Earplug-induced changes in acoustic reflex thresholds suggest that increased subcortical neural gain may be necessary but not sufficient for the occurrence of tinnitus.

The occurrence of tinnitus is associated with hearing loss and neuroplastic changes in the brain, but disentangling correlation and causation has remained difficult in both human and animal studies. Here we use earplugs to cause a period of monaural deprivation to induce a temporary, fully reversible tinnitus sensation, to test whether differences in subcortical changes in neural response gain, as reflected through changes in acoustic reflex thresholds (ARTs), could explain the occurrence of tinnitus. Forty-four subjects with normal hearing wore an earplug in one ear for either 4 (n = 27) or 7 days (n = 17). Thirty subjects reported tinnitus at the end of the deprivation period. ARTs were measured before the earplug period and immediately after taking the earplug out. At the end of the earplug period, ARTs in the plugged ear were decreased by 5.9 ±â€¯1.1 dB in the tinnitus-positive group, and by 6.3 ±â€¯1.1 dB in the tinnitus-negative group. In the control ear, ARTs were increased by 1.3 ±â€¯0.8 dB in the tinnitus-positive group, and by 1.6 ±â€¯2.0 dB in the tinnitus-negative group. There were no significant differences between the groups with 4 and 7 days of auditory deprivation. Our results suggest that either the subcortical neurophysiological changes underlying the ART reductions might not be related to the occurrence of tinnitus, or that they might be a necessary component of the generation of tinnitus, but with additional changes at a higher level of auditory processing required to give rise to tinnitus. This article is part of a Special Issue entitled: Hearing Loss, Tinnitus, Hyperacusis, Central Gain.

Modeling Speech Level as a Function of Background Noise Level and Talker-to-Listener Distance for Talkers Wearing Hearing Protection Devices.

Purpose: Studying the variations in speech levels with changing background noise level and talker-to-listener distance for talkers wearing hearing protection devices (HPDs) can aid in understanding communication in background noise. Method: Speech was recorded using an intra-aural HPD from 12 different talkers at 5 different distances in 3 different noise conditions and 2 quiet conditions. Results: This article proposes models that can predict the difference in speech level as a function of background noise level and talker-to-listener distance for occluded talkers. The proposed model complements the existing model presented by Pelegrín-García, Smits, Brunskog, and Jeong (2011) and expands on it by taking into account the effects of occlusion and background noise level on changes in speech sound level. Conclusions: Three models of the relationship between vocal effort, background noise level, and talker-to-listener distance for talkers wearing HPDs are presented. The model with the best prediction intervals is a talker-dependent model that requires the users' unoccluded speech level at 10 m as a reference. A model describing the relationship between speech level, talker-to-listener distance, and background noise level for occluded talkers could eventually be incorporated with radio protocols to transmit verbal communication only to an intended set of listeners within a given spatial range-this range being dependent on the changes in speech level and background noise level.

Does Combat Hearing Preservation Equipment Affect Balance?

OBJECTIVES: (1) To investigate whether the occlusion effect and hearing attenuation produced by 3M Combat Arms Ear Plugs (CAEP) affects balance when compared to no hearing protection and (2) to investigate whether the occlusion effect and noise-canceling capabilities of the Nacre QuietPro system affects balance when compared to no hearing protection. METHODS: This prospective study collected pilot data for investigation of mechanisms of balance. 20 subjects with normal hearing and no vestibular dysfunction were tested with blackened goggles in three conditions-no hearing protection, CAEP, and with the Nacre QuietPro. RESULTS: A static posturogrpahy forceplate was used to measure center of gravity angular acceleration for a period of 20 seconds. The order of the conditions tested was randomized for each individual. Mean angular acceleration and standard deviation (degrees/second) of the three conditions were: (1) no hearing protection (control), 0.65 + 0.19, (2) CAEP, 0.69 + 0.23, and (3) QuietPro, 0.70 + 0.20 (one-way analysis of variance [ANOVA], df = 2, F = 0.38, p = 0.706). CONCLUSIONS: The components of an intact balance system include a variety of neural inputs, to include vesitbuloocular, vestibulospinal, and labyrinthine afferents. Both the CAEP and Nacre QuietPro are hearing preservation devices utilized during Operation Iraqi Freedom and Operation Enduring Freedom in Afghanistan. Our pilot data show no decrement in balance with utilization of these combat hearing preservation devices.

Sensory reweighting after loss of auditory cues in healthy adults.

We maintain our balance using information provided by the visual, somatosensory, and vestibular systems on the position of our body in space. Recent evidence has suggested that auditory input also plays a significant role for postural control, yet further investigations are required to better understand the contributions of audition to this process in healthy adults. To date, the process of sensory reweighting when auditory cues are disturbed during postural control has been overlooked. The aim of this study is to determine the impact of hearing protection on sensory reweighting for postural control in healthy adults. For this, we studied 14 healthy adults on a force platform using four different postural conditions either with or without attenuation of auditory cues. Our results suggest that disturbing auditory cues increases the reliance on visual cues for postural control. This is the first study to demonstrate such a sensory reweighting occurs in the event of a sudden disturbance of auditory cues in healthy adults.

Impression Material in the External and Middle Ear: an Overview of the Literature and a Stepwise Approach for Removal.

Here, we provide a literature overview of cases with protruding molding material for earplugs or hearing aids and subsequent required treatment, including our own cases. Patients at risk are those with impaired tympanic membranes or who previously underwent otologic surgery. Symptoms such as otalgia, tinnitus, and vertigo are alarming but do not always arise. In case of doubt, a CT scan is of additive value to prepare for adequate surgical removal and to limit potential damage. A stepwise approach for the clinician on how to address these challenging cases is presented, based upon the literature and our own experience.

Speech recognition in noise under hearing protection: A computational study of the combined effects of hearing loss and hearing protector attenuation.

OBJECTIVE: To investigate the effects of hearing protection on speech recognition in noise. DESIGN: Computational study using a speech recognition model that was previously empirically validated. STUDY SAMPLE: Recognition scores were calculated in unprotected and protected conditions for four sets of hearing protector attenuation functions in two different noises, for three simulated hearing profiles illustrative of those anticipated in the noisy workplace. RESULTS: For a normal-hearing profile, recognition scores were not sensitive to the slope of the attenuation function and the overall amount of noise reduction, but protected conditions provided a small but consistent 7-12% benefit compared to unprotected listening. For profiles simulating hearing loss, recognition scores were much more sensitive to the attenuation function. Substantial drops of 30% or more were found compared to unprotected listening in some conditions of steep attenuation slopes and large noise reductions. Attenuation functions modelled from real hearing protectors with nearly-flat attenuation yielded a benefit compared to unprotected listening for all hearing profiles studied. These findings were true in both noises. CONCLUSIONS: Limiting the slope of the hearing protector attenuation function and/or the overall amount of noise reduction is useful and warranted for workers with hearing loss to prevent adverse effects on speech recognition.

Variations in voice level and fundamental frequency with changing background noise level and talker-to-listener distance while wearing hearing protectors: A pilot study.

OBJECTIVE: Speech production in noise with varying talker-to-listener distance has been well studied for the open ear condition. However, occluding the ear canal can affect the auditory feedback and cause deviations from the models presented for the open-ear condition. Communication is a main concern for people wearing hearing protection devices (HPD). Although practical, radio communication is cumbersome, as it does not distinguish designated receivers. A smarter radio communication protocol must be developed to alleviate this problem. Thus, it is necessary to model speech production in noise while wearing HPDs. Such a model opens the door to radio communication systems that distinguish receivers and offer more efficient communication between persons wearing HPDs. DESIGN: This paper presents the results of a pilot study aimed to investigate the effects of occluding the ear on changes in voice level and fundamental frequency in noise and with varying talker-to-listener distance. STUDY SAMPLE: Twelve participants with a mean age of 28 participated in this study. RESULTS: Compared to existing data, results show a trend similar to the open ear condition with the exception of the occluded quiet condition. CONCLUSIONS: This implies that a model can be developed to better understand speech production for the occluded ear.

Speech understanding in noise with integrated in-ear and muff-style hearing protection systems.

Integrated hearing protection systems are designed to enhance free field and radio communications during military operations while protecting against the damaging effects of high-level noise exposure. A study was conducted to compare the effect of increasing the radio volume on the intelligibility of speech over the radios of two candidate systems, in-ear and muff-style, in 85-dBA speech babble noise presented free field. Twenty normal-hearing, English-fluent subjects, half male and half female, were tested in same gender pairs. Alternating as talker and listener, their task was to discriminate consonant-vowel-consonant syllables that contrasted either the initial or final consonant. Percent correct consonant discrimination increased with increases in the radio volume. At the highest volume, subjects achieved 79% with the in-ear device but only 69% with the muff-style device, averaged across the gender of listener/talker pairs and consonant position. Although there was no main effect of gender, female listener/talkers showed a 10% advantage for the final consonant and male listener/talkers showed a 1% advantage for the initial consonant. These results indicate that normal hearing users can achieve reasonably high radio communication scores with integrated in-ear hearing protection in moderately high-level noise that provides both energetic and informational masking. The adequacy of the range of available radio volumes for users with hearing loss has yet to be determined.

Speech recognition in noise with active and passive hearing protectors: a comparative study.

The perceived negative influence of standard hearing protectors on communication is a common argument for not wearing them. Thus, "augmented" protectors have been developed to improve speech intelligibility. Nevertheless, their actual benefit remains a point of concern. In this paper, speech perception with active earplugs is compared to standard passive custom-made earplugs. The two types of active protectors included amplify the incoming sound with a fixed level or to a user selected fraction of the maximum safe level. For the latter type, minimal and maximal amplification are selected. To compare speech intelligibility, 20 different speech-in-noise fragments are presented to 60 normal-hearing subjects and speech recognition is scored. The background noise is selected from realistic industrial noise samples with different intensity, frequency, and temporal characteristics. Statistical analyses suggest that the protectors' performance strongly depends on the noise condition. The active protectors with minimal amplification outclass the others for the most difficult and the easiest situations, but they also limit binaural listening. In other conditions, the passive protectors clearly surpass their active counterparts. Subsequently, test fragments are analyzed acoustically to clarify the results. This provides useful information for developing prototypes, but also indicates that tests with human subjects remain essential.

Predictors of use of hearing protection among a representative sample of farmers.

Farmers experience higher rates of noise-induced hearing loss (NIHL) than workers in most other industries. We developed a model of farmers' use of hearing protection, and tested it with a random sample (n = 532) of farmers from the upper Midwest. Barriers to using hearing protection (e.g., difficulty communicating; OR = .44, p < .003) were negatively related to use. Greater access/availability of hearing protectors (OR = 1.75, p < .010) and male gender (OR = .43, p < .019) were positively related to use. The model correctly predicted use of hearing protection for 74% of the cases. Overall, farmers demonstrated low hearing protector use, and results were similar to those from previous studies of non-farm workers. Findings from this study will be useful in designing interventions to increase farmers' hearing protector use and decrease their rates of NIHL.

An evaluation of musician earplugs with college music students.

Musician earplugs are marketed and recommended for use in music settings but no studies have evaluated these products with musicians. This study evaluated the influences of earplugs on college students' perception and abilities to communicate in a musical environment, attitudes of earplugs, comfort over time, and the influence of earplugs on ability to play music. College students (N = 323) were provided with earplugs for use during and following an experimental condition designed to mimic a night club. Results underline the challenges of earplugs in environments that are both loud and require verbal interaction. Responses to comfort questions were variable and suggest a multi-factorial set of influences that may include intrinsic variables. Despite these limitations, subjects in this study generally liked the earplugs and believed that they are valuable. However, the earplugs were not viewed favorably by musicians willing to use the earplugs while playing music. This study supports the view that earplugs are subject to many problems and should be considered as a last resort.

Factors affecting Thai workers' use of hearing protection.

This study used an ecological model to examine Thai workers' beliefs and attitudes toward using occupational hearing protection. Data collection involved focus group sessions with 28 noise-exposed workers at four factories in Chiang Mai Province and an interview with a safety officer at each organization. Detailed content analysis resulted in the identification of three types of factors influencing the use of hearing protection: intrapersonal, including preventing impaired hearing, noise annoyance, personal discomfort, and interference with communication; interpersonal, including coworker modeling, supervisor support, and supervisor modeling; and organizational, including organizational rules and regulations, provision of hearing protection devices, dissemination of knowledge and information, noise monitoring, and hearing testing. Effective hearing protection programs depend on knowledge of all of these factors. Strategies to promote workers' use of hearing protection should include the complete range of factors having the potential to affect workers' hearing.

Perception and attitudes of firefighters on noise exposure and hearing loss.

Noise exposure of firefighters results in increased risk of hearing loss. Noise-induced hearing loss (NIHL) can be prevented by the consistent use of hearing protection devices (HPDs). However, little is known about firefighters' perceptions and attitudes on NIHL and HPD use. The purposes of the study were (1) to identify common noise sources of fire fighting equipment and activities; and (2) to describe the attitudes and beliefs of firefighters concerning the importance of their hearing, occupational noise exposure, NIHL, and HPD use. A nonexperimental, descriptive focus group design was used to gather qualitative data from firefighters at two fire houses in southeast Michigan. The study identified sources of noise unique to fire fighting, such as driving fire/emergency trucks with sirens on; operating water pumps, saws, and other equipment; and shouting to communicate with civilians and fellow firefighters. Firefighters acknowledged the significance of good hearing in fire fighting service but perceived NIHL was unavoidable on the job and viewed it as a small risk compared with other hazards. HPDs were not used regularly because firefighters believed they interfered with the ability to hear commands during emergency conditions, interfered with other required safety equipment, and were generally forgotten when gearing up. Firefighters recognized the importance of hearing health and the benefit of a hearing conservation program, including annual training, and identified several topics that should be included in a training program. These findings will provide critical information in planning what type of program should be developed and carried out for the fire fighting population.

Signal recognition and hearing protectors with normal and impaired hearing.

Recognition of acoustic signals when perception is subject to interference from noise has already been extensively studied. In this study the influence of hearing protectors (HP) (plugs, muffs) and hearing loss on signal recognition is examined. Different spectrums and levels of the noise are also included. The test results are shown as the masked threshold for the signals heard and identified. In the case of normally hearing subjects a frequency-independent HP (plug) improves hearing performance, while frequency-dependent HP (muffs) tends to worsen it, especially with low-frequency noise. Hearing losses even worsen hearing performance when plugs are worn. Design suggestions are made to optimise signal recognition. Minimum signal-to-noise ratio and the use of HP are discussed.

The effects of hearing protectors on auditory localization: evidence from audio-visual target acquisition.

Response times (RT) in an audio-visual target acquisition task were collected from 3 participants while wearing either circumaural earmuffs, foam earplugs, or no hearing protection. Analyses revealed that participants took significantly longer to locate and identify an audio-visual target in both hearing protector conditions than they did in the unoccluded condition, suggesting a disturbance of the cues used by listeners to localize sounds in space. RTs were significantly faster in both hearing protector conditions than in a non-audio control condition, indicating that auditory localization was not completely disrupted. Results are discussed in terms of safety issues involved with wearing hearing protectors in an occupational environment.