Changes In Otoacoustic Emissions Research Articles

Easy and Hard Auditory Tasks Distinguished by Otoacoustic Emissions and Event-related Potentials: Insights into Efferent System Activity

The medial olivocochlear (MOC) system is thought to be responsible for modulation of peripheral hearing through descending (efferent) pathways. This study investigates the connection between peripheral hearing function and auditory attention tasks of different degrees of difficulty. Peripheral hearing function was evaluated by analyzing the amount of change in otoacoustic emissions (OAEs) by contralateral acoustic stimulation (CAS), a well-known effect of the MOC system. Simultaneously, levels of attention were evaluated by event-related potentials (ERPs). The ERPs showed clear differences in processing tasks of different difficulty, but paradoxically there was no difference in the amount of OAE change brought about by CAS. There was also no effect on OAE latency, nor was there any difference in noise level or number of rejected trials. However, we observed that the changes in OAEs by CAS for easy and hard tasks were correlated with the magnitude of the P3 wave in the ERP. This suggests there might be some sort of mutual compensation mechanism – presently unknown – between periphery and cortex.

STUDY OF OTOACOUSTIC EMISSIONS AS AN ADJUVANT IN THE DIAGNOSIS OF ENDOLYMPHATIC HYDROPS

Endolymphatic hydrops (EH) results from increased endolymph volume in the inner ear, which leads to episodic vertigo, ear fullness, and sensorineural hearing loss. In these patients, Vestibular Evoked Myogenic Potential (VEMP) examination has high sensitivity and specificity for diagnosis. These patients have also been suggested to have frequency-specific changes in otoacoustic emissions (OAE). The aim of this study is to evaluate the result of the OAE examination in patients with altered VEMP and clinical history compatible with EH. The medical records and exams of 107 patients with previous diagnosis of EH were retrospectively analyzed. The results of OAE were studied for their validation in the diagnosis of patients with EH. The results showed that 98.1% of the evaluated patients presented at least one OAE frequency with no response in low or high, with a 95% confidence interval of 95.6% to 100%. When comparing the cases with normal and altered audiometry, there was a significant difference regarding the left side (p=0.041), right (p<0.001) and left (p=0.001), low (p=0.006) and high (p<0.001). Overall, a trend towards significant difference was observed (p=0.077). It is concluded that there is a significant alteration in the OAE of patients with EH, showing that such exam has the potential for diagnosis and follow-up.

A Time-Course-Based Estimation of the Human Medial Olivocochlear Reflex Function Using Clicks.

The auditory efferent system, especially the medial olivocochlear reflex (MOCR), is implicated in both typical auditory processing and in auditory disorders in animal models. Despite the significant strides in both basic and translational research on the MOCR, its clinical applicability remains under-utilized in humans due to the lack of a recommended clinical method. Conventional tests employ broadband noise in one ear while monitoring change in otoacoustic emissions (OAEs) in the other ear to index efferent activity. These methods, (1) can only assay the contralateral MOCR pathway and (2) are unable to extract the kinetics of the reflexes. We have developed a method that re-purposes the same OAE-evoking click-train to also concurrently elicit bilateral MOCR activity. Data from click-train presentations at 80 dB peSPL at 62.5 Hz in 13 young normal-hearing adults demonstrate the feasibility of our method. Mean MOCR magnitude (1.7 dB) and activation time-constant (0.2 s) are consistent with prior MOCR reports. The data also suggest several advantages of this method including, (1) the ability to monitor MEMR, (2) obtain both magnitude and kinetics (time constants) of the MOCR, (3) visual and statistical confirmation of MOCR activation.

Effect of Radiofrequency Waves of Mobile Phones on Distortion Product Otoacoustic Emissions

Abstract Objective The prolonged exposure to electromagnetic fields of mobile phones can damage the cochlear hair cells, which can be detected by otoacoustic emission (OAE). To know the effect of mobile phones on hearing, the young volunteers were subjected to prolonged mobile phone usage and changes in OAE were recorded. Materials and Methods Twenty-eight volunteers with normal hearing were made to talk one full hour continuously on the mobile phone. Distortion product otoacoustic emission (DPOAE) was measured prior to the usage of mobile phones and immediately after the use (post-exposure 1) and 24 hours after the use (post-exposure 2). The values were compared. Results Out of the 28 volunteers, 20 were females and 8 were males. Twenty-one volunteers preferred the right ear while using mobile phones, 7 preferred the left ear. There was no statistically significant difference between the baseline DPOAE values and values of post-exposure 1 and 2 when only the preferred ear was taken into consideration. When the preferred ear was compared with nonpreferred ear, a statistically significant difference was found only in the low frequencies between the pre-exposure and post-exposure 1 values. Conclusion This study shows there was no significant correlation between OAE and prolonged mobile phone exposure when the preferred ear was not considered.

Prevention of Noise-Induced Hearing Loss Using Investigational Medicines for the Inner Ear: Previous Trial Outcomes Should Inform Future Trial Design.

Significance:Noise-induced hearing loss (NIHL) is an important public health issue resulting in decreased quality of life for affected individuals, and significant costs to employers and governmental agencies.Recent Advances:Advances in the mechanistic understanding of NIHL have prompted a growing number of proposed, in-progress, and completed clinical trials for possible protections against NIHL via antioxidants and other drug agents. Thirty-one clinical trials evaluating prevention of either temporary or permanent NIHL were identified and are reviewed.Critical Issues:This review revealed little consistency in the noise-exposed populations in which drugs are evaluated or the primary outcomes used to measure NIHL prevention. Changes in pure-tone thresholds were the most common primary outcomes; specific threshold metrics included both average hearing loss and incidence of significant hearing loss. Changes in otoacoustic emission (OAE) amplitude were relatively common secondary outcomes. Extended high-frequency (EHF) hearing and speech-in-noise perception are commonly adversely affected by noise exposure but are not consistently included in clinical trials assessing prevention of NIHL.Future Directions:Multiple criteria are available for monitoring NIHL, but the specific criterion to be used to define clinically significant otoprotection remains a topic of discussion. Audiogram-based primary outcome measures can be combined with secondary outcomes, including OAE amplitude, EHF hearing, speech-in-noise testing, tinnitus surveys, and patient-reported outcomes. Standardization of test protocols for the above primary and secondary outcomes, and associated reporting criterion for each, would facilitate clinical trial design and comparison of results across investigational drug agents. Antioxid. Redox Signal. 36, 1171–1202.

Auditory Performance in Recovered SARS-COV-2 Patients.

Objective:While COVID-19 symptoms impact rhinology (anosmia) and laryngology (airways), two major disciplines of the otolaryngology armamentarium, the virus has seemed to spare the auditory system. A recent study, however, reported changes in otoacoustic emission (OAE) signals measured in SARS-COV-2 positive patients. We sought to assess the effect of COVID-19 infection on auditory performance in a cohort of recovered SARS-COV-2 patients and controls. To avoid a potential bias of previous audiological dysfunction not related to SARS-COV-2 infection, the study encompasses patients with normal auditory history. We hypothesized that if SARS-COV-2 infection predisposes to hearing loss, we would observe subtle and early audiometric deficits in our cohort in the form of subclinical auditory changes.Study Design:Cross-sectional study.Setting:Tertiary referral center.Patients:The Institutional Review Board approved the study and we recruited participants who had been positive for SARS-COV-2 infection, according to an Reverse Transcription Polymerase Chain Reaction (RT-PCR) test on two nasopharyngeal swabs. The patients included in this study were asymptomatic for the SARS-COV-2 infection and were evaluated following recovery, confirmed by repeated swab testing. The control group comprised healthy individuals matched for age and sex, and with a normal auditory and otologic history.Intervention(s):The eligibility to participate in this study included a normal audiogram, no previous auditory symptoms, normal otoscopy examination with an intact tympanic membrane, and bilateral tympanometry type A. None of our volunteers reported any new auditory symptoms following SARS-COV-2 infection. Ototacoustic emissions (OAE) and auditory brainstem response (ABR) measurements were used to evaluate the auditory function.Main Outcome Measure(s):OAE and ABR measurements.Results:We have found no significant differences between recovered asymptomatic SARS-COV-2 patients and controls in any of transitory evoked otoacoustic emission (TEOAE), distortion product otoacoustic emissions (DPOAE), or ABR responses.Conclusions:There is no cochlear dysfunction represented by ABR, TEOAE, and DPOAE responses in recovered COVID-19 asymptomatic patients. Retrocochlear function was also preserved as evident by the ABR responses. A long-term evaluation of a larger cohort of SARS-COV-2 patients will help to identify a possible contribution of SARS-COV-2 infection to recently published anecdotal auditory symptoms associated with COVID-19.

Idiopathic Sudden Sensorineural Hearing Loss: Should Otoacoustic Emissions Be Added to the Monitoring Protocol? A Systematic Review

Idiopathic sudden sensorineural hearing loss (ISSNHL) refers to a loss of hearing, most commonly unilateral, that occurs suddenly (≤72 h) with no identifiable cause or etiology. To date, there is no standard protocol to predict prognosis (hearing recovery) for patients with ISSNHL. However, studies have shown that changes in otoacoustic emissions (OAEs) often occur prior to changes in audiometric hearing thresholds. OAEs originate from the electrochemical motility of the outer hair cells (OHC) and reflect the integrity of the inner ear, specifically the cochlear amplifier. Therefore, OAEs may be useful as a prognostic predictive factor in patients with ISSNHL from the initial onset of symptoms through recovery. A systematic review of the literature was undertaken to assess the relationship between pure tone thresholds, OAEs, and subjective hearing improvement and/or recovery. Fourteen studies were identified for inclusion, and they overwhelmingly support the inclusion of OAEs in the protocol to monitor ISSNHL recovery. This finding supports the development of a standard diagnostic protocol that includes OAEs to predict patient hearing outcomes.

Oto-acoustic emissions and brainstem evoked response audiometry in patients of tinnitus with normal hearing.

Tinnitus is defined as the perception of sound that results completely from activity within the nervous system without any corresponding mechanical, vibratory activity within the cochlea, and not related to external stimulation of any kind. It disrupts the daily life of 1 out of every 200 adults. The source of tinnitus generation is not limited to the peripheral auditory system. However, there are abnormalities seen in BERA in tinnitus patients depicting auditory pathway involvement. Oto-acoustic emissions are mechanical vibrations generated in the cochlea, which are evaluated by TEOAE and DPOAE whereas BERA evaluates both cochlea and brainstem auditory pathway for any conduction abnormalities. The aim of the study is to analyze the changes in OAE and BERA in patients suffering from tinnitus with normal hearing, which may help us to understand the patho-physiology of tinnitus. This is a prospective study conducted in a tertiary care hospital in Northern India between 1st December 2015 to 31st July 2017. All patients of tinnitus with normal hearing were included in the study group, whereas Individuals with normal hearing with no other ear complaints were included in control group. Total 160 Ears were evaluated with 80 ears in both study and control group each. Patients with PTA >25dB, age >55 years or any chronic medical illness were excluded from the study. 80 individuals (46 Males and 34 Females) were divided into study and control Group (80 Ears each). Tinnitus was bilateral in 28 subjects (53.84%) and unilateral in 24 subjects (46.16%). Both control and study group showed significant difference in TEOAE and DPOAE study. In TEOAE, 8 (10%) ears in control group and 30 ears (37.5%) in study group showed test result as REFER whereas in DPOAE 10 (12.5%) ears in control group and 35 (43.8%) ears showed test result as REFER. All these result were statistically significant. In BERA the latency of wave I was significantly prolonged in study group as compared to control group, while difference between all other parameters between the two groups was insignificant. There were various significant abnormalities seen in parameters of Oto-Acoustic Emissions (OAE) and Brainstem Evoked Response Audiometry (BERA). So these tests should be included in the test battery for the screening of patients complaining of tinnitus even with normal hearing.

Efferent Modulation of Stimulus Frequency Otoacoustic Emission Fine Structure.

Otoacoustic emissions, sounds generated in the inner ear, have become a convenient non-invasive tool to examine the efferent modulation of cochlear mechanics. Activation of the medial olivocochlear (MOC) efferents has been shown to alter the magnitude of these emissions. When the effects of efferent activation on the detailed spectral structures of these emissions have been examined, a shift of the spectral patterns toward higher frequencies has been reported for distortion product and spontaneous otoacoustic emissions. Stimulus frequency otoacoustic emissions (SFOAEs) have been proposed as the preferred emission type in the study of efferent modulation due to the simplicity of their production leading to the possibility of clearer interpretation of results. The effects of efferent activation on the complex spectral patterns of SFOAEs have not been examined to the best of our knowledge. We have examined the effects of activating the MOC efferents using broadband noise in normal-hearing humans. The detailed spectral structure of SFOAEs, known as fine structure, was recorded with and without contralateral acoustic stimulation. Results indicate that SFOAEs are reduced in magnitude and their fine structure pushed to higher frequencies by contralateral acoustic stimulation. These changes are similar to those observed in distortion product or spontaneous otoacoustic emissions and behavioral hearing thresholds. Taken together with observations made about magnitude and phase changes in otoacoustic emissions and hearing thresholds upon contralateral acoustic stimulation, all changes in otoacoustic emission and hearing threshold fine structure appear to be driven by a common set of mechanisms. Specifically, frequency shifts in fine structure patterns appear to be linked to changes in SFOAE phase due to contralateral acoustic stimulation.

Medial olivocochlear efferent reflex inhibition of human cochlear nerve responses

Inhibition of cochlear amplifier gain by the medial olivocochlear (MOC) efferent system has several putative roles: aiding listening in noise, protection against damage from acoustic overexposure, and slowing age-induced hearing loss. The human MOC reflex has been studied almost exclusively by measuring changes in otoacoustic emissions. However, to help understand how the MOC system influences what we hear, it is important to have measurements of the MOC effect on the total output of the organ of Corti, i.e., on cochlear nerve responses that couple sounds to the brain. In this work we measured the inhibition produced by the MOC reflex on the amplitude of cochlear nerve compound action potentials (CAPs) in response to moderate level (52–60 dB peSPL) clicks from five, young, normal hearing, awake, alert, human adults. MOC activity was elicited by 65 dB SPL, contralateral broadband noise (CAS). Using tympanic membrane electrodes, approximately 10 h of data collection were needed from each subject to yield reliable measurements of the MOC reflex inhibition on CAP amplitudes from one click level. The CAS produced a 16% reduction of CAP amplitude, equivalent to a 1.98 dB effective attenuation (averaged over five subjects). Based on previous reports of efferent effects as functions of level and frequency, it is possible that much larger effective attenuations would be observed at lower sound levels or with clicks of higher frequency content. For a preliminary comparison, we also measured MOC reflex inhibition of DPOAEs evoked from the same ears with f2's near 4 kHz. The resulting effective attenuations on DPOAEs were, on average, less than half the effective attenuations on CAPs.

Changes in otoacoustic emissions during selective auditory and visual attention.

Previous studies have demonstrated that the otoacoustic emissions (OAEs) measured during behavioral tasks can have different magnitudes when subjects are attending selectively or not attending. The implication is that the cognitive and perceptual demands of a task can affect the first neural stage of auditory processing-the sensory receptors themselves. However, the directions of the reported attentional effects have been inconsistent, the magnitudes of the observed differences typically have been small, and comparisons across studies have been made difficult by significant procedural differences. In this study, a nonlinear version of the stimulus-frequency OAE (SFOAE), called the nSFOAE, was used to measure cochlear responses from human subjects while they simultaneously performed behavioral tasks requiring selective auditory attention (dichotic or diotic listening), selective visual attention, or relative inattention. Within subjects, the differences in nSFOAE magnitude between inattention and attention conditions were about 2-3 dB for both auditory and visual modalities, and the effect sizes for the differences typically were large for both nSFOAE magnitude and phase. These results reveal that the cochlear efferent reflex is differentially active during selective attention and inattention, for both auditory and visual tasks, although they do not reveal how attention is improved when efferent activity is greater.

Effects of sevoflurane and desflurane on otoacoustic emissions in humans.

Otoacoustic emissions (OAEs) are non-invasive, easy to apply and objective test methods which are widely used to determine the presence of hearing in audiology clinics. Under certain circumstances, the study should be applied under general anesthesia. The aim of this study was to determine the influence of new short-acting inhalation agents, desflurane and sevoflurane, on OAE in humans. These short-acting agents are widely used in general anesthesia. Thirty-one healthy patients who underwent septoplasty and turbinoplasty surgery were included in this study. Unpremedicated patients were anesthetized and monitored by a standard protocol except the inhalation agents. Desflurane and sevoflurane were added to the inhaled gas mixture at ~1MAC, 5-6 % and 1.5-2 %, respectively. Transient evoked otoacoustic emissions and distortion product otoacoustic emissions measured in both ears of each patient preoperatively in the operating room before induction, 5 min after induction, after the completion of surgical procedure while the anesthetic agents are still given and 1 h after surgery in the ward. Between-group and within-group comparisons and correlations with hemodynamic parameters were performed for statistical analysis. The measurements of 26 ears in desflurane group and 28 ears in sevoflurane group were evaluated. There were no differences in initial measurements between groups (p > 0.05). Both groups presented significant decrease in intraoperative measurements and changes in time were statistically significant (p < 0.05). The changes in OAEs were similar to changes in systemic blood pressures. Correlation between OAEs and systemic blood pressures were significant (p < 0.05). In conclusion, sevoflurane and desflurane decreased OAEs around 2-3 dB; OAEs are still measurable under inhalation agents. This provides some findings about the OAE status of patient, but the evaluations should be done with the impact of anesthetic agents in mind.

Understanding subtle changes in auditory function with otoacoustic emissions

Otoacoustic emissions (OAEs), a sensitive measure of cochlear processing, may be altered by subtle changes in auditory function that are not measurable by usual clinical methods. We studied auditory function in carriers of genetic mutations related to recessive hereditary hearing loss where we hypothesized that carrying a single mutation copy may compromise auditory function and be reflected when sensitive assays are used. Parents and siblings who were confirmed carriers of recessive mutations associated with GJB2 (connexin 26) or Usher syndrome, as well as obligate carriers of mutations related to recessive hearing loss of unknown genetic origin, were compared to age and gender matched control subjects. All participants had normal pure tone and middle ear responses. Metrics included transient OAEs, distortion product OAEs, and OAE fine structure. DPOAE fine structure was specifically explored based on the ability to isolate components that could be differentially affected by genetic mutations. The results support the hypothesis that carriers of gene mutations related to hearing loss display subtle auditory abnormalities that can be observed in OAEs. These findings will be related to other studies of subtle changes in OAEs in disorders affecting auditory function. [Work supported by NIH NIDCD R01-DC03679 and VU Development Funds.]

Changes in oto-acoustic emissions after exposure to live music

Distortion Product Oto-acoustic Emissions (DPOAE) and Transient Evoked Oto-acoustic Emissions (TEOAE) were measured in subjects before and after attendance to live music. The changes measured were compared to the exposure levels measured at the position of the subject. The main objectives of this experiment were two fold: 1) to assess the validity of the proposed measurement protocol to measure changes in DPOAE and TEOAE after a concert; 2) to test the reliability of the oto-acoustic emission measurement system under field conditions; Initial results shows that it is possible to measure changes in hearing after exposures of relative short duration (&amp;lt;1.5 hours). There are large individual differences both in sound exposure levels as well as in the changes on oto-acoustic emissions produced by similar exposures. Current results will be presented.

Amplitude changes in otoacoustic emissions after exposure to industrial noise

Noise-induced hearing loss (NIHL) is a frequent problem in industrial settings, especially where a high noise level is present. It is permanent, and irreversible, but preventable. Routine audiometry (an objective and time consuming) test is used for NIHL screening. Otoacoustic emissions (OAEs) are recently proposed as a more sensitive test for early diagnosis of NIHL. In this study, we aimed to compare the results of pure tone audiometry (PTA) with OAE in the diagnosis of NIHL. In a cross-sectional study on 120 workers (in three groups: Not exposed to noise, exposed to noise without NIHL and exposed to noise with NIHL), we compared the results of PTA and OAE. OAE can detect some changes in the function of hearing system in subjects exposed to noise, and these changes are apparently prior to hearing loss, which is diagnosed by PTA. OAE is a more sensitive method for the early diagnosis of cochlear damage than PTA, and can be performed in industrial settings for NIHL screening.

State-of-the-Art Topics Highlight Audiology Offerings

You have accessThe ASHA LeaderASHA Convention Coverage1 Aug 2010State-of-the-Art Topics Highlight Audiology Offerings Anthony T. CacacePhD, CCC-A Anthony T. Cacace Google Scholar More articles by this author , PhD, CCC-A https://doi.org/10.1044/leader.ACC3.15092010.20 SectionsAbout ToolsAdd to favorites ShareFacebookTwitterLinked In In keeping within the Convention theme, “Leadership Into New Frontiers,” it is fitting that the success of the 2010 Convention would be linked directly to those individuals responsible for selecting much of the subject matter. These individuals are the topic coordinators for the 2010 Convention—leaders in audiology and experts in the selected areas of interest. Indeed, we are fortunate to have such a pool of scientists and clinicians within our organization and we now recognize these individuals, thank them for their efforts, and acknowledge their dedication to advancing the field. Each has taken responsibility for coordinating Convention offerings in specific areas of audiology: Andrew Stuart, East Carolina University—adult diagnostic testing Lenore Holte, University of Iowa—infant diagnostic testing Larry Humes, Indiana University—auditory processing disorders Robert Novak, Purdue University—hearing aids and adult rehabilitation Susan Nittrouer, Ohio State University—rehabilitation for infants and children with hearing loss Faith Akin, James H. Quillen VA Medical Center—vestibular/balance-related issues and traumatic brain injury John Preece, City University of New York—hearing science Combined, this group of individuals has organized offerings on contemporary, state-of-the-art topics that attendees expect and require to engage their broad range of interests. The educational core of the audiology sessions comprises seminars and short courses that provide practical, theoretical, and evidence-based information. In technical sessions, new research that stimulates and expands the knowledge will be presented. Technical sessions—categorized into adult diagnostic testing, auditory processing disorders (APDs), and hearing science—are always highlights of the Convention. Topics in adult diagnostic testing include steady-state auditory-evoked potentials, reliability of distortion product otoacoustic emission (OAE) growth functions, and the incidental detection of cerebellar pontine angle tumors. APD sessions will examine advanced concepts in cortical auditory event-related potentials, auditory processing in autism spectrum disorders, and age-related cortical processing in the presence of noise. The hearing science area covers human and animal studies, age-related auditory changes in diabetes, developmental changes in OAEs and broadband middle-ear power reflectance, electrophysiological investigations, perceptual studies, and issues related to tinnitus. Of particular interest are the variety of one- and two-hour seminars covering the content areas of infant diagnostic testing; intervention for hearing loss in adults; rehabilitation for infants, children, and adults with hearing loss; and vestibular- and balance-related issues. Topics will include updates on frequency-lowering techniques in hearing aids, expanded cochlear implant candidacy criteria, use of music in rehabilitation, methods for improving speech perception in noise, updates on the management of benign paroxysmal positional vertigo, and much more. Short courses focus on intervention for hearing loss in adults specifically related to person-centered aural rehabilitation and the ever-expanding vestibular and balance-related areas. Issues in this domain include recent developments in otolithic function and assessment, vestibular consequences of blast injury, and assessment of balance function in children. A special session on auditory processing and literacy put together by John Durrant of the University of Pittsburgh and colleagues also will be noteworthy. Taken together, these audiology sessions offer impressive and comprehensive coverage of important areas that should be of interest to all who attend. I look forward to meeting ASHA audiologists in Philadelphia! Author Notes Anthony T. Cacace, PhD, CCC-A, audiology co-chair of the 2010 Convention and a professor in the Department of Communication Sciences and Disorders at Wayne State University, can be reached at [email protected]. Advertising Disclaimer | Advertise With Us Advertising Disclaimer | Advertise With Us Additional Resources FiguresSourcesRelatedDetails Volume 15Issue 9August 2010 Get Permissions Add to your Mendeley library History Published in print: Aug 1, 2010 Metrics Downloaded 54 times Topicsasha-topicsleader_do_tagleader-topicsasha-article-typesCopyright & Permissions© 2010 American Speech-Language-Hearing AssociationLoading ...

Reflex control of the human inner ear: a half-octave offset in medial efferent feedback that is consistent with an efferent role in the control of masking.

The high sensitivity and frequency selectivity of the mammalian cochlea is due to amplification produced by outer hair cells (OHCs) and controlled by medial olivocochlear (MOC) efferents. Data from animals led to the view that MOC fibers provide frequency-specific inhibitory feedback; however, these studies did not measure intact MOC reflexes. To test whether MOC inhibition is primarily at the frequency that elicits the MOC activity, acoustically elicited MOC effects were quantified in humans by the change in otoacoustic emissions produced by 60-dB SPL tone and half-octave-band noise elicitors at different frequencies relative to a 40-dB SPL, 1-kHz probe tone. On average, all elicitors produced MOC effects that were skewed (elicitor frequencies -1 octave below the probe produced larger effects than those -1 octave above). The largest MOC effects were from elicitors below the probe frequency for contra- and bilateral elicitors but were from elicitors centered at the probe frequency for ipsilateral elicitors. Typically, ipsilateral elicitors produced larger effects than contralateral elicitors and bilateral elicitors produced effects near the ipsi+contra sum. Elicitors at levels down to 30-dB SPL produced similar patterns. Tuning curves (TCs) interpolated from these data were V-shaped with Q10s approximately 2. These are sharper than MOC-fiber TCs found near 1 kHz in cats and guinea pigs. Because cochlear amplification is skewed (more below the best frequency of a cochlear region), these data are consistent with an anti-masking role of MOC efferents that reduces masking by reducing the cochlear amplification seen at 1 kHz.

Modification of otoacoustic emissions following ear-level exposure to MP3 player music

The purpose of this study was to examine if a pre-determined exposure level and duration of MP3 player music would result in significant changes in cochlear function when measured with audiometric and physiological methods. Distortion-product otoacoustic emissions (DPOAEs), synchronized spontaneous otoacoustic emissions (SSOAEs), and hearing thresholds were measured in 20 normal-hearing adults before and after a 30-minute MP3 player music exposure. DPOAEs were acquired with 65/45 dB SPL primary tones (f2=0.842–7.996 kHz) with a frequency resolution of 8 points/octave. A probe microphone system recorded ear-canal music levels and was used to equalize levels at approximately 85 dBC across individuals during the music presentation. Comparison of pre- and post-exposure measurements revealed no significant differences in hearing thresholds, but DPOAE levels in half-octave bands centered from 1.4–6.0 kHz were significantly reduced following the music exposure. Post-exposure shifts in SSOAE frequency and level were highly variable in individuals identified with SSOAEs. The results for the exposure conditions explored in this study indicate that changes in otoacoustic emissions may precede the development of music-induced hearing threshold shifts.

Olivocochlear Efferents: Anatomy, Physiology, Function, and the Measurement of Efferent Effects in Humans

This review covers the basic anatomy and physiology of the olivocochlear reflexes and the use of otoacoustic emissions (OAEs) in humans to monitor the effects of one group, the medial olivocochlear (MOC) efferents. MOC fibers synapse on outer hair cells (OHCs), and activation of these fibers inhibits basilar membrane responses to low-level sounds. This MOC-induced decrease in the gain of the cochlear amplifier is reflected in changes in OAEs. Any OAE can be used to monitor MOC effects on the cochlear amplifier. Each OAE type has its own advantages and disadvantages. The most straightforward technique for monitoring MOC effects is to elicit MOC activity with an elicitor sound contralateral to the OAE test ear. MOC effects can also be monitored using an ipsilateral elicitor of MOC activity, but the ipsilateral elicitor brings additional problems caused by suppression and cochlear slow intrinsic effects. To measure MOC effects accurately, one must ensure that there are no middle-ear-muscle contractions. Although standard clinical middle-ear-muscle tests are not adequate for this, adequate tests can usually be done with OAE-measuring instruments. An additional complication is that most probe sounds also elicit MOC activity, although this does not prevent the probe from showing MOC effects elicited by contralateral sound. A variety of data indicate that MOC efferents help to reduce acoustic trauma and lessen the masking of transients by background noise; for instance, they aid in speech comprehension in noise. However, much remains to be learned about the role of efferents in auditory function. Monitoring MOC effects in humans using OAEs should continue to provide valuable insights into the role of MOC efferents and may also provide clinical benefits.

Low-level otoacoustic emissions may predict susceptibility to noise-induced hearing loss

In a longitudinal study with 338 volunteers, audiometric thresholds and otoacoustic emissions were measured before and after 6 months of noise exposure on an aircraft carrier. While the average amplitudes of the otoacoustic emissions decreased significantly, the average audiometric thresholds did not change. Furthermore, there were no significant correlations between changes in audiometric thresholds and changes in otoacoustic emissions. Changes in transient-evoked otoacoustic emissions and distortion-product otoacoustic emissions were moderately correlated. Eighteen ears acquired permanent audiometric threshold shifts. Only one-third of those ears showed significant otoacoustic emission shifts that mirrored their permanent threshold shifts. A Bayesian analysis indicated that permanent threshold shift status following a deployment was predicted by baseline low-level or absent otoacoustic emissions. The best predictor was transient-evoked otoacoustic emission amplitude in the 4-kHz half-octave frequency band, with risk increasing more than sixfold from approximately 3% to 20% as the emission amplitude decreased. It is possible that the otoacoustic emissions indicated noise-induced changes in the inner ear, undetected by audiometric tests. Otoacoustic emissions may therefore be a diagnostic predictor for noise-induced-hearing-loss risk.