Predicting audiometric status from distortion product otoacoustic emissions using multivariate analyses

A Variable-Stimulus Distortion Product Otoacoustic Emission Screening Method to Match Cochlear Place-Specific Properties

OBJECTIVES

Distortion product otoacoustic emissions (DPOAEs) are a popular screening tool for hearing loss in specific populations (e.g., newborns). Current screening protocols use stimulus conditions that are agnostic to local mechanical properties of the cochlea and are also limited to a narrow frequency range. We have recently reported locally optimized stimulus frequency ratio and level combinations for recording DPOAEs up to stimulus frequencies of 19 kHz. In normally functioning cochlea, optimized stimuli improved the signal to noise ratios and allowed the registration of higher DPOAE levels, especially at higher frequencies. The purpose of this study was to evaluate the clinical performance of these physiologically motivated, locally appropriate, stimulus parameters for a screening application to identify the presence of hearing loss.

DESIGN

Subjects were 24 adults with sensorineural hearing loss and 31 adults with normal hearing. The cubic DPOAE was measured and analyzed up to frequencies of 16 kHz using a range of stimulus conditions. Receiver operating characteristic curves were used to identify stimulus combinations most sensitive to screening for hearing loss.

RESULTS

Receiver operating characteristic curves demonstrated improved test efficacy for hearing loss detection when using stimulus frequency ratios and levels that are frequency-dependent and consistent with known mechanical properties of the cochlea.

CONCLUSIONS

We propose a new DPOAE recording paradigm (variable-stimuli DP) using stimuli aligned to local cochlear properties which may improve early and accurate detection of decline in cochlear function.

Detection of mild sensory hearing loss using a joint reflection-distortion otoacoustic emission profile

Measuring and analyzing both nonlinear-distortion and linear-reflection otoacoustic emissions (OAEs) combined creates what we have termed a "joint-OAE profile." Here, we test whether these two classes of emissions have different sensitivities to hearing loss and whether our joint-OAE profile can detect mild-moderate hearing loss better than conventional OAE protocols have. 2f1-f2 distortion-product OAEs and stimulus-frequency OAEs were evoked with rapidly sweeping tones in 300 normal and impaired ears. Metrics included OAE amplitude for fixed-level stimuli as well as slope and compression features derived from OAE input/output functions. Results show that mild-moderate hearing loss impacts distortion and reflection emissions differently. Clinical decision theory was applied using OAE metrics to classify all ears as either normal-hearing or hearing-impaired. Our best OAE classifiers achieved 90% or better hit rates (with false positive rates of 5%-10%) for mild hearing loss, across a nearly five-octave range. In summary, results suggest that distortion and reflection emissions have distinct sensitivities to hearing loss, which supports the use of a joint-OAE approach for diagnosis. Results also indicate that analyzing both reflection and distortion OAEs together to detect mild hearing loss produces outstanding accuracy across the frequency range, exceeding that achieved by conventional OAE protocols.

Revisiting the transient-evoked otoacoustic emissions passing criteria used for newborn hearing screening

OBJECTIVE

To assess transient-evoked otoacoustic emissions (TEOAE) data from 15 years of a newborn hearing screening program and evaluate how well various criteria separate ears with and without hearing loss.

DESIGN

Retrospective review of TEOAE data using logistic regression, receiver operating characteristic curves, and cumulative percentage graphs.Study sample: Children with hearing loss who passed TEOAE screening as a newborn were compared to children who failed TEOAE screening and normal hearing children who either passed or failed. Exclusions were applied for acquired hearing loss or auditory neuropathy.

RESULTS

Ears with hearing loss that passed screening had significantly lower TEOAE response levels compared to ears with normal hearing. Noise levels, test times, and number of sweeps were also lower. Most of these ears had mild hearing loss. Logistic regression results showed that high-frequency TEOAE response level is the best predictor of hearing loss. A multivariate "logit" score calculated from the regression was the best indicator for separating ears with hearing loss from ears with normal hearing.

CONCLUSIONS

TEOAE response levels or an algorithm which incorporates logit scores should be considered as a minimum passing criterion to increase the sensitivity of the TEOAE screening.

Rethinking the clinical utility of distortion-product otoacoustic emission (DPOAE) signal-to-noise ratio

OBJECTIVE

Distortion-product otoacoustic emission (DPOAE) levels are repeatable over time in normal-hearing individuals making DPOAE levels an ideal measurement for monitoring cochlear status in clinic and research applications. However, if DPOAE signal-to-noise ratio (SNR) values instead of levels are used for monitoring, the repeatability of this value needs to be established. This retrospective, cross-sectional study sought to determine DPOAE SNR repeatability in younger children, older children, young adults and a patient population with normal hearing.

DESIGN

Each participant attended four sessions where DPOAE discrete frequency sweeps were collected at conventional (≤ 8 kHz) and/or extended-high frequencies (> 8 kHz). To examine the extent of variability to be expected for DPOAE SNR, average absolute SNR differences-between-trials were determined and compared to average absolute DPOAE level differences-between-trials.

STUDY SAMPLES

One hundred forty-five participants, incorporating four different groups from three different studies. Ages ranged from 3 to 55 years.

RESULTS

Average SNR differences-between-trials across all frequencies are greater than differences for average DPOAE levels. Improved calibration methods result in SNR differences-between-trials that are similar across all frequencies.

CONCLUSIONS

When monitoring cochlear health over an extended bandwidth, DPOAE levels are less variable across trials than SNR values, thus allowing earlier indicators of cochlear damage.

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.

Estimating Hearing Thresholds From Stimulus-Frequency Otoacoustic Emissions

It is of clinical interest to estimate pure-tone thresholds from potentially available objective measures, such as stimulus-frequency otoacoustic emissions (SFOAEs). SFOAEs can determine hearing status (normal hearing vs. hearing loss), but few studies have explored their further potential in predicting audiometric thresholds. The current study investigates the ability of SFOAEs to predict hearing thresholds at octave frequencies from 0.5 to 8 kHz. SFOAE input/output functions and pure-tone thresholds were measured from 230 ears with normal hearing and 737 ears with sensorineural hearing loss. Two methods were used to predict hearing thresholds. Method 1 is a linear regression model; Method 2 proposed in this study is a back propagation (BP) network predictor built on the bases of a BP neural network and principal component analysis. In addition, a BP network classifier was built to identify hearing status. Both Methods 1 and 2 were able to predict hearing thresholds from 0.5 to 8 kHz, but Method 2 achieved better performance than Method 1. The BP network classifiers achieved excellent performance in determining the presence or absence of hearing loss at all test frequencies. The results show that SFOAEs are not only able to identify hearing status with great accuracy at all test frequencies but, more importantly, can predict hearing thresholds at octave frequencies from 0.5 to 8 kHz, with best performance at 0.5 to 4 kHz. The BP network predictor is a potential tool for quantitatively predicting hearing thresholds, at least at 0.5 to 4 kHz.

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.

Cochlear Mechanisms and Otoacoustic Emission Test Performance

OBJECTIVES

This study aims to determine the impact of controlling cochlear-source mechanism on the accuracy with which auditory status is identified using otoacoustic emissions (OAEs) in two groups of subjects with normal hearing (NH) and subjects with mild to moderate hearing loss.

DESIGN

Data were collected from 212 subjects with NH and with mild to moderate hearing loss who fell into two categories based on a distortion product OAE (DPOAE) screening protocol: the uncertain-identification group (where errors were likely) and the certain-identification group (where errors were unlikely). DPOAE fine-structure patterns were recorded at intervals surrounding f2 = 1, 2 and 4 kHz (f2/f1 ratio = 1.22), with L2 = 35, 45, and 55 dB SPL (L1/L2 ratio = 10 dB). The discrete cosine transform was used to smooth fine structure, limiting the source contribution to the distortion source only. Reflection-source OAEs were also recorded using amplitude-modulated stimulus frequency OAEs (AM-SFOAE). Area under the relative operating characteristic (AROC) curve was used to quantify test accuracy when the source contribution was controlled versus the condition where both sources contribute. Additionally, failure rate, fixed at 5% for NH ears, as a function of behavioral-threshold category was evaluated.

RESULTS

When data for the entire subject group were examined, reducing the reflection-source contribution to the DPOAE did not result in better test performance than the best control condition at any frequency tested. When the subjects with NH were restricted to those with confirmed fine structure, AROC analyses indicated that reducing the reflection-source contribution resulted in several small increases in the accuracy (2%-5%) with which auditory status was identified relative to the best control condition. This improvement was observed for the lowest stimulus levels (i.e., L2 = 35 or 45 dB SPL). In this subset of subjects, distortion-source DPOAEs resulted in more accurate identification of mild hearing loss for a fixed false-positive rate of 5% in NH ears at lower L2's, conditions with poor accuracy in the larger group of subjects. The impact of controlling the source contribution on the identification of moderate losses was less clear in the reduced subject group, with some conditions where the distortion-source DPOAE was more accurate than the control condition and other conditions where there was no change. There was no evidence that reflection-source AM-SFOAEs more accurately identified ears with hearing loss when compared to any of the DPOAE conditions in either the large or reduced group of subjects.

CONCLUSION

While improvements in test accuracy were observed for some subjects and some conditions (e.g., mild hearing losses and low stimulus levels in the reduced subset of subjects), these results suggest that restricting cochlear source contribution by "smoothing" DPOAE fine structure is not expected to improve DPOAE test accuracy in a general population of subjects. Likewise, recording reflection-source OAEs using the AM-SFOAE technique would not be expected to more accurately identify hearing status compared to mixed- or single-source DPOAEs.

Emerging Distortion Product Otoacoustic Emission Techniques to Identify Preclinical Warning Signs of Basal Cochlear Dysfunction Due to Ototoxicity

Hundreds of medications commonly prescribed for anticancer treatments and some infections are known to cause hearing damage, referred to as ototoxicity. Preventing or minimizing ototoxicity is critical in order to preserve quality of life for patients receiving treatment and to reduce the societal burden of hearing loss. Current clinical evaluations are restricted to a limited frequency range (≤8 kHz); however, this approach does not permit the earliest detection of ototoxicity, most likely to be observed at the highest frequencies (9–20 kHz). Distortion product otoacoustic emissions (DPOAEs) offer a noninvasive, objective approach to monitor cochlear health in those unable to respond via conventional methods. The current report analyzes different DPOAE paradigms used in patients undergoing chemotherapy treatments with various platinum derivatives. Individualized serial monitoring protocols were completed at the highest frequencies with measurable DPOAEs. This allowed the exploration of potential clinical translation opportunities for further quantification of the earliest signs of underlying cochlear damage, which may go undetected with conventional methods. Clinical practice has the potential to be enhanced by emerging DPOAE applications, including targeted monitoring protocols and high-frequency stimuli to assess cochlear function, especially at the highest frequencies, and advanced calibration techniques to ensure the stability of serial measurements.

Optimizing Clinical Interpretation of Distortion Product Otoacoustic Emissions in Infants

OBJECTIVES

The purpose of this study was to analyze distortion product otoacoustic emission (DPOAE) level and signal to noise ratio in a group of infants from birth to 4 months of age to optimize prediction of hearing status. DPOAEs from infants with normal hearing (NH) and hearing loss (HL) were used to predict the presence of conductive HL (CHL), sensorineural HL (SNHL), and mixed HL (MHL). Wideband ambient absorbance was also measured and compared among the HL types.

DESIGN

This is a prospective, longitudinal study of 279 infants with verified NH and HL, including conductive, sensorineural, and mixed types that were enrolled from a well-baby nursery and two neonatal intensive care units in Cincinnati, Ohio. At approximately 1 month of age, DPOAEs (1-8 kHz), wideband absorbance (0.25-8 kHz), and air and bone conduction diagnostic tone burst auditory brainstem response (0.5-4 kHz) thresholds were measured. Hearing status was verified at approximately 9 months of age with visual reinforcement audiometry (0.5-4 kHz). Auditory brainstem response air conduction thresholds were used to assign infants to an NH or HL group, and the efficacy of DPOAE data to classify ears as NH or HL was analyzed using receiver operating characteristic (ROC) curves. Two summary statistics of the ROC curve were calculated: the area under the ROC curve and the point of symmetry on the curve at which the sensitivity and specificity were equal. DPOAE level and signal to noise ratio cutoff values were defined at each frequency as the symmetry point on their respective ROC curve, and DPOAE results were combined across frequency in a multifrequency analysis to predict the presence of HL.

RESULTS

Single-frequency test performance of DPOAEs was best at mid to high frequencies (3-8 kHz) with intermediate performance at 1.5 and 2 kHz and chance performance at 1 kHz. Infants with a conductive component to their HL (CHL and MHL combined) displayed significantly lower ambient absorbance values than the NH group. No differences in ambient absorbance were found between the NH and SNHL groups. Multifrequency analysis resulted in the best prediction of HL for the SNHL/MHL group with poorer sensitivity values when infants with CHL were included.

CONCLUSIONS

Clinical interpretation of DPOAEs in infants can be improved by using age-appropriate normative ranges and optimized cutoff values. DPOAE interpretation is most predictive at higher F2 test frequencies in young infants (2-8 kHz) due to poor test performance at 1 to 1.5 kHz. Multifrequency rules can be used to improve sensitivity while balancing specificity. Last, a sensitive middle ear measure such as wideband absorbance should be included in the test battery to assess possibility of a conductive component to the HL.

Chirp-Evoked Otoacoustic Emissions and Middle Ear Absorbance for Monitoring Ototoxicity in Cystic Fibrosis Patients

OBJECTIVES

The goal of this study was to investigate the use of transient-evoked otoacoustic emissions (TEOAEs) and middle ear absorbance measurements to monitor auditory function in patients with cystic fibrosis (CF) receiving ototoxic medications. TEOAEs were elicited with a chirp stimulus using an extended bandwidth (0.71 to 8 kHz) to measure cochlear function at higher frequencies than traditional TEOAEs. Absorbance over a wide bandwidth (0.25 to 8 kHz) provides information on middle ear function. The combination of these time-efficient measurements has the potential to identify early signs of ototoxic hearing loss.

DESIGN

A longitudinal study design was used to monitor the hearing of 91 patients with CF (median age = 25 years; age range = 15 to 63 years) who received known ototoxic medications (e.g., tobramycin) to prevent or treat bacterial lung infections. Results were compared to 37 normally hearing young adults (median age = 32.5 years; age range = 18 to 65 years) without a history of CF or similar treatments. Clinical testing included 226-Hz tympanometry, pure-tone air-conduction threshold testing from 0.25 to 16 kHz and bone conduction from 0.25 to 4 kHz. Experimental testing included wideband absorbance at ambient and tympanometric peak pressure and TEOAEs in three stimulus conditions: at ambient pressure and at tympanometric peak pressure using a chirp stimulus with constant incident pressure level across frequency and at ambient pressure using a chirp stimulus with constant absorbed sound power across frequency.

RESULTS

At the initial visit, behavioral audiometric results indicated that 76 of the 157 ears (48%) from patients with CF had normal hearing, whereas 81 of these ears (52%) had sensorineural hearing loss for at least one frequency. Seven ears from four patients had a confirmed behavioral change in hearing threshold for ≥3 visits during study participation. Receiver operating characteristic curve analyses demonstrated that all three TEOAE conditions were useful for distinguishing CF ears with normal hearing from ears with sensorineural hearing loss, with an area under the receiver operating characteristic curve values ranging from 0.78 to 0.92 across methods for frequency bands from 2.8 to 8 kHz. Case studies are presented to illustrate the relationship between changes in audiometric thresholds, TEOAEs, and absorbance across study visits. Absorbance measures permitted identification of potential middle ear dysfunction at 5.7 kHz in an ear that exhibited a temporary hearing loss.

CONCLUSIONS

The joint use of TEOAEs and absorbance has the potential to explain fluctuations in audiometric thresholds due to changes in cochlear function, middle ear function, or both. These findings are encouraging for the joint use of TEOAE and wideband absorbance objective tests for monitoring ototoxicity, particularly, in patients who may be too ill for behavioral hearing tests. Additional longitudinal studies are needed in a larger number of CF patients receiving ototoxic drugs to further evaluate the clinical utility of these measures in an ototoxic monitoring program.

MPZL2, Encoding the Epithelial Junctional Protein Myelin Protein Zero-like 2, Is Essential for Hearing in Man and Mouse

In a Dutch consanguineous family with recessively inherited nonsyndromic hearing impairment (HI), homozygosity mapping combined with whole-exome sequencing revealed a MPZL2 homozygous truncating variant, c.72del (p.Ile24Metfs^∗22). By screening a cohort of phenotype-matched subjects and a cohort of HI subjects in whom WES had been performed previously, we identified two additional families with biallelic truncating variants of MPZL2. Affected individuals demonstrated symmetric, progressive, mild to moderate sensorineural HI. Onset of HI was in the first decade, and high-frequency hearing was more severely affected. There was no vestibular involvement. MPZL2 encodes myelin protein zero-like 2, an adhesion molecule that mediates epithelial cell-cell interactions in several (developing) tissues. Involvement of MPZL2 in hearing was confirmed by audiometric evaluation of Mpzl2-mutant mice. These displayed early-onset progressive sensorineural HI that was more pronounced in the high frequencies. Histological analysis of adult mutant mice demonstrated an altered organization of outer hair cells and supporting cells and degeneration of the organ of Corti. In addition, we observed mild degeneration of spiral ganglion neurons, and this degeneration was most pronounced at the cochlear base. Although MPZL2 is known to function in cell adhesion in several tissues, no phenotypes other than HI were found to be associated with MPZL2 defects. This indicates that MPZL2 has a unique function in the inner ear. The present study suggests that deleterious variants of Mplz2/MPZL2 affect adhesion of the inner-ear epithelium and result in loss of structural integrity of the organ of Corti and progressive degeneration of hair cells, supporting cells, and spiral ganglion neurons.

Comparative multivariate analyses of transient otoacoustic emissions and distorsion products in normal and impaired hearing

BACKGROUND AND AIM

The clinical utility of otoacoustic emissions as a noninvasive objective test of cochlear function has been long studied. Both transient otoacoustic emissions and distorsion products can be used to identify hearing loss, but to what extent they can be used as predictors for hearing loss is still debated. Most studies agree that multivariate analyses have better test performances than univariate analyses. The aim of the study was to determine transient otoacoustic emissions and distorsion products performance in identifying normal and impaired hearing loss, using the pure tone audiogram as a gold standard procedure and different multivariate statistical approaches.

METHODS

The study included 105 adult subjects with normal hearing and hearing loss who underwent the same test battery: pure-tone audiometry, tympanometry, otoacoustic emission tests. We chose to use the logistic regression as a multivariate statistical technique. Three logistic regression models were developed to characterize the relations between different risk factors (age, sex, tinnitus, demographic features, cochlear status defined by otoacoustic emissions) and hearing status defined by pure-tone audiometry. The multivariate analyses allow the calculation of the logistic score, which is a combination of the inputs, weighted by coefficients, calculated within the analyses. The accuracy of each model was assessed using receiver operating characteristics curve analysis. We used the logistic score to generate receivers operating curves and to estimate the areas under the curves in order to compare different multivariate analyses.

RESULTS

We compared the performance of each otoacoustic emission (transient, distorsion product) using three different multivariate analyses for each ear, when multi-frequency gold standards were used. We demonstrated that all multivariate analyses provided high values of the area under the curve proving the performance of the otoacoustic emissions. Each otoacoustic emission test presented high values of area under the curve, suggesting that implementing a multivariate approach to evaluate the performances of each otoacoustic emission test would serve to increase the accuracy in identifying the normal and impaired ears. We encountered the highest area under the curve value for the combined multivariate analysis suggesting that both otoacoustic emission tests should be used in assessing hearing status. Our multivariate analyses revealed that age is a constant predictor factor of the auditory status for both ears, but the presence of tinnitus was the most important predictor for the hearing level, only for the left ear. Age presented similar coefficients, but tinnitus coefficients, by their high value, produced the highest variations of the logistic scores, only for the left ear group, thus increasing the risk of hearing loss. We did not find gender differences between ears for any otoacoustic emission tests, but studies still debate this question as the results are contradictory. Neither gender, nor environment origin had any predictive value for the hearing status, according to the results of our study.

CONCLUSION

Like any other audiological test, using otoacoustic emissions to identify hearing loss is not without error. Even when applying multivariate analysis, perfect test performance is never achieved. Although most studies demonstrated the benefit of using the multivariate analysis, it has not been incorporated into clinical decisions maybe because of the idiosyncratic nature of multivariate solutions or because of the lack of the validation studies.

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.

Interindividual variation of sensitivity to frequency modulation: its relation with click-evoked and distortion product otoacoustic emissions

The frequency modulation detection limen (FMDL) with a low modulation rate has been used as a measure of the listener's sensitivity to the temporal fine structure of a stimulus, which is represented by the pattern of neural phase locking at the auditory periphery. An alternative to the phase locking cue, the excitation pattern cue, has been suggested to contribute to frequency modulation (FM) detection. If the excitation pattern cue has a significant contribution to low-rate FM detection, the functionality of cochlear mechanics underlying the excitation pattern should be reflected in low-rate FMDLs. This study explored the relationship between cochlear mechanics and low-rate FMDLs by evaluating physiological measures of cochlear functions, namely distortion product otoacoustic emissions (DPOAEs) and click-evoked otoacoustic emissions (CEOAEs). DPOAEs and CEOAEs reflect nonlinear cochlear gain. CEOAEs have been considered also to reflect the degree of irregularity, such as spatial variations in number or geometry of outer hair cells, on the basilar membrane. The irregularity profile could affect the reliability of the phase locking cue, thereby influencing the FMDLs. The features extracted from DPOAEs and CEOAEs, when combined, could account for more than 30 % of the inter-listener variation of low-rate FMDLs. This implies that both cochlear gain and irregularity on the basilar membrane have some influence on sensitivity to low-rate FM: the loss of cochlear gain or broader tuning might influence the excitation pattern cue, and the irregularity on the basilar membrane might disturb the ability to use the phase locking cue.

Characteristics of the 2f(1)-f(2) distortion product otoacoustic emission in a normal hearing population

Distortion-product otoacoustic emission (DPOAE) fine structure and component characteristics are reported between 0.75 and 16 kHz in 356 clinically normal hearing human subjects ages 10 to 65 yr. Stimulus tones at 55/40, 65/55, and 75/75 dB SPL were delivered using custom designed drivers and a calibration method that compensated for the depth of insertion of the otoacoustic emission (OAE) probe in the ear canal. DPOAE fine structure depth and spacing were found to be consistent with previous reports with depth varying between 3 and 7 dB and average spacing ratios (f/Δf) between 15 and 25 depending on stimulus level and frequency. In general, fine structure depth increased with increasing frequency, likely due to a diminishing difference between DPOAE component levels. Fine structure spacing became wider with increasing age above 8 kHz. DPOAE components were extracted using the inverse fast Fourier transform method, adhering to a strict signal to noise ratio criterion for clearer interpretation. Component data from four age groups between 18 and 55 yr old were available for the stimulus levels of 75/75 dB SPL. The age groups could be differentiated with greater than 90% accuracy when using the level of the component presumed to originate from the DPOAE characteristic frequency place. This accuracy held even for frequencies at and below 4 kHz where the age groups exhibited similar average hearing thresholds.

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

Estimating audiometric thresholds using objective measures can be clinically useful when reliable behavioral information cannot be obtained. Transient-evoked otoacoustic emissions (TEOAEs) are effective for determining hearing status (normal hearing vs hearing loss), but previous studies have found them less useful for predicting audiometric thresholds. Recent work has demonstrated the presence of short-latency TEOAE components in normal-hearing ears, which have typically been eliminated from the analyses used in previous studies. The current study investigated the ability of short-latency components to predict hearing status and thresholds from 1-4 kHz. TEOAEs were measured in 77 adult ears with thresholds ranging from normal hearing to moderate sensorineural hearing loss. Emissions were bandpass filtered at center frequencies from 1 to 4 kHz. TEOAE waveforms were analyzed within two time windows that contained either short- or long-latency components. Waveforms were quantified by root-mean-square amplitude. Long-latency components were better overall predictors of hearing status and thresholds, relative to short-latency components. There were no significant improvements in predictions when short-latency components were included with long-latency components in multivariate analyses. The results showed that short-latency TEOAE components, as analyzed in the current study, were less predictive of both hearing status and thresholds from 1-4 kHz than long-latency components.

Relation of distortion-product otoacoustic emission input-output functions to loudness

The aim of this study is to further explore the relationship between distortion-product otoacoustic emission (DPOAE) measurements and categorical loudness scaling (CLS) measurements using multiple linear regression (MLR) analysis. Recently, Thorson et al. [J. Acoust. Soc. Am. 131, 1282-1295 (2012)] obtained predictions of CLS loudness ratings from DPOAE input/output (I/O) functions using MLR analysis. The present study extends that work by (1) considering two different (and potentially improved) MLR models, one for predicting loudness rating at specified input level and the other for predicting the input level for each loudness category and (2) validating the new models' predictions using an independent set of data. Strong correlations were obtained between predicted and measured data during the validation process with overall root-mean-square errors in the range 10.43-16.78 dB for the prediction of CLS input level, supporting the view that DPOAE I/O measurements can predict CLS loudness ratings and input levels, and thus may be useful for fitting hearing aids.

Behavioral hearing thresholds between 0.125 and 20 kHz using depth-compensated ear simulator calibration

OBJECTIVES

The purpose of this study was to obtain behavioral hearing thresholds for frequencies between 0.125 and 20 kHz from a large population between 10 and 65 yr old using a clinically feasible calibration method expected to compensate well for variations in the distance between the eardrum and an insert-type sound source. Previous reports of hearing thresholds in the extended high frequencies (>8 kHz) have either used calibration techniques known to be inaccurate or specialized equipment not suitable for clinical use.

DESIGN

Hearing thresholds were measured from 352 human subjects between 10 and 65 yr old having clinically normal-hearing thresholds (<20 dB HL) up to 4 kHz. An otoacoustic emission probe fitted with custom sound sources was used, and the stimulus levels individually tailored on the basis of an estimate of the insertion depth of the measurement probe. The calibrated stimulus levels were determined on the basis of measurements made at various depths of insertion in a standard ear simulator. Threshold values were obtained for 21 frequencies between 0.125 and 20 kHz using a modified Békésy technique. Forty-six of the subjects returned for a second measurement months later from the initial evaluation.

RESULTS

In agreement with previous reports, hearing thresholds at extended high frequencies were found to be sensitive to age-related changes in auditory function. In contrast with previous reports, no gender differences were found in average hearing thresholds at most evaluated frequencies. Two aging processes, one faster than the other in time scale, seem to influence hearing thresholds in different frequency ranges. The standard deviation (SD) of test-retest threshold difference for all evaluated frequencies was 5 to 10 dB, comparable to that reported in the literature for similar measurement techniques but smaller than that observed for data obtained using the standard clinical procedure.

CONCLUSIONS

The depth-compensated ear simulator-based calibration method and the modified Békésy technique allow reliable measurement of hearing thresholds over the entire frequency range of human hearing. Hearing thresholds at the extended high frequencies are sensitive to aging and reveal subtle differences, which are not evident in the frequency range evaluated regularly (≤8 kHz). Previously reported gender-related differences in hearing thresholds may be related to ear-canal acoustics and the calibration procedure and not because of differences in hearing sensitivity.

Comparing behavioral and physiological measures of combination tones: sex and race differences

Both distortion-product otoacoustic emissions (DPOAEs) and performance in an auditory-masking task involving combination tones were measured in the same frequency region in the same ears. In the behavioral task, a signal of 3.6 kHz (duration 300 ms, rise/fall time 20 ms) was masked by a 3.0-kHz tone (62 dB SPL, continuously presented). These two frequencies can produce a combination tone at 2.4 kHz. When a narrowband noise (2.0-2.8 kHz, 17 dB spectrum level) was added as a second masker, detection of the 3.6-kHz signal worsened by 6-9 dB (the Greenwood effect), revealing that listeners had been using the combination tone at 2.4 kHz as a cue for detection at 3.6 kHz. Several outcomes differed markedly by sex and racial background. The Greenwood effect was substantially larger in females than in males, but only for the White group. When the magnitude of the Greenwood effect was compared with the magnitude of the DPOAE measured in the 2.4 kHz region, the correlations typically were modest, but were high for Non-White males. For many subjects, then, most of the DPOAE measured in the ear canal apparently is not related to the combination-tone cue that is masked by the narrowband noise.

Multivariate DPOAE metrics for identifying changes in hearing: perspectives from ototoxicity monitoring

Distortion-product otoacoustic emissions (DPOAEs) provide a window into real-time cochlear mechanical function. Yet, relationships between the changes in DPOAE metrics and auditory sensitivity are still poorly understood. Explicating these relationships might support the use of DPOAEs in hearing conservation programs (HCPs) for detecting early damage leading to noise-induced hearing loss (NIHL) so that mitigating steps might be taken to limit any lasting damage. This report describes the development of DPOAE-based statistical models to assess the risk of hearing loss from cisplatin treatment among cancer patients. Ototoxicity risk assessment (ORA) models were constructed using a machine learning paradigm in which partial least squares and leave-one-out cross-validation were applied, yielding optimal screening algorithms from a set of known risk factors for ototoxicity and DPOAE changes from pre-exposure baseline measures. Single DPOAE metrics alone were poorer indicators of the risk of ototoxic hearing shifts than the best performing multivariate models. This finding suggests that multivariate approaches applied to the use of DPOAEs in a HCP, will improve the ability of DPOAE measures to identify ears with noise-induced mechanical damage and/or hearing loss at each monitoring interval. This prediction must be empirically assessed in noise-exposed subjects.

Routine hearing screening in primary care for adult populations using distortion product Otoacoustic Emissions testing

PURPOSE

The purpose of this study was to determine the prevalence of undiagnosed hearing loss in adults in two busy primary care rural health centers.

DATA SOURCES

Using Otoacoustic Emissions (OAE) testing, participants were screened for hearing loss by trained personnel. Participants were those who presented to the primary care provider with complaints other than hearing loss or ear problems.

CONCLUSION

Of the 86 participants, 48.8% were found to have failed OAE testing, indicating some type of undiagnosed hearing loss. The average age of the participants was 49.27 years, yet nearly half had hearing loss. This finding makes hearing screening in the adult population, other than the elderly, an important issue.

IMPLICATIONS FOR PRACTICE

Hearing loss affects over 40% of the adult population. Undiagnosed and untreated hearing loss can be associated with depression, decreased social activities, and low self-esteem. The project identified the need for routine hearing screening and thus may become the foundation for the development and implementation of a hearing-screening program for primary care. The primary care nurse practitioner needs to incorporate hearing screening into the exam for early identification and for proper referral.

Reliability of distortion-product otoacoustic emissions and their relation to loudness

The reliability of distortion-product otoacoustic emission (DPOAE) measurements and their relation to loudness measurements was examined in 16 normal-hearing subjects and 58 subjects with hearing loss. The level of the distortion product (L(d)) was compared across two sessions and resulted in correlations that exceeded 0.90. The reliability of DPOAEs was less when parameters from nonlinear fits to the input/output (I/O) functions were compared across visits. Next, the relationship between DPOAE I/O parameters and the slope of the low-level portion of the categorical loudness scaling (CLS) function (soft slope) was assessed. Correlations of 0.65, 0.74, and 0.81 at 1, 2, and 4 kHz were observed between CLS soft slope and combined DPOAE parameters. Behavioral threshold had correlations of 0.82, 0.83, and 0.88 at 1, 2, and 4 kHz with CLS soft slope. Combining DPOAEs and behavioral threshold provided little additional information. Lastly, a multivariate approach utilizing the entire DPOAE I/O function was used to predict the CLS rating for each input level (dB SPL). Standard error of the estimate when using this method ranged from 2.4 to 3.0 categorical units (CU), suggesting that DPOAE I/O functions can predict CLS measures within the CU step size used in this study (5).

Do "optimal" conditions improve distortion product otoacoustic emission test performance?

OBJECTIVES

To determine whether an "optimal" distortion product otoacoustic emission (DPOAE) protocol that (1) used optimal stimulus levels and primary-frequency ratios for each f2, (2) simultaneously measured 2f2 - f1 and 2f1 - f2 distortion products, (3) controlled source contribution, (4) implemented improved calibration techniques, (5) accounted for the influence of middle ear reflectance, and (6) applied multivariate analyses to DPOAE data results in improved accuracy in differentiating between normal-hearing and hearing-impaired ears, compared with a standard clinical protocol.

DESIGN

Data were collected for f2 frequencies ranging from 0.75 to 8 kHz in 28 normal-hearing and 78 hearing-impaired subjects. The protocol included a control condition incorporating standard stimulus levels and primary-frequency ratios calibrated with a standard SPL method and three experimental conditions using optimized stimuli calibrated with an alternative forward pressure level method. The experimental conditions differed with respect to the level of the reflection-source suppressor tone and included conditions referred to as the null suppressor (i.e., no suppressor tone presented), low-level suppressor (i.e., suppressor tone presented at 58 dB SPL), and high-level suppressor (i.e., suppressor tone presented at 68 dB SPL) conditions. The area under receiver operating characteristic (A(ROC)) curves and sensitivities for fixed specificities (and vice versa) were estimated to evaluate test performance in each condition.

RESULTS

A(ROC) analyses indicated (1) improved test performance in all conditions using multivariate analyses, (2) improved performance in the null suppressor and low suppressor experimental conditions compared with the control condition, and (3) poorer performance below 4 kHz with the high-level suppressor. As expected from A(ROC), sensitivities for fixed specificities and specificities for fixed sensitivities were highest for the null suppressor and low suppressor conditions and lowest for standard clinical procedures. The influence of 2f2 - f1 and reflectance on test performance were negligible.

CONCLUSIONS

Predictions of auditory status based on DPOAE measurements in clinical protocols may be improved by the inclusion of (1) optimized stimuli, (2) alternative calibration techniques, (3) low-level suppressors, and (4) multivariate analyses.

Distortion-product otoacoustic emission test performance for ototoxicity monitoring

INTRODUCTION

A nonbehavioral method for monitoring ototoxicity in patients treated with cisplatin is needed because patients enduring chemotherapy may not be well or cooperative enough to undergo repeated hearing tests. Distortion-product otoacoustic emissions (DPOAEs) provide a nonbehavioral measure of auditory function that is sensitive to cisplatin exposure. However, interpreting DPOAE findings in the context of ototoxicity monitoring requires that their accuracy be determined in relation to a clinically accepted gold standard test.

OBJECTIVES

Among patients receiving cisplatin for the treatment of cancer, we sought to (1) identify the combination of DPOAE metrics and ototoxicity risk factors that best classified ears with and without ototoxic-induced hearing changes; and (2) evaluate the test performance achieved by the composite measure as well as by DPOAEs alone.

DESIGN

Odds of experiencing hearing changes at a given patient visit were determined using data collected prospectively from 24 Veterans receiving cisplatin. Pure-tone thresholds were examined within an octave of each subject's high-frequency hearing limit. DPOAE were collected as a set of four response growth (input/output) functions near the highest f2 frequency that yielded a robust response at L2 = L1 = 65 dB SPL. Logistic regression modeled the risk of hearing change using several DPOAE metrics, drug treatment factors, and other patient factors as independent variables. An optimal discriminant function was derived by reducing the model so that only statistically significant variables were included. Receiver operating characteristic curve analyses were used to evaluate test performance.

RESULTS

At higher cisplatin doses, ears with better hearing at baseline were more likely to exhibit ototoxic hearing changes than those with poorer hearing. Measures of pre-exposure hearing, cumulative drug dose, and DPOAEs generated a highly accurate discriminant function with a cross-validated area under the receiver operating characteristic curve of 0.9. DPOAEs alone also provided an indication of ototoxic hearing change when measured at the highest DPOAE test frequency that yielded a robust response.

CONCLUSIONS

DPOAEs alone and especially in combination with pre-exposure hearing and cisplatin dose provide an indication of whether or not hearing has changed as a result of cisplatin administration. These promising results need to be validated in a separate sample.

Ototoxicity risk assessment combining distortion product otoacoustic emissions with a cisplatin dose model

An objective method for identifying ototoxic hearing loss among patients receiving cisplatin is necessary since the ability of patients to take a behavioral test may change over the course of treatment. Data from 56 monitoring visits by 19 Veterans taking cisplatin were used to identify combinations of distortion-product otoacoustic emission (DPOAE) metrics and ototoxicity risk factors that best identified ototoxic hearing loss. Models were tested that incorporated DPOAE metrics generated statistically using partial least-squares analysis. Models were also tested that incorporated a priori DPOAE change criteria, such as a minimum DPOAE level shift of 6 dB. Receiver Operating Characteristic analysis was used to compare the accuracy of these models. The best performing model incorporated weighted combinations of pre-treatment hearing, cumulative cisplatin dose and DPOAE metrics that were determined using partial least-squares and evaluated over a quarter octave range near each subjects' high frequency DPOAE limit. Using this model and the DPOAE recording methods described herein, the chance of ototoxic hearing change can be determined at any given observed change in DPOAE level. This approach appears to provide an accurate and rapid ototoxicity risk assessment (ORA) that once validated can be used clinically.

Clinical test performance of distortion-product otoacoustic emissions using new stimulus conditions

OBJECTIVES

To determine whether new stimulus parameters, which have been shown to produce large distortion-product otoacoustic emission (DPOAE) levels in a group of normal-hearing listeners (Neely et al. 2005; Johnson et al. 2006), result in more accurate identification of auditory status and more accurate predictions of behavioral threshold than traditional stimulus conditions.

DESIGN

DPOAE input/output (I/O) functions for eight f2 frequencies ranging from 0.7 to 8 kHz were recorded from 96 ears with normal hearing and 226 ears with sensorineural hearing losses ranging from mild to profound. The primary-level differences and primary-frequency ratios were set according to the stimulus relations developed by Johnson et al. (2006). The accuracy of the dichotomous decision task (area under the relative operating characteristic curve [AROC]) for these new stimulus conditions was evaluated as a function of L2 and was compared with previous reports in the literature where traditional stimuli were used (Stover et al. 1996). Here, traditional stimuli are defined as L1 = L2 + 10 and f2/f1 = 1.22 for all L2 and f2 values. In addition to I/O functions, DPgrams with L2 = 55-dB sound pressure level (SPL) and f2 ranging from 0.7 to 8 kHz were recorded for each subject using the traditional stimuli. This provided a direct within-subject comparison of AROC for moderate-level stimuli when the new and traditional stimuli were used. Finally, the accuracy with which DPOAE thresholds predicted behavioral thresholds was evaluated in relation to previous reports in the literature for two definitions of DPOAE threshold, one where the entire I/O function was used to make the prediction and a second where the lowest L2 producing a signal to noise ratio > or =3 dB was used.

RESULTS

There was no evidence that the new stimuli improved the accuracy with which auditory status was identified from DPOAE responses. With both the new and traditional stimuli, moderate stimulus levels (L2 = 40- to 55-dB SPL) resulted in the most accurate identification of auditory status. When L2 = 55-dB SPL, the new stimuli produced AROC values that were equivalent to those observed with traditional stimuli. The new stimuli resulted in more accurate prediction of behavioral threshold for several f2 values when using the entire I/O function, although the effect was small. Furthermore, using the entire I/O function to predict behavioral threshold results in more accurate predictions of behavioral threshold than using the signal to noise ratio definition, although this approach can be applied to a smaller percentage of ears.

CONCLUSIONS

The new stimuli that had been shown previously to produce large DPOAE levels in normal-hearing listeners (Neely et al. 2005; Johnson et al. 2006) do not result in more accurate identification of auditory status and have only a small positive effect on the prediction of behavioral threshold.

Using benefit-cost ratio to select Universal Newborn Hearing Screening test criteria

OBJECTIVES

Current protocols presumably use criteria that are chosen on the basis of the sensitivity and specificity rates they produce. Such an approach emphasizes test performance but does not include societal implications of the benefit of early identification. The purpose of the present analysis was to evaluate an approach to selecting criteria for use in Universal Newborn Hearing Screening (UNHS) programs that uses benefit-cost ratio (BCR) to demonstrate an alternative method to audiologists, administrators, and others involved in UNHS protocol decisions.

DESIGN

Existing data from more than 1200 ears were used to analyze BCR as a function of Distortion Product Otoacoustic Emission (DPOAE) level. These data were selected because both audiometric and DPOAE data were available on every ear. Although these data were not obtained in newborns, this compromise was necessary because audiometric outcomes (especially in infants with congenital hearing loss) in neonates are either lacking or limited in number. As such, it is important to note that the characteristics of responses from the group of subjects that formed the bases of the present analyses are different from those for neonates. This limits the extent to which actual criterion levels can be selected but should not affect the general approach of using BCR as a framework for considering UNHS criteria. Estimates of the prevalence of congenital hearing loss identified through UNHS in 37 states and U.S. territories in 2004 were used to calculate BCR. A range of estimates for the lifetime monetary benefits and yearly costs for UNHS were used, based on data available in the literature. Still, exact benefits and costs are difficult to know. Both one-step (DPOAE alone) and two-step (DPOAE followed by automated auditory brainstem response, AABR) screening paradigms were considered in the calculation of BCR. The influence of middle ear effusion was simulated by incorporating a range of expected DPOAE level reductions into an additional BCR analyses

RESULTS

Our calculations indicate that for a range of proposed benefit and cost estimates, the monetary benefits of both one-step (DPOAE alone) and two-step (DPOAE followed by AABR) NHS programs outweigh programmatic costs. Our calculations indicate that BCR is robust in that it can be applied regardless of the values that are assigned to benefit and cost. Maximum BCR was identified and remained stable regardless of these values; however, it was recognized that the use of maximum BCR could result in reduced test sensitivity and may not be optimal for use in UNHS programs. The inclusion of secondary AABR screening increases BCR but does not alter the DPOAE criterion level at which maximum BCR occurs. The model of middle ear effusion reduces overall DPOAE level, subsequently lowering the DPOAE criterion level at which maximum BCR was obtained

CONCLUSION

BCR is one of several alternative methods for choosing UNHS criteria, in which the evaluation of costs and benefits allows clinical and societal considerations to be incorporated into the pass/refer decision in a meaningful way. Although some of the benefits of early identification of hearing impairment cannot be estimated through a monetary analysis, such as improved psychosocial development and quality of life, this article provides an alternative to audiologists and administrators for selecting UNHS protocols that includes consideration of societal implications of UNHS screening criteria. BCR suggests that UNHS is a worthwhile investment for society as benefits always outweigh costs, at least for the estimations included in this article. Although the use of screening criteria that maximize BCR results in lower test sensitivity compared with other criteria, BCR may be used to select criteria that result in increased test sensitivity and still provide a high, although not maximal, BCR. Using BCR analysis provides a framework in which the societal implications of NHS protocols are considered and emphasizes the value of UNHS.

[Distortion product otoacoustic emission levels and input/output-growth functions in normal-hearing individuals with tinnitus and/or hyperacusis]

The purpose of this study was to determine whether distortion product otoacoustic emissions (DPOAEs) can be used to distinguish among four groups with audiometrically normal-hearing sensitivity: (1) control adults without tinnitus or hyperacusis, (2) patients with tinnitus alone, (3) patients with hyperacusis alone, and (4) patients with both tinnitus and hyperacusis. Two types of DPOAE measures were evaluated: (1) the distortion product (DP-)gram measured with fixed primary levels as a function of frequency, and (2) DPOAE input/output (I/O) functions for a range of primary levels between 45 and 70 dB sound pressure level (SPL) at 1000, 2000, and 4000 Hz. DP-grams did not clearly distinguish between the control and patient groups. There was, however, a consistent trend for the three patient groups to have decreased average DP levels at 4000 and 6000 Hz; this notch in the DP-gram was not observed in the response configuration for the control group. In the three patient groups, 51 to 74% of these individuals had DP levels that were outside of the 95% confidence range for the control group. The average slopes of the I/O growth functions for each of the patient groups were consistently steeper than those for the control group; however, the slope values were indistinguishable among the patient groups. About 60% of the patients' DPOAE responses (in each group) were categorized as abnormal based on their slope values. Thus, DPOAE measures can be used with at least partial success to distinguish controls from patients with tinnitus, hyperacusis, or both tinnitus and hyperacusis, but not to discriminate among the respective patient groups. These findings suggest that the pathology represented among the patient groups is consistent at the level of the cochlea; however, diagnostic tests targeted at higher centers of processing are needed if the individuals in these groups are to be distinguished among themselves. In all participants, DPOAEs with fixed primary levels as a function of frequency were measured. There was a consistent trend for the three patient groups to have decreased average DP-gram levels at 4000 and 6000 Hz; this notch in the DP-gram was not observed in the response configuration for the control group. In the three patient groups, 51 to 74% of these individuals had DP levels that were outside of the 95% confidence range for the control group. Thus, DPOAE measures can be used with at least partial success to distinguish controls from patients with tinnitus, hyperacusis, or both tinnitus and hyperacusis, but not to discriminate among the respective patient groups. These findings suggest that the pathology represented among the patient groups is consistent at the level of the cochlea; however, diagnostic tests targeted at higher centers of processing are needed if the individuals in these groups are to be distinguished among themselves.

Analysis of distortion product otoacoustic emission spectra in normal-hearing adults

PURPOSE

To evaluate the ability of distortion product otoacoustic emission (DPOAE) spectral characteristics to distinguish between ears with variable hearing sensitivity within the normal range.

METHOD

Distortion product grams (DP-grams) were acquired with primary tones decremented in 1/8-octave steps and primary-tone levels presented at 65 dB SPL (L1) and 45 dB SPL (L2) across an f2 frequency range of 842-7996 Hz from 22 normal-hearing adults (44 ears). Hearing thresholds of ears classified in Group A (n = 22) were better than ears classified in Group B (n = 22). Examined parameters of the DP-grams included spectral peak occurrence, peak height, peak width, and DPOAE levels. Analyses of variance were conducted to determine whether DP-gram parameters differed between Group A and Group B.

RESULTS

For the low-resolution DP-grams examined in this study, no significant between-group differences in peak occurrence, peak height, and peak width were observed. DPOAE levels were significantly higher in ears classified in Group A compared with ears classified in Group B in individuals with symmetrical hearing.

CONCLUSIONS

Although spectral peaks are evident in DP-grams acquired with low resolution of the primary tones, DPOAE levels are more effective in distinguishing ears with greater hearing sensitivity from less sensitive ears.

Detecting incipient inner-ear damage from impulse noise with otoacoustic emissions

Audiometric thresholds and otoacoustic emissions (OAEs) were measured in 285 U.S. Marine Corps recruits before and three weeks after exposure to impulse-noise sources from weapons' fire and simulated artillery, and in 32 non-noise-exposed controls. At pre-test, audiometric thresholds for all ears were <or=25 dB HL from 0.5 to 3 kHz and <or=30 dB HL at 4 kHz. Ears with low-level or absent OAEs at pre-test were more likely to be classified with significant threshold shifts (STSs) at post-test. A subgroup of 60 noise-exposed volunteers with complete data sets for both ears showed significant decreases in OAE amplitude but no change in audiometric thresholds. STSs and significant emission shifts (SESs) between 2 and 4 kHz in individual ears were identified using criteria based on the standard error of measurement from the control group. There was essentially no association between the occurrence of STS and SES. There were more SESs than STSs, and the group of SES ears had more STS ears than the group of no-SES ears. The increased sensitivity of OAEs in comparison to audiometric thresholds was shown in all analyses, and low-level OAEs indicate an increased risk of future hearing loss by as much as ninefold.

Racial and gender effects on pure-tone thresholds and distortion-product otoacoustic emissions (DPOAEs) in normal-hearing young adults

This study examined racial and gender effects on behavioral thresholds and distortion-product otoacoustic emissions (DPOAEs) in the same subjects. Pure-tone behavioral thresholds and DPOAEs were measured in 60 young normal-hearing adult subjects (20 Caucasian, 20 Asian, 20 African-American, with ten females and ten males in each group). Behavioral thresholds were measured from 1000 through 16,000 Hz using Békèsy tracking. A DPOAE frequency sweep was measured with primary stimulus levels of L(1)/L(2)=60/45 dB SPL, and an f(2)/f(1) of 1.2 at discrete f(2) frequencies between 2000 through 12,000 Hz for each subject. Significant racial and gender differences in behavioral thresholds were found at 14,000 and 16,000 Hz, with the African Americans and females having the best hearing sensitivity. Based on the current results, similar findings for DPOAE frequency sweeps can be expected amongst different racial groups given that no significant differences were identified between the groups. To further define the effects of race and gender on auditory measures, future studies should include larger numbers of subjects, measurement of body size and middle ear reflectance, and examine emission generators.

Distortion product otoacoustic emissions: cochlear-source contributions and clinical test performance

It has been proposed that the clinical accuracy of distortion product otoacoustic emissions (DPOAEs) is affected by the interaction of distortion and reflection sources contributing to the response. This study evaluated changes in dichotomous-decision test performance and threshold-prediction accuracy when DPOAE source contribution was controlled. Data were obtained from 205 normal and impaired ears with L(2) ranging from 0 to 80 dB SPL and f(2)=2 and 4 kHz. Data were collected for control conditions (no suppressor, f(3)) and with f(3) presented at three levels that previously had been shown to reduce the reflection-source contribution. The results indicated that controlling source contribution with a suppressor did not improve diagnostic accuracy (as reflected by relative operating characteristic curve area) and frequently resulted in poorer test performance compared to control conditions. Likewise, correlations between DPOAE and behavioral thresholds were not strengthened when using the suppressors to control source contribution. While improvements in test accuracy were observed for a subset of subjects (normal ears with the smallest DPOAEs and impaired ears with the largest DPOAEs), the lack of improvement for the larger, unselected subject group suggests that DPOAEs should be recorded in the clinic without attempting to control the source contribution with a suppressor.

A comparative study of distortion-product-otoacoustic-emission fine structure in human newborns and adults with normal hearing

Distortion product otoacoustic emissions (DPOAE) measured in human newborns are not adult-like. More than a decade of work from various investigators has created a well-developed body of evidence describing these differences but the putative anatomy or physiology has only been partially explained. Recently, Abdala and Keefe [J. Acoust. Soc. Am. 120, 3832-3842 (2006)] have identified outer and middle ear immaturities that at least partially describe the differences observed between newborn and adult input-output functions and suppression tuning curves. DPOAE fine structure characteristics and their maturation have not been examined to any extent in the literature. Fine structure characteristics in two groups of ten newborns and young adults with normal hearing sensitivity are compared here. Consistent with previous reports, the newborns show higher DPOAE levels; greater fine structure depth and wider fine structure spacing is also observed in the newborns. Differences in fine structure morphology are also observed between the two age groups. While some of these findings are attributable to an immature outer and middle ear system in the newborns, it is argued that some observed differences in fine structure characteristics might be due to remnant immaturities in passive motion of the basilar membrane in the newborn cochlea.

Otoacoustic emission sensitivity to low levels of noise-induced hearing loss

With the aim of investigating the capability of otoacoustic emission (OAE) in the detection of low levels of noise-induced hearing loss, audiometric and otoacoustic data of young workers (age: 18-35) exposed to different levels of industrial noise have been recorded. These subjects are participating in a long-term longitudinal study, in which audiometric, exposure (both professional and extra-professional), and OAE data (transient evoked and distortion product) will be collected for a period of several years. All measurements have been performed, during routine occupational health surveillance, with a standard clinical apparatus and acquisition procedure, which can be easily used in the occupational safety practice. The first study was focused on the correlation between transient evoked OAE signal-to-noise ratio and distortion product (DPOAE) OAE level and the audiometric threshold, investigating the causes of the rather large intersubject variability of the OAE levels. The data analysis has shown that, if both OAE data and audiometric data are averaged over a sufficiently large bandwidth, the correlation between DPOAE levels and audiometric hearing threshold is sufficient to design OAE-based diagnostic tests with good sensitivity and specificity also in a very mild hearing loss range, between 10 and 20 dB.

A validation and potential clinical application of multivariate analyses of distortion-product otoacoustic emission data

OBJECTIVE

To test the generalizability of multivariate analyses of distortion-product otoacoustic emission (DPOAE) data. Previously published multivariate solutions were applied to a new set of data to determine if test-performance improvements, evident in previous reports, are retained. An additional objective was to provide an alternative approach for making multivariate dichotomous decisions of hearing status in the clinic, based on DPOAE measurements.

DESIGN

DPOAE level and noise were obtained in 345 ears of 187 subjects. Approximately one third of the subjects had normal hearing, whereas the remainder had hearing loss, ranging from 25 to more than 120 dB HL. DPOAE data were collected at each of nine frequencies. After data collection, clinical decision theory, in combination with univariate (DPOAE level and signal-to-noise ratio [SNR]) and multivariate (logistic regression) analyses, was used to construct relative operating characteristic (ROC) curves and to generate ROC curve areas. In addition, test performance was assessed by fixing the false-alarm rate and comparing different approaches to analyses in terms of their failure rates as a function of magnitude of hearing loss. The DPOAE test results were compared with either single-frequency or multifrequency gold standards. The multivariate solutions were taken from previously published work (Dorn et al., 1999; Gorga, et al., 1999).

RESULTS

DPOAE level and SNR resulted in roughly equivalent test performance (ROC curve areas and failure rates among ears with hearing loss), although DPOAE level performed better for frequencies above 1 kHz, and SNR performed better for frequencies at 0.75 and 1 kHz. Multivariate analyses resulted in better test performance for nearly all conditions, compared with the univariate approaches that used either DPOAE level or SNR. The improvements in test performance were greatest for the frequencies at which the univariate analyses performed poorest (0.75 kHz, 1 kHz, and 8 kHz). Less difference was observed between univariate and multivariate approaches when multifrequency gold standards were used; however, even for the multifrequency cases, multivariate analyses generally resulted in better performance. An approach that might facilitate the interpretation of multifrequency DPOAE measurements in the clinic is described.

CONCLUSIONS

Previously described multivariate analyses were robust in that they improved test performance when applied to an entirely new set of DPOAE data. This, in turn, suggests that the previously described multivariate solutions may have clinical utility in that they are expected to improve test performance at no additional cost in terms of data-acquisition or data-analysis time. In addition to demonstrating that these solutions generalized to new data, an alternative approach to interpreting multifrequency DPOAE measurements is provided that includes the advantages of using multivariate analyses. This new metric may be useful when DPOAEs are used for screening purposes.

Neonatal hearing screening: evaluation of tone-burst and click-evoked otoacoustic emission test criteria

OBJECTIVE

Click-evoked otoacoustic emissions (CEOAEs) are widely used in universal neonatal hearing screening programs. A common finding in many such programs is a relatively high false-positive rate. This is often due to infant physiological noise adversely affecting the emission recording, leading to a "refer" screening outcome. In an attempt to reduce false-positive screening outcomes related to the effects of noise on otoacoustic emission response detection, tone-burst-evoked otoacoustic emissions (TBOAEs) were included in a neonatal hearing screening program because TBOAEs may elicit a greater signal-to-noise ratio than CEOAEs. The research project compared the pass/refer rate for a CEOAE-based test using established pass/refer criteria with the pass/refer rate for screening criteria that were based on TBOAE results alone or on combined CEOAE and TEOAE results.

DESIGN

Neonates were recruited at the Hong Kong Adventist Hospital, and both CEOAEs and TBOAEs were performed. Six passing criteria were used in this study, based on CEOAEs only; CEOAEs plus 1 kHz TBOAEs; CEOAEs plus 2 kHz TBOAEs; CEOAEs plus 3 kHz TBOAEs; CEOAEs plus 1, 2, and 3 kHz TBOAEs; and TBOAEs only.

RESULTS

Data from 298 neonates (546 ears) were obtained. Criteria set 1, using CEOAEs only, demonstrated a pass rate of 79.1%, and 114 ears were referred. Criteria set 2, using CEOAEs together with TBOAEs recorded at 1 kHz, passed 39 more ears than Protocol 1, and the pass rate was 86.3%. Hence, the overall referral rate for total number of screened ears decreased by 7.2 percentage points. Criteria set 3, using CEOAEs together with TBOAEs recorded at 2 kHz, and Criteria set 4, using CEOAEs in conjunction with TBOAEs recorded at 3 kHz, gave pass rates similar to Criteria set 1. Criteria set 5, using TBOAE information at frequencies where CEOAEs were not rated as "pass," raised the pass rate from 79.1 to 87.6%, reducing the overall referral rate by 8.5 percentage points. Criteria set 6, in which neonates were screened with TBOAEs recorded at 1, 2, and 3 kHz, gave a pass rate of 78.4%, similar to results for the CEOAE-only procedure.

CONCLUSIONS

Both Criteria sets 2 and 5, which combined CEOAE and TBOAE recordings, gave significantly higher pass rates than Criteria sets 1, 3, 4, and 6. The results suggest that the introduction of combined CEOAE and TBOAE protocols may assist in the reduction of refer outcomes, and hence the false-positive rates, of neonatal hearing screening programs.

Distortion-product otoacoustic emission spectra and high-resolution audiometry in noise-induced hearing loss

Distortion product otoacoustic emissions (DPOAE) elicited by 60dB SPL pure tones at f1 and f2 were collected at 2f1-f2, in 1/10th octave steps, in a sample of 36 ears from 27 patients with noise-induced hearing loss (NIHL). They were analyzed in the frequency domain against the outcome of high-resolution pure-tone audiometry, performed with the help of a Békésy sweep-frequency automatic audiometer. The characteristics of DPOAE level plots as a function of frequency (the so-called DP-grams), relative to the DPOAE levels of a control age-matched group, were compared to their alleged counterparts on the audiograms, i.e., the lower and upper frequency boundaries of the interval with hearing loss. Ears with NIHL split into two subgroups, one (n = 25) with a notch in the DP-gram such that its lower boundary matched the lower limit of the audiometric notch (linear regression with a slope of 0.91, r(2) = 0.644, p < 0.001). Likewise, when it existed, its upper boundary matched its upper counterpart on the audiogram (linear regression with a slope of 0.96, r(2) = 0.89, p < 0.001). In this respect, DP-grams performed better than transient-evoked OAE spectra, which exhibited poor correlations with audiogram patterns. The second subgroup (n = 11) exhibited normal DPOAEs at all frequencies despite audiometric losses similar to those of the first subgroup. In all cases, DPOAE levels were poor predictors of the degree of hearing losses. It is hypothesized that NIHL in the second subgroup involves inner hair cells or auditory neurons, instead of outer hair cells in the first subgroup. Provided NIHL affected outer hair cells, DP-grams provided a comparatively accurate predictor of the spectral extent of hearing loss.

Audiometric predictions using stimulus-frequency otoacoustic emissions and middle ear measurements

OBJECTIVE

The goals of the study are to determine how well stimulus-frequency otoacoustic emissions (SFOAEs) identify hearing loss, classify hearing loss as mild or moderate-severe, and correlate with pure-tone thresholds in a population of adults with normal middle ear function. Other goals are to determine if middle ear function as assessed by wideband acoustic transfer function (ATF) measurements in the ear canal account for the variability in normal thresholds, and if the inclusion of ATFs improves the ability of SFOAEs to identify hearing loss and predict pure-tone thresholds.

DESIGN

The total suppressed SFOAE signal and its corresponding noise were recorded in 85 ears (22 normal ears and 63 ears with sensorineural hearing loss) at octave frequencies from 0.5 to 8 kHz, using a nonlinear residual method. SFOAEs were recorded a second time in three impaired ears to assess repeatability. Ambient-pressure ATFs were obtained in all but one of these 85 ears and were also obtained from an additional 31 normal-hearing subjects in whom SFOAE data were not obtained. Pure-tone air and bone conduction thresholds and 226-Hz tympanograms were obtained on all subjects. Normal tympanometry and the absence of air-bone gaps were used to screen subjects for normal middle ear function. Clinical decision theory was used to assess the performance of SFOAE and ATF predictors in classifying ears as normal or impaired, and linear regression analysis was used to test the ability of SFOAE and ATF variables to predict the air conduction audiogram.

RESULTS

The ability of SFOAEs to classify ears as normal or hearing impaired was significant at all test frequencies. The ability of SFOAEs to classify impaired ears as either mild or moderate-severe was significant at test frequencies from 0.5 to 4 kHz. SFOAEs were present in cases of severe hearing loss. SFOAEs were also significantly correlated with air conduction thresholds from 0.5 to 8 kHz. The best performance occurred with the use of the SFOAE signal-to-noise ratio as the predictor, and the overall best performance was at 2 kHz. The SFOAE signal-to-noise measures were repeatable to within 3.5 dB in impaired ears. The ATF measures explained up to 25% of the variance in the normal audiogram; however, ATF measures did not improve SFOAEs predictors of hearing loss except at 4 kHz.

CONCLUSIONS

In common with other OAE types, SFOAEs are capable of identifying the presence of hearing loss. In particular, SFOAEs performed better than distortion-product and click-evoked OAEs in predicting auditory status at 0.5 kHz; SFOAE performance was similar to that of other OAE types at higher frequencies except for a slight performance reduction at 4 kHz. Because SFOAEs were detected in ears with mild to severe cases of hearing loss, they may also provide an estimate of the classification of hearing loss. Although SFOAEs were significantly correlated with hearing threshold, they do not appear to have clinical utility in predicting a specific behavioral threshold. Information on middle ear status as assessed by ATF measures offered minimal improvement in SFOAE predictions of auditory status in a population of normal and impaired ears with normal middle ear function. However, ATF variables did explain a significant fraction of the variability in the audiograms of normal ears, suggesting that audiometric thresholds in normal ears are partially constrained by middle ear function as assessed by ATF tests.

Detection of hearing loss using 2f2-f1 and 2f1-f2 distortion-product otoacoustic emissions

Although many distortion-product otoacoustic emissions (DPOAEs) may be measured in the ear canal in response to 2 pure tone stimuli, the majority of clinical studies have focused exclusively on the DPOAE at the frequency 2f1-f2. This study investigated another DPOAE, 2f2-f1, in an attempt to determine the following: (a) the optimal stimulus parameters for its clinical measurement and (b) its utility in differentiating between normal-hearing and hearing-impaired ears at low-to-mid frequencies (<or=2,000 Hz) when measured either alone or in conjunction with the 2f1-f2 DPOAE. Two experiments were conducted. In Experiment 1, the effects of primary level, level separation, and frequency separation (f2/f1) on 2f2-f1 DPOAE level were evaluated in normal-hearing ears for low-to-mid f2 frequencies (700-2,000 Hz). Moderately high-level primaries (60-70 dB SPL) presented at equal levels or with f2 slightly higher than f1 produced the highest 2f2-f1 DPOAE levels. When the f2/f1 ratio that produced the highest 2f2-f1 DPOAE levels was examined across participants, the mean optimal f2/f1 ratio across f2 frequencies and primary level separations was 1.08. In Experiment 2, the accuracy with which DPOAE level or signal-to-noise ratio identified hearing status at the f2 frequency as normal or impaired was evaluated using clinical decision analysis. The 2f2-f1 and 2f1-f2 DPOAEs were measured from both normal-hearing and hearing-impaired ears using 2 sets of stimulus parameters: (a) the traditional parameters for measuring the 2f1-f2 DPOAE (f2/f1 = 1.22; L1, L2 = 65, 55 dB SPL) and (b) the new parameters that were deemed optimal for the 2f2-f1 DPOAE in Experiment 1 (f2/f1 = 1.073, L1 and L2 = 65 dB SPL). Identification of hearing status using 2f2-f1 DPOAE level and signal-to-noise ratio was more accurate when the new stimulus parameters were used compared with the results achieved when the 2f2-f1 DPOAE was recorded using the traditional parameters. However, identification of hearing status was less accurate for the 2f2-f1 DPOAE measured using the new parameters than for the 2f1-f2 DPOAE measured using the traditional parameters. No statistically significant improvements in test performance were achieved when the information from the 2 DPOAEs was combined, either by summing the DPOAE levels or by using logistic regression analysis.

Otoacoustic emissions in the general adult population of Nord-Trøndelag, Norway: III. Relationships with pure-tone hearing thresholds

This study aims to describe the association between otoacoustic emissions (OAEs) and pure-tone hearing thresholds (PTTs) in an unscreened adult population (N =6415), to determine the efficiency by which TEOAEs and DPOAEs can identify ears with elevated PTTs, and to investigate whether a combination of DPOAE and TEOAE responses improves this performance. Associations were examined by linear regression analysis and ANOVA. Test performance was assessed by receiver operator characteristic (ROC) curves. The relation between OAEs and PTTs appeared curvilinear with a moderate degree of non-linearity. Combining DPOAEs and TEOAEs improved performance. Test performance depended on the cut-off thresholds defining elevated PTTs with optimal values between 25 and 45 dB HL, depending on frequency and type of OAE measure. The unique constitution of the present large sample, which reflects the general adult population, makes these results applicable to population-based studies and screening programs.

Effects of aspirin on distortion product otoacoustic emission suppression in human adults: a comparison with neonatal data

One of the distortion product otoacoustic emission (DPOAE) paradigms used to study cochlear function is DPOAE (2f1-f2) ipsilateral suppression. Newborns do not have adultlike DPOAE suppression. At 6000 Hz, infants show excessively narrow DPOAE suppression tuning and shallow growth of suppression for low-frequency suppressor tones. The source of this immaturity is not known but the outer hair cell (OHC) is one possible locus. In the present study, DPOAE suppression was measured at f2 = 1500 and 6000 Hz from two groups with impaired OHC function in an attempt to model the observed immaturity in neonates: adults with aspirin-induced OHC dysfunction and subjects with sensorineural hearing loss (SNHL). Their DPOAE suppression results were compared to those obtained from a group of term newborns to address whether infant DPOAE suppression resembles suppression from individuals with known OHC dysfunction. Results indicate that aspirin systematically alters DPOAE suppression in adults at f2 = 6000 Hz, but not 1500 Hz. However, neither aspirin-induced OHC dysfunction nor naturally occurring SNHL produces "neonatal-like" DPOAE suppression at either test frequency. This finding does not support the hypothesis that non-adultlike DPOAE suppression characterizing newborns can be explained by minor impairments or alterations of OHC function.

Gender effects on high frequency distortion product otoacoustic emissions in humans

OBJECTIVE

Gender has been reported to affect many tests of the auditory system, including distortion product otoacoustic emission (DPOAE) group delay and level when elicited with lower frequency stimuli (<8 kHz). Using custom equipment, the effect of gender on DPOAEs at higher frequencies was explored. It is expected that differences in group delay reported at very low frequencies (e.g., 0.78 Hz) will not be replicated at higher frequencies. Additionally, it was hypothesized that female subjects would display larger-level DPOAEs at higher frequencies, based on evidence that female subjects tend to have larger emissions when elicited with lower frequency stimuli.

DESIGN

DPOAEs were measured in 37 subjects (20 females and 17 males) with normal behavioral thresholds, middle ear function, and present acoustic reflexes at 1 kHz with contralateral stimulation. Behavioral thresholds were measured through 16 kHz using Békèsy tracking. Ratio and frequency sweeps were used to calculate DPOAE group delay and measure DPOAE levels, respectively. Ratio sweeps were obtained at f2 frequencies of 1, 2, 4, 8, 10, 12, 14, and 16 kHz, with L1 = 60 and L2 = 45 dB SPL, with the ratio (f2/f1) varied from 1.11 to 1.3. Frequency sweeps were measured with L1 = 60 and L2 = 45 dB SPL and an f2/f1 of 1.2 at discrete f2 frequencies between 1 and 16 kHz. Data were subjected to repeated-measures analysis of variance.

RESULTS

Significant frequency-by-gender interactions were found for group delay (for data from 1 to 8 kHz) and level (for data from 9 to 15 kHz). The frequency-by-gender interaction and the main effect of gender were not significant for the behavioral results.

CONCLUSIONS

Gender-based norms for auditory-evoked potentials measures are standard in clinical settings. The results of the present study, in agreement with previous studies, indicate that significant interactions exist between gender and DPOAE group delay values in the lower frequencies, and between gender and DPOAE levels at the higher frequencies. To reach the goal of using high frequency DPOAEs in clinical protocols, such as for auditory neuropathy/dys-synchrony diagnosis and ototoxicity monitoring, DPOAEs elicited with conventional and higher frequency stimuli must be understood, including the role of gender to determine if an effect on clinical protocols would exist.

Effects of a Suppressor Tone on Distortion Product Otoacoustic Emissions Fine Structure: Why a Universal Suppressor Level Is Not a Practical Solution to Obtaining Single-Generator DP-Grams

OBJECTIVES

The use of a suppressor tone has been proposed as the method of choice in obtaining single-generator distortion product (DP) grams, the speculation being that such DP grams will be more predictive of hearing thresholds. Current distortion product otoacoustic emissions (DPOAE) theory points to the ear canal DPOAE signal being a complex interaction between multiple components. The effectiveness of a suppressor tone is predicted to be dependent entirely on the relative levels of these components. We examine the validity of using a suppressor tone through a detailed examination of the effects of a suppressor on DPOAE fine structure in individual ears.

DESIGN

DPOAE fine structure, recorded in 10 normal-hearing individuals with a suppressor tone at 45, 55, and 65 dB SPL, was compared with recordings without a suppressor. Behavioral hearing thresholds were also measured in the same subjects, using 2-dB steps.

RESULTS

The effect of the suppressor tone on DPOAE fine structure varied between ears and was dependent on frequency within ears. Correlation between hearing thresholds and DPOAE level measured without a suppressor was similar to previous reports. The effects of the suppressor are explained in the theoretical framework of a model involving multiple DPOAE components.

CONCLUSIONS

Our results suggest that a suppressor tone can have highly variable effects on fine structure across individuals or even across frequency within one ear, thereby making the use of a suppressor less viable as a clinical tool for obtaining single-generator DP grams.

A longitudinal study of changes in evoked otoacoustic emissions and pure-tone thresholds as measured in a hearing conservation program

Non-linear transient-evoked otoacoustic emissions (TEOAEs) at 74dB pSPL, distortion-product otoacoustic emissions (DPOAEs) at 65/45dB SPL and pure-tone audiometry were used to detect noise-induced, inner car changes in a longitudinal study. Repeated-measures ANOVAs were made on the Noise (n=69) and Quiet (n=42) groups. The Noise group's hearing thresholds increased by 1.2 dB and DPOAE amplitude decreased by -0.9 dB. For both groups, TEOAE amplitude decreased by approximately -0.6 dB. Eight of 12 ears with permanent threshold shift (PTS) and 10 of 13 ears with temporary threshold shift (TTS) showed TEOAE decrements or low baseline TEOAE amplitudes. Fewer TTS and PTS ears also showed DPOAE decrements, and there was never a DPOAE decrement without a corresponding TEOAE decrement or low TEOAE baseline. Some TTS ears showed permanent emission decrements. Although otoacoustic emissions show promise in detecting noise-induced inner ear changes, it is premature to use them in hearing conservation programs.