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To evaluate two real-time methods for reducing distortion product otoacoustic emission (DPOAE) fine structure in terms of DPOAE amplitude and fine structure depth.A prospective, repeated-measures design was used to assess DPOAE characteristics in response to a conventional stimulation method (Conv.), as well as for methods implementing either a generic suppressor tone (Supp.) or frequency modulation of the fEighty-three young adults (58 females) between the ages of 20 and 34 years with normal hearing completed testing for this study.Use of the Conv. and FM methods resulted in consistently higher DPOAE levels relative to the Supp. method, with average advantages of 6 and 5 dB, respectively. For all methods, increased fine structure depth was observed for stimulation with lower level (25-45 dB SPL) and lower frequency (1000-3000 Hz) primary tones. Finally, use of the Supp. and FM methods resulted in significantly decreased fine structure depth relative to the Conv. method.Through frequency modulation of the f

PurposeDistortion product otoacoustic emission (DPOAE) amplitude is sensitive to the primary tone level separation effective within the cochlea. Despite potential for middle ear sound transmission characteristics to affect this separation, no primary tone level optimization formula accounts for its influence. This study was conducted to determine if inclusion of ear- and frequency-specific immittance features improves primary tone level optimization formula performance beyond that achieved using a univariate,L2-based formula.MethodFor 30 adults with normal hearing, DPOAE, wideband absorbance, and 226-Hz tympanometry measures were completed. A mixed linear modeling technique, incorporating both primary tone and acoustic immittance features, was used to generate a multivariable formula for the middle ear–specific recommendation of primary tone level separations forf2= 1–6 kHz. The accuracy with whichL1OPT, or theL1observed to maximize DPOAE level for each givenL2, could be predicted using the multivariable formula was then compared with that of a traditional,L2-based univariate formula for each individual ear.ResultsUse of the multivariable formulaL1= 0.47L2+ 2.40A+f2param+ 38 [dB SPL] resulted in significantly more accurateL1OPTpredictions than did the univariate formulaL1= 0.49L2+ 41 [dB SPL]. Although average improvement was small, meaningful improvements were identified within individual ears, especially forf2= 1 and 6 kHz.ConclusionIncorporation of a wideband absorbance measure into a primary tone level optimization formula resulted in a minor average improvement inL1OPTprediction accuracy when compared with a traditional univariate optimization formula. Further research is needed to identify characteristics of ears that might disproportionately benefit from the additional measure.

Objectives Distortion product otoacoustic emissions (DPOAEs) are a time-efficient, non-invasive means of assessing the integrity of active inner ear mechanics. Unfortunately, the presence of even relatively minor conductive hearing loss (CHL) has been suggested to reduce the clinical utility of DPOAEs significantly. The primary aims of this study were to systematically evaluate the impact of CHL on DPOAE amplitude and to determine if ear-specific primary tone level manipulations can be used to mitigate CHL impact and recover DPOAE measurability. Methods For 30 young adults (57 ears) with normal hearing, DPOAEs were obtained for f2 = 1–6 kHz. Observed DPOAE amplitudes were used to generate ear- and frequency-specific models with the primary tone levels, L1 and L2, as inputs and predicted DPOAE amplitude, LDP, as output. These models were then used to simulate the effect of CHL (0–15 dB), as well as L1 manipulations (0–15 dB), on DPOAE measurability. Results Mean LDP for every CHL condition was significantly different from that for all other conditions (p = Conclusion Subclinical CHL loss is sufficient to significantly impair DPOAE measurability in a meaningful proportion of otherwise healthy ears. However, through strategic alteration of primary tone levels, the clinician can mitigate CHL impact and at least partially recover DPOAE measurability.

Objectives: Conductive hearing loss (CHL) systematically alters distortion product otoacoustic emission (DPOAE) levels through attenuation of both the primary tones and the evoked response by the middle ear, as well as through modification of the effective L-1-L-2 relationship within the cochlea. It has been postulated that, if optimal primary tone level relationships for an ear without CHL are known or can be estimated accurately and a CHL can be presumed to attenuate both primary tones to a similar extent, the adjustment to L-1 required to restore an optimal L-1-L-2 separation following CHL induction can be utilized to estimate CHL magnitude objectively. The primary aim of this study was to assess the feasibility of objectively estimating experimentally produced CHL in humans by comparing CHL estimates resulting from DPOAE- and pure-tone audiometry-based methods. A secondary aim was to compare the accuracy of DPOAE- based CHL estimates when obtained using generic, as opposed to ear-specific, optimal primary tone level formula parameters. Design: For a single ear of 30 adults with normal hearing, auditory threshold for a 1 kHz tone was obtained using automated Bekesy audiometry at an ear-canal pressure of 0 daPa, as well as at a negative pressure sufficient for increasing threshold by 3 to 10 dB. The difference in threshold for the ear-canal pressure conditions was defined as the pure-tone audiometry-based estimate of CHL (CHLPT). For the same two ear-canal pressures, optimal DPOAE primary tone level relationships were identified for f(2) = 1 kHz. Specifically, for 20

Subclinical conductive hearing losses (CHLs) can affect otoacoustic emissions and therefore limit their potential in the assessment of the cochlear function. Theoretical considerations to estimate a minor CHL from DPOAE measurements [Kummer et al. (2006). HNO 54, 457-467] are evaluated experimentally. They are based on the fact, that the level difference of the stimulus tones L(1) and L(2) for optimal excitation of the inner ear is given by L(1)=aL(2)+b. A CHL is presumed to attenuate both L(1) and L(2) to the same extent such that excitation of the inner ear is no longer optimal. From the change of L(1) that is necessary to restore optimal excitation of the inner ear and thus to produce maximal DPOAE levels, the CHL can be estimated. In 10 guinea pig ears an experimental CHL was produced, quantified by determination of compound action potential (CAP) thresholds at 8 kHz (CHL(CAP)) and estimated from DPOAE measurements at 8 kHz (CHL(DPOAE)). CHLs up to 12 dB could be assessed. CHL(DPOAE) correlated well with CHL(CAP) (R=0.741, p=0.0142). Mean difference between CHL(DPOAE) and CHL(CAP) was 4.2±2.6 dB. Estimation of minor CHL from DPOAE measurements might help to increase the diagnostic value of DPOAEs.

Event-related potentials (ERPs) as part of the EEG are applied to assess auditory processing in children. Mismatch negativity (MMN) is a change-specific component of ERPs that indicates a pre-cognitive discrimination process. MMN responses were recorded in 10 healthy preschool children to four different types of signal changes. The signals investigated were processed using a discrete wavelet transform (DWT) to analyze the characteristics of the ERP components. All children showed distinct MMN that was significant in all tasks. The MMN amplitudes varied between subjects and depended on the different tasks. The wavelet transform allowed simplified analysis and quantification of the MMN component, as well as the double-peak structure of the P1 component. The variation in MMN amplitudes suggests the possibility of determining individual auditory profiles. Owing to the shorter time required, the MMN paradigm suggested combined with the DWT proposed offers a new objective investigation method for children.

The detection of metric dimensions of laryngeal structures yields valuable information for both clinical and research purposes. The use of a laser projection system combined with a high-speed camera system enables the derivation of absolute spatial dimensions of the larynx. Vocal fold length, vibratory amplitudes and velocity can be derived. This was shown on 13 female and 9 male larynges during phonation of a vowel at different pitches. The vocal fold length, the amplitude of oscillation and the velocity of vibration were analyzed in between pitches of 119 to 236 Hz in the male group and 181 to 555 Hz in the female group. The vocal folds' length ranged from 8.4 to 14.3 mm in the male group and from 7.7 to 15.6 mm in the female group. Corresponding amplitudes varied from 0.33 to 1.24 mm (male) and from 0.38 to 0.82 mm (female). The maximal velocity of vibration was between 0.48 and 0.85 m/s in males and between 0.47 and 1.3 m/s in females without showing significant correlation between each parameter. The described technique enables the detection of absolute spatial laryngeal dimensions of female and male subjects at different pitches. Dynamic processes such as velocity of vibration can be quantified. The detection of metric data serves to optimize biomechanical model computations and provides valuable information in diagnostics and interpretation of organic and non-organic voice disorders.

The suppression tuning properties of the 2 f1-f2 distortion-product otoacoustic emission (DPOAE) were measured in 16 ears of normally hearing human subjects. DPOAE were elicited by fixed, low-level primary tones in four frequency regions with the second primary tone frequency f2 at 1, 2, 4, and 6 kHz. For various suppressor frequencies, suppression of the DPOAE was measured as a function of the suppressor tone level, enabling the assessment of the threshold and the growth of suppression. Depending on the distance of the suppressor tone to f2, there were marked differences in the suppression behavior of different suppressor frequencies. The threshold of suppression was minimal slightly above f2 and hardly increased with increasing frequency, but increased continuously with decreasing suppressor frequency. The growth of suppression, however, did not systematically change below f2, but decreased rapidly above f2. Both changes resulted in asymmetrical, V-shaped suppression tuning curves. They were sharply tuned to a frequency slightly above f2, with Q10 dB values up to 7.87. This is consistent with the assumption that the main source of the DPOAE is at the f2 site. In some cases, the DPOAE was particularly sensitive to suppressor tones near the DPOAE frequency. In one individual case, facilitation was found for corresponding frequency-level ranges of the suppressor tone. This may suggest a secondary emission source at the distortion product place.

OBJECTIVES Minor conductive hearing loss (CHL) can compromise the evaluation of the inner ear function with distortion product otoacoustic emissions (DPOAE). Elevation of the intracranial pressure (ICP) is also expected to alter the middle ear (ME) sound transmission. An impaired ME sound transmission leads to an attenuation of the DPOAE primary tone levels (L1 and L2) during forward transmission and of DPOAE levels (LDP) during backward transmission. The effect of the attenuation of L1 and L2 is complex and might have unexpected effects on DPOAE levels. In this work, CHL- and ICP-induced alterations of LDP versus L1 growth functions (constant L2 and increasing L1) are investigated. The first aim of this study is to explain how alterations of ME sound transmission can affect DPOAEs and to characterize the dependency of DPOAE level alterations on L2,L1 combinations and on the individual shape of LDP versus L1 growth functions. The second aim is to identify analogies between CHL- and ICP-induced alterations of DPOAEs and to discuss implications for a potential noninvasive ICP monitoring. DESIGN This study focuses on general theoretical considerations, supported by selected experimental observations in different species and simulations. DPOAEs were measured in guinea pigs before and after induction of a CHL (1 ear) and during increased ICP (1 ear), and in humans during changes of the postural position to alter the ICP (4 ears). RESULTS In both CHL and elevated ICP, DPOAE levels are not only reduced, but LDP versus L1 growth functions exhibit a shift to higher L1. The absolute DPOAE level alterations strongly depend on the L2,L1 combinations and the individual shape of the LDP versus L1 growth functions. In steeper LDP versus L1 growth functions, the DPOAE level alterations exhibit a larger variation. DPOAE levels can even increase. The largest variation can be found in ears with a nonmonotonic DPOAE growth behavior. An example of a guinea pig ear is presented with a nonmonotonic DPOAE growth behavior and a CHL of 4 dB, where the DPOAE level alterations varied between -32 and +9 dB depending on L1. CONCLUSIONS The data enable a more comprehensive view of DPOAE level alterations during CHL and elevated ICP. The observations also explain the problem that DPOAE and ICP alterations do not correlate linearly. An evaluation of the shift of the LDP versus L1 growth function along the L1 axis provides a potential tool to improve both the assessment of the inner ear function in the presence of a CHL and noninvasive ICP monitoring with DPOAEs.

Objective: To compare the maturation of speech-evoked N170 components of cortical auditory evoked potentials with that of tone-evoked N1 components. Patients and Methods: Cortical auditory evoked potentials to speech and tone stimuli were derived in 42 children from age 4 to 14 years. The N170 was derived from the difference curve of responses to monosyllabic words with initial consonant-to-vowel transitions and their intensity-equivalent noise signals. Results: The incidence of N1 increased from 71% below age 9 to 91% above, that of N170 tended to increase from 40 to 67% above. From age 9, adult-like morphologies of the difference waveforms were found and the time constants of N1 and N170 latency maturation were nearly identical. Conclusion: The N170 component is interpreted as a response to speech-specific acoustic changes such as the consonant-vowel transition. The late appearance of N170 indicates an electrophysiological correlate of speech perception that continues to develop into adolescence. Its clinical application, however, is limited due to the low incidence of N170.

Previous studies described a systematic asymmetry of the level of the 2 f 1 − f 2 distortion product otoacoustic emission (DP) in the space of the primary tones levels L 1 and L 2 in normal-hearing humans. Optimal primary tone level separations L 1 − L 2 , which result in maximum DP levels, were close to L 1 = L 2 at high levels, but continuously increased with decreasing stimulus level towards L 1 > L 2 (Gaskill and Brown, 1990, J. Acoust. Soc. Am. 88, 821–839). At these optimal L 1 − L 2 , however, not only DP levels in normal hearing were maximal, but also trauma-induced DP reductions. A linear equation that approximates optimal L 1 − L 2 level separations thus was suggested to be optimum for use in clinical applications (Whitehead et al., 1995, J. Acoust. Soc. Am. 97, 2359–2377). It was the aim of this study to extend the generality of optimal L 1 − L 2 separations to the typical human test frequency range for f 2 frequencies between 1 and 8 kHz. DPs were measured in 22 normal-hearing human ears at 61 primary tone level combinations, with L 2 between 5 and 65 dB SPL and L 1 between 30 and 70 dB SPL ( f 2 / f 1 =1.2). It was found that the systematic dependence of the maximum DP level on the L 1 − L 2 separation is independent on frequency. Optimal L 1 − L 2 level separations may well be approximated by a linear equation L 1 = a L 2 +(1− a ) b (after Whitehead et al., 1995) with parameters a =0.4 and b =70 dB SPL at f 2 frequencies between 1 and 8 kHz and L 2 levels between 20 and 65 dB SPL. Below L 2 =20 dB SPL, the optimal L 1 was found to be almost constant. Following previous notions (Gaskill and Brown, 1990), an analysis of basilar membrane response data in experimental animals (after Ruggero and Rich, 1991, Hear. Res. 51, 215–230) is further presented that relates optimal L 1 − L 2 separations to frequency-selective compression of the basilar membrane. Based on the assumption that optimal conditions for the DP generation are equal primary tone responses at the f 2 place, a linear increase of the optimal L 1 − L 2 level separation is graphically demonstrated, similar to our results in human ears.

High-resolution hearing threshold and 2 f1-f2 distortion product otoacoustic emission (DP) were measured with the same in-the-ear sound probe and same calibration at 51 frequencies between 500 and 8000 Hz in 39 sensorineural hearing loss ears associated with tinnitus. Using a primary tone setting L1 = 0.4L2 + 39 that accounts for the nonlinear interaction of the two primary tones at the DP generation site at f2, DPs were elicited in a wide range from L2 = 65 to 20 dB SPL. We failed to find a uniform DP behavior in the 39 tinnitus ears tested. Seventeen of them behaved like impaired ears without tinnitus. In these ears a linearized DP growth was observed where the DP level decreased and the slope of the DP I/O functions steepened with increasing hearing loss and as a result both the DP level and the DP slope strongly correlated with hearing threshold. The other population, 22 tinnitus ears, exhibited a poor or even inverse relationship between DP level and hearing threshold, i.e., displayed an increase of DP level with increasing hearing loss. Despite the severe hearing loss but due to the high level, DPs could be recorded well in the frequency range that corresponded to the appearance of the tinnitus. The DP slope, however, increased with increasing hearing loss and, therefore, did still correlate with hearing threshold revealing pathological alteration. The data suggest that the DP level alone is hardly capable of assessing hearing impairment in tinnitus ears and may even be misleading. Thus just the DP slope seems to be the only reliable indicator of cochlear malfunction around the tinnitus frequency. The observed nonuniform DP behavior suggests different cochlear impairments in tinnitus ears. In those ears where the DP level decreases and the slope of the I/O functions increases with hearing loss, cochlear sensitivity and tuning are supposed to be diminished. In those ears where the DP level increases with increasing hearing loss, a reinforced mechanical distortion is hypothetized to be generated by cochlear hyperactivity that can be the source of both the abnormally high DP level and the tinnitus.