The effect of hearing protection worn by talker and/or target listener on speech production in quiet and noise.

Speech production while wearing hearing protectors poses significant challenges due to their occlusion effect and disruption of the Lombard effect. An experiment was conducted with 24 individuals as they read a list of 12 sentences in open ears and while wearing an earmuff in quiet and in four different noises [pink, International Female Fluctuating Masker (IFFM), speech-spectrum noise (SSnoise), and helicopter] at two levels (70 and 85 dBA). An acoustic manikin, fitted or not with an identical protector, served as the target listener. In noise, speech levels decreased when the talkers wore the earmuff but increased when the target listener was fitted with the earmuff. When the earmuff was used by both the talkers and target listener, speech levels were lower by 3-6 dB at the higher noise level compared to when they were both open ears. Speech levels were typically lower, but extended speech intelligibility index estimates were consistently higher, in fluctuating (IFFM, helicopter) than in continuous noises (pink, SSnoise). Talkers' pitch frequency and voice spectrum measurements followed very closely the changes in speech levels, showing no evidence of compensatory voice modifications. Implications of the lower talker speech levels when wearing hearing protectors are discussed in terms of protector selection, training, and individuals with hearing loss.

Effect of Hearing and Head Protection on the Localization of Tonal and Broadband Reverse Alarms.

OBJECTIVE: This study explored the effects of hearing protection devices (HPDs) and head protection on the ability of normal-hearing individuals to localize reverse alarms in background noise. BACKGROUND: Among factors potentially contributing to accidents involving heavy vehicles, reverse alarms can be difficult to localize in space, leading to errors in identifying the source of danger. Previous studies have shown that traditional tonal alarms are more difficult to localize than broadband alarms. In addition, HPDs and safety helmets may further impair localization. METHOD: Standing in the middle of an array of eight loudspeakers, participants with and without HPDs (passive and level-dependent) had to identify the loudspeaker emitting a single cycle of the alarm while performing a task on a tablet computer. RESULTS: The broadband alarm was easier to localize than the tonal alarm. Passive HPDs had a significant impact on sound localization (earmuffs generally more so than earplugs), particularly double hearing protection, and level-dependent HPDs did not fully restore sound localization abilities. The safety helmet had a much lesser impact on performance than HPDs. CONCLUSION: Where good sound localization abilities are essential in noisy workplaces, the broadband alarm should be used, double hearing protection should be avoided, and earplug-style passive or level-dependent devices may be a better choice than earmuff-style devices. Construction safety helmets, however, seem to have only a minimal effect on sound localization. APPLICATION: Results of this study will help stakeholders make decisions that are more informed in promoting safer workplaces.

Development of the Canadian Digit Triplet Test in English and French.

The Canadian Digit Triplet Test was developed in English and French, the official languages of Canada. Four versions were developed on a common software platform using recordings produced by two fluent bilinguals, one male and one female, following procedures recommended by international guidelines. Phase I of test development focused on homogenizing digit recognition across tokens and positions within the triplets for young adults with normal hearing (n = 48). In phase II, normative data were collected for young adults with normal hearing (n = 64). Statistical properties were found to be uniform across test versions and comparable to digit triplet tests in other languages.

Effects of hearing loss and language proficiency on speech intelligibility over radio transmission with tactical communication devices.

Objective: Study the effects of hearing loss and language proficiency in a speech task over radio transmission.Design: Four TCAPS device conditions (2 models × 2 talk-through modes) were investigated with the Modified Rhyme Test (MRT) conducted in talker-listener pairs immersed in 85-dBA noise. Speech quality ratings and preferred radio volume levels were also collected.Study sample: Thirty-six participants divided into three groups (control, non-fluent, hearing-impaired) took part in the experiment. Participants acted as talkers and listeners when paired with a unique standard individual (fluent and normal hearing) of the same gender.Results: MRT scores were significantly lower in many device conditions when the non-fluent group of participants acted as listeners and talkers and when the hearing-impaired participants acted as listeners, compared to the control group. MRT results were also consistently poorer with one device configured for bone-conducted voice pick-up in the occluded ear compared to another one equipped with an external mouth microphone. Talk-through settings had little effect. MRT results were reflected in the subjective quality ratings. Participants with hearing loss used higher radio volume levels.Conclusions: Language proficiency, hearing loss and method of sensing the talker's voice are key issues to consider with TCAPS devices.

An indirect calculation method for estimating occupational sound exposure from communication headsets.

Measurement of noise exposure from communication headsets is challenging due to the need for specialized equipment, methods, and training. Canadian standard Z107.56-13 [(2013). Measurement of Noise Exposure (Canadian Standards Association, Mississauga, Canada)] introduced a calculation procedure to promote a simpler method that stakeholders in hearing loss prevention could readily apply using widely accessible sound level equipment. The original procedure specified a fixed signal-to-noise ratio (SNR) of 15 dB above the protected background noise when estimating the speech listening level through the headset communication channel. The relationship between background noise level, noise type, headset noise reduction (NR), and speech listening level is revisited in this study. In a noise simulation room, 24 participants were asked to adjust the headset volume while listening to speech and executing a visual reaction task. Results indicate that the growth in speech listening levels with noise is not adequately represented by a fixed SNR, and that one-sided listening increases speech levels by about 5-7 dB in quiet and in noise compared to two-sided listening. Moreover, use of an octave-band procedure with derating to estimate headset NR best captured the speech listening level data. A revised calculation procedure based on linear regression modeling is described with parameters adjusted separately for one-sided and two-sided headsets.

Development of hearing standards for Ontario's Constable Selection System.

Objective: Develop valid and defensible hearing standards for Ontario constables to ensure safe and efficient operations. Design: Research involved three steps: (1) identification of hearing critical (HC) tasks, (2) characterisation of real-world noise environments where these tasks are performed (3) and establishment of screening criteria and protocols for determining fitness for duty. Study sample: Three panels of subject matter experts (SMEs) from different Ontario police services participated in Steps 1 and 3. Result: Fifty-one HC tasks conducted in 25 different environments were identified. Acceptable levels of speech communication in noise were based on environments with the highest frequency, importance and difficulty ratings. The ability to understand soft speech was also deemed critical. These translated into a 2 dB maximum elevation in the Noise Composite speech recognition threshold (SRT) with the Hearing-In-Noise-Test and a threshold in quiet of 35 dBA or better. Conclusions: Speech communication modelling methodology greatly facilitates the task of developing fitness for duty hearing standards, but participation of SMEs is crucial for face validity.

Evidence-Based Occupational Hearing Screening I: Modeling the Effects of Real-World Noise Environments on the Likelihood of Effective Speech Communication.

OBJECTIVES: The objectives of this study were to (1) identify essential hearing-critical job tasks for public safety and law enforcement personnel; (2) determine the locations and real-world noise environments where these tasks are performed; (3) characterize each noise environment in terms of its impact on the likelihood of effective speech communication, considering the effects of different levels of vocal effort, communication distances, and repetition; and (4) use this characterization to define an objective normative reference for evaluating the ability of individuals to perform essential hearing-critical job tasks in noisy real-world environments. DESIGN: Data from five occupational hearing studies performed over a 17-year period for various public safety agencies were analyzed. In each study, job task analyses by job content experts identified essential hearing-critical tasks and the real-world noise environments where these tasks are performed. These environments were visited, and calibrated recordings of each noise environment were made. The extended speech intelligibility index (ESII) was calculated for each 4-sec interval in each recording. These data, together with the estimated ESII value required for effective speech communication by individuals with normal hearing, allowed the likelihood of effective speech communication in each noise environment for different levels of vocal effort and communication distances to be determined. These likelihoods provide an objective norm-referenced and standardized means of characterizing the predicted impact of real-world noise on the ability to perform essential hearing-critical tasks. RESULTS: A total of 16 noise environments for law enforcement personnel and eight noise environments for corrections personnel were analyzed. Effective speech communication was essential to hearing-critical tasks performed in these environments. Average noise levels, ranged from approximately 70 to 87 dBA in law enforcement environments and 64 to 80 dBA in corrections environments. The likelihood of effective speech communication at communication distances of 0.5 and 1 m was often less than 0.50 for normal vocal effort. Likelihood values often increased to 0.80 or more when raised or loud vocal effort was used. Effective speech communication at and beyond 5 m was often unlikely, regardless of vocal effort. CONCLUSIONS: ESII modeling of nonstationary real-world noise environments may prove an objective means of characterizing their impact on the likelihood of effective speech communication. The normative reference provided by these measures predicts the extent to which hearing impairments that increase the ESII value required for effective speech communication also decrease the likelihood of effective speech communication. These predictions may provide an objective evidence-based link between the essential hearing-critical job task requirements of public safety and law enforcement personnel and ESII-based hearing assessment of individuals who seek to perform these jobs.

Detection and reaction thresholds for reverse alarms in noise with and without passive hearing protection.

OBJECTIVE: To measure masked detection and reaction thresholds for two reverse alarms (tonal and broadband) and compare results to available standards and psychoacoustic criteria for setting alarm levels. DESIGN: Alarm detection and reaction thresholds were adaptively measured in 80-dBA background noises without hearing protection (Experiment 1), and with a passive earmuff-style hearing protection device (HPD) (Experiment 2). STUDY SAMPLE: Twenty-four young adults with normal hearing in each experimental group. RESULTS: Reverse alarms remained audible at levels well-below background noises [thresholds: -11 to -25 dB signal-to-noise ratio (SNR)], with and without the selected HPD. Detection was more influenced by alarm and noise type, while reaction was more susceptible to HPD use. HPD use resulted in lower detection thresholds by up to 2.5 dB compared to unprotected listening but increased reaction thresholds by 5-10 dB depending on the alarm. CONCLUSIONS: Since noise type appears to have a more limited effect on reaction thresholds, adjusting alarms based on a global dBA method appears preferable to methods based on masked detection thresholds. However, while the >0 dB SNR recommended in ISO 9533 seems adequate for unprotected listening, an additional 5-10 dB may be warranted to elicit the same reaction when the selected HPD is used.

Evidence-based occupational hearing screening II: validation of a screening methodology using measures of functional hearing ability.

OBJECTIVE: Validate use of the Extended Speech Intelligibility Index (ESII) for prediction of speech intelligibility in non-stationary real-world noise environments. Define a means of using these predictions for objective occupational hearing screening for hearing-critical public safety and law enforcement jobs. DESIGN: Analyses of predicted and measured speech intelligibility in recordings of real-world noise environments were performed in two studies using speech recognition thresholds (SRTs) and intelligibility measures. ESII analyses of the recordings were used to predict intelligibility. Noise recordings were made in prison environments and at US Army facilities for training ground and airborne forces. Speech materials included full bandwidth sentences and bandpass filtered sentences that simulated radio transmissions. STUDY SAMPLE: A total of 22 adults with normal hearing (NH) and 15 with mild-moderate hearing impairment (HI) participated in the two studies. RESULTS: Average intelligibility predictions for individual NH and HI subjects were accurate in both studies (r2 ≥ 0.94). Pooled predictions were slightly less accurate (0.78 ≤ r2 ≤ 0.92). CONCLUSIONS: An individual's SRT and audiogram can accurately predict the likelihood of effective speech communication in noise environments with known ESII characteristics, where essential hearing-critical tasks are performed. These predictions provide an objective means of occupational hearing screening.

Self-masking and overlap-masking from reverberation using the speech-evoked auditory brainstem response.

This study introduces an improved method to investigate the effects of reverberation using the speech-evoked auditory brainstem response (ABR) that more realistically captures the influence of self- and overlap-masking induced by room reverberation. Speech-evoked ABR was measured under three acoustic scenarios: anechoic, mild reverberation with dominance of early reflections, and severe reverberation with dominance of late reverberation. Responses were significantly weaker and had longer latencies with severe reverberation relative to anechoic and mild reverberation. Although larger responses and shorter latencies were observed with mild reverberation than anechoic, possibly due to early reflections, these reached significance in only one of six ABR response measures.

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.

Comparison of direct measurement methods for headset noise exposure in the workplace.

The measurement of noise exposure from communication headsets poses a methodological challenge. Although several standards describe methods for general noise measurements in occupational settings, these are not directly applicable to noise assessments under communication headsets. For measurements under occluded ears, specialized methods have been specified by the International Standards Organization (ISO 11904) such as the microphone in a real ear and manikin techniques. Simpler methods have also been proposed in some national standards such as the use of general purpose artificial ears and simulators in conjunction with single number corrections to convert measurements to the equivalent diffuse field. However, little is known about the measurement agreement between these various methods and the acoustic manikin technique. Twelve experts positioned circum-aural, supra-aural and insert communication headsets on four different measurement setups (Type 1, Type 2, Type 3.3 artificial ears, and acoustic manikin). Fit-refit measurements of four audio communication signals were taken under quiet laboratory conditions. Data were transformed into equivalent diffuse-field sound levels using third-octave procedures. Results indicate that the Type 1 artificial ear is not suited for the measurement of sound exposure under communication headsets, while Type 2 and Type 3.3 artificial ears are in good agreement with the acoustic manikin technique. Single number corrections were found to introduce a large measurement uncertainty, making the use of the third-octave transformation preferable.

The interaction of hearing loss and level-dependent hearing protection on speech recognition in noise.

OBJECTIVES: To determine the effects of different control settings of level-dependent hearing protectors on speech recognition performance in interaction with hearing loss. DESIGN: Controlled laboratory experiment with two level-dependent devices (Peltor® PowerCom Plus™ and Nacre QuietPro®) in two military noises. STUDY SAMPLE: Word recognition scores were collected in protected and unprotected conditions for 45 participants grouped into four hearing profile categories ranging from within normal limits to moderate-to-severe hearing loss. RESULTS: When the level-dependent mode was switched off to simulate conventional hearing protection, there were large differences across hearing profile categories regarding the effects of wearing the devices on speech recognition in noise; participants with normal hearing showed little effect while participants in the most hearing-impaired category showed large decrements in scores compared to unprotected listening. Activating the level-dependent mode of the devices produced large speech recognition benefits over the passive mode at both low and high gain pass-through settings. The category of participants with the most impaired hearing benefitted the most from the level-dependent mode. CONCLUSIONS: The findings indicate that level-dependent hearing protection circuitry can provide substantial benefits in speech recognition performance in noise, compared to conventional passive protection, for individuals covering a wide range of hearing losses.

Comparison of sound propagation and perception of three types of backup alarms with regards to worker safety.

A technology of backup alarms based on the use of a broadband signal has recently gained popularity in many countries. In this study, the performance of this broadband technology is compared to that of a conventional tonal alarm and a multi-tone alarm from a worker-safety standpoint. Field measurements of sound pressure level patterns behind heavy vehicles were performed in real work environments and psychoacoustic measurements (sound detection thresholds, equal loudness, perceived urgency and sound localization) were carried out in the laboratory with human subjects. Compared with the conventional tonal alarm, the broadband alarm generates a much more uniform sound field behind vehicles, is easier to localize in space and is judged slighter louder at representative alarm levels. Slight advantages were found with the tonal alarm for sound detection and for perceived urgency at low levels, but these benefits observed in laboratory conditions would not overcome the detrimental effects associated with the large and abrupt variations in sound pressure levels (up to 15-20 dB within short distances) observed in the field behind vehicles for this alarm, which are significantly higher than those obtained with the broadband alarm. Performance with the multi-tone alarm generally fell between that of the tonal and broadband alarms on most measures.

Perception of Prosody in Hearing-Impaired Individuals and Users of Hearing Assistive Devices: An Overview of Recent Advances.

PURPOSE: Prosody perception is an essential component of speech communication and social interaction through which both linguistic and emotional information are conveyed. Considering the importance of the auditory system in processing prosody-related acoustic features, the aim of this review article is to review the effects of hearing impairment on prosody perception in children and adults. It also assesses the performance of hearing assistive devices in restoring prosodic perception. METHOD: Following a comprehensive online database search, two lines of inquiry were targeted. The first summarizes recent attempts toward determining the effects of hearing loss and interacting factors such as age and cognitive resources on prosody perception. The second analyzes studies reporting beneficial or detrimental impacts of hearing aids, cochlear implants, and bimodal stimulation on prosodic abilities in people with hearing loss. RESULTS: The reviewed studies indicate that hearing-impaired individuals vary widely in perceiving affective and linguistic prosody, depending on factors such as hearing loss severity, chronological age, and cognitive status. In addition, most of the emerging information points to limitations of hearing assistive devices in processing and transmitting the acoustic features of prosody. CONCLUSIONS: The existing literature is incomplete in several respects, including the lack of a consensus on how and to what extent hearing prostheses affect prosody perception, especially the linguistic function of prosody, and a gap in assessing prosody under challenging listening situations such as noise. This review article proposes directions that future research could follow to provide a better understanding of prosody processing in those with hearing impairment, which may help health care professionals and designers of assistive technology to develop innovative diagnostic and rehabilitation tools. SUPPLEMENTAL MATERIAL: https://doi.org/10.23641/asha.21809772.

Speech perception in noise: exploring the effect of linguistic context in children with and without auditory processing disorder.

OBJECTIVE: The objective of this study was to investigate whether the speech perception problems in noise of children with auditory processing disorder (APD) stem from an auditory or a higher order dysfunction. DESIGN: A repeated measures design comparing the sentence key word recognition scores of children with APD and a control group was used. Four sentence lists from the Test de phrases dans le bruit (TPB) were presented with a babble masker at four different signal-to-noise ratios. The TPB is a Canadian French adaptation of the speech perception in noise test. STUDY SAMPLE: Ten participants between 9-12 years with APD participated in this study, as well as ten age- and gender-matched children with no sign of APD. RESULTS: Group analyses revealed that children with APD had poorer overall sentence key word recognition scores than the control group. Analysis of the difference scores between the high and low predictability sentences indicated that the benefit derived from linguistic context is similar between the groups. However, individual patterns of results revealed different profiles within the APD group. CONCLUSION: Further study using a larger sample is warranted to deepen our understanding of the nature of APD and identify characteristic profiles to enable better tailoring of therapeutic programs.

Evaluation of auditory functions for Royal Canadian Mounted Police officers.

BACKGROUND: Auditory fitness for duty (AFFD) testing is an important element in an assessment of workers' ability to perform job tasks safely and effectively. Functional hearing is particularly critical to job performance in law enforcement. Most often, assessment is based on pure-tone detection thresholds; however, its validity can be questioned and challenged in court. In an attempt to move beyond the pure-tone audiogram, some organizations like the Royal Canadian Mounted Police (RCMP) are incorporating additional testing to supplement audiometric data in their AFFD protocols, such as measurements of speech recognition in quiet and/or in noise, and sound localization. PURPOSE: This article reports on the assessment of RCMP officers wearing hearing aids in speech recognition and sound localization tasks. The purpose was to quantify individual performance in different domains of hearing identified as necessary components of fitness for duty, and to document the type of hearing aids prescribed in the field and their benefit for functional hearing. The data are to help RCMP in making more informed decisions regarding AFFD in officers wearing hearing aids. RESEARCH DESIGN: The proposed new AFFD protocol included unaided and aided measures of speech recognition in quiet and in noise using the Hearing in Noise Test (HINT) and sound localization in the left/right (L/R) and front/back (F/B) horizontal planes. Sixty-four officers were identified and selected by the RCMP to take part in this study on the basis of hearing thresholds exceeding current audiometrically based criteria. This article reports the results of 57 officers wearing hearing aids. RESULTS: Based on individual results, 49% of officers were reclassified from nonoperational status to operational with limitations on fine hearing duties, given their unaided and/or aided performance. Group data revealed that hearing aids (1) improved speech recognition thresholds on the HINT, the effects being most prominent in Quiet and in conditions of spatial separation between target and noise (Noise Right and Noise Left) and least considerable in Noise Front; (2) neither significantly improved nor impeded L/R localization; and (3) substantially increased F/B errors in localization in a number of cases. Additional analyses also pointed to the poor ability of threshold data to predict functional abilities for speech in noise (r² = 0.26 to 0.33) and sound localization (r² = 0.03 to 0.28). Only speech in quiet (r² = 0.68 to 0.85) is predicted adequately from threshold data. CONCLUSIONS: Combined with previous findings, results indicate that the use of hearing aids can considerably affect F/B localization abilities in a number of individuals. Moreover, speech understanding in noise and sound localization abilities were poorly predicted from pure-tone thresholds, demonstrating the need to specifically test these abilities, both unaided and aided, when assessing AFFD. Finally, further work is needed to develop empirically based hearing criteria for the RCMP and identify best practices in hearing aid fittings for optimal functional hearing abilities.

Adaptive environment classification system for hearing aids.

An adaptive sound classification framework is proposed for hearing aid applications. The long-term goal is to develop fully trainable instruments in which both the acoustical environments encountered in daily life and the hearing aid settings preferred by the user in each environmental class could be learned. Two adaptive classifiers are described, one based on minimum distance clustering and one on Bayesian classification. Through unsupervised learning, the adaptive systems allow classes to split or merge based on changes in the ongoing acoustical environments. Performance was evaluated using real-world sounds from a wide range of acoustical environments. The systems were first initialized using two classes, speech and noise, followed by a testing period when a third class, music, was introduced. Both systems were successful in detecting the presence of an additional class and estimating its underlying parameters, reaching a testing accuracy close to the target rates obtained from best-case scenarios derived from non-adaptive supervised versions of the classifiers (about 3% lower performance). The adaptive Bayesian classifier resulted in a 4% higher overall accuracy upon splitting adaptation than the minimum distance classifier. Merging accuracy was found to be the same in the two systems and within 1%-2% of the best-case supervised versions.

Functionally-based screening criteria for hearing-critical jobs based on the Hearing in Noise Test.

Effective communication is a crucial requirement in many workplaces to ensure safe and effective operations. Often, critical verbal communications are carried out in noise, which can be very challenging, particularly for individuals with hearing loss. Diagnostic measures of hearing, such as the audiogram, are not adequate to make accurate predictions of speech intelligibility in real-world environments for specific workers, and thus are not generally suitable as a basis for making employment decisions. Instead, the Hearing in Noise Test (HINT) has been identified and validated for use in predicting speech intelligibility in a wide range of communication environments. The approach to validation of the HINT takes into account the expected voice level of the talker, the communication distance between the talker and the listener, and a statistical model of speech intelligibility in real-world occupational noises. For each hearing-critical task, a HINT screening threshold score is derived upon specification of the minimum level of performance required of the workers. The HINT is available in several languages, so the tools developed are applicable in a wide range of settings, including multilingual workplaces.