Macrophages Promote Repair of Inner Hair Cell Ribbon Synapses following Noise-Induced Cochlear Synaptopathy.

Resident cochlear macrophages rapidly migrate into the inner hair cell synaptic region and directly contact the damaged synaptic connections after noise-induced synaptopathy. Eventually, such damaged synapses are spontaneously repaired, but the precise role of macrophages in synaptic degeneration and repair remains unknown. To address this, cochlear macrophages were eliminated using colony stimulating factor 1 receptor (CSF1R) inhibitor, PLX5622. Sustained treatment with PLX5622 in CX3CR1 GFP/+ mice of both sexes led to robust elimination of resident macrophages (∼94%) without significant adverse effects on peripheral leukocytes, cochlear function, and structure. At 1 day (d) post noise exposure of 93 or 90 dB SPL for 2 hours, the degree of hearing loss and synapse loss were comparable in the presence and absence of macrophages. At 30 d after exposure, damaged synapses appeared repaired in the presence of macrophages. However, in the absence of macrophages, such synaptic repair was significantly reduced. Remarkably, on cessation of PLX5622 treatment, macrophages repopulated the cochlea, leading to enhanced synaptic repair. Elevated auditory brainstem response thresholds and reduced auditory brainstem response Peak 1 amplitudes showed limited recovery in the absence of macrophages but recovered similarly with resident and repopulated macrophages. Cochlear neuron loss was augmented in the absence of macrophages but showed preservation with resident and repopulated macrophages after noise exposure. While the central auditory effects of PLX5622 treatment and microglia depletion remain to be investigated, these data demonstrate that macrophages do not affect synaptic degeneration but are necessary and sufficient to restore cochlear synapses and function after noise-induced synaptopathy.SIGNIFICANCE STATEMENT The synaptic connections between cochlear inner hair cells and spiral ganglion neurons can be lost because of noise over exposure or biological aging. This loss may represent the most common causes of sensorineural hearing loss also known as hidden hearing loss. Synaptic loss results in degradation of auditory information, leading to difficulty in listening in noisy environments and other auditory perceptual disorders. We demonstrate that resident macrophages of the cochlea are necessary and sufficient to restore synapses and function following synaptopathic noise exposure. Our work reveals a novel role for innate-immune cells, such as macrophages in synaptic repair, that could be harnessed to regenerate lost ribbon synapses in noise- or age-linked cochlear synaptopathy, hidden hearing loss, and associated perceptual anomalies.

Hypoactivation of the central auditory system in listeners who are hypertolerant of background noise.

Listeners exhibit varying levels of tolerance for background noise during speech communication. It has been proposed that low tolerance of background noise may be the consequence of abnormally amplified gain in the central auditory system (CAS). Here, using a dataset of young adults with normal hearing thresholds, we asked whether central gain mechanisms might also explain cases of hypertolerance of background noise, as well as cases of reduced, but not abnormal, tolerance. We used the auditory brainstem response to derive a measure of CAS gain (wave V/wave I ratio) to compare listeners' background noise tolerance while listening to speech, grouping them into three categories: hyper, high, and medium tolerance. We found that hypertolerant listeners had reduced CAS gain compared to those with high tolerance. This effect was driven by wave V not wave I. In addition, the medium tolerant listeners trended toward having reduced wave I and reduced wave V amplitudes and generally higher levels of exposure to loud sound, suggestive of the early stages of noise-compromised peripheral function without an apparent compensatory increase in central gain. Our results provide physiological evidence that 1) reduced CAS gain may account for hypertolerance of background noise but that 2) increased CAS gain is not a prerequisite for medium tolerance of background noise.NEW & NOTEWORTHY Our findings strengthen the proposed mechanistic connection between background noise tolerance and auditory physiology by suggesting a link between hypertolerance and reduced central auditory gain, measured by the auditory brainstem response.

Gap detection ability declines with central auditory neurodegeneration following age-related cochlear synaptopathy.

Age-related hearing impairment (ARHI) is commonly associated with decreased auditory temporal resolution caused by auditory neurodegeneration. Age-related deterioration in gap detection ability, resulting in poor temporal auditory processing, is often attributed to pathophysiological changes in both the peripheral and central auditory systems. This study aimed to investigate whether the gap detection ability declines in the early stages of ageing and to determine its usefulness in detecting peripheral and central auditory degeneration. The study used 1-month-old (1 M), 6-month-old (6 M) and 12-month-old (12 M) mice to examine changes in gap detection ability and associated auditory pathophysiology. Although hearing thresholds did not significantly differ between the groups, the amplitude of auditory brainstem response (ABR) wave I decreased significantly in an age-dependent manner, consistent with age-related cochlear synaptopathy. The relative ABR amplitude ratio of waves 2 and 5 to wave 1 was significantly increased in 12 M mice, indicating that the central auditory system had increased in relative neuroactivity. A significant increase in gap detection thresholds was observed in 12 M mice compared to 1 M mice. Although cochlear synaptopathy and central hyperactivity were positively correlated with gap detection thresholds, central hyperactivity strongly influenced gap detection ability. In the cochlear nucleus and auditory cortex, the inhibitory synaptic expression of GAD65 and the expression of parvalbumin were significantly decreased in 12 M mice, consistent with central hyperactivity. Evaluating gap detection performance may allow the identification of decreased auditory temporal resolution in the early stages of ARHI, which is strongly associated with auditory neurodegeneration.

Cause, severity, and efficacy of treatment for hearing loss in children with Trisomy 18: A single institution-based retrospective study.

Trisomy 18 is a common chromosomal aberration syndrome, characterized by variable clinical manifestations, including cardiovascular, pulmonary, genitourinary, and musculoskeletal findings, leading to a shorter survival and severe developmental delay in survivors. However, recently, intensive therapeutic intervention has allowed for prolonging survival. In terms of otological complications, only a limited number of relevant reports have been published. To demonstrate the characteristic of hearing loss (HL) in children with Trisomy 18, we retrospectively evaluated 22 patients (44 ears) by comprehensive auditory evaluation with the auditory steady-state response (ASSR) test and temporal bone computed tomography (CT). ASSR revealed that 20 patients (91%) had bilateral moderate to profound HL, more frequent and severe than that in Trisomy 21; among 42 ears having HL, 12 ears (29%) had conductive HL, and 26 ears (62%) had mixed HL. CT scans of 38 ears revealed that 34 ears (89%) had an external and middle ear malformation. Hearing aids (HA) were fitted in 17 patients (air and bone-conduction HAs). The threshold hearing with HA was improved in all of them. Accurate otological evaluation using ASSR and CT and intervention by HAs could be a feasible choice for children with Trisomy 18.

Hearing in helmeted guineafowl (Numida meleagris): audiogram from 2 Hz to 10 kHz and localization acuity for brief noise bursts.

Behavioral hearing thresholds and noise localization acuity were determined using a conditioned avoidance/suppression procedure for three Helmeted guineafowl (Numida meleagris). The guineafowl responded to frequencies as low as 2 Hz at 82.5 dB SPL, and as high as 8 kHz at 84.5 dB SPL. At a level of 60 dB SPL, their hearing range spanned 8.12 octaves (24.6 Hz-6.86 kHz). Like most birds, they do not hear sounds above 8 kHz. However, the guineafowl demonstrated good low-frequency hearing (frequencies below 32 Hz), showing thresholds that are more sensitive than both the peafowl and pigeon, both of which hear infrasound. It thus appears that infrasound perception may be more common than previously thought and may have implications for species that inhabit areas with wind energy facilities. The guineafowls' minimum audible angle for a 100-ms broadband noise burst was 13.8 °, at the median for birds and near the mean for mammals. Unlike in mammals, the small sample of bird species and limited representation of lifestyles do not yet allow for meaningful interpretations of the selective pressures or mechanisms that underlie their abilities to locate sound sources.

Size matters: individual variation in auditory sensitivity may influence sexual selection in Pacific treefrogs (Pseudacris regilla).

The matched filter hypothesis proposes a close match between senders and receivers and is supported by several studies on variation in signal properties and sensory-processing mechanisms among species and populations. Importantly, within populations, individual variation in sensory processing may affect how receivers perceive signals. Our main goals were to characterize hearing sensitivity of Pacific treefrogs (Pseudacris regilla), assess patterns of individual variation in hearing sensitivity, and evaluate how among-individual variation in hearing sensitivity and call frequency content affect auditory processing of communication signals. Overall, males and females are most sensitive to frequencies between 2.0 and 2.5 kHz, which matches the dominant frequency of the call, and have a second region of high sensitivity between 400 and 800 Hz that does not match the fundamental frequency of the call. We found high levels of among-individual variation in hearing sensitivity, primarily driven by subject size. Importantly, patterns of among-individual variation in hearing differ between males and females. Cross-correlation analyses reveal that among-individual variation in hearing sensitivity may lead to differences on how receivers, particularly females, perceive male calls. Our results suggest that individual variation in sensory processing may affect signal perception and influence the evolution of sexually selected traits.

Repeated boat noise exposure damages inner ear sensory hair cells and decreases hearing sensitivity in Atlantic croaker (Micropogonias undulatus).

Anthropogenic noise is becoming a major underwater pollutant because of rapidly increasing boat traffic worldwide. But its impact on aquatic organisms remains largely unknown. Previous studies have focused mainly on high-frequency and impulsive noises (i.e. sonar); however, boat noise is more pervasive, continuous, and its highest intensity and component frequencies overlap the auditory bandwidth of most fishes. We assessed the impacts of boat noise on saccular sensory hair cell density and hearing thresholds of a soniferous species, Atlantic croaker (Micropogonias undulatus). In two laboratory experiments, individuals were subjected to simulated boat noise: a single 15-min exposure and 3 days of intermittent noise (simulating passing vessels). Immediately after both experiments, fish were either (1) tested for hearing sensitivity with auditory evoked potential (AEP) tests or (2) euthanized for fluorescent phalloidin and TUNEL labeling for hair cell density counts. Relative to controls, no differences were observed in auditory thresholds nor hair cell density between individuals subjected to a single 15-min noise exposure. However, fish from the 3-day experiment showed decreased sensory hair cell density, increased apoptotic cells, and higher hearing thresholds than control fish at 300, 800 and 1000 Hz. Our results demonstrate that impacts from boat noise depend upon the duration and frequency of exposure. For a species reliant on vocalization for communication, these impacts may hinder spawning success, increase predation risks and significantly alter the ecosystem.

Therapeutic effect of intraperitoneal dexamethasone on noise-induced permanent threshold shift in mice model.

The purpose of the study was to which investigate whether dexamethasone, which has anti-inflammatory and immune response suppression roles, could treat noise-induced hearing loss caused by damage to hair cells in the cochlea. The experiment used 8-week-old CBA mice exposed to white noise at an intensity of 110 dB SPL for 2 h, with hearing loss confirmed by the auditory brainstem response test. Dexamethasone was administered by intraperitoneal injection for 5 days, and the therapeutic effect was investigated for 3 weeks. The experimental groups were 3 mg/kg of dexamethasone (3 mpk) and 10 mg/kg of dexamethasone (10 mpk), and the control group was a saline-administered group. The results showed that compared to the control group, the hearing threshold value was recovered by 10 dB SPL compared to the saline group from the 14th day in the 3 mpk group. In the 10 mpk group, thresholds were recovered from the 7th day compared to the saline group. This difference was similar at 4 kHz, and in the case of the 10 mpk group, the threshold was recovered by 20 dB SPL compared to the saline group. The study also confirmed the restoration of nerve cell activity and showed a recovery effect of about 20 µV in the amplitude value change in the 10 mpk group. In conclusion, the study suggests that dexamethasone has a therapeutic effect for noise-induced hearing loss by increasing the activity of nerve cells and showing a recovery effect from hair cells damaged by noise.

Patient and Device Factors Contributing to Electrically Evoked Stapedial Reflex Thresholds in Cochlear Implanted Adults.

INTRODUCTION: Optimal cochlear implant (CI) outcomes are due to, at least in part, appropriate device programming. Objective measures, such as electrically evoked stapedial reflex thresholds (ESRTs), can be used to more accurately set programming levels. However, underlying factors that contribute to ESRT levels are not well understood. The objective of the current study was to analyze how demographic variables of patient sex and age, along with CI electrode location, influence ESRTs in adult CI recipients. METHODS: A single institution retrospective review was performed. Electronic medical records, CI programming records, and clinic database of postoperative computerized tomography were reviewed to gather information regarding patient demographics, ESRTs, and electrode array metrics including medial-lateral distance and scalar location. Linear mixed models were constructed to determine how demographic variables and electrode position influence ESRTs recorded in 138 adult CI recipients. RESULTS: ESRTs were significantly affected by recipient age, with older listeners demonstrating higher ESRT levels. On average, males had higher ESRT levels when compared to females. In a subset of the study sample, ESRT levels increased with increasing medial-lateral distance; however, there was not a statistically significant effect of electrode type (lateral/straight arrays compared to perimodiolar arrays). ESRTs were not affected by scalar location. DISCUSSION/CONCLUSIONS: The results suggest that key demographic and electrode position characteristics influence the level of ESRTs in adult CI recipients. While ESRTs are widely used to assist with CI programming, underlying factors are not well understood. The significant factors of aging and sex could be due to middle ear mechanics or neural health differences. However, further data are needed to better understand these associations.

Predicting Matrix Test Effectiveness for Evaluating Auditory Performance in Noise Using Pure-Tone Audiometry and Speech Recognition in Quiet in Cochlear Implant Recipients.

INTRODUCTION: Auditory performance in noise of cochlear implant recipients can be assessed with the adaptive Matrix test (MT); however, when the speech-to-noise ratio (SNR) exceeds 15 dB, the background noise has any negative impact on the speech recognition. Here, we aim to evaluate the predictive power of aided pure-tone audiometry and speech recognition in quiet and establish cut-off values for both tests that indicate whether auditory performance in noise can be assessed using the Matrix sentence test in a diffuse noise environment. METHODS: Here, we assessed the power of pure-tone audiometry and speech recognition in quiet to predict the response to the MT. Ninety-eight cochlear implant recipients were assessed using different sound processors from Advanced Bionics (n = 56) and CochlearTM (n = 42). Auditory tests were performed at least 1 year after cochlear implantation or upgrading the sound processor to ensure the best benefit of the implant. Auditory assessment of the implanted ear in free-field conditions included: pure-tone average (PTA), speech discrimination score (SDS) in quiet at 65 dB, and speech recognition threshold (SRT) in noise that is the SNR at which the patient can correctly recognize 50% of the words using the MT in a diffuse sound field. RESULTS: The SRT in noise was determined in 60 patients (61%) and undetermined in 38 (39%) using the MT. When cut-off values for PTA <36 dB and SDS >41% were used separately, they were able to predict a positive response to the MT in 83% of recipients; using both cut-off values together, the predictive value reached 92%. DISCUSSION: As the pure-tone audiometry is standardized universally and the speech recognition in quiet could vary depending on the language used; we propose that the MT should be performed in recipients with PTA <36 dB, and in recipients with PTA >36 dB, a list of Matrix sentences at a fixed SNR should be presented to determine the percentage of words understood. This approach should enable clinicians to obtain information about auditory performance in noise whenever possible.

Supra-Threshold LS CE-Chirp Auditory Brainstem Response in the Elderly.

INTRODUCTION: Aging deteriorates peripheral and central auditory structures and functions. In elders, for an accurate audiological evaluation, it is important to explore beyond the cochlear receptor. Audiograms provide an estimation of hearing thresholds, while the amplitudes and latencies of supra-threshold auditory brainstem response (ABR) can offer noninvasive measures of the auditory pathways functioning. Regarding ABR, in young populations, level-specific chirp (LS CE-chirp) stimulus has been proposed as an alternative synchronizing method to obtain larger ABR responses than those evoked by clicks. However, the supra-threshold characteristics of chirp evoked ABR, and their association to hearing thresholds is relatively unknown in the elderly. The aim of this study was to evaluate supra-threshold LS CE-chirp ABRs in an aged population by comparing their features with click ABRs, and evaluating their relationship with audiometric hearing thresholds. METHODS: We carried out a cross-sectional study to characterize the hearing of 125 adults aged over 65 years. We determined the audiometric hearing thresholds and supra-threshold ABRs elicited by LS CE-chirp and click stimuli at 80 dB nHL. We evaluated associations by means of partial correlations and covariate adjustment. We performed specific frequencies' analysis and subgroup analysis per hearing level. RESULTS: Wave V responses had significantly shorter latencies and larger amplitudes when elicited by LS CE-chirp as compared to click-evoked responses. Audiometric hearing thresholds correlated with age, but ABR characteristics did not. We found mild correlations between hearing thresholds and ABR characteristics, predominantly at higher frequencies and with chirp. We found scarce evidence of correlation between ABR characteristics and the average of behavioral hearing thresholds between 0.5 to 4 kHz (0.5-4 kHz PTA). After subgroup analysis according to the hearing level, no stronger or more significant correlations were found between ABR characteristics and 0.5-4 kHz PTA. DISCUSSION: In this study, we found that supra-threshold LS CE-chirp ABR presented some of the previously described similitudes and differences with supra-threshold click ABR in younger populations. Although, the average amplitude and latency of wave V evoked by LS CE-chirp were larger and faster than those evoked by clicks, these results should be taken with caution at the individual level, and further studies are required to state that LS CE-chirp ABRs are better than click ABRs in elders for clinical evaluations. We did not find consistent associations between hearing thresholds and supra-threshold wave V features, suggesting that these measures should be considered independently in the elderly.

Effect of Stimulus Bandwidth on the Auditory Steady-State Response in Scalp- and Ear-EEG.

OBJECTIVES: The auditory steady-state response (ASSR) enables hearing threshold estimation based on electroencephalography (EEG) recordings. The choice of stimulus type has an impact on both the detectability and the frequency specificity of the ASSR. Amplitude modulated pure tones provide the most frequency-specific ASSR, but responses to pure tones are weak. The ASSR can be enhanced by increasing the bandwidth of the stimulus, but this comes at the cost of a decrease in the frequency specificity of the measured response. The objective of the present study is to investigate the relationship between stimulus bandwidth and ASSR amplitude. DESIGN: The amplitude of ASSR was measured for five types of stimuli: 1 kHz pure tone and band-pass noise with 1/3, 1/2, 1, and 2 octave bandwidths centered at 1 kHz. All stimuli were amplitude modulated with a 40 Hz sinusoid. Responses to all stimulus types were measured at 30, 40, and 50 dB SL. ASSRs were measured concurrently using both conventional scalp-EEG and ear-EEG. RESULTS: Stimulus bandwidth and sound intensity were both found to have a significant effect on the ASSR amplitude for scalp- and ear-EEG recordings. In scalp-EEG ASSRs to all bandwidth stimuli were found to be significantly larger than ASSRs to pure tone at low sound intensity. At higher sound intensities, however, significantly larger responses were only obtained for 1- and 2-octave bandwidth stimuli. In ear-EEG, only the ASSR to 2 octave bandwidth stimulus was significantly larger than the ASSR to amplitude modulated pure tones. CONCLUSIONS: At low presentation levels, even small increases in stimulus bandwidth (1/3 and 1/2 octave) improve the detectability of ASSR in scalp-EEG with little or no impact on the frequency specificity. In comparison, a larger increase in stimulus bandwidth was needed to improve the ASSR detectability in the ear-EEG recordings.

Preserved Auditory Steady State Response and Envelope-Following Response in Severe Brainstem Dysfunction Highlight the Need for Cross-Checking.

OBJECTIVES: Commercially available auditory steady state response (ASSR) systems are widely used to obtain hearing thresholds in the pediatric population objectively. Children are often examined during natural or induced sleep so that the recorded ASSRs are of subcortical origin, the inferior colliculus being often designated as the main ASSR contributor in these conditions. This report presents data from a battery of auditory neurophysiological objective tests obtained in 3 cases of severe brainstem dysfunction in sleeping children. In addition to ASSRs, envelope-following response (EFR) recordings designed to distinguish peripheral (cochlear nerve) from central (brainstem) were recorded to document the effect of brainstem dysfunction on the two types of phase-locked responses. DESIGN: Results obtained in the 3 children with severe brainstem dysfunctions were compared with those of age-matched controls. The cases were identified as posterior fossa tumor, undiagnosed (UD), and Pelizaeus-Merzbacher-Like Disease. The standard audiological objective tests comprised tympanograms, distortion product otoacoustic emissions, click-evoked auditory brainstem responses (ABRs), and ASSRs. EFRs were recorded using horizontal (EFR-H) and vertical (EFR-V) channels and a stimulus phase rotation technique allowing isolation of the EFR waveforms in the time domain to obtain direct latency measurements. RESULTS: The brainstem dysfunctions of the 3 children were revealed as abnormal (weak, absent, or delayed) ABRs central waves with a normal wave I. In addition, they all presented a summating and cochlear microphonic potential in their ABRs, coupled with a normal wave I, which implies normal cochlear and cochlear nerve function. EFR-H and EFR-V waveforms were identified in the two cases in whom they were recorded. The EFR-Hs onset latencies, response durations, and phase-locking values did not differ from their respective age-matched control values, indicating normal cochlear nerve EFRs. In contrast, the EFR-V phase-locking value and onset latency varied from their control values. Both patients had abnormal but identifiable and significantly phase-locked brainstem EFRs, even in a case with severely distorted ABR central waves. ASSR objective audiograms were recorded in two cases. They showed normal or slightly elevated (explained by a slight transmission loss) thresholds that do not yield any clue about their brainstem dysfunction, revealing the method's lack of sensitivity to severe brainstem dysfunction. CONCLUSIONS: The present study, performed on 3 sleeping children with severe brainstem dysfunction but normal cochlear responses (cochlear microphonic potential, summating potential, and ABR wave I), revealed the differential sensitivity of three auditory electrophysiological techniques. Estimated thresholds obtained by standard ASSR recordings (cases UD and Pelizaeus-Merzbacher-Like Disease) provided no clue to the brainstem dysfunction clearly revealed by the click-evoked ABR. EFR recordings (cases posterior fossa tumor and UD) showed preserved central responses with abnormal latencies and low phase-locking values, whereas the peripheral EFR attributed to the cochlear nerve was normal. The one case (UD) for which the three techniques could be performed confirms this sensitivity gradient, emphasizing the need for applying the Cross-Check Principle by avoiding resorting to ASSR recording alone. The entirely normal EFR-H recordings observed in two cases further strengthen the hypothesis of its cochlear nerve origin in sleeping children.

Preservation of Distortion Product Otoacoustic Emissions in OTOF -Related Hearing Impairment.

OBJECTIVES: Attenuation of otoacoustic emissions over time has been reported for many patients with hearing impairment harboring mutations in the OTOF gene. In this study, the time course of changes of distortion product otoacoustic emissions (DPOAEs) has been analyzed in a cohort of patients in the light of tympanometry results. DESIGN: The changes of DPOAEs in 16 patients with OTOF -related hearing impairment were retrospectively analyzed. RESULTS: All but one subject showed DPOAEs bilaterally at the time of diagnosis. Three patients diagnosed as adults still had DPOAEs at ages of 27, 31, and 47 years, respectively. Follow-up was available for 7 children diagnosed at the age of 1 to 3 years, who still showed preservation of DPOAEs at ages of 5 to 16 years. The responses were absent or attenuated in amplitude at some follow-up appointments in association with type B or C tympanograms. CONCLUSIONS: DPOAEs are preserved much longer than expected in a cohort of patients with OTOF -related hearing impairment. The previously reported loss of DPOAEs may have been caused in some children by increased middle ear impedance due to otitis media.

Deep Learning Models for Predicting Hearing Thresholds Based on Swept-Tone Stimulus-Frequency Otoacoustic Emissions.

OBJECTIVES: This study aims to develop deep learning (DL) models for the quantitative prediction of hearing thresholds based on stimulus-frequency otoacoustic emissions (SFOAEs) evoked by swept tones. DESIGN: A total of 174 ears with normal hearing and 388 ears with sensorineural hearing loss were studied. SFOAEs in the 0.3 to 4.3 kHz frequency range were recorded using linearly swept tones at a rate of 2 Hz/msec, with stimulus level changing from 40 to 60 dB SPL in 10 dB steps. Four DL models were used to predict hearing thresholds at octave frequencies from 0.5 to 4 kHz. The models-a conventional convolutional neural network (CNN), a hybrid CNN-k-nearest neighbor (KNN), a hybrid CNN-support vector machine (SVM), and a hybrid CNN-random forest (RF)-were individually built for each frequency. The input to the DL models was the measured raw SFOAE amplitude spectra and their corresponding signal to noise ratio spectra. All DL models shared a CNN-based feature self-extractor. They differed in that the conventional CNN utilized a fully connected layer to make the final regression decision, whereas the hybrid CNN-KNN, CNN-SVM, and CNN-RF models were designed by replacing the last fully connected layer of CNN model with a traditional machine learning (ML) regressor, that is, KNN, SVM, and RF, respectively. The model performance was evaluated using mean absolute error and SE averaged over 20 repetitions of 5 × 5 fold nested cross-validation. The performance of the proposed DL models was compared with two types of traditional ML models. RESULTS: The proposed SFOAE-based DL models resulted in an optimal mean absolute error of 5.98, 5.22, 5.51, and 6.06 dB at 0.5, 1, 2, and 4 kHz, respectively, superior to that obtained by the traditional ML models. The produced SEs were 8.55, 7.27, 7.58, and 7.95 dB at 0.5, 1, 2, and 4 kHz, respectively. All the DL models outperformed any of the traditional ML models. CONCLUSIONS: The proposed swept-tone SFOAE-based DL models were capable of quantitatively predicting hearing thresholds with satisfactory performance. With DL techniques, the underlying relationship between SFOAEs and hearing thresholds at disparate frequencies was explored and captured, potentially improving the diagnostic value of SFOAEs.

Assessment of Interaural Attenuation in Infants and Young Children Using Bone-Conducted Auditory Brainstem Response.

OBJECTIVES: In hearing assessment, the term interaural attenuation (IAA) is used to quantify the reduction in test signal intensity as it crosses from the side of the test ear to the nontest ear. In the auditory brainstem response (ABR) testing of infants and young children, the size of the IAA of bone-conducted (BC) stimuli is essential for the appropriate use of masking, which is needed for the accurate measurement of BC ABR thresholds. This study aimed to assess the IAA for BC ABR testing using 0.5 to 4 kHz narrowband (NB) CE-chirp LS stimuli in infants and toddlers with normal hearing from birth to three years of age and to examine the effects of age and frequency on IAA. DESIGN: A total of 55 infants and toddlers with normal hearing participated in the study. They were categorized into three age groups: the young group (n = 31, infants from birth to 3 mo), middle-aged group (n = 13, infants aged 3-12 mo), and older group (n = 11, toddlers aged 12-36 mo). The participants underwent BC ABR threshold measurements for NB CE-chirp LS stimuli at 0.5 to 4 kHz. For each participant, one ear was randomly defined as the "test ear" and the other as the "nontest ear." BC ABR thresholds were measured under two conditions. In both conditions, traces were recorded from the channel ipsilateral to the test ear, whereas masking was delivered to the nontest ear. In condition A, the bone oscillator was placed on the mastoid of the test ear, whereas in condition B, the bone oscillator was placed on the mastoid contralateral to the test ear. The difference between the thresholds obtained under conditions A and B was calculated to assess IAA. RESULTS: The means of IAA (and range) in the young age group for the frequencies 0.5, 1, 2, and 4 kHz were 5.38 (0-15) dB, 11.67 (0-30) dB, 21.15 (10-40) dB, and 23.53 (15-35) dB, respectively. Significant effects were observed for both age and frequency on BC IAA. BC IAA levels decreased with age from birth to 36 mo. In all age groups, smaller values were observed at lower frequencies and increased values were observed at higher frequencies. CONCLUSIONS: BC IAA levels were both age and frequency dependent. The study found that the BC IAA values for lower stimulus frequencies were smaller than previously assumed, even in infants younger than 3 mo. These results suggest that masking should be applied in BC ABR threshold assessments for NB CE-chirp LS stimuli at 0.5, 1, and 2 kHz, even in young infants. Masking may not be necessary for testing at 4 kHz if a clear response is obtained at 15 dB normal-hearing level (nHL) in infants younger than 3 mo.

Quick Estimation of Minimum Hearing Levels Using a Binaural Multifrequency Stimulus Paradigm: Proof of Concept.

OBJECTIVES: Objective estimation of minimum hearing levels using auditory brainstem responses (ABRs) elicited by single frequency tone-bursts presented monaurally is currently considered the gold standard. However, the data acquisition time to estimate thresholds (for both ears across four audiometric frequencies) using this method usually exceeds the sleep time (ranging between 35 and 49 minutes) in infants below 4 months, thus providing incomplete information of hearing status which in turn delays timely clinical intervention. Alternate approaches using faster rate, or tone-burst trains have not been readily accepted due to additional hardware and software requirements. We propose here a novel binaural multifrequency stimulation paradigm wherein several stimuli of different frequencies are presented binaurally in an interleaved manner. The rationale here is that the proposed paradigm will increase acquisition efficiency, significantly reduce test time, and improve accuracy by incorporating an automatic wave V detection algorithm. It is important to note that this paradigm can be easily implemented in most commercial ABR systems currently used by most clinicians. DESIGN: Using this binaural multifrequency paradigm, ear specific ABRs were recorded in 30 normal-hearing young adults to both tone-bursts, and narrow-band (NB) iChirps at 500, 1000, 2000, and 4000 Hz. Comparison of ABRs elicited by tone-bursts and narrow-band chirps allowed us to determine if NB iChirps elicited a more robust wave V component compared with the tone-bursts. ABR data were characterized by measures of minimum hearing levels; wave V amplitude; and response detectability for two electrode configurations (high forehead-C7; and high forehead-linked mastoids). RESULTS: Consistent with the research literature, wave V response amplitudes were relatively more robust for NB iChirp stimuli compared with tone-burst stimuli. The easier identification and better detectability of wave V for the NB iChirps at lower stimulus levels contributed to their better thresholds compared with tone-burst elicited responses. It is important to note that binaural multifrequency hearing levels close to minimum hearing levels were determined in approximately 22 minutes using this paradigm-appreciably quicker than the 45 to 60 minutes or longer time required for threshold determination using the conventional single frequency method. CONCLUSIONS: Our novel and simple paradigm using either NB iChirps or tone-bursts provides a reliable method to rapidly estimate the minimum hearing levels across audiometric frequencies for both ears. Incorporation of an automatic wave V detection algorithm increases objectivity and further reduce test time and facilitate early hearing identification and intervention.

Auditory Electrophysiological Thresholds With Different Chirps and Their Correlation With Behavioral Thresholds in Hearing-Impaired Children.

OBJECTIVES: Research focusing on changes in the clinical practice of audiological diagnosis has become increasingly necessary, particularly in pediatric audiology. The pursuit of accurate and reliable examinations has intensified given the importance of early detection and intervention in cases of childhood hearing loss. Thus, this study aims to investigate the correlation between electrophysiological auditory thresholds, as obtained through frequency-specific auditory brainstem responses with two distinct chirp stimuli (narrow-band CE-Chirp Level Specific and narrow-band iChirp), in children with hearing impairments. In addition, this research set out to correlate these thresholds with behavioral responses while simultaneously comparing the examination durations relative to the type of stimuli and the degree of hearing loss. DESIGN: A cohort of 20 children (aged 6 months to 12 years) with varying degrees of hearing impairment (ranging from mild to profound) were recruited. The participants underwent bilateral measurement of their electrophysiological thresholds via auditory brainstem responses across different frequencies (500, 1000, 2000, and 4000 Hz), and the timeframe for determining these thresholds was carefully recorded. Subsequently, behavioral thresholds were ascertained using pure-tone audiometry or visual reinforcement audiometry based on the child's age. The data collected was subsequently analyzed using Pearson and Spearman correlation coefficients. To compare examination times, the Student t test and the Kruskal-Wallis test were used. RESULTS: There was a pronounced correlation between the thresholds obtained through both narrow-band chirp stimuli. Moreover, a substantial correlation was found between electrophysiological and behavioral thresholds at 1000, 2000, and 4000 Hz, especially when compared with pure-tone audiometry. The mean differences between the electrophysiological and behavioral thresholds were below 6 dB nHL, and the exam duration was relatively consistent across both devices, averaging 47.63 (±19.41) min for the narrow-band CE-Chirp Level Specific and 52.42 (±26) min for the narrow-band iChirp. Notably, variations in exam duration did not relate to varying degrees of hearing loss when using the narrow-band CE-Chirp Level Specific. Nevertheless, the narrow-band iChirp indicated significantly shorter durations in instances of profound degree measurements, demonstrating a statistically significant difference. CONCLUSIONS: The narrow-band CE-Chirp Level Specific and narrow-band iChirp stimuli provided similar estimates of electrophysiological auditory thresholds in children with hearing impairments, giving accurate estimations of behavioral thresholds. The time it took to complete the assessment is comparable between both stimuli. For the narrow-band iChirp, the degree of hearing loss was shown to impact the testing time, and children with profound hearing loss underwent faster exams. Ultimately, this study exhibits significant clinical implications as it reveals that the narrow-band CE-Chirp Level Specific and narrow-band iChirp stimuli could be remarkably promising for clinically exploring electrophysiological thresholds in children with hearing impairments.

Occupational Lead Exposure Ototoxicity Evaluated With Distortion-Product Otoacoustic Emissions.

OBJECTIVES: To evaluate the extent of hearing loss among pottery workers in Mexico exposed to lead. DESIGN: The authors conducted a cross-sectional study including 315 adult pottery workers. Auditory function was evaluated by air conduction pure-tone audiometry (pure-tone average) and distortion-product otoacoustic emission (DPOAE) levels (amplitude and signal-to-noise ratio). Lead exposure was assessed with a single blood sample test and classified as low, medium, and high according to blood lead tertiles. Logistic regression models were calculated for the association between blood lead levels, pure-tone average, and DPOAE records. RESULTS: Median (25th-75th) blood lead levels were 14 µg/dL (7.5-22.6 µg/dL). The audiometric pattern and DPOAE records were similar across blood lead levels groups in all frequencies, and no statistically significant differences were found. Adjusted logistic regression models showed no increase in the odds for hearing thresholds >25 dB (HL) and DPOAE absence associated with blood lead levels, and no dose-response pattern was observed ( p > 0.05). CONCLUSIONS: Given the results from this cross-sectional study, no association was found between blood lead levels and hearing loss assessed with DPOAE. Future longitudinal work should consider chronic lead exposure estimates among underrepresented populations, which can potentially inform safer work practices to minimize the risk of ototoxicity.

EEG-based auditory attention decoding with audiovisual speech for hearing-impaired listeners.

Auditory attention decoding (AAD) was used to determine the attended speaker during an auditory selective attention task. However, the auditory factors modulating AAD remained unclear for hearing-impaired (HI) listeners. In this study, scalp electroencephalogram (EEG) was recorded with an auditory selective attention paradigm, in which HI listeners were instructed to attend one of the two simultaneous speech streams with or without congruent visual input (articulation movements), and at a high or low target-to-masker ratio (TMR). Meanwhile, behavioral hearing tests (i.e. audiogram, speech reception threshold, temporal modulation transfer function) were used to assess listeners' individual auditory abilities. The results showed that both visual input and increasing TMR could significantly enhance the cortical tracking of the attended speech and AAD accuracy. Further analysis revealed that the audiovisual (AV) gain in attended speech cortical tracking was significantly correlated with listeners' auditory amplitude modulation (AM) sensitivity, and the TMR gain in attended speech cortical tracking was significantly correlated with listeners' hearing thresholds. Temporal response function analysis revealed that subjects with higher AM sensitivity demonstrated more AV gain over the right occipitotemporal and bilateral frontocentral scalp electrodes.