Visual speech gestures modulate efferent auditory system.

Autism spectrum disorder (ASD) is a developmental disability that is poorly understood. ASD can influence communication, social interaction, and behavior. Children with ASD often have sensory hypersensitivities, including auditory hypersensitivity (hyperacusis). In adults with hyperacusis who are otherwise neurotypical, the medial olivocochlear (MOC) efferent reflex is stronger than usual. In children with ASD, the MOC reflex has been measured, but without also assessing hyperacusis. We assessed the MOC reflex in children with ASD by measuring the strength of MOC-induced inhibition of transient-evoked otoacoustic emissions (TEOAEs), a noninvasive physiological measure that reflects cochlear amplification. MOC activity was evoked by contralateral noise. Hyperacusis was assessed subjectively on the basis of the children's symptoms. We found a significant correlation between hyperacusis scores and MOC strength in children with ASD. When children were divided into ASD-with-severe-hyperacusis (ASDs), ASD-with-not-severe-hyperacusis (ASDns), and neurotypical (NT) groups, the last two groups had similar hyperacusis and MOC reflexes, whereas the ASDs group, on average, had hyperacusis and MOC reflexes that were approximately twice as strong. The MOC inhibition of TEOAEs averaged larger at all frequencies in the ASDs compared with ASDns and NT groups. The results suggest that the MOC reflex can be used to estimate hyperacusis in children with ASD and might be used to validate future questionnaires to assess hyperacusis. Our results also provide evidence that strong MOC reflexes in children with ASD are associated with hyperacusis and that hyperacusis is a comorbid condition and is not a necessary, integral part of the abnormal neural processing associated with ASD.NEW & NOTEWORTHY Children with autism spectrum disorder (ASD) are a heterogeneous group, some with hyperacusis and some without. Our research shows that hyperacusis can be estimated in children with ASD by using medial olivocochlear (MOC) reflex measurements. By establishing that an objective measure correlates with attributes of hyperacusis, our results enable future work to enable subtyping of children with ASD to provide improved individualized treatments to at-risk children and those without adequate language to describe their hyperacusis symptoms.

Introduction: Although noise-induced hearing loss is the most significant occupational hazard affecting the auditory system, studies on hearing conservation have shown that frequent exposure to chemicals in the workplace may also cause hearing disorders. Objective: The aim of this study was to evaluate the medial olivocochlear system in individuals exposed to pesticides. Method: This is a cross-sectional descriptive epidemiological study. After applying the inclusion criteria, we evaluated 205 students from an agricultural school located in the city of Nova Friburgo, state of Rio de Janeiro, Brazil, who were exposed to pesticides. Participants were evaluated based on a questionnaire to assess the degree of pesticide exposure, transient-evoked otoacoustic emissions (TEOAEs), and investigation of the suppressive effect of TEOAEs. Results: The assessment considering the suppression of TEOAEs demonstrated that 38% of participants had absence of suppression in the right ear, 45.9% had absence of suppression in the left ear, 38% had unilateral absence, and 39% had bilateral absence. Our findings suggest that there is an association between absence of suppression and quartiles of exposure. Conclusion: Chronic exposure to pesticides can affect the medial olivocochlear system, regardless of concomitant exposure to noise.

RESUMO Objetivo: investigar o efeito supressor das emissões otoacústicas por estímulos transientes em indivíduos com queixa zumbido e audiometria normal e analisar sua relação com as variáveis idade, sexo, lateralidade do zumbido e grau de incômodo. Métodos: foram avaliados 60 sujeitos, 14 do gênero masculino e 46 do gênero feminino, entre 20 e 59 anos de idade, sendo 30 com queixa de zumbido (grupo experimental) e 30 sem zumbido (grupo controle). Foi realizada a pesquisa da supressão das emissões otoacústicas por estímulos transientes, para ruído branco de 50 dBNA, na condição contralateral nas bandas de frequência de 700, 1000, 1400, 2000, 2800 and 4000Hz. Resultado: no grupo experimental, a supressão das emissões otoacústicas transientes média variou de 2,14 a 4,38. No grupo controle o valor médio da supressão das emissões otoacústicas transientes variou de 2,27 a 4,88. Conclusão: os valores de supressão das emissões otoacústicas foram semelhantes nos indivíduos com e sem zumbido, embora o grupo com o sintoma tenha tido resultados menores, sugerindo pior desempenho do Complexo Olivar Superior.

Cholinergic transmission is essential for survival and reproduction, as it is involved in several physiological responses. In the auditory system, both ascending and descending auditory pathways are modulated by cholinergic transmission, affecting the perception of sounds. The auditory efferent system is a neuronal network comprised of several feedback loops, including corticofugal and brainstem pathways to the cochlear receptor. The auditory efferent system’s -final and mandatory synapses that connect the brain with the cochlear receptor- involve medial olivocochlear neurons and outer hair cells. A unique cholinergic transmission mediates these synapses through α9/α10 nicotinic receptors. To study this receptor, it was generated a strain of mice carrying a null mutation of the Chrna9 gene (α9-KO mice), lacking cholinergic transmission between medial olivocochlear neurons and outer hair cells, providing a unique opportunity to study the role of medial olivocochlear cholinergic transmission in auditory and cognitive functions. In this article, we review behavioral and physiological studies carried out to research auditory efferent function in the context of audition, cognition, and hearing impairments. Auditory studies have shown that hearing thresholds in the α9-KO mice are normal, while more complex auditory functions, such as frequency selectivity and sound localization, are altered. The corticofugal pathways have been studied in α9-KO mice using behavioral tasks, evidencing a reduced capacity to suppress auditory distractors during visual selective attention. Finally, we discuss the evolutionary role of the auditory efferent system detecting vocalizations in noise and its role in auditory disorders, such as the prevention of age-related hearing loss.

Tone decay (TD), the ipsilateral comparison paradigm (ICP), and the monaural simple adaptation (SA) procedure assess loudness adaptation differently; this may all be peripheral but it has not been previously compared in one study. Transient evoked oto-acoustic emissions (TEOAE) have their source in the outer hair cells of the cochlear periphery. A significant correlation (r=−0.60) between contralateral suppression of transient evoked OAEs and tone decay adaptation (r=−0.60) has been reported [Collet et al., Audiology 31, 1–7 (1992)]. A significant correlation (r=−0.36) between ICP adaptation and contralateral suppression of TEOAEs has been found [Ernest M. Weiler, Hongwei Dou et al., J. Acoust. Soc. Am. 103, 3052 (1998)]. Comparison of TD, ICP, and SA with suppression of TEOAEs used repeated measures testing of 75 students (20–35 yrs) of mixed nationalities. Significant correlations were found, but not at all values, between TD, ICP, SA, and suppression of TEOAEs at 80, 60, and 70 dB. A principle components factor analysis found factor I based on suppression, and factor II based on monaural adaptation. It was concluded that the ICP, TD, and SA are primarily peripheral in origin. TD and ICP each include variation in stimulus intensity which may play a role in triggering perception of loudness adaptation.

Previous work demonstrates the importance of a high signal to noise ratio (SNR) when using transient evoked otoacoustic emissions (TEOAEs) to assay the medial olivocochlear reflex (MOCR). Increasing stimulus level provides one means to increase TEOAE SNR. However, this may come at the expense of a smaller MOCR effect. It is not clear whether the gain in SNR associated with the use of higher stimulus levels outweighs the disadvantage of a potentially smaller MOCR effect. The present study investigated the strength and detectability of the MOCR when assayed using TEOAEs at different stimulus levels. The hypothesis was that although the strength of the MOCR decreases with increasing stimulus level, the occurrence of statistically significant MOCR effects increases due to an increase in TEOAE SNR. Twenty-five young adult females with normal hearing participated in the study. TEOAEs were measured in the right ear with and without broadband noise presented in the left ear. The strength of the MOCR was quantified as the percent difference in the TEOAE between the contralateral noise and quiet conditions. Statistical bootstrapping was used to detect significant MOCR effects in individual subjects across different frequency bands and stimulus levels. The relationship between a detectable MOCR (response variable) and frequency, stimulus level, TEOAE SNR, MOCR strength, and subject (predictor variables) was evaluated using generalized linear mixed-effect models. The number of statistically significant MOCR effects increased with stimulus level at all frequencies. Occurrence was highest for the 2-kHz TEOAE frequency band and lowest for the 4-kHz frequency band. The strength of the MOCR decreased with increasing click level. TEOAE SNR, MOCR strength, and stimulus level were significant predictors of a detectable MOCR: The likelihood of a detectable MOCR increased with TEOAE SNR, MOCR strength, and stimulus level. Despite a reduction in the strength of the MOCR with increasing stimulus level, the detectability of the MOCR increased. This is due, in part, to an increase in TEOAE SNR with stimulus level. For clinical implementation of TEOAE-based MOCR assays, achieving a high SNR is necessary to permit the detection of the MOCR in individual patients.

Contralateral acoustic stimulation reduces the amplitude of the transient evoked otoacoustic emission (TEOAE) in humans. The mechanism is thought to be mediated, at least in part, through the medial olivocochlear efferent system innervating the outer hair cells. To assess its usefulness as a possible clinical test, TEOAE suppression was measured in each ear of 12 subjects over a 6-week period, and these data are shown in detail for four subjects representing extremes of variability in a tinnitus and a non-tinnitus group. Intra-subject test results (n = 18) exhibited a varying extent of suppression values and the variance of each session, consisting of three tests, was not statistically different from one session to another. There was no dependence on variables such as ear (right or left), session, day of testing or their interaction. There was a significant difference in the variability between the tinnitus and the normal group.

The contralateral medial olivocochlear reflex (MOCR) strength may indicate various auditory conditions in humans, but a clinically viable assay and equipment are needed for quick, accurate, and reliable measurements. The first experiment compared an earlier version of the assay, which used a nonlinear-mode chirp stimulus, with a new assay using a linear-mode click stimulus, designed to give reliable MOCR measurements in most normal-hearing ears. The second experiment extended the improved assay on a purpose-built binaural hardware platform that used forward-pressure level (FPL) calibration for both the stimulus and the contralateral MOCR elicitor. Transient-evoked otoacoustic emission (TEOAE) tests were measured with and without a 60-dB SPL MOCR-evoking contralateral broadband noise. The normalized MOCR strength (MOCR%) was derived from the TEOAE responses for each trial pair using the complex pressure difference weighted by the TEOAE magnitude. Experiment 1 compared MOCR% within-subject and across-day using two TEOAE stimuli: nonlinear-mode chirps (50 dB SPL, bandpass 1-5 kHz, 14 ms window delayed by 2 ms) and linear-mode clicks (50 dB SPL, bandpass 0.5-2.5 kHz, 13 ms window delayed by 5 ms). TEOAE responses were analyzed in the 0.5 to 2.5 kHz band. Thirty adult participants with normal hearing (30 ears) completed the study. The TEOAE stimulus was calibrated in situ using spectral flattening, and the contralateral noise was calibrated in a coupler. Twelve TEOAE trial pairs were collected for each participant and condition. Experiment 2 used a purpose-built binaural system. The TEOAE stimuli were linear-mode clicks (50 dB SPL, bandpass 1-3 kHz, 13 ms window delayed by 5 ms), analyzed in the 1 to 3 kHz band over ~12 trial pairs. After a probe refit, an additional trial pair was collected for the two early-stopping signal-to-noise ratio criteria (15 and 20 dB). They were evaluated for single-trial reliability and test time. Nineteen adult participants with normal hearing (38 ears) completed the study. The TEOAE clicks and contralateral elicitor noise were calibrated in situ using FPL and delivered with automated timing. MOCR% for linear-mode clicks was distinguishable from measurement variability in 98% to 100% of participants' ears (both experiments), compared with only 73% for the nonlinear-mode chirp (experiment 1). MOCR detectability was assessed using the MOCR% across-subject/within-subject variance ratio. The ratio in experiment 1 for linear-mode clicks was higher (8.0) than for nonlinear-mode chirps (6.4). The ratio for linear-mode clicks (8.9) in experiment 2 was slightly higher than for the comparable linear-mode stimulus (8.0) in experiment 1. TEOAEs showed excellent reliability with high signal-to-noise ratios in both experiments, but reliability was higher for linear-mode clicks than nonlinear-mode chirps. MOCR reliability for the two stimuli was comparable. The FPL pressure response retest reliability derived from the SPL at the microphone was higher than the SPL retest reliability across 0.4 to 8 kHz. Stable results required 2 to 3 trial pairs for the linear-mode click (experiments 1 and 2) and three for the nonlinear-mode chirp (experiment 1), taking around 2 min on average. The linear-mode click assay produced measurable, reliable, and stable TEOAE and MOCR results on both hardware platforms in around 2 min per ear. The stimulus design and response window ensured that any stimulus artifact in linear mode was unlikely to confound the results. The refined assay is ready to produce high-quality data quickly for clinical and field studies to develop population norms, recognize diagnostic patterns, and determine risk profiles.

BackgroundWhilst otoacoustic emission (OAE) testing has proved to be valuable in revealing information about cochlear outer hair cell integrity, it does not provide insight into the afferent and efferent pathways once the stimulus has reached neural receptors. This information can be obtained objectively through contralateral acoustic stimulation (CAS) suppression. However, obtaining normative data is essential in the implementation of such tests.ObjectivesThe primary aim was to undertake a small pilot study to collect the CAS suppression across a predefined frequency range in order to provide a preliminary normative data set to be used with the newly developed transient evoked otoacoustic emission (TEOAE)-CAS module (PATH MEDICAL, Germering, Germany). Secondary aims included the analysis of the relationships between left and right CAS suppression, between male and female CAS suppression and between TEOAE signal-to-noise ratio (SNR) and CAS suppression.MethodsThe purpose of this study was to determine preliminary normative data for contralateral TEOAE suppression from 40 normal ears of 20 healthy young adults (10 males and 10 females). Subjects were recruited using purposive sampling. The CAS suppression responses were obtained automatically by means of the data-collection protocol on the device used. From the data obtained, correlations between TEOAE SNR and CAS suppression were made using Pearson’s correlation coefficient.ResultsThe data were statistically processed to form a normative database which possesses the potential of serving as a basis for further research aimed at determining the utility of CAS suppression testing when evaluating ear pathology. A mean CAS suppression of 0.8 decibels (dB) (0.61 SD) was obtained. There was no statistically significant relationship between TEOAE SNR and CAS suppression. There was no significant suppression difference in terms of laterality of ears or gender.ConclusionNormative values for CAS suppression of TEOAEs in a group of normal-hearing individuals were obtained using the newly developed TEOAE-CAS module (PATH MEDICAL, Germering, Germany). The availability of normative data for contralateral TEOAE suppression using the studied module allows for it to become commercially available, which will enable researchers and audiologists to perform this measurement in different populations in the evaluation of ear pathology.

The medial olivocochlear (MOC) system, which originates in the brainstem and projects to the outer hair cells in the cochlea, is thought to be involved in improving signal detection in noisy backgrounds. This proposition arises from the observation that the input-output functions of auditory primary afferent fibres to pure tones recorded in a continuous background noise are unmasked by MOC activation, improving the dynamic range, and is supported by both animal and human behavioural experiments. However, it is not known how the unmasking effects observed in the cochlea are translated into higher auditory brain centres, such as the cochlear nucleus, where intrinsic circuitry can potentially modulate any effect. In this study we have investigated the effects of continuous background noise without and with MOC system activation, on responses of different neuron types in the ventral cochlear nucleus of the guinea pig. Results show that the unmasking effects of MOC system activation on tone responses in continuous background noise are present in the cochlear nucleus. These unmasking effects manifest themselves as decompression of input-output functions as well as an improved slope, which results in an improvement in intensity discrimination of the tones. The data show, however, that the strength of the unmasking effects of MOC system activation varies between the different neuronal types. Unmasking was not detected in onset chopper neurons despite its demonstrable presence in other neuronal types in the same animals. These observations may reflect the level of involvement of different neuronal types in intensity discrimination.

The medial olivocochlear reflex (MOCR) is a brainstem-mediated reflex that reduces cochlear amplifier gain when elicited by sound. The MOCR may provide benefits such as protection from acoustic trauma and improved hearing in background noise. Measurement of MOCR effects may also have clinical applications. MOCR effects can be measured using transient-evoked otoacoustic emissions (TEOAEs), as amplitudes of TEOAEs are typically reduced during MOCR activation. The primary purpose of the current study was to quantify the repeatability of MOCR effects on TEOAEs because high repeatability in a healthy population is a necessary (but not sufficient) component of a clinically-useful test. A secondary purpose was to assess the relationship between MOCR strength and speech perception in noise. Twenty-one normal hearing subjects ages 18-30 participated. TEOAEs were elicited using 35 dB SL clicks. The MOCR was elicited using contralateral acoustic stimulation (CAS) consisting of 35 dB SL broadband noise. Sixteen measurements were made across a 5-week period (4 visits × 4 measurements per visit). TEOAEs were bandpass filtered in 1/6-octaves from 1-2 kHz. An individualized time-frequency analysis was used to select the largest TEOAE envelope peak within a restricted time analysis window. Responses were characterized as the complex ratio of TEOAEs obtained with versus without CAS. The statistical significance of effects was assessed. Results revealed generally high levels of stability across time, as assessed by the interquartile ranges of all results and as assessed by Cronbach’s alpha. Four MOCR measurements appeared to be adequate to obtain a reliable baseline measurement. Individualized time-frequency analyses were also important for obtaining reliable measurements. However, several subjects showed stable baseline measurements but unusual patterns of variability at subsequent sessions. These changes did not appear to be the result of changes in auditory status, methodological issues, or equipment issues. No

Historically, audiological procedures have focused on the assessment of the afferent (ascending) cochlear-VIIIth nerve system and have, for the most part, ignored the efferent (descending) auditory system. We report afferent and efferent auditory test results for two cases with a cholesterol cyst of the right petrous apex; one lesion involves the afferent segment of the auditory system, and the second lesion involves both the afferent and efferent segments of the auditory system. These "natural experiments" provide a unique opportunity to study the effect of a space-occupying lesion of the petrous apex on afferent and efferent function of the auditory system. Transient evoked otoacoustic emission (TEOAE) suppression studies were performed to assess the effect of the cholesterol cyst on the efferent system of the two cases. In addition, three complementary afferent tests of brain stem auditory function were administered: 1) acoustic reflex thresholds (ARTs); 2) masking level difference (MLD); and 3) auditory brain stem response (ABR). These tests are complementary because the superior olivary complex (SOC) is involved not only in the mediation of the sound evoked efferent reflex assessed in TEOAE suppression, but in the mediation of the ARTs, the MLD, and the ABR. The two cases with midline petrous apex lesions, one not involving the VIII-cochlear efferent auditory system, differed from each other with regards to TEOAEs suppression, and ARTs. Specifically, the case with only afferent involvement produced normal TEOAE suppression, a normal MLD, normal ARTs, and abnormal waves III and V of the ABR, whereas the case with both afferent and efferent involvement produced abnormal TEOAE suppression, a normal MLD, abnormal ARTs, and abnormal waves III and V of the ABR. These cases illustrate that although several auditory tests can be mediated within the same or adjacent anatomical structures, i.e., the SOC, they may not be equally affected by the same lesion due to different physiology. Further, the TEOAE suppression paradigm is a clinically relevant test to assay the sound evoked efferent reflex that is mediated by the medial olivocochlear system of the SOC.

SummaryAuditory processing depends on afferent and efferent auditory pathways integrity. The efferent auditory system may be assessed in humans by two non-invasive and objective methods: acoustic reflex and otoacoustic emissions suppression.AimAnalyze the efferent auditory system activity by otoacoustic emission suppression and acoustic reflex sensitization in human subjects with auditory processing disorders.MethodProspective study: fifty children with auditory processing disorders (study group) and thirty-eight children without auditory processing disorders (control group) were evaluated using otoacoustic emission with and without contralateral noise; and acoustic reflex with and without contralateral facilitating stimuli.ResultsOAE suppression mean value was equal to or less than 1.50 dB for the control group, and equal to or less than 1.26 dB for the study group. The mean sensitization reflex value was equal to or less than 14.60 dB for the study group and equal to or less than 15.21 dB for the control group. There was no statistically significant difference between the responses from the control group and the study group in both procedures.ConclusionThe study group had lower OAE suppression values and higher acoustic reflex sensitization values when compared to the control group.

Whether the auditory and visual systems use a similar coding strategy to represent motion direction is an open question. We investigated this question in the barn owl's optic tectum (OT) testing stimulus-specific adaptation (SSA) to the direction of motion. SSA, the reduction of the response to a repetitive stimulus that does not generalize to other stimuli, has been well established in OT neurons. SSA suggests a separate representation of the adapted stimulus in upstream pathways. So far, only SSA to static stimuli has been studied in the OT. Here, we examined adaptation to moving auditory and visual stimuli. SSA to motion direction was examined using repeated presentations of moving stimuli, occasionally switching motion to the opposite direction. Acoustic motion was either mimicked by varying binaural spatial cues or implemented in free field using a speaker array. While OT neurons displayed SSA to motion direction in visual space, neither stimulation paradigms elicited significant SSA to auditory motion direction. These findings show a qualitative difference in how auditory and visual motion is processed in the OT and support the existence of dedicated circuitry for representing motion direction in the early stages of visual but not the auditory system.

Influence of aging on active cochlear micromechanical properties and on the medial olivocochlear system in humans