Distortion-product otoacoustic emission input/output characteristics in normal-hearing and hearing-impaired human ears

NADPH Oxidase 3: Beyond the Inner Ear

Reactive oxygen species (ROS) were formerly known as mere byproducts of metabolism with damaging effects on cellular structures. The discovery and description of NADPH oxidases (Nox) as a whole enzyme family that only produce this harmful group of molecules was surprising. After intensive research, seven Nox isoforms were discovered, described and extensively studied. Among them, the NADPH oxidase 3 is the perhaps most underrated Nox isoform, since it was firstly discovered in the inner ear. This stigma of Nox3 as "being only expressed in the inner ear" was also used by me several times. Therefore, the question arose whether this sentence is still valid or even usable. To this end, this review solely focuses on Nox3 and summarizes its discovery, the structural components, the activating and regulating factors, the expression in cells, tissues and organs, as well as the beneficial and detrimental effects of Nox3-mediated ROS production on body functions. Furthermore, the involvement of Nox3-derived ROS in diseases progression and, accordingly, as a potential target for disease treatment, will be discussed.

Characterizing the Relationship Between Reflection and Distortion Otoacoustic Emissions in Normal-Hearing Adults

Otoacoustic emissions (OAEs) arise from one (or a combination) of two basic generation mechanisms in the cochlea: nonlinear distortion and linear reflection. As a result of having distinct generation processes, these two classes of emissions may provide non-redundant information about hair-cell integrity and show distinct sensitivities to cochlear pathology. Here, we characterize the relationship between reflection and distortion emissions in normal hearers across a broad frequency and stimulus-level space using novel analysis techniques. Furthermore, we illustrate the promise of this approach in a small group of individuals with mild-moderate hearing loss. A "joint-OAE profile" was created by measuring interleaved swept-tone stimulus-frequency OAEs (SFOAEs) and 2f1-f2 distortion-product OAEs (DPOAEs) in the same ears using well-considered parameters. OAE spectra and input/output functions were calculated across five octaves. Using our specific recording protocol and analysis scheme, SFOAEs in normal hearers had higher levels than did DPOAEs, with the most pronounced differences occurring at the highest stimulus levels. Also, SFOAE compression occurred at higher stimulus levels (than did DPOAE compression) and its growth in the compressed region was steeper. The diagnostic implications of these findings and the influence of the measurement protocol on both OAEs (and on their relationship) are discussed.

Combined effects of the exposure to silver nanoparticles and noise on hearing function and cochlea structure of the male rats

AIMS

This study intended to investigate whether exposure to the combination of noise and Ag-NPs in rats induces cochlear damage and hearing dysfunction.

MAIN METHODS

A total of 24Wistar rats were divided into four treatment groups and received/exposed to saline (IP), Ag-NPs (100 mg/kg, 5d/w for 4 weeks), 8 kHz narrowband noise (104 dB SPL, 6 h/day, 5d/w for 4 weeks) and Ag-NPs plus noise. The DPOAE, serum levels of MDA and SOD and changes in body weight were assessed. The rat cochlea was further stained for investigating the mRNA expression (TL-6, NOX3, and TNF-), IHC (TUJ-1 and MHC7), and histological alterations. The Ag-NPs characteristics were also analysed by SEM and XRD.

KEY FINDINGS

DPOAE values were remarkably reduced (p < 0.05) among the exposed groups. Furthermore, exposure to noise and Ag-NPs significantly increased MDA levels and decreased the SOD activity in the serum. In comparison to the control group, the expression of IL-6, TNF-, and NOX3 was shown to be elevated in the Ag-NPs plus noise group. The body weight also increased significantly in all groups with the exception of the Ag-NPs plus noise group. IHC tests showed remarkable down-regulation of TUJ1 and MYO7A. Morphological changes confirmed our findings as well. SEM and XRD data validated the production of Ag-NPs.

SIGNIFICANCE

According to the findings of this study, sub-acute exposure to noise and Ag-NPs causes permanent damage to the hair cells that are in charge of high-frequency perception.

Weakened Cochlear Nonlinearity During Human Aging and Perceptual Correlates

OBJECTIVE

As humans age, compressive nonlinearity-a hallmark of healthy cochlear function-changes. The nonlinear distortion-component of the distortion product otoacoustic emission (DPOAE) provides a noninvasive gauge of cochlear nonlinearity. Earlier published work has suggested that weakened nonlinearity begins in middle age; the current work extends this investigation into the eight decade of life using advanced DPOAE data collection and analysis methods as well as multiple metrics of nonlinearity, including a test of loudness scaling.

DESIGN

The 2f1-f2 DPOAE was recorded in 20 young adults, 25 middle-aged adults and 32 older adults from f2 = 0.78 to 9.4 kHz with primary tones (f2/f1 = 1.22) swept upward at a rate of 0.5 octave/sec. Only frequencies with audiometric thresholds ≤20 dB HL were included in the analysis and to the extent possible, ears were audiometrically matched to eliminate hearing threshold as a contributing factor to the observed age effects. Input/output functions were generated for the separated distortion-component of the DPOAE to probe compressive nonlinearity of the cochlea, and ipsilateral suppression of the DPOAE was conducted to probe two-tone suppression. To investigate the perceptual effects of weakening nonlinearity on loudness perception, the same subjects performed categorical loudness scaling. Age effects on both DPOAE and loudness scaling variables were assessed, and correlations were conducted between key OAE and perceptual metrics.

RESULTS

Age × Frequency ANOVAs revealed that the compression knee of the DPOAE I/O function occurred at higher stimulus levels in both groups of older adults compared to young adults, suggesting an expanded linear range with aging; also, the compressive slope (growth beyond the knee point) was steeper in older-adults compared to young adults. These results were most notable at high frequencies. ANOVAs including age and auditory threshold as factors confirmed that the age effect observed was independent of threshold. Additionally, in smaller subsets of subjects with audiometrically matched data, these same trends persisted, further ruling out hearing threshold as an influential factor. The growth of DPOAE ipsilateral suppression was shallower near 4 kHz in middle-aged and older adults compared to young adults and elevated suppression thresholds were observed. Results of categorical loudness scaling showed steeper growth of loudness for older adults and, at fixed sensation levels (dB SL), the older-adult group rated tones as louder than did their young-adult counterparts, suggesting abnormal loudness growth and perception. Several correlations between the compression knee of the DPOAE I/O function and key metrics of loudness scaling were significant and accounted for up to one-third of the variance.

CONCLUSIONS

Results indicate that the aging cochlea begins to show weakened nonlinearity in middle age and it progressively weakens further into senescence. The perceptual impact of weakened nonlinearity during aging is manifested as abnormal loudness judgments; that is, in older-adult ears, a tone considered comfortable or medium in young-adult ears can be considered loud. The biophysical origin of this weakened nonlinearity is not known. It is hypothesized to reflect aging-related damage to, or loss of, outer hair cells and their stereocilia. More work is warranted to better define the perceptual impact of a linearized cochlear response in older adults and to consider how this deficit might impact the fitting of hearing aids and other intervention strategies.

Comparison of Behavioral and Physiological Measures of the Status of the Cochlear Nonlinearity

While an audiogram is a useful method of characterizing hearing loss, it has been suggested that including a complementary, suprathreshold measure, for example, a measure of the status of the cochlear active mechanism, could lead to improved diagnostics and improved hearing-aid fitting in individual listeners. While several behavioral and physiological methods have been proposed to measure the cochlear-nonlinearity characteristics, evidence of a good correspondence between them is lacking, at least in the case of hearing-impaired listeners. If this lack of correspondence is due to, for example, limited reliability of one of such measures, it might be a reason for limited evidence of the benefit of measuring peripheral compression. The aim of this study was to investigate the relation between measures of the peripheral-nonlinearity status estimated using two psychoacoustical methods (based on the notched-noise and temporal-masking curve methods) and otoacoustic emissions, on a large sample of hearing-impaired listeners. While the relation between the estimates from the notched-noise and the otoacoustic emissions experiments was found to be stronger than predicted by the audiogram alone, the relations between the two measures and the temporal-masking based measure did not show the same pattern, that is, the variance shared by any of the two measures with the temporal-masking curve-based measure was also shared with the audiogram.

Cochlear supporting cells require GAS2 for cytoskeletal architecture and hearing

In mammals, sound is detected by mechanosensory hair cells that are activated in response to vibrations at frequency-dependent positions along the cochlear duct. We demonstrate that inner ear supporting cells provide a structural framework for transmitting sound energy through the cochlear partition. Humans and mice with mutations in GAS2, encoding a cytoskeletal regulatory protein, exhibit hearing loss due to disorganization and destabilization of microtubule bundles in pillar and Deiters' cells, two types of inner ear supporting cells with unique cytoskeletal specializations. Failure to maintain microtubule bundle integrity reduced supporting cell stiffness, which in turn altered cochlear micromechanics in Gas2 mutants. Vibratory responses to sound were measured in cochleae from live mice, revealing defects in the propagation and amplification of the traveling wave in Gas2 mutants. We propose that the microtubule bundling activity of GAS2 imparts supporting cells with mechanical properties for transmitting sound energy through the cochlea.

On the use of envelope following responses to estimate peripheral level compression in the auditory system

Individual estimates of cochlear compression may provide complementary information to traditional audiometric hearing thresholds in disentangling different types of peripheral cochlear damage. Here we investigated the use of the slope of envelope following response (EFR) magnitude-level functions obtained from four simultaneously presented amplitude modulated tones with modulation frequencies of 80-100 Hz as a proxy of peripheral level compression. Compression estimates in individual normal hearing (NH) listeners were consistent with previously reported group-averaged compression estimates based on psychoacoustical and distortion-product oto-acoustic emission (DPOAE) measures in human listeners. They were also similar to basilar membrane (BM) compression values measured invasively in non-human mammals. EFR-based compression estimates in hearing-impaired listeners were less compressive than those for the NH listeners, consistent with a reduction of BM compression. Cochlear compression was also estimated using DPOAEs in the same NH listeners. DPOAE estimates were larger (less compressive) than EFRs estimates, showing no correlation. Despite the numerical concordance between EFR-based compression estimates and group-averaged estimates from other methods, simulations using an auditory nerve (AN) model revealed that compression estimates based on EFRs might be highly influenced by contributions from off-characteristic frequency (CF) neural populations. This compromises the possibility to estimate on-CF (i.e., frequency-specific or "local") peripheral level compression with EFRs.

A convolutional neural-network model of human cochlear mechanics and filter tuning for real-time applications

Auditory models are commonly used as feature extractors for automatic speech-recognition systems or as front-ends for robotics, machine-hearing and hearing-aid applications. Although auditory models can capture the biophysical and nonlinear properties of human hearing in great detail, these biophysical models are computationally expensive and cannot be used in real-time applications. We present a hybrid approach where convolutional neural networks are combined with computational neuroscience to yield a real-time end-to-end model for human cochlear mechanics, including level-dependent filter tuning (CoNNear). The CoNNear model was trained on acoustic speech material and its performance and applicability were evaluated using (unseen) sound stimuli commonly employed in cochlear mechanics research. The CoNNear model accurately simulates human cochlear frequency selectivity and its dependence on sound intensity, an essential quality for robust speech intelligibility at negative speech-to-background-noise ratios. The CoNNear architecture is based on parallel and differentiable computations and has the power to achieve real-time human performance. These unique CoNNear features will enable the next generation of human-like machine-hearing applications.

Derivation of input-output functions from distortion-product otoacoustic emission level maps

Distortion-product otoacoustic emissions (DPOAEs) emerge from the cochlea when elicited with two tones of frequencies f₁ and f₂. DPOAEs mainly consist of two components, a nonlinear-distortion and a coherent-reflection component. Input-output (I/O) functions of DPOAE pressure at the cubic difference frequency, f_DP=2f₁-f₂, enable the computation of estimated distortion-product thresholds (EDPTs), offering a noninvasive approach to estimate auditory thresholds. However, wave interference between the DPOAE components and suboptimal stimulus-level pairs reduces the accuracy of EDPTs. Here, the amplitude P of the nonlinear-distortion component is extracted from short-pulse DPOAE time signals. DPOAE level maps representing the growth behavior of P in L₁,L₂ space are recorded for 21 stimulus-level pairs and 14 frequencies with f₂=1 to 14 kHz (f₂/f₁=1.2) from 20 ears. Reproducing DPOAE growth behavior using a least-squares fit approach enables the derivation of ridge-based I/O functions from model level maps. Objective evaluation criteria assess the fit results and provide EDPTs, which correlate significantly with auditory thresholds (p < 0.001). In conclusion, I/O functions derived from model level maps provide EDPTs with high precision but without the need of predefined optimal stimulus-level pairs.

A Clinical Study of Effect of Hyperpyrexia on Otoacoustic Emissions in Children

Various degrees of sensory neural hearing loss can be seen in the progression of some hereditary periodic fever syndromes. Otoacoustic emission testing can help to establish the inner ear involvement at an early period of a periodic fever with a risk of hearing loss (Abdul Kadir et al. in J Int Adv Otol 9(2.79):08-11, 2014). Sensorineural hearing loss is the common most complication of bacterial meningitis in childhood (Richardson in Pediatrics 102(6):1364-1368, 1998). When present from birth, or acquired in the pre-school years, hearing loss of any degree, even mild hearing loss, interferes with speech and language development. In addition to obvious communication deficits, the consequences of hearing loss in children and adults include psychosocial problems, such as frustration, irritability, anxiety, the tendency to withdraw from social interactions, and even depression (Dhar and Hall in Otoacoustic emissions: principles, procedures, and protocols, Plural Publishing, San Diego, 2011). OAE are acoustic signals emitted from cochlea to the middle ear and into the external ear where they are recorded. Evoked OAE are undetectable when deafness is above 30-35 dB Sound pressure level (Biswas in Clinical audio-vestibulometry for otologists and neurologists, Bhalani Publishing House, Mumbai, 1995). OAEs permit early detection of inner ear abnormalities associated with a wide variety of diseases and disorders, including Alport syndrome etc. With early detection, the serious consequences of hearing loss can sometimes be prevented. With proper identification and diagnosis of hearing impairment, timely and effective management for the same can be taken. Data for this study was collected from children (5-14 years) attending the Department of Otorhinolaryngology and Paediatrics Out-patient departments in P.E.S.I.M.S.R, Kuppam. Among the study population 43 (57.3%) were male and 32 (42.7%) were females showing the slight male preponderance. study was done on children with temperature > 1000 F, children with temperature were screened with OAE, and OAE was recorded in same children once fever has subsided and results were compared. This is a new study where we compared same group of children with fever and once fever has subsided. In most other studies, study group was compared to the healthy control group. In our study, children with fever having abnormal FDP values at f1were 9, they reverted back to base line once fever has subsided. This shows that there is no much damage to inner ear at lower frequencies. Almost 47 abnormal FDP values at f2 reverted back to normal. At higher frequencies (f3 and f4), there is no much change in abnormal FDPs with fever and after fever has subsided, this shows that there is more damage to inner ear at higher frequencies. This study demonstrated that hyperpyrexia causes hearing loss in children with fever probably due to cochlear involvement. We conclude that OAE can be used as a screening tool in detecting hearing loss among children because the technique is simple, reproducible, not expensive, not time consuming also effectively narrows down the children with high chances of hearing loss thereby effectively improves the chances of early diagnosis and hence children can be rehabilitated early, making a marked change in their future.

The dynamic gammawarp auditory filterbank

Auditory filterbanks are an integral part of many metrics designed to predict speech intelligibility and speech quality. Considerations in these applications include accurate reproduction of auditory filter shapes, the ability to reproduce the impact of hearing loss as well as normal hearing, and computational efficiency. This paper presents an alternative method for implementing a dynamic compressive gammachirp (dcGC) auditory filterbank [Irino and Patterson (2006). IEEE Trans. Audio Speech Lang. Proc. 14, 2222-2232]. Instead of using a cascade of second-order sections, this approach uses digital frequency warping to give the gammawarp filterbank. The set of warped finite impulse response filter coefficients is constrained to be symmetrical, which results in the same phase response for all filters in the filterbank. The identical phase responses allow the dynamic variation in the gammachirp filter magnitude response to be realized as a sum, using time-varying weights, of three filters that provide the responses for high-, mid-, and low-intensity input signals, respectively. The gammawarp filterbank offers a substantial improvement in execution speed compared to previous dcGC implementations; for a dcGC filterbank, the gammawarp implementation is 24 to 38 times faster than the dcGC Matlab code of Irino.

Changes in the Compressive Nonlinearity of the Cochlea During Early Aging: Estimates From Distortion OAE Input/Output Functions

OBJECTIVES

The level-dependent growth of distortion product otoacoustic emissions (DPOAEs) provides an indirect metric of cochlear compressive nonlinearity. Recent evidence suggests that aging reduces nonlinear distortion emissions more than those associated with linear reflection. Therefore, in this study, we generate input/output (I/O) functions from the isolated distortion component of the DPOAE to probe the effects of early aging on the compressive nonlinearity of the cochlea.

DESIGN

Thirty adults whose ages ranged from 18 to 64 years participated in this study, forming a continuum of young to middle-age subjects. When necessary for analyses, subjects were divided into a young-adult group with a mean age of 21 years, and a middle-aged group with a mean age of 52 years. All young-adult subjects and 11 of the middle-aged subjects had normal hearing; 4 middle-aged ears had slight audiometric threshold elevation at mid-to-high frequencies. DPOAEs (2f1 - f2) were recorded using primary tones swept upward in frequency from 0.5 to 8 kHz, and varied from 25 to 80 dB sound pressure level. The nonlinear distortion component of the total DPOAE was separated and used to create I/O functions at one-half octave intervals from 1.3 to 7.4 kHz. Four features of OAE compression were extracted from a fit to these functions: compression threshold, range of compression, compression slope, and low-level growth. These values were compared between age groups and correlational analyses were conducted between OAE compression threshold and age with audiometric threshold controlled.

RESULTS

Older ears had reduced DPOAE amplitude compared with young-adult ears. The OAE compression threshold was elevated at test frequencies above 2 kHz in the middle-aged subjects by 19 dB (35 versus 54 dB SPL), thereby reducing the compression range. In addition, middle-aged ears showed steeper amplitude growth beyond the compression threshold. Audiometric threshold was initially found to be a confound in establishing the relationship between compression and age; however, statistical analyses allowed us to control its variance. Correlations performed while controlling for age differences in high-frequency audiometric thresholds showed significant relationships between the DPOAE I/O compression threshold and age: Older subjects tended to have elevated compression thresholds compared with younger subjects and an extended range of monotonic growth.

CONCLUSIONS

Cochlear manifestations of nonlinearity, such as the DPOAE, weaken during early aging, and DPOAE I/O functions become linearized. Commensurate changes in high-frequency audiometric thresholds are not sufficient to fully explain these changes. The results suggest that age-related changes in compressive nonlinearity could produce a reduced dynamic range of hearing, and contribute to perceptual difficulties in older listeners.

Otoacoustic emissions in young adults exposed to drums noise of a college band

ABSTRACT Purpose: to identify cochlear dysfunction and occurrence of tinnitus in young adults exposed to drums noise of a college band. Methods: the sample included 50 subjects: 25 musicians (study group) and 25 non-musicians (control group). The procedures included anamnesis, pure tone audiometry, acoustic impedance and Transient Evoked Otoacoustic Emissions, Distortion Product Otoacoustic Emissions and Distortion Product Otoacoustic Emissions Input-Output function. Results: positive correlation between the occurrence of tinnitus and the variables exposure time and use of personal stereos was found. Overall, the study group showed significantly lower Transient Evoked Otoacoustic Emissions, when compared to the control group. In the study group, there was a tendency toward worse response in 6 kHz(f2) in Distortion Product Otoacoustic Emissions in both ears. The Distortion Product Otoacoustic Emissions Input-Output function did not differ between groups nor did its slope. Conclusion: in general, otoacoustic emissions were worse in noise-exposed young people (study group) when compared to the unexposed (control group), indicating that the test may be important in early identification of cochlear changes.

A systematic review of stimulus parameters for eliciting distortion product otoacoustic emissions from adult humans

OBJECTIVE

The objective of this study is to review the scientific literature to determine if a set of stimulus parameters can be described to elicit distortion product otoacoustic emissions (DPOAEs) of higher absolute level and/or greater reliability in healthy adult humans and higher sensitivity and specificity in adults with cochlear lesions.

DESIGN

Systematic review.

STUDY SAMPLE

Searches of four electronic databases yielded 47 studies that had used different parameters to elicit DPOAEs from within or between-groups of adult humans.

RESULTS

The wide range of stimulus parameters used in the reviewed studies saw a wide range of reported values for DPOAE level, reliability, and sensitivity and specificity to cochlear lesions.

CONCLUSION

The most commonly used stimulus parameters for eliciting DPOAEs from adult humans have included frequency ratios for the two primary tones (f₂/f₁) of between 1.04 and 1.4 and levels (L₁/L₂) of 65/55 dB SPL. The most commonly used parameters for eliciting DPOAEs of higher level in healthy adults appear to be linked to f₂/f₁ values between 1.20 and 1.22 and L₁/L₂ levels of 75/75 dB SPL. The stimulus parameters for eliciting DPOAEs of greater reliability in healthy adults and higher sensitivity and specificity in adults with cochlear lesions have yet to be clearly determined.

Input-output functions of the nonlinear-distortion component of distortion-product otoacoustic emissions in normal and hearing-impaired human ears

Distortion-product otoacoustic emissions (DPOAEs) arise in the cochlea in response to two tones with frequencies f₁ and f₂ and mainly consist of two components, a nonlinear-distortion and a coherent-reflection component. Wave interference between these components limits the accuracy of DPOAEs when evaluating the function of the cochlea with conventional continuous stimulus tones. Here, DPOAE components are separated in the time domain from DPOAE signals elicited with short stimulus pulses. The extracted nonlinear-distortion components are used to derive estimated distortion-product thresholds (EDPTs) from semi-logarithmic input-output (I/O) functions for 20 normal-hearing and 21 hearing-impaired subjects. I/O functions were measured with frequency-specific stimulus levels at eight frequencies f₂ = 1,…, 8 kHz (f₂/f₁ = 1.2). For comparison, DPOAEs were also elicited with continuous primary tones. Both acquisition paradigms yielded EDPTs, which significantly correlated with behavioral thresholds (p < 0.001) and enabled derivation of estimated hearing thresholds (EHTs) from EDPTs using a linear regression relationship. DPOAE-component separation in the time domain significantly reduced the standard deviation of EHTs compared to that derived from continuous DPOAEs (p < 0.01). In conclusion, using frequency-specific stimulus levels and DPOAE-component separation increases the reliability of DPOAE I/O functions for assessing cochlear function and estimating behavioral thresholds.

Relationship Between Distortion Product - Otoacoustic Emissions (DPOAEs) and High-Frequency Acoustic Immittance Measures

BACKGROUND Pathologies that alter the impedance of the middle ear may consequently modify the DPOAE amplitude. The aim of this study was to correlate information from 2 different clinical procedures assessing middle ear status. Data from DPOAE responses (both DP-Gram and DP I/O functions) were correlated with data from multi-component tympanometry at 1000 Hz. MATERIAL AND METHODS The subjects were divided into a double-peak group (DPG) and a single-peak group (SPG) depending on 1000 Hz tympanogram pattern. Exclusion criteria (described in the Methods section) were applied to both groups and finally only 31 ears were assigned to each group. The subjects were also assessed with traditional tympanometry and behavioral audiometry. RESULTS Compared to the single-peak group, in terms of the 226 Hz tympanometry data, subjects in the DPG group presented: (i) higher values of ear canal volume; (ii) higher peak pressure, and (iii) significantly higher values of acoustic admittance. DPOAE amplitudes were lower in the DPG group only at 6006 Hz, but the difference in amplitude between the DPG and SPG groups decreased as the frequency increased. Statistical differences were observed only at 1001 Hz and a borderline difference at 1501 Hz. In terms of DPOAE I/O functions, significant differences were observed only in 4 of the 50 tested points. CONCLUSIONS The 1000-Hz tympanometric pattern significantly affects the structure of DPOAE responses only at 1001 Hz. In this context, changes in the properties of the middle ear (as detected by the 1000 Hz tympanometry) can be considered as prime candidates for the observed variability in the DP-grams and the DP I/O functions.

Distortion product otoacoustic emissions in college music majors and nonmusic majors

The presence and absence of distortion product otoacoustic emissions (DPOAEs) as well as DPOAE amplitudes were compared between college music majors and a control group of nonmusic majors. Participants included 28 music majors and 35 nonmusic majors enrolled at a university with ages ranging from 18-25 years. DPOAEs and hearing thresholds were measured bilaterally on all the participants. DPOAE amplitudes were analyzed at the following f2 frequencies: 1,187 Hz, 1,500 Hz, 1,906 Hz, 2,531 Hz, 3,031 Hz, 3812 Hz, 4,812 Hz, and 6,031 Hz. Significantly more music majors (7/28) than nonmusic majors (0/35) exhibited absent DPOAEs for at least one frequency in at least one ear. Both groups of students reported similar histories of recreational and occupational noise exposures that were unrelated to studying music, and none of the students reported high levels of noise exposure within the previous 48 h. There were no differences in audiometric thresholds between the groups at any frequency. At DPOAE f2 frequencies from 3,031 Hz to 6,031 Hz, nonsignificantly lower amplitudes of 2-4 dB were seen in the right ears of music majors versus nonmajors, and in the right ears of music majors playing brass instruments compared to music majors playing nonbrass instruments. Given the greater prevalence of absent DPOAEs in university music majors compared to nonmusic majors, it appears that early stages of cochlear damage may be occurring in this population. Additional research, preferably longitudinal and across multiple colleges/universities, would be beneficial to more definitively determine when the music students begin to show signs of cochlear damage, and to identify whether any particular subgroups of music majors are at a greater risk of cochlear damage.

Revisiting Oto-Acoustic Emissions

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

Distortion-product otoacoustic emission growth curves in neonates

BACKGROUND

The recording of otoacoustic emissions (OAE) enabled us to prove that the cochlea is able not only to receive sounds but also to produce acoustic energy. Through the use of distortion-product otoacoustic emission measurements, the growth of the response was seen according to the intensity of the sound stimulus presented (growth curve).

OBJECTIVE

to determine the thresholds for the emergence of distortion-product otoacoustic emissions (DPOAE) on frequencies of 2000 and 4000 Hz with a stimulus varying from 20 to 65 dB SPL, and to establish the slope values obtained in the growth curves.

METHODS

39 neonates aged 5 to 28 days without risk indicators of hearing loss were studied. The DPOAE growth curves were obtained on the frequencies from 2000 Hz and 4000 Hz with a level of intensity ranging from 20 to 65 dB SPL divided into two paradigms (20 to 40 dB SPL and 40-65 dB SPL).

RESULTS

there was a statistically significant difference in the thresholds for the emergence of DPOAE depending on the criteria used. The thresholds were on average higher at 4000 Hz than 2000 Hz and the slope was higher on average at 2000 Hz than 4000 Hz, although not statistically significant in either case.

CONCLUSION

the thresholds were on average 30 dB SPL at 2000 Hz and 35 dB SPL at 4000 Hz. The slope values varied between 3 and 4 on average, reaching 15 in some cases.

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.

Growth of suppression using distortion-product otoacoustic emission measurements in hearing-impaired humans

Growth of distortion-product otoacoustic emission suppression was measured in 65 subjects with mild-to-moderate sensorineural hearing loss (HI). Measurements were made at four probe frequencies (f(2)) and up to five L(2) levels. Eleven suppressor frequencies (f(3)) were used for each f(2), L(2) combination. These data were compared to data from normal-hearing (NH) subjects (Gorga et al., 2011a). In both NH and HI subjects, growth of suppression depended on the relation between f(2) and f(3), such that the slope was close to one when f(3) ≈ f(2), steeper than one when f(3) < f(2), and shallower than one when f(3) > f(2). Differences in growth of suppression between NH and HI subjects were not observed for fixed f(2), L(2) combinations, however large differences were observed in suppressor "threshold" when compared at the same probe sensation level (dB SL). Smaller group differences were observed when compared at the same probe sound-pressure level (dB SPL). Therefore, the extent of these differences depended on how probe level (L(2)) was specified. When the results from NH and HI subjects are compared with each other and with psychophysical studies of masking, differences are observed that have implications for the remediation of mild-to-moderate hearing loss.

Level-dependent changes in perception of speech envelope cues

Level-dependent changes in temporal envelope fluctuations in speech and related changes in speech recognition may reveal effects of basilar-membrane nonlinearities. As a result of compression in the basilar-membrane response, the "effective" magnitude of envelope fluctuations may be reduced as speech level increases from lower level (more linear) to mid-level (more compressive) regions. With further increases to a more linear region, speech envelope fluctuations may become more pronounced. To assess these effects, recognition of consonants and key words in sentences was measured as a function of speech level for younger adults with normal hearing. Consonant-vowel syllables and sentences were spectrally degraded using "noise vocoder" processing to maximize perceptual effects of changes to the speech envelope. Broadband noise at a fixed signal-to-noise ratio maintained constant audibility as speech level increased. Results revealed significant increases in scores and envelope-dependent feature transmission from 45 to 60 dB SPL and decreasing scores and feature transmission from 60 to 85 dB SPL. This quadratic pattern, with speech recognition maximized at mid levels and poorer at lower and higher levels, is consistent with a role of cochlear nonlinearities in perception of speech envelope cues.

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).

Comparison of distortion-product otoacoustic emission growth rates and slopes of forward-masked psychometric functions

Slopes of forward-masked psychometric functions (FM PFs) were compared with distortion-product otoacoustic emission (DPOAE) input/output (I/O) parameters at 1 and 6 kHz to test the hypothesis that these measures provide similar estimates of cochlear compression. Implicit in this hypothesis is the assumption that both DPOAE I/O and FM PF slopes are functionally related to basilar-membrane (BM) response growth. FM PF-slope decreased with signal level, but this effect was reduced or reversed with increasing hearing loss; there was a trend of decreasing psychometric function (PF) slope with increasing frequency, consistent with greater compression at higher frequencies. DPOAE I/O functions at 6 kHz exhibited an increase in the breakpoint of a two-segment slope as a function of hearing loss with a concomitant decrease in the level of the distortion product (L(d)). Results of the comparison between FM PF and DPOAE I/O parameters revealed only a weak correlation, suggesting that one or both of these measures may provide unreliable information about BM compression.

Otoacoustic emissions growth rate threshold: distortion product in neonates

BACKGROUND

Distortion product otoacoustic emission measures (DPOAE) verifies, among other characteristics, the emergence and growth rate of the DPOAE response according to sound stimulus intensity (growth curve).

AIM

To estimate the DPOAE threshold in neonates according to the DPOAE growth curve at 2 kHz and 4 kHz, with stimulus presentation ranging between 35 and 70 dB SPL.

METHOD

Participants were 51 neonates, with 24 to 84 hours of life and with no indication of risk for hearing impairment. The DPOAE were registered in the growth curve function at 2 kHz and at 4 kHz. Neonates were evaluated during the period of hospital stay, after birth. Three possible thresholds were considered (LIM 1, LIM 2 and LIM 3) based on the presence of response at 3 dB SPL in the signal to noise ratio.

RESULTS

The average thresholds intensities ranged from 47.55 to 49.85 dB at 2 kHz and from 55.52 to 59.94 dB at 4 kHz. The mean amplitude response ranged from 6.67 to 8.27 dB at 2 kHz and from 6.99 to 11.35 dB at 4 kHz. There was significant difference between the three thresholds for the two studied frequencies.

CONCLUSION

The procedure was feasible for the neonatal population revealing mean thresholds of up to 60 dB for both frequencies. Even though participants presented elevated thresholds, robust amplitude responses were observed.

Correspondence between behavioral and individually "optimized" otoacoustic emission estimates of human cochlear input/output curves

Previous studies have shown a high within-subject correspondence between distortion product otoacoustic emission (DPOAE) input/output (I/O) curves and behaviorally inferred basilar membrane (BM) I/O curves for frequencies above approximately 2 kHz. For lower frequencies, DPOAE I/O curves contained notches and plateaus that did not have a counterpart in corresponding behavioral curves. It was hypothesized that this might improve by using individualized optimal DPOAE primary levels. Here, data from previous studies are re-analyzed to test this hypothesis by comparing behaviorally inferred BM I/O curves and DPOAE I/O curves measured with well-established group-average primary levels and two individualized primary level rules: one optimized to maximize DPOAE levels and one intended for primaries to evoke comparable BM responses at the f(2) cochlear region. Test frequencies were 0.5, 1, and 4 kHz. Behavioral I/O curves were obtained from temporal (forward) masking curves. Results showed high within-subject correspondence between behavioral and DPOAE I/O curves at 4 kHz only, regardless of the primary level rule. Plateaus and notches were equally common in low-frequency DPOAE I/O curves for individualized and group-average DPOAE primary levels at 0.5 and 1 kHz. Results are discussed in terms of the adequacy of DPOAE I/O curves for inferring individual cochlear nonlinearity characteristics.