Effects of High-Intensity Airborne Ultrasound Exposure on Behavioural and Electrophysiological Measures of Auditory Function

Regulations on safe ultrasound exposure limits are based on a very limited number of studies, which have only considered audiometric threshold shifts as indicators of hearing deficits. The purpose of the current study was to assess the effects of exposure to high-intensity ultrasound on a range of measures of hearing function, which included audiometric thresholds, as well as subclinical measures of hearing deficits: speech-in-noise understanding, supra-threshold auditory brainstem response wave I amplitude and latency, and frequency following response levels to amplitude modulated (AM) tones. Changes in these measures were assessed before and after exposure of the left ear to high-intensity ultrasound in a group of nine young listeners. These changes were compared to those observed in a control group of nine young listeners. Exposure consisted in the presentation of a 40-kHz AM tone at levels of 105, 110, 115, and 120 dB SPL for 10 minutes at each level, plus an exposure to a 40-kHz unmodulated tone during an ultrasound detection task, for a total duration of 50 seconds. None of the measures of hearing function was found to change significantly more for the left compared to the right ear, for participants of the exposure group compared to control participants. Electroencephalographic recordings obtained during exposure to the AM tone did not show significant phase-locked activity at the modulation frequency or at low-frequency subharmonics of the ultrasound tone. One out of nine participants was able to perform the ultrasound detection task above chance level, although due to limitations of the experimental setup the mechanism by which she could detect the presentation of the tone remains unclear

Perceptual consequences of "hidden" hearing loss

Dramatic results from recent animal experiments show that noise exposure can cause a selective loss of high-threshold auditory nerve fibers without affecting absolute sensitivity permanently. This cochlear neuropathy has been described as hidden hearing loss, as it is not thought to be detectable using standard measures of audiometric threshold. It is possible that hidden hearing loss is a common condition in humans and may underlie some of the perceptual deficits experienced by people with clinically normal hearing. There is some evidence that a history of noise exposure is associated with difficulties in speech discrimination and temporal processing, even in the absence of any audiometric loss. There is also evidence that the tinnitus experienced by listeners with clinically normal hearing is associated with cochlear neuropathy, as measured using Wave I of the auditory brainstem response. To date, however, there has been no direct link made between noise exposure, cochlear neuropathy, and perceptual difficulties. Animal experiments also reveal that the aging process itself, in the absence of significant noise exposure, is associated with loss of auditory nerve fibers. Evidence from human temporal bone studies and auditory brainstem response measures suggests that this form of hidden loss is common in humans and may have perceptual consequences, in particular, regarding the coding of the temporal aspects of sounds. Hidden hearing loss is potentially a major health issue, and investigations are ongoing to identify the causes and consequences of this troubling condition

Effect of human auditory efferent feedback on cochlear gain and compression

The manunalian auditory system includes a brainstem-mediated efferent pathway from the superior olivary complex by way of the medial olivocochlear system, which reduces the cochlear response to sound (Warr and Guinan, 1979; Liberman et al., 1996). The human medial olivocochlear response has an onset delay of between 25 and 40 ms and rise and decay constants in the region of 280 and 160 ms, respectively (Backus and Guinan, 2006). Physiological studies with nonhuman mammals indicate that onset and decay characteristics of efferent activation are dependent on the temporal and level characteristics of the auditory stimulus (Bacon and Smith, 1991; Guinan and Stankovic, 1996). This study uses a novel psychoacoustical masking technique using a precursor sound to obtain a measure of the efferent effect in humans. This technique avoids confounds currently associated with other psychoacoustical measures. Both temporal and level dependency of the efferent effect was measured, providing a comprehensive measure of the effect of human auditory efferents on cochlear gain and compression. Results indicate that a precursor (>20 dB SPL) induced efferent activation, resulting in a decrease in both maximum gain and maximum compression, with linearization of the compressive function for input sound levels between 50 and 70 dB SPL. Estimated gain decreased as precursor level increased, and increased as the silent interval between the precursor and combined masker-signal stimulus increased, consistent with a decay of the efferent effect Human auditory efferent activation linearizes the cochlear response for mid-level sounds while reducing maximum gain

The role of the clinically obtained acoustic reflex as a research tool for sub-clinical hearing pathologies

The acoustic reflex (AR) shows promise as an objective test for the presence of cochlear synaptopathy in rodents. The AR has also been shown to be reduced in humans with tinnitus compared to those without. The aim of the present study was twofold: (a) to determine if AR strength (quantified as both threshold and growth) varied with lifetime noise exposure, and thus provided an estimate of the degree of synaptopathy and (b) to identify which factors should be considered when using the AR as a quantitative measure rather than just present/absent responses. AR thresholds and growth functions were measured using ipsilateral and contralateral, broadband and tonal elicitors in adults with normal hearing and varying levels of lifetime noise exposure. Only the clinical standard 226 Hz probe tone was used. AR threshold and growth were not related to lifetime noise exposure, suggesting that routine clinical AR measures are not a sensitive measure when investigating the effects of noise exposure in audiometrically normal listeners. Our secondary, exploratory analyses revealed that AR threshold and growth were significantly related to middle-ear compliance. Listeners with higher middle-ear compliance (though still in the clinically normal range) showed lower AR thresholds and steeper AR growth functions. Furthermore, there was a difference in middle-ear compliance between the sexes, with males showing higher middle-ear compliance values than females. Therefore, it may be necessary to factor middle-ear compliance values into any analysis that uses the AR as an estimate of auditory function

Relations between speech-reception, psychophysical temporal processing, and subcortical electrophysiological measures of auditory function in humans

There is a large amount of variability in performance in masked-speech reception tasks, as well as in psychophysical auditory temporal processing tasks, between listeners with normal or relatively normal low-frequency hearing. In this study we used a cross-sectional dataset collected on 102 listeners (34 young, 34 middle-aged, 34 older) to assess whether variance in these tasks could be explained by variance in subcortical electrophysiological measures of auditory function (auditory brainstem responses and frequency following responses), and whether variance in speech-reception performance could be explained by variance in auditory temporal processing tasks. The potential confounding effect of high-frequency sensitivity was strictly controlled for by using highpass masking noise. Because each high-level construct (masked-speech reception, auditory temporal processing, and subcortical electrophysiological function) was indexed by several variables, we used principal component analyses to reduce the dimensionality of the dataset. Multiple-regression models were then used to assess the associations between the extracted principal components while controlling for a range of possible confounders including age and audiometric thresholds. We found that masked-speech reception was credibly associated with psychophysical auditory temporal processing abilities. No credible associations were found between masked-speech reception and electrophysiological measures of subcortical auditory function, or between psychophysical measures of auditory temporal processing and electrophysiological measures of subcortical auditory function. These results suggest that either the electrophysiological measures of subcortical auditory function used were not sufficiently sensitive to the subcortical neural processes limiting performance in the speech-reception and psychophysical auditory temporal-processing tasks, or that variance in these tasks is largely unrelated to variance in subcortical neural processes in listeners with near-normal hearing

Effects of age on psychophysical measures of auditory temporal processing and speech reception at low and high levels

Age-related cochlear synaptopathy (CS) has been shown to occur in rodents with minimal noise exposure, and has been hypothesized to play a crucial role in age-related hearing declines in humans. It is not known to what extent age-related CS occurs in humans, and how it affects the coding of supra-threshold sounds and speech in noise. Because in rodents CS affects mainly low- and medium-spontaneous rate (L/M-SR) auditory-nerve fibers with rate-level functions covering medium-high levels, it should lead to greater deficits in the processing of sounds at high than at low stimulus levels. In this cross-sectional study the performance of 102 listeners across the age range (34 young, 34 middle-aged, 34 older) was assessed in a set of psychophysical temporal processing and speech reception in noise tests at both low, and high stimulus levels. Mixed-effect multiple regression models were used to estimate the effects of age while partialing out effects of audiometric thresholds, lifetime noise exposure, cognitive abilities (assessed with additional tests), and musical experience. Age was independently associated with performance deficits on several tests. However, only for one out of 13 tests were age effects credibly larger at the high compared to the low stimulus level. Overall these results do not provide much evidence that age-related CS, to the extent to which it may occur in humans according to the rodent model of greater L/M-SR synaptic loss, has substantial effects on psychophysical measures of auditory temporal processing or on speech reception in noise

Effects of Age on Electrophysiological Measures of Cochlear Synaptopathy in Humans

Age-related cochlear synaptopathy (CS) has been shown to occur in rodents with minimal noise exposure, and has been hypothesized to play a crucial role in age-related hearing declines in humans. Because CS affects mainly low-spontaneous rate auditory nerve fibers, differential electrophysiological measures such as the ratio of the amplitude of wave I of the auditory brainstem response (ABR) at high to low click levels (WIH/WIL), and the difference between frequency following response (FFR) levels to shallow and deep amplitude modulated tones (FFRS-FFRD), have been proposed as CS markers. However, age-related audiometric threshold shifts, particularly prominent at high frequencies, may confound the interpretation of these measures in cross-sectional studies of age-related CS. To address this issue, we measured WIH/WIL and FFRS-FFRD using highpass masking (HP) noise to eliminate the contribution of high-frequency cochlear regions to the responses in a cross-sectional sample of 102 subjects (34 young, 34 middle-aged, 34 older). WIH/WIL in the presence of the HP noise did not decrease as a function of age. However, in the absence of HP noise, WIH/WIL showed credible age-related decreases even after partialing out the effects of audiometric threshold shifts. No credible age-related decreases of FFRS-FFRD were found. Overall, the results do not provide evidence of age-related CS in the low-frequency region where the responses were restricted by the HP noise, but are consistent with the presence of age-related CS in higher frequency regions

Specificity of the human frequency following response for carrier and modulation frequency assessed using adaptation

The frequency following response (FFR) is a scalp-recorded measure of phase-locked brainstem activity to stimulus-related periodicities. Three experiments investigated the specificity of the FFR for carrier and modulation frequency using adaptation. FFR waveforms evoked by alternating-polarity stimuli were averaged for each polarity and added, to enhance envelope, or subtracted, to enhance temporal fine structure information. The first experiment investigated peristimulus adaptation of the FFR for pure and complex tones as a function of stimulus frequency and fundamental frequency (F0). It showed more adaptation of the FFR in response to sounds with higher frequencies or F0s than to sounds with lower frequency or F0s. The second experiment investigated tuning to modulation rate in the FFR. The FFR to a complex tone with a modulation rate of 213 Hz was not reduced more by an adaptor that had the same modulation rate than by an adaptor with a different modulation rate (90 or 504 Hz), thus providing no evidence that the FFR originates mainly from neurons that respond selectively to the modulation rate of the stimulus. The third experiment investigated tuning to audio frequency in the FFR using pure tones. An adaptor that had the same frequency as the target (213 or 504 Hz) did not generally reduce the FFR to the target more than an adaptor that differed in frequency (by 1.24 octaves). Thus, there was no evidence that the FFR originated mainly from neurons tuned to the frequency of the target. Instead, the results are consistent with the suggestion that the FFR for low-frequency pure tones at medium to high levels mainly originates from neurons tuned to higher frequencies. Implications for the use and interpretation of the FFR are discussed

Which interventions increase hearing protection behaviors during noisy recreational activities?:A systematic review

Background Hearing loss and tinnitus are global concerns that can be reduced through hearing protection behaviors (e.g., earplug use). Little is known about the effectiveness of interventions to increase hearing protection use in recreational domains. For the first time we review systematically the effectiveness of such interventions. Methods Systematic searches of nine databases, as well as grey literature and hand-searching, were conducted. Any study design was included if it assessed quantitatively a purposeful attempt to increase hearing protection in recreational settings. Studies were excluded if they assessed noise exposure from occupational sources and headphones/earphones, as these have been reviewed elsewhere. PROSPERO protocol: CRD42018098573. Results Eight studies were retrieved following the screening of 1908 articles. Two pretest-posttest studies detected a small to medium effect (d ≥ 0·3 ≤ 0·5), one a small effect (d ~ =0·2) and two no real effect. Three posttest experimental studies detected small to medium effects (d ≥ 0·3 ≤ 0·5). Studies were rated as “poor quality” and 17 out of a possible 93 behavior change techniques were coded, with the majority targeting the intervention function ‘education’. Conclusions Hearing loss and tinnitus due to recreational noise exposure are major public health concerns yet very few studies have examined preventive interventions. The present systematic review sets the agenda for the future development and testing of evidence-based interventions designed to prevent future hearing loss and tinnitus caused by noise in recreational settings, by recommending systematic approaches to intervention design, and implementation of intervention functions beyond education, such as incentivization, enablement and modeling

Identifying targets for interventions to increase uptake and use of hearing protection in noisy recreational settings

Interventions to increase hearing protection behaviours within noisy recreational settings are limited by the lack of an underpinning evidence base. The aim of the present study was to identify targets for interventions in a population exposed to recreational noise, including those who had used hearing protection (ever-performers) versus those who had not (never-performers). A cross-sectional survey was administered to 185 UK adults who had been involved in noisy recreational activities. Participants had an average age of 36.79 years; the majority were women (68.1%), from a white ethnic background (87.6%), and with non-manual occupations (75.7%). Using Chi-square, MANOVA and ANOVA, we looked for differences in sociodemographic variables and variables from the capabilities, opportunities and motivations model of behaviour change (COM-B) between ever- and never-performers. Ever-performers were more likely to be younger (p p p p p < 0.001) compared to ever-performers. For the first time, the present study identifies potential groups at whom hearing protection interventions might be targeted and what those interventions may contain. Further work is required to develop interventions targeted at older people, women and those in non-manual occupations. Lack of motivation is a key concern, and further work that uses specific theoretical frameworks, such as the PRIME (Plans, Responses, Impulses, Motives, and Evaluations) theory of motivation, may shed light on the kinds of interventions that are needed to boost hearing protection use effectively