Speech intelligibility and localization in a multi-source environment

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.

Learning effects in speech-in-noise tasks: Effect of masker modulation and masking release

Previous research has shown that learning effects are present for speech intelligibility in temporally modulated (TM) noise, but not in stationary noise. The present study aimed to gain more insight into the factors that might affect the time course (the number of trials required to reach stable performance) and size [the improvement in the speech reception threshold (SRT)] of the learning effect. Two hypotheses were addressed: (1) learning effects are present in both TM and spectrally modulated (SM) noise and (2) the time course and size of the learning effect depend on the amount of masking release caused by either TM or SM noise. Eighteen normal-hearing adults (23-62 years) participated in SRT measurements, in which they listened to sentences in six masker conditions, including stationary, TM, and SM noise conditions. The results showed learning effects in all TM and SM noise conditions, but not for the stationary noise condition. The learning effect was related to the size of masking release: a larger masking release was accompanied by an increased time course of the learning effect and a larger learning effect. The results also indicate that speech is processed differently in SM noise than in TM noise.

Spatial Hearing in Children With and Without Hearing Loss: Where and What the Speech Is Matters for Local Speech Intelligibility

PURPOSE

This study examined children's ability to perceive speech from multiple locations on the horizontal plane. Children with hearing loss were compared to normal-hearing peers while using amplification with and without advanced noise management.

METHOD

Participants were 21 children with normal hearing (9-15 years) and 12 children with moderate symmetrical hearing loss (11-15 years). Word recognition, nonword detection, and word recall were assessed. Stimuli were presented randomly from multiple discrete locations in multitalker noise. Children with hearing loss were fit with devices having separate omnidirectional and noise management programs. The noise management feature is designed to preserve audibility in noise by rapidly analyzing input from all locations and reducing the noise management when speech is detected from locations around the hearing aid user.

RESULTS

Significant effects of left/right and front/back lateralization occurred as well as effects of hearing loss and hearing aid noise management. Children with normal hearing experienced a left-side advantage for word recognition and a right-side advantage for nonword detection. Children with hearing loss demonstrated poorer performance overall on all tasks with better word recognition from the back, and word recall from the right, in the omnidirectional condition. With noise management, performance improved from the front compared to the back for all three tasks and from the right for word recognition and word recall.

CONCLUSIONS

The shape of children's local speech intelligibility on the horizontal plane is not omnidirectional. It is task dependent and shaped further by hearing loss and hearing aid signal processing. Front/back shifts in children with hearing loss are consistent with the behavior of hearing aid noise management, while the right-side biases observed in both groups are consistent with the effects of specialized speech processing in the left hemisphere of the brain.

Effects of spatial configuration and fundamental frequency on speech intelligibility in multiple-talker conditions in the ipsilateral horizontal plane and median planea)

Spatial separation and fundamental frequency (F0) separation are effective cues for improving the intelligibility of target speech in multi-talker scenarios. Previous studies predominantly focused on spatial configurations within the frontal hemifield, overlooking the ipsilateral side and the entire median plane, where localization confusion often occurs. This study investigated the impact of spatial and F0 separation on intelligibility under the above-mentioned underexplored spatial configurations. The speech reception thresholds were measured through three experiments for scenarios involving two to four talkers, either in the ipsilateral horizontal plane or in the entire median plane, utilizing monotonized speech with varying F0s as stimuli. The results revealed that spatial separation in symmetrical positions (front-back symmetry in the ipsilateral horizontal plane or front-back, up-down symmetry in the median plane) contributes positively to intelligibility. Both target direction and relative target-masker separation influence the masking release attributed to spatial separation. As the number of talkers exceeds two, the masking release from spatial separation diminishes. Nevertheless, F0 separation remains as a remarkably effective cue and could even facilitate spatial separation in improving intelligibility. Further analysis indicated that current intelligibility models encounter difficulties in accurately predicting intelligibility in scenarios explored in this study.

Effects of type of emission and masking sound, and their spatial correspondence, on blind and sighted people's ability to echolocate

Ambient sound can mask acoustic signals. The current study addressed how echolocation in people is affected by masking sound, and the role played by type of sound and spatial (i.e. binaural) similarity. We also investigated the role played by blindness and long-term experience with echolocation, by testing echolocation experts, as well as blind and sighted people new to echolocation. Results were obtained in two echolocation tasks where participants listened to binaural recordings of echolocation and masking sounds, and either localized echoes in azimuth or discriminated echo audibility. Echolocation and masking sounds could be either clicks or broad band noise. An adaptive staircase method was used to adjust signal-to-noise ratios (SNRs) based on participants' responses. When target and masker had the same binaural cues (i.e. both were monoaural sounds), people performed better (i.e. had lower SNRs) when target and masker used different types of sound (e.g. clicks in noise-masker or noise in clicks-masker), as compared to when target and masker used the same type of sound (e.g. clicks in click-, or noise in noise-masker). A very different pattern of results was observed when masker and target differed in their binaural cues, in which case people always performed better when clicks were the masker, regardless of type of emission used. Further, direct comparison between conditions with and without binaural difference revealed binaural release from masking only when clicks were used as emissions and masker, but not otherwise (i.e. when noise was used as masker or emission). This suggests that echolocation with clicks or noise may differ in their sensitivity to binaural cues. We observed the same pattern of results for echolocation experts, and blind and sighted people new to echolocation, suggesting a limited role played by long-term experience or blindness. In addition to generating novel predictions for future work, the findings also inform instruction in echolocation for people who are blind or sighted.

Multimodal language in child-directed versus adult-directed speech

Speakers design their multimodal communication according to the needs and knowledge of their interlocutors, phenomenon known as audience design. We use more sophisticated language (e.g., longer sentences with complex grammatical forms) when communicating with adults compared with children. This study investigates how speech and co-speech gestures change in adult-directed speech (ADS) versus child-directed speech (CDS) for three different tasks. Overall, 66 adult participants (Mage = 21.05, 60 female) completed three different tasks (story-reading, storytelling and address description) and they were instructed to pretend to communicate with a child (CDS) or an adult (ADS). We hypothesised that participants would use more complex language, more beat gestures, and less iconic gestures in the ADS compared with the CDS. Results showed that, for CDS, participants used more iconic gestures in the story-reading task and storytelling task compared with ADS. However, participants used more beat gestures in the storytelling task for ADS than CDS. In addition, language complexity did not differ across conditions. Our findings indicate that how speakers employ different types of gestures (iconic vs beat) according to the addressee's needs and across different tasks. Speakers might prefer to use more iconic gestures with children than adults. Results are discussed according to audience design theory.

Relationships between bilateral auditory brainstem activity and inter-implant interval in children with cochlear implants

PURPOSE

To investigate the effect of the interval between bilateral cochlear implantation on the development of bilateral peripheral auditory pathways as revealed by the electrically evoked auditory brainstem response (EABR).

METHODS

Fifty-eight children with profound bilateral sensorineural hearing loss were recruited. Among them, 33 children received sequential bilateral cochlear implants (CIs), and 25 children received simultaneous bilateral CIs. The bilateral EABRs evoked by electrical stimulation from the CI electrode were recorded on the day of second-side CI activation.

RESULTS

The latencies of wave III (eIII) and wave V (eV) were significantly shorter on the first CI side than on the second CI side in children with sequential bilateral CIs but were similar between the two sides in children with simultaneous bilateral CIs. Furthermore, the latencies were prolonged from apical to basal channels along the cochlea in the two groups. In children with sequential CIs, the inter-implant interval was negatively correlated with the eV latency on the first CI side and was positively correlated with bilateral differences in the eIII and eV latencies.

CONCLUSIONS

Unilateral CI use promotes the maturation of ipsilateral auditory conduction function. However, a longer inter-implant interval results in more unbalanced development of bilateral auditory brainstem pathways. Bilateral cochlear implantation with no or a short interval is recommended.

Spatial Release From Masking With Bilateral Bone Conduction Stimulation at Mastoid for Normal Hearing Subjects

This study investigates the effect of spatial release from masking (SRM) in bilateral bone conduction (BC) stimulation at the mastoid. Nine adults with normal hearing were tested to determine SRM based on speech recognition thresholds (SRTs) in simulated spatial configurations ranging from 0 to 180 degrees. These configurations were based on nonindividualized head-related transfer functions. The participants were subjected to sound stimulation through either air conduction (AC) via headphones or BC. The results indicated that both the angular separation between the target and the masker, and the modality of sound stimulation, significantly influenced speech recognition performance. As the angular separation between the target and the masker increased up to 150°, both BC and AC SRTs decreased, indicating improved performance. However, performance slightly deteriorated when the angular separation exceeded 150°. For spatial separations less than 75°, BC stimulation provided greater spatial benefits than AC, although this difference was not statistically significant. For separations greater than 75°, AC stimulation offered significantly more spatial benefits than BC. When speech and noise originated from the same side of the head, the "better ear effect" did not significantly contribute to SRM. However, when speech and noise were located on opposite sides of the head, this effect became dominant in SRM.

Effects of entropy in real-world noise on speech perception in listeners with normal hearing and hearing lossa)

Hearing aids show more benefit in traditional laboratory speech-in-noise tests than in real-world noisy environments. Real-world noise comprises a large range of acoustic properties that vary randomly and rapidly between and within environments, making quantifying real-world noise and using it in experiments and clinical tests challenging. One approach is to use acoustic features and statistics to quantify acoustic properties of real-world noise and control for them or measure their relationship to listening performance. In this study, the complexity of real-world noise from different environments was quantified using entropy in both the time- and frequency-domains. A distribution of noise segments from low to high entropy were extracted. Using a trial-by-trial design, listeners with normal hearing and hearing loss (in aided and unaided conditions) repeated back sentences embedded in these noise segments. Entropy significantly affected speech perception, with a larger effect of entropy in the time-domain than the frequency-domain, a larger effect for listeners with normal hearing than for listeners with hearing loss, and a larger effect for listeners with hearing loss in the aided than unaided condition. Speech perception also differed between most environment types. Combining entropy with the environment type improved predictions of speech perception above the environment type alone.

Cochlear Implant Facilitates the Use of Talker Sex and Spatial Cues to Segregate Competing Speech in Unilaterally Deaf Listeners

OBJECTIVES

Talker sex and spatial cues can facilitate segregation of competing speech. However, the spectrotemporal degradation associated with cochlear implants (CIs) can limit the benefit of talker sex and spatial cues. Acoustic hearing in the nonimplanted ear can improve access to talker sex cues in CI users. However, it's unclear whether the CI can improve segregation of competing speech when maskers are symmetrically placed around the target (i.e., when spatial cues are available), compared with acoustic hearing alone. The aim of this study was to investigate whether a CI can improve segregation of competing speech by individuals with unilateral hearing loss.

DESIGN

Speech recognition thresholds (SRTs) for competing speech were measured in 16 normal-hearing (NH) adults and 16 unilaterally deaf CI users. All participants were native speakers of Mandarin Chinese. CI users were divided into two groups according to thresholds in the nonimplanted ear: (1) single-sided deaf (SSD); pure-tone thresholds <25 dB HL at all audiometric frequencies, and (2) Asymmetric hearing loss (AHL; one or more thresholds > 25 dB HL). SRTs were measured for target sentences produced by a male talker in the presence of two masker talkers (different male or female talkers). The target sentence was always presented via loudspeaker directly in front of the listener (0°), and the maskers were either colocated with the target (0°) or spatially separated from the target at ±90°. Three segregation cue conditions were tested to measure masking release (MR) relative to the baseline condition: (1) Talker sex, (2) Spatial, and (3) Talker sex + Spatial. For CI users, SRTs were measured with the CI on or off.

RESULTS

Binaural MR was significantly better for the NH group than for the AHL or SSD groups ( P < 0.001 in all cases). For the NH group, mean MR was largest with the Talker sex + spatial cues (18.8 dB) and smallest for the Talker sex cues (10.7 dB). In contrast, mean MR for the SSD group was largest with the Talker sex + spatial cues (14.7 dB), and smallest with the Spatial cues (4.8 dB). For the AHL group, mean MR was largest with the Talker sex + spatial cues (7.8 dB) and smallest with the Talker sex (4.8 dB) and the Spatial cues (4.8 dB). MR was significantly better with the CI on than off for both the AHL ( P = 0.014) and SSD groups ( P < 0.001). Across all unilaterally deaf CI users, monaural (acoustic ear alone) and binaural MR were significantly correlated with unaided pure-tone average thresholds in the nonimplanted ear for the Talker sex and Talker sex + spatial conditions ( P < 0.001 in both cases) but not for the Spatial condition.

CONCLUSION

Although the CI benefitted unilaterally deaf listeners' segregation of competing speech, MR was much poorer than that observed in NH listeners. Different from previous findings with steady noise maskers, the CI benefit for segregation of competing speech from a different talker sex was greater in the SSD group than in the AHL group.

Differing Bilateral Benefits for Spatial Release From Masking and Sound Localization Accuracy Using Bone Conduction Devices

OBJECTIVES

Normal binaural hearing facilitates spatial hearing and therefore many everyday listening tasks, such as understanding speech against a backdrop of competing sounds originating from various locations, and localization of sounds. For stimulation with bone conduction hearing devices (BCD), used to alleviate conductive hearing losses, limited transcranial attenuation results in cross-stimulation so that both cochleae are stimulated from the position of the bone conduction transducer. As such, interaural time and level differences, hallmarks of binaural hearing, are unpredictable at the level of the inner ears. The aim of this study was to compare spatial hearing by unilateral and bilateral BCD stimulation in normal-hearing listeners with simulated bilateral conductive hearing loss.

DESIGN

Bilateral conductive hearing loss was reversibly induced in 25 subjects (mean age = 28.5 years) with air conduction and bone conduction (BC) pure-tone averages across 0.5, 1, 2, and 4 kHz (PTA 4 ) <5 dB HL. The mean (SD) PTA 4 for the simulated conductive hearing loss was 48.2 dB (3.8 dB). Subjects participated in a speech-in-speech task and a horizontal sound localization task in a within-subject repeated measures design (unilateral and bilateral bone conduction stimulation) using Baha 5 clinical sound processors on a softband. For the speech-in-speech task, the main outcome measure was the threshold for 40% correct speech recognition when masking speech and target speech were both colocated (0°) and spatially and symmetrically separated (target 0°, maskers ±30° and ±150°). Spatial release from masking was quantified as the difference between colocated and separated masking and target speech thresholds. For the localization task, the main outcome measure was the overall variance in localization accuracy quantified as an error index (0.0 = perfect performance; 1.0 = random performance). Four stimuli providing various spatial cues were used in the sound localization task.

RESULTS

The bilateral BCD benefit for recognition thresholds of speech in competing speech was statistically significant but small regardless if the masking speech signals were colocated with, or spatially and symmetrically separated from, the target speech. Spatial release from masking was identical for unilateral and bilateral conditions, and significantly different from zero. A distinct bilateral BCD sound localization benefit existed but varied in magnitude across stimuli. The smallest benefit occurred for a low-frequency stimulus (octave-filtered noise, CF = 0.5 kHz), and the largest benefit occurred for unmodulated broadband and narrowband (octave-filtered noise, CF = 4.0 kHz) stimuli. Sound localization by unilateral BCD was poor across stimuli.

CONCLUSIONS

Results suggest that the well-known transcranial transmission of BC sound affects bilateral BCD benefits for spatial processing of sound in differing ways. Results further suggest that patients with bilateral conductive hearing loss and BC thresholds within the normal range may benefit from a bilateral fitting of BCD, particularly for horizontal localization of sounds.

Auditory spatial analysis in reverberant multi-talker environments with congruent and incongruent audio-visual room information

In a multi-talker situation, listeners have the challenge of identifying a target speech source out of a mixture of interfering background noises. In the current study, it was investigated how listeners analyze audio-visual scenes with varying complexity in terms of number of talkers and reverberation. The visual information of the room was either congruent with the acoustic room or incongruent. The listeners' task was to locate an ongoing speech source in a mixture of other speech sources. The three-dimensional audio-visual scenarios were presented using a loudspeaker array and virtual reality glasses. It was shown that room reverberation, as well as the number of talkers in a scene, influence the ability to analyze an auditory scene in terms of accuracy and response time. Incongruent visual information of the room did not affect this ability. When few talkers were presented simultaneously, listeners were able to detect a target talker quickly and accurately even in adverse room acoustical conditions. Reverberation started to affect the response time when four or more talkers were presented. The number of talkers became a significant factor for five or more simultaneous talkers.

Effects of Simulated and Profound Unilateral Sensorineural Hearing Loss on Recognition of Speech in Competing Speech

OBJECTIVES

Unilateral hearing loss (UHL) is a condition as common as bilateral hearing loss in adults. Because of the unilaterally reduced audibility associated with UHL, binaural processing of sounds may be disrupted. As a consequence, daily tasks such as listening to speech in a background of spatially distinct competing sounds may be challenging. A growing body of subjective and objective data suggests that spatial hearing is negatively affected by UHL. However, the type and degree of UHL vary considerably in previous studies. The aim here was to determine the effect of a profound sensorineural UHL, and of a simulated UHL, on recognition of speech in competing speech, and the binaural and monaural contributions to spatial release from masking, in a demanding multisource listening environment.

DESIGN

Nine subjects (25 to 61 years) with profound sensorineural UHL [mean pure-tone average (PTA) across 0.5, 1, 2, and 4 kHz = 105 dB HL] and normal contralateral hearing (mean PTA = 7.2 dB HL) were included based on the criterion that the target and competing speech were inaudible in the ear with hearing loss. Thirteen subjects with normal hearing (19 to 60 years; mean left PTA = 4.1 dB HL; mean right PTA = 5.5 dB HL) contributed data in normal and simulated "mild-to-moderate" UHL conditions (PTA = 38.6 dB HL). The main outcome measure was the threshold for 40% correct speech recognition in colocated (0°) and spatially and symmetrically separated (±30° and ±150°) competing speech conditions. Spatial release from masking was quantified as the threshold difference between colocated and separated conditions.

RESULTS

Thresholds in profound UHL were higher (worse) than normal hearing in separated and colocated conditions, and comparable to simulated UHL. Monaural spatial release from masking, that is, the spatial release achieved by subjects with profound UHL, was significantly different from zero and 49% of the magnitude of the spatial release from masking achieved by subjects with normal hearing. There were subjects with profound UHL who showed negative spatial release, whereas subjects with normal hearing consistently showed positive spatial release from masking in the normal condition. The simulated UHL had a larger effect on the speech recognition threshold for separated than for colocated conditions, resulting in decreased spatial release from masking. The difference in spatial release between normal-hearing and simulated UHL conditions increased with age.

CONCLUSIONS

The results demonstrate that while recognition of speech in colocated and separated competing speech is impaired for profound sensorineural UHL, spatial release from masking may be possible when competing speech is symmetrically distributed around the listener. A "mild-to-moderate" simulated UHL decreases spatial release from masking compared with normal-hearing conditions and interacts with age, indicating that small amounts of residual hearing in the UHL ear may be more beneficial for separated than for colocated interferer conditions for young listeners.

Head Shadow, Summation, and Squelch in Bilateral Cochlear-Implant Users With Linked Automatic Gain Controls

Speech understanding in noise is poorer in bilateral cochlear-implant (BICI) users compared to normal-hearing counterparts. Independent automatic gain controls (AGCs) may contribute to this because adjusting processor gain independently can reduce interaural level differences that BICI listeners rely on for bilateral benefits. Bilaterally linked AGCs may improve bilateral benefits by increasing the magnitude of interaural level differences. The effects of linked AGCs on bilateral benefits (summation, head shadow, and squelch) were measured in nine BICI users. Speech understanding for a target talker at 0° masked by a single talker at 0°, 90°, or −90° azimuth was assessed under headphones with sentences at five target-to-masker ratios. Research processors were used to manipulate AGC type (independent or linked) and test ear (left, right, or both). Sentence recall was measured in quiet to quantify individual interaural asymmetry in functional performance. The results showed that AGC type did not significantly change performance or bilateral benefits. Interaural functional asymmetries, however, interacted with ear such that greater summation and squelch benefit occurred when there was larger functional asymmetry, and interacted with interferer location such that smaller head shadow benefit occurred when there was larger functional asymmetry. The larger benefits for those with larger asymmetry were driven by improvements from adding a better-performing ear, rather than a true binaural-hearing benefit. In summary, linked AGCs did not significantly change bilateral benefits in cases of speech-on-speech masking with a single-talker masker, but there was also no strong detriment across a range of target-to-masker ratios, within a small and diverse BICI listener population.

Impact of non-individualised head related transfer functions on speech-in-noise performances within a synthesised virtual environment

When performing binaural spatialisation, it is widely accepted that the choice of the head related transfer functions (HRTFs), and in particular the use of individually measured ones, can have an impact on localisation accuracy, externalization, and overall realism. Yet the impact of HRTF choices on speech-in-noise performances in cocktail party-like scenarios has not been investigated in depth. This paper introduces a study where 22 participants were presented with a frontal speech target and two lateral maskers, spatialised using a set of non-individual HRTFs. Speech reception threshold (SRT) was measured for each HRTF. Furthermore, using the SRT predicted by an existing speech perception model, the measured values were compensated in the attempt to remove overall HRTF-specific benefits. Results show significant overall differences among the SRTs measured using different HRTFs, consistently with the results predicted by the model. Individual differences between participants related to their SRT performances using different HRTFs could also be found, but their significance was reduced after the compensation. The implications of these findings are relevant to several research areas related to spatial hearing and speech perception, suggesting that when testing speech-in-noise performances within binaurally rendered virtual environments, the choice of the HRTF for each individual should be carefully considered.

Complex Acoustic Environments: Review, Framework, and Subjective Model

The concept of complex acoustic environments has appeared in several unrelated research areas within acoustics in different variations. Based on a review of the usage and evolution of this concept in the literature, a relevant framework was developed, which includes nine broad characteristics that are thought to drive the complexity of acoustic scenes. The framework was then used to study the most relevant characteristics for stimuli of realistic, everyday, acoustic scenes: multiple sources, source diversity, reverberation, and the listener’s task. The effect of these characteristics on perceived scene complexity was then evaluated in an exploratory study that reproduced the same stimuli with a three-dimensional loudspeaker array inside an anechoic chamber. Sixty-five subjects listened to the scenes and for each one had to rate 29 attributes, including complexity, both with and without target speech in the scenes. The data were analyzed using three-way principal component analysis with a (2 3 2) Tucker3 model in the dimensions of scales (or ratings), scenes, and subjects, explaining 42% of variation in the data. “Comfort” and “variability” were the dominant scale components, which span the perceived complexity. Interaction effects were observed, including the additional task of attending to target speech that shifted the complexity rating closer to the comfort scale. Also, speech contained in the background scenes introduced a second subject component, which suggests that some subjects are more distracted than others by background speech when listening to target speech. The results are interpreted in light of the proposed framework.

Tonal Language Speakers Are Better Able to Segregate Competing Speech According to Talker Sex Differences

Purpose The aim of this study was to compare release from masking (RM) between Mandarin-speaking and English-speaking listeners with normal hearing for competing speech when target-masker sex cues, spatial cues, or both were available. Method Speech recognition thresholds (SRTs) for competing speech were measured in 21 Mandarin-speaking and 15 English-speaking adults with normal hearing using a modified coordinate response measure task. SRTs were measured for target sentences produced by a male talker in the presence of two masker talkers (different male talkers or female talkers). The target sentence was always presented directly in front of the listener, and the maskers were either colocated with the target or were spatially separated from the target (+90°, -90°). Stimuli were presented via headphones and were virtually spatialized using head-related transfer functions. Three masker conditions were used to measure RM relative to the baseline condition: (a) talker sex cues, (b) spatial cues, or (c) combined talker sex and spatial cues. Results The results showed large amounts of RM according to talker sex and/or spatial cues. There was no significant difference in SRTs between Chinese and English listeners for the baseline condition, where no talker sex or spatial cues were available. Furthermore, there was no significant difference in RM between Chinese and English listeners when spatial cues were available. However, RM was significantly larger for Chinese listeners when talker sex cues or combined talker sex and spatial cues were available. Conclusion Listeners who speak a tonal language such as Mandarin Chinese may be able to take greater advantage of talker sex cues than listeners who do not speak a tonal language.

Binaural sensitivity and release from speech-on-speech masking in listeners with and without hearing loss

Listeners with sensorineural hearing loss routinely experience less spatial release from masking (SRM) in speech mixtures than listeners with normal hearing. Hearing-impaired listeners have also been shown to have degraded temporal fine structure (TFS) sensitivity, a consequence of which is degraded access to interaural time differences (ITDs) contained in the TFS. Since these "binaural TFS" cues are critical for spatial hearing, it has been hypothesized that degraded binaural TFS sensitivity accounts for the limited SRM experienced by hearing-impaired listeners. In this study, speech stimuli were noise-vocoded using carriers that were systematically decorrelated across the left and right ears, thus simulating degraded binaural TFS sensitivity. Both (1) ITD sensitivity in quiet and (2) SRM in speech mixtures spatialized using ITDs (or binaural release from masking; BRM) were measured as a function of TFS interaural decorrelation in young normal-hearing and hearing-impaired listeners. This allowed for the examination of the relationship between ITD sensitivity and BRM over a wide range of ITD thresholds. This paper found that, for a given ITD sensitivity, hearing-impaired listeners experienced less BRM than normal-hearing listeners, suggesting that binaural TFS sensitivity can account for only a modest portion of the BRM deficit in hearing-impaired listeners. However, substantial individual variability was observed.

The Effects of Dynamic-range Automatic Gain Control on Sentence Intelligibility With a Speech Masker in Simulated Cochlear Implant Listening

OBJECTIVES

"Channel-linked" and "multi-band" front-end automatic gain control (AGC) were examined as alternatives to single-band, channel-unlinked AGC in simulated bilateral cochlear implant (CI) processing. In channel-linked AGC, the same gain control signal was applied to the input signals to both of the two CIs ("channels"). In multi-band AGC, gain control acted independently on each of a number of narrow frequency regions per channel.

DESIGN

Speech intelligibility performance was measured with a single target (to the left, at -15 or -30°) and a single, symmetrically-opposed masker (to the right) at a signal-to-noise ratio (SNR) of -2 decibels. Binaural sentence intelligibility was measured as a function of whether channel linking was present and of the number of AGC bands. Analysis of variance was performed to assess condition effects on percent correct across the two spatial arrangements, both at a high and a low AGC threshold. Acoustic analysis was conducted to compare postcompressed better-ear SNR, interaural differences, and monaural within-band envelope levels across processing conditions.

RESULTS

Analyses of variance indicated significant main effects of both channel linking and number of bands at low threshold, and of channel linking at high threshold. These improvements were accompanied by several acoustic changes. Linked AGC produced a more favorable better-ear SNR and better preserved broadband interaural level difference statistics, but did not reduce dynamic range as much as unlinked AGC. Multi-band AGC sometimes improved better-ear SNR statistics and always improved broadband interaural level difference statistics whenever the AGC channels were unlinked. Multi-band AGC produced output envelope levels that were higher than single-band AGC.

CONCLUSIONS

These results favor strategies that incorporate channel-linked AGC and multi-band AGC for bilateral CIs. Linked AGC aids speech intelligibility in spatially separated speech, but reduces the degree to which dynamic range is compressed. Combining multi-band and channel-linked AGC offsets the potential impact of diminished dynamic range with linked AGC without sacrificing the intelligibility gains observed with linked AGC.

Improving Localization and Speech Reception in Noise for Bilateral Cochlear Implant Recipients

This study looked at different methods to preserve interaural level difference (ILD) cues for bilateral cochlear implant (BiCI) recipients. One possible distortion to ILD is from automatic gain control (AGC). Localization accuracy of BiCI recipients using default versus increased AGC threshold and linked AGCs versus independent AGCs was examined. In addition, speech reception in noise was assessed using linked versus independent AGCs and enabling and disabling Autosensitivity™ Control. Subjective information via a diary and questionnaire was also collected about maps with linked and independent AGCs during a take-home experience. Localization accuracy improved in the increased AGC threshold and the linked AGCs conditions. Increasing the AGC threshold resulted in a 4° improvement in root mean square error averaged across all speaker locations. Using linked AGCs, BiCI participants experienced an 8° improvement for all speaker locations and a 19° improvement at the speaker location most affected by the AGC. Speech reception threshold in noise improved by an average of 2.5 dB when using linked AGCs versus independent AGCs. In addition, the effect of linked AGCs on speech in noise was compared with that of Autosensitivity™ Control. The Speech, Spatial, and Qualities of Hearing Scale-12 question comparative survey showed an improvement when using maps with linked AGCs. These findings support the hypothesis that ILD cues may be preserved by increasing the AGC threshold or linking AGCs.

Evaluation of Speech, Spatial Perception and Hearing Quality in Unilateral, Bimodal and Bilateral Cochlear Implant Users

Objective

The aim of the study was to conduct a scale-based evaluation of the hearing skills of unilateral, bimodal and bilateral cochlear implant (CI) users, including distinguishing, orientating and locating speech and environmental sounds in their surrounding environment that they are exposed to in different contexts of everyday life. The scale results were compared between groups.

Methods

A total of 74 cochlear implant users, 30 unilateral, 30 bimodal and 14 bilateral, were included in the study. Their ages ranged from 11 to 64 years. Participants were assessed using the Speech, Spatial and Qualities of Hearing Scale (SSQ).

Results

Bilateral CI users' subjective ratings of their own hearing skills were found to be significantly better than those of bimodal and unilateral CI users; bimodal users' subjective ratings were also found to be significantly better than those of unilateral CI users. Paired comparisons showed statistically significant differences between the groups in terms of total scores of Speech, Spatial, Qualities of Hearing and General SSQ (p<0.05).

Conclusion

Our findings show that bilateral use of cochlear implants should be recommended for those presently using bimodal and unilateral devices. Moreover, subjective tests should be used regularly along with objective tests for evaluating CI patients.

Subclinical Auditory Neural Deficits in Patients With Type 1 Diabetes Mellitus

Supplemental Digital Content is available in the text.

Objectives:

Diabetes mellitus (DM) is associated with a variety of sensory complications. Very little attention has been given to auditory neuropathic complications in DM. The aim of this study was to determine whether type 1 DM (T1DM) affects neural coding of the rapid temporal fluctuations of sounds, and how any deficits may impact on behavioral performance.

Design:

Participants were 30 young normal-hearing T1DM patients, and 30 age-, sex-, and audiogram-matched healthy controls. Measurements included electrophysiological measures of auditory nerve and brainstem function using the click-evoked auditory brainstem response, and of brainstem neural temporal coding using the sustained frequency-following response (FFR); behavioral tests of temporal coding (interaural phase difference discrimination and the frequency difference limen); tests of speech perception in noise; and self-report measures of auditory disability using the Speech, Spatial and Qualities of Hearing Scale.

Results:

There were no significant differences between T1DM patients and controls in the auditory brainstem response. However, the T1DM group showed significantly reduced FFRs to both temporal envelope and temporal fine structure. The T1DM group also showed significantly higher interaural phase difference and frequency difference limen thresholds, worse speech-in-noise performance, as well as lower overall Speech, Spatial and Qualities scores than the control group.

Conclusions:

These findings suggest that T1DM is associated with degraded neural temporal coding in the brainstem in the absence of an elevation in audiometric threshold, and that the FFR may provide an early indicator of neural damage in T1DM, before any abnormalities can be identified using standard clinical tests. However, the relation between the neural deficits and the behavioral deficits is uncertain.

Cortical mechanisms of spatial hearing

Humans and other animals use spatial hearing to rapidly localize events in the environment. However, neural encoding of sound location is a complex process involving the computation and integration of multiple spatial cues that are not represented directly in the sensory organ (the cochlea). Our understanding of these mechanisms has increased enormously in the past few years. Current research is focused on the contribution of animal models for understanding human spatial audition, the effects of behavioural demands on neural sound location encoding, the emergence of a cue-independent location representation in the auditory cortex, and the relationship between single-source and concurrent location encoding in complex auditory scenes. Furthermore, computational modelling seeks to unravel how neural representations of sound source locations are derived from the complex binaural waveforms of real-life sounds. In this article, we review and integrate the latest insights from neurophysiological, neuroimaging and computational modelling studies of mammalian spatial hearing. We propose that the cortical representation of sound location emerges from recurrent processing taking place in a dynamic, adaptive network of early (primary) and higher-order (posterior-dorsal and dorsolateral prefrontal) auditory regions. This cortical network accommodates changing behavioural requirements and is especially relevant for processing the location of real-life, complex sounds and complex auditory scenes.

Neurophysiological, linguistic, and cognitive predictors of children's ability to perceive speech in noise

Hearing in noisy environments is a complicated task that engages attention, memory, linguistic knowledge, and precise auditory-neurophysiological processing of sound. Accumulating evidence in school-aged children and adults suggests these mechanisms vary with the task’s demands. For instance, co-located speech and noise demands a large cognitive load and recruits working memory, while spatially separating speech and noise diminishes this load and draws on alternative skills. Past research has focused on one or two mechanisms underlying speech-in-noise perception in isolation; few studies have considered multiple factors in tandem, or how they interact during critical developmental years. This project sought to test complementary hypotheses involving neurophysiological, cognitive, and linguistic processes supporting speech-in-noise perception in young children under different masking conditions (co-located, spatially separated). Structural equation modeling was used to identify latent constructs and examine their contributions as predictors. Results reveal cognitive and language skills operate as a single factor supporting speech-in-noise perception under different masking conditions. While neural coding of the F0 supports perception in both co-located and spatially separated conditions, neural timing predicts perception of spatially separated listening exclusively. Together, these results suggest co-located and spatially separated speech-in-noise perception draw on similar cognitive/linguistic skills, but distinct neural factors, in early childhood.

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

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

Auditory Localization and Spatial Release From Masking in Children With Suspected Auditory Processing Disorder

OBJECTIVES

We sought to investigate whether children referred to our audiology clinic with a complaint of listening difficulty, that is, suspected of auditory processing disorder (APD), have difficulties localizing sounds in noise and whether they have reduced benefit from spatial release from masking.

DESIGN

Forty-seven typically hearing children in the age range of 7 to 17 years took part in the study. Twenty-one typically developing (TD) children served as controls, and the other 26 children, referred to our audiology clinic with listening problems, were the study group: suspected APD (sAPD). The ability to localize a speech target (the word "baseball") was measured in quiet, broadband noise, and speech-babble in a hemi-anechoic chamber. Participants stood at the center of a loudspeaker array that delivered the target in a diffused noise-field created by presenting independent noise from four loudspeakers spaced 90° apart starting at 45°. In the noise conditions, the signal-to-noise ratio was varied between -12 and 0 dB in 6-dB steps by keeping the noise level constant at 66 dB SPL and varying the target level. Localization ability was indexed by two metrics, one assessing variability in lateral plane [lateral scatter (Lscat)] and the other accuracy in the front/back dimension [front/back percent correct (FBpc)]. Spatial release from masking (SRM) was measured using a modified version of the Hearing in Noise Test (HINT). In this HINT paradigm, speech targets were always presented from the loudspeaker at 0°, and a single noise source was presented either at 0°, 90°, or 270° at 65 dB A. The SRM was calculated as the difference between the 50% correct HINT speech reception threshold obtained when both speech and noise were collocated at 0° and when the noise was presented at either 90° or 270°.

RESULTS

As expected, in both groups, localization in noise improved as a function of signal-to-noise ratio. Broadband noise caused significantly larger disruption in FBpc than in Lscat when compared with speech babble. There were, however, no group effects or group interactions, suggesting that the children in the sAPD group did not differ significantly from TD children in either localization metric (Lscat and FBpc). While a significant SRM was observed in both groups, there were no group effects or group interactions. Collectively, the data suggest that children in the sAPD group did not differ significantly from the TD group for either binaural measure investigated in the study.

CONCLUSIONS

As is evident from a few poor performers, some children with listening difficulties may have difficulty in localizing sounds and may not benefit from spatial separation of speech and noise. However, the heterogeneity in APD and the variability in our data do not support the notion that localization is a global APD problem. Future studies that employ a case study design might provide more insights.

Implicit representation of the auditory space: contribution of the left and right hemispheres

Spatial cues contribute to the ability to segregate sound sources and thus facilitate their detection and recognition. This implicit use of spatial cues can be preserved in cases of cortical spatial deafness, suggesting that partially distinct neural networks underlie the explicit sound localization and the implicit use of spatial cues. We addressed this issue by assessing 40 patients, 20 patients with left and 20 patients with right hemispheric damage, for their ability to use auditory spatial cues implicitly in a paradigm of spatial release from masking (SRM) and explicitly in sound localization. The anatomical correlates of their performance were determined with voxel-based lesion-symptom mapping (VLSM). During the SRM task, the target was always presented at the centre, whereas the masker was presented at the centre or at one of the two lateral positions on the right or left side. The SRM effect was absent in some but not all patients; the inability to perceive the target when the masker was at one of the lateral positions correlated with lesions of the left temporo-parieto-frontal cortex or of the right inferior parietal lobule and the underlying white matter. As previously reported, sound localization depended critically on the right parietal and opercular cortex. Thus, explicit and implicit use of spatial cues depends on at least partially distinct neural networks. Our results suggest that the implicit use may rely on the left-dominant position-linked representation of sound objects, which has been demonstrated in previous EEG and fMRI studies.

Effects of Acquired Aphasia on the Recognition of Speech Under Energetic and Informational Masking Conditions

Persons with aphasia (PWA) often report difficulty understanding spoken language in noisy environments that require listeners to identify and selectively attend to target speech while ignoring competing background sounds or “maskers.” This study compared the performance of PWA and age-matched healthy controls (HC) on a masked speech identification task and examined the consequences of different types of masking on performance. Twelve PWA and 12 age-matched HC completed a speech identification task comprising three conditions designed to differentiate between the effects of energetic and informational masking on receptive speech processing. The target and masker speech materials were taken from a closed-set matrix-style corpus, and a forced-choice word identification task was used. Target and maskers were spatially separated from one another in order to simulate real-world listening environments and allow listeners to make use of binaural cues for source segregation. Individualized frequency-specific gain was applied to compensate for the effects of hearing loss. Although both groups showed similar susceptibility to the effects of energetic masking, PWA were more susceptible than age-matched HC to the effects of informational masking. Results indicate that this increased susceptibility cannot be attributed to age, hearing loss, or comprehension deficits and is therefore a consequence of acquired cognitive-linguistic impairments associated with aphasia. This finding suggests that aphasia may result in increased difficulty segregating target speech from masker speech, which in turn may have implications for the ability of PWA to comprehend target speech in multitalker environments, such as restaurants, family gatherings, and other everyday situations.

Effects of directional hearing aid settings on different laboratory measures of spatial awareness perception

Hearing loss can negatively influence the spatial hearing abilities of hearing-impaired listeners, not only in static but also in dynamic auditory environments. Therefore, ways of addressing these deficits with advanced hearing aid algorithms need to be investigated. In a previous study based on virtual acoustics and a computer simulation of different bilateral hearing aid fittings, we investigated auditory source movement detectability in older hearing- impaired (OHI) listeners. We found that two directional processing algorithms could substantially improve the detectability of left-right and near-far source movements in the presence of reverberation and multiple interfering sounds. In the current study, we carried out similar measurements with a loudspeaker-based setup and wearable hearing aids. We fitted a group of 15 OHI listeners with bilateral behind-the-ear devices that were programmed to have three different directional processing settings. Apart from source movement detectability, we assessed two other aspects of spatial awareness perception. Using a street scene with up to five environmental sound sources, the participants had to count the number of presented sources or to indicate the movement direction of a single target signal. The data analyses showed a clear influence of the number of concurrent sound sources and the starting position of the moving target signal on the participants' performance, but no influence of the different hearing aid settings. Complementary artificial head recordings showed that the acoustic differences between the three hearing aid settings were rather small. Another explanation for the lack of effects of the tested hearing aid settings could be that the simulated street scenario was not sufficiently sensitive. Possible ways of improving the sensitivity of the laboratory measures while maintaining high ecological validity and complexity are discussed.

Unilateral Hearing Loss: Understanding Speech Recognition and Localization Variability-Implications for Cochlear Implant Candidacy

OBJECTIVES

At a minimum, unilateral hearing loss (UHL) impairs sound localization ability and understanding speech in noisy environments, particularly if the loss is severe to profound. Accompanying the numerous negative consequences of UHL is considerable unexplained individual variability in the magnitude of its effects. Identification of covariables that affect outcome and contribute to variability in UHLs could augment counseling, treatment options, and rehabilitation. Cochlear implantation as a treatment for UHL is on the rise yet little is known about factors that could impact performance or whether there is a group at risk for poor cochlear implant outcomes when hearing is near-normal in one ear. The overall goal of our research is to investigate the range and source of variability in speech recognition in noise and localization among individuals with severe to profound UHL and thereby help determine factors relevant to decisions regarding cochlear implantation in this population.

DESIGN

The present study evaluated adults with severe to profound UHL and adults with bilateral normal hearing. Measures included adaptive sentence understanding in diffuse restaurant noise, localization, roving-source speech recognition (words from 1 of 15 speakers in a 140° arc), and an adaptive speech-reception threshold psychoacoustic task with varied noise types and noise-source locations. There were three age-sex-matched groups: UHL (severe to profound hearing loss in one ear and normal hearing in the contralateral ear), normal hearing listening bilaterally, and normal hearing listening unilaterally.

RESULTS

Although the normal-hearing-bilateral group scored significantly better and had less performance variability than UHLs on all measures, some UHL participants scored within the range of the normal-hearing-bilateral group on all measures. The normal-hearing participants listening unilaterally had better monosyllabic word understanding than UHLs for words presented on the blocked/deaf side but not the open/hearing side. In contrast, UHLs localized better than the normal-hearing unilateral listeners for stimuli on the open/hearing side but not the blocked/deaf side. This suggests that UHLs had learned strategies for improved localization on the side of the intact ear. The UHL and unilateral normal-hearing participant groups were not significantly different for speech in noise measures. UHL participants with childhood rather than recent hearing loss onset localized significantly better; however, these two groups did not differ for speech recognition in noise. Age at onset in UHL adults appears to affect localization ability differently than understanding speech in noise. Hearing thresholds were significantly correlated with speech recognition for UHL participants but not the other two groups.

CONCLUSIONS

Auditory abilities of UHLs varied widely and could be explained only in part by hearing threshold levels. Age at onset and length of hearing loss influenced performance on some, but not all measures. Results support the need for a revised and diverse set of clinical measures, including sound localization, understanding speech in varied environments, and careful consideration of functional abilities as individuals with severe to profound UHL are being considered potential cochlear implant candidates.

Bilateral cochlear implantation or bimodal listening in the paediatric population: Retrospective analysis of decisive criteria

INTRODUCTION

In children with bilateral severe to profound hearing loss, bilateral hearing can be achieved by either bimodal stimulation (CIHA) or bilateral cochlear implantation (BICI). The aim of this study was to analyse the audiologic test protocol that is currently applied to make decisions regarding the bilateral hearing modality in the paediatric population.

METHODS

Pre- and postoperative audiologic test results of 21 CIHA, 19 sequential BICI and 12 simultaneous BICI children were examined retrospectively.

RESULTS

Deciding between either simultaneous BICI or unilateral implantation was mainly based on the infant's preoperative Auditory Brainstem Response thresholds. Evolution from CIHA to sequential BICI was mainly based on the audiometric test results in the contralateral (hearing aid) ear after unilateral cochlear implantation. Preoperative audiometric thresholds in the hearing aid ear were significantly better in CIHA versus sequential BICI children (p < 0.001 and p = 0.001 in unaided and aided condition, respectively). Decisive values obtained in the hearing aid ear in favour of BICI were: An average hearing threshold measured at 0.5, 1, 2 and 4 kHz of at least 93 dB HL without, and at least 52 dB HL with hearing aid together with a 40% aided speech recognition score and a 70% aided score on the phoneme discrimination subtest of the Auditory Speech Sounds Evaluation test battery.

CONCLUSIONS

Although pure tone audiometry offers no information about bimodal benefit, it remains the most obvious audiometric evaluation in the decision process on the mode of bilateral stimulation in the paediatric population. A theoretical test protocol for adequate evaluation of bimodal benefit in the paediatric population is proposed.

Binaural masking release in symmetric listening conditions with spectro-temporally modulated maskers

Speech reception thresholds (SRTs) decrease as target and maskers are spatially separated (spatial release from masking, SRM). The current study systematically assessed how SRTs and SRM for a frontal target in a spatially symmetric masker configuration depend on spectro-temporal masker properties, the availability of short-time interaural level difference (ILD) and interaural time difference (ITD), and informational masking. Maskers ranged from stationary noise to single, interfering talkers and were modified by head-related transfer functions to provide: (i) different binaural cues (ILD, ITD, or both) and (ii) independent maskers in each ear ("infinite ILD"). Additionally, a condition was tested in which only information from short-time spectro-temporal segments of the ear with a favorable signal-to-noise ratio (better-ear glimpses) was presented. For noise-based maskers, ILD, ITD, and spectral changes related to masker location contributed similarly to SRM, while ILD cues played a larger role if temporal modulation was introduced. For speech maskers, glimpsing and perceived location contributed roughly equally and ITD contributed less. The "infinite ILD" condition might suggest better-ear glimpsing limitations resulting in a maximal SRM of 12 dB for maskers with low or absent informational masking. Comparison to binaural model predictions highlighted the importance of short-time processing and helped to clarify the contribution of the different binaural cues and mechanisms.

Modeling speech localization, talker identification, and word recognition in a multi-talker setting

This study introduces a model for solving three different auditory tasks in a multi-talker setting: target localization, target identification, and word recognition. The model was used to simulate psychoacoustic data from a call-sign-based listening test involving multiple spatially separated talkers [Brungart and Simpson (2007). Percept. Psychophys. 69(1), 79-91]. The main characteristics of the model are (i) the extraction of salient auditory features ("glimpses") from the multi-talker signal and (ii) the use of a classification method that finds the best target hypothesis by comparing feature templates from clean target signals to the glimpses derived from the multi-talker mixture. The four features used were periodicity, periodic energy, and periodicity-based interaural time and level differences. The model results widely exceeded probability of chance for all subtasks and conditions, and generally coincided strongly with the subject data. This indicates that, despite their sparsity, glimpses provide sufficient information about a complex auditory scene. This also suggests that complex source superposition models may not be needed for auditory scene analysis. Instead, simple models of clean speech may be sufficient to decode even complex multi-talker scenes.

Use of a glimpsing model to understand the performance of listeners with and without hearing loss in spatialized speech mixtures

In many situations, listeners with sensorineural hearing loss demonstrate reduced spatial release from masking compared to listeners with normal hearing. This deficit is particularly evident in the "symmetric masker" paradigm in which competing talkers are located to either side of a central target talker. However, there is some evidence that reduced target audibility (rather than a spatial deficit per se) under conditions of spatial separation may contribute to the observed deficit. In this study a simple "glimpsing" model (applied separately to each ear) was used to isolate the target information that is potentially available in binaural speech mixtures. Intelligibility of these glimpsed stimuli was then measured directly. Differences between normally hearing and hearing-impaired listeners observed in the natural binaural condition persisted for the glimpsed condition, despite the fact that the task no longer required segregation or spatial processing. This result is consistent with the idea that the performance of listeners with hearing loss in the spatialized mixture was limited by their ability to identify the target speech based on sparse glimpses, possibly as a result of some of those glimpses being inaudible.

Subjective perceptual organization of a complex auditory scene

Empirical research on the sequential decomposition of an auditory scene primarily relies on interleaved sound mixtures of only two tone sequences (e.g., ABAB…). This oversimplifies the sound decomposition problem by limiting the number of putative perceptual organizations. The current study used a sound mixture composed of three different tones (ABCABC…) that could be perceptually organized in many different ways. Participants listened to these sequences and reported their subjective perception by continuously choosing one out of 12 visually presented perceptual organization alternatives. Different levels of frequency and spatial separation were implemented to check whether participants' perceptual reports would be systematic and plausible. As hypothesized, while perception switched back and forth in each condition between various perceptual alternatives (multistability), spatial as well as frequency separation generally raised the proportion of segregated and reduced the proportion of integrated alternatives. During segregated percepts, in contrast to the hypothesis, many participants had a tendency to perceive two streams in the foreground, rather than reporting alternatives with a clear foreground-background differentiation. Finally, participants perceived the organization with intermediate feature values (e.g., middle tones of the pattern) segregated in the foreground slightly less often than similar alternatives with outer feature values (e.g., higher tones).

Aging and the effect of target-masker alignment

Similarity between target and competing speech messages plays a large role in how easy or difficult it is to understand messages of interest. Much research on informational masking has used highly aligned target and masking utterances that are very similar semantically and syntactically. However, listeners rarely encounter situations in real life where they must understand one sentence in the presence of another (or more than one) highly aligned, syntactically similar competing sentence(s). The purpose of the present study was to examine the effect of syntactic/semantic similarity of target and masking speech in different spatial conditions among younger, middle-aged, and older adults. The results of this experiment indicate that differences in speech recognition between older and younger participants were largest when the masker surrounded the target and was more similar to the target, especially at more adverse signal-to-noise ratios. Differences among listeners and the effect of similarity were much less robust, and all listeners were relatively resistant to masking, when maskers were located on one side of the target message. The present results suggest that previous studies using highly aligned stimuli may have overestimated age-related speech recognition problems.

The Norwegian Hearing in Noise Test for Children

OBJECTIVES

The aims of this study were to create 12 ten-sentence lists for the Norwegian Hearing in Noise Test for children, and to use these lists to collect speech reception thresholds (SRTs) in quiet and in noise to assess speech perception in normal hearing children 5 to 13 years of age, to establish developmental trends, and to compare the results with those of adults. Data were collected in an anechoic chamber and in an audiometric test room, and the effect of slight room reverberation was estimated.

DESIGN

The Norwegian Hearing in Noise Test for children was formed from a subset of the adult sentences. Selected sentences were repeatable by 5- and 6-year-old children in quiet listening conditions. Twelve sentence lists were created based on the sentences' phoneme distributions. Six-year-olds were tested with these lists to determine list equivalence. Slopes of performance intensity (PI) functions relating mean word scores and signal to noise ratios (SNRs) were estimated for a group of 7-year-olds and adults. HINT normative data were collected for 219 adults and children 5 to 13 years of age in anechoic and audiometric test rooms, using noise levels 55, 60, or 65 dBA. Target sentences always originated from the front; whereas, the noise was presented either from the front, noise front (NF), from the right, noise right (NR) or from the left, noise left (NL). The NR and NL scores were averaged to yield a noise side (NS) score. All 219 subjects were tested in the NF condition, and 95 in the NR and NL conditions. Retest of the NF at the end of the test session was done for 53 subjects. Longitudinal data were collected by testing 9 children as 6, 8, and 13 years old.

RESULTS

NF and NS group means for adults were -3.7 and -11.8 dB SNR, respectively. Group means for 13-year-olds were -3.3 and -9.7, and for the 6-year-olds group means were -0.3 and -5.7 dB SNR, as measured in an anechoic chamber. NF SRTs measured in an audiometric test room were 0.7 to 1.5 higher (poorer) than in the anechoic chamber. Developmental trends were comparable in both rooms. PI slopes were 8.0% dB SNR for the 7-year-olds and 10.1% for the adults. NF SRTs in the anechoic chamber improved by 0.7 dB per year over an age range of 5 to 10 years. Using a PI slope 8 to 10% per dB, the estimated increase in percent intelligibility was 4 to 7% per year. Adult SRTs were about 3 dB lower than those for 6-year-olds, corresponding to 25 to 30% better intelligibility for adults.

CONCLUSIONS

Developmental trends in HINT performance for Norwegian children with normal hearing are similar to those seen in other languages, including American English and Canadian French. SRTs approach adult normative values by the age of 13; however, the benefits of spatial separation of the speech and noise sources are less than those seen for adults.

On the Contribution of Target Audibility to Performance in Spatialized Speech Mixtures

Hearing loss has been shown to reduce speech understanding in spatialized multitalker listening situations, leading to the common belief that spatial processing is disrupted by hearing loss. This paper describes related studies from three laboratories that explored the contribution of reduced target audibility to this deficit. All studies used a stimulus configuration in which a speech target presented from the front was masked by speech maskers presented symmetrically from the sides. Together these studies highlight the importance of adequate stimulus audibility for optimal performance in spatialized speech mixtures and suggest that reduced access to target speech information might explain a substantial portion of the "spatial" deficit observed in listeners with hearing loss.

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

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

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.

Robust auditory localization using probabilistic inference and coherence-based weighting of interaural cues

Robust sound source localization is performed by the human auditory system even in challenging acoustic conditions and in previously unencountered, complex scenarios. Here a computational binaural localization model is proposed that possesses mechanisms for handling of corrupted or unreliable localization cues and generalization across different acoustic situations. Central to the model is the use of interaural coherence, measured as interaural vector strength (IVS), to dynamically weight the importance of observed interaural phase (IPD) and level (ILD) differences in frequency bands up to 1.4 kHz. This is accomplished through formulation of a probabilistic model in which the ILD and IPD distributions pertaining to a specific source location are dependent on observed interaural coherence. Bayesian computation of the direction-of-arrival probability map naturally leads to coherence-weighted integration of location cues across frequency and time. Results confirm the model's validity through statistical analyses of interaural parameter values. Simulated localization experiments show that even data points with low reliability (i.e., low IVS) can be exploited to enhance localization performance. A temporal integration length of at least 200 ms is required to gain a benefit; this is in accordance with previous psychoacoustic findings on temporal integration of spatial cues in the human auditory system.

An evaluation of the performance of two binaural beamformers in complex and dynamic multitalker environments

OBJECTIVE

Binaural beamformers are super-directional hearing aids created by combining microphone outputs from each side of the head. While they offer substantial improvements in SNR over conventional directional hearing aids, the benefits (and possible limitations) of these devices in realistic, complex listening situations have not yet been fully explored. In this study we evaluated the performance of two experimental binaural beamformers.

DESIGN

Testing was carried out using a horizontal loudspeaker array. Background noise was created using recorded conversations. Performance measures included speech intelligibility, localization in noise, acceptable noise level, subjective ratings, and a novel dynamic speech intelligibility measure.

STUDY SAMPLE

Participants were 27 listeners with bilateral hearing loss, fitted with BTE prototypes that could be switched between conventional directional or binaural beamformer microphone modes.

RESULTS

Relative to the conventional directional microphones, both binaural beamformer modes were generally superior for tasks involving fixed frontal targets, but not always for situations involving dynamic target locations.

CONCLUSIONS

Binaural beamformers show promise for enhancing listening in complex situations when the location of the source of interest is predictable.

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.

Deafness in cochlear and auditory nerve disorders

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

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.