Thomas Janssen

The level and growth behavior of the 2 f1−f2 distortion product otoacoustic emission and its relationship to auditory sensitivity in normal hearing and cochlear hearing loss

The 2 f1-f2 distortion product otoacoustic emission (DP) was measured in 20 normal hearing subjects and 15 patients with moderate cochlear hearing loss and compared to the pure-tone hearing threshold, measured with the same probe system at the f2 frequencies. DPs were elicited over a wide primary tone level range between L2 = 20 and 65 dB SPL. With decreasing L2, the L1-L2 primary tone level difference was continuously increased according to L1 = 0.4L2 + 39 dB, to account for differences of the primary tone responses at the f2 place. Above 1.5 kHz, DPs were measurable with that paradigm on average within 10 dB of the average hearing threshold in both subject groups. The growth of the DP was compressive in normal hearing subjects, with strong saturation at moderate primary tone levels. In cases of cochlear impairment, reductions of the DP level were greatest at lowest, but smallest at highest stimulus levels, such that the growth of the DP became linearized. The correlation of the DP level to the hearing threshold was found to depend on the stimulus level. Maximal correlations were found in impaired ears at moderate primary tone levels around L2 = 45 dB SPL, but at lowest stimulus levels in normal hearing (L2 = 25 dB SPL). At these levels, 17/20 impaired ears and 14/15 normally hearing ears showed statistically significant correlations. It is concluded that for a clinical application and prediction of the hearing threshold, DPs should be measured not only at high, but also at lower primary tone levels.

Pure-tone threshold estimation from extrapolated distortion product otoacoustic emission I/O-functions in normal and cochlear hearing loss ears

A new method for direct pure-tone threshold estimation from input/output functions of distortion product otoacoustic emissions (DPOAEs) in humans is presented. Previous methods use statistical models relating DPOAE level to hearing threshold including additional parameters e.g., age or slope of DPOAE I/O-function. Here we derive a DPOAE threshold from extrapolated DPOAE I/O-functions directly. Cubic 2 f1-f2 distortion products and pure-tone threshold at f2 were measured at 51 frequencies between f2=500 Hz and 8 kHz at up to ten primary tone levels between L2=65 and 20 dB SPL in 30 normally hearing and 119 sensorineural hearing loss ears. Using an optimized primary tone level setting (L1 = 0.4L2 + 39 dB) that accounts for the nonlinear interaction of the two primaries at the DPOAE generation site at f2, the pressure of the 2 f1-f2 distortion product pDP is a linear function of the primary tone level L2. Linear regression yields correlation coefficients higher than 0.8 in the majority of the DPOAE I/O-functions. The linear behavior is sufficiently fulfilled for all frequencies in normal and impaired hearing. This suggests that the observed linear functional dependency is quite general. Extrapolating towards pDP=0 yields the DPOAE threshold for L2. There is a significant correlation between DPOAE threshold and pure-tone threshold (r=0.65, p<0.001). Thus, the DPOAEs that reflect the functioning of an essential element of peripheral sound processing enable a reliable estimation of cochlear hearing threshold up to hearing losses of 50 dBHL without any statistical data.

Suppression tuning characteristics of the 2 f1−f2 distortion‐product otoacoustic emission in humans

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.

Growth behavior of the 2 f1−f2 distortion product otoacoustic emission in tinnitus

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.

Evidence for a bipolar change in distortion product otoacoustic emissions during contralateral acoustic stimulation in humans

The aim of this study was to investigate the activity of the medial olivocochlear (MOC) efferents during contralateral (CAS) and ipsilateral acoustic stimulation (IAS) by recording distortion product otoacoustic emission (DPOAE) suppression and DPOAE adaptation in humans. The main question was: do large bipolar changes in DPOAE level (transition from enhancement to suppression) also occur in humans when changing the primary tone level within a small range as described by Maison and Liberman for guinea pigs [J. Neurosci. 20, 4701-4707 (2000)]? In the present study, large bipolar changes in DPOAE level (14 dB on average across subjects) were found during CAS predominantly at frequencies where dips in the DPOAE fine structure occurred. Thus, effects of the second DPOAE source might be responsible for the observed bipolar effect. In contrast, comparable effects were not found during IAS as was reported in guinea pigs. Reproducibility of CAS DPOAEs was better than that for IAS DPOAEs. Thus, contralateral DPOAE suppression is suggested to be superior to ipsilateral DPOAE adaptation with regard to measuring the MOC reflex strength and for evaluating the vulnerability of the cochlea to acoustic overexposure in a clinical context.

Tinnitus and 2f1-f2 distortion product otoacoustic emissions following salicylate overdose.

A 22-year-old woman consumed approximately 10 g of salicylate with suicidal intent. She had a severe hearing loss and a strong tinnitus within 22 h of the overdose, and then 24 h later a subsequent hearing restoration and tinnitus abolishment. Transiently evoked otoacoustic emissions (TEOAEs) and 2f1−f2 distortion product otoacoustic emissions (DPOAEs) were measured in both states. In the state of intoxication DPOAEs could be recorded well in the frequency range that corresponded to the appearance of the tinnitus despite the 50-dB hearing loss. The corresponding DPOAE I/O-functions were linearized, indicating loss of outer hair cell compression. After recovery, DPOAE level and DPOAE growth were within the normal range and showed normal physiological compression. The TEOAEs were missing in the acute state of intoxication. This case supports the hypothesis that aspirin-induced tinnitus is generated at the outer hair cell level. Whereas TEOAEs only give evidence that something might have changed in the cochl...

Distortion product otoacoustic emissions for hearing threshold estimation and differentiation between middle-ear and cochlear disorders in neonates.

Our aim in the present study was to apply extrapolated DPOAE I/O-functions [J. Acoust. Soc. Am. 111, 1810-1818 (2002); 113, 3275-3284 (2003)] in neonates in order to investigate their ability to estimate hearing thresholds and to differentiate between middle-ear and cochlear disorders. DPOAEs were measured in neonates after birth (mean age = 3.2 days) and 4 weeks later (follow-up) at 11 test frequencies between f2 = 1.5 and 8 kHz and compared to that found in normal hearing subjects and cochlear hearing loss patients. On average, in a single ear hearing threshold estimation was possible at about 2/3 of the test frequencies. A sufficient test performance of the approach is therefore suggested. Thresholds were higher at the first measurement compared to that found at the follow-up measurement. Since thresholds varied with frequency, transitory middle ear dysfunction due to amniotic fluid instead of cochlear immaturity is suggested to be the cause for the change in thresholds. DPOAE behavior in the neonate ears differed from that found in the cochlear hearing loss ears. From a simple model it was concluded that the difference between the estimated DPOAE threshold and the DPOAE detection threshold is able to differentiate between sound conductive and cochlear hearing loss.

Similarity in loudness and distortion product otoacoustic emission input/output functions: implications for an objective hearing aid adjustment.

The aim of the present study was to compare distortion product otoacoustic emissions (DPOAEs) to loudness with regard to the potentiality of DPOAEs to determine characteristic quantities of the cochlear-impaired ear and to derive objective hearing aid parameters. Recently, Neely et al. [J. Acoust. Soc. Am. 114, 1499-1507 (2003)] compared DPOAE input/output functions to the Fletcher and Munson [J. Acoust. Soc. Am. 5, 82-108 (1933)] loudness function finding a close resemblance in the slope characteristics of both measures. The present study extended their work by performing both loudness and DPOAE measurements in the same subject sample, and by developing a method for the estimation of gain needed to compensate for loss of cochlear sensitivity and compression. DPOAEs and loudness exhibited similar behavior when plotted on a logarithmic scale and slope increased with increasing hearing loss, confirming the findings of Neely et al. To compensate for undesired nonpathological impacts on the magnitude of DPOAE level, normalization of DPOAE data was implemented. A close resemblance between gain functions based on loudness and normalized DPOAE data was achieved. These findings suggest that DPOAEs are able to quantify the loss of cochlear sensitivity and compression and thus might provide parameters for a noncooperative hearing aid adjustment.

Investigation of potential effects of cellular phones on human auditory function by means of distortion product otoacoustic emissions

Outer hair cells (OHC) are thought to act like piezoelectric transducers that amplify low sounds and hence enable the ears exquisite sensitivity. Distortion product otoacoustic emissions (DPOAE) reflect OHC function. The present study investigated potential effects of electromagnetic fields (EMF) of GSM (Global System for Mobile Communication) cellular phones on OHCs by means of DPOAEs. DPOAE measurements were performed during exposure, i.e., between consecutive GSM signal pulses, and during sham exposure (no EMF) in 28 normally hearing subjects at tone frequencies around 4 kHz. For a reliable DPOAE measurement, a 900-MHz GSM-like signal was used where transmission pause was increased from 4.034 ms (GSM standard) to 24.204 ms. Peak transmitter power was set to 20 W, corresponding to a specific absorption rate (SAR) of 0.1 W/kg. No significant change in the DPOAE level in response to the EMF exposure was found. However, when undesired side effects on DPOAEs were compensated, in some subjects an extremely small EMF-exposure-correlated change in the DPOAE level (< 1 dB) was observed. In view of the very large dynamic range of hearing in humans (120 dB), it is suggested that this observation is physiologically irrelevant.

Diagnostik des kochleären Verstärkers mit DPOAE-Wachstumsfunktionen

Extrapolated DPOAE growth functions can be applied in ENT diagnostics for a specific assessment of cochlear dysfunction. In screening newborn hearing, they are able to detect transitory sound conductive hearing loss and thus help to reduce the rate of false positive TEOAE responses in the early postnatal period. Since DPOAE growth functions are correlated with loudness functions, DPOAEs offer the potential for basic hearing aid adjustment, especially in children. Extrapolated DPOAE I/O-functions provide a tool for a fast, automated frequency-specific and quantitative evaluation of hearing loss. However, DPOAE diagnostics is limited to a hearing loss of 50 dB HL. Thus, a combined measurement of DPOAE and AMFR would be useful.