Metabolic and Sensory Components of Age-Related Hearing Loss: Associations With Distortion- and Reflection-Based Otoacoustic Emissions.

Age-related hearing loss is difficult to study in humans because multiple genetic and environmental risk factors may contribute to pathology and cochlear function declines in older adults. These pathologies, including degeneration of the stria vascularis, are hypothesized to affect outer hair cells responsible for active cochlear amplification of low-level sounds. Otoacoustic emission (OAE) measures are used to quantify the energy added to the traveling wave in cochlear amplification, which typically weakens with increased pure-tone thresholds and for older individuals. Thus, the current study evaluated two OAE measures for individuals with different components of age-related hearing loss. We examined two retrospective adult lifespan datasets (18 to 89+ years of age) from independent sites (Medical University of South Carolina and Boys Town National Research Hospital), which included demographics, noise history questionnaires, distortion-product otoacoustic emissions (DPOAE), and cochlear reflectance (CR). Metabolic and sensory estimates of age-related hearing loss were derived from the audiograms in each dataset, and then tested for associations with DPOAE and CR. The results showed that metabolic estimates increased for older participants and were associated with lower overall DPOAE and CR magnitudes across frequency (i.e., lower fitted intercepts). Sensory estimates were significantly higher for males, who reported more positive noise histories compared to females and were associated with steeper negative across-frequency slopes for DPOAEs. Although significant associations were observed between OAE configurations, DPOAEs appeared uniquely sensitive to metabolic estimates. The current findings suggest that distortion-based measures may provide greater sensitivity than reflection-based measures to the components of age-related hearing loss.

Conductive Hearing Loss Estimated From Wideband Acoustic Immittance Measurements in Ears With Otitis Media With Effusion.

OBJECTIVES: Previous work has shown that wideband acoustic immittance (WAI) is sensitive to the volume of effusion present in ears with otitis media with effusion (OME). Prior work also demonstrates that the volume of the effusion appears to drive, or at least play a significant role in, how much conductive hearing loss (CHL) a child has due to a given episode of OME. Given this association, the goal of this work was to determine how well CHL could be estimated directly from WAI in ears with OME. DESIGN: Sixty-three ears from a previously published study on OME (ages 9 months to 11 years, 2 months) were grouped based on effusion volume (full, partial, or clear) determined during tympanostomy tube placement surgery and compared with age-matched normal control ears. Audiometric thresholds were obtained for a subset of the 34 ears distributed across the four groups. An electrical-analog model of ear-canal acoustics and middle-ear mechanics was fit to the measured WAI from individual ears. Initial estimates of CHL were derived from either (1) average absorbance or (2) the model component thought to represent damping in the ossicular chain. RESULTS: The analog model produced good fits for all effusion-volume groups. The two initial CHL estimates were both well correlated (87% and 81%) with the pure-tone average hearing thresholds used to define the CHL. However, in roughly a third of the ears (11/34), the estimate based on damping was too large by nearly a factor of two. This observation motivated improved CHL estimates. CONCLUSIONS: Our CHL estimation method can estimate behavioral audiometric thresholds (CHL) within a margin of error that is small enough to be clinically meaningful. The importance of this finding is increased by the challenges associated with behavioral audiometric testing in pediatric populations, where OME is the most common. In addition, the discovery of two clusters in the damping-related CHL estimate suggests the possible existence of two distinctly different types of ears: pressure detectors and power detectors.

Preserving Wideband Tympanometry Information With Artifact Mitigation.

OBJECTIVE: Absorbance measured using wideband tympanometry (WBT) has been shown to be sensitive to changes in middle and inner ear mechanics, with potential to diagnose various mechanical ear pathologies. However, artifacts in absorbance due to measurement noise can obscure information related to pathologies and increase intermeasurement variability. Published reports frequently present absorbance that has undergone smoothing to minimize artifact; however, smoothing changes the true absorbance and can destroy important narrow-band characteristics such as peaks and notches at different frequencies. Because these characteristics can be unique to specific pathologies, preserving them is important for diagnostic purposes. Here, we identify the cause of artifacts in absorbance and develop a technique to mitigate artifacts while preserving the underlying WBT information. DESIGN: A newly developed Research Platform for the Interacoustics Titan device allowed us to study raw microphone recordings and corresponding absorbances obtained by WBT measurements. We investigated WBT measurements from normal hearing ears and ears with middle and inner ear pathologies for the presence of artifact and noise. Furthermore, it was used to develop an artifact mitigation procedure and to evaluate its effectiveness in mitigating artifacts without distorting the true WBT information. RESULTS: We observed various types of noise that can plague WBT measurements and that contribute to artifacts in computed absorbances, particularly intermittent low-frequency noise. We developed an artifact mitigation procedure that incorporates a high-pass filter and a Tukey window. This artifact mitigation resolved the artifacts from low-frequency noise while preserving characteristics in absorbance in both normal hearing ears and ears with pathology. Furthermore, the artifact mitigation reduced intermeasurement variability. CONCLUSIONS: Unlike smoothing algorithms used in the past, our artifact mitigation specifically removes artifacts caused by noise. It does not change frequency response characteristics, such as narrow-band peaks and notches in absorbance at different frequencies that can be important for diagnosis. Also, by reducing intermeasurement variability, the artifact mitigation can improve the test-retest reliability of these measurements.

Understanding Self-reported Hearing Disability in Adults With Normal Hearing.

OBJECTIVES: Despite a diagnosis of normal hearing, many people experience hearing disability (HD) in their everyday lives. This study assessed the ability of a number of demographic and auditory variables to explain and predict self-reported HD in people regarded as audiologically healthy via audiometric thresholds. DESIGN: One-hundred eleven adults (ages 19 to 74) with clinically normal hearing (i.e., audiometric thresholds ≤25 dB HL at all octave and interoctave frequencies between 0.25 and 8 kHz and bilaterally symmetric hearing) were asked to complete the 12-item version of the Speech, Spatial, and Qualities of Hearing Scale (SSQ12) as a measure of self-reported HD. Patient history and a number of standard and expanded measures of hearing were assessed in a multivariate regression analysis to predict SSQ12 score. Patient history included age, sex, history of noise exposure, and tinnitus. Hearing-related measures included audiometry at standard and extended high frequencies, word recognition, otoacoustic emissions, auditory brainstem response, the Montreal Cognitive Assessment, and FM detection threshold. RESULTS: History of impulse noise exposure, speech-intelligibility index, and FM detection threshold accurately predicted SSQ12 and were able to account for 40% of the SSQ12 score. These three measures were also able to predict whether participants self-reported HD with a sensitivity of 89% and specificity of 86%. CONCLUSIONS: Although participant audiometric thresholds were within normal limits, higher thresholds, history of impulse noise exposure, and FM detection predicted self-reported HD.

Evaluation of Remote Categorical Loudness Scaling.

PURPOSE: The aims of this study were to (a) demonstrate the feasibility of administering categorical loudness scaling (CLS) tests in a remote setting, (b) assess the reliability of remote compared with laboratory CLS results, and (c) provide preliminary evidence of the validity of remote CLS testing. METHOD: CLS data from 21 adult participants collected in a home setting were compared to CLS data collected in a laboratory setting from previous studies. Five participants took part in studies in both settings. Precalibrated equipment was delivered to participants who performed headphone output level checks and measured ambient noise levels. After a practice run, CLS measurements were collected for two runs at 1 and 4 kHz. RESULTS: Mean headphone output levels were within 1.5 dB of the target calibration level. Mean ambient noise levels were below the target level. Within-run variability was similar between the two settings, but across-run bias was smaller for data collected in the laboratory setting compared with the remote setting. Systematic differences in CLS functions were not observed for the five individuals who participated in both settings. CONCLUSIONS: This study demonstrated that precise stimulus levels can be delivered and background noise levels can be controlled in a home environment. Across-run bias for remote CLS was larger than for in-laboratory CLS, indicating that further work is needed to improve the reliability of CLS data collected in remote settings. Supplemental Material https://doi.org/10.23641/asha.17131856.

The influence of otitis media with effusion on middle-ear impedance estimated from wideband acoustic immittance measurements.

The goal of this work was to estimate the middle-ear input impedance ( Zme) from wideband acoustic immittance (WAI) measures and determine whether Zme improves the clinical utility of WAI. The data used in this study were from a previously reported set of WAI measurements in ears with otitis media with effusion [OME; Merchant, Al-Salim, Tempero, Fitzpatrick, and Neely (2021). Ear Hear., published online]. Ears with OME were grouped based on effusion volume, which was confirmed during tube surgery. Zme was estimated from the measured ear-canal impedance. An electrical-analog model of ear-canal acoustics and middle-ear mechanics was used to model the ear canal and Zme. The model results fit the measured responses well for all conditions. A regression approach was used to classify the responses of different variable types to effusion volume groups and determine the specificity and sensitivity of the binary classifications. The Zme magnitude increased with increasing effusion volume. The area under the receiver operating characteristic curve (AUC) was compared for binary decisions of the OME categories. The Zme estimate resulted in a clinically meaningful improvement in the AUC for distinguishing healthy ears from ears with OME. Overall, these results suggest that Zme estimation may provide useful information of potential clinical value to improve the diagnostic utility of WAI measurements for OME.

On causality and aural impulse responses synthesized using the inverse discrete Fourier transform.

Causality is a fundamental property of physical systems and dictates that a time impulse response characterizing any causal system must be one-sided. However, when synthesized using the inverse discrete Fourier transform (IDFT) of a corresponding band-limited numerical frequency transfer function, several papers have reported two-sided IDFT impulse responses of ear-canal reflectance and ear-probe source parameters. Judging from the literature on ear-canal reflectance, the significance and source of these seemingly non-physical negative-time components appear largely unclear. This paper summarizes and clarifies different sources of negative-time components through ideal and practical examples and illustrates the implications of constraining aural IDFT impulse responses to be one-sided. Two-sided IDFT impulse responses, derived from frequency-domain measurements of physical systems, normally occur due to the two-sided properties of the discrete Fourier transform. Still, reflectance IDFT impulse responses may serve a number of practical and diagnostic purposes.

Improving the Differential Diagnosis of Otitis Media With Effusion Using Wideband Acoustic Immittance.

OBJECTIVES: The objective of this work is to determine whether there is a systematic effect of middle ear effusion volume on wideband acoustic immittance in children with surgically confirmed otitis media with effusion. DESIGN: Wideband acoustic immittance was measured in 49 ears from children (9 months to 11 years) who had a diagnosis of otitis media with effusion and compared to 14 ears from children (10 months to 10 years) without a recent history of otitis media. For children with otitis media with effusion, wideband acoustic immittance testing took place in the child's preoperative waiting room before surgical placement of tympanostomy tubes. Testing was completed in a pressurized condition (wideband tympanometry) for all ears as well as in an ambient condition in a subset of ears. Intraoperative findings regarding effusion volume were reported by the surgeons immediately before tube placement and confirmed following myringotomy. This classified the volume of effusion as compared to middle ear volume categorically as either full, partial, or clear of effusion. The type of wideband acoustic immittance explored in this work was absorbance. Absorbance responses were grouped based on effusion volume into one of four groups: full effusions, partial effusions, ears clear of effusion at the time of surgery, and normal control ears. Standard tympanometry was also completed on all ears. RESULTS: Absorbance is systematically reduced as the volume of the middle ear effusion increases. This reduction is present at most frequencies but is greatest in the frequency range from 1 to 5 kHz. A multivariate logistic regression approach was utilized to classify ears based on effusion volume. The regression approach classified ears as effusion present (full and partial ears) or absent (clear ears and normal control ears) with 100% accuracy, ears with effusion present as either partial or full with 100% accuracy, and ears without effusion as either normal control ears or ears clear of effusion with 75% accuracy. Regression performance was also explored when the dataset was split into a training set (70% of the data) and a validation test set (30% of the data) to simulate how this approach would perform on unseen data in a clinical setting. Accuracy, sensitivity, specificity, and area under the receiver operating characteristic curve are reported. Overall, this approach demonstrates high sensitivity and specificity for classifying ears as effusion being present or absent and as present effusions being full or partial with areas under the curve ranging from 1 to 0.944. Despite the lack of effusion present in both clear ears and normal control ears, this approach was able to distinguish between these ears, but with a more moderate sensitivity and specificity. No systematic effect of effusion volume was found on standard tympanometry. CONCLUSIONS: Wideband acoustic immittance, and more specifically, absorbance, is a strong and sensitive indicator of the volume of a middle ear effusion in children with otitis media with effusion.

Maximum Expected Information Approach for Improving Efficiency of Categorical Loudness Scaling.

Categorical loudness scaling (CLS) measures provide useful information about an individual's loudness perception across the dynamic range of hearing. A probability model of CLS categories has previously been described as a multi-category psychometric function (MCPF). In the study, a representative "catalog" of potential listener MCPFs was used in conjunction with maximum-likelihood estimation to derive CLS functions for participants with normal hearing and with hearing loss. The approach of estimating MCPFs for each listener has the potential to improve the accuracy of the CLS measurements, particularly when a relatively low number of data points are available. The present study extends the MCPF approach by using Bayesian inference to select stimulus parameters that are predicted to yield maximum expected information (MEI) during data collection. The accuracy and reliability of the MCPF-MEI approach were compared to the standardized CLS measurement procedure (ISO 16832:2006, 2006). A non-adaptive, fixed-level, paradigm served as a "gold-standard" for this comparison. The test time required to obtain measurements in the standard procedure is a major barrier to its clinical uptake. Test time was reduced from approximately 15 min to approximately 3 min with the MEI-adaptive procedure. Results indicated that the test-retest reliability and accuracy of the MCPF-MEI adaptive procedures were similar to the standardized CLS procedure. Computer simulations suggest that the reliability and accuracy of the MEI procedure were limited by intrinsic uncertainty of the listeners represented in the MCPF catalog. In other words, the MCPF provided insufficient predictive power to significantly improve adaptive-tracking efficiency under practical conditions. Concurrent optimization of both the MCPF catalog and the MEI-adaptive procedure have the potential to produce better results. Regardless of the adaptive-tracking method used in the CLS procedure, the MCPF catalog remains clinically useful for enabling maximum-likelihood determination of loudness categories.

A model of auditory brainstem response wave I morphology.

Use of the auditory brainstem response (ABR) in research has increased in the search for physiological correlates of noise-induced damage to the cochlea. The extraction of data from the ABR has traditionally relied on visual determination of peaks and troughs to calculate metrics such as wave amplitude. Visual determination can be reliable when evaluated by trained, experienced personnel, but noisy waveforms and overlapping waves produce uncertain data. The present study proposes and validates a method of fitting summed Gaussian functions to the summating potential and wave I of the ABR. This method could be useful to the research community studying these potentials by providing more accurate measures of wave amplitude than by visual determination.

Age Effects on Cochlear Reflectance in Adults.

OBJECTIVES: Cochlear reflectance (CR) is the cochlear contribution to ear-canal reflectance. CR is a type of otoacoustic emission that is calculated as a transfer function between forward pressure and reflected pressure. The purpose of this study was to assess effects of age on CR in adults and interactions among age, sex, and hearing loss. DESIGN: Data were collected from 60 adults selected for their age (e.g., 20-29, 30-39, 40-49, 50-59, 60-69, 70-79 years) and normal middle ear status. A wideband noise stimulus presented at three stimulus levels (30, 40, 50 dB SPL) was used to elicit CR. Half-octave bands of CR signal magnitude (CRM), CR noise, and the CR signal-to-noise ratio (CR-SNR) were extracted from the wideband CR response. Regression analyses were conducted to assess interactions among CR, age, sex, and pure-tone thresholds at closely matched frequency bands across stimulus levels. RESULTS: Although increased age was generally associated with lower CRM and CR-SNR at some band frequencies and stimulus levels, no significant effects of age remained after controlling for effects of pure-tone thresholds. Increases in pure-tone thresholds were associated with lower CRM and CR-SNR at most frequency bands and stimulus levels. Effects of hearing sensitivity were significant at some frequencies and levels after controlling for age and sex. CONCLUSIONS: When effects of age were controlled, adults with better hearing had significantly larger CRM and CR-SNR than those with poorer hearing. In contrast, when effects of hearing were controlled, no significant effects of age on CRM and CR-SNR remained.

Examining physiological and perceptual consequences of noise exposure.

The consequences of noise exposure on the auditory system are not entirely understood. In animals, noise exposure causes selective synaptopathy-an uncoupling of auditory nerve fibers from sensory cells-mostly in fibers that respond to high sound levels. Synaptopathy can be measured physiologically in animals, but a direct relationship between noise exposure and synaptopathy in humans has yet to be proven. Sources of variability, such as age, indirect measures of noise exposure, and comorbid auditory disorders, obfuscate attempts to find concrete relationships between noise exposure, synaptopathy, and perceptual consequences. This study adds to the ongoing effort by examining relationships between noise exposure, auditory brainstem response (ABR) amplitudes, and speech perception in adults of various ages and audiometric thresholds and a subset of younger adults with clinically normal hearing. Regression models including noise exposure, age, hearing thresholds, and sex as covariates were compared to find a best-fitting model of toneburst ABR wave I amplitude at two frequencies and word recognition performance in three listening conditions: background noise, time compression, and time compression with reverberation. The data suggest the possibility of detecting synaptopathy in younger adults using physiological measures, but that age and comorbid hearing disorders may hinder attempts to assess noise-induced synaptopathy.

Effect of Middle-Ear Pathology on High-Frequency Ear Canal Reflectance Measurements in the Frequency and Time Domains.

The effects of middle-ear pathology on wideband acoustic immittance and reflectance at frequencies above 6-8 kHz have not been documented, nor has the effect of such pathologies on the time-domain reflectance. We describe an approach that utilizes sound frequencies as high as 20 kHz and quantifies reflectance in both the frequency and time domains. Experiments were performed with fresh normal human temporal bones before and after simulating various middle-ear pathologies, including malleus fixation, stapes fixation, and disarticulation. In addition to experimental data, computational modeling was used to obtain fitted parameter values of middle-ear elements that vary systematically due to the simulated pathologies and thus may have diagnostic implications. Our results demonstrate that the time-domain reflectance, which requires acoustic measurements at high frequencies, varies with middle-ear condition. Furthermore, the extended bandwidth frequency-domain reflectance data was used to estimate parameters in a simple model of the ear canal and middle ear that separates three major conductive pathologies from each other and from the normal state.

The Role of Cognition in Common Measures of Peripheral Synaptopathy and Hidden Hearing Loss.

Purpose The aim of this study was to quantify the portion of variance in several measures suggested to be indicative of peripheral noise-induced cochlear synaptopathy and hidden hearing disorder that can be attributed to individual cognitive capacity. Method Regression and relative importance analysis was used to model several behavioral and physiological measures of hearing in 32 adults ranging in age from 20 to 74 years. Predictors for the model were hearing sensitivity and performance on a number of cognitive tasks. Results There was a significant influence of cognitive capacity on several measures of cochlear synaptopathy and hidden hearing disorder. These measures include frequency modulation detection threshold, time-compressed word recognition in quiet and reverberation, and the strength of the frequency-following response of the speech-evoked auditory brainstem response. Conclusions Measures of hearing that involve temporal processing are significantly influenced by cognitive abilities, specifically, short-term and working memory capacity, executive function, and attention. Research using measures of temporal processing to diagnose peripheral disorders, such as noise-induced synaptopathy, need to consider cognitive influence even in a young, healthy population.

Reliability of Measures Intended to Assess Threshold-Independent Hearing Disorders.

OBJECTIVES: Recent animal studies have shown that noise exposure can cause cochlear synaptopathy without permanent threshold shift. Because the noise exposure preferentially damaged auditory nerve fibers that processed suprathreshold sounds (low-spontaneous rate fibers), it has been suggested that synaptopathy may underlie suprathreshold hearing deficits in humans. Recently, several researchers have suggested measures to identify the pathology or pathologies underlying suprathreshold hearing deficits in humans based on results from animal studies; however, the reliability of some of these measures have not been assessed. The purpose of this study was to assess the test-retest reliability of measures that may have the potential to relate suprathreshold hearing deficits to site(s)-of-lesion along the peripheral auditory system in humans. DESIGN: Adults with audiometric normal hearing were tested on a battery of behavioral and physiologic measures that included (1) thresholds in quiet (TIQ), (2) thresholds in noise (TIN), (3) frequency-modulation detection threshold (FMDT), (4) word recognition in four listening conditions, (5) distortion-product otoacoustic emissions (DPOAE), (6) middle ear muscle reflex (MEMR), (7) tone burst-elicited auditory brainstem response (tbABR), and (8) speech-evoked ABR (sABR). Data collection for each measure was repeated over two visits separated by at least one week. The residuals of the correlation between the suprathreshold measures and TIQ serve as functional and quantitative proxies for threshold-independent hearing disorders because they represent the portion of the raw measures that is not dependent on TIQ. Reliability of the residual measures was assessed using intraclass correlation (ICC). RESULTS: Reliability for the residual measures was good (ICC ≥ 0.75) for FMDT, DPOAEs, and MEMR. Residual measures showing moderate reliability (0.5 ≤ ICC < 0.75) were tbABR wave I amplitude, TIN, and word recognition in quiet, noise, and time-compressed speech with reverberation. Wave V of the tbABR, waves of the sABR, and recognition of time-compressed words had poor test-retest reliability (ICC < 0.5). CONCLUSIONS: Reliability of residual measures was mixed, suggesting that care should be taken when selecting measures for diagnostic tests of threshold-independent hearing disorders. Quantifying hidden hearing loss as the variance in suprathreshold measures of auditory function that is not due to TIQ may provide a reliable estimate of threshold-independent hearing disorders in humans.

Influence of Instantaneous Compression on Recognition of Speech in Noise with Temporal Dips.

BACKGROUND: In listening environments with background noise that fluctuates in level, listeners with normal hearing can "glimpse" speech during dips in the noise, resulting in better speech recognition in fluctuating noise than in steady noise at the same overall level (referred to as masking release). Listeners with sensorineural hearing loss show less masking release. Amplification can improve masking release but not to the same extent that it does for listeners with normal hearing. PURPOSE: The purpose of this study was to compare masking release for listeners with sensorineural hearing loss obtained with an experimental hearing-aid signal-processing algorithm with instantaneous compression (referred to as a suppression hearing aid, SHA) to masking release obtained with fast compression. The suppression hearing aid mimics effects of normal cochlear suppression, i.e., the reduction in the response to one sound by the simultaneous presentation of another sound. RESEARCH DESIGN: A within-participant design with repeated measures across test conditions was used. STUDY SAMPLE: Participants included 29 adults with mild-to-moderate sensorineural hearing loss and 21 adults with normal hearing. INTERVENTION: Participants with sensorineural hearing loss were fitted with simulators for SHA and a generic hearing aid (GHA) with fast (but not instantaneous) compression (5 ms attack and 50 ms release times) and no suppression. Gain was prescribed using either an experimental method based on categorical loudness scaling (CLS) or the Desired Sensation Level (DSL) algorithm version 5a, resulting in a total of four processing conditions: CLS-GHA, CLS-SHA, DSL-GHA, and DSL-SHA. DATA COLLECTION: All participants listened to consonant-vowel-consonant nonwords in the presence of temporally-modulated and steady noise. An adaptive-tracking procedure was used to determine the signal-to-noise ratio required to obtain 29% and 71% correct. Measurements were made with amplification for participants with sensorineural hearing loss and without amplification for participants with normal hearing. ANALYSIS: Repeated-measures analysis of variance was used to determine the influence of within-participant factors of noise type and, for participants with sensorineural hearing loss, processing condition on masking release. Pearson correlational analysis was used to assess the effect of age on masking release for participants with sensorineural hearing loss. RESULTS: Statistically significant masking release was observed for listeners with sensorineural hearing loss for 29% correct, but not for 71% correct. However, the amount of masking release was less than masking release for participants with normal hearing. There were no significant differences among the amplification conditions for participants with sensorineural hearing loss. CONCLUSIONS: The results suggest that amplification with either instantaneous or fast compression resulted in similar masking release for listeners with sensorineural hearing loss. However, the masking release was less for participants with hearing loss than it was for those with normal hearing.

Cochlear Reflectance and Otoacoustic Emission Predictions of Hearing Loss.

OBJECTIVES: Cochlear reflectance (CR) is the cochlear contribution to ear-canal reflectance. CR is a type of otoacoustic emission (OAE) that is calculated as a transfer function between forward pressure and reflected pressure. The purpose of this study was to compare wideband CR to distortion-product (DP) OAEs in two ways: (1) in a clinical-screening paradigm where the task is to determine whether an ear is normal or has hearing loss and (2) in the prediction of audiometric thresholds. The goal of the study was to assess the clinical utility of CR. DESIGN: Data were collected from 32 normal-hearing and 124 hearing-impaired participants. A wideband noise stimulus presented at 3 stimulus levels (30, 40, 50 dB sound pressure level) was used to elicit the CR. DPOAEs were elicited using primary tones spanning a wide frequency range (1 to 16 kHz). Predictions of auditory status (i.e., hearing-threshold category) and predictions of audiometric threshold were based on regression analysis. Test performance (identification of normal versus impaired hearing) was evaluated using clinical decision theory. RESULTS: When regressions were based only on physiological measurements near the audiometric frequency, the accuracy of CR predictions of auditory status and audiometric threshold was less than reported in previous studies using DPOAE measurements. CR predictions were improved when regressions were based on measurements obtained at many frequencies. CR predictions were further improved when regressions were performed on males and females separately. CONCLUSIONS: Compared with CR measurements, DPOAE measurements have the advantages in a screening paradigm of better test performance and shorter test time. The full potential of CR measurements to predict audiometric thresholds may require further improvements in signal-processing methods to increase its signal to noise ratio. CR measurements have theoretical significance in revealing the number of cycles of delay at each frequency that is most sensitive to hearing loss.

Comparison of distortion-product otoacoustic emission and stimulus-frequency otoacoustic emission two-tone suppression in humans.

Distortion-product otoacoustic emission (DPOAE) and stimulus-frequency otoacoustic emission (SFOAE) are two types of acoustic signals emitted by the inner ear in response to tonal stimuli. The levels of both emission types may be reduced by the inclusion of additional (suppressor) tones with the stimulus. Comparison of two-tone suppression properties across emission type addresses a clinically relevant question of whether these two types of emission provide similar information about cochlear status. The purpose of this study was to compare DPOAE suppression to SFOAE suppression from the same ear in a group of participants with normal hearing. Probe frequency was approximately 1000 Hz, and the suppressor frequency varied from -1.5 to 0.5 octaves relative to the probe frequency. DPOAE and SFOAE suppression were compared in terms of (1) suppression growth rate (SGR), (2) superimposed suppression tuning curves (STCs), and (3) STC-derived metrics, such as high-frequency slope, cochlear amplifier gain, and QERB (ERB, equivalent rectangular bandwidth). Below the probe frequency, the SGR was slightly greater than one for SFOAEs and slightly less than two for DPOAEs. There were no differences in STC metrics across emission types. These observations may provide useful constraints on physiology-based models of otoacoustic emission suppression.

Evanescent waves in simulated ear canals: Experimental demonstration and method for compensation.

Evanescent waves emerge from a small sound source that radiates into a waveguide with a larger cross-sectional area, but unlike planar waves, do not propagate far from the source. Evanescent waves thus contaminate in-ear calibration of acoustic stimuli. Measurements with an otoacoustic-emission (OAE) probe inserted at the entrance of long tubes of various diameters show a decline in the evanescent wave with distance from the source when advancing a probe tube through the OAE probe and into the long tube. The amplitude of the evanescent pressure increases with frequency and depends strongly on the diameter of the long tube. Modifying the shape of the aperture of the probe's sound source, thus effectively enlarging its diameter and redirecting acoustic flow, greatly reduced evanescent waves. The reduction in evanescent-wave pressure was observed in calibration cavities used to determine the Thévenin-equivalent source pressure and impedance of the probe. Errors in source calibrations were considerably larger in the unmodified configuration. An alternative method is proposed for calculation of acoustic source parameters that models the evanescent-wave pressure and reduces its influence on the calculation. This reduction greatly improves the quality of source calibrations, which should improve the accuracy of ear-canal impedance measurements and related quantities.

Influence of suppression on restoration of spectral loudness summation in listeners with hearing loss.

Loudness depends on both the intensity and spectrum of a sound. Listeners with normal hearing perceive a broadband sound as being louder than an equal-level narrowband sound because loudness grows nonlinearly with level and is then summed across frequency bands. This difference in loudness as a function of bandwidth is reduced in listeners with sensorineural hearing loss (SNHL). Suppression, the reduction in the cochlear response to one sound by the simultaneous presentation of another sound, is also reduced in listeners with SNHL. Hearing-aid gain that is based on loudness measurements with pure tones may fail to restore normal loudness growth for broadband sounds. This study investigated whether hearing-aid amplification that mimics suppression can improve loudness summation for listeners with SNHL. Estimates of loudness summation were obtained using measurements of categorical loudness scaling (CLS). Stimuli were bandpass-filtered noises centered at 2 kHz with bandwidths in the range of 0.1-6.4 kHz. Gain was selected to restore normal loudness based on CLS measurements with pure tones. Gain that accounts for both compression and suppression resulted in better restoration of loudness summation, compared to compression alone. However, restoration was imperfect, suggesting that additional refinements to the signal processing and gain-prescription algorithms are needed.