Monaural Thresholds Research Articles

Effect of subject state on auditory brainstem response threshold using Kalman-weighted averaging

ObjectivesThis study aims to explore the impact of a subject's testing state on auditory brainstem response (ABR) thresholds using a novel ABR system (Vivosonic Integrity™), which incorporates Kalman-weighted averaging and bluetooth electrical isolation to address the limitation of conventional ABR limitation to obtain a stable result under non-sedated conditions, especially for infants and children. MethodTwenty-four adults (18–34 years old, 48 ears) with normal hearing were enrolled for ABR testing under three different states (lying quietly in the supine position or sleeping—lying; watching silent videos quietly in a seated position—sitting; and writing in a seated position—writing), which simulate the behaviors of young children most often encountered during non-sedated Kalman-weighted ABR testing in clinical practice. The click ABR (cABR) and tone-burst ABR (tbABR) thresholds (0.5, 1, 2, and 4 kHz) of each subject and the time taken to reach the monaural threshold for each kind of stimulus were recorded. Results(1) The cABR and tbABR thresholds were observed to increase in the following order: lying < sitting < writing. Significant threshold differences were found between any two states, except for between the sitting and lying states for the cABR and between sitting and writing for the 0.5 kHz tbABR. (2) The time required for cABR testing in the writing state was significantly longer than that in the lying and sitting states. The time required for 1 and 4 kHz tbABR testing in the lying state was significantly shorter than that in the sitting or writing state. For 2 KHz tbABR, only testing time under writing was significantly longer than that under lying. There were no significant differences in the time used for 0.5 kHz tbABR testing among different states. ConclusionsDifferent testing states have significant impacts on the thresholds of ABRs using Kalman-weighted averaging. A subject's state during ABR testing warrants consideration, and normal levels and correction values to estimate the hearing threshold from the ABR threshold should be determined for different testing states.

Evaluating tests of binaural hearing for hearing impaired listeners using a portable device

Individuals with sensorineural hearing loss may have similar monaural thresholds (i.e., pure tone audiogram) but perform quite differently on tests of speech-in-noise. Additional testing using complex, binaural signals may be able to differentiate individuals with similar pure-tone hearing. Here, individuals with mild-to-moderate hearing losses were evaluated using tests of spectral, temporal, and spectrotemporal modulation, diotic and dichotic frequency modulation, gap detection, 2 kHz tone-in-noise, and spatial release from masking. Binaural psychoacoustic measurements were evaluated on an iPad using the Portable Automated Rapid Test (PART) app. Normal hearing listeners were evaluated as controls. Normal hearing results were similar to normative data previously collected by Lelo de Larrea-Mancera and colleagues (2020) and hearing-impaired results were elevated for most binaural measurements evaluated compared to normal hearing controls. Binaural psychoacoustic data were successfully measured for individuals with mild-to-moderate amounts of hearing loss using a portable system. Results show that evaluating complex stimuli on clinical populations using a portable device is feasible. Additionally, if accomplished on a larger scale the current test battery may likely add useful information on how hearing-impaired listeners process complex binaural stimuli and could compliment current clinical diagnostic test battery and, potentially, guide hearing aid fittings.

Auditory Processing Disorder: Is The Diagnosis Already Possible In First Graders?

Significant differences in performance on an eclectic German test battery for Auditory Processing Disorders (APD) was found in the most diagnostic tools between children with APD and controls in the 2nd, 3rd and 4th school year of primary education. Aim of the present study was to examine whether it is also the case for first graders. The performance in the behavioral test battery (including 14 specific auditory tests) was compared in two subject groups (aged 6-8 yrs): 41 first graders with APD of a clinical database, 37 typically developing first graders without APD (controls). Significant mean group differences were detected in the performance on 12 of 14 tests, because children with APD showed lower scores (excepted from two PaTsy-subtests: sound frequencies; sound intensities). The significance concerning the monaural threshold values narrowly retained statistical significance with Bonferroni correction. The controls mastered the PaTsy-subtests only in 86-89 % of all cases, children with APD in 73-83 %. The test scores of both boys and girls with APD were lower than those of their peers without APD. First graders with versus without APD could be significantly distinguished. Generally, there was seen a trend that in first graders the same performance was reduced as in elementary school pupils of higher grade level. For use in clinical diagnosis of APD, nonverbal auditory tests for the investigated specific age segment appears debatable.

Relating age and hearing loss to monaural, bilateral, and binaural temporal sensitivity.

Older listeners are more likely than younger listeners to have difficulties in making temporal discriminations among auditory stimuli presented to one or both ears. In addition, the performance of older listeners is often observed to be more variable than that of younger listeners. The aim of this work was to relate age and hearing loss to temporal processing ability in a group of younger and older listeners with a range of hearing thresholds. Seventy-eight listeners were tested on a set of three temporal discrimination tasks (monaural gap discrimination, bilateral gap discrimination, and binaural discrimination of interaural differences in time). To examine the role of temporal fine structure in these tasks, four types of brief stimuli were used: tone bursts, broad-frequency chirps with rising or falling frequency contours, and random-phase noise bursts. Between-subject group analyses conducted separately for each task revealed substantial increases in temporal thresholds for the older listeners across all three tasks, regardless of stimulus type, as well as significant correlations among the performance of individual listeners across most combinations of tasks and stimuli. Differences in performance were associated with the stimuli in the monaural and binaural tasks, but not the bilateral task. Temporal fine structure differences among the stimuli had the greatest impact on monaural thresholds. Threshold estimate values across all tasks and stimuli did not show any greater variability for the older listeners as compared to the younger listeners. A linear mixed model applied to the data suggested that age and hearing loss are independent factors responsible for temporal processing ability, thus supporting the increasingly accepted hypothesis that temporal processing can be impaired for older compared to younger listeners with similar hearing and/or amounts of hearing loss.

Lateralized enhancement of auditory cortex activity and increased sensitivity to self-generated sounds.

Performing actions with auditory consequences modulates the response in auditory cortex to otherwise identical stimuli passively heard. Such modulation has been suggested to occur through a corollary discharge sent from the motor cortex during voluntary actions. However, the relationship between the effector used to generate the sound, type of modulation and changes in perceptual sensitivity are unclear. Here we use functional magnetic resonance imaging on healthy subjects and demonstrate bilateral enhancement in the auditory cortex to self-generated versus externally generated sounds. Furthermore, we find that this enhancement is stronger when the sound-producing hand is contralateral to the auditory cortex. At the behavioural level, binaural hearing thresholds are lower for self-generated sounds and monaural thresholds are lower for sounds triggered by the hand ipsilateral to the stimulated ear. Together with functional connectivity analysis, our results suggest that a corollary discharge sent from active motor cortex enhances activity in the auditory cortex and increases perceptual sensitivity in a lateralized manner.

Coincidence detection in the medial superior olive: mechanistic implications of an analysis of input spiking patterns.

Coincidence detection by binaural neurons in the medial superior olive underlies sensitivity to interaural time difference (ITD) and interaural correlation (ρ). It is unclear whether this process is akin to a counting of individual coinciding spikes, or rather to a correlation of membrane potential waveforms resulting from converging inputs from each side. We analyzed spike trains of axons of the cat trapezoid body (TB) and auditory nerve (AN) in a binaural coincidence scheme. ITD was studied by delaying “ipsi-” vs. “contralateral” inputs; ρ was studied by using responses to different noises. We varied the number of inputs; the monaural and binaural threshold and the coincidence window duration. We examined physiological plausibility of output “spike trains” by comparing their rate and tuning to ITD and ρ to those of binaural cells. We found that multiple inputs are required to obtain a plausible output spike rate. In contrast to previous suggestions, monaural threshold almost invariably needed to exceed binaural threshold. Elevation of the binaural threshold to values larger than 2 spikes caused a drastic decrease in rate for a short coincidence window. Longer coincidence windows allowed a lower number of inputs and higher binaural thresholds, but decreased the depth of modulation. Compared to AN fibers, TB fibers allowed higher output spike rates for a low number of inputs, but also generated more monaural coincidences. We conclude that, within the parameter space explored, the temporal patterns of monaural fibers require convergence of multiple inputs to achieve physiological binaural spike rates; that monaural coincidences have to be suppressed relative to binaural ones; and that the neuron has to be sensitive to single binaural coincidences of spikes, for a number of excitatory inputs per side of 10 or less. These findings suggest that the fundamental operation in the mammalian binaural circuit is coincidence counting of single binaural input spikes.

Towards a unifying basis of auditory thresholds: binaural summation.

Absolute auditory threshold decreases with increasing sound duration, a phenomenon explainable by the assumptions that the sound evokes neural events whose probabilities of occurrence are proportional to the sound's amplitude raised to an exponent of about 3 and that a constant number of events are required for threshold (Heil and Neubauer, Proc Natl Acad Sci USA 100:6151-6156, 2003). Based on this probabilistic model and on the assumption of perfect binaural summation, an equation is derived here that provides an explicit expression of the binaural threshold as a function of the two monaural thresholds, irrespective of whether they are equal or unequal, and of the exponent in the model. For exponents >0, the predicted binaural advantage is largest when the two monaural thresholds are equal and decreases towards zero as the monaural threshold difference increases. This equation is tested and the exponent derived by comparing binaural thresholds with those predicted on the basis of the two monaural thresholds for different values of the exponent. The thresholds, measured in a large sample of human subjects with equal and unequal monaural thresholds and for stimuli with different temporal envelopes, are compatible only with an exponent close to 3. An exponent of 3 predicts a binaural advantage of 2 dB when the two ears are equally sensitive. Thus, listening with two (equally sensitive) ears rather than one has the same effect on absolute threshold as doubling duration. The data suggest that perfect binaural summation occurs at threshold and that peripheral neural signals are governed by an exponent close to 3. They might also shed new light on mechanisms underlying binaural summation of loudness.

Can monaural temporal masking asymmetry explain the transient and/or ongoing precedence effect?

Investigations of the precedence effect show that interaural differences within the first of two pairs of brief binaural sounds contribute more to lateralization than those within the second pair. The present study asked whether this phenomenon could be explained by asymmetries in monaural masking, and compared the results to a second experiment investigating the same question with the “ongoing” precedence effect. Leading and lagging stimuli were binaural pairs of 1-ms frozen noise bursts, with a 2-ms delay between pairs, and had ITDs of +500 and −500 ms, respectively. Detection thresholds for lead or lag in the presence of the other were assessed monaurally using a 4AFC task. Results showed that threshold for the lead was 12 dB better than that for the lag, on average. Ongoing stimuli were created by repeating the transient stimuli 63 times, with a new noise token on each repeat. Although the leading burst in each binaural pair contributes more to lateralization than the lagging burst, monaural thresholds for the leading bursts were not better than those for the lagging bursts. The results suggest that the transient precedence effect, but not the ongoing precedence effect, might be explained by temporal masking asymmetry. [Work supported by NIH DC01625].

Monaural and binaural aerial hearing thresholds in a California sea lion (Zalophus californianus)

Though studies have focused on some aspects of binaural hearing in otariid pinnipeds, none have directly measured monaural hearing thresholds. Recent auditory evoked potential (AEP) testing with a young male California sea lion suggested that hearing threshold differences potentially existed between the subject's two ears. To further investigate these findings, aerial psychophysical audiograms were collected for this sea lion. Using headphones to deliver stimuli, monaural and binaural thresholds were measured at seven frequencies from 0.5 to 32 kHz in one-octave steps. The binaural and two monaural (left and right ears) psychophysical audiograms were all similar in that they had the typical mammalian U-shape, with peak sensitivity from 8 to 16 kHz. The right ear showed generally elevated psychophysical thresholds when compared to the left, although all differences were less than 7 dB. The psychophysical and AEP audiograms were similar in terms of shape; however, the directions of monaural threshold differences determined with AEP methods were not always consistent with those obtained using psychophysical methods. [Work supported by ONR.]

Psychoacoustic Tests for Central Auditory Processing: Normative Data

The comprehension of spoken language is based on the analysis of complex acoustic signals by the central auditory system, Direct relationships between gradual, spectrotemporal modifications of speech sounds and the impairment of the comprehension of such altered sounds have been found in many psychophysical studies. Thus, it is reasonable to assume that deficits in the understanding of speech seen in patients with acquired brain lesions may, to a certain degree, result from impaired central processing of acoustic signals. We report normative data collected from 94 young normal-hearing subjects on a battery of psychoacoustic tests designed to evaluate signal processing at different levels of the central auditory system. Monaural pure tone thresholds were used to evaluate the performance of peripheral hearing. The integrity of auditory brainstem processing was evaluated by quantifying masking level difference (MLD) values and gap detection (GD) thresholds. Three monaural speech tests (time-compressed speech [CS], filtered speech [FS] and speech in noise [SIN]) were conducted to evaluate the processing of distorted speech materials by cortical auditory processing mechanisms. Evaluating performance of naïve, young normal-hearing subjects, as we did here, is indispensable for (a) evaluating the effectiveness of potential tests, (b) evaluating their suitability for the examination of patients, and (c) the revision and further development of central auditory tests.

Fine‐structure processing, frequency selectivity and speech perception in hearing‐impaired listeners

Hearing‐impaired people often experience great difficulty with speech communication when background noise is present, even if reduced audibility has been compensated for. Other impairment factors must be involved. In order to minimize confounding effects, the subjects participating in this study consisted of groups with homogeneous, symmetric audiograms. The perceptual listening experiments assessed the intelligibility of full‐spectrum as well as low‐pass filtered speech in the presence of stationary and fluctuating interferers, the individual's frequency selectivity and the integrity of temporal fine‐structure processing. The latter was addressed in a binaural and a monaural experiment. In the binaural experiment, the lateralization threshold was measured for low‐frequency tones with ongoing interaural phase delays. In the monaural experiment, detection thresholds for low‐rate frequency modulation were obtained. In addition, these binaural and monaural thresholds were measured in a stationary background noise in order to assess the persistence of the fine‐structure processing to interfering noise. Apart from elevated speech reception thresholds, the hearing impaired listeners showed poorer performance than the normally hearing in terms of frequency selectivity and fine‐structure processing, despite normal audiometric thresholds at the test frequencies. However, the binaural fine‐structure processing was not found to be particularly vulnerable to interfering noise in these listeners.

Forward-masked monaural and interaural intensity discrimination

Intensity-discrimination thresholds were measured for a 25-ms, 6-kHz pure tone for pedestal levels from 40 to 90 dB sound pressure level (SPL) with and without a forward masker (100-ms narrowband Gaussian noise, N(0)=70 dB). When the masker was present, the masker and probe were separated by 100 ms of silence. Unmasked and masked thresholds were measured in a two-interval monaural procedure and, separately, in a single-interval interaural procedure in which the pedestal and incremented pedestals were presented simultaneously to opposite ears. While the monaural thresholds were elevated markedly by the forward masker for mid-level pedestals, interaural thresholds were nearly unaffected by the masker across pedestal levels. The results argue against the notion that the monaural elevation in forward-masked thresholds is due to degraded encoding of intensity information at early stages of auditory processing.

Comparing monaural and interaural temporal windows: Effects of a temporal fringe on sensitivity to intensity differences

In an effort to provide a unifying framework for understanding monaural and binaural processing of intensity differences, an experiment was performed to assess whether temporal weighting functions estimated in two-interval monaural intensity-discrimination tasks could account for data in single-interval interaural intensity-discrimination tasks. In both tasks, stimuli consisted of a 50-ms burst of noise with a 5-ms probe segment at temporal positions ranging between the onset and offset of the overall stimulus. During the probe segment, one monaural interval or binaural channel of each trial contained an intensity increment and the other contained a decrement. Listeners were instructed to choose the interval/channel containing the increment. The pattern of monaural thresholds was roughly symmetrical (an inverted U) across temporal position of the probe but interaural thresholds were substantially higher for a brief time interval following stimulus onset. A two-sided exponential temporal window fit to the monaural data accounted for the interaural data well when combined with a post-onset-weighting function that described greatest weighting of binaural information at stimulus onset. A second experiment showed that the specific procedure used in measuring fringed interaural-intensity-difference-discrimination thresholds affects thresholds as a function of fringe duration and influences the form of the best-fitting post-onset-weighting function.

Monaural and interaural intensity discrimination: level effects and the "binaural advantage".

This study examined whether the level effects seen in monaural intensity discrimination (Weber's law and the "near miss") in a two-interval task are also observed in discrimination of interaural intensity differences (IIDs) in a single-interval task. Both tasks were performed for various standard levels of 4-kHz pure tones and broadband noise. The Weber functions (10 log deltaI/I versus I in dB) in the monaural and binaural conditions were parallel. For noise, the Weber functions had slopes close to zero (Weber's law) while the Weber functions for the tones had a mean slope of -0.089 (near miss). The near miss for the monaural and binaural tasks with tones was eliminated when a high-pass masker was gated with the listening intervals. The near-miss was also observed for 250- and 1000-Hz tones in the binaural task despite overall decreased sensitivity to changes in IID at 1000 Hz. The binaural thresholds showed a small (about 2-dB) advantage over monaural thresholds only in the broadband noise conditions. More important, however, is the fact that the level effects seen monaurally are also seen binaurally. This suggests that the basic mechanisms responsible for Weber's law and the near miss are common to monaural and binaural processing.

Level effects in monaural and interaural intensity discrimination

Discrimination of interaural level differences (ILDs) is often assessed using a two-interval task in which ILD changes between intervals. In such a situation, overall level is usually roved in order to minimize monaural cues. This roving makes it difficult to assess level-dependent effects. In the present experiment, monaural intensity discrimination in a 2IFC task was compared to ILD discrimination in a single-interval task, thus producing an analogous situation in terms of number of ‘‘observations’’ and eliminating the need for an overall level rove. Monaural intensity DLs and ILD discrimination thresholds were measured as a function of level for 4-kHz tones and for broadband noise. The Weber functions (10&amp;lt;th&amp;gt;logΔI/I vs I in dB) in the monaural and binaural conditions were parallel. For the noise the Weber functions had slopes close to zero (Weber’s law); for the tones the slopes were −0.082 (near-miss to Weber’s law). Overall, the binaural thresholds showed a small, approximately 2 dB, advantage over the monaural thresholds. The important aspect, however, is that the level effects seen monaurally are also seen binaurally. This suggests that the basic processes responsible for Weber’s law and the near-miss occur prior to binaural interaction. [Work supported by NIDCD DC05343 and DC00683.]

A Case Study of Partial Agenesis of the Corpus Callosum: Audiological Implications

This case study presents four and a half years of audiological observations, testing and aural habilitation of a female child with a partial agenesis of the corpus callosum (ACC). The ACC was diagnosed by MRI scan performed at 6 months of age to eliminate neurological causes for the developmental delay. This child was also born with a cleft palate and was diagnosed with Robinow Syndrome at 3 years and 3 months of age. The audiological results showed an improvement in hearing thresholds over the 4-year period. The child’s ophthalmologist also reported an improvement in visual skills over time. The most interesting aspect of the child’s hearing was the discrepancy between the monaural and the binaural results. That is, when assessed binaurally she often presented with a mild to moderate mixed loss and, when assessed monaurally, she showed a moderate to severe mixed loss for the right ear and a severe mixed loss for the left ear. Over time, the discrepancy between the monaural and binaural results changed. When assessed binaurally, the loss decreased to normal low frequency hearing sloping to a mild high frequency loss. When assessed monaurally, the most recent results showed a mild loss for the right ear and a moderate loss for the left ear. This discrepancy between binaural and monaural results was evident for both aided and unaided tests. For the most recent thresholds, the binaural results were consistent with the right monaural thresholds for the first time over the four and a half years. Parental reports of the child’s hearing were consistent with the binaural clinical results. This case indicates the need for audiologists to (1) carefully monitor the hearing of children with ACC, (2) obtain monaural and binaural hearing and aided thresholds results, and (3) compare these children’s functional abilities with the objective test results obtained. This case does question whether hearing aids are appropriate for children with ACC. If hearing aids are deemed to be appropriate, then hearing aids with compression characteristics should be considered.

Detection of amplitude modulation and discrimination of interaural differences in modulation phase for high-frequency carriers

Using a 4-kHz pure-tone carrier and modulation frequencies (fm) of 2–512 Hz, thresholds for monaural detection of sinusoidal amplitude modulation (SAM) were measured, as were threshold modulation depths for the discrimination of interaurally in-phase and out-of-phase SAM envelopes. For one listener, interaural differences in envelope phase for fm up to 256 Hz were discriminable at modulation depths (m) for which the monaural modulation itself was just detectable, and all monaural and binaural thresholds were within a range of 5 dB (20 log m) across fm. For a second listener, binaural thresholds increased more rapidly with increasing fm than monaural thresholds. Another experiment examined the notion that interaurally delayed SAM envelopes are processed as time-varying interaural level differences. In this task, listeners discriminated interaurally in-phase SAM envelopes from SAM envelopes carrying a fixed interaural phase difference (IPD). Threshold m was measured for several fm and IPD combinations. For a given IPD, thresholds were either constant or decreased with increasing fm. The data suggest that dynamically varying interaural level differences are the cue to discrimination at low fm, while the fixed interaural time difference is the likely cue at high fm. [Work supported by NIDCD DC00683.]

Frequency selective effects of alcohol on auditory detection and frequency discrimination thresholds.

In the first of two experiments, the effects of ethyl alcohol on monaural and binaural thresholds for pure tones were measured for a range of frequencies. The results showed a frequency-specific effect in which low frequencies were more severely affected than higher ones. Also, monaural thresholds tended to be more affected by alcohol than binaural ones. The second experiment extended this exploration by measuring frequency discrimination at several different frequencies. In this case, we also obtained a frequency-dependent effect: the increase in discrimination thresholds above 1000 Hz was three times greater than that for lower frequencies. The data suggest that the choice of stimuli may influence the ability to detect changes in auditory performance after alcohol and may account in part for the differences among earlier studies. The results are consistent with the hypothesis that alcohol is acting centrally, at the level of mechanisms involved in the temporal and binaural summation of auditory signals, rather than influencing peripheral structures.

Effect of audiometric test room noise on monaural and binaural thresholds

This study determined if the maximum permissible ambient noise levels (MPANLs) for audiometry specified in the revision of ANSI S3.1-199x provided the same amount of threshold shift for monaural and binaural listening. Sound-field monaural and binaural warble-tone thresholds (125–8000 Hz) were obtained on 24 normal-hearing subjects in quiet (ambient) and in two background noise conditions. One noise condition approximated the ANSI S3.1-199x ears not covered MPANLs (ANSI noise). The other noise condition was 20 dB higher than the ANSI MPANLs (ANSI noise + 20). Monaural thresholds were about 2 dB higher than binaural thresholds in quiet and in each noise condition. The difference between the monaural minus the binaural threshold shifts in each noise condition (ANSI noise + 20 minus ambient; ANSI noise minus ambient) averaged over frequency was typically less than 1 dB. Thus the MPANLs in the revision of ANSI S3.1-199x are appropriate for both monaural and binaural testing.

Individual differences in sensitivity to interaural disparities of time and of level

The sensitivities of 22 women and 23 men to interaural temporal differences (ITDs) in low-frequency noise bursts and interaural level differences (ILDs) in high-frequency noise bursts were measured in discrimination and absolute judgment tasks. The discrimination abilities of both groups of observers were symmetrical in that there were no differences in performance between interaural disparities favoring either the right or the left ear. The women were somewhat less sensitive and more variable in their performances than were the men in both the temporal and level difference discrimination tasks. However, the mean differences between the sexes, 28 μs and 0.9 dB, were not large compared with the variability across individuals. Individuals who performed well-discriminating ILDs also performed well with ITDs. Many observers exhibited ILD subjective midlines which were offset to the left of objective center in the absolute judgement task. This effect was unrelated to ILD discrimination ability, to monaural thresholds, or to absolute judgements based on ITDs.