Functional Hearing Difficulties in Blast-Exposed Service Members With Normal to Near-Normal Hearing Thresholds.

OBJECTIVES: Estimated prevalence of functional hearing and communication deficits (FHCDs), characterized by abnormally low speech recognition and binaural tone detection in noise or an abnormally high degree of self-perceived hearing difficulties, dramatically increases in active-duty service members (SMs) who have hearing thresholds slightly above the normal range and self-report to have been close to an explosive blast. Knowing the exact nature of the underlying auditory-processing deficits that contribute to FHCD would not only provide a better characterization of the effects of blast exposure on the human auditory system, but also allow clinicians to prescribe appropriate therapies to treat or manage patient complaints. DESIGN: Two groups of SMs were initially recruited: (1) a control group (N = 78) with auditory thresholds ≤20 dB HL between 250 and 8000 Hz, no history of blast exposure, and who passed a short FHCD screener, and (2) a group of blast-exposed SMs (N = 26) with normal to near-normal auditory thresholds between 250 and 4000 Hz, and who failed the FHCD screener (cutoffs based on the study by Grant et al.). The two groups were then compared on a variety of audiometric, behavioral, cognitive, and electrophysiological measures. These tests were selected to characterize various aspects of auditory system processing from the cochlear to the cortex. A third, smaller group of blast-exposed SMs who performed within normal limits on the FHCD screener were also recruited (N = 11). This third subject group was unplanned at the onset of the study and was added to evaluate the effects of blast exposure on hearing and communication regardless of performance on the FHCD screener. RESULTS: SMs in the blast-exposed group with FHCD performed significantly worse than control participants on several metrics that measured peripheral and mostly subcortical auditory processing. Cognitive processing was mostly unaffected by blast exposure with the exception of cognitive tests of language-processing speed and working memory. Blast-exposed SMs without FHCD performed similarly to the control group on tests of peripheral and brainstem processing, but performed similarly to blast-exposed SMs with FHCD on measures of cognitive processing. Measures derived from EEG recordings of the frequency-following response revealed that blast-exposed SMs who exhibited FHCD demonstrated increased spontaneous neural activity, reduced amplitude of the envelope-following response, poor internal signal to noise ratio, reduced response stability, and an absent or delayed onset response, compared with the other two participant groups. CONCLUSIONS: Degradation in the neural encoding of acoustic stimuli is likely a major contributing factor leading to FHCD in blast-exposed SMs with normal to near-normal audiometric thresholds. Blast-exposed SMs, regardless of their performance on the FHCD screener, exhibited a deficit in language-processing speed and working memory, which could lead to difficulties in decoding rapid speech and in understanding speech in challenging speech communication settings. Further tests are needed to align these findings with clinical treatment protocols being used for patients with suspected auditory-processing disorders.

Developing an Evidence-Based Military Auditory Fitness-for-Duty Standard Based on the 80-Word Modified Rhyme Test.

OBJECTIVES: One important function of military audiology is to conduct evaluations of service members (SMs) with hearing loss to ensure they are fit for deployment in dangerous operational environments. The objective of this study was to establish evidence-based auditory fitness-for-duty criteria based on speech-in-noise performance on the 80- and 160-word clinical versions of the Modified Rhyme Test (MRT 80 and MRT 160 ). DESIGN: Approximately 2400 SMs with various levels of hearing loss were recruited to complete the MRT 80 in conjunction with their annual hearing conservation evaluations. These SMs were also asked to perform one or more operationally-relevant listening tasks based on audio recordings made in highly realistic military training environments. The scores on these tests were compared to determine how well a proposed cutoff criterion for the MRT 80 was able to identify individuals who are hard of hearing with an exceptionally high risk of abnormally poor performance on operationally-relevant hearing tasks. RESULTS: The results show that a cutoff criterion that combines the percent correct score on two lists of the MRT 80 (i.e. MRT 160 ) with information about the better-ear threshold at 2 kHz is generally able to separate listeners with hearing loss into those who are likely to perform relatively well on operational listening tests and those who are likely to perform poorly on these tasks. This is consistent with current military acquisition standards, which identify the MRT as the preferred test for evaluating speech intelligibility for radios, headsets, and other communication equipment. It is also consistent with prior studies conducted in high-fidelity military simulations which have shown a significant correlation between MRT performance and operational outcomes. CONCLUSIONS: The proposed selection criteria, along with the new hearing profile standards that were recently adopted by the US Army, appear to provide an effective evidence-based methodology for identifying those SMs with hearing loss who are most at risk for poor performance on hearing-critical military tasks.

Short-term retention of learning after rapid adaptation to native and non-native speecha).

Non-native, accented speech spoken by unfamiliar talkers can be challenging to recognize, but rapid improvements in perception are often observed after a short period of exposure. However, it is not clear whether these improvements are retained over multiple sessions. Stimulus variability facilitates learning for non-native speech, so it is possible it may also induce increased retention of learning for speech produced with an unfamiliar accent. In this paper, we conduct a retrospective analysis of a dataset well suited to examine learning of non-native English speech on both a within-session and across-session basis. During data collection, participants completed a protocol involving recognition of matrix sentences recorded by native and non-native talkers with different first languages. Listeners completed the protocol in a self-paced approach, including 15 blocks of 50 trials over 4-7 days, separated by an average of 1-2 days. Learning was strongest within the first day, and improvements were retained at subsequent test sessions. The pace of learning was faster for stimuli produced by native speakers of English as compared to non-native English speakers.

Field assessment of acute auditory responses to environmental exposures in close quarters tactics training.

OBJECTIVE: The purpose of this study was to evaluate auditory performance of military instructors as part of a training course involving noise and blast exposure. Boothless audiometry was used to estimate the test-retest reliability of the auditory measures under realistic field conditions and to determine risk of acute auditory injury during standard training practices. DESIGN AND STUDY SAMPLE: Thirteen U.S. Marine instructors participated in study activities. An audiologic testing suite embedded in a noise-attenuating headset was used to test various tone detection tasks on subjects after exposure. Acoustic exposures were captured with sound level meters. RESULTS: Boothless audiometry provide highly repeatable results for various tests of auditory performance in the field environment. In this test population, changes in auditory performance pre- and post-noise exposure were minimal for most measures. The notable exception was binaural (NoSπ) tone detection, which showed significant degradations both as a function of pre- and post-noise exposure on the same day and as a result of cumulative noise exposure over the period of the study. CONCLUSIONS: Study outcomes are consistent with prior laboratory and epidemiological work and suggest a link between the binaural processes required for NoSπ detection and the hearing-related issues reported by blast-exposed service members.

Single-Sided Deafness Cochlear Implant Sound-Localization Behavior With Multiple Concurrent Sources.

OBJECTIVES: For listeners with one deaf ear and the other ear with normal/near-normal hearing (single-sided deafness [SSD]) or moderate hearing loss (asymmetric hearing loss), cochlear implants (CIs) can improve speech understanding in noise and sound-source localization. Previous SSD-CI localization studies have used a single source with artificial sounds such as clicks or random noise. While this approach provides insights regarding the auditory cues that facilitate localization, it does not capture the complex nature of localization behavior in real-world environments. This study examined SSD-CI sound localization in a complex scenario where a target sound was added to or removed from a mixture of other environmental sounds, while tracking head movements to assess behavioral strategy. DESIGN: Eleven CI users with normal hearing or moderate hearing loss in the contralateral ear completed a sound-localization task in monaural (CI-OFF) and bilateral (CI-ON) configurations. Ten of the listeners were also tested before CI activation to examine longitudinal effects. Two-second environmental sound samples, looped to create 4- or 10-sec trials, were presented in a spherical array of 26 loudspeakers encompassing ±144° azimuth and ±30° elevation at a 1-m radius. The target sound was presented alone (localize task) or concurrently with one or three additional sources presented to different loudspeakers, with the target cued by being added to (Add) or removed from (Rem) the mixture after 6 sec. A head-mounted tracker recorded movements in six dimensions (three for location, three for orientation). Mixed-model regression was used to examine target sound-identification accuracy, localization accuracy, and head movement. Angular and translational head movements were analyzed both before and after the target was switched on or off. RESULTS: Listeners showed improved localization accuracy in the CI-ON configuration, but there was no interaction with test condition and no effect of the CI on sound-identification performance. Although high-frequency hearing loss in the unimplanted ear reduced localization accuracy and sound-identification performance, the magnitude of the CI localization benefit was independent of hearing loss. The CI reduced the magnitude of gross head movements used during the task in the azimuthal rotation and translational dimensions, both while the target sound was present (in all conditions) and during the anticipatory period before the target was switched on (in the Add condition). There was no change in pre- versus post-activation CI-OFF performance. CONCLUSIONS: These results extend previous findings, demonstrating a CI localization benefit in a complex listening scenario that includes environmental and behavioral elements encountered in everyday listening conditions. The CI also reduced the magnitude of gross head movements used to perform the task. This was the case even before the target sound was added to the mixture. This suggests that a CI can reduce the need for physical movement both in anticipation of an upcoming sound event and while actively localizing the target sound. Overall, these results show that for SSD listeners, a CI can improve localization in a complex sound environment and reduce the amount of physical movement used.

Digital sampling of acoustic impulse noise: Implications for exposure measurement and damage risk criteria.

Current standards for the measurement of impulse noise (e.g., MIL-STD-1474E) recommend using a sampling rate of at least 200 kHz in order to accurately estimate the risk of hearing damage. The given motivation for this high sampling rate is to ensure a temporal resolution in the impulse waveform fine enough to accurately capture the peak pressure. However, the Nyquist-Shannon sampling theorem specifies that a sampled signal can accurately reconstruct both the amplitude and phase information of a signal given the sampling rate is at least twice the highest frequency present in the original signal. Thus, it is possible to reconstruct a band limited signal with the same temporal resolution as one captured at a higher sampling rate if the contributions of energy above the Nyquist rate can be ignored. In this study, resampling techniques are applied to a signal sampled at 48 kHz to extract A-weighted sound pressure energy estimates within 0.1 dB of those obtained at a higher sampling rate. Our results suggest sampling rates for impulsive noise should be based on the range of frequencies expected to make a contribution to injury risk rather than on concerns about temporal resolution.

Effects of better-ear glimpsing, binaural unmasking, and spectral resolution on spatial release from masking in cochlear-implant users.

Bilateral cochlear-implant (BICI) listeners obtain less spatial release from masking (SRM; speech-recognition improvement for spatially separated vs co-located conditions) than normal-hearing (NH) listeners, especially for symmetrically placed maskers that produce similar long-term target-to-masker ratios at the two ears. Two experiments examined possible causes of this deficit, including limited better-ear glimpsing (using speech information from the more advantageous ear in each time-frequency unit), limited binaural unmasking (using interaural differences to improve signal-in-noise detection), or limited spectral resolution. Listeners had NH (presented with unprocessed or vocoded stimuli) or BICIs. Experiment 1 compared natural symmetric maskers, idealized monaural better-ear masker (IMBM) stimuli that automatically performed better-ear glimpsing, and hybrid stimuli that added worse-ear information, potentially restoring binaural cues. BICI and NH-vocoded SRM was comparable to NH-unprocessed SRM for idealized stimuli but was 14%-22% lower for symmetric stimuli, suggesting limited better-ear glimpsing ability. Hybrid stimuli improved SRM for NH-unprocessed listeners but degraded SRM for BICI and NH-vocoded listeners, suggesting they experienced across-ear interference instead of binaural unmasking. In experiment 2, increasing the number of vocoder channels did not change NH-vocoded SRM. BICI SRM deficits likely reflect a combination of across-ear interference, limited better-ear glimpsing, and poorer binaural unmasking that stems from cochlear-implant-processing limitations other than reduced spectral resolution.

Assessment methods for determining small changes in hearing performance over time.

Although the behavioral pure-tone threshold audiogram is considered the gold standard for quantifying hearing loss, assessment of speech understanding, especially in noise, is more relevant to quality of life but is only partly related to the audiogram. Metrics of speech understanding in noise are therefore an attractive target for assessing hearing over time. However, speech-in-noise assessments have more potential sources of variability than pure-tone threshold measures, making it a challenge to obtain results reliable enough to detect small changes in performance. This review examines the benefits and limitations of speech-understanding metrics and their application to longitudinal hearing assessment, and identifies potential sources of variability, including learning effects, differences in item difficulty, and between- and within-individual variations in effort and motivation. We conclude by recommending the integration of non-speech auditory tests, which provide information about aspects of auditory health that have reduced variability and fewer central influences than speech tests, in parallel with the traditional audiogram and speech-based assessments.

Reference equivalent threshold sound pressure levels for the Wireless Automated Hearing Test System.

This paper presents reference equivalent threshold sound pressure levels (RETSPLs) for the Wireless Automated Hearing Test System (WAHTS), a recently commercialized device developed for use as a boothless audiometer. Two initial studies were conducted following the ISO 389-9 standard [ISO 389-9 (2009). "Acoustics-Reference zero for the calibration of audiometric equipment. Part 9: Preferred test conditions for the determinations of reference hearing threshold levels" (International Organization for Standardization, Geneva)]. Although the standard recruitment criteria are intended to yield otologically normal test subjects, the recruited populations appeared to have slightly elevated thresholds [5-10 dB hearing level (HL)]. Comparison of WAHTS thresholds to other clinical audiometric equipment revealed bias errors that were consistent with the elevated thresholds of the RETSPL populations. As the objective of RETSPLs is to ensure consistent thresholds regardless of the equipment, this paper presents the RETSPLs initially obtained following ISO 389-9:2009 and suggested correction to account for the elevated HLs of the originally recruited populations. Two additional independent studies demonstrate the validity of these corrected thresholds.

Evaluation of Extended-Wear Hearing Aids as a Solution for Intermittently Noise-Exposed Listeners With Hearing Loss.

OBJECTIVES: Many individuals with noise-related hearing loss continue working in environments where they are periodically exposed to high levels of noise, which increases their risk for further hearing loss. These individuals often must remove their hearing aids in operational environments because of incompatibility with the mandated personal protective equipment, thus reducing situational awareness. Extended-wear hearing aids might provide a solution for these individuals because they can be worn for weeks or months at a time, protect users from high-level noise exposures, and are compatible with communication headsets, earmuffs, and other types of personal protective equipment. The purpose of this study was to evaluate localization ability and speech understanding, feasibility of fitting and use, and acceptability in terms of comfort in a population of noise-exposed, active duty Service members. DESIGN: Participants in the study were active duty Service members who were experienced hearing aid users and were currently using standard hearing aids bilaterally. Participants were fitted with extended-wear hearing aids for up to 14 weeks. Laboratory measures included functional gain, sound localization, and speech recognition (in quiet and in noise). Performance was compared between unaided, standard hearing aids, extended-wear hearing aids, and extended-wear hearing aids combined with a tactical communication device (3M Peltor ComTac). In addition, self-perceived benefit between extended-wear hearing aids and standard hearing aids was compared. RESULTS: The extended-wear hearing aids provided more attenuation of external sound when turned off compared to standard hearing aids. Speech understanding in quiet and in noise was comparable between extended-wear hearing aids and standard hearing aids and was better when a tactical communication device was worn in addition to extended-wear hearing aids. Localization with extended-wear hearing aids was the worst, intermediate with the standard hearing aids, and the best when the ears were unaided. The extended-wear hearing aids and standard hearing aids provided similar self-perceived communication benefits relative to unaided ears. Device failure and issues with extended-wear hearing aids fit and comfort contributed to a high participant withdrawal rate. CONCLUSIONS: Overall, the hearing benefits of extended-wear hearing aids for Service members with hearing loss were comparable to those obtained with standard hearing aids, except for sound localization, which was poorer with extended-wear hearing aids. Extended-wear hearing aids provide the additional benefits of protecting the ears from high-level impulsive noise and being compatible with tactical communication and protection systems and other existing personal protective equipment and communication gear. The withdrawal rate in this study, however, suggests that extended-wear hearing aids may not be suitable for active duty Service members in locations where properly trained hearing professionals are not available to replace or re-insert extended-wear hearing aids when needed due to discomfort or device failure.

Estimated Prevalence of Functional Hearing Difficulties in Blast-Exposed Service Members With Normal to Near-Normal-Hearing Thresholds.

OBJECTIVES: Over the past decade, U.S. Department of Defense and Veterans Affairs audiologists have reported large numbers of relatively young adult patients who have normal to near-normal audiometric thresholds but who report difficulty understanding speech in noisy environments. Many of these service members also reported having experienced exposure to explosive blasts as part of their military service. Recent studies suggest that some blast-exposed patients with normal to near-normal-hearing thresholds not only have an awareness of increased hearing difficulties, but also poor performance on various auditory tasks (sound source localization, speech recognition in noise, binaural integration, gap detection in noise, etc.). The purpose of this study was to determine the prevalence of functional hearing and communication deficits (FHCD) among healthy Active-Duty service men and women with normal to near-normal audiometric thresholds. DESIGN: To estimate the prevalence of such FHCD in the overall military population, performance of roughly 3400 Active-Duty service members with hearing thresholds mostly within the normal range were measured on 4 hearing tests and a brief 6-question survey to assess FHCD. Subjects were subdivided into 6 groups depending on the severity of the blast exposure (3 levels: none, far away, or close enough to feel heat or pressure) and hearing thresholds (2 levels: audiometric thresholds of 20 dB HL or better, slight elevation in 1 or more thresholds between 500 and 4000 Hz in either ear). RESULTS: While the probability of having hearing difficulty was low (≈4.2%) for the overall population tested, that probability increased by 2 to 3 times if the service member was blast-exposed from a close distance or had slightly elevated hearing thresholds (>20 dB HL). Service members having both blast exposure and mildly elevated hearing thresholds exhibited up to 4 times higher risk for performing abnormally on auditory tasks and more than 5 times higher risk for reporting abnormally low ratings on the subjective questionnaire, compared with service members with no history of blast exposure and audiometric thresholds ≤20 dB HL. Blast-exposed listeners were roughly 2.5 times more likely to experience subjective or objective hearing deficits than those with no-blast history. CONCLUSIONS: These elevated rates of abnormal performance suggest that roughly 33.6% of Active-Duty service members (or approximately 423,000) with normal to near-normal-hearing thresholds (i.e., H1 profile) are at some risk for FHCD, and about 5.7% (approximately 72,000) are at high risk, but are currently untested and undetected within the current fitness-for-duty standards. Service members identified as "at risk" for FHCD according to the metrics used in the present study, in spite of their excellent hearing thresholds, require further testing to determine whether they have sustained damage to peripheral and early-stage auditory processing (bottom-up processing), damage to cognitive processes for speech (top-down processing), or both. Understanding the extent of damage due to noise and blast exposures and the balance between bottom-up processing deficits and top-down deficits will likely lead to better therapeutic strategies.

Development of an 80-word clinical version of the modified rhyme test (MRT80).

The modified rhyme test [MRT; House, Williams, Hecker, and Kryter. (1965). J. Acoust. Soc. Am. 37, 158-166] is a widely used test for measuring the intelligibility of communication systems [ANSI (2009). S3.2 (American National Standards Institute, New York)] but has never gained widespread acceptance as a clinical test of speech intelligibility for listeners who are hearing impaired (HI). In this study, a clinical version of the MRT consisting of two 80-word lists was developed and tested on 2394 service members with varying levels of hearing loss. The test used a factorial design incorporating two speech levels [70 and 78 dB sound pressure level (SPL)], two signal-to-noise ratios (+4 and -4 dB), and two binaural conditions (diotic and binaural). High-frequency emphasis reduced the impact of audibility for HI listeners, focusing the test on the distortion component of hearing loss. The results show that listeners with normal hearing (NH) obtained an average score of 80% correct on the MRT80 test. Listeners with a moderate hearing impairment scored an average of 70% correct. The overall level had little impact on performance for either NH or HI listeners. The results demonstrate that the MRT80 test could be a useful test to assess the distortion effects of hearing loss on speech intelligibility, particularly in cases where it is desirable to use a closed-set test for automatic administration.

The cafeteria study: Effects of facial masks, hearing protection, and real-world noise on speech recognition.

The objective of this study was to evaluate the impact of wearing various types of personal protective equipment on speech recognition in a real-world, noisy listening environment. Groups of four young, normal-hearing adults participated in a live version of the Modified Rhyme Test in a noisy public cafeteria with and without the use of a non-medical disposable facial mask or combat earplugs in two different modes. Speech recognition, response time, and subjective difficulty were measured per individual. In addition, the signal-to-noise ratio was estimated during the interval when the talker spoke the target word. Results showed that the listeners' speech recognition performance declined not only when the listener wore earplugs, but also when the talker wore earplugs. The measured signal-to-noise ratio significantly decreased when the talker wore earplugs, suggesting that occlusion may have caused the talkers to reduce their voice levels. Results also showed a decline in speech recognition performance when the talker wore a facial mask. Listeners rated all conditions in which talkers and listeners wore personal protective equipment as more difficult than the baseline condition. These data suggest that speech recognition in real-world listening environments can be impaired by personal protective equipment worn by both talkers and listeners.

Functional impact of bothersome tinnitus on cognitive test performance.

OBJECTIVE: Individuals with bothersome tinnitus frequently report their concentration is affected. Given that tinnitus is the leading service-connected disability compensated by the United States Department of Veterans Affairs, it is essential to determine whether tinnitus has a functional impact on the operational performance of Service members. Previous studies demonstrated that people with tinnitus perform more poorly on cognitive tests of selective attention and memory than those without tinnitus. This study aimed to compare performance between participants with and without tinnitus on visually based tests of selective attention (flanker task) and short-term memory (spatial letter location) that were self-administered under three auditory conditions (quiet, broadband noise and speech) using a tablet-based test protocol. DESIGN: Experimental. STUDY SAMPLE: Thirty participants with bothersome tinnitus and 30 control participants, matched for age and hearing loss. RESULTS: The results revealed a significantly larger flanker effect and shorter memory span in the tinnitus group compared to the control group, consistent with previous studies. Performance accuracy was comparable between the groups. CONCLUSIONS: The results suggest bothersome tinnitus may affect cognitive efficiency more than cognitive performance. The tablet-based protocol has the potential to be implemented clinically as a functional measure of the impact of bothersome tinnitus on concentration.

Long-Term Sensorineural Hearing Loss in Patients With Blast-Induced Tympanic Membrane Perforations.

OBJECTIVE: To describe characteristics of sensorineural hearing loss (SNHL) in patients with blast-induced tympanic membrane (TM) perforations that required surgery. DESIGN: A retrospective review of hearing outcomes in those who had tympanoplasty for combat blast-induced TM perforations. These were sequential cases from one military otolaryngologist from 2007 to 2012. A total of 87 patients were reviewed, and of those, 49 who had appropriate preinjury, preoperative, and long-term audiograms were included. Those with pre-existing hearing loss were excluded. Preinjury audiograms were used to assess how sensorineural thresholds changed in the ruptured ears, and in the contralateral ear in those with unilateral perforations. RESULTS: The mean time from injury to the final postoperative audiogram was 522 days. In the ears with TM perforations, 70% had SNHLs of 10 dB or less (by bone conduction pure tone averages). Meanwhile, approximately 8% had threshold shifts >30 dB, averaging 50 dB. The strongest predictor of severe or profound hearing loss was ossicular discontinuity. Thresholds also correlated with bilateral injury and perforation size. In those with unilateral perforations, the SNHL was almost always larger on the side with the perforation. Those with SNHL often had a low-to-mid frequency threshold shift and, in general, audiograms that were flatter across frequencies than those of a typical population of military personnel with similar levels of overall hearing loss. CONCLUSIONS: There is a bimodal distribution of hearing loss in those who experience a blast exposure severe enough to perforate at least one TM. Most ears recover close to their preinjury thresholds, but a minority experience much larger sensorineural threshold shifts. Blast exposed ears also tend to have a flatter audiogram than most service members with similar levels of hearing loss.

Predicting Speech-in-Noise Deficits from the Audiogram.

OBJECTIVES: In occupations that involve hearing critical tasks, individuals need to undergo periodic hearing screenings to ensure that they have not developed hearing losses that could impair their ability to safely and effectively perform their jobs. Most periodic hearing screenings are limited to pure-tone audiograms, but in many cases, the ability to understand speech in noisy environments may be more important to functional job performance than the ability to detect quiet sounds. The ability to use audiometric threshold data to identify individuals with poor speech-in-noise performance is of particular interest to the U.S. military, which has an ongoing responsibility to ensure that its service members (SMs) have the hearing abilities they require to accomplish their mission. This work investigates the development of optimal strategies for identifying individuals with poor speech-in-noise performance from the audiogram. DESIGN: Data from 5487 individuals were used to evaluate a range of classifiers, based exclusively on the pure-tone audiogram, for identifying individuals who have deficits in understanding speech in noise. The classifiers evaluated were based on generalized linear models (GLMs), the speech intelligibility index (SII), binary threshold criteria, and current standards used by the U.S. military. The classifiers were evaluated in a detection theoretic framework where the sensitivity and specificity of the classifiers were quantified. In addition to the performance of these classifiers for identifying individuals with deficits understanding speech in noise, data from 500,733 U.S. Army SMs were used to understand how the classifiers would affect the number of SMs being referred for additional testing. RESULTS: A classifier based on binary threshold criteria that was identified through an iterative search procedure outperformed a classifier based on the SII and ones based on GLMs with large numbers of fitted parameters. This suggests that the saturating nature of the SII is important, but that the weights of frequency channels are not optimal for identifying individuals with deficits understanding speech in noise. It is possible that a highly complicated model with many free parameters could outperform the classifiers considered here, but there was only a modest difference between the performance of a classifier based on a GLM with 26 fitted parameters and one based on a simple all-frequency pure-tone average. This suggests that the details of the audiogram are a relatively insensitive predictor of performance in speech-in-noise tasks. CONCLUSIONS: The best classifier identified in this study, which was a binary threshold classifier derived from an iterative search process, does appear to reliably outperform the current thresholds criteria used by the U.S. military to identify individuals with abnormally poor speech-in-noise performance, both in terms of fewer false alarms and a greater hit rate. Substantial improvements in the ability to detect SMs with impaired speech-in-noise performance can likely only be obtained by adding some form of speech-in-noise testing to the hearing monitoring program. While the improvements were modest, the overall benefit of adopting the proposed classifier is likely substantial given the number of SMs enrolled in U.S. military hearing conservation and readiness programs.

Objective Assessment of Speech Intelligibility in Crowded Public Spaces.

The objective of this study was to obtain a normative database of speech intelligibility data for young normal-hearing listeners communicating in public spaces. A total of 174 listeners participated in an interactive speech intelligibility task that required four-person groups to conduct a live version of the Modified Rhyme Test in noisy public spaces. The public spaces tested included a college library, a college cafeteria, a casual dining restaurant during lunch hour, and a crowded bar during happy hour. At the start of each trial, one of the participants was randomly selected as the talker, and a tablet computer was used to prompt them to say a word aloud from the Modified Rhyme Test. Then, the other three participants were required to select this word from one of six rhyming alternatives displayed on three other tablet computers. The tablet computers were also used to record the SPL at each listener location during and after the interval where the target talker was speaking. These SPL measurements were used to estimate the signal-to-noise ratio (SNR) in each trial of the experiment. As expected, the results show that speech intelligibility decreases, response time increases, and perceived difficulty increases as the background noise level increases. There was also a systematic decrease in SNR with increasing background noise, with SNR decreasing 0.44 dB for every 1 dB increase in ambient noise level above 60 dB. Overall, the results of this study have demonstrated how low-cost tablet computer-based data collection systems can be used to collect live-talker speech intelligibility data in real-world environments. We believe these techniques could be adapted for use in future studies focused on obtaining ecologically valid assessments of the effects of age, hearing impairment, amplification, and other factors on speech intelligibility performance in real-world environments.

The Quest for Ecological Validity in Hearing Science: What It Is, Why It Matters, and How to Advance It.

Ecological validity is a relatively new concept in hearing science. It has been cited as relevant with increasing frequency in publications over the past 20 years, but without any formal conceptual basis or clear motive. The sixth Eriksholm Workshop was convened to develop a deeper understanding of the concept for the purpose of applying it in hearing research in a consistent and productive manner. Inspired by relevant debate within the field of psychology, and taking into account the World Health Organization's International Classification of Functioning, Disability, and Health framework, the attendees at the workshop reached a consensus on the following definition: "In hearing science, ecological validity refers to the degree to which research findings reflect real-life hearing-related function, activity, or participation." Four broad purposes for striving for greater ecological validity in hearing research were determined: A (Understanding) better understanding the role of hearing in everyday life; B (Development) supporting the development of improved procedures and interventions; C (Assessment) facilitating improved methods for assessing and predicting ability to accomplish real-world tasks; and D (Integration and Individualization) enabling more integrated and individualized care. Discussions considered the effects of variables and phenomena commonly present in hearing-related research on the level of ecological validity of outcomes, supported by examples from a few selected outcome domains and for different types of studies. Illustrated with examples, potential strategies were offered for promoting a high level of ecological validity in a study and for how to evaluate the level of ecological validity of a study. Areas in particular that could benefit from more research to advance ecological validity in hearing science include: (1) understanding the processes of hearing and communication in everyday listening situations, and specifically the factors that make listening difficult in everyday situations; (2) developing new test paradigms that include more than one person (e.g., to encompass the interactive nature of everyday communication) and that are integrative of other factors that interact with hearing in real-life function; (3) integrating new and emerging technologies (e.g., virtual reality) with established test methods; and (4) identifying the key variables and phenomena affecting the level of ecological validity to develop verifiable ways to increase ecological validity and derive a set of benchmarks to strive for.

Attenuation characteristics of an extended-wear hearing aid: Impulse and continuous noise.

The extended-wear hearing aid (EWHA) is a hearing assistive device that combines a low-power analog amplification circuit with a soft biocompatible foam plug that allows it to remain in the ear canal for several months at a time without replacement. EWHAs fit snugly in the ear canal and are not vented and so produce insertion losses comparable to a passive earplug when inserted into the ear canal with the active circuitry turned off. However, EWHAs are not marketed as hearing protection devices, and other than a general warning to users that the device will have impaired auditory awareness when the device is inserted in the "off" mode, relatively little has been reported about the attenuation characteristics of EWHAs. In this study, commercially-available EWHAs were evaluated using the ANSI standard procedures for measuring hearing protector attenuation in impulse noise [ANSI (2010). S1242-2010, Methods for the Measurement of Insertion Loss of Hearing Protective Devices in Continuous or Impulsive Noise Using Microphone-In-Real-Ear or Acoustic Text Fixture Procedures (American National Standards Institute, New York)] and in continuous noise [ANSI (2006). S12.6, Methods for Measuring the Real-Ear Attenuation of Hearing Protectors (American National Standards Institute, New York)]. Attenuation values were also measured in double and triple protection conditions that combined EWHAs with traditional earplugs and earmuffs. The results show that properly-fit EWHAs can provide passive attenuation comparable to conventional passive earplugs, which may make it possible to use them to provide persistent protection from intermittent noise sources.

TabSINT: open-source mobile software for distributed studies of hearing.

Objective: The recent emphasis on outcomes-based medical research has motivated a need for technology that allows researchers and clinicians to reach a larger and more diverse subject population for recruitment and testing.Design: This article reports on open-source mobile software (TabSINT) that enables researchers to administer customised hearing tests and questionnaires on tablets located across multiple sites. Researchers create and modify test protocols using text-based templates and deploy it to the tablets via a cloud-based repository or USB-computer connection. Results are exported locally to the tablet SD card and can also be automatically posted to a cloud-based database.Results: Between 2014 and 2019, TabSINT collected 25,000+ test results using more than 200+ unique test protocols for researchers located worldwide.Conclusions:TabSINT is a powerful software system with the potential to greatly enhance research across multiple disciplines by enabling access to subject cohorts in remote and disparate locations. Released open-source, this software is available to researchers across the world to use and adapt to their specific needs. Researchers with engineering resources can contribute to the repository to extend the capability and robustness of this software.