Interaural Difference Thresholds Research Articles

Interhemispheric Auditory Cortical Synchronization in Asymmetric Hearing Loss.

Objectives:Auditory cortical activation of the two hemispheres to monaurally presented tonal stimuli has been shown to be asynchronous in normal hearing (NH) but synchronous in the extreme case of adult-onset asymmetric hearing loss (AHL) with single-sided deafness. We addressed the wide knowledge gap between these two anchoring states of interhemispheric temporal organization. The objectives of this study were as follows: (1) to map the trajectory of interhemispheric temporal reorganization from asynchrony to synchrony using magnitude of interaural threshold difference as the independent variable in a cross-sectional study and (2) to evaluate reversibility of interhemispheric synchrony in association with hearing in noise performance by amplifying the aidable poorer ear in a repeated measures, longitudinal study.Design:The cross-sectional and longitudinal cohorts were comprised of 49 subjects (AHL; N = 21; 11 male, 10 female; mean age = 48 years) and NH (N = 28; 16 male, 12 female; mean age = 45 years). The maximum interaural threshold difference of the two cohorts spanned from 0 to 65 dB. Magnetoencephalography analyses focused on latency of the M100 peak response from auditory cortex in both hemispheres between 50 msec and 150 msec following monaural tonal stimulation at the frequency (0.5, 1, 2, 3, or 4 kHz) corresponding to the maximum and minimum interaural threshold difference for better and poorer ears separately. The longitudinal AHL cohort was drawn from three subjects in the cross-sectional AHL cohort (all male; ages 49 to 60 years; varied AHL etiologies; no amplification for at least 2 years). All longitudinal study subjects were treated by monaural amplification of the poorer ear and underwent repeated measures examination of the M100 response latency and quick speech in noise hearing in noise performance at baseline, and postamplification months 3, 6, and 12.Results:The M100 response peak latency values in the ipsilateral hemisphere lagged those in the contralateral hemisphere for all stimulation conditions. The mean (SD) interhemispheric latency difference values (ipsilateral less contralateral) to better ear stimulation for three categories of maximum interaural threshold difference were as follows: NH (≤ 10 dB)—8.6 (3.0) msec; AHL (15 to 40 dB)—3.0 (1.2) msec; AHL (≥ 45 dB)—1.4 (1.3) msec. In turn, the magnitude of difference values were used to define interhemispheric temporal organization states of asynchrony, mixed asynchrony and synchrony, and synchrony, respectively. Amplification of the poorer ear in longitudinal subjects drove interhemispheric organization change from baseline synchrony to postamplification asynchrony and hearing in noise performance improvement in those with baseline impairment over a 12-month period.Conclusions:Interhemispheric temporal organization in AHL was anchored between states of asynchrony in NH and synchrony in single-sided deafness. For asymmetry magnitudes between 15 and 40 dB, the intermediate mixed state of asynchrony and synchrony was continuous and reversible. Amplification of the poorer ear in AHL improved hearing in noise performance and restored normal temporal organization of auditory cortices in the two hemispheres. The return to normal interhemispheric asynchrony from baseline synchrony and improvement in hearing following monoaural amplification of the poorer ear evolved progressively over a 12-month period.

Ear Preference and Interaural Threshold Asymmetry.

To define the relationships among ear preference strength, audiometric interaural asymmetry magnitude, and hearing impairment. Prospective, cross-sectional. Academic audiology clinic. Adults. Diagnostic. Patient-reported ear preference strength using a seven-category preference (no preference; left or right somewhat, strongly, or completely) scheme, hearing disability level on the Speech, Spatial, and Qualities of Hearing scale, and audiometric interaural threshold asymmetry were analyzed in three study cohorts: 1) normal hearing (thresholds ≤ 25 dB, n = 66), 2) symmetric hearing loss (any single threshold > 25 dB, n = 81), and 3) asymmetric hearing loss (maximum average interaural threshold difference at any two adjacent frequencies (IThrDmax2)≥ 15 dB, n = 112). Receiver operating characteristic curves for somewhat, strongly, and completely ear preference levels using IThrDmax2 cutoff values at 15, 30, and 45 dB showed good to excellent classifier performance (all curve areas ≥ 0.84). The mapping of ear preference strength to the most likely IThrDmax2 range by odds ratio analysis demonstrated: no preference (< 15 dB), somewhat (15-29 dB), strongly (30-44 dB), and completely (≥ 45 dB). Complete dependence on one ear was associated with the most severe degradation in spatial hearing function. Categorical ratings of ear preference strength may be mapped to ranges of audiometric threshold asymmetry magnitude and spatial hearing disability level. Querying ear preference strength in routine clinical practice would enable practitioners to identify patients with asymmetric hearing more expeditiously and promote timely evaluation and treatment.

Magnitude and phase of three-dimensional (3D) velocity vector: Application to measurement of cochlear promontory motion during bone conduction sound transmission

Recent measurements of vibrational motion to assess sound transmission through ear structures and skull contents have included three-dimensional (3D) behavior. The 3D motion of a point has been described with the three orthogonal components in the 3D space. In this article, a method to represent the 3D velocity with the magnitude and phase of the resultant velocity is introduced. This method was applied to the measurement of cochlear promontory motion as an indication of bone conduction (BC) sound transmission. The promontory motions were measured on the ipsilateral and contralateral sides, and the transcranial attenuation and phase delay of the contralateral side relative to the ipsilateral side were calculated. The transcranial attenuation and phase delay calculated with the maximum magnitudes and corresponding phases of the resultant were a better fit to the interaural threshold difference and transcranial time interval between the ipsilateral and contralateral sides as reported in the literature, than the attenuation and phase delay calculated with any individual Cartesian motion component.

Influence of thresholds on amplitudes in vestibular evoked myogenic potentials

To investigate the relationship between the threshold and the interaural amplitude difference ratio (IADR) in cervical vestibular evoked myogenic potential (cVEMP) testing and pursuit the clinical significance of the parameters. cVEMP responses were recorded while the SCM contraction was controlled using a pressure cuff. The intensities of the sound stimulation decreased from 95 dB n HL by 5 dB, until no responses were evoked. Thresholds, interaural threshold difference (ITD), amplitudes, and interaural amplitude difference ratio at the stimulation of 95 dB n HL were calculated and the relationship between them was examined. All subjects showed cVEMP responses bilaterally. Thresholds measured were overall 76 dB n HL and most (92%) ears showed the ITD of 0 or 5 dB. The amplitudes of cVEMP responses showed a positive correlation with the sound intensities, and more specifically with the sound intensity above each threshold value. There was no significant difference in IADR values by the ITD. Based on our study, the ITD is less than 10 dB in most normal subjects and estimation of threshold should be added to cVEMP testing for probing vestibular asymmetry. Getting a threshold might be helpful in determining whether the abnormal interaural amplitude difference ratio is related to the abnormal ITD.

Audiometric asymmetry and tinnitus laterality

To identify an optimal audiometric asymmetry index for predicting tinnitus laterality. Retrospective medical record review. Data from adult tinnitus patients (80 men and 44 women) were extracted for demographic, audiometric, tinnitus laterality, and related information. The main measures were sensitivity, specificity, positive predictive value (PPV), and receiver operating characteristic (ROC) curves. Three audiometric asymmetry indices were constructed using one, two, or three frequency elements to compute the average interaural threshold difference (aITD). Tinnitus laterality predictive performance of a particular index was assessed by increasing the cutoff or minimum magnitude of the aITD from 10 to 35 dB in 5-dB steps to determine its ROC curve. Single frequency index performance was inferior to the other two (P < .05). Double and triple frequency indices were indistinguishable (P > .05). Two adjoining frequency elements with aITD ≥ 15 dB performed optimally for predicting tinnitus laterality (sensitivity = 0.59, specificity = 0.71, and PPV = 0.76). Absolute and relative magnitudes of hearing loss in the poorer ear were uncorrelated with tinnitus distress. An optimal audiometric asymmetry index to predict tinnitus laterality is one whereby 15 dB is the minimum aITD of two adjoining frequencies, inclusive of the maximal ITD. Tinnitus laterality dependency on magnitude of interaural asymmetry may inform design and interpretation of neuroimaging studies. Monaural acoustic tinnitus therapy may be an initial consideration for asymmetric hearing loss meeting the criterion of aITD ≥ 15 dB.

Asymmetric sensorineural hearing thresholds in the non‐noise‐exposed UK population: a retrospective analysis

To estimate the distribution of inter-aural sensorineural hearing threshold level differences in the non-noise-exposed adult population of the UK. A two-stage population study carried out in 1979-1986, initially by postal questionnaire, followed up in a proportion of participants by clinical and audiological examination. Volunteers (n = 48 313) initially selected at random from the electoral registers of four cities, subsequently selected at random from questionnaire respondents stratified by answers to questions about hearing. Inter-aural hearing threshold level differences measured audiometrically, as a function of age and gender. Tables of inter-aural threshold level differences provided as a resource with potential medicolegal, clinical and research applications. Based on the average of the frequencies 0.5, 1, 2 and 4 kHz, approximately 1% of the general UK population aged 18-80 years have an asymmetry of 15 dB or more. The prevalence is greater in older than in younger people. Inter-aural threshold differences greater than attributable to measurement error are not uncommon in the adult population, even after screening for conductive hearing loss and substantial noise exposure. They are typically of unknown origin.

Identification of predictors and development of a screening protocol for cerebello‐pontine lesions in patients presenting with audio‐vestibular dysfunction

Magnetic resonance imaging (MRI) scanning in the investigation of cerebellopontine angle lesions represents a finite resource, the use of which needs to be carefully rationalised. Our aim was to identify predictive factors that can distinguish between patients with and without cerebellopontine angle lesions, and develop a screening protocol which could be useful in the clinical setting as an aid to clinical judgment. Case-control study. Secondary care. Audio-vestibular features were collated on 136 patients (M : F 1.39 : 1) and 288 controls (M : F 1 : 1.1). Diagnostic by analysis of symptoms and audiometric data using logistic regression, receiver-operator characteristic curves and backwards elimination. Development of a predictive algorithm comprising those factors which are most strongly predictive of the presence of a cerebellopontine angle lesion. Positive predictors of a cerebellopontine angle lesion include the interaural threshold difference at 1 (P = 0.044) and 4 kHz (P = 0.034). The threshold in the better hearing ear at 0.25 kHz exerts a negative predictive (i.e. protective) effect (P = 0.005). The presence of tinnitus does not appear to influence the outcome on logistic regression. Although vertigo does exert an influence on the overall model, its impact is highly equivocal. We have identified audiometric factors which exert a positive and negative predictive influence on the presence of a cerebellopontine angle lesion, and audiovestibular symptoms which appear to exert little effect on the model. Our predictive equation represents a user-friendly standardised method of risk-stratification of patients within a general otolaryngology clinic.

Processing of interaural intensity differences in the LSO: role of interaural threshold differences.

Cells in the lateral superior olive (LSO) are known to be sensitive to interaural intensity differences (IIDs) in that they are excited by IIDs that favor the ipsilateral ear and inhibited by IIDs that favor the contralateral ear. For each LSO neuron there is a particular IID that causes a complete inhibition of discharges, and the IID of complete inhibition varies from neuron to neuron. This variability in IID sensitivity among LSO neurons is a key factor that allows for the coding of a variety of IIDs among the population of cells. A fundamental question concerning the coding of IIDs is: how does each cell in the LSO derive its particular IID sensitivity? Although there have been a large number of neurophysiological studies on the LSO, this question has received little attention. Indeed, the only reports that have directly addressed this question are those of Reed and Blum, who modeled the binaural properties of LSO neurons and proposed that the IID at which discharges are completely suppressed should correspond to the difference in threshold between the excitatory, ipsilateral and inhibitory, contralateral inputs that innervate each LSO cell. The main purpose of this study was to test the threshold difference hypothesis proposed by Reed and Blum by recording responses to monaural stimulation and to IIDs from single cells in the LSO of the mustache bat. Our results show that although the IID sensitivities of some LSO cells correspond to the difference in threshold between the excitatory and inhibitory ears, in the majority of cells the difference in thresholds did not correspond to the cell's IID sensitivity. The results lead us to propose two models to account for IID sensitivities. One model is similar to that proposed by Reed and Blum and emphasizes differences in the thresholds of the excitatory and inhibitory inputs. This model accounts for the minority of cells in which the IID of complete inhibition corresponded to the difference in threshold of the inputs from the two ears. The other model, which accounts for the cells in which the IID of complete inhibition did not correspond to the difference in the thresholds of the inputs from the two ears (the majority of cells), places emphasis on differences in latencies of the excitatory and inhibitory inputs. The models incorporate features that are concordant with the known properties of the neurons that project to the LSO and together can account for the diversity of IID sensitivities among the population of LSO neurons.

[Effect of inner ear hearing loss on delayed otoacoustic emissions (TEOAE) and distortion products (DPOAE)].

The assessment of inner ear hearing loss by means of evoked otoacoustic emissions (EOAE) is already established in practice. Nevertheless, empirical data on the relations between emission and audiologic parameters are required. EOAEs werde measured and analysed in 240 ears with sensorineural hearing loss (excluding cases with conductive and retrocochlear disorders) of 120 patients using ILO88/92 equipment with standard test conditions. Audiologic examination consisted of pure tone audiogram, tympanometry and auditory brainstem responses. The results of TEOAE (Transitory Evoked Otoacoustic Emissions), measured with clicks at 80 dB SPL, and DPOAE (Distortion Product Otoacoustic Emissions), measured with frequencies ranging from f2 = 1 kHz to 4 kHz at 70 dB SPL (L2 = L1, f2 = 1.2 f1), were compared to each other and to the hearing thresholds determined by subjective pure tone audiometry. A significant negative correlation is found between the amplitude of TEOAEs and the average hearing loss in the range of 0.5 to 4 kHz. Similarly, the amplitude of DPOAEs is significantly correlated to the hearing threshold encountered at the higher of the two stimulus frequencies. Nevertheless, the prediction of hearing loss from the response amplitude is not possible because of its large amplitude variations between individuals. The analysis of the relation between incidence of EOAEs and hearing loss shows that in ears exceeding a hearing loss of 34 +/- 4 dB (minimal value of subjective thresholds in the range 0.5 to 4 kHz) no TEOAEs can be registered. For DPOAEs, the responses disappear if the hearing loss at the higher stimulus frequency exceeds 47 +/- 3 dB (limits for 50% OAE incidence are given in both cases). In conclusion, the hearing thresholds of ears exhibiting DPOAEs but no TEOAEs are located between approximately 30 and 50 dB HL. The sharpness of the transition between clear responses and absent responses decreases with increasing age. Therefore, the combination of TEOAE and DPOAE recording with the purpose of hearing threshold assessment is especially useful in young patients. Further evaluation shows that male and female patients do not differ in the hearing loss dependent prevalence of otoacoustic emissions. On he other hand, a systematic but not significant influence of the audiogram shape on the parameters of the discrimination function can be observed: steep audiograms are described with a discrimination function, which drops to zero at higher levels of hearing loss and with a larger slope than shallow audiograms. The comparison of right and left ear emissions of the same patient shows that large amplitude differences occur even in cases of comparable subjective thresholds; missing emissions in one ear are observed if and only if the interaural threshold difference exceeds 30 dB.

Vascular Compression of the Eighth Cranial Nerve as a Cause of Vertigo.

Some patients have vertigo that is more or less constant, associated with varying degrees of nausea, and only relieved by bedrest. This disorder, named disabling positional vertigo (DPV), was found to be caused by a blood vessel or vessels compressing the eighth cranial nerve in its intracranial portion, and it can be relieved by microvascular decompression (MVD) of the nerve. Important in the differential diagnosis of DPV are a detailed history, the results of audiometry (10 to 15 dB interaural threshold difference or a small mid-frequency notch), acoustic middle ear reflex response testing (may be abnormal), and recordings of brainstem auditory evoked potentials (BAEP). BAEP in such cases show increased conduction time in the auditory nerve and/or prolonged latency of wave V recorded from the contralateral ear, possibly the result of brainstem compression. Abnormalities on vestibular testing often do not reflect the severity of the illness. Forty-one patients who underwent MVD to treat DPV in one year at the author's institution have been followed for 4.5 to 5.5 years. By self-evaluation, 20 had excellent and 10 good results of the operation. The success of this procedure is even higher today, since it was found that very small blood vessels, including veins, can cause DPV; thus all vessels touching the nerve are now managed. Complications of MVD are rare. The most frequent, hearing loss, occurred in only one patient in this series.

Binaural detection and discrimination for listeners with high-frequency sensorineural hearing losses

As part of a survey study of binaural performance, NoSπ detection thresholds and just-noticeable differences (jnd's) in interaural time delay (ITD) and interaural intensity difference (IID) were measured for listeners with high-frequency sensorineural hearing losses. Thresholds and jnd's were obtained with 1/3-oct noise bursts at 500 and 4000 Hz for a variety of interaural reference conditions, including ITDs and IIDs up to 600 μs and 46 dB. The present data for high-frequency hearing loss subjects show poorer than normal binaural performance even at 500 Hz, a region where auditory thresholds are normal; however, binaural detection and discrimination performance at 4000 Hz is generally poorer than at 500 Hz. This is in agreement with previously reported results [e.g., J. Koehnke and H. S. Colburn, J. Acoust. Soc. Am. Suppl. 1 81, S27 (1987)]. In cases with unilateral losses studied to date, the compensation for interaural threshold differences through appropriate choice of the reference interaural intensity differences does not improve binaural performance. [Work supported by NIH.]

Hearing loss in sports hunters exposed to occupational noise.

The hearing level of 133 railway workers who also hunted for sport was evaluated and compared with that of 82 non-hunting colleagues. Both groups were affected by hearing loss, mostly involving the high-frequency range. Hunters were found to differ from non-hunters by having significantly worse hearing threshold in the ear contralateral to the shoulder supporting the firearm. The interaural threshold difference at 4 kHz was related to the number of rounds fired and exposure duration, thus providing an estimate of the adverse effect of gunfire noise to which the hunters had been exposed.

Age categorization of high-frequency auditory threshold data.

This article presents high-frequency (8- to 20-kHz) auditory threshold measurements for 157 subjects with normal conventional hearing, ranging in age from 6-30 years. Normative descriptive data are provided in five semidecade age categories. Intra-age category mean and variance values for threshold sensitivity and interaural threshold differences are included. Generally, the data are consistent with the expectation of a gradual diminution of high-frequency sensitivity through the adolescent and early adult years. Several unresolved issues related to high-frequency normative data and clinical applicability of high-frequency threshold measurements are discussed.

A Clinical Procedure for Evaluating Auditory Localization

Auditory localization is an important aspect of general hearing ability, yet there is no generally accepted, routine clinical procedure for measuring this function. A test is presented in which the patient is seated in the center of an array of seven loudspeakers. His task is to identify which loudspeaker is the source of a recorded speech signal for each of 21 test items. This procedure was evaluated by testing a group of normal-hearing subjects once with both ear canals open and with one ear canal occluded. The occlusion of the ear canal induced a sufficient interaural threshold difference in the subjects that a reduction in auditory localization ability could be expected. The procedure discriminated well between unoccluded and occluded conditions. It shows promise for clinical use and warrants further clinical investigation.

Electrocochleographical Studies in Humans

Electrocochleographical studies were performed with the active electrode on the ear-drum. A close correspondence of the thresholds of 8th nerve action potentials (AP) and the subjective hearing thresholds was observed. The input-output curves of AP demonstrated L and H slopes. In persons with complete unilateral hearing losses no responses could be recorded from the deaf ear either to ipsilateral or contralateral sound stimulation. The effects of contralateral stimulation on AP were studied in persons with large interaural threshold differences. Two types of influences were described, the first being inhibitory and the second facilitatory. It has been suggested that the first effect depends on the reflex activity of the middle ear muscles, whereas the second effect should be attributed to the activity of auditory feed-back controlling system.

Bone-conduction threshold sensitivity in relation to mastoid sclerosis.

The effect of mastoid sclerosis on bone-conduction threshold sensitivity was assessed by retrospective comparison of audiologic data from 14 persons with unilateral mastoid sclerosis and 13 persons with normally pneumatized mastoids. All subjects with normal mastoids had unilateral sensorineural loss; most sclerotic mastoid subjects had normal hearing in the ear associated with a normally pneumatized mastoid and mixed or pure sensorineural loss on the sclerotic side. Mean interaural threshold differences and distributions of differences were similar for both groups. Sclerotic mastoids do not appear to have a significant effect on bone-conduction thresholds.

SOUND LOCALIZATION IN FREE FIELD AND INTERAURAL THRESHOLD DIFFERENCES.

It is a well known fact that the ability of locating sound sources by persons with normal hearing depends on the type of signal. It is moreover a fact that persons with unilateral deafness, at least to certain types of signals, lose the ability of sound localizing.Experiments were performed with the intention of making certain the relation between the ability of sound localization in the horisontal plane and the threshold difference between the two ears, one of which had normal hearing. The listeners with eliminated visual orientation were placed in different angular positions to the sound source in an anechoic chamber. Different types of signals were used. The results will be discussed in regard to a practical point of view.