Binaural Intelligibility Level Difference Research Articles

Development and validation of a French speech-in-noise self-test using synthetic voice in an adult population

BackgroundSpeech-in-noise (SIN) audiometry is a valuable part of audiological diagnostics and clinical measurements, providing information on an individual's ability to understand in noise. To date, such tests have been developed with natural voice presented monaurally or binaurally (via diotic and dichotic presentation). The time required to develop such tests is often long. The use of synthetic voice would simplify the test creation process and self-testing would improve accessibility.DesignMeasurements were performed using an Android tablet (Samsung Galaxy Tab A7) and calibrated Bluetooth headphones (Tilde Pro C, Orosound). Normative values were first defined using natural or synthetic voice on 69 normal-hearing participants. A total of 463 participants then undertook the SIN test comprising synthetic voice and dichotic antiphasic presentation. Of these, 399 also performed the SIN test with diotic presentation.ResultsNo significant differences in the speech reception threshold (SRT) were found between natural and synthetic voices for diotic presentations (p = 0.824, paired Student t-test) with normative values of −10.7 dB SNR (SD = 1.5 dB) and −10.4 dB SNR (SD = 1.4 dB), respectively. For the SoNoise test with synthetic voice and dichotic antiphasic presentation, the results showed a normative value of −17.5 dB SNR (SD = 1.5 dB), and a strong correlation (r = 0.797, p < 0.001) with the four-frequency pure-tone average (4f-PTA). Receiver operating curves (ROC) were then calculated: for a 4f-PTA of 20 dB hearing level (HL), the SRT was −14.5 dB SNR with a sensitivity of 84% and specificity of 89%. For a 4f-PTA of 30 dB HL, the SRT was −13.7 dB SNR with a sensitivity of 89% and specificity of 91%. For a 4f-PTA of 35 dB HL, the SRT was −13.0 dB SNR with a sensitivity of 88% and specificity of 93%. The normative binaural intelligibility level difference (BILD) value was 8.6 dB (SD = 2.0 dB) with normal-hearing participants. The learning effect due to the task and interface was 1.7 dB (1st to 7th test) and test duration was 3 min.ConclusionThe SoNoise test in its synthetic dichotic antiphasic presentation is a fast and reliable tool to diagnose hearing impairment at 20, 30, and 35 dB HL cut-offs.

The Benefit of Binaural Hearing Among Listeners with Sensorineural Hearing Loss

The performance of binaural processing may be disturbed in the presence of hearing loss, especially of sensorineural type. To assess the impact of hearing loss on speech perception in noise regarding binaural processing, series of speech recognition measurements in controlled laboratory conditions were carried out. The spatial conditions were simulated using dummy head recordings played back on headphones. The Intelligibility Level Difference (ILD) was determined by measuring the change in the speech reception thresholds (SRT) between two configurations of a masking signal source (N) and a speech source (S), namely the S0N90 condition (where numbers stand for angles in horizontal plane) and the co-located condition (S0N0). To disentangle the head shadow effect (better ear effect) from binaural processing in the brain, the difference between binaural and monaural S0N90 condition (so-called Binaural Intelligibility Level Difference, BILD) value was calculated. Measurements were performed with a control group of normal-hearing listeners and a group of sensorineural hearing-impaired subjects. In all conditions performance of the hearing-impaired listeners was significantly lower than normal-hearing ones, resulting in higher SRT values (3 dB difference in the S0N0 configuration, 7.6 dB in S0N90 and 5 dB in monaural S0N90). The SRT improvement due to the spatial separation of target and masking signal (ILD) was also higher in the control group (8.1 dB) than in hearing-impaired listeners (3.5 dB). Moreover, a significant deterioration of the binaural processing described by BILD was found in people with sensorineural deficits. This parameter for normal-hearing listeners reached a value of 3 to 6 dB (4.6 dB on average) and decreased more than two times in the hearing-impaired group to 1.9 dB on average (with a deviation of 1.4 dB). These findings could not be explained by individual average hearing threshold (standard in audiological diagnostics) only. The outcomes indicate that there is a contribution of suprathershold deficits and it may be useful to consider binaural SRT measurements in noise in addition to the pure tone audiometry resulting in better diagnostics and hearing aid fitting.

Binaural temporal coding and the middle ear muscle reflex in audiometrically normal young adults

Noise exposure may damage the synapses that connect inner hair cells with auditory nerve fibers, before outer hair cells are lost. In humans, this cochlear synaptopathy (CS) is thought to decrease the fidelity of peripheral auditory temporal coding. In the current study, the primary hypothesis was that higher middle ear muscle reflex (MEMR) thresholds, as a proxy measure of CS, would be associated with smaller values of the binaural intelligibility level difference (BILD). The BILD, which is a measure of binaural temporal coding, is defined here as the difference in thresholds between the diotic and the antiphasic versions of the digits in noise (DIN) test. This DIN BILD may control for factors unrelated to binaural temporal coding such as linguistic, central auditory, and cognitive factors. Fifty-six audiometrically normal adults (34 females) aged 18 – 30 were tested. The test battery included standard pure tone audiometry, tympanometry, MEMR using a 2 kHz elicitor and 226 Hz and 1 kHz probes, the Noise Exposure Structured Interview, forward digit span test, extended high frequency (EHF) audiometry, and diotic and antiphasic DIN tests. The study protocol was pre-registered prior to data collection. MEMR thresholds did not predict the DIN BILD. Secondary analyses showed no association between MEMR thresholds and the individual diotic and antiphasic DIN thresholds. Greater lifetime noise exposure was non-significantly associated with higher MEMR thresholds, larger DIN BILD values, and lower (better) antiphasic DIN thresholds, but not with diotic DIN thresholds, nor with EHF thresholds. EHF thresholds were associated with neither MEMR thresholds nor any of the DIN outcomes, including the DIN BILD. Results provide no evidence that young, audiometrically normal people incur CS with impacts on binaural temporal processing.

Sensitivity of the antiphasic digits-in-noise test to simulated unilateral and bilateral conductive hearing loss

Objectives The objective of this study is (1) to assess whether the presentation level of the antiphasic digits-in-noise (DIN) test affects the speech recognition threshold (SRT), (2) to evaluate how accurately simulated unilateral and bilateral conductive hearing loss is detected (CHL) and (3) to determine whether increasing the presentation level normalises the antiphasic DIN SRT. Design Participants performed antiphasic and diotic DINs at different presentation levels with unilateral, bilateral or no earplugs. Study sample Twenty-four and twelve normal hearing adults. Results Without earplugs, antiphasic DIN SRTs did not differ between 60 and 80 dB SPL. At 60 dB SPL, the antiphasic DIN correctly classified 92% of the unilateral earplug cases; the diotic DIN 25%. The binaural intelligibility level difference did not differ between the no-earplug condition and the condition with bilateral earplugs when the presentation was increased with the attenuation level. Conclusions In normal hearing participants, diotic and antiphasic DIN SRTs are independent of presentation level above a minimum level of 60 dB SPL. The antiphasic DIN is more sensitive than the diotic DIN for detecting unilateral CHL; not for bilateral CHL. The effect of CHL on DIN SRTs can be largely compensated by increasing the presentation level. Audibility plays an important role in the antiphasic and diotic DIN.

Diotic and Antiphasic Digits-in-noise Testing as a Hearing Screening and Triage Tool to Classify Type of Hearing Loss.

The digits-in-noise test (DIN) is a popular self-test measure that has traditionally been used to screen for hearing loss by providing either a pass or refer result. Standard approaches either tested each ear monaurally or used a binaural diotic version where identical digits and noise were presented simultaneously to both ears. Recently, a dichotic, antiphasic version was developed, increasing sensitivity of the DIN to unilateral or asymmetric sensorineural hearing loss (SNHL) and conductive hearing loss (CHL). The purpose of this study was to determine predictors and normative ranges of the antiphasic and diotic DIN and to determine if a combination of diotic and antiphasic DIN could accurately categorize hearing into (1) normal, (2) bilateral SNHL, or (3) unilateral SNHL or CHL. The analytical sample consisted of 489 participants between the ages of 18 and 92 years with varying types, symmetry, and degrees of hearing loss. Degree and type of hearing loss were determined based on standard clinical four-frequency (0.5-4 kHz) pure-tone air and bone conduction threshold averages. The sample consisted of bilateral normal hearing (n = 293), bilateral SNHL (n = 172), unilateral SNHL (n = 42), and CHL (n = 32). All participants (n = 489) first completed an antiphasic DIN (digit stimuli 180° out-of-phase between ears), while 393 of the sample also completed a diotic DIN. Two procedures were assessed for their ability to categorize hearing into one of the three hearing groups. The first used a fixed antiphasic cutoff combined with a cutoff formed by a linear combination of antiphasic and diotic speech recognition threshold (SRT) or binaural intelligibility-level difference. Poorer ear pure-tone average was the strongest predictor of antiphasic DIN score, whereas better ear pure-tone average explained more of the variance in diotic SRT. The antiphasic DIN sensitivity and specificity was 90% and 84%, respectively, for detecting hearing loss, with outstanding area under the receiver operating characteristics values exceeding 0.93 to identify hearing loss in the poorer ear. The first fixed SRT cutoff procedure could categorize 75% of all participants correctly, while the second procedure increased correct categorization to 79%. False negative rates for both procedures were below 10%. A sequential antiphasic and diotic DIN could categorize hearing to a reasonable degree into three groups of (1) normal hearing; (2) bilateral SNHL; and (3) unilateral asymmetric SNHL or CHL. This type of approach could optimize care pathways using remote and contactless testing, by identifying unilateral SNHL and CHL as cases requiring medical referral. In contrast, bilateral SNHL cases could be referred directly to an audiologist, or nontraditional models like OTC hearing aids.

Speech Recognition in Noise Using Binaural Diotic and Antiphasic Digits-in-Noise in Children: Maturation and Self-Test Validity.

Digits-in-noise (DIN) tests have become popular for hearing screening over the past 15 years. Several recent studies have highlighted the potential utility of DIN as a school-aged hearing test. However, age may influence test performance in children due to maturation. In addition, a new antiphasic stimulus paradigm has been introduced, allowing binaural intelligibility level difference (BILD) to be measured by using a combination of conventional diotic and antiphasic DIN. This study determined age-specific normative data for diotic and antiphasic DIN, and a derived measure, BILD, in children. A secondary aim evaluated the validity of DIN as a smartphone self-test in a subgroup of young children. A cross-sectional, quantitative design was used. Participants with confirmed normal audiometric hearing were tested with a diotic and antiphasic DIN. During the test, arrangements of three spoken digits were presented in noise via headphones at varying signal-to-noise ratio (SNR). Researchers entered each three-digit spoken sequence repeated by the participant on a smartphone keypad. Overall, 621 (428 male and 193 female) normal hearing children (bilateral pure tone threshold of ≤ 20 dB hearing level at 1, 2, and 4 kHz) ranging between the ages of 6 and 13 years were recruited. A subgroup of 7-year-olds (n = 30), complying with the same selection criteria, was selected to determine the validity of self-testing. DIN testing was completed via headphones coupled to a smartphone. Diotic and antiphasic DIN speech recognition thresholds (SRTs) were analyzed and compared for each age group. BILD was calculated through subtraction of antiphasic from diotic SRTs. Multiple linear regressions were run to determine the effect of age on SRT and BILD. In addition, piecewise linear regressions were fit across different age groups. Wilcoxon signed-rank tests were used to determine differences between self- and facilitated tests. Age was a significant predictor, of both diotic and antiphasic DIN SRTs (p < 0.05). SRTs improved by 0.15 dB and 0.35 dB SNR per year for diotic and antiphasic SRTs, respectively. However, age effects were only significant up to 10 and 12 years for antiphasic and diotic SRTs, respectively. Age significantly (p < 0.001) predicted BILD, which increased by 0.18 dB per year. A small SRT advantage for facilitated over self-testing was seen but was not significant (p > 0.05). Increasing age was significantly associated with improved SRT and BILD using diotic and antiphasic DINs. DIN could be used as a smartphone self-test in young children from 7 years of age with appropriate quality control measures to avoid potential false positives.

Remote collection of speech recognition data: Considerations for testing children

This talk will provide an overview of the methods and lessons learned over the course of three studies in which children’s masked speech recognition performance was assessed remotely. The first study evaluated the binaural intelligibility level difference in typically developing children using families’ personal computers and headphones. The second study examined the impact of face coverings on consonant identification in noise with and without access to visual cues. Participants were children with and without hearing loss. The third experiment evaluated the feasibility of remote speech recognition testing for children with Down syndrome. The latter two experiments entailed providing families with laboratory hardware, following appropriate social distancing and infection control measures. Findings from all three studies will be discussed, highlighting comparisons with data obtained in the laboratory. Recommendations for remote studies involving children will be provided, based on our experiences and the resultant data.

Feasibility of remote assessment of the binaural intelligibility level difference in school-age children.

This work evaluated the feasibility and reliability of remotely assessing masked speech recognition and the binaural intelligibility level difference (BILD) in children. Participants were 28 children (6–17 years) and 11 adults (22–45 years) with self-reported normal hearing. A three-alternative forced-choice word recognition task was completed using participants' personal hardware (headphones and computer) and custom software that uploaded results to a central database. Results demonstrate that assessment of masked speech recognition and the BILD is feasible and generally reliable in a remote setting. Variability of results across individuals would likely have been reduced by distributing or specifying appropriate headphones.

Binaural intelligibility level difference with a mixed-rate strategy simulation

In noisy situations, bilateral cochlear implant (BiCI) listeners demonstrate poorer spatial release from masking compared to normal hearing (NH) listeners. One reason for this difference could be the limited access for BiCI listeners to fine structure interaural time differences (ITDs) which are crucial for binaural unmasking. Clinical processors convey speech envelopes using pulsatile high-rate (~1000 Hz) carriers, and discard the original temporal fine structure. At high rates, BiCI listeners are not sensitive to ITDs, whereas low rates (&amp;lt; 300 Hz) result in better ITD sensitivity. To preserve both ITD sensitivity and well-sampled speech envelopes, high and low rates are needed. The present study examines whether a mixed rate strategy will enable binaural unmasking in NH listeners using a 16-channel mixed-rate vocoder. Binaural intelligibility level differences were calculated from speech reception thresholds measurements in five mixed-rate configurations. Targets had a 0-μs ITD and masking speech-shaped noises were co-located or separated by applying a 400-μs ITD to the low-rate channels. Results from this experiment will help determine the potential benefits of a mixed-rate strategy to restore spatial unmasking abilities of CI listeners in noisy situations.

Speech reception with different bilateral directional processing schemes: Influence of binaural hearing, audiometric asymmetry, and acoustic scenario

Hearing aid (HA) users can differ markedly in their benefit from directional processing (or beamforming) algorithms. The current study therefore investigated candidacy for different bilateral directional processing schemes. Groups of elderly listeners with symmetric (N = 20) or asymmetric (N = 19) hearing thresholds for frequencies below 2 kHz, a large spread in the binaural intelligibility level difference (BILD), and no difference in age, overall degree of hearing loss, or performance on a measure of selective attention took part. Aided speech reception was measured using virtual acoustics together with a simulation of a linked pair of completely occluding behind-the-ear HAs. Five processing schemes and three acoustic scenarios were used. The processing schemes differed in the tradeoff between signal-to-noise ratio (SNR) improvement and binaural cue preservation. The acoustic scenarios consisted of a frontal target talker presented against two speech maskers from ±60° azimuth or spatially diffuse cafeteria noise. For both groups, a significant interaction between BILD, processing scheme, and acoustic scenario was found. This interaction implied that, in situations with lateral speech maskers, HA users with BILDs larger than about 2 dB profited more from preserved low-frequency binaural cues than from greater SNR improvement, whereas for smaller BILDs the opposite was true. Audiometric asymmetry reduced the influence of binaural hearing. In spatially diffuse noise, the maximal SNR improvement was generally beneficial. N0Sπ detection performance at 500 Hz predicted the benefit from low-frequency binaural cues. Together, these findings provide a basis for adapting bilateral directional processing to individual and situational influences. Further research is needed to investigate their generalizability to more realistic HA conditions (e.g., with low-frequency vent-transmitted sound).

Characterizing the binaural contribution to speech-in-noise reception in elderly hearing-impaired listeners

To scrutinize the binaural contribution to speech-in-noise reception, four groups of elderly participants with or without audiometric asymmetry <2 kHz and with or without near-normal binaural intelligibility level difference (BILD) completed tests of monaural and binaural phase sensitivity as well as cognitive function. Groups did not differ in age, overall degree of hearing loss, or cognitive function. Analyses revealed an influence of BILD status but not audiometric asymmetry on monaural phase sensitivity, strong correlations between monaural and binaural detection thresholds, and monaural and binaural but not cognitive BILD contributions. Furthermore, the N0Sπ threshold at 500 Hz predicted BILD performance effectively.

Binaural Hearing Ability With Bilateral Bone Conduction Stimulation in Subjects With Normal Hearing: Implications for Bone Conduction Hearing Aids.

The purpose of this study is to evaluate binaural hearing ability in adults with normal hearing when bone conduction (BC) stimulation is bilaterally applied at the bone conduction hearing aid (BCHA) implant position as well as at the audiometric position on the mastoid. The results with BC stimulation are compared with bilateral air conduction (AC) stimulation through earphones. Binaural hearing ability is investigated with tests of spatial release from masking and binaural intelligibility level difference using sentence material, binaural masking level difference with tonal chirp stimulation, and precedence effect using noise stimulus. In all tests, results with bilateral BC stimulation at the BCHA position illustrate an ability to extract binaural cues similar to BC stimulation at the mastoid position. The binaural benefit is overall greater with AC stimulation than BC stimulation at both positions. The binaural benefit for BC stimulation at the mastoid and BCHA position is approximately half in terms of decibels compared with AC stimulation in the speech based tests (spatial release from masking and binaural intelligibility level difference). For binaural masking level difference, the binaural benefit for the two BC positions with chirp signal phase inversion is approximately twice the benefit with inverted phase of the noise. The precedence effect results with BC stimulation at the mastoid and BCHA position are similar for low frequency noise stimulation but differ with high-frequency noise stimulation. The results confirm that binaural hearing processing with bilateral BC stimulation at the mastoid position is also present at the BCHA implant position. This indicates the ability for binaural hearing in patients with good cochlear function when using bilateral BCHAs.

Cochlear implantation in recipients with single-sided deafness: Audiological performance

Objective: To examine the auditory benefit of cochlear implants (CI) in patients with single-sided deafness (SSD).Material and methods: Twenty patients with a normal pure tone audiogram (n = 8) or moderate hearing loss (n = 12) in one ear and a CI system MED-EL SONATA/CONCERTO + OPUS2 (n = 12), COCHLEAR CI24RE(ST) + CP810 (n = 7) and Advanced Bionics HiRes90 K + Harmony (n = 1) in the contralateral ear and with at least 6 months of CI experience were tested with respect to directional hearing, speech perception in noise, binaural loudness matching, and binaural pitch matching. Twenty-six normal hearing controls were included for normative reference.Results: Addition of the CI significantly improves directional hearing (percentage of correct source identifications improved from 14.9 to 15.6%, root mean square error decreased from 125 to 93°) and improves speech perception in noise (speech perception threshold median improved from −2.3 to −6.0 dB signal to noise ratio, equivalent to a binaural intelligibility level difference = 3.7 dB). Alternate binaural loudness balancing showed that matching takes place at levels between 48 and 55 dB HL (group averages). In the pitch matching experiment, the standard deviation of the relative interaural frequency difference at 500, 1000, and 2000 Hz was 24.5, 22.8, and 24.0%, respectively (compared to 11.7, 14.4, and 12.3% in the control group).Conclusions: In SSD, cochlear implantation considerably improves audiological performance in terms of directional hearing, binaural signal equivalence, and speech perception.

The binaural masking-level difference of mandarin tone detection and the binaural intelligibility-level difference of mandarin tone recognition in the presence of speech-spectrum noise.

Binaural hearing involves using information relating to the differences between the signals that arrive at the two ears, and it can make it easier to detect and recognize signals in a noisy environment. This phenomenon of binaural hearing is quantified in laboratory studies as the binaural masking-level difference (BMLD). Mandarin is one of the most commonly used languages, but there are no publication values of BMLD or BILD based on Mandarin tones. Therefore, this study investigated the BMLD and BILD of Mandarin tones. The BMLDs of Mandarin tone detection were measured based on the detection threshold differences for the four tones of the voiced vowels /i/ (i.e., /i1/, /i2/, /i3/, and /i4/) and /u/ (i.e., /u1/, /u2/, /u3/, and /u4/) in the presence of speech-spectrum noise when presented interaurally in phase (S0N0) and interaurally in antiphase (SπN0). The BILDs of Mandarin tone recognition in speech-spectrum noise were determined as the differences in the target-to-masker ratio (TMR) required for 50% correct tone recognitions between the S0N0 and SπN0 conditions. The detection thresholds for the four tones of /i/ and /u/ differed significantly (p<0.001) between the S0N0 and SπN0 conditions. The average detection thresholds of Mandarin tones were all lower in the SπN0 condition than in the S0N0 condition, and the BMLDs ranged from 7.3 to 11.5 dB. The TMR for 50% correct Mandarin tone recognitions differed significantly (p<0.001) between the S0N0 and SπN0 conditions, at –13.4 and –18.0 dB, respectively, with a mean BILD of 4.6 dB. The study showed that the thresholds of Mandarin tone detection and recognition in the presence of speech-spectrum noise are improved when phase inversion is applied to the target speech. The average BILDs of Mandarin tones are smaller than the average BMLDs of Mandarin tones.

Binaural Masking Release in Children With Down Syndrome

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

Binaural hearing ability with mastoid applied bilateral bone conduction stimulation in normal hearing subjects

The ability to use binaural cues when stimulation was by bilaterally applied bone conduction (BC) transducers was investigated in 20 normal hearing participants. The results with BC stimulation were compared with normal air conduction (AC) stimulation through earphones. The binaural hearing ability was tested by spatial release from masking, binaural intelligibility level difference (BILD), binaural masking level difference (BMLD) using chirp stimulation, and test of the precedence effect. In all tests, the participants revealed a benefit of bilateral BC stimulation indicating use of binaural cues. In the speech based tests, the binaural benefit for BC stimulation was approximately half that with AC stimulation. For the BC BMLD test with chirp stimulation, there were indications of superposition of the ipsilateral and contralateral pathways at the cochlear level affecting the results. The precedence effect test indicated significantly worse results for BC stimulation than for AC stimulation with low-frequency stimulation while they were close for high-frequency stimulation; broad-band stimulation gave results that were slightly worse than the high-frequency results.

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

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

A computational model of binaural speech intelligibility level difference

This study addresses two questions relating to the binaural intelligibility level difference (BILD). First, we ask whether the BILD is underlain by an equalization‐cancellation (EC) mechanism, in which a disparity between the interaural time difference of the target and masker is exploited within each frequency channel, rather than across channels. Second, we consider the effects of three sources of internal noise on the EC mechanism: jitter in neural delays, noise in the equalization process and nonlinearities in the auditory pathway. These issues are investigated using a computational model consisting of peripheral auditory model, binaural processor, auditory scene processor and automatic speech recognition system. The binaural model is based on EC processing, with performance limited by internal noise. The auditory scene processor groups speech harmonics by common F0 and identifies 'glimpses' in which the signal‐to‐noise ratio is favorable for speech. The performance of human listeners and the computational model are compared on the same speech intelligibility test (Edmonds & Culling, 2005, JASA 117(5), 3069‐3078). The BILD of human listeners can be replicated by adjusting parameters that determine the internal noise in the EC model; however, the speech reception threshold of the model is lower than that of human listeners.

Original Article: Binaural masking level difference for speech signals in noise: Diferencia en el nivel de enmascaramiento binaural para señates vocales en ruido

This study investigates the binaural masking level difference in both detection and recognition of speech embedded in noise when the signal is phase-shifted 180° between the left and the right ear. Swedish spondaic words masked by noise were presented binaurally to 10 normally hearing subjects. The results are presented in terms of speech detection threshold, speech recognition threshold, a psychometric function of speech recognition versus signal-to-noise ratio, and speech intelligibility as a function of binaural intelligibility level difference. Both speech detection threshold and speech intelligibility improved when the speech signal was phase-shifted 180°. The binaural intelligibility level difference ranged from 5.7 to 7.7 dB.

Changes in the binaural intelligibility level difference (BILD) with age

The time course of the development of the BILD was measured in a cross-sectional study of 113 subjects with normal hearing who were approximately evenly distributed in age on a logarithmic scale between 3 and 30 years. An adaptive procedure was used to measure the minimal level at which subjects could distinguish the names of 14 familiar toys in the NoSo and NoSπ conditions in pink noise (60 dB A) and in quiet. Between age 3 and adulthood, thresholds fell by 5 dB (NoSo), 11 dB (NoSπ), and 13 dB (quiet), and the BILD (NoSo–NoSπ) increased from 2.5 to 8.5 dB. The changes in thresholds followed the same time course in the three conditions, suggesting a common cause. If it is assumed that the within-subjects standard deviation of thresholds can be taken as an index of the variability of the internal representations of speech and noise, the data can be described adequately by a model in which the internal signal-to-noise ratio required for correct identification declines with age as subjects become more familiar with the acoustic differences between the test words. Thus, it may be possible to account for the development of the BILD without invoking the maturation of binaural analysis.