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INTRODUCTION: Although existing auditory injury prevention standards benefit warfighters, the Department of Defense could do more to understand and address auditory injuries (e.g., hearing loss, tinnitus, and central processing deficits) among service members. The Blast Injury Prevention Standards Recommendation (BIPSR) Process is designed to address the needs of all the Military Services for biomedically valid Military Health System (MHS) Blast Injury Prevention Standards. MATERIALS AND METHODS: Through the BIPSR Process, stakeholders provided their intended uses and requested functionalities for an MHS Blast Injury Prevention Standard. The BIPSR Process established a broad-based, non-advocacy panel of auditory injury Subject Matter Expert (SME) Panel with members drawn from industry, academia, and government. The SME Panel selected evaluation factors, weighted priorities, and then evaluated the resulting candidate MHS Auditory Blast Injury Prevention Standards against the evaluation criteria. The SME Panel members provided rationales for their decisions, documented discussions, and used iterative rounds of feedback to promote consensus building among members. The BIPSR Process used multi-attribute utility theory to combine members' evaluations and compare the candidate standards. RESULTS: The SME Panel identified and collated information about existing auditory injury datasets to identify gaps and promote data sharing and comprehensive evaluations of standards for preventing auditory blast injury. The panel evaluated the candidate standards and developed recommendations for an MHS Blast Injury Prevention Standard. CONCLUSIONS: The BIPSR Process illuminated important characteristics, capabilities, and limitations of candidate standards and existing datasets (e.g., limited human exposure data to evaluate the validity of injury prediction) for auditory blast injury prevention. The evaluation resulted in the recommendation to use the 8-hour Equivalent Level (LAeq8hr) as the interim MHS Auditory Blast Injury Prevention Standard while the community performs additional research to fill critical knowledge gaps.
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Traumatismos por Explosión , Pérdida Auditiva , Servicios de Salud Militares , Personal Militar , Acúfeno , Humanos , Traumatismos por Explosión/prevención & control , Explosiones , Acúfeno/prevención & controlRESUMEN
INTRODUCTION: Repetitive exposure to blast overpressure waves can be a part of routine military and law enforcement training. However, our understanding of the effects of that repetitive exposure on human neurophysiology remains limited. To link an individual's cumulative exposure with their neurophysiological effects, overpressure dosimetry needs to be concurrently collected with relevant physiological signals. Eye tracking has shown promise for providing insight into neurophysiological change because of neural injury, but video-based technology limits usage to a laboratory or clinic. In the present work, we show capability for using electrooculography-based eye tracking to enable physiological assessment in the field during activities involved repetitive blast exposures. MATERIALS AND METHODS: Overpressure dosimetry was accomplished by using a body-worn measurement system that captures continuous sound pressure levels as well as pressure waveforms of blast event in the range of 135-185 dB peak (0.1-36 kPa). Electrooculography eye tracking was performed using a commercial Shimmer Sensing system, which captured horizontal eye movements of both the left and right eyes, as well as vertical eye movements of the right eye, from which blinks can also be extracted. Data were collected during breaching activities that included repetitive use of explosives. Participants in the study were U.S. Army Special Operators and Federal Bureau of Investigations special agents. Approval for research was received by the Massachucetts Institute of Technology Committee on the Use of Humans as Experimental Subjects, the Air Force Human Research Protections Office, and the Federal Bureau of Investigations Institutional Review Board. RESULTS: The energy from overpressure events was accumulated and summarized into an 8-hour equivalent of sound pressure level (i.e., LZeq8hr). The total exposure in a single day, i.e., the LZeq8hr, ranged from 110 to 160 dB. Oculomotor features, such as blink and saccade rate, as well as variance in blink waveforms, show changes across the period of overpressure exposure. However, the features that showed significant change across the population were not necessarily the ones that showed significant correlation with the levels of overpressure exposure. A regression model built to predict overpressure levels from oculomotor features alone showed a significant association (R = 0.51, P < .01). Investigation of the model indicates that changes in the saccade rate and blink waveforms are driving the relationship. CONCLUSIONS: This study successfully demonstrated that eye tracking can be performed during training activities, such as explosive breaching, and that the modality may provide insight into neurophysiological change across periods of overpressure exposure. The results presented herein show that electrooculography-based eye tracking may be a useful method of assessing individualized physiological effects of overpressure exposure in the field. Future work is focused on time-dependent modeling to assess continuous changes in eye movements as this will enable building dose-response curves.
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Traumatismos por Explosión , Tecnología de Seguimiento Ocular , Humanos , Ojo , Movimientos Oculares , ExplosionesRESUMEN
Although a causal relationship exists between military occupational noise exposure and hearing loss, researchers have struggled to identify and/or characterize specific operational noise exposures that produce measurable changes in hearing function shortly following an exposure. Growing evidence suggests that current standards for noise-exposure limits are not good predictors of true hearing damage. In this study, the aim was to capture the dose-response relationship during military rifle training exercises for noise exposure and hearing threshold. To capture exposure, a wearable system capable of measuring impulse noise simultaneously on-body and in-ear, behind hearing protection was used. To characterize hearing threshold changes, portable audiometry was employed within 2 h before and after exposure. The median 8-h time-weighted, protected, free-field equivalent in-ear exposure was 87.5 dBA at one site and 80.7 dBA at a second site. A significant dose-response correlation between in-ear noise exposure and postexposure hearing threshold changes across our population ( R = 0.40 , p = 0.0281) was observed. The results demonstrate an approach for establishing damage risk criteria (DRC) for in-ear, protected measurements based on hearing threshold changes. While an in-ear DRC does not currently exist, it may be critical for predicting the risk of injury for noise environments where protection is mandatory and fit status can vary.
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Pérdida Auditiva Provocada por Ruido , Personal Militar , Ruido en el Ambiente de Trabajo , Exposición Profesional , Humanos , Ruido en el Ambiente de Trabajo/prevención & control , Estudios Prospectivos , Audición , Umbral Auditivo/fisiologíaRESUMEN
Repetitive exposure to non-concussive blast expo-sure may result in sub-clinical neurological symptoms. These changes may be reflected in the neural control gait and balance. In this study, we collected body-worn accelerometry data on individuals who were exposed to repetitive blast overpressures as part of their occupation. Accelerometry features were gener-ated within periods of low-movement and gait. These features were the eigenvalues of high-dimensional correlation matrices, which were constructed with time-delay embedding at multiple delay scales. When focusing on the gait windows, there were significant correlations of the changes in features with the cumulative dose of blast exposure. When focusing on the low-movement frames, the correlation with exposure were lower than that of the gait frames and statistically insignificant. In a cross-validated model, the overpressure exposure was predicted from gait features alone. The model was statistically significant and yielded an RMSE of 1.27 dB. With continued development, the model may be used to assess the physiological effects of repetitive blast exposure and guide training procedures to minimize impact on the individual.
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Traumatismos por Explosión , Acelerometría , Traumatismos por Explosión/diagnóstico , Explosiones , Marcha , Humanos , MovimientoRESUMEN
Noise exposure is encountered nearly everyday in both recreational and occupational settings, and can lead to a number of health concerns including hearing-loss, tinnitus, social-isolation and possibly dementia. Although guidelines exist to protect workers from noise, it remains a challenge to accurately quantify the noise exposure experienced by an individual due to the complexity and non-stationarity of noise sources. This is especially true for impulsive noise sources, such as weapons fire and industrial impact noise which are difficult to quantify due to technical challenges relating to sensor design and size, weight and power requirements. Because of this, personal noise dosimeters are often limited to a maximum 140 dB SPL and are not sufficient to measure impulse noise. This work details the design of a body-worn noise dosimeter (mNOISE) that processes both impulse and continuous noise ranging in level from 40 dBA-185 dBP (i.e. a quiet whisper to a shoulder fired rocket). Also detailed is the capability of the device to log the kurtosis of the sound pressure waveform in real-time, which is thought to be useful in characterizing complex noise exposures. Finally, we demonstrate the use of mNOISE in a military-flight noise environment. Clinical Relevance- On-body noise exposure monitoring can be used by audiologists industrial hygiene personnel and others to determine threshold of injury adequate hearing protection requirements and ultimately reduce permanent noise-induced hearing loss.
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Pérdida Auditiva Provocada por Ruido , Ruido en el Ambiente de Trabajo , Exposición Profesional , Pérdida Auditiva Provocada por Ruido/etiología , Pérdida Auditiva Provocada por Ruido/prevención & control , Humanos , Ruido en el Ambiente de Trabajo/efectos adversos , Ocupaciones , Dosímetros de Radiación/efectos adversosRESUMEN
Tinnitus, or ringing in the ears, is a prevalent condition that imposes a substantial health and financial burden on the patient and to society. The diagnosis of tinnitus, like pain, relies on patient self-report, which can complicate the distinction between actual and fraudulent claims. Here, we combined tablet-based self-directed hearing assessments with neural network classifiers to automatically differentiate participants with tinnitus (N = 24) from a malingering cohort, who were instructed to feign an imagined tinnitus percept (N = 28). We identified clear differences between the groups, both in their overt reporting of tinnitus features, but also covert differences in their fingertip movement trajectories on the tablet surface as they performed the reporting assay. Using only 10 min of data, we achieved 81% accuracy classifying patients and malingerers (ROC AUC = 0.88) with leave-one-out cross validation. Quantitative, automated measurements of tinnitus salience could improve clinical outcome assays and more accurately determine tinnitus incidence.
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Everyday environments often contain distracting competing talkers and background noise, requiring listeners to focus their attention on one acoustic source and reject others. During this auditory attention task, listeners may naturally interrupt their sustained attention and switch attended sources. The effort required to perform this attention switch has not been well studied in the context of competing continuous speech. In this work, we developed two variants of endogenous attention switching and a sustained attention control. We characterized these three experimental conditions under the context of decoding auditory attention, while simultaneously evaluating listening effort and neural markers of spatial-audio cues. A least-squares, electroencephalography (EEG)-based, attention decoding algorithm was implemented across all conditions. It achieved an accuracy of 69.4% and 64.0% when computed over nonoverlapping 10 and 5-s correlation windows, respectively. Both decoders illustrated smooth transitions in the attended talker prediction through switches at approximately half of the analysis window size (e.g., the mean lag taken across the two switch conditions was 2.2 s when the 5-s correlation window was used). Expended listening effort, as measured by simultaneous EEG and pupillometry, was also a strong indicator of whether the listeners sustained attention or performed an endogenous attention switch (peak pupil diameter measure [ p=0.034 ] and minimum parietal alpha power measure [ p=0.016 ]). We additionally found evidence of talker spatial cues in the form of centrotemporal alpha power lateralization ( p=0.0428 ). These results suggest that listener effort and spatial cues may be promising features to pursue in a decoding context, in addition to speech-based features.
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Percepción del Habla , Estimulación Acústica/métodos , Atención , Electroencefalografía , Esfuerzo de Escucha , PupilaRESUMEN
Future wearable technology may provide for enhanced communication in noisy environments and for the ability to pick out a single talker of interest in a crowded room simply by the listener shifting their attentional focus. Such a system relies on two components, speaker separation and decoding the listener's attention to acoustic streams in the environment. To address the former, we present a system for joint speaker separation and noise suppression, referred to as the Binaural Enhancement via Attention Masking Network (BEAMNET). The BEAMNET system is an end-to-end neural network architecture based on self-attention. Binaural input waveforms are mapped to a joint embedding space via a learned encoder, and separate multiplicative masking mechanisms are included for noise suppression and speaker separation. Pairs of output binaural waveforms are then synthesized using learned decoders, each capturing a separated speaker while maintaining spatial cues. A key contribution of BEAMNET is that the architecture contains a separation path, an enhancement path, and an autoencoder path. This paper proposes a novel loss function which simultaneously trains these paths, so that disabling the masking mechanisms during inference causes BEAMNET to reconstruct the input speech signals. This allows dynamic control of the level of suppression applied by BEAMNET via a minimum gain level, which is not possible in other state-of-the-art approaches to end-to-end speaker separation. This paper also proposes a perceptually-motivated waveform distance measure. Using objective speech quality metrics, the proposed system is demonstrated to perform well at separating two equal-energy talkers, even in high levels of background noise. Subjective testing shows an improvement in speech intelligibility across a range of noise levels, for signals with artificially added head-related transfer functions and background noise. Finally, when used as part of an auditory attention decoder (AAD) system using existing electroencephalogram (EEG) data, BEAMNET is found to maintain the decoding accuracy achieved with ideal speaker separation, even in severe acoustic conditions. These results suggest that this enhancement system is highly effective at decoding auditory attention in realistic noise environments, and could possibly lead to improved speech perception in a cognitively controlled hearing aid.
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Cognición , Audífonos/normas , Ruido , Adulto , Atención , Aglomeración , Señales (Psicología) , Potenciales Evocados Auditivos , Humanos , Masculino , Percepción del HablaRESUMEN
Lapses in vigilance and slowed reactions due to mental fatigue can increase risk of accidents and injuries and degrade performance. This paper describes a method for rapid, unobtrusive detection of mental fatigue based on changes in electrodermal arousal (EDA), and changes in neuromotor coordination derived from speaking. Twenty-nine Soldiers completed a 2-hour battery of cognitive tasks intended to induce fatigue. Behavioral markers derived from audio and video during speech were acquired before and after the 2hour cognitive load tasks, as was EDA. Exposure to cognitive load produced detectable increases in neuromotor variability in speech and facial measures after load and even after a recovery period. A Gaussian mixture model classifier with crossvalidation and fusion across speech, video, and EDA produced an accuracy of AUC=0.99 in detecting a change in cognitive fatigue relative to a personalized baseline.
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Nivel de Alerta , Fatiga Mental , Cognición , Humanos , Fatiga Mental/diagnóstico , Habla , VigiliaRESUMEN
Modern operational environments can place significant demands on a service member's cognitive resources, increasing the risk of errors or mishaps due to overburden. The ability to monitor cognitive burden and associated performance within operational environments is critical to improving mission readiness. As a key step toward a field-ready system, we developed a simulated marksmanship scenario with an embedded working memory task in an immersive virtual reality environment. As participants performed the marksmanship task, they were instructed to remember numbered targets and recall the sequence of those targets at the end of the trial. Low and high cognitive load conditions were defined as the recall of three- and six-digit strings, respectively. Physiological and behavioral signals recorded included speech, heart rate, breathing rate, and body movement. These features were input into a random forest classifier that significantly discriminated between the low- and high-cognitive load conditions (AUC = 0.94). Behavioral features of gait were the most informative, followed by features of speech. We also showed the capability to predict performance on the digit recall (AUC = 0.71) and marksmanship (AUC = 0.58) tasks. The experimental framework can be leveraged in future studies to quantify the interaction of other types of stressors and their impact on operational cognitive and physical performance.
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OBJECTIVE: Military job and training activities place significant demands on service members' (SMs') cognitive resources, increasing risk of injury and degrading performance. Early detection of cognitive fatigue is essential to reduce risk and support optimal function. This paper describes a multimodal approach, based on changes in measures of speech motor coordination and electrodermal activity (EDA), for predicting changes in performance following sustained cognitive effort. METHODS: Twenty-nine active duty SMs completed computer-based cognitive tasks for 2 h (load period). Measures of speech derived from audio were acquired, along with concurrent measures of EDA, before and after the load period. Cognitive performance was assessed before and during the load period using the Automated Neuropsychological Assessment Metrics Military Battery (ANAM MIL). Subjective assessments of cognitive effort and alertness were obtained intermittently. RESULTS: Across the load period, participants' ratings of cognitive workload increased, while alertness ratings declined. Cognitive performance declined significantly during the first half of the load period. Three speech and arousal features predicted cognitive performance changes during this period with statistically significant accuracy: EDA (r = 0.43, p = 0.01), articulator velocity coordination (r = 0.50, p = 0.00), and vocal creak (r = 0.35, p = 0.03). Fusing predictions from these features predicted performance changes with r = 0.68 (p = 0.00). CONCLUSIONS: Results suggest that speech and arousal measures may be used to predict changes in performance associated with cognitive fatigue. This work supports ongoing efforts to develop reliable, unobtrusive measures for cognitive state assessment aimed at reducing injury risk, informing return to work decisions, and supporting diverse mobile healthcare applications in civilian and military settings.
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Cognición/fisiología , Respuesta Galvánica de la Piel/fisiología , Personal Militar/psicología , Pruebas Neuropsicológicas/normas , Habla/fisiología , Adolescente , Adulto , Femenino , Humanos , Estudios Longitudinales , Masculino , Persona de Mediana Edad , Adulto JovenRESUMEN
Many individuals struggle to understand speech in listening scenarios that include reverberation and background noise. An individual's ability to understand speech arises from a combination of peripheral auditory function, central auditory function, and general cognitive abilities. The interaction of these factors complicates the prescription of treatment or therapy to improve hearing function. Damage to the auditory periphery can be studied in animals; however, this method alone is not enough to understand the impact of hearing loss on speech perception. Computational auditory models bridge the gap between animal studies and human speech perception. Perturbations to the modeled auditory systems can permit mechanism-based investigations into observed human behavior. In this study, we propose a computational model that accounts for the complex interactions between different hearing damage mechanisms and simulates human speech-in-noise perception. The model performs a digit classification task as a human would, with only acoustic sound pressure as input. Thus, we can use the model's performance as a proxy for human performance. This two-stage model consists of a biophysical cochlear-nerve spike generator followed by a deep neural network (DNN) classifier. We hypothesize that sudden damage to the periphery affects speech perception and that central nervous system adaptation over time may compensate for peripheral hearing damage. Our model achieved human-like performance across signal-to-noise ratios (SNRs) under normal-hearing (NH) cochlear settings, achieving 50% digit recognition accuracy at -20.7 dB SNR. Results were comparable to eight NH participants on the same task who achieved 50% behavioral performance at -22 dB SNR. We also simulated medial olivocochlear reflex (MOCR) and auditory nerve fiber (ANF) loss, which worsened digit-recognition accuracy at lower SNRs compared to higher SNRs. Our simulated performance following ANF loss is consistent with the hypothesis that cochlear synaptopathy impacts communication in background noise more so than in quiet. Following the insult of various cochlear degradations, we implemented extreme and conservative adaptation through the DNN. At the lowest SNRs (<0 dB), both adapted models were unable to fully recover NH performance, even with hundreds of thousands of training samples. This implies a limit on performance recovery following peripheral damage in our human-inspired DNN architecture.
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OBJECTIVES: Hearing-protection devices (HPDs) are made available, and often are required, for industrial use as well as military training exercises and operational duties. However, these devices often are disliked, and consequently not worn, in part because they compromise situational awareness through reduced sound detection and localization performance as well as degraded speech intelligibility. In this study, we carried out a series of tests, involving normal-hearing subjects and multiple background-noise conditions, designed to evaluate the performance of four HPDs in terms of their modifications of auditory-detection thresholds, sound-localization accuracy, and speech intelligibility. In addition, we assessed their impact on listening effort to understand how the additional effort required to perceive and process auditory signals while wearing an HPD reduces available cognitive resources for other tasks. DESIGN: Thirteen normal-hearing subjects participated in a protocol, which included auditory tasks designed to measure detection and localization performance, speech intelligibility, and cognitive load. Each participant repeated the battery of tests with unoccluded ears and four hearing protectors, two active (electronic) and two passive. The tasks were performed both in quiet and in background noise. RESULTS: Our findings indicate that, in variable degrees, all of the tested HPDs induce performance degradation on most of the conducted tasks as compared to the open ear. Of particular note in this study is the finding of increased cognitive load or listening effort, as measured by visual reaction time, for some hearing protectors during a dual-task, which added working-memory demands to the speech-intelligibility task. CONCLUSIONS: These results indicate that situational awareness can vary greatly across the spectrum of HPDs, and that listening effort is another aspect of performance that should be considered in future studies. The increased listening effort induced by hearing protectors may lead to earlier cognitive fatigue in noisy environments. Further study is required to characterize how auditory performance is limited by the combination of hearing impairment and the use of HPDs, and how the effects of such limitations can be linked to safe and effective use of hearing protection to maximize job performance.
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Localización de Sonidos , Percepción del Habla , Percepción Auditiva , Concienciación , Audición , HumanosRESUMEN
Until recently, most hearing conservation programs, including those in the military, have used permanent shifts in the pure-tone audiometric threshold as the gold standard for measuring hearing impairment in noise-exposed populations. However, recent results from animal studies suggest that high-level noise exposures can cause the permanent destruction of synapses between the inner hair cells and auditory nerve fibers, even in cases where pure-tone audiometric thresholds eventually return to their normal pre-exposure baselines. This has created a dilemma for researchers, who are now increasingly interested in studying the long-term effects that temporary hearing shifts might have on hearing function, but are also concerned about the ethical considerations of exposing human listeners to high levels of noise for research purposes. One method that remains viable to study the effects of high noise exposures on human listeners, or to evaluate the efficacy of interventions designed to prevent noise-related inner ear damage, is to identify individuals in occupations with unavoidable noise exposures and measure hearing before and as soon as possible after exposure. This paper discusses some of the important factors to be considered in studies that attempt to measure acute hearing changes in noise-exposed military populations.
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Traumatismos por Explosión/epidemiología , Pérdida Auditiva Provocada por Ruido/epidemiología , Personal Militar/estadística & datos numéricos , Enfermedades Profesionales/epidemiología , Traumatismos por Explosión/fisiopatología , Traumatismos por Explosión/prevención & control , Dispositivos de Protección de los Oídos , Pérdida Auditiva Provocada por Ruido/fisiopatología , Pérdida Auditiva Provocada por Ruido/prevención & control , Humanos , Ruido en el Ambiente de Trabajo/efectos adversos , Enfermedades Profesionales/fisiopatología , Enfermedades Profesionales/prevención & control , Estados UnidosRESUMEN
Auditory attention decoding (AAD) through a brain-computer interface has had a flowering of developments since it was first introduced by Mesgarani and Chang (2012) using electrocorticograph recordings. AAD has been pursued for its potential application to hearing-aid design in which an attention-guided algorithm selects, from multiple competing acoustic sources, which should be enhanced for the listener and which should be suppressed. Traditionally, researchers have separated the AAD problem into two stages: reconstruction of a representation of the attended audio from neural signals, followed by determining the similarity between the candidate audio streams and the reconstruction. Here, we compare the traditional two-stage approach with a novel neural-network architecture that subsumes the explicit similarity step. We compare this new architecture against linear and non-linear (neural-network) baselines using both wet and dry electroencephalogram (EEG) systems. Our results indicate that the new architecture outperforms the baseline linear stimulus-reconstruction method, improving decoding accuracy from 66% to 81% using wet EEG and from 59% to 87% for dry EEG. Also of note was the finding that the dry EEG system can deliver comparable or even better results than the wet, despite the latter having one third as many EEG channels as the former. The 11-subject, wet-electrode AAD dataset for two competing, co-located talkers, the 11-subject, dry-electrode AAD dataset, and our software are available for further validation, experimentation, and modification.
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Atención/fisiología , Corteza Auditiva/fisiología , Interfaces Cerebro-Computador , Electroencefalografía , Estimulación Acústica , Algoritmos , Corteza Auditiva/diagnóstico por imagen , Electrocorticografía , Audífonos/tendencias , Humanos , Modelos Lineales , Redes Neurales de la Computación , Ruido , Dinámicas no Lineales , Percepción del Habla/fisiologíaRESUMEN
Accurate quantification of noise exposure in military environments is challenging due to movement of listeners and noise sources, spectral and temporal noise characteristics, and varied use of hearing protection. This study evaluates a wearable recording device designed to measure on-body and in-ear noise exposure, specifically in an environment with significant impulse noise resulting from firearms. A commercial audio recorder was augmented to obtain simultaneous measurements inside the ear canal behind an integrated hearing protector, and near the outer ear. Validation measurements, conducted with an acoustic test fixture and shock tube, indicated high impulse peak insertion loss with a proper fit of the integrated hearing protector. The recording devices were worn by five subjects during a live-fire data collection at Marine Corps Base Quantico where Marines fired semi-automatic rifles. The field test demonstrated the successful measurement of high-level impulse waveforms with the on-body and in-ear recording system. Dual channels allowed for instantaneous fit estimates for the hearing protection component, and the device worked as intended in terms of hearing protection and noise dosimetry. Accurate measurements of noise exposure and hearing protector fit should improve the ability to model and assess the risks of noise-induced hearing loss.
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Pruebas de Impedancia Acústica/instrumentación , Armas de Fuego , Ruido en el Ambiente de Trabajo/estadística & datos numéricos , Exposición Profesional/análisis , Dispositivos Electrónicos Vestibles , Pruebas de Impedancia Acústica/métodos , Adulto , Oído/fisiopatología , Femenino , Pérdida Auditiva Provocada por Ruido/etiología , Pérdida Auditiva Provocada por Ruido/prevención & control , Humanos , Masculino , Personal Militar , Espectrografía del SonidoRESUMEN
INTRODUCTION: The phenomenon recently described as "hidden hearing loss" was the subject of a meeting co-hosted by the Department of Defense Hearing Center of Excellence and MIT Lincoln Laboratory to consider the potential relevance of noise-related synaptopathic injury to military settings and performance, service-related injury scenarios, and military medical priorities. Participants included approximately 50 researchers and subject matter experts from academic, federal, and military laboratories. Here we present a synthesis of discussion topics and concerns, as well as specific research objectives identified to develop militarily relevant knowledge. MATERIALS AND METHODS: We consider findings from studies to date that have demonstrated cochlear synaptopathy and neurodegenerative processes apparently linked to noise exposure in animal models. We explore the potential relevance of these findings to the prediction and prevention of military hearing injuries, and to comorbid injuries in the neurological domain. RESULTS: Noise-induced cochlear synaptopathic injury is not detected by conventional audiometric assessment of threshold sensitivity. Animal studies suggest there may be a generous window of opportunity for intervention to mitigate or prevent cochlear neurodegenerative processes, e.g., by administration of neurotrophins or antioxidants. However, it is not yet known if the mechanisms that underlie "hidden hearing loss" also occur in human beings or, if so, how to identify them early, and how and when to intervene. CONCLUSION: Neurological injuries resulting from noise exposures via the auditory system have potentially significant implications for military Service Member performance, long-term Veteran health, and noise exposure standards. Mediated via auditory pathways, such injuries have possible relationship to clinical impairments including speech perception, and may be a largely overlooked contributor to cognitive symptoms associated with other military service-related injuries such as blast exposure and brain trauma. The potential health and performance consequences of noise-induced cochlear synaptopathic injury are easily overlooked, especially if it is assumed that hearing threshold sensitivity loss is the major concern. There should be a renewed impetus to further characterize and model synaptopathic mechanisms of auditory injury; study its potential impact on human auditory function, cognition, and performance metrics of military relevance; and develop solutions for auditory protection (including noise dosimetry) and treatment if appropriate following noise or blast exposure in military scenarios. We identify specific problems, solution objectives, and research objectives. Recommended research calls for a multidisciplinary approach to address cochlear nerve synaptopathy, central (brain) dysfunction, noise exposure measurement and metrics, and clinical assessment.
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Cóclea/lesiones , Pérdida Auditiva Provocada por Ruido/diagnóstico , Animales , Audiometría/métodos , Audiometría/tendencias , Cóclea/fisiopatología , Modelos Animales de Enfermedad , Humanos , Personal Militar/estadística & datos numéricos , Ruido/efectos adversosRESUMEN
Noise exposure and the subsequent hearing loss are well documented aspects of military life. Numerous studies have indicated high rates of noise-induced hearing injury (NIHI) in active-duty service men and women, and recent statistics from the U.S. Department of Veterans Affairs indicate a population of veterans with hearing loss that is growing at an increasing rate. In an effort to minimize hearing loss, the U.S. Department of Defense (DoD) updated its Hearing Conservation Program in 2010, and also has recently revised the DoD Design Criteria Standard Noise Limits (MIL-STD-1474E) which defines allowable noise levels in the design of all military acquisitions including weapons and vehicles. Even with such mandates, it remains a challenge to accurately quantify the noise exposure experienced by a Warfighter over the course of a mission or training exercise, or even in a standard work day. Noise dosimeters are intended for exactly this purpose, but variations in device placement (e.g., free-field, on-body, in/near-ear), hardware (e.g., microphone, analog-to-digital converter), measurement time (e.g., work day, 24-h), and dose metric calculations (e.g., time-weighted energy, peak levels, Auditory Risk Units), as well as noise types (e.g., continuous, intermittent, impulsive) can cause exposure measurements to be incomplete, inaccurate, or inappropriate for a given situation. This paper describes the design of a noise dosimeter capable of acquiring exposure data across tactical environments. Two generations of prototypes have been built at MIT Lincoln Laboratory with funding from the U.S. Army, Navy, and Marine Corps. Details related to hardware, signal processing, and testing efforts are provided, along with example tactical military noise data and lessons learned from early fieldings. Finally, we discuss the continued need to prioritize personalized dosimetry in order to improve models that predict or characterize the risk of auditory damage, to integrate dosimeters with hearing-protection devices, and to inform strategies and metrics for reducing NIHI.
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Acústica/instrumentación , Monitoreo del Ambiente/instrumentación , Pérdida Auditiva Provocada por Ruido/prevención & control , Audición , Personal Militar , Ruido en el Ambiente de Trabajo/prevención & control , Enfermedades Profesionales/prevención & control , Exposición Profesional/prevención & control , Monitoreo del Ambiente/métodos , Diseño de Equipo , Femenino , Pérdida Auditiva Provocada por Ruido/diagnóstico , Pérdida Auditiva Provocada por Ruido/etiología , Pérdida Auditiva Provocada por Ruido/fisiopatología , Humanos , Masculino , Ruido en el Ambiente de Trabajo/efectos adversos , Enfermedades Profesionales/diagnóstico , Enfermedades Profesionales/etiología , Enfermedades Profesionales/fisiopatología , Exposición Profesional/efectos adversos , Valor Predictivo de las Pruebas , Factores Protectores , Factores de Riesgo , Espectrografía del Sonido , Factores de TiempoRESUMEN
The medial olivocochlear reflex (MOCR) has been hypothesized to provide benefit for listening in noisy environments. This advantage can be attributed to a feedback mechanism that suppresses auditory nerve (AN) firing in continuous background noise, resulting in increased sensitivity to a tone or speech. MOC neurons synapse on outer hair cells (OHCs), and their activity effectively reduces cochlear gain. The computational model developed in this study implements the time-varying, characteristic frequency (CF) and level-dependent effects of the MOCR within the framework of a well-established model for normal and hearing-impaired AN responses. A second-order linear system was used to model the time-course of the MOCR using physiological data in humans. The stimulus-level-dependent parameters of the efferent pathway were estimated by fitting AN sensitivity derived from responses in decerebrate cats using a tone-in-noise paradigm. The resulting model uses a binaural, time-varying, CF-dependent, level-dependent OHC gain reduction for both ipsilateral and contralateral stimuli that improves detection of a tone in noise, similarly to recorded AN responses. The MOCR may be important for speech recognition in continuous background noise as well as for protection from acoustic trauma. Further study of this model and its efferent feedback loop may improve our understanding of the effects of sensorineural hearing loss in noisy situations, a condition in which hearing aids currently struggle to restore normal speech perception.
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Cóclea/fisiología , Nervio Coclear/fisiología , Núcleo Olivar/fisiología , Reflejo Acústico/fisiología , Simulación por Computador , Células Ciliadas Auditivas Externas/fisiología , Humanos , Modelos Neurológicos , RuidoRESUMEN
Neurobiological correlates of adaptation to spectrally degraded speech were investigated with fMRI before and after exposure to a portable real-time speech processor that implements an acoustic simulation model of a cochlear implant (CI). The speech processor, in conjunction with isolating insert earphones and a microphone to capture environment sounds, was worn by participants over a two week chronic exposure period. fMRI and behavioral speech comprehension testing were conducted before and after this two week period. After using the simulator each day for 2h, participants significantly improved in word and sentence recognition scores. fMRI shows that these improvements came accompanied by changes in patterns of neuronal activation. In particular, we found additional recruitment of visual, motor, and working memory areas after the perceptual training period. These findings suggest that the human brain is able to adapt in a short period of time to a degraded auditory signal under a natural learning environment, and gives insight on how a CI might interact with the central nervous system. This paradigm can be furthered to investigate neural correlates of new rehabilitation, training, and signal processing strategies non-invasively in normal hearing listeners to improve CI patient outcomes.