Short-latency transient-evoked otoacoustic emissions as predictors of hearing status and thresholds

The Origin Along the Cochlea of Otoacoustic Emissions Evoked by Mid-Frequency Tone Pips

PURPOSE

Tone-pip-evoked otoacoustic emissions (PEOAEs) are transient-evoked otoacoustic emissions (OAEs) that are hypothesized to originate from reflection of energy near the best-frequency (BF) cochlear place of the stimulus frequency. However, individual PEOAEs have energy with a wide range of delays. We sought to determine whether some PEOAE energy is consistent with having been generated far from BF.

METHODS

PEOAEs from 35 and 47 dB SPL tone pips were obtained by removing pip-stimulus energy by subtracting the ear-canal sound pressure from scaled-down 59 dB SPL tone pips (which evoke relatively small OAEs). PEOAE delays were measured at each peak in the PEOAE absolute-value waveforms. While measuring PEOAEs and auditory-nerve compound action potentials (CAPs), amplification was blocked sequentially from apex to base by cochlear salicylate perfusion. The perfusion time when a CAP was reduced identified when the perfusion reached the tone-pip BF place. The perfusion times when each PEOAE peak was reduced identified where along the cochlea it received cochlear amplification. PEOAEs and CAPs were measured simultaneously using one pip frequency in each ear (1.4 to 4 kHz across 16 ears).

RESULTS

Most PEOAE peaks received amplification primarily between the BF place and 1-2 octaves basal of the BF place. PEOAE peaks with short delays received amplification basal of BF place. PEOAE peaks with longer delays sometimes received amplification apical of BF place, consistent with previous stimulus-frequency-OAE results.

CONCLUSION

PEOAEs provide information about cochlear amplification primarily within ~ 1.5 octave of the tone-pip BF place, not about regions > 3 octaves basal of BF.

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

OBJECTIVES

This study aims to develop deep learning (DL) models for the quantitative prediction of hearing thresholds based on stimulus-frequency otoacoustic emissions (SFOAEs) evoked by swept tones.

DESIGN

A total of 174 ears with normal hearing and 388 ears with sensorineural hearing loss were studied. SFOAEs in the 0.3 to 4.3 kHz frequency range were recorded using linearly swept tones at a rate of 2 Hz/msec, with stimulus level changing from 40 to 60 dB SPL in 10 dB steps. Four DL models were used to predict hearing thresholds at octave frequencies from 0.5 to 4 kHz. The models-a conventional convolutional neural network (CNN), a hybrid CNN-k-nearest neighbor (KNN), a hybrid CNN-support vector machine (SVM), and a hybrid CNN-random forest (RF)-were individually built for each frequency. The input to the DL models was the measured raw SFOAE amplitude spectra and their corresponding signal to noise ratio spectra. All DL models shared a CNN-based feature self-extractor. They differed in that the conventional CNN utilized a fully connected layer to make the final regression decision, whereas the hybrid CNN-KNN, CNN-SVM, and CNN-RF models were designed by replacing the last fully connected layer of CNN model with a traditional machine learning (ML) regressor, that is, KNN, SVM, and RF, respectively. The model performance was evaluated using mean absolute error and SE averaged over 20 repetitions of 5 × 5 fold nested cross-validation. The performance of the proposed DL models was compared with two types of traditional ML models.

RESULTS

The proposed SFOAE-based DL models resulted in an optimal mean absolute error of 5.98, 5.22, 5.51, and 6.06 dB at 0.5, 1, 2, and 4 kHz, respectively, superior to that obtained by the traditional ML models. The produced SEs were 8.55, 7.27, 7.58, and 7.95 dB at 0.5, 1, 2, and 4 kHz, respectively. All the DL models outperformed any of the traditional ML models.

CONCLUSIONS

The proposed swept-tone SFOAE-based DL models were capable of quantitatively predicting hearing thresholds with satisfactory performance. With DL techniques, the underlying relationship between SFOAEs and hearing thresholds at disparate frequencies was explored and captured, potentially improving the diagnostic value of SFOAEs.

Model-based prediction of otoacoustic emission level, noise level, and signal-to-noise ratio during time-synchronous averaging

Although averaging is effective in reducing noise, its efficiency rapidly decreases beyond several hundred averages. Depending on environmental and patient noise levels, several hundred averages may be insufficient for informed clinical decision making. The predictable nature of the otoacoustic emission (OAE) and noise during time-synchronous averaging implicates the use of predictive modeling as an alternative to increased averaging when noise is high. Click-evoked OAEs were measured in 98, normal-hearing subjects. Average OAE and noise levels were calculated for subsets of the total number of averages and then fit using variants of a power function. The accuracy of the models was quantified as the difference between the measured value and model output. Models were used to predict the OAE signal-to-noise ratio (SNR) for a criterion noise level. Based on predictions, the OAE was categorized as present or absent. Model-based decisions were compared to decisions from direct measurements. Model accuracy improved as the number of averages (and SNR in the case of OAEs) from which the model was derived increased. Model-based classifications permitted correct categorization of the OAE status from fewer averages than measurement-based classifications. Furthermore, model-based predictions resulted in fewer false positives (i.e., absent OAE despite normal hearing).

Medial Olivocochlear Reflex Strength in Ears With Low-to-Moderate Annual Noise Exposure

PURPOSE

Studies in lower mammals demonstrate enhancement of the medial olivocochlear reflex (MOCR) following noise exposure. A similar effect may occur in humans, and there is some evidence of an individual's acoustic history affecting the MOCR. The current work evaluates the relationship between an individual's annual noise exposure history and their MOCR strength. Given the potential role of the MOCR as a biological hearing protector, it is important to identify factors associated with MOCR strength.

METHOD

Data were collected from 98 normal-hearing young adults. Annual noise exposure history was estimated using the Noise Exposure Questionnaire. MOCR strength was assayed using click-evoked otoacoustic emissions (CEOAEs) measured with and without noise presented to the contralateral ear. MOCR metrics included the MOCR-induced otoacoustic emission (OAE) magnitude shift and phase shift. A CEOAE signal-to-noise ratio (SNR) of at least 12 dB was required for estimation of the MOCR metrics. Linear regression was applied to evaluate the relationship between MOCR metrics and annual noise exposure.

RESULTS

Annual noise exposure was not a statistically significant predictor of the MOCR-induced CEOAE magnitude shift. However, annual noise exposure was a statistically significant predictor of the MOCR-induced CEOAE phase shift-the MOCR-induced phase shift decreased with increasing noise exposure. Additionally, annual noise exposure was a statistically significant predictor of OAE level.

CONCLUSIONS

Findings contrast with recent work that suggests MOCR strength increases with annual noise exposure. Compared with previous work, data for this study were collected using more stringent SNR criteria, which is expected to increase the precision of the MOCR metrics. Additionally, data were collected for a larger subject population with a wider range of noise exposures. Whether findings generalize to other exposure durations and levels is unknown and requires future study.

Joint Profile Characteristics of Long-Latency Transient Evoked and Distortion Otoacoustic Emissions

PURPOSE

In clinical practice, otoacoustic emissions (OAEs) are interpreted as either "present" or "absent." However, OAEs have the potential to inform about etiology and severity of hearing loss if analyzed in other dimensions. A proposed method uses the nonlinear component of the distortion product OAEs together with stimulus frequency OAEs to construct a joint reflection-distortion profile. The objective of the current study is to determine if joint reflection-distortion profiles can be created using long-latency (LL) components of transient evoked OAEs (TEOAEs) as the reflection-type emission.

METHOD

LL TEOAEs and the nonlinear distortion OAEs were measured from adult ears. Individual input-output (I/O) functions were created, and OAE level was normalized by dividing by the stimulus level yielding individual gain functions. Peak strength, compression threshold, and OAE level at compression threshold were derived from individual gain functions to create joint reflection-distortion profiles.

RESULTS

TEOAEs with a poststimulus window starting at 6 ms had I/O functions with compression characteristics similar to LL TEOAE components. The model fit the LL gain functions, which had R ² > .93, significantly better than the nonlinear distortion OAE gain functions, which had R ² = .596-.99. Interquartile ranges for joint reflection-distortion profiles were larger for compression threshold and OAE level at compression threshold but smaller for peak strength than those previously published.

CONCLUSIONS

The gain function fits LL TEOAEs well. Joint reflection-distortion profiles are a promising method that could enhance diagnosis of hearing loss, and use of the LL TEOAE in the profile for peak strength may be important because of narrow interquartile ranges.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.20323593.

Contralateral noise effects on otoacoustic emissions and electrophysiologic responses in normal-hearing adults

Contralateral noise inhibits the amplitudes of cochlear and neural responses. These measures may hold potential diagnostic utility. The medial olivocochlear (MOC) reflex underlies the inhibition of cochlear responses but the extent to which it contributes to inhibition of neural responses remains unclear. Mertes and Leek [J. Acoust. Soc. Am. 140, 2027-2038 (2016)] recently examined contralateral inhibition of cochlear responses [transient-evoked otoacoustic emissions (TEOAEs)] and neural responses [auditory steady-state responses (ASSRs)] in humans and found that the two measures were not correlated, but potential confounds of older age and hearing loss were present. The current study controlled for these confounds by examining a group of young, normal-hearing adults. Additionally, measurements of the auditory brainstem response (ABR) were obtained. Responses were elicited using clicks with and without contralateral broadband noise. Changes in TEOAE and ASSR magnitude as well as ABR wave V latency were examined. Results indicated that contralateral inhibition of ASSRs was significantly larger than that of TEOAEs and that the two measures were uncorrelated. Additionally, there was no significant change in wave V latency. Results suggest that further work is needed to understand the mechanism underlying contralateral inhibition of the ASSR.

Distortion Product Otoacoustic Emission Component Behavior as a Function of Primary Frequency Ratio and Primary Level

OBJECTIVES

Distortion product otoacoustic emissions (DPOAEs) are composed of distortion and reflection components. Much is known about the influence of the stimulus frequency ratio (f 2 /f 1 ) on the overall/composite DPOAE level. However, the influence of f 2 /f 1 on individual DPOAE components is not as well examined. The goals of this pilot study were to systematically evaluate the effects of f 2 /f 1 on DPOAE components in clinically normal-hearing young adult ears. To extend the limited reports in the literature, this examination was carried out over an extended frequency range using two stimulus-level combinations.

DESIGN

DPOAEs were recorded from seven normal-hearing, young adult ears for f 2 frequencies between 0.75 and 16 kHz over a range of f 2 /f 1 using two stimulus-level combinations. The distortion (DPOAE D ) and reflection (DPOAE R ) components were separated using an inverse fast Fourier transform algorithm. Optimal ratios for the composite DPOAE and DPOAE components were determined from smoothed versions of level versus ratio functions in each case.

RESULTS

The optimal ratio for the composite DPOAE level increased with stimulus level and decreased as a function of frequency above 1 kHz. The optimal ratios for the DPOAE components followed a similar trend, decreasing with increasing frequency. The optimal ratio for DPOAE D was generally higher than that for DPOAE R . The overall level for DPOAE D was greater than that of DPOAE R , both decreasing with increasing frequency. DPOAE R , but not DPOAE D , became unrecordable above the noise floor at the higher frequencies.

CONCLUSIONS

DPOAE components behave similarly but not identically as a function of f 2 /f 1 . The ear canal DPOAE is generally dominated by DPOAE D . The behavior of DPOAE D as a function of f 2 /f 1 is entirely consistent with known properties of cochlear mechanics. The behavior of DPOAE R is more variable across ears, perhaps reflective of the increased number of parameters that influence its final form. Attempting to use an f 2 /f 1 that would allow a greater bias of the ear canal DPOAE toward one component or the other does not appear to be practical.

Objective Assessment System for Hearing Prediction Based on Stimulus-Frequency Otoacoustic Emissions

Stimulus-frequency otoacoustic emissions (SFOAEs) can be useful tools for assessing cochlear function noninvasively. However, there is a lack of reports describing their utility in predicting hearing capabilities. Data for model training were collected from 245 and 839 ears with normal hearing and sensorineural hearing loss, respectively. Based on SFOAEs, this study developed an objective assessment system consisting of three mutually independent modules, with the routine test module and the fast test module used for threshold prediction and the hearing screening module for identifying hearing loss. Results evaluated via cross-validation show that the routine test module and the fast test module predict hearing thresholds with similar performance from 0.5 to 8 kHz, with mean absolute errors of 7.06–11.61 dB for the routine module and of 7.40–12.60 dB for the fast module. However, the fast module involves less test time than is needed in the routine module. The hearing screening module identifies hearing status with a large area under the receiver operating characteristic curve (0.912–0.985), high accuracy (88.4–95.9%), and low false negative rate (2.9–7.0%) at 0.5–8 kHz. The three modules are further validated on unknown data, and the results are similar to those obtained through cross-validation, indicating these modules can be well generalized to new data. Both the routine module and fast module are potential tools for predicting hearing thresholds. However, their prediction performance in ears with hearing loss requires further improvement to facilitate their clinical utility. The hearing screening module shows promise as a clinical tool for identifying hearing loss.

Medial olivocochlear reflex effects on amplitude growth functions of long- and short-latency components of click-evoked otoacoustic emissions in humans

Functional outcomes of medial olivocochlear reflex (MOCR) activation, such as improved hearing in background noise and protection from noise damage, involve moderate to high sound levels. Previous noninvasive measurements of MOCR in humans focused primarily on otoacoustic emissions (OAEs) evoked at low sound levels. Interpreting MOCR effects on OAEs at higher levels is complicated by the possibility of the middle-ear muscle reflex and by components of OAEs arising from different locations along the length of the cochlear spiral. We overcame these issues by presenting click stimuli at a very slow rate and by time-frequency windowing the resulting click-evoked (CE)OAEs into short-latency (SL) and long-latency (LL) components. We characterized the effects of MOCR on CEOAE components using multiple measures to more comprehensively assess these effects throughout much of the dynamic range of hearing. These measures included CEOAE amplitude attenuation, equivalent input attenuation, phase, and slope of growth functions. Results show that MOCR effects are smaller on SL components than LL components, consistent with SL components being generated slightly basal of the characteristic frequency region. Amplitude attenuation measures showed the largest effects at the lowest stimulus levels, but slope change and equivalent input attenuation measures did not decrease at higher stimulus levels. These latter measures are less commonly reported and may provide insight into the variability in listening performance and noise susceptibility seen across individuals.NEW & NOTEWORTHY The auditory efferent system, operating at moderate to high sound levels, may improve hearing in background noise and provide protection from noise damage. We used otoacoustic emissions to measure these efferent effects across a wide range of sound levels and identified level-dependent and independent effects. Previous reports have focused on level-dependent measures. The level-independent effects identified here may provide new insights into the functional relevance of auditory efferent activity in humans.

Maximising the ability of stimulus-frequency otoacoustic emissions to predict hearing status and thresholds using machine-learning models

OBJECTIVE

This study aimed to maximise the ability of stimulus-frequency otoacoustic emissions (SFOAEs) to predict hearing status and thresholds based on machine-learning models.

DESIGN

SFOAE data and audiometric thresholds were collected at octave frequencies from 0.5 to 8 kHz. Support vector machine, k-nearest neighbour, back propagation neural network, decision tree, and random forest algorithms were used to build classification models for status identification and to develop regression models for threshold prediction.

STUDY SAMPLE

About 230 ears with normal hearing and 737 ears with sensorineural hearing loss.

RESULTS

All classification models yielded areas under the receiver operating characteristic curve of 0.926-0.994 at 0.5-8 kHz, superior to the previous SFOAE study. The regression models produced lower standard errors (8.1-12.2 dB, mean absolute errors: 5.53-8.97 dB) as compared to those for distortion-product and transient-evoked otoacoustic emissions previously reported (8.6-19.2 dB).

CONCLUSIONS

SFOAEs using machine-learning approaches offer promising tools for the prediction of hearing capabilities, at least at 0.5-4 kHz. Future research may focus on further improvements in accuracy and reductions in test time to improve clinical utility.

Cochlear Reflectance and Otoacoustic Emission Predictions of Hearing Loss

OBJECTIVES

Cochlear reflectance (CR) is the cochlear contribution to ear-canal reflectance. CR is a type of otoacoustic emission (OAE) that is calculated as a transfer function between forward pressure and reflected pressure. The purpose of this study was to compare wideband CR to distortion-product (DP) OAEs in two ways: (1) in a clinical-screening paradigm where the task is to determine whether an ear is normal or has hearing loss and (2) in the prediction of audiometric thresholds. The goal of the study was to assess the clinical utility of CR.

DESIGN

Data were collected from 32 normal-hearing and 124 hearing-impaired participants. A wideband noise stimulus presented at 3 stimulus levels (30, 40, 50 dB sound pressure level) was used to elicit the CR. DPOAEs were elicited using primary tones spanning a wide frequency range (1 to 16 kHz). Predictions of auditory status (i.e., hearing-threshold category) and predictions of audiometric threshold were based on regression analysis. Test performance (identification of normal versus impaired hearing) was evaluated using clinical decision theory.

RESULTS

When regressions were based only on physiological measurements near the audiometric frequency, the accuracy of CR predictions of auditory status and audiometric threshold was less than reported in previous studies using DPOAE measurements. CR predictions were improved when regressions were based on measurements obtained at many frequencies. CR predictions were further improved when regressions were performed on males and females separately.

CONCLUSIONS

Compared with CR measurements, DPOAE measurements have the advantages in a screening paradigm of better test performance and shorter test time. The full potential of CR measurements to predict audiometric thresholds may require further improvements in signal-processing methods to increase its signal to noise ratio. CR measurements have theoretical significance in revealing the number of cycles of delay at each frequency that is most sensitive to hearing loss.

Olivocochlear efferent contributions to speech-in-noise recognition across signal-to-noise ratios

The medial olivocochlear (MOC) efferent system modifies cochlear output to aid signal detection in noise, but the precise role of efferents in speech-in-noise understanding remains unclear. The current study examined the contribution of the MOC reflex for speech recognition in noise in 30 normal-hearing young adults (27 females, mean age = 22.7 yr). The MOC reflex was assessed using contralateral inhibition of transient-evoked otoacoustic emissions. Speech-in-noise perception was evaluated using the coordinate response measure presented in ipsilateral speech-shaped noise at signal-to-noise ratios (SNRs) ranging from -12 to 0 dB. Performance was assessed without and with the presence of contralateral noise to activate the MOC reflex. Performance was significantly better with contralateral noise only at the lowest SNR. There was a trend of better performance with increasing contralateral inhibition at the lowest SNR. Threshold of the psychometric function was significantly correlated with contralateral inhibition. Response time on the speech task was not significantly correlated with contralateral inhibition. Results suggest that the MOC reflex contributes to listening in low SNRs and the relationship between the MOC reflex and perception is highly dependent upon the task characteristics.

Comparison of Transient-Evoked Otoacoustic Emission Waveforms and Latencies Between Nonlinear Measurement Techniques

The nonlinear differential technique is commonly used to remove stimulus artifact when measuring transient-evoked otoacoustic emissions (TEOAE). However, to ensure removal of stimulus artifact, the initial 2.5-ms of the sound pressure recording must be discarded. Discarding this portion of the response precludes measurement of TEOAE energy above approximately 5 kHz and may limit measurement of shorter-latency TEOAE components below 5 kHz. The contribution from short-latency components influences the overall latency of the emission, including its dependence on frequency and stimulus level. The double source, double-evoked technique provides an alternative means to eliminate stimulus energy from the TEOAE and permits retention of the entire response. This study describes the effect of measurement technique on TEOAE waveforms and latencies. TEOAEs were measured in 26 normal hearing subjects using the nonlinear differential and double source, double-evoked techniques. The nonlinear differential technique limited measurement of short-latency TEOAE components at frequencies as low as ~3 kHz. Loss of these components biased TEOAE latencies to later moments in time and reduced the dependence of latency on stimulus level and frequency. In studies investigating TEOAE latency, the double source, double-evoked technique is recommended as it permits measurement of the both long- and short-latency components of the TEOAE.

Influence of medial olivocochlear efferents on the sharpness of cochlear tuning estimates in children

The present study objectively quantified the efferent-induced changes in the sharpness of cochlear tuning estimates and compared these alterations in cochlear tuning between adults and children. Click evoked otoacoustic emissions with and without contralateral broadband noise were recorded from 15 young adults and 14 children aged between 5 and 10 yrs. Time-frequency distributions of click evoked otoacoustic emissions were obtained via the S-transform, and the otoacoustic emission latencies were used to estimate the sharpness of cochlear tuning. Contralateral acoustic stimulation caused a significant reduction in the sharpness of cochlear tuning estimates in the low to mid frequency region, but had no effect in the higher frequencies (3175 and 4000 Hz). The magnitude of efferent-induced changes in cochlear tuning estimates was similar between adults and children. The current evidence suggests that the stimulation of the medial olivocochlear efferent neurons causes similar alterations in cochlear frequency selectivity in adults and children.

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.

Revisiting Oto-Acoustic Emissions

Oto-acoustic emissions (OAEs) are an audiometric diagnostic test that allows quick objective measure of hair cell function in the inner ear. It is a reflection of hearing function at the interface of conductive and sensorineural components in the human ear. Unfortunately, it is not commonly used due to the unique expertise and niche equipment required to successfully carry it out. This article is to further shed light about the use of such tests to junior doctors so that such resources can be better utilised. It also reviews the current and possible future applications of OAEs at the frontiers in otology today.

Tuning of SFOAEs Evoked by Low-Frequency Tones Is Not Compatible with Localized Emission Generation

Stimulus-frequency otoacoustic emissions (SFOAEs) appear to be well suited for assessing frequency selectivity because, at least on theoretical grounds, they originate over a restricted region of the cochlea near the characteristic place of the evoking tone. In support of this view, we previously found good agreement between SFOAE suppression tuning curves (SF-STCs) and a control measure of frequency selectivity (compound action potential suppression tuning curves (CAP-STC)) for frequencies above 3 kHz in chinchillas. For lower frequencies, however, SF-STCs and were over five times broader than the CAP-STCs and demonstrated more high-pass rather than narrow band-pass filter characteristics. Here, we test the hypothesis that the broad tuning of low-frequency SF-STCs is because emissions originate over a broad region of the cochlea extending basal to the characteristic place of the evoking tone. We removed contributions of the hypothesized basally located SFOAE sources by either pre-suppressing them with a high-frequency interference tone (IT; 4.2, 6.2, or 9.2 kHz at 75 dB sound pressure level (SPL)) or by inducing acoustic trauma at high frequencies (exposures to 8, 5, and lastly 3-kHz tones at 110-115 dB SPL). The 1-kHz SF-STCs and CAP-STCs were measured for baseline, IT present and following the acoustic trauma conditions in anesthetized chinchillas. The IT and acoustic trauma affected SF-STCs in an almost indistinguishable way. The SF-STCs changed progressively from a broad high-pass to narrow band-pass shape as the frequency of the IT was lowered and for subsequent exposures to lower-frequency tones. Both results were in agreement with the "basal sources" hypothesis. In contrast, CAP-STCs were not changed by either manipulation, indicating that neither the IT nor acoustic trauma affected the 1-kHz characteristic place. Thus, unlike CAPs, SFOAEs cannot be considered as a place-specific measure of cochlear function at low frequencies, at least in chinchillas.

On the spatial distribution of the reflection sources of different latency components of otoacoustic emissions

The experimental observation of long- and short-latency components in both stimulus-frequency and transient-evoked otoacoustic emissions admits a comprehensive explanation within the coherent reflection mechanism, in a linear active transmission-line cochlear model. A local complex reflectivity function associated with roughness was defined and analyzed by varying the tuning factor of the model, systematically showing, for each frequency, a multiple-peak spatial structure, compatible with the observed multiple-latency structure of otoacoustic emissions. Although this spatial pattern and the peak relative intensity changes with the chosen random roughness function, the multiple-peak structure is a reproducible feature of different "digital ears," in good agreement with experimental data. If one computes the predicted transmission delays as a function of frequency and position for each source, one gets a good match to the latency-frequency patterns that are directly computed from synthesized otoacoustic spectra using time-frequency analysis. This result clarifies the role of the spatial distribution of the otoacoustic emission sources, further supporting the interpretation of different-latency otoacoustic components as due to reflection sources localized at different places along the basilar membrane.

Basal contributions to short-latency transient-evoked otoacoustic emission components

The presence of short-latency (SL), less compressive-growing components in bandpass-filtered transient-evoked otoacoustic emission (TEOAE) waveforms may implicate contributions from cochlear regions basal to the tonotopic place. Recent empirical work suggests a region of SL generation between ∼1/5 and 1/10-octave basal to the TEOAE frequency's tonotopic place. However, this estimate may be biased to regions closer to the tonotopic place as the TEOAE extraction technique precluded measurement of components with latencies shorter than ∼5 ms. Using a variant of the non-linear, double-evoked extraction paradigm that permitted extraction of components with latencies as early as 1 ms, the current study empirically estimated the spatial-extent of the cochlear region contributing to 2 kHz SL TEOAE components. TEOAEs were evoked during simultaneous presentation of a suppressor stimulus, in order to suppress contributions to the TEOAE from different places along the cochlear partition. Three or four different-latency components of similar frequency content (∼2 kHz) were identified for most subjects. Component latencies ranged from 1.4 to 9.6 ms; latency was predictive of the component's growth rate and the suppressor frequency to which the component's magnitude was most sensitive to change. As component latency decreased, growth became less compressive and suppressor-frequency sensitivity shifted to higher frequencies. The shortest-latency components were most sensitive to suppressors approximately 3/5-octave higher than their nominal frequency of 2 kHz. These results are consistent with a distributed region of generation extending to approximately 3/5-octave basal to the TEOAE frequency's tonotopic place. The empirical estimates of TEOAE generation are similar to model-based estimates where generation of the different-latency components occurs through linear reflection from impedance discontinuities distributed across the cochlear partition.

Reliability and clinical test performance of cochlear reflectance

OBJECTIVE

Cochlear reflectance (CR) is the cochlear contribution to ear-canal reflectance. CR is equivalent to an otoacoustic emission (OAE) deconvolved by forward pressure in the ear canal. Similar to other OAE measures, CR level is related to cochlear status. When measured using wideband noise stimuli, potential advantages of CR over other types of OAEs include (1) the capability to cover a wider frequency range more efficiently by requiring fewer measurements, (2) minimal influence on the recorded emission from the measurement system and middle ear, (3) lack of entrainment of spontaneous OAEs, and (4) easier interpretation because of the existence of an equivalent linear model, which validates the application of linear systems theory. The purposes of this study were to evaluate the reliability, assess the accuracy in a clinical screening paradigm, and determine the relation of CR to audiometric thresholds. Thus, this study represents an initial assessment of the clinical utility of CR.

DESIGN

Data were collected from 32 normal-hearing and 58 hearing-impaired participants. A wideband noise stimulus presented at seven stimulus levels (10 to 70 dB SPL, 10 dB steps) was used to elicit the CR. Reliability of CR was assessed using Cronbach's α, standard error of measurement, and absolute differences between CR data from three separate test sessions. Test performance was evaluated using clinical decision theory. The ability of CR to predict audiometric thresholds was evaluated using regression analysis.

RESULTS

CR repeatability across test sessions was similar to that of other clinical measurements. However, both the accuracy with which CR distinguished normal-hearing from hearing-impaired ears and the accuracy with which CR predicted audiometric thresholds were less than those reported in previous studies using distortion-product OAE measurements.

CONCLUSIONS

CR measurements are repeatable between test sessions, can be used to predict auditory status, and are related to audiometric thresholds. However, under current conditions, CR does not perform as well as other OAE measurements. Further developments in CR measurement and analysis methods may improve performance. CR has theoretical advantages for cochlear modeling, which may lead to improved interpretation of cochlear status.

Experimental evidence for the basal generation place of the short-latency transient-evoked otoacoustic emissions

Time-frequency analysis of the transient-evoked otoacoustic emission response was performed on a population of subjects affected by sensory-neural hearing loss characterized by a sharp audiometric profile, caused by firearm noise exposure (42 ears), and on a control population of normal-hearing subjects (84 ears). Time-frequency filtering permitted a careful evaluation of the relation between the audiometric profile and the spectral shape of the long- and short-latency otoacoustic components. Both filtered spectra closely follow the shape of the audiometric profile, with a frequency shift between them. The typical frequency shift was evaluated by averaging the otoacoustic spectra and the audiograms among groups of ears with the same cutoff frequency. Assuming that the otoacoustic emission source function depends on the local effectiveness of the cochlear amplifier, this experimental evidence suggests that the short-latency response is generated at a cochlear place displaced towards the base by about 0.5-1 mm with respect to the generation place of the long-latency component. The analysis of the control group demonstrates that, below 4 kHz, the observed effect is not dependent on the data acquisition and analysis procedure. These results confirm previous theoretical estimates and independent experimental evidence based on the measured latency difference between the two components.