiments. First, speech-on-speech masking performance was measured as the threshold target-to-masker ratio (TMR) needed to understand a target talker in the presence of either same- or different-gender masker talkers. These target-masker gender combinations were tested with two spatial configurations (maskers co-located or 60° symmetrically spatially separated from the target) in both monaural and binaural listening conditions. Second, binaural pitch fusion range measurements were conducted using harmonic tone complexes around a 200-Hz fundamental frequency. Third, absolute localization acuity was measured using broadband (125-8000 Hz) noise and one-third octave noise bands centered at 500 and 3000 Hz. Voice-gender differences between target and maskers improved TMR thresholds for both listener groups in the binaural condition as well as both monaural (left ear and right ear) conditions, with greater benefit in co-located than spatially separated conditions. Voice-gender difference benefit was correlated with the breadth of binaural pitch fusion in the binaural condition, but not the monaural conditions, ruling out a role of monaural abilities in the relationship between binaural fusion and voice-gender difference benefits. Spatial separation benefit was not significantly correlated with absolute localization acuity. In addition, greater spatial separation benefit was observed in NH listeners than in bilateral HA users, indicating a decreased ability of HA users to benefit from spatial release from masking (SRM). These findings suggest that sharp binaural pitch fusion may be important for maximal speech perception in multi-talker environments for both NH listeners and bilateral HA users.

Spatial release from masking in reverberation for school-age children

Understanding speech in noisy environments, such as classrooms, is a challenge for children. When a spatial separation is introduced between the target and masker, as compared to when both are co-located, children demonstrate intelligibility improvement of the target speech. Such intelligibility improvement is known as spatial release from masking (SRM). In most reverberant environments, binaural cues associated with the spatial separation are distorted; the extent to which such distortion will affect children's SRM is unknown. Two virtual acoustic environments with reverberation times between 0.4 s and 1.1 s were compared. SRM was measured using a spatial separation with symmetrically displaced maskers to maximize access to binaural cues. The role of informational masking in modulating SRM was investigated through voice similarity between the target and masker. Results showed that, contradictory to previous developmental findings on free-field SRM, children's SRM in reverberation has not yet reached maturity in the 7-12 years age range. When reducing reverberation, an SRM improvement was seen in adults but not in children. Our findings suggest that, even though school-age children have access to binaural cues that are distorted in reverberation, they demonstrate immature use of such cues for speech-in-noise perception, even in mild reverberation.

Functional Consequences of Poor Binaural Hearing in Development: Evidence From Children With Unilateral Hearing Loss and Children Receiving Bilateral Cochlear Implants

Poor binaural hearing in children was hypothesized to contribute to related cognitive and academic deficits. Children with unilateral hearing have normal hearing in one ear but no access to binaural cues. Their cognitive and academic deficits could be unique from children receiving bilateral cochlear implants (CIs) at young ages who have poor access to spectral cues and impaired binaural sensitivity. Both groups are at risk for vestibular/balance deficits which could further contribute to memory and learning challenges. Eighty-eight children (43 male:45 female, aged 9.89  ±  3.40 years), grouped by unilateral hearing loss (n = 20), bilateral CI (n = 32), and typically developing (n = 36), completed a battery of sensory, cognitive, and academic tests. Analyses revealed that children in both hearing loss groups had significantly poorer skills (accounting for age) on most tests than their normal hearing peers. Children with unilateral hearing loss had more asymmetric speech perception than children with bilateral CIs (p < .0001) but balance and language deficits (p = .0004, p < .0001, respectively) were similar in the two hearing loss groups (p > .05). Visuospatial memory deficits occurred in both hearing loss groups (p = .02) but more consistently across tests in children with unilateral hearing loss. Verbal memory was not significantly different than normal (p > .05). Principal component analyses revealed deficits in a main cluster of visuospatial memory, oral language, mathematics, and reading measures (explaining 46.8% data variability). The remaining components revealed clusters of self-reported hearing, balance and vestibular function, and speech perception deficits. The findings indicate significant developmental impacts of poor binaural hearing in children.

The Feasibility and Reliability of a Digits-in-Noise Test in the Clinical Follow-Up of Children With Mild to Profound Hearing Loss

OBJECTIVES

Speech perception in noise is an important aspect of the rehabilitation of children with hearing loss. We aimed to evaluate the feasibility and reliability of the Dutch digits-in-noise (DIN) test in the clinical follow-up of children with hearing aids (HAs) and/or cochlear implants (CIs). A second aim of the study was to gain insight in the speech perception in noise performance of children with different degrees of hearing loss.

DESIGN

We retrospectively analyzed DIN test data of Dutch-speaking children with hearing loss (N = 188; 5 to 18 years old). A free-field version of the DIN-test was used. Children with open-set phoneme recognition in quiet of >70% at 65 dB SPL (best aided condition) were included. Ages ranged from 5 to 18 years old. All were experienced HA or CI users and had used their device(s) for at least 1 year before the measurement in the study. The DIN-test was performed in the framework of a clinical rehabilitation program. During testing, children wore their own devices with normal daily programs.

RESULTS

The average speech reception threshold (SRT) was -3.6 dB (SD 3.6) for the first list and significantly improved to -4.0 dB (SD 3.1) for the second list. HA users had a 4-dB better SRT compared with CI users. The larger the child's hearing loss, the worse the SRT is. However, 15% of the children who completed a first list of 24 trials were unable to complete a second list. Mean adaptive staircase trajectories across trials suggested that learning occurred throughout the first list, and that loss of sustained attention contributed to response variability during the second list.

CONCLUSION

The DIN test can be used to assess speech perception in noise abilities for children with different degrees of hearing loss and using HAs or CIs. The children with hearing loss required a higher signal-to-noise ratio (SNR) than did normal-hearing children and the required SNR is larger as the hearing loss increases. However, the current measurement procedure should be optimized for use in standard pediatric audiological care, as 15% of the children were unable to conduct a second list after the first list to reach a more stable SNR.

Spatial Hearing Difficulties in Reaching Space in Bilateral Cochlear Implant Children Improve With Head Movements

Supplemental Digital Content is available in the text.

The aim of this study was to assess three-dimensional (3D) spatial hearing abilities in reaching space of children and adolescents fitted with bilateral cochlear implants (BCI). The study also investigated the impact of spontaneous head movements on sound localization abilities.

Benefits of triple acoustic beamforming during speech-on-speech masking and sound localization for bilateral cochlear-implant users

Bilateral cochlear-implant (CI) users struggle to understand speech in noisy environments despite receiving some spatial-hearing benefits. One potential solution is to provide acoustic beamforming. A headphone-based experiment was conducted to compare speech understanding under natural CI listening conditions and for two non-adaptive beamformers, one single beam and one binaural, called "triple beam," which provides an improved signal-to-noise ratio (beamforming benefit) and usable spatial cues by reintroducing interaural level differences. Speech reception thresholds (SRTs) for speech-on-speech masking were measured with target speech presented in front and two maskers in co-located or narrow/wide separations. Numerosity judgments and sound-localization performance also were measured. Natural spatial cues, single-beam, and triple-beam conditions were compared. For CI listeners, there was a negligible change in SRTs when comparing co-located to separated maskers for natural listening conditions. In contrast, there were 4.9- and 16.9-dB improvements in SRTs for the beamformer and 3.5- and 12.3-dB improvements for triple beam (narrow and wide separations). Similar results were found for normal-hearing listeners presented with vocoded stimuli. Single beam improved speech-on-speech masking performance but yielded poor sound localization. Triple beam improved speech-on-speech masking performance, albeit less than the single beam, and sound localization. Thus, triple beam was the most versatile across multiple spatial-hearing domains.

The Role of Interaural Differences, Head Shadow, and Binaural Redundancy in Binaural Intelligibility Benefits Among School-Aged Children

In complex listening environments, children can benefit from auditory spatial cues to understand speech in noise. When a spatial separation is introduced between the target and masker and/or listening with two ears versus one ear, children can gain intelligibility benefits with access to one or more auditory cues for unmasking: monaural head shadow, binaural redundancy, and interaural differences. This study systematically quantified the contribution of individual auditory cues in providing binaural speech intelligibility benefits for children with normal hearing between 6 and 15 years old. In virtual auditory space, target speech was presented from  + 90° azimuth (i.e., listener's right), and two-talker babble maskers were either co-located (+ 90° azimuth) or separated by 180° (-90° azimuth, listener's left). Testing was conducted over headphones in monaural (i.e., right ear) or binaural (i.e., both ears) conditions. Results showed continuous improvement of speech reception threshold (SRT) between 6 and 15 years old and immature performance at 15 years of age for both SRTs and intelligibility benefits from more than one auditory cue. With early maturation of head shadow, the prolonged maturation of unmasking was likely driven by children's poorer ability to gain full benefits from interaural difference cues. In addition, children demonstrated a trade-off between the benefits from head shadow versus interaural differences, suggesting an important aspect of individual differences in accessing auditory cues for binaural intelligibility benefits during development.

Spatial Release From Informational and Energetic Masking in Bimodal and Bilateral Cochlear Implant Users

Purpose Spatially separating speech and background noise improves speech understanding in normal-hearing listeners, an effect referred to as spatial release from masking (SRM). In cochlear implant (CI) users, SRM has often been demonstrated using asymmetric noise configurations, which maximize benefit from head shadow and the potential availability of binaural cues. In contrast, SRM in symmetrical configurations has been minimal to absent in CI users. We examined the interaction between two types of maskers (informational and energetic) and SRM in bimodal and bilateral CI users. We hypothesized that SRM would be absent or "negative" using symmetrically separated noise maskers. Second, we hypothesized that bimodal listeners would exhibit greater release from informational masking due to access to acoustic information in the non-CI ear. Method Participants included 10 bimodal and 10 bilateral CI users. Speech understanding in noise was tested in 24 conditions: 3 spatial configurations (S₀N₀, S₀N_45&315, S₀N_90&270) × 2 masker types (speech, signal-correlated noise) × 2 listening configurations (best-aided, CI-alone) × 2 talker gender conditions (different-gender, same-gender). Results In support of our first hypothesis, both groups exhibited negative SRM with increasing spatial separation. In opposition to our second hypothesis, both groups exhibited similar magnitudes of release from informational masking. The magnitude of release was greater for bimodal listeners, though this difference failed to reach statistical significance. Conclusions Both bimodal and bilateral CI recipients exhibited negative SRM. This finding is consistent with CI signal processing limitations, the audiologic factors associated with SRM, and known effects of behind-the-ear microphone technology. Though release from informational masking was not significantly different across groups, the magnitude of release was greater for bimodal listeners. This suggests that bimodal listeners may be at least marginally more susceptible to informational masking than bilateral CI users, though further research is warranted.

Auditory Attention and Spatial Unmasking in Children With Cochlear Implants

The ability to attend to target speech in background noise is an important skill, particularly for children who spend many hours in noisy environments. Intelligibility improves as a result of spatial or binaural unmasking in the free-field for normal-hearing children; however, children who use bilateral cochlear implants (BiCIs) demonstrate little benefit in similar situations. It was hypothesized that poor auditory attention abilities might explain the lack of unmasking observed in children with BiCIs. Target and interferer speech stimuli were presented to either or both ears of BiCI participants via their clinical processors. Speech reception thresholds remained low when the target and interferer were in opposite ears, but they did not show binaural unmasking when the interferer was presented to both ears and the target only to one ear. These results demonstrate that, in the most extreme cases of stimulus separation, children with BiCIs can ignore an interferer and attend to target speech, but there is weak or absent binaural unmasking. It appears that children with BiCIs mostly experience poor encoding of binaural cues rather than deficits in ability to selectively attend to target speech.

Speech-in-Noise and Quality-of-Life Measures in School-Aged Children With Normal Hearing and With Unilateral Hearing Loss

OBJECTIVES

(1) Measure sentence recognition in co-located and spatially separated target and masker configurations in school-aged children with unilateral hearing loss (UHL) and with normal hearing (NH). (2) Compare self-reported hearing-related quality-of-life (QoL) scores in school-aged children with UHL and NH.

DESIGN

Listeners were school-aged children (6 to 12 yrs) with permanent UHL (n = 41) or NH (n = 35) and adults with NH (n = 23). Sentence reception thresholds (SRTs) were measured using Hearing In Noise Test-Children sentences in quiet and in the presence of 2-talker child babble or a speech-shaped noise masker in target/masker spatial configurations: 0/0, 0/-60, 0/+60, or 0/±60 degrees azimuth. Maskers were presented at a fixed level of 55 dBA, while the level of the target sentences varied adaptively to estimate the SRT. Hearing-related QoL was measured using the Hearing Environments and Reflection on Quality of Life (HEAR-QL-26) questionnaire for child subjects.

RESULTS

As a group, subjects with unaided UHL had higher (poorer) SRTs than age-matched peers with NH in all listening conditions. Effects of age, masker type, and spatial configuration of target and masker signals were found. Spatial release from masking was significantly reduced in conditions where the masker was directed toward UHL subjects' normal-hearing ear. Hearing-related QoL scores were significantly poorer in subjects with UHL compared to those with NH. Degree of UHL, as measured by four-frequency pure-tone average, was significantly correlated with SRTs only in the two conditions where the masker was directed towards subjects' normal-hearing ear, although the unaided Speech Intelligibility Index at 65 dB SPL was significantly correlated with SRTs in four conditions, some of which directed the masker to the impaired ear or both ears. Neither pure-tone average nor unaided Speech Intelligibility Index was correlated with QoL scores.

CONCLUSIONS

As a group, school-aged children with UHL showed substantial reductions in masked speech perception and hearing-related QoL, irrespective of sex, laterality of hearing loss, and degree of hearing loss. While some children demonstrated normal or near-normal performance in certain listening conditions, a disproportionate number of thresholds fell in the poorest decile of the NH data. These findings add to the growing literature challenging the past assumption that one ear is "good enough."

Speech-in-Noise Perception in Children With Cochlear Implants, Hearing Aids, Developmental Language Disorder and Typical Development: The Effects of Linguistic and Cognitive Abilities

Children with hearing loss, and those with language disorders, can have excellent speech recognition in quiet, but still experience unique challenges when listening to speech in noisy environments. However, little is known about how speech-in-noise (SiN) perception relates to individual differences in cognitive and linguistic abilities in these children. The present study used the Norwegian version of the Hearing in Noise Test (HINT) to investigate SiN perception in 175 children aged 5.5-12.9 years, including children with cochlear implants (CI, n = 64), hearing aids (HA, n = 37), developmental language disorder (DLD, n = 16) and typical development (TD, n = 58). Further, the study examined whether general language ability, verbal memory span, non-verbal IQ and speech perception of monosyllables and sentences in quiet were predictors of performance on the HINT. To allow comparisons across ages, scores derived from age-based norms were used for the HINT and the tests of language and cognition. There were significant differences in SiN perception between all the groups except between the HA and DLD groups, with the CI group requiring the highest signal-to-noise ratios (i.e., poorest performance) and the TD group requiring the lowest signal-to-noise ratios. For the full sample, language ability explained significant variance in HINT performance beyond speech perception in quiet. Follow-up analyses for the separate groups revealed that language ability was a significant predictor of HINT performance for children with CI, HA, and DLD, but not for children with TD. Memory span and IQ did not predict variance in SiN perception when language ability and speech perception in quiet were taken into account. The finding of a robust relation between SiN perception and general language skills in all three clinical groups call for further investigation into the mechanisms that underlie this association.

Auditory, Cognitive, and Linguistic Factors Predict Speech Recognition in Adverse Listening Conditions for Children With Hearing Loss

Objectives: Children with hearing loss listen and learn in environments with noise and reverberation, but perform more poorly in noise and reverberation than children with normal hearing. Even with amplification, individual differences in speech recognition are observed among children with hearing loss. Few studies have examined the factors that support speech understanding in noise and reverberation for this population. This study applied the theoretical framework of the Ease of Language Understanding (ELU) model to examine the influence of auditory, cognitive, and linguistic factors on speech recognition in noise and reverberation for children with hearing loss.

Design: Fifty-six children with hearing loss and 50 age-matched children with normal hearing who were 7–10 years-old participated in this study. Aided sentence recognition was measured using an adaptive procedure to determine the signal-to-noise ratio for 50% correct (SNR50) recognition in steady-state speech-shaped noise. SNR50 was also measured with noise plus a simulation of 600 ms reverberation time. Receptive vocabulary, auditory attention, and visuospatial working memory were measured. Aided speech audibility indexed by the Speech Intelligibility Index was measured through the hearing aids of children with hearing loss.

Results: Children with hearing loss had poorer aided speech recognition in noise and reverberation than children with typical hearing. Children with higher receptive vocabulary and working memory skills had better speech recognition in noise and noise plus reverberation than peers with poorer skills in these domains. Children with hearing loss with higher aided audibility had better speech recognition in noise and reverberation than peers with poorer audibility. Better audibility was also associated with stronger language skills.

Conclusions: Children with hearing loss are at considerable risk for poor speech understanding in noise and in conditions with noise and reverberation. Consistent with the predictions of the ELU model, children with stronger vocabulary and working memory abilities performed better than peers with poorer skills in these domains. Better aided speech audibility was associated with better recognition in noise and noise plus reverberation conditions for children with hearing loss. Speech audibility had direct effects on speech recognition in noise and reverberation and cumulative effects on speech recognition in noise through a positive association with language development over time.

Spatial Release From Masking Under Different Reverberant Conditions in Young and Elderly Subjects: Effect of Moving or Stationary Maskers at Circular and Radial Conditions

Purpose Normal-hearing and hard-of-hearing listeners suffer from reduced speech intelligibility in noisy and reverberant environments. Although daily listening environments are in constant motion, most researchers have only studied speech-in-noise perception for stationary masker locations. The aim of this study was to investigate the spatial release from masking (SRM) of circularly and radially moving maskers under different room acoustic conditions for young and elderly subjects. Method Twelve young subjects with normal hearing and 12 elderly subjects with normal hearing or mild hearing loss were tested. Several different room acoustic conditions were simulated and reproduced via headphones using binaural synthesis. The target speech stream consisted of German digit triplets, and masker stream consisted of quasistationary noise with matched long-term averaged speech spectra. During the experiment, the position of the masker was changed to be in different stationary positions, or varied continuously. In the latter case, it was moved either on a circular trajectory spanning a 90° azimuth angle or on a radial trajectory linearly increasing the distance to the receiver from 0.5 m to 1.8 m. Absorption characteristics of the virtual room's surfaces were changed, recreating an anechoic room, a treated room with mean reverberation times (RT60) = 0.48 s, and an untreated room with mean RT60 = 1.26 s. Results For the circular condition, a significant difference was found between moving and stationary maskers, F(4, 44) = 20.91, p < .001, with a bigger SRM for stationary maskers than moving masker conditions. Also, both age groups displayed a significant decrease in SRM over the reverberation conditions: F(2, 22) = 12.24, p < .001. For the radial condition, both age groups showed a significant decrease in SRM over the reverberation conditions, F(2, 22) = 13.62, p < .001, as well as the moving and stationary masker conditions, F(8, 88) = 29.23, p < .001. In general, the SRM of a moving masker decreased when the reverberation increased, especially for elderly subjects. Conclusions A radially moving masker led to improved SRM in an anechoic environment for both age groups, whereas a circularly moving masker caused degraded SRM, especially for elderly subjects in the highly reverberant environment. Supplemental Material https://doi.org/10.23641/asha.9795371.

Sound Localization in Toddlers with Normal Hearing and with Bilateral Cochlear Implants Revealed Through a Novel "Reaching for Sound" Task

BACKGROUND

Spatial hearing abilities in children with bilateral cochlear implants (BiCIs) are typically improved when two implants are used compared with a single implant. However, even with BiCIs, spatial hearing is still worse compared to normal-hearing (NH) age-matched children. Here, we focused on children who were younger than three years, hence in their toddler years. Prior research with this age focused on measuring discrimination of sounds from the right versus left.

PURPOSE

This study measured both discrimination and sound location identification in a nine-alternative forced-choice paradigm using the "reaching for sound" method, whereby children reached for sounding objects as a means of capturing their spatial hearing abilities.

RESEARCH DESIGN

Discrimination was measured with sounds randomly presented to the left versus right, and loudspeakers at fixed angles ranging from ±60° to ±15°. On a separate task, sound location identification was measured for locations ranging from ±60° in 15° increments.

STUDY SAMPLE

Thirteen children with BiCIs (27-42 months old) and fifteen age-matched (NH).

DATA COLLECTION AND ANALYSIS

Discrimination and sound localization were completed for all subjects. For the left-right discrimination task, participants were required to reach a criterion of 4/5 correct trials (80%) at each angular separation prior to beginning the localization task. For sound localization, data was analyzed in two ways. First, percent correct scores were tallied for each participant. Second, for each participant, the root-mean-square-error was calculated to determine the average distance between the response and stimulus, indicative of localization accuracy.

RESULTS

All BiCI users were able to discriminate left versus right at angles as small as ±15° when listening with two implants; however, performance was significantly worse when listening with a single implant. All NH toddlers also had >80% correct at ±15°. Sound localization results revealed root-mean-square errors averaging 11.15° in NH toddlers. Children in the BiCI group were generally unable to identify source location on this complex task (average error 37.03°).

CONCLUSIONS

Although some toddlers with BiCIs are able to localize sound in a manner consistent with NH toddlers, for the majority of toddlers with BiCIs, sound localization abilities are still emerging.

Effect of channel separation and interaural mismatch on fusion and lateralization in normal-hearing and cochlear-implant listeners

Bilateral cochlear implantation has provided access to some of the benefits of binaural hearing enjoyed by normal-hearing (NH) listeners. However, a gap in performance still exists between the two populations. Single-channel stimulation studies have shown that interaural place-of-stimulation mismatch (IPM) due to differences in implantation depth leads to decreased binaural fusion and lateralization of interaural time and level differences (ITDs and ILDs, respectively). While single-channel studies are informative, multi-channel stimulation is needed for good speech understanding with cochlear implants (CIs). Some multi-channel studies have shown that channel interaction due to current spread can affect ITD sensitivity. In this work, we studied the effect of IPM and channel spacing, along with their potential interaction, on binaural fusion and ITD/ILD lateralization. Experiments were conducted in adult NH listeners and CI listeners with a history of acoustic hearing. Results showed that IPM reduced the range of lateralization for ITDs but not ILDs. CI listeners were more likely to report a fused percept in the presence of IPM with multi-channel stimulation than NH listeners. However, no effect of channel spacing was found. These results suggest that IPM should be accounted for in clinical mapping practices in order to maximize bilateral CI benefits.

Spatial Release From Masking in 2-Year-Olds With Normal Hearing and With Bilateral Cochlear Implants

This study evaluated spatial release from masking (SRM) in 2- to 3-year-old children who are deaf and were implanted with bilateral cochlear implants (BiCIs), and in age-matched normal-hearing (NH) toddlers. Here, we examined whether early activation of bilateral hearing has the potential to promote SRM that is similar to age-matched NH children. Listeners were 13 NH toddlers and 13 toddlers with BiCIs, ages 27 to 36 months. Speech reception thresholds (SRTs) were measured for target speech in front (0°) and for competitors that were either Colocated in front (0°) or Separated toward the right (+90°). SRM was computed as the difference between SRTs in the front versus in the asymmetrical condition. Results show that SRTs were higher in the BiCI than NH group in all conditions. Both groups had higher SRTs in the Colocated and Separated conditions compared with Quiet, indicating masking. SRM was significant only in the NH group. In the BiCI group, the group effect of SRM was not significant, likely limited by the small sample size; however, all but two children had SRM values within the NH range. This work shows that to some extent, the ability to use spatial cues for source segregation develops by age 2 to 3 in NH children and is attainable in most of the children in the BiCI group. There is potential for the paradigm used here to be used in clinical settings to evaluate outcomes of bilateral hearing in very young children.

The MAndarin spoken word-Picture IDentification test in noise-Adaptive (MAPID-A) measures subtle speech-recognition-in-noise changes and spatial release from masking in very young children

Background

Spatial release of masking (SRM) is a measure of an individual’s ability to perform speech-noise segregation, which is usually quantified by the extent of improvement of the individual’s speech recognition performance when the noise is switched from a spatially co-located position (e.g., speech and noise both presented from the front) to a spatially separated position (e.g., speech presented from the front and noise presented from the right side) with reference to the target speech. SRM is a combined measure of head shadow and binaural unmasking benefits. SRM has only been investigated in young children at group level but not at individual participant level in the international literature due to the lack of reliable speech recognition test materials able to detect subtle statistically significant within-participant changes in speech-recognition-in-noise thresholds.

Method

The performance to signal-to-noise ratio (P-SNR) functions of twenty-four disyllabic words were obtained from 40 native Mandarin-speaking children aged 3.6–6.2 years with reported normal speech, language and hearing. The test items’ difficulty levels were homogenized by adjusting the speech intensity level of each item so that the adjusted signal-to-noise ratio for 50% correct score (SNR-50%) point of each item would overlap at the mean SNR-50% point of all test items. In the MAPID-A, the homogenized test items were randomly presented in an adaptive testing procedure at a fixed noise intensity level, but the speech intensity level of the upcoming test item varied in 2-dB SNR steps depending on the recognition result of the previous test item. The SNR reversal point is marked by a change from a decrease to an increase in the SNR or vice versa. Two successive SNR reversal points marked the boundaries of an excursion. The mid-points from 12 excursions (in dB SNR) were averaged to produce the adaptive SNR-50% measure (aSNR-50%).

Results

The aSNR-50% results were obtained from another 12 children aged 4.8–5.3 years with reported normal speech, language and hearing. The average 99% confidence interval (CI) of all participants’ mean aSNR-50% values was ±1.61 dB SNR; therefore, 3.22 dB SNR was the average critical difference required to confirm a significant difference in the scores obtained from the same participant between two test conditions. Statistically significant within-participant SRM was identified in 95% of the participants; in other words, aSNR-50% obtained from the spatially separated condition outperformed aSNR-50% obtained from the spatially co-located condition. The adaptive testing procedure was highly reliable, with an within-participant test-retest reliability of 90.6%. and significantly limited testing time to an average of 4.2 min. This research study has fulfilled its aim on detecting subtle within-participant SRM in very young children starting from 4 years of age with a reliable statistical procedure. MAPID-A offers a reliable and efficient clinical tool to investigate speech-recognition-in-noise and SRM performances in young Mandarin-speaking children.

Conclusions

The narrow CIs, high test-retest reliability, and short testing time has proven that the MAPID-A is a promising sensitive, reliable and time-efficient clinical tool to detect subtle within-participant speech-recognition-in-noise changes in children as young as 4–5 years. The MAPID-A offers a clinical tool to behaviorally track young children’s development in speech-recognition-in-noise and SRM, and to potentially review the development of the auditory neural pathway and the cerebral dominance for speech-recognition-in-noise in young children.

Factors influencing speech perception in noise for 5-year-old children using hearing aids or cochlear implants

OBJECTIVE

We investigated the factors influencing speech perception in babble for 5-year-old children with hearing loss who were using hearing aids (HAs) or cochlear implants (CIs).

DESIGN

Speech reception thresholds (SRTs) for 50% correct identification were measured in two conditions - speech collocated with babble, and speech with spatially separated babble. The difference in SRTs between the two conditions give a measure of binaural unmasking, commonly known as spatial release from masking (SRM). Multiple linear regression analyses were conducted to examine the influence of a range of demographic factors on outcomes.

STUDY SAMPLE

Participants were 252 children enrolled in the Longitudinal Outcomes of Children with Hearing Impairment (LOCHI) study.

RESULTS

Children using HAs or CIs required a better signal-to-noise ratio to achieve the same level of performance as their normal-hearing peers but demonstrated SRM of a similar magnitude. For children using HAs, speech perception was significantly influenced by cognitive and language abilities. For children using CIs, age at CI activation and language ability were significant predictors of speech perception outcomes.

CONCLUSIONS

Speech perception in children with hearing loss can be enhanced by improving their language abilities. Early age at cochlear implantation was also associated with better outcomes.

Bilateral Versus Unilateral Cochlear Implantation in Adult Listeners: Speech-On-Speech Masking and Multitalker Localization

Binaural hearing helps normal-hearing listeners localize sound sources and understand speech in noise. However, it is not fully understood how far this is the case for bilateral cochlear implant (CI) users. To determine the potential benefits of bilateral over unilateral CIs, speech comprehension thresholds (SCTs) were measured in seven Japanese bilateral CI recipients using Helen test sentences (translated into Japanese) in a two-talker speech interferer presented from the front (co-located with the target speech), ipsilateral to the first-implanted ear (at +90° or -90°), and spatially symmetric at ±90°. Spatial release from masking was calculated as the difference between co-located and spatially separated SCTs. Localization was assessed in the horizontal plane by presenting either male or female speech or both simultaneously. All measurements were performed bilaterally and unilaterally (with the first implanted ear) inside a loudspeaker array. Both SCTs and spatial release from masking were improved with bilateral CIs, demonstrating mean bilateral benefits of 7.5 dB in spatially asymmetric and 3 dB in spatially symmetric speech mixture. Localization performance varied strongly between subjects but was clearly improved with bilateral over unilateral CIs with the mean localization error reduced by 27°. Surprisingly, adding a second talker had only a negligible effect on localization.

Better-ear glimpsing with symmetrically-placed interferers in bilateral cochlear implant users

For a frontal target in spatially symmetrically placed interferers, normal hearing (NH) listeners can use "better-ear glimpsing" to select time-frequency segments with favorable signal-to-noise ratio in either ear. With an ideal monaural better-ear mask (IMBM) processing, some studies showed that NH listeners can reach similar performance as in the natural binaural listening condition, although interaural phase differences at low frequencies can further improve performance. In principle, bilateral cochlear implant (BiCI) listeners could use the same better-ear glimpsing, albeit without exploiting interaural phase differences. Speech reception thresholds of NH and BiCI listeners were measured in three interferers (speech-shaped stationary noise, nonsense speech, or single talker) either co-located with the target, symmetrically placed at ±60°, or independently presented to each ear, with and without IMBM processing. Furthermore, a bilateral noise vocoder based on the BiCI electrodogram was used in the same NH listeners. Headphone presentation and direct stimulation with head-related transfer functions for spatialization were used in NH and BiCI listeners, respectively. Compared to NH listeners, both NH listeners with vocoder and BiCI listeners showed strongly reduced binaural benefit from spatial separation. However, both groups greatly benefited from IMBM processing as part of the stimulation strategy.

Effect of audibility on better-ear glimpsing as a function of frequency in normal-hearing and hearing-impaired listeners

Better-ear glimpsing (BEG) is an auditory phenomenon that helps understanding speech in noise by utilizing interaural level differences (ILDs). The benefit provided by BEG is limited in hearing-impaired (HI) listeners by reduced audibility at high frequencies. Rana and Buchholz [(2016). J. Acoust. Soc. Am. 140(2), 1192-1205] have shown that artificially enhancing ILDs at low and mid frequencies can help HI listeners understanding speech in noise, but the achieved benefit is smaller than in normal-hearing (NH) listeners. To understand how far this difference is explained by differences in audibility, audibility was carefully controlled here in ten NH and ten HI listeners and speech reception thresholds (SRTs) in noise were measured in a spatially separated and co-located condition as a function of frequency and sensation level. Maskers were realized by noise-vocoded speech and signals were spatialized using artificially generated broadband ILDs. The spatial benefit provided by BEG and SRTs improved consistently with increasing sensation level, but was limited in the HI listeners by loudness discomfort. Further, the HI listeners performed similar to NH listeners when differences in audibility were compensated. The results help to understand the hearing aid gain that is required to maximize the spatial benefit provided by ILDs as a function of frequency.

Spatial Release From Masking in Children: Effects of Simulated Unilateral Hearing Loss

OBJECTIVES

The purpose of this study was twofold: (1) to determine the effect of an acute simulated unilateral hearing loss on children's spatial release from masking in two-talker speech and speech-shaped noise, and (2) to develop a procedure to be used in future studies that will assess spatial release from masking in children who have permanent unilateral hearing loss. There were three main predictions. First, spatial release from masking was expected to be larger in two-talker speech than in speech-shaped noise. Second, simulated unilateral hearing loss was expected to worsen performance in all listening conditions, but particularly in the spatially separated two-talker speech masker. Third, spatial release from masking was expected to be smaller for children than for adults in the two-talker masker.

DESIGN

Participants were 12 children (8.7 to 10.9 years) and 11 adults (18.5 to 30.4 years) with normal bilateral hearing. Thresholds for 50%-correct recognition of Bamford-Kowal-Bench sentences were measured adaptively in continuous two-talker speech or speech-shaped noise. Target sentences were always presented from a loudspeaker at 0° azimuth. The masker stimulus was either co-located with the target or spatially separated to +90° or -90° azimuth. Spatial release from masking was quantified as the difference between thresholds obtained when the target and masker were co-located and thresholds obtained when the masker was presented from +90° or -90° azimuth. Testing was completed both with and without a moderate simulated unilateral hearing loss, created with a foam earplug and supra-aural earmuff. A repeated-measures design was used to compare performance between children and adults, and performance in the no-plug and simulated-unilateral-hearing-loss conditions.

RESULTS

All listeners benefited from spatial separation of target and masker stimuli on the azimuth plane in the no-plug listening conditions; this benefit was larger in two-talker speech than in speech-shaped noise. In the simulated-unilateral-hearing-loss conditions, a positive spatial release from masking was observed only when the masker was presented ipsilateral to the simulated unilateral hearing loss. In the speech-shaped noise masker, spatial release from masking in the no-plug condition was similar to that obtained when the masker was presented ipsilateral to the simulated unilateral hearing loss. In contrast, in the two-talker speech masker, spatial release from masking in the no-plug condition was much larger than that obtained when the masker was presented ipsilateral to the simulated unilateral hearing loss. When either masker was presented contralateral to the simulated unilateral hearing loss, spatial release from masking was negative. This pattern of results was observed for both children and adults, although children performed more poorly overall.

CONCLUSIONS

Children and adults with normal bilateral hearing experience greater spatial release from masking for a two-talker speech than a speech-shaped noise masker. Testing in a two-talker speech masker revealed listening difficulties in the presence of disrupted binaural input that were not observed in a speech-shaped noise masker. This procedure offers promise for the assessment of spatial release from masking in children with permanent unilateral hearing loss.

The Acoustics of Word-Initial Fricatives and Their Effect on Word-Level Intelligibility in Children With Bilateral Cochlear Implants

OBJECTIVES

Previous research has found that relative to their peers with normal hearing (NH), children with cochlear implants (CIs) produce the sibilant fricatives /s/ and /∫/ less accurately and with less subphonemic acoustic contrast. The present study sought to further investigate these differences across groups in two ways. First, subphonemic acoustic properties were investigated in terms of dynamic acoustic features that indexed more than just the contrast between /s/ and /∫/. Second, the authors investigated whether such differences in subphonemic acoustic contrast between sibilant fricatives affected the intelligibility of sibilant-initial single word productions by children with CIs and their peers with NH.

DESIGN

In experiment 1, productions of /s/ and /∫/ in word-initial prevocalic contexts were elicited from 22 children with bilateral CIs (aged 4 to 7 years) who had at least 2 years of CI experience and from 22 chronological age-matched peers with NH. Acoustic features were measured from 17 points across the fricatives: peak frequency was measured to index the place of articulation contrast; spectral variance and amplitude drop were measured to index the degree of sibilance. These acoustic trajectories were fitted with growth-curve models to analyze time-varying spectral change. In experiment 2, phonemically accurate word productions that were elicited in experiment 1 were embedded within four-talker babble and played to 80 adult listeners with NH. Listeners were asked to repeat the words, and their accuracy rate was used as a measure of the intelligibility of the word productions. Regression analyses were run to test which acoustic properties measured in experiment 1 predicted the intelligibility scores from experiment 2.

RESULTS

The peak frequency trajectories indicated that the children with CIs produced less acoustic contrast between /s/ and /∫/. Group differences were observed in terms of the dynamic aspects (i.e., the trajectory shapes) of the acoustic properties. In the productions by children with CIs, the peak frequency and the amplitude drop trajectories were shallower, and the spectral variance trajectories were more asymmetric, exhibiting greater increases in variance (i.e., reduced sibilance) near the fricative-vowel boundary. The listeners' responses to the word productions indicated that when produced by children with CIs, /∫/-initial words were significantly more intelligible than /s/-initial words. However, when produced by children with NH, /s/-initial words and /∫/-initial words were equally intelligible. Intelligibility was partially predicted from the acoustic properties (Cox & Snell pseudo-R > 0.190), and the significant predictors were predominantly dynamic, rather than static, ones.

CONCLUSIONS

Productions from children with CIs differed from those produced by age-matched NH controls in terms of their subphonemic acoustic properties. The intelligibility of sibilant-initial single-word productions by children with CIs is sensitive to the place of articulation of the initial consonant (/∫/-initial words were more intelligible than /s/-initial words), but productions by children with NH were equally intelligible across both places of articulation. Therefore, children with CIs still exhibit differential production abilities for sibilant fricatives at an age when their NH peers do not.

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

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

Listening to Sentences in Noise: Revealing Binaural Hearing Challenges in Patients with Schizophrenia

OBJECTIVE

The present, case-control, study investigates binaural hearing performance in schizophrenia patients towards sentences presented in quiet and noise.

METHODS

Participants were twenty-one healthy controls and sixteen schizophrenia patients with normal peripheral auditory functions. The binaural hearing was examined in four listening conditions by using the Malay version of hearing in noise test. The syntactically and semantically correct sentences were presented via headphones to the randomly selected subjects. In each condition, the adaptively obtained reception thresholds for speech (RTS) were used to determine RTS noise composite and spatial release from masking.

RESULTS

Schizophrenia patients demonstrated significantly higher mean RTS value relative to healthy controls (p=0.018). The large effect size found in three listening conditions, i.e., in quiet (d=1.07), noise right (d=0.88) and noise composite (d=0.90) indicates statistically significant difference between the groups. However, noise front and noise left conditions show medium (d=0.61) and small (d=0.50) effect size respectively. No statistical difference between groups was noted in regards to spatial release from masking on right (p=0.305) and left (p=0.970) ear.

CONCLUSION

The present findings suggest an abnormal unilateral auditory processing in central auditory pathway in schizophrenia patients. Future studies to explore the role of binaural and spatial auditory processing were recommended.

Binaural sensitivity in children who use bilateral cochlear implants

Children who are deaf and receive bilateral cochlear implants (BiCIs) perform better on spatial hearing tasks using bilateral rather than unilateral inputs; however, they underperform relative to normal-hearing (NH) peers. This gap in performance is multi-factorial, including the inability of speech processors to reliably deliver binaural cues. Although much is known regarding binaural sensitivity of adults with BiCIs, less is known about how the development of binaural sensitivity in children with BiCIs compared to NH children. Sixteen children (ages 9-17 years) were tested using synchronized research processors. Interaural time differences and interaural level differences (ITDs and ILDs, respectively) were presented to pairs of pitch-matched electrodes. Stimuli were 300-ms, 100-pulses-per-second, constant-amplitude pulse trains. In the first and second experiments, discrimination of interaural cues (either ITDs or ILDs) was measured using a two-interval left/right task. In the third experiment, subjects reported the perceived intracranial position of ITDs and ILDs in a lateralization task. All children demonstrated sensitivity to ILDs, possibly due to monaural level cues. Children who were born deaf had weak or absent sensitivity to ITDs; in contrast, ITD sensitivity was noted in children with previous exposure to acoustic hearing. Therefore, factors such as auditory deprivation, in particular, lack of early exposure to consistent timing differences between the ears, may delay the maturation of binaural circuits and cause insensitivity to binaural differences.

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

Spatial attention in bilateral cochlear-implant users

Cochlear-implant (CI) users have difficulty understanding speech in the presence of interfering sounds. This study was designed to determine if binaural unmasking of speech is limited by peripheral or central encoding. Speech was presented to bilateral CI listeners using their clinical processors; unprocessed or vocoded speech was presented to normal-hearing (NH) listeners. Performance was worst for all listener groups in conditions where both the target and interferer were presented monaurally or diotically (i.e., no spatial differences). Listeners demonstrated improved performance compared to the monaural and diotic conditions when the target and interferer were presented to opposite ears. However, only some CI listeners demonstrated improved performance if the target was in one ear and the interferer was presented diotically, and there was no change for the group on average. This is unlike the 12-dB benefit observed in the NH group when presented the CI simulation. The results suggest that CI users can direct attention to a target talker if the target and interferer are presented to opposite ears; however, larger binaural benefits are limited for more realistic listening configurations, likely due to the imprecise peripheral encoding of the two sounds.

Does Bilateral Experience Lead to Improved Spatial Unmasking of Speech in Children Who Use Bilateral Cochlear Implants?

HYPOTHESIS

In children with bilateral cochlear implants (BiCIs), experience over a 1 to 3-year period can improve speech understanding and spatial unmasking of speech.

BACKGROUND

One reason for providing children with BiCIs is to improve spatial hearing abilities. Little is known about changes in performance with added bilateral experience, and the relation between sound localization and spatial unmasking of speech.

METHODS

Twenty children with BiCIs participated. Testing was conducted typically within a year of bilateral activation, and at 1, 2, or 3 follow-up annual intervals. All testing was done while children listened with both devices activated. Target speech was presented from front (co-located); interfering speech was from front, right (asymmetrical), or right and left (symmetrical). Speech reception thresholds (SRTs) were measured in each condition. Spatial release from masking (SRM) was quantified as the difference in SRTs between conditions with interferers at 0 degrees and 90 degrees. For 11 of the children, data are also compared with sound localization measures obtained on the same visit to the laboratory but published elsewhere.

RESULTS

Change in SRM with bilateral experience varied; some children showed improvement and others did not. Regression analyses identified relationships between SRTs and SRM. Comparison of the SRM with localization data suggests little evidence for correlations between the two spatial tasks.

CONCLUSION

In children with BiCIs spatial hearing mechanisms involved in SRM and sound localization may be different. Reasons for reduced SRM include asymmetry between the ears, and individual differences in the ability to inhibit interfering information, switch and/or sustain attention.

Bilateral cochlear implants in children: Effects of auditory experience and deprivation on auditory perception

Spatial hearing skills are essential for children as they grow, learn and play. These skills provide critical cues for determining the locations of sources in the environment, and enable segregation of important sounds, such as speech, from background maskers or interferers. Spatial hearing depends on availability of monaural cues and binaural cues. The latter result from integration of inputs arriving at the two ears from sounds that vary in location. The binaural system has exquisite mechanisms for capturing differences between the ears in both time of arrival and intensity. The major cues that are thus referred to as being vital for binaural hearing are: interaural differences in time (ITDs) and interaural differences in levels (ILDs). In children with normal hearing (NH), spatial hearing abilities are fairly well developed by age 4-5 years. In contrast, most children who are deaf and hear through cochlear implants (CIs) do not have an opportunity to experience normal, binaural acoustic hearing early in life. These children may function by having to utilize auditory cues that are degraded with regard to numerous stimulus features. In recent years there has been a notable increase in the number of children receiving bilateral CIs, and evidence suggests that while having two CIs helps them function better than when listening through a single CI, these children generally perform worse than their NH peers. This paper reviews some of the recent work on bilaterally implanted children. The focus is on measures of spatial hearing, including sound localization, release from masking for speech understanding in noise and binaural sensitivity using research processors. Data from behavioral and electrophysiological studies are included, with a focus on the recent work of the authors and their collaborators. The effects of auditory plasticity and deprivation on the emergence of binaural and spatial hearing are discussed along with evidence for reorganized processing from both behavioral and electrophysiological studies. The consequences of both unilateral and bilateral auditory deprivation during development suggest that the relevant set of issues is highly complex with regard to successes and the limitations experienced by children receiving bilateral cochlear implants. This article is part of a Special Issue entitled .

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

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

The effect of early auditory experience on the spatial listening skills of children with bilateral cochlear implants

OBJECTIVES

Both electrophysiological and behavioural studies suggest that auditory deprivation during the first months and years of life can impair listening skills. Electrophysiological studies indicate that 3½ years may be a critical age for the development of symmetrical cortical responses in children using bilateral cochlear implants. This study aimed to examine the effect of auditory experience during the first 3½ years of life on the behavioural spatial listening abilities of children using bilateral cochlear implants, with reference to normally hearing children. Data collected during research and routine clinical testing were pooled to compare the listening skills of children with bilateral cochlear implants and different periods of auditory deprivation.

METHODS

Children aged 4-17 years with bilateral cochlear implants were classified into three groups. Children born profoundly deaf were in the congenital early bilateral group (received bilateral cochlear implants aged ≤3½ years, n=28) or congenital late bilateral group (received first implant aged ≤3½ years and second aged >3½ years, n=38). Children with some bilateral acoustic hearing until the age of 3½ years, who subsequently became profoundly deaf and received bilateral cochlear implants, were in the acquired/progressive group (n=16). There were 32 children in the normally hearing group. Children completed tests of sound-source localization and spatial release from masking (a measure of the ability to use both ears to understand speech in noise).

RESULTS

The acquired/progressive group localized more accurately than both groups of congenitally deaf children (p<0.05). All three groups of children with cochlear implants showed similar spatial release from masking. The normally hearing group localized more accurately than all groups with bilateral cochlear implants and displayed more spatial release from masking than the congenitally deaf groups on average (p<0.05).

CONCLUSION

Children with bilateral cochlear implants and early experience of acoustic hearing showed more accurate localization skills, on average, than children born profoundly deaf.

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

OBJECTIVES

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

PATIENT

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

METHODS

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

RESULTS

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

CONCLUSION

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

Development of Sound Localization Strategies in Children with Bilateral Cochlear Implants

Localizing sounds in our environment is one of the fundamental perceptual abilities that enable humans to communicate, and to remain safe. Because the acoustic cues necessary for computing source locations consist of differences between the two ears in signal intensity and arrival time, sound localization is fairly poor when a single ear is available. In adults who become deaf and are fitted with cochlear implants (CIs) sound localization is known to improve when bilateral CIs (BiCIs) are used compared to when a single CI is used. The aim of the present study was to investigate the emergence of spatial hearing sensitivity in children who use BiCIs, with a particular focus on the development of behavioral localization patterns when stimuli are presented in free-field horizontal acoustic space. A new analysis was implemented to quantify patterns observed in children for mapping acoustic space to a spatially relevant perceptual representation. Children with normal hearing were found to distribute their responses in a manner that demonstrated high spatial sensitivity. In contrast, children with BiCIs tended to classify sound source locations to the left and right; with increased bilateral hearing experience, they developed a perceptual map of space that was better aligned with the acoustic space. The results indicate experience-dependent refinement of spatial hearing skills in children with CIs. Localization strategies appear to undergo transitions from sound source categorization strategies to more fine-grained location identification strategies. This may provide evidence for neural plasticity, with implications for training of spatial hearing ability in CI users.

Spatial release from masking in children with bilateral cochlear implants and with normal hearing: Effect of target-interferer similarity

In complex auditory environments, it is often difficult to separate a target talker from interfering speech. For normal hearing (NH) adult listeners, similarity between the target and interfering speech leads to increased difficulty in separating them; that is, informational masking occurs due to confusability of the target and interferers. This study investigated performance of children with bilateral cochlear implants (BiCIs) when target and interferers were either same-sex (male) talkers, or different-sex talkers (male target, female interferer). Comparisons between children with BiCIs and NH, when matched for age, were also conducted. Speech intelligibility was measured for target and interferers spatially co-located, or spatially separated with the interferers positioned symmetrically (+90° and -90°) or asymmetrically (both at +90°, right). Spatial release from masking (SRM) was computed as the difference between co-located and separated conditions. Within group BiCI comparisons revealed that in the co-located condition speech intelligibility was worse with the same-sex vs different-sex stimuli. There was also a trend for more SRM with the same-sex vs different-sex stimuli. When comparing BiCI to NH listeners, SRM was larger for the NH groups, suggesting that NH children are better able to make use of spatial cues to improve speech understanding in noise.

Impact of a moving noise masker on speech perception in cochlear implant users

Objectives

Previous studies investigating speech perception in noise have typically been conducted with static masker positions. The aim of this study was to investigate the effect of spatial separation of source and masker (spatial release from masking, SRM) in a moving masker setup and to evaluate the impact of adaptive beamforming in comparison with fixed directional microphones in cochlear implant (CI) users.

Design

Speech reception thresholds (SRT) were measured in S₀N₀ and in a moving masker setup (S₀N_move) in 12 normal hearing participants and 14 CI users (7 subjects bilateral, 7 bimodal with a hearing aid in the contralateral ear). Speech processor settings were a moderately directional microphone, a fixed beamformer, or an adaptive beamformer. The moving noise source was generated by means of wave field synthesis and was smoothly moved in a shape of a half-circle from one ear to the contralateral ear. Noise was presented in either of two conditions: continuous or modulated.

Results

SRTs in the S₀N_move setup were significantly improved compared to the S₀N₀ setup for both the normal hearing control group and the bilateral group in continuous noise, and for the control group in modulated noise. There was no effect of subject group. A significant effect of directional sensitivity was found in the S₀N_move setup. In the bilateral group, the adaptive beamformer achieved lower SRTs than the fixed beamformer setting. Adaptive beamforming improved SRT in both CI user groups substantially by about 3 dB (bimodal group) and 8 dB (bilateral group) depending on masker type.

Conclusions

CI users showed SRM that was comparable to normal hearing subjects. In listening situations of everyday life with spatial separation of source and masker, directional microphones significantly improved speech perception with individual improvements of up to 15 dB SNR. Users of bilateral speech processors with both directional microphones obtained the highest benefit.

Development of the auditory system

Auditory development involves changes in the peripheral and central nervous system along the auditory pathways, and these occur naturally, and in response to stimulation. Human development occurs along a trajectory that can last decades, and is studied using behavioral psychophysics, as well as physiologic measurements with neural imaging. The auditory system constructs a perceptual space that takes information from objects and groups, segregates sounds, and provides meaning and access to communication tools such as language. Auditory signals are processed in a series of analysis stages, from peripheral to central. Coding of information has been studied for features of sound, including frequency, intensity, loudness, and location, in quiet and in the presence of maskers. In the latter case, the ability of the auditory system to perform an analysis of the scene becomes highly relevant. While some basic abilities are well developed at birth, there is a clear prolonged maturation of auditory development well into the teenage years. Maturation involves auditory pathways. However, non-auditory changes (attention, memory, cognition) play an important role in auditory development. The ability of the auditory system to adapt in response to novel stimuli is a key feature of development throughout the nervous system, known as neural plasticity.

Development of spatial release from masking in mandarin-speaking children with normal hearing

PURPOSE

This study investigated the development of spatial release from masking in children using closed-set Mandarin disyllabic words and monosyllabic words carrying lexical tones as test stimuli and speech spectrum-weighted noise as a masker.

METHOD

Twenty-six children ages 4-9 years and 12 adults, all with normal hearing, participated in speech recognition tests under 2 conditions: (a) speech and noise spatially mixed and presented from the front (NF), and (b) speech presented from the front with noise spatially separated and presented from the side (NS) with different signal-to-noise ratios (SNRs). Performance-SNR psychometric functions were obtained that generated the SNR for a 50% correct score (SNR-50%) as the outcome measure.

RESULTS

In the child participants, SNR-50% improved with age in NS but not NF. The difference in SNR-50% between NS and NF-the spatial release from masking (SRM)-increased with age with an average improvement of 0.1-0.15 dB per month.

CONCLUSIONS

SRM has a long developmental time, at least up to 9 years of age, which is significantly longer than some previous developmental studies have suggested. The child participants had not yet reached the adult SRM performance level. SRM is a potential clinical measure to reflect the maturation of spatial auditory processing.

What can we expect of normally-developing children implanted at a young age with respect to their auditory, linguistic and cognitive skills?

As a result of neonatal hearing screening and subsequent early cochlear implantation (CI) profoundly deaf children have access to important information to process auditory signals and master spoken language skills at a young age. Nevertheless, auditory, linguistic and cognitive outcome measures still reveal great variability in individual achievements: some children with CI(s) perform within normal limits, while others lag behind. Understanding the causes of this variation would allow clinicians to offer better prognoses to CI candidates and efficient follow-up and rehabilitation. This paper summarizes what we can expect of normally developing children with CI(s) with regard to spoken language, bilateral and binaural auditory perception, speech perception and cognitive skills. Predictive factors of performance and factors influencing variability are presented, as well as some novel data on cognitive functioning and speech perception in quiet and in noise. Subsequently, we discuss technical and non-technical issues which should be considered in the future in order to optimally guide the child with profound hearing difficulties. This article is part of a Special Issue entitled <Lasker Award>.

Spatial hearing benefits demonstrated with presentation of acoustic temporal fine structure cues in bilateral cochlear implant listeners

Most contemporary cochlear implant (CI) processing strategies discard acoustic temporal fine structure (TFS) information, and this may contribute to the observed deficits in bilateral CI listeners' ability to localize sounds when compared to normal hearing listeners. Additionally, for best speech envelope representation, most contemporary speech processing strategies use high-rate carriers (≥900 Hz) that exceed the limit for interaural pulse timing to provide useful binaural information. Many bilateral CI listeners are sensitive to interaural time differences (ITDs) in low-rate (<300 Hz) constant-amplitude pulse trains. This study explored the trade-off between superior speech temporal envelope representation with high-rate carriers and binaural pulse timing sensitivity with low-rate carriers. The effects of carrier pulse rate and pulse timing on ITD discrimination, ITD lateralization, and speech recognition in quiet were examined in eight bilateral CI listeners. Stimuli consisted of speech tokens processed at different electrical stimulation rates, and pulse timings that either preserved or did not preserve acoustic TFS cues. Results showed that CI listeners were able to use low-rate pulse timing cues derived from acoustic TFS when presented redundantly on multiple electrodes for ITD discrimination and lateralization of speech stimuli.

Improving speech-in-noise recognition for children with hearing loss: potential effects of language abilities, binaural summation, and head shadow

OBJECTIVE

This study examined speech recognition in noise for children with hearing loss, compared it to recognition for children with normal hearing, and examined mechanisms that might explain variance in children's abilities to recognize speech in noise.

DESIGN

Word recognition was measured in two levels of noise, both when the speech and noise were co-located in front and when the noise came separately from one side. Four mechanisms were examined as factors possibly explaining variance: vocabulary knowledge, sensitivity to phonological structure, binaural summation, and head shadow.

STUDY SAMPLE

Participants were 113 eight-year-old children. Forty-eight had normal hearing (NH) and 65 had hearing loss: 18 with hearing aids (HAs), 19 with one cochlear implant (CI), and 28 with two CIs.

RESULTS

Phonological sensitivity explained a significant amount of between-groups variance in speech-in-noise recognition. Little evidence of binaural summation was found. Head shadow was similar in magnitude for children with NH and with CIs, regardless of whether they wore one or two CIs. Children with HAs showed reduced head shadow effects.

CONCLUSION

These outcomes suggest that in order to improve speech-in-noise recognition for children with hearing loss, intervention needs to be comprehensive, focusing on both language abilities and auditory mechanisms.

Effect of mismatched place-of-stimulation on binaural fusion and lateralization in bilateral cochlear-implant users

Bilateral cochlear implants (CIs) have provided some success in improving spatial hearing abilities to patients, but with large variability in performance. One reason for the variability is that there may be a mismatch in the place-of-stimulation arising from electrode arrays being inserted at different depths in each cochlea. Goupell et al. [(2013b). J. Acoust. Soc. Am. 133(4), 2272-2287] showed that increasing interaural mismatch led to non-fused auditory images and poor lateralization of interaural time differences in normal hearing subjects listening to a vocoder. However, a greater bandwidth of activation helped mitigate these effects. In the present study, the same experiments were conducted in post-lingually deafened bilateral CI users with deliberate and controlled interaural mismatch of single electrode pairs. Results show that lateralization was still possible with up to 3 mm of interaural mismatch, even when off-center, or multiple, auditory images were perceived. However, mismatched inputs are not ideal since it leads to a distorted auditory spatial map. Comparison of CI and normal hearing listeners showed that the CI data were best modeled by a vocoder using Gaussian-pulsed tones with 1.5 mm bandwidth. These results suggest that interaural matching of electrodes is important for binaural cues to be maximally effective.