Multi-modal deep learning for joint prediction of otitis media and diagnostic difficulty.

Objectives: In this study, we propose a diagnostic model for automatic detection of otitis media based on combined input of otoscopy images and wideband tympanometry measurements. Methods: We present a neural network-based model for the joint prediction of otitis media and diagnostic difficulty. We use the subclassifications acute otitis media and otitis media with effusion. The proposed approach is based on deep metric learning, and we compare this with the performance of a standard multi-task network. Results: The proposed deep metric approach shows good performance on both tasks, and we show that the multi-modal input increases the performance for both classification and difficulty estimation compared to the models trained on the modalities separately. An accuracy of 86.5% is achieved for the classification task, and a Kendall rank correlation coefficient of 0.45 is achieved for difficulty estimation, corresponding to a correct ranking of 72.6% of the cases. Conclusion: This study demonstrates the strengths of a multi-modal diagnostic tool using both otoscopy images and wideband tympanometry measurements for the diagnosis of otitis media. Furthermore, we show that deep metric learning improves the performance of the models.

A spectro-temporal modulation test for predicting speech reception in hearing-impaired listeners with hearing aids.

Spectro-temporal modulation (STM) detection sensitivity has been shown to be associated with speech-in-noise reception in hearing-impaired (HI) individuals. Based on previous research, a recent study [Zaar, Simonsen, Dau, and Laugesen (2023). Hear Res 427:108650] introduced an STM test paradigm with audibility compensation, employing STM stimulus variants using noise and complex tones as carrier signals. The study demonstrated that the test was suitable for the target population of elderly individuals with moderate-to-severe hearing loss and showed promising predictions of speech-reception thresholds (SRTs) measured in a realistic set up with spatially distributed speech and noise maskers and linear audibility compensation. The present study further investigated the suggested STM test with respect to (i) test-retest variability for the most promising STM stimulus variants, (ii) its predictive power with respect to realistic speech-in-noise reception with non-linear hearing-aid amplification, (iii) its connection to effects of directionality and noise reduction (DIR+NR) hearing-aid processing, and (iv) its relation to DIR+NR preference. Thirty elderly HI participants were tested in a combined laboratory and field study, collecting STM thresholds with a complex-tone based and a noise-based STM stimulus design, SRTs with spatially distributed speech and noise maskers using hearing aids with non-linear amplification and two different levels of DIR+NR, as well as subjective reports and preference ratings obtained in two field periods with the two DIR+NR hearing-aid settings. The results indicate that the noise-carrier based STM test variant (i) showed optimal test-retest properties, (ii) yielded a highly significant correlation with SRTs (R2=0.61) exceeding and complementing the predictive power of the audiogram, (iii) yielded significant correlation (R2=0.51) with the DIR+NR-induced SRT benefit, and (iv) did not provide significant correlation with subjective preference for DIR+NR settings in the field. Overall, the suggested STM test represents a valuable tool for diagnosing speech-reception problems that remain when hearing-aid amplification has been provided and the resulting need for and benefit from DIR+NR hearing-aid processing.

Aided Cortical Auditory Evoked Potentials in Infants With Frequency-Specific Synthetic Speech Stimuli: Sensitivity, Repeatability, and Feasibility.

OBJECTIVES: The cortical auditory evoked potential (CAEP) test is a candidate for supplementing clinical practice for infant hearing aid users and others who are not developmentally ready for behavioral testing. Sensitivity of the test for given sensation levels (SLs) has been reported to some degree, but further data are needed from large numbers of infants within the target age range, including repeat data where CAEPs were not detected initially. This study aims to assess sensitivity, repeatability, acceptability, and feasibility of CAEPs as a clinical measure of aided audibility in infants. DESIGN: One hundred and three infant hearing aid users were recruited from 53 pediatric audiology centers across the UK. Infants underwent aided CAEP testing at age 3 to 7 months to a mid-frequency (MF) and (mid-)high-frequency (HF) synthetic speech stimulus. CAEP testing was repeated within 7 days. When developmentally ready (aged 7-21 months), the infants underwent aided behavioral hearing testing using the same stimuli, to estimate the decibel (dB) SL (i.e., level above threshold) of those stimuli when presented at the CAEP test sessions. Percentage of CAEP detections for different dB SLs are reported using an objective detection method (Hotellings T 2 ). Acceptability was assessed using caregiver interviews and a questionnaire, and feasibility by recording test duration and completion rate. RESULTS: The overall sensitivity for a single CAEP test when the stimuli were ≥0 dB SL (i.e., audible) was 70% for the MF stimulus and 54% for the HF stimulus. After repeat testing, this increased to 84% and 72%, respectively. For SL >10 dB, the respective MF and HF test sensitivities were 80% and 60% for a single test, increasing to 94% and 79% for the two tests combined. Clinical feasibility was demonstrated by an excellent >99% completion rate, and acceptable median test duration of 24 minutes, including preparation time. Caregivers reported overall positive experiences of the test. CONCLUSIONS: By addressing the clinical need to provide data in the target age group at different SLs, we have demonstrated that aided CAEP testing can supplement existing clinical practice when infants with hearing loss are not developmentally ready for traditional behavioral assessment. Repeat testing is valuable to increase test sensitivity. For clinical application, it is important to be aware of CAEP response variability in this age group.

Comparison of hearing aid fitting effectiveness with audiograms from either user-operated or traditional audiometry in a clinical setting: a study protocol for a blinded non-inferiority randomised controlled trial.

INTRODUCTION: There is a worldwide need to enhance the capacity of audiometry testing. The objective of this study is to compare the User-operated Audiometry (UAud) system with traditional audiometry in a clinical setting, by investigating if hearing aid effectiveness based on UAud is non-inferior to hearing aid effectiveness based on traditional audiometry, and whether thresholds obtained with the user-operated version of the Audible Contrast Threshold (ACT) test correlates to traditional measures of speech intelligibility. METHODS AND ANALYSIS: The design will be a blinded non-inferiority randomised controlled trial. 250 adults referred for hearing aid treatment will be enrolled in the study. Study participants will be tested using both traditional audiometry as well as the UAud system and they will answer the questionnaire Speech, Spatial and Qualities of Hearing Scale (SSQ12) at baseline. Participants will be randomly divided to receive hearing aids fitted based on either UAud or traditional audiometry. Three months after participants have started using their hearing aids, they will undergo a hearing in noise test with hearing aids to measure their speech-in-noise performance and answer the following questionnaires: SSQ12, the Abbreviated Profile of Hearing Aid Benefit and the International Outcome Inventory for Hearing Aids. The primary outcome is a comparison of the change in SSQ12 scores from baseline to follow-up between the two groups. Participants will undergo the user-operated ACT test of spectro-temporal modulation sensitivity as part of the UAud system. The ACT results will be compared with measures of speech intelligibility from the traditional audiometry session and follow-up measurements. ETHICS AND DISSEMINATION: The project was evaluated by the Research Ethics Committee of Southern Denmark and judged not to need approval. The findings will be submitted to an international peer-reviewed journal and presented at national and international conferences. TRIAL REGISTRATION NUMBER: NCT05043207.

Toward a clinically viable spectro-temporal modulation test for predicting supra-threshold speech reception in hearing-impaired listeners.

The ability of hearing-impaired listeners to detect spectro-temporal modulation (STM) has been shown to correlate with individual listeners' speech reception performance. However, the STM detection tests used in previous studies were overly challenging especially for elderly listeners with moderate-to-severe hearing loss. Furthermore, the speech tests considered as a reference were not optimized to yield ecologically valid outcomes that represent real-life speech reception deficits. The present study investigated an STM detection measurement paradigm with individualized audibility compensation, focusing on its clinical viability and relevance as a real-life supra-threshold speech intelligibility predictor. STM thresholds were measured in 13 elderly hearing-impaired native Danish listeners using four previously established (noise-carrier based) and two novel complex-tone carrier based STM stimulus variants. Speech reception thresholds (SRTs) were measured (i) in a realistic spatial speech-on-speech set up and (ii) using co-located stationary noise, both with individualized amplification. In contrast with previous related studies, the proposed measurement paradigm yielded robust STM thresholds for all listeners and conditions. The STM thresholds were positively correlated with the SRTs, whereby significant correlations were found for the realistic speech-test condition but not for the stationary-noise condition. Three STM stimulus variants (one noise-carrier based and two complex-tone based) yielded significant predictions of SRTs, accounting for up to 53% of the SRT variance. The results of the study could form the basis for a clinically viable STM test for quantifying supra-threshold speech reception deficits in aided hearing-impaired listeners.

A Deep Learning Approach for Detecting Otitis Media From Wideband Tympanometry Measurements.

OBJECTIVE: In this study, wepropose an automatic diagnostic algorithm for detecting otitis media based on wideband tympanometry measurements. METHODS: We develop a convolutional neural network for classification of otitis media based on the analysis of the wideband tympanogram. Saliency maps are computed to gain insight into the decision process of the convolutional neural network. Finally, we attempt to distinguish between otitis media with effusion and acute otitis media, a clinical subclassification important for the choice of treatment. RESULTS: The approach shows high performance on the overall otitis media detection with an accuracy of 92.6%. However, the approach is not able to distinguish between specific types of otitis media. CONCLUSION: Out approach can detect otitis media with high accuracy and the wideband tympanogram holds more diagnostic information than the commonly used techniques wideband absorbance measurements and simple tympanograms. SIGNIFICANCE: This study shows how advanced deep learning methods enable automatic diagnosis of otitis media based on wideband tympanometry measurements, which could become a valuable diagnostic tool.

Inter-rater reliability of the diagnosis of otitis media based on otoscopic images and wideband tympanometry measurements.

OBJECTIVES: This study aims to investigate the inter-rater reliability and agreement of the diagnosis of otitis media with effusion, acute otitis media, and no effusion cases based on an otoscopy image and in some cases an additional wideband tympanometry measurement of the patient. METHODS: 1409 cases were examined and diagnosed by an otolaryngologist in the clinic, and otoscopy examination and wideband tympanometry (WBT) measurement were conducted. Afterwards, four otolaryngologists (Ear, Nose, and Throat doctors, ENTs), who did not perform the acute examination of the patients, evaluated the otoscopy images and WBT measurements results for diagnosis (acute otitis media, otitis media with effusion, or no effusion). They also specified their diagnostic certainty for each case, and reported whether they used the image, wideband tympanometry, or both, for diagnosis. RESULTS: All four ENTs agreed on the diagnosis in 57% of the cases, with a pairwise agreement of 74%, and a Light's Kappa of 0.58. There are, however, large differences in agreement and certainty between the three diagnoses. Acute otitis media yields the highest agreement (77% between all four ENTs) and certainty (0.90), while no effusion shows much lower agreement and certainty (34% and 0.58, respectively). There is a positive correlation between certainty and agreement between the ENTs across all cases, and both certainty and agreement increase for cases where a WBT measurement is shown in addition to the otoscopy image. CONCLUSIONS: The inter-rater reliability between four ENTs was high when diagnosing acute otitis media and lower when diagnosing otitis media with effusion. However, WBT can add valuable information to get closer to the ground-truth diagnosis without myringotomy. Furthermore, the diagnostic certainty increases when the WBT is examined together with the otoscopy image.

Equivalent threshold sound pressure levels for click and CE-Chirp® stimuli delivered by the SnapPROBE™.

OBJECTIVE: To estimate the equivalent threshold sound pressure levels (ETSPLs) for nine stimuli used today and in the future for universal newborn hearing screening and diagnostics delivered by the Interacoustics SnapPROBE™. DESIGN: The Click and eight variants of the CE-Chirp® were included to establish ETSPLs when delivered by the SnapPROBE™. The short duration stimuli were presented at a 20/s repetition rate for about 1-2 s following the international standards for establishing ETSPLs. STUDY SAMPLE: 50 ears from a total of 27 normal hearing young adult subjects (female/male = 16/11; age = 21-25 years, mean age = 23.1 years). RESULTS: Peak-to-peak equivalent signal levels and root mean square signal levels (at 20/s repetition rate) for the nine stimuli are stated. CONCLUSIONS: The ETSPLs are in alignment overall with those found in previous studies, while some levels are about 2-6 dB higher for this study compared to the Interacoustics Titan IOW probe and the ER-3A insert earphone. The results are relevant for present and future universal newborn hearing screening and diagnostics carried out with the SnapPROBE™ to ensure that correct stimulation levels are applied.

Do Room Acoustics Affect the Amplitude of Sound-Field Auditory Steady-State Responses?

The sound-field auditory steady-state response (ASSR) is a promising measure for the objective validation of hearing-aid fitting in patients who are unable to respond to behavioral testing reliably. To record the sound-field ASSR, the stimulus is reproduced through a loudspeaker placed in front of the patient. However, the reverberation and background noise of the measurement room could reduce the stimulus modulation used for eliciting the ASSR. As the ASSR level is heavily dependent on the stimulus modulation, any reduction due to room acoustics could affect the clinical viability of sound-field ASSR testing. This study investigated the effect of room acoustics on the level and detection rate of sound-field ASSR. The study also analyzed whether early decay time and an auditory-inspired relative modulation power model could be used to predict the changes in the recorded ASSR in rooms. A monaural auralization approach was used to measure sound-field ASSR via insert earphones. ASSR was measured for 15 normal-hearing adult subjects using narrow-band CE-Chirps® centered at the octave bands of 500, 1000, 2000, and 4000 Hz. These stimuli were convolved with simulated impulse responses of three rooms inspired by audiological testing rooms. The results showed a significant reduction of the ASSR level for the room conditions compared with the reference anechoic condition. Despite this reduction, the detection rates for the first harmonics of the ASSR were unaffected when sufficiently long recordings (up to 6 min) were made. Furthermore, the early decay time and relative modulation power appear to be useful predictors of the ASSR level in the measurement rooms.

Potential Destructive Binaural Interaction Effects in Auditory Steady-State Response Measurements.

An aided sound-field auditory steady-state response (ASSR) has the potential to be used to objectively validate hearing-aid (HA) fittings in clinics. Each aided ear should ideally be tested independently, but it is suspected that binaural testing may be used by clinics to reduce test time. This study simulates dichotic ASSR sound-field conditions to examine the risk of making false judgments due to unchecked binaural effects. Unaided ASSRs were recorded with a clinical two-channel electroencephalography (EEG) system for 15 normal hearing subjects using a three-band CE-Chirp® stimulus. It was found that the noise corrected power of a response harmonic can be suppressed by up to 10 dB by introducing large interaural time differences equal to half the time period of the stimulus envelope, which may occur in unilateral HA users. These large interaural time differences also changed the expression of ASSR power across the scalp, resulting in dramatically altered topographies. This would lead to considerably lower measured response power and possibly nondetections, evidencing that even well fit HAs are fit poorly (false referral), whereas monaural ASSR tests would pass. No effect was found for simulated lateralizations of the stimulus, which is beneficial for a proposed aided ASSR approach. Full-scalp ASSR recordings match previously found 40 Hz topographies but demonstrate suppression of cortical ASSR sources when using stimuli in interaural envelope antiphase.

Deep metric learning for otitis media classification.

In this study, we propose an automatic diagnostic algorithm for detecting otitis media based on otoscopy images of the tympanic membrane. A total of 1336 images were assessed by a medical specialist into three diagnostic groups: acute otitis media, otitis media with effusion, and no effusion. To provide proper treatment and care and limit the use of unnecessary antibiotics, it is crucial to correctly detect tympanic membrane abnormalities, and to distinguish between acute otitis media and otitis media with effusion. The proposed approach for this classification task is based on deep metric learning, and this study compares the performance of different distance-based metric loss functions. Contrastive loss, triplet loss and multi-class N-pair loss are employed, and compared with the performance of standard cross-entropy and class-weighted cross-entropy classification networks. Triplet loss achieves high precision on a highly imbalanced data set, and the deep metric methods provide useful insight into the decision making of a neural network. The results are comparable to the best clinical experts and paves the way for more accurate and operator-independent diagnosis of otitis media.

Reproducing ear-canal reflectance using two measurement techniques in adult ears.

Clinical diagnostic applications of ear-canal reflectance have been researched extensively in the literature, however, the measurement uncertainty associated with the conventional measurement technique using an insert ear probe is unknown in human ear canals. Ear-canal reflectance measured using an ear probe is affected by multiple sources of error, including incorrect estimates of the ear-canal cross-sectional area and oblique ear-probe insertions. In this paper, ear-canal reflectance measurements are reproduced in an occluded-ear simulator and in 54 adult ear canals using two different measurement techniques: a conventional ear probe and a two-microphone probe that enables the separation of reverse- and forward-propagating plane waves. The two-microphone probe is inserted directly into test subjects' ear canals, and the two-microphone method is distinguished by not requiring the ear-canal cross-sectional area to calculate the ear-canal reflectance. The results show a reasonable agreement between the two measurement techniques. The paper further examines the influence of oblique ear-probe insertions and the compensation for such oblique insertions, which results in an improved agreement between the two measurement techniques.

Compensating for oblique ear-probe insertions in ear-canal reflectance measurements.

Measurements of the ear-canal reflectance using an ear probe require estimating the characteristic impedance of the ear canal in situ. However, an oblique insertion of the ear probe into a uniform waveguide prevents accurately estimating its characteristic impedance using existing time-domain methods. This is caused by the non-uniformity immediately in front of the ear probe when inserted at an oblique angle, resembling a short horn loading, and introduces errors into the ear-canal reflectance. This paper gives an overview of the influence of oblique ear-probe insertions and shows how they can be detected and quantified by estimating the characteristic impedance using multiple truncation frequencies, i.e., limiting the utilized frequency range. Additionally, a method is proposed to compensate for the effects on reflectance of an oblique ear-probe insertion into a uniform waveguide. The incident impedance of the horn loading is estimated, i.e., were the uniform waveguide anechoic, which replaces the characteristic impedance when calculating reflectance. The method can compensate for an oblique ear-probe insertion into a uniform occluded-ear simulator and decrease the dependency of reflectance on insertion depth in an ear canal. However, more research is required to further assess the method in ear canals.

A coupler-based calibration method for ear-probe microphones.

The calibration of ear-probe microphones can increase the precision of calibrating stimulus levels in situ and of measuring acoustic responses from the ear. This paper proposes a methodology to measure the sensitivity of an ear-probe microphone, requiring only an acoustic coupler and a calibrated reference microphone. The input impedance of the coupler is measured, enabled by a preliminary acoustic Thévenin calibration of the ear probe, and the plane-wave transfer impedance of the coupler is calculated analytically. Using these two quantities, the pressure transfer function between the reference microphone and the ear-probe microphone is estimated. This enables estimating the sensitivity of the ear-probe microphone. The proposed and an existing method were compared, resulting in substantially similar ear-probe microphone sensitivities. The proposed method is practically feasible in producing reliable measurements of sound pressure in the ear canal and calibrating stimulus levels in a clinical setting.

On the Cost of Introducing Speech-Like Properties to a Stimulus for Auditory Steady-State Response Measurements.

Validating hearing-aid fittings in prelingual infants is challenging because typical measures (aided audiometry, etc.) are impossible with infants. One objective alternative uses an aided auditory steady-state response (ASSR) measurement. To make an appropriate measurement, the hearing aid's signal-processing features must be activated (or deactivated) as if the ASSR stimulus was real speech. Rather than manipulating the hearing-aid settings to achieve this, an ASSR stimulus with speech-like properties was developed. This promotes clinical simplicity and face validity of the validation. The stimulus consists of narrow-band CE-Chirps®, modified to mimic the International Speech Test Signal (ISTS). This study examines the cost of introducing the speech-like features into the ASSR stimulus. Thus, 90 to 100 Hz ASSRs were recorded to the ISTS-modified stimulus as well as an equivalent stimulus without the ISTS modification, presented through insert phones to 10 young normal-hearing subjects. Noise-corrected ASSR magnitudes and clinically relevant detection times were estimated and analyzed with mixed-model analyses of variance. As a supplement, the observed changes to the ASSR magnitudes were compared with an objective characterization of the stimuli based on modulation power. The main findings were a reduction in ASSR magnitude of 4 dB and an increase in detection time by a factor of 1.5 for the ISTS-modified stimulus compared with the standard. Detection rates were unaffected given sufficient recording time. For clinical use of the hearing-aid validation procedure, the key metric is the detection time. While this varied considerably across subjects, the observed 50% mean increase corresponds to less than 1 min of additional recording time.

Incorporating evanescent modes and flow losses into reference impedances in acoustic Thévenin calibration.

This paper proposes an alternative approach to acoustic Thévenin calibration of an ear probe. An existing methodology derives the Thévenin-equivalent source parameters from the measured probe pressures in a number of short waveguides by solving an overdetermined system of equations. This existing methodology is affected by errors caused by evanescent modes when the waveguide model lengths are estimated. These errors introduce a parallel acoustic compliance into the source parameters. The proposed methodology takes into account evanescent modes and flow losses in the transition between the probe tube and waveguides during calibration. This is achieved by positioning the probe tube, without an ear tip, flush with the input plane in waveguides of well-defined dimensions and utilizing the physical rather than estimated lengths to calculate the analytical waveguide models. Terms that model evanescent modes and flow losses are added to the plane-wave impedance and adjusted to minimize the calibration error. It is shown that this method can reduce the calibration error across a wide frequency range and remove the parallel compliance from the source parameters. This approach leads to an independence of the source parameters on the calibration waveguide radius, though subsequent impedance measurements are still affected by evanescent modes.

Sensitivity to Angular and Radial Source Movements as a Function of Acoustic Complexity in Normal and Impaired Hearing.

In contrast to static sounds, spatially dynamic sounds have received little attention in psychoacoustic research so far. This holds true especially for acoustically complex (reverberant, multisource) conditions and impaired hearing. The current study therefore investigated the influence of reverberation and the number of concurrent sound sources on source movement detection in young normal-hearing (YNH) and elderly hearing-impaired (EHI) listeners. A listening environment based on natural environmental sounds was simulated using virtual acoustics and rendered over headphones. Both near-far ('radial') and left-right ('angular') movements of a frontal target source were considered. The acoustic complexity was varied by adding static lateral distractor sound sources as well as reverberation. Acoustic analyses confirmed the expected changes in stimulus features that are thought to underlie radial and angular source movements under anechoic conditions and suggested a special role of monaural spectral changes under reverberant conditions. Analyses of the detection thresholds showed that, with the exception of the single-source scenarios, the EHI group was less sensitive to source movements than the YNH group, despite adequate stimulus audibility. Adding static sound sources clearly impaired the detectability of angular source movements for the EHI (but not the YNH) group. Reverberation, on the other hand, clearly impaired radial source movement detection for the EHI (but not the YNH) listeners. These results illustrate the feasibility of studying factors related to auditory movement perception with the help of the developed test setup.

Selection of test-setup parameters to target specific signal-to-noise regions in speech-on-speech intelligibility testing.

OBJECTIVE: To investigate the magnitude of the change in speech-reception threshold (SRT) provided by altering four different test-setup parameters. Furthermore, to determine whether these changes in SRT are of a sufficient magnitude, such that they can be used to design a test-setup in future experiments that target a predefined signal-to-noise ratio (SNR) region. This could be particularly important if the test contrast investigated is confounded with test SNR. DESIGN: The investigated test-setup parameters were: Spatial separation between target (0°) and maskers (±15°, ±30°, ±45°, or ±75°), number of maskers (two, four or six), scoring method (scoring percent-correct words or sentences) and masker gender (same or opposite to target). Twenty SRTs were measured per test subject. STUDY SAMPLE: Twenty hearing-impaired test subjects participated over two visits. RESULTS: Alteration of masker gender, spatial separation between target and masker (±15°, ±30°, ± 45°), and scoring method was shown to offer SRT changes of a sufficient magnitude. The different test setups resulted in average SRTs ranging from -4.0 to 3.3 dB. CONCLUSION: Deliberately selecting test setup parameters can change the overall difficulty of the test by up to 7.3 dB SRT. Thus, a future experiment can, to this extent, be designed to target a specific SNR region.

Compensating for evanescent modes and estimating characteristic impedance in waveguide acoustic impedance measurements.

The ear-canal acoustic impedance and reflectance are useful for assessing conductive hearing disorders and calibrating stimulus levels in situ. However, such probe-based measurements are affected by errors due to the presence of evanescent modes and incorrect estimates or assumptions regarding characteristic impedance. This paper proposes a method to compensate for evanescent modes in measurements of acoustic impedance, reflectance, and sound pressure in waveguides, as well as estimating the characteristic impedance immediately in front of the probe. This is achieved by adjusting the characteristic impedance and subtracting an acoustic inertance from the measured impedance such that the non-causality in the reflectance is minimized in the frequency domain using the Hilbert transform. The method is thus capable of estimating plane-wave quantities of the sought-for parameters by supplying only an arbitrary initial value for the characteristic impedance. From a comparison with a simulated waveguide, it is shown that this method can accurately estimate these quantities in a waveguide that is uniform at the position of the probe. Finally, it is demonstrated how evanescent modes, characteristic impedance, and the proposed methodology can affect the measured acoustic impedance and reflectance of an occluded-ear simulator.

Temporal Fine-Structure Coding and Lateralized Speech Perception in Normal-Hearing and Hearing-Impaired Listeners.

This study investigated the relationship between speech perception performance in spatially complex, lateralized listening scenarios and temporal fine-structure (TFS) coding at low frequencies. Young normal-hearing (NH) and two groups of elderly hearing-impaired (HI) listeners with mild or moderate hearing loss above 1.5 kHz participated in the study. Speech reception thresholds (SRTs) were estimated in the presence of either speech-shaped noise, two-, four-, or eight-talker babble played reversed, or a nonreversed two-talker masker. Target audibility was ensured by applying individualized linear gains to the stimuli, which were presented over headphones. The target and masker streams were lateralized to the same or to opposite sides of the head by introducing 0.7-ms interaural time differences between the ears. TFS coding was assessed by measuring frequency discrimination thresholds and interaural phase difference thresholds at 250 Hz. NH listeners had clearly better SRTs than the HI listeners. However, when maskers were spatially separated from the target, the amount of SRT benefit due to binaural unmasking differed only slightly between the groups. Neither the frequency discrimination threshold nor the interaural phase difference threshold tasks showed a correlation with the SRTs or with the amount of masking release due to binaural unmasking, respectively. The results suggest that, although HI listeners with normal hearing thresholds below 1.5 kHz experienced difficulties with speech understanding in spatially complex environments, these limitations were unrelated to TFS coding abilities and were only weakly associated with a reduction in binaural-unmasking benefit for spatially separated competing sources.