Probe Microphone Research Articles

Matched transaural synthesis with probe microphones for psychoacoustical experiments.

Transaural synthesis using loudspeaker signals determined through contemporaneous ear canal calibration is proposed as an alternative to headphone presentation for critical psychoacoustical experiments. The proposed technique can afford greater accuracy, improved reproducibility, and continuous signal monitoring. It allows the experimenter to compare listener responses to real and virtual presentations. In this article, the advantages of transaural (three or four loudspeakers) compared to crosstalk cancellation (two loudspeakers) are shown through computer modeling and manikin measurements in a moderately reverberant room. Measurements employ binaurally challenging signals and speech from a distant source. Transaural synthesis is shown to be a better solution to the essential inverse problem resulting in reduced average synthesis amplitudes, fewer large-amplitude outliers, improved amplitude and phase accuracy for real and imagined sources, and improved noise immunity. Immunity to inadvertent listener head rotation depends sensitively on loudspeaker placement and is not an advantage in general. Appendixes review the relevant mathematical foundation and extend it to the relationship between ear canal signals and eardrum signals.

Influence of external ear occlusion on food perception.

The present study aimed to explore if food perception can be influenced by sound mastication level when the external ear canal was occluded. Fifty-nine adults (38 women) with normal hearing, smell, and taste participated in the study. They tasted five crispy and five soft food items over two sessions: one with and one without an earplug inserted in the external ear canal. Participants were asked to rate freshness and taste of the food as well as their willingness to eat more of it and how much they usually like this kind of food. The sound pressure level related to the food mastication was recorded with a probe microphone placed in the external ear canal. Compared to the open ear canal condition, levels of the mastication sounds were higher when the participants had their ears occluded, as well as for crispy than for soft food. Regarding food freshness, food appreciation, and willingness to eat more of the same food, there was no significant difference concerning food type, ear condition, and sex. For soft foods, men rated their usual liking of this food higher when they were wearing ear plugs compared to the opened condition. Plugging the ear canals led to increased mastication sound levels. Participants did not seem to consider these additional acoustic cues when they rated food freshness, food appreciation, and willingness of eating the specific food. Only men seemed to take these cues into account when they rated their habit consumption of soft food.

Can Self-Reported Personal Audio System Volume Predict Actual Listening Levels in Young Adults?

Most young adults report using personal audio systems (PAS) with earphones as part of their daily activities. PAS exposure is intermittent and research examining the levels these young adults are listening to is increasing. On average, preferred listening levels are below what would be considered at risk in an occupational setting. The purpose of this study was to evaluate how two questions predicted preferred listening level in young adults with normal hearing; specifically, whether these young adults could identify if they listen at a high level or not. One hundred and sixty young adults (111 women, 49 men) with normal hearing completed a questionnaire that had questions about PAS listening habits and then had preferred listening level assessed using a probe microphone system while listening to 1 hour of music through earphones. Otoscopy, tympanometry, and pure-tone thresholds were completed in a randomly determined test ear. As part of the Risk Factors Survey, two closed-set questions were completed. First, "For a typical day, what is the most common volume used during this day?" with the following response options "Low," "Medium/Comfortable," "Loud," or "Very Loud." And second, "Do you listen to your personal music system at a volume where you…" with the following response options "Easily hear people," "Have a little trouble hearing people," "Have a lot of trouble hearing people," or "Cannot hear people." Using a probe microphone, chosen listening level (A-weighted, diffuse-field correction and a conversion to free-field equivalent [LDFeq]) was calculated over 1 hour while the participant listened to music with earphones. Sensitivity and specificity were determined to see how well young adults could identify themselves as listening at a high level (>85 dBA) or not. Linear regression analyses were performed to determine the amount of variance explained by the two survey questions as predictors of measured LDFeq. Almost half of the participants reported a longest single use of a PAS as <1 hour daily and more than half reported listening at a medium/comfortable volume and had a little trouble hearing people. Mean LDFeq was 72.5 dBA, with young adult men having a significantly higher mean LDFeq (76.5 dBA) compared with young adult women (70.8 dBA). Sensitivity was 88.9% and specificity was 70.6% for the question asking about volume on a typical day. For the question asking about being able to hear other people while listening to music sensitivity was 83.3% and specificity was 82.5%. Two variables, listening volume on a typical day and sex, accounted for 28.4% of the variability associated with LDFeq; the answer to the question asking about being able to hear others and sex accounted for 22.8% of the variability associated with LDFeq. About 11% of young adults in the present study listen to a PAS with earphones at a high level (>85 dBA) while in a quiet background. The participants who do report listening at a high level, however, do well at self-reporting this risk behavior in survey questions.

The Effects of Nonlinear Frequency Compression and Digital Noise Reduction on Word Recognition and Satisfaction Ratings in Noise in Adult Hearing Aid Users.

Nonlinear frequency compression (NLFC) and digital noise reduction (DNR) are hearing aid features often used simultaneously in the adult population with hearing loss. Although each feature has been studied extensively in isolation, the effects of using them in combination are unclear. The effects of NLFC and DNR in noise on word recognition and satisfaction ratings in noise in adult hearing aid users were evaluated. A repeated measures design was used. Two females and 13 males between the ages of 55 and 83 yr who were experienced hearing aid users participated. Thirteen were experienced with NLFC and all were experienced with DNR. Each participant was fit with Phonak Bolero Q90-P hearing instruments using their specific audiometric data and the Desired Sensation Level v5.0 (adult) fitting strategy. Fittings were verified with probe microphone measurements using speech at 65-dB sound pressure level (SPL). NLFC verification was performed using the Protocol for the Provision of Amplification, Version 2014.01. All testing was conducted in a double-walled sound booth. Four hearing aid conditions were used for all testing: Baseline (NLFC off, DNR off), NLFC only, DNR only, and Combination (NLFC on, DNR on). A modified version of the Pascoe's High-Frequency Word List was presented at 65-dB SPL with speech spectrum noise at 6-dB signal-to-noise ratio (SNR) and 1-dB SNR for each hearing aid condition. Listener satisfaction ratings were obtained after each listening condition in terms of word comfort, word clarity, and average satisfaction. Two-way repeated measures analyses of variance were conducted to assess listener performance. Pairwise comparisons were then completed for significant main effects. Word recognition results indicated a significant SNR effect only (6 dB SNR > 1 dB SNR). Satisfaction ratings results indicated a significant SNR and hearing aid condition effect for clarity, comfort, and average satisfaction. Clarity ratings were significantly higher for DNR and Combination than NLFC. Comfort ratings were significantly higher for DNR than NLFC. Average satisfaction was significantly higher for DNR and Combination than for NLFC. Also, average ratings were significantly higher for Combination than Baseline. Activating NLFC or DNR in isolation or in combination did not significantly impact word recognition in noise. Activating NLFC in isolation reduced satisfaction ratings relative to the DNR or Combination conditions. The isolated use of DNR significantly improved all satisfaction ratings when compared with the isolated use of NLFC. These findings suggest NLFC should not be used in isolation and should be coupled with DNR for best results. Future research should include a field trial as this was a limitation of the study.

Validation of clinical techniques for verification of uniform attenuation earplugs

Objective: Uniform attenuation earplugs (UAE) theoretically provide near even attenuation across frequencies when built to a manufacturer’s specifications. Unfortunately, there is no current research available confirming if custom-molded uniform attenuation earplugs (UAE) are made to specifications nor is there guidance available on clinical methods of measuring attenuation of uniform attenuation earplug (UAE) devices. The goal of this study was to evaluate different procedures for UAE verification and to determine the most accurate clinically accessible verification protocol. Design: Attenuation was measured using probe microphone techniques, as well as real-ear attenuation at threshold (REAT) measurements under circumaural earphones, soundfield speakers and supra-aural earphones. Comparisons were made to a reference system created in the laboratory. Study sample: Seventeen adult participants, totaling 30 ears. Results: The results of this study demonstrate that the REAT measured in the soundfield using a narrowband noise stimulus with masking in the contralateral ear is currently the most accurate and widely available method of verifying UAEs. Conclusions: Factoring in clinical efficiency, the authors of this study recommend verifying attenuation levels using a soundfield REAT procedure as best clinical practice. In addition, the data suggests that REAT measurements under circumaural earphones are an acceptable second choice method.

Headphones and other risk factors for hearing in young adults.

Background:Personal listening device (PLD) use with headphones is increasing in young adults and in most listening environments occur in background noise. Headphone choice can be important because certain headphones are more effective in limiting background noise than stock earbuds. Binge drinking, marijuana, and hard drug use have also been associated with high-volume PLD use. The purpose of this study was to explore the relationship between preferred headphone type, listening level, and other health risk behaviors.Methods:Two-hundred and twenty undergraduates were recruited and completed a PLD use and risk behavior survey. Survey data included self-reported alcohol and marijuana use. Bilateral otoscopy, tympanometry, and pure-tone threshold testing (0.25–8 kHz) were completed. Participants listened to one hour of music using preferred headphone type with a probe microphone in the ear canal to measure equivalent continuous sound level (LAeq).Results:Mean LAeq was similar for the three types of headphones used. Participants who reported higher amounts of drinks per month and smoking marijuana within the last month had significantly higher LAeq levels than those who reported lower amounts of drinks per month and not smoking marijuana in the last month. There was no significant interaction between headphone type and reported drinks per month or marijuana use.Conclusion:Young adults with normal hearing who have higher preferred listening levels also reported more alcohol and marijuana use, although headphone type was not associated with any of these variables.

Effects of Forward- and Emitted-Pressure Calibrations on the Variability of Otoacoustic Emission Measurements Across Repeated Probe Fits.

The stimuli used to evoke otoacoustic emissions (OAEs) are typically calibrated based on the total SPL measured at the probe microphone. However, due to the acoustics of the ear-canal space (i.e., standing-wave interference), this method can underestimate the stimulus pressure reaching the tympanic membrane at certain frequencies. To mitigate this effect, stimulus calibrations based on forward pressure level (FPL) can be applied. Furthermore, the influence of ear-canal acoustics on measured OAE levels can be compensated by expressing them in emitted pressure level (EPL). To date, studies have used artificial shallow versus deep probe fits to assess the effects of calibration method on changes in probe insertion. In an attempt to better simulate a clinical setting, the combined effects of FPL calibration of stimulus level and EPL compensation of OAE level on response variability during routine (noncontrived) probe fittings were examined. The distortion component of the distortion-product OAE (DPOAE) and the stimulus-frequency OAE (SFOAE) were recorded at low and moderate stimulus levels in 20 normal-hearing young-adult subjects across a five-octave range. In each subject, three different calibration approaches were compared: (1) the conventional SPL-based stimulus calibration with OAE levels expressed in SPL; (2) FPL stimulus calibration with OAEs expressed in SPL; and (3) FPL stimulus calibration with OAEs expressed in EPL. Test and retest measurements were obtained during the same session and, in a subset of subjects, several months after the initial test. The effects of these different procedures on the inter- and intra-subject variability of OAE levels were assessed across frequency and level. There were no significant differences in the inter-subject variability of OAE levels across the three calibration approaches. However, there was a significant effect on OAE intra-subject variability. The FPL/EPL approach resulted in the overall lowest test-rest differences in DPOAE level for frequencies above 4 kHz, where standing-wave interference is strongest. The benefit was modest, ranging on average from 0.5 to 2 dB and was strongest at the lower stimulus level. SFOAE level variability did not show significant differences among the three procedures, perhaps due to insufficient signal-to-noise ratio and nonoptimized stimulus levels. Correlations were found between the short-term replicability of DPOAEs and the benefit derived from the FPL/EPL procedure: the more variable the DPOAE, the stronger the benefit conferred by the advanced calibration methods. Stimulus and response calibration procedures designed to mitigate the effects of standing-wave interference on both the stimulus and the OAE enhance the repeatability of OAE measurements and reduce their dependence on probe position, even when probe shifts are small. Modest but significant improvements in short-term test-retest repeatability were observed in the mid- to high-frequency region when using combined FPL/EPL procedures. The authors posit that the benefit will be greater in a more heterogeneous group of subjects and when different testers participate in the fitting and refitting of subjects, which is a common practice in the audiology clinic. The impact of calibration approach on OAE inter-subject variability was not significant, possibly due to a homogeneous subject population and because factors other than probe position are at play.

Ins, Outs of Frequency-lowering Processing

Ins, Outs of Frequency-lowering Processing

Imaging of the human tympanic membrane by endoscopic optical coherence tomography

Abstract Endoscopic optical coherence tomography is a non-invasive and contactless imaging technique based on white light interferometry. It enables high-resolution three-dimensional imaging of scattering tissue up to a depth of about 2 mm. In addition, Doppler-OCT can detect sub-resolution movements. These features can be used to examine the tympanic membrane, the surrounding tissue and nearby areas of the tympanic cavity. For this purpose, we present an endoscopic OCT system, which provides access to the tympanic membrane. The design of the endoscope is based on a gradientindex (GRIN) lens system. This allows a broad field of view and a large working distance. An additional VIS beam path allows visual imaging and orientation inside the auditory canal. Therefore, illumination fibers are attached a round the GRIN-system. The resulting endoscope has a length of 55 mm and a diameter of 3.5 mm. By attaching an earphone and a probe microphone, the oscillation of the tympanic membrane can be measured under acoustic stimulation. With the endoscopic OCT system, we provide an examination tool for the diagnosis of a broad number of diseases like conductive hearing loss.

Effects of Amplification on Neural Phase Locking, Amplitude, and Latency to a Speech Syllable.

Older adults often have trouble adjusting to hearing aids when they start wearing them for the first time. Probe microphone measurements verify appropriate levels of amplification up to the tympanic membrane. Little is known, however, about the effects of amplification on auditory-evoked responses to speech stimuli during initial hearing aid use. The present study assesses the effects of amplification on neural encoding of a speech signal in older adults using hearing aids for the first time. It was hypothesized that amplification results in improved stimulus encoding (higher amplitudes, improved phase locking, and earlier latencies), with greater effects for the regions of the signal that are less audible. Thirty-seven adults, aged 60 to 85 years with mild to severe sensorineural hearing loss and no prior hearing aid use, were bilaterally fit with Widex Dream 440 receiver-in-the-ear hearing aids. Probe microphone measures were used to adjust the gain of the hearing aids and verify the fitting. Unaided and aided frequency-following responses and cortical auditory-evoked potentials to the stimulus /ga/ were recorded in sound field over the course of 2 days for three conditions: 65 dB SPL and 80 dB SPL in quiet, and 80 dB SPL in six-talker babble (+10 signal to noise ratio). Responses from midbrain were analyzed in the time regions corresponding to the consonant transition (18 to 68 ms) and the steady state vowel (68 to 170 ms). Generally, amplification increased phase locking and amplitude and decreased latency for the region and presentation conditions that had lower stimulus amplitudes-the transition region and 65 dB SPL level. Responses from cortex showed decreased latency for P1, but an unexpected decrease in N1 amplitude. Previous studies have demonstrated an exaggerated cortical representation of speech in older adults compared to younger adults, possibly because of an increase in neural resources necessary to encode the signal. Therefore, a decrease in N1 amplitude with amplification and with increased presentation level may suggest that amplification decreases the neural resources necessary for cortical encoding. Increased phase locking and amplitude and decreased latency in midbrain suggest that amplification may improve neural representation of the speech signal in new hearing aid users. The improvement with amplification was also found in cortex, and, in particular, decreased P1 latencies and lower N1 amplitudes may indicate greater neural efficiency. Further investigations will evaluate changes in subcortical and cortical responses during the first 6 months of hearing aid use.

Unsteady surface pressure characteristics of asymmetrically beveled trailing edges

The characteristics of unsteady surface pressure (USP) created by turbulent flow over a family of asymmetrically beveled trailing edges were studied experimentally. The geometries had a trailing edge angle $$\theta =25^\circ$$ with a flat lower surface and a rounded upper surface with radii of curvature between zero and ten times the airfoil thickness. The Reynolds number was $$Re=2.1\times 10^6$$ based on chord. A detailed description of the USP and flow field around the trailing edge was obtained using remote microphone probes (RMP) and particle image velocimetry (PIV), respectively. The lower surface exhibited USP auto-spectral density magnitudes that were similar to those of a zero-pressure-gradient turbulent boundary layer at higher frequency. The low-frequency pressure fluctuations were influenced by the turbulent wake, leading to large increases in magnitude closer to the trailing edge. An empirical model of these results is proposed. The beveled upper surface was characterized by a region of favorable pressure gradient, followed by a strong adverse pressure gradient. The cases with smaller radius of curvature were found to exhibit separated flow over the trailing edge. The spectral magnitudes were largest in these regions, and significant attention is given to the proper scaling of these results. The PIV measurements provided the length and velocity scales for this purpose.

Evaluation of the Repeatability and Accuracy of the Wideband Real-Ear-to-Coupler Difference.

The real-ear-to-coupler difference (RECD) is an ANSI standardized method for estimating ear canal sound pressure level (SPL) thresholds and assisting in the prediction of real-ear aided responses. It measures the difference in dB between the SPL produced in the ear canal and the SPL produced in an HA-1 2-cc coupler by the same sound source. Recent evidence demonstrates that extended high-frequency bandwidth, beyond the hearing aid bandwidth typically measured, is capable of providing additional clinical benefit. The industry has, in turn, moved toward developing hearing aids and verification equipment capable of producing and measuring extended high-frequency audible output. As a result, a revised RECD procedure conducted using a smaller, 0.4-cc coupler, known as the wideband-RECD (wRECD), has been introduced to facilitate extended high-frequency coupler-based measurements up to 12.5 kHz. This study aimed to (1) compare test-retest repeatability between the RECD and wRECD and (2) measure absolute agreement between the RECD and wRECD when both are referenced to a common coupler. RECDs and wRECDs were measured bilaterally in adult ears by calculating the dB difference in SPL between the ear canal and coupler responses. Real-ear probe microphone measures were completed twice per ear per participant for both foam-tip and customized earmold couplings using the Audioscan Verifit 1 and Verifit 2 fitting systems, followed by measurements in the respective couplers. Twenty-one adults (mean age = 67 yr, range = 19-78) with typical aural anatomy (as determined by measures of impedance and otoscopy) participated in this study, leading to a sample size of 42 ears. Repeatability within RECD and wRECD was assessed for each coupling configuration using a repeated-measures analysis of variance (ANOVA) with test-retest and frequency as within-participants factors. Repeatability between the RECD and wRECD was assessed within each configuration using a repeated-measures ANOVA with test-retest, frequency, and coupler type as within-participants factors. Agreement between the RECD and wRECD was assessed for each coupling configuration using a repeated-measures ANOVA with RECD value, coupler type, and frequency as within-participants factors. Post hoc comparisons with Bonferroni corrections were used when appropriate to locate the frequencies at which differences occurred. A 3-dB criterion was defined to locate differences of clinical significance. Average absolute test-retest differences were within ±3 dB within each coupler and coupling configuration, and between the RECD and wRECD. The RECD and wRECD were in absolute agreement following HA-1-referenced transforms, with most frequencies agreeing within ±1 dB, except at 0.2 kHz for the earmold, and 0.2-0.25 kHz for the foam tip, where the average RECD exceeded the average wRECD by slightly >3 dB. Test-retest repeatability of the RECD (up to 8 kHz) and wRECD (up to 12.5 kHz) is acceptable and similar to previously reported data. The RECD and wRECD are referenced to different couplers, but can be rendered comparable with a simple transform, producing values that are in accordance with the ANSI S3.46-2013 standard.

The Middle Ear Muscle Reflex in Rat: Developing a Biomarker of Auditory Nerve Degeneration.

The long-term goal of this research is to determine whether the middle ear muscle reflex can be used to predict the number of healthy auditory nerve fibers in hearing-impaired ears. In this study, we develop a high-impedance source and an animal model of the middle ear muscle reflex and explore the influence of signal frequency and level on parameters of the reflex to determine an optimal signal to examine auditory nerve fiber survival. A high-impedance source was developed using a hearing aid receiver attached to a 0.06 diameter 10.5-cm length tube. The impedance probe consisted of a microphone probe placed near the tip of a tube coupled to a sound source. The probe was calibrated by inserting it into a syringe of known volumes and impedances. The reflex in the anesthetized rat was measured with elicitor stimuli ranging from 3 to 16 kHz presented at levels ranging from 35 to 100 dB SPL to one ear while the reflex was measured in the opposite ear containing the probe and probe stimulus. The amplitude of the reflex increased with elicitor level and was largest at 3 kHz. The lowest threshold was approximately 54 dB SPL for the 3-kHz stimulus. The rate of decay of the reflex was greatest at 16 kHz followed by 10 and 3 kHz. The rate of decay did not change significantly with elicitor signal level for 3 and 16 kHz, but decreased as the level of the 10-kHz elicitor increased. A negative feedback model accounts for the reflex decay by having the strength of feedback dependent on auditory nerve input. The rise time of the reflex varied with frequency and changed with level for the 10- and 16-kHz signals but not significantly for the 3-kHz signal. The latency of the reflex increased with a decrease in elicitor level, and the change in latency with level was largest for the 10-kHz stimulus. Because the amplitude of the reflex in rat was largest with an elicitor signal at 3 kHz, had the lowest threshold, and yielded the least amount of decay, this may be the ideal frequency to estimate auditory nerve survival in hearing-impaired ears.

Effects of self-generated noise on quiet threshold by transducer type in school-age children and adults

This study tested the hypothesis that higher levels of self-generated noise in children results in larger child-adult differences for the detection of low-frequency sounds when testing is conducted using transducers associated with a pronounced occlusion effect. Detection thresholds were measured at 125, 250, 500, and 1000 Hz using standard clinical procedures with supra-aural headphones, insert earphones, or a loudspeaker. Probe microphone recordings were made during testing with each transducer. Listeners were 4.5- to 11-year-olds, and adults. Preliminary results are consistent with the a priori hypothesis. For all listeners, thresholds at 125 and 250 Hz were highest with supra-aural headphones and lowest with free-field presentation. This transducer effect was most pronounced for younger children. Child-adult differences were smaller at 500 and 1000 Hz, an observation consistent with reduced effects of self-generated noise with increasing frequency. Trial-by-trial analysis of probe microphone recordings will be presented.

Survey of Current Practice in the Fitting and Fine-Tuning of Common Signal-Processing Features in Hearing Aids for Adults.

Current guidelines for adult hearing aid fittings recommend the use of a prescriptive fitting rationale with real-ear verification that considers the audiogram for the determination of frequency-specific gain and ratios for wide dynamic range compression. However, the guidelines lack recommendations for how other common signal-processing features (e.g., noise reduction, frequency lowering, directional microphones) should be considered during the provision of hearing aid fittings and fine-tunings for adult patients. The purpose of this survey was to identify how audiologists make clinical decisions regarding common signal-processing features for hearing aid provision in adults. An online survey was sent to audiologists across the United States. The 22 survey questions addressed four primary topics including demographics of the responding audiologists, factors affecting selection of hearing aid devices, the approaches used in the fitting of signal-processing features, and the strategies used in the fine-tuning of these features. A total of 251 audiologists who provide hearing aid fittings to adults completed the electronically distributed survey. The respondents worked in a variety of settings including private practice, physician offices, university clinics, and hospitals/medical centers. Data analysis was based on a qualitative analysis of the question responses. The survey results for each of the four topic areas (demographics, device selection, hearing aid fitting, and hearing aid fine-tuning) are summarized descriptively. Survey responses indicate that audiologists vary in the procedures they use in fitting and fine-tuning based on the specific feature, such that the approaches used for the fitting of frequency-specific gain differ from other types of features (i.e., compression time constants, frequency lowering parameters, noise reduction strength, directional microphones, feedback management). Audiologists commonly rely on prescriptive fitting formulas and probe microphone measures for the fitting of frequency-specific gain and rely on manufacturers' default settings and recommendations for both the initial fitting and the fine-tuning of signal-processing features other than frequency-specific gain. The survey results are consistent with a lack of published protocols and guidelines for fitting and adjusting signal-processing features beyond frequency-specific gain. To streamline current practice, a transparent evidence-based tool that enables clinicians to prescribe the setting of other features from individual patient characteristics would be desirable.

Relationship of Grammatical Context on Children's Recognition of s/z-Inflected Words.

Access to aided high-frequency speech information is currently assessed behaviorally using recognition of plural monosyllabic words. Because of semantic and grammatical cues that support word+morpheme recognition in sentence materials, the contribution of high-frequency audibility to sentence recognition is less than that for isolated words. However, young children may not yet have the linguistic competence to take advantage of these cues. A low-predictability sentence recognition task that controls for language ability could be used to assess the impact of high-frequency audibility in a context that more closely represents how children learn language. To determine if differences exist in recognition of s/z-inflected monosyllabic words for children with normal hearing (CNH) and children who are hard of hearing (CHH) across stimuli context (presented in isolation versus embedded medially within a sentence that has low semantic and syntactic predictability) and varying levels of high-frequency audibility (4- and 8-kHz low-pass filtered for CNH and 8-kHz low-pass filtered for CHH). A prospective, cross-sectional design was used to analyze word+morpheme recognition in noise for stimuli varying in grammatical context and high-frequency audibility. Low-predictability sentence stimuli were created so that the target word+morpheme could not be predicted by semantic or syntactic cues. Electroacoustic measures of aided access to high-frequency speech sounds were used to predict individual differences in recognition for CHH. Thirty-five children, aged 5-12 yrs, were recruited to participate in the study; 24 CNH and 11 CHH (bilateral mild to severe hearing loss) who wore hearing aids (HAs). All children were native speakers of English. Monosyllabic word+morpheme recognition was measured in isolated and sentence-embedded conditions at a +10 dB signal-to-noise ratio using steady state, speech-shaped noise. Real-ear probe microphone measures of HAs were obtained for CHH. To assess the effects of high-frequency audibility on word+morpheme recognition for CNH, a repeated-measures ANOVA was used with bandwidth (8 kHz, 4 kHz) and context (isolated, sentence embedded) as within-subjects factors. To compare recognition between CNH and CHH, a mixed-model ANOVA was completed with context (isolated, sentence-embedded) as a within-subjects factor and hearing status as a between-subjects factor. Bivariate correlations between word+morpheme recognition scores and electroacoustic measures of high-frequency audibility were used to assess which measures might be sensitive to differences in perception for CHH. When high-frequency audibility was maximized, CNH and CHH had better word+morpheme recognition in the isolated condition compared with sentence-embedded. When high-frequency audibility was limited, CNH had better word+morpheme recognition in the sentence-embedded condition compared with the isolated condition. CHH whose HAs had greater high-frequency speech bandwidth, as measured by the maximum audible frequency, had better word+morpheme recognition in sentences. High-frequency audibility supports word+morpheme recognition within low-predictability sentences for both CNH and CHH. Maximum audible frequency can be used to estimate word+morpheme recognition for CHH. Low-predictability sentences that do not contain semantic or grammatical context may be of clinical use in estimating children's use of high-frequency audibility in a manner that approximates how they learn language.

In situ Probe Microphone Measurement for Testing the Direct Acoustical Cochlear Stimulator.

Hypothesis: Acoustical measurements can be used for functional control of a direct acoustic cochlear stimulator (DACS).Background: The DACS is a recently released active hearing implant that works on the principle of a conventional piston prosthesis driven by the rod of an electromagnetic actuator. An inherent part of the DACS actuator is a thin titanium diaphragm that allows for movement of the stimulation rod while hermetically sealing the housing. In addition to mechanical stimulation, the actuator emits sound into the mastoid cavity because of the motion of the diaphragm.Methods: We investigated the use of the sound emission of a DACS for intra-operative testing. We measured sound emission in the external auditory canal (PEAC) and velocity of the actuators stimulation rod (Vact) in five implanted ears of whole-head specimens. We tested the influence various positions of the loudspeaker and a probe microphone on PEAC and simulated implant malfunction in one example.Results: Sound emission of the DACS with a signal-to-noise ratio >10 dB was observed between 0.5 and 5 kHz. Simulated implant misplacement or malfunction could be detected by the absence or shift in the characteristic resonance frequency of the actuator. PEAC changed by <6 dB for variations of the microphone and loudspeaker position.Conclusion: Our data support the feasibility of acoustical measurements for in situ testing of the DACS implant in the mastoid cavity as well as for post-operative monitoring of actuator function.

Contralateral routing of signals disrupts monaural level and spectral cues to sound localisation on the horizontal plane

ObjectivesContra-lateral routing of signals (CROS) devices re-route sound between the deaf and hearing ears of unilaterally-deaf individuals. This rerouting would be expected to disrupt access to monaural level cues that can support monaural localisation in the horizontal plane. However, such a detrimental effect has not been confirmed by clinical studies of CROS use. The present study aimed to exercise strict experimental control over the availability of monaural cues to localisation in the horizontal plane and the fitting of the CROS device to assess whether signal routing can impair the ability to locate sources of sound and, if so, whether CROS selectively disrupts monaural level or spectral cues to horizontal location, or both. DesignUnilateral deafness and CROS device use were simulated in twelve normal hearing participants. Monaural recordings of broadband white noise presented from three spatial locations (−60°, 0°, and +60°) were made in the ear canal of a model listener using a probe microphone with and without a CROS device. The recordings were presented to participants via an insert earphone placed in their right ear. The recordings were processed to disrupt either monaural level or spectral cues to horizontal sound location by roving presentation level or the energy across adjacent frequency bands, respectively. Localisation ability was assessed using a three-alternative forced-choice spatial discrimination task. ResultsParticipants localised above chance levels in all conditions. Spatial discrimination accuracy was poorer when participants only had access to monaural spectral cues compared to when monaural level cues were available. CROS use impaired localisation significantly regardless of whether level or spectral cues were available. For both cues, signal re-routing had a detrimental effect on the ability to localise sounds originating from the side of the deaf ear (−60°). CROS use also impaired the ability to use level cues to localise sounds originating from straight ahead (0°). ConclusionsThe re-routing of sounds can restrict access to the monaural cues that provide a basis for determining sound location in the horizontal plane. Perhaps encouragingly, the results suggest that both monaural level and spectral cues may not be disrupted entirely by signal re-routing and that it may still be possible to reliably identify sounds originating on the hearing side.

Real-time estimation of the passive attenuation for otoacoustic emission measurement probes

Despite hearing loss prevention programs in place at work, noise-induced hearing loss (NIHL) remains the first reported occupational disease. To improve the detection of over-exposure to noise, an initial proof-of-concept for field monitoring of inner-ear health using otoacoustic emissions (OAE) was developed and successfully validated in laboratory conditions. However, in real-life situations, the unsupervised placement of the OAE probes remains a challenge: proper fit of the probe in the ear canal is required to ensure adequate hearing protection of the wearer, to improve the signal-to-noise ratio of OAE measurements and to maintain the proper calibration of stimuli signals in the case of the Distortion Product OAE (DPOAE) approach used. Algorithms were recently developed to quantify, in real-time, from the OAE probe microphones and receivers signals, the passive attenuation of the OAE probes. The validation of this approach was conducted, in laboratory conditions, on five human subjects exposed to industrial and pink noise recordings at realistic levels.

Big Stimulus, Little Ears: Safety in Administering Vestibular-Evoked Myogenic Potentials in Children.

Cervical and ocular vestibular-evoked myogenic potentials (VEMPs) have become common clinical vestibular assessments. However, VEMP testing requires high intensity stimuli, raising concerns regarding safety with children, where sound pressure levels may be higher due to their smaller ear canal volumes. The purpose of this study was to estimate the range of peak-to-peak equivalent sound pressure levels (peSPLs) in child and adult ears in response to high intensity stimuli (i.e., 100 dB normal hearing level [nHL]) commonly used for VEMP testing and make a determination of whether acoustic stimuli levels with VEMP testing are safe for use in children. Prospective experimental. Ten children (4-6 years) and ten young adults (24-35 years) with normal hearing sensitivity and middle ear function participated in the study. Probe microphone peSPL measurements of clicks and 500 Hz tonebursts (TBs) were recorded in tubes of small, medium, and large diameter, and in a Brüel & Kjær Ear Simulator Type 4157 to assess for linearity of the stimulus at high levels. The different diameter tubes were used to approximate the range of cross-sectional areas in infant, child, and adult ears, respectively. Equivalent ear canal volume and peSPL measurements were then recorded in child and adult ears. Lower intensity levels were used in the participant's ears to limit exposure to high intensity sound. The peSPL measurements in participant ears were extrapolated using predictions from linear mixed models to determine if equivalent ear canal volume significantly contributed to overall peSPL and to estimate the mean and 95% confidence intervals of peSPLs in child and adult ears when high intensity stimulus levels (100 dB nHL) are used for VEMP testing without exposing subjects to high-intensity stimuli. Measurements from the coupler and tubes suggested: 1) each stimuli was linear, 2) there were no distortions or nonlinearities at high levels, and 3) peSPL increased with decreased tube diameter. Measurements in participant ears suggested: 1) peSPL was approximately 3 dB larger in child compared to adult ears, and 2) peSPL was larger in response to clicks compared to 500 Hz TBs. The model predicted the following 95% confidence interval for a 100 dB nHL click: 127-136.5 dB peSPL in adult ears and 128.7-138.2 dB peSPL in child ears. The model predicted the following 95% confidence interval for a 100 dB nHL 500 Hz TB stimulus: 122.2-128.2 dB peSPL in adult ears and 124.8-130.8 dB peSPL in child ears. Our findings suggest that 1) when completing VEMP testing, the stimulus is approximately 3 dB higher in a child's ear, 2) a 500 Hz TB is recommended over a click as it has lower peSPL compared to the click, and 3) both duration and intensity should be considered when choosing VEMP stimuli. Calculating the total sound energy exposure for your chosen stimuli is recommended as it accounts for both duration and intensity. When using this calculation for children, consider adding 3 dB to the stimulus level.