Influence of spontaneous otoacoustic emissions on distortion product otoacoustic emission amplitudes

Although the influence of the levels and ratios of the primary stimulus on the amplitude of distortion product otoacoustic emissions (DPOAEs) has been studied intensely, the influence of the presence of spontaneous otoacoustic emissions (SOAEs) has been investigated less thoroughly. The present investigation analysed whether the unilateral presence of 58 SOAEs in 43 normal-hearing adults was related to larger DPOAEs in the ear with SOAEs compared to the contralateral ear having no SOAEs. The study was designed such that the only factor that could influence the amplitude of DPOAEs was the presence of SOAEs. Input/output (I/O) functions were collected in response to primary tones that were presented in 5-dB steps from 70 to 40 dB SPL at the frequency of the unilaterally recorded SOAE of each subject. The primary outcome was the demonstration of statistically significant (P < 0.05) larger DPOAEs in ears exhibiting SOAEs than in ears without measurable SOAEs, except at the highest stimulus level of 70 dB SPL. These results suggest that SOAEs play an additive role in the measurement of DPOAEs. The enhancing effect of the unilateral presence of SOAEs on DPOAEs was statistically significant for 65 dB SPL and lower levels of primary tones. The authors speculate that passive cochlear properties begin to participate in the generation of DPOAEs at primary-stimulus levels greater than 65 dB SPL.     

Statistical evaluation of hearing screening by distortion product otoacoustic emissions

The aim of this study was to provide a statistical evaluation of the screening properties of distortion product otoacoustic emissions (DPOEs) in individuals with clinically normal hearing and in patients with pure sensorineural deafness of various degrees. The main informational parameters used were sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), and the analysis of receiver operating characteristic (ROC) curves. For each frequency tested, ears were classified as a function of their audiometric threshold. Two groups were defined relative to an arbitrary reference, the "audiometric criterion." The PPV decreased and NPV increased with increases in the audiometric criterion. Each point of the ROC curve represents the relationship between the false alarm rate and the hit rate for each audiometric criterion ranging between 10 and 75 dB hearing level: the lower the audiometric criterion, the lower the hit rate value, and the lower the false alarm value. The audiometric criterion giving the highest hit rate and the lowest false alarm rate was 55 to 60 dB hearing level for primaries at 60 and 70 dB sound pressure level, or 25 to 30 dB hearing level for primaries at 30, 40, and 50 dB sound pressure level. These two different behaviors of ROC curves are consistent with the hypothesis that DPOEs do not represent activity at a single location along the basilar membrane.     

Changes in distortion product otoacoustic emissions during prolonged noise exposure

The aim of this study was to evaluate the reduction in 2f1-f2 distortion product otoacoustic emission (DPOAE) amplitude resulting from prolonged noise exposures. A group of five chinchillas was exposed continuously to an octave-band noise centered at 4.0 kHz for a total of 42 days, 6 days at each of seven exposure levels. Exposure level increased in 8-dB steps from 48 to 96 dB SPL. DPOAE input-output (I/O) functions were measured at octave intervals over a range of primary tone f2 frequencies between 1.2 and 9.6 kHz. Measurements were obtained (1) pre-exposure, (2) during days 3-6 of each 6-day exposure, and (3) 4 weeks after the final exposure. Continuous noise exposure caused a reduction in DPOAE amplitude that was greatest at f2 frequencies within and above (3.4-6.8 kHz) the octave-band noise exposure. For these f2 frequencies, DPOAE amplitudes decreased as exposure level increased up to approximately 72-80 dB SPL; higher exposure levels failed to cause any further reduction in DPOAE amplitude. The noise level at which DPOAE amplitude began to decrease was approximately 50 dB SPL. Above this critical level, DPOAE amplitude decreased 1.3 dB for every dB increase in noise level up to approximately 75 dB SPL.     

Vulnerability and adaptation of distortion product otoacoustic emissions to endocochlear potential variation

The endocochlear potential (EP) was reversibly decreased in adult gerbils by the intraperitoneal injection of furosemide, while cochlear functioning was monitored by measurement of distortion production otoacoustic emissions (DPE) at a range of stimulus intensities. Stimulus frequencies for DPEs were f1 = 6.8 and f2 = 8 kHz (f2/f1 = 1.18). Emissions monitored in the ear canal and scala media were 2f1-f2, 3f1-2f2, 2f2-f1, and f2-f1. Typically, the EP decreased smoothly, reached a minimum one-half hour after injection, then recovered slowly over several hours. Emissions at 2f1-f2 and 3f1-2f2 at low stimulus levels were particularly vulnerable to the change in EP. These vulnerable emissions showed characteristic trajectories in which the amplitudes changed little with the initial EP decrease, then dropped sharply as the EP continued to decrease. However, the amplitudes then began to recover even before the EP reached minimum, and recovered completely while the EP remained subnormal. The trajectories of the other odd order emissions were similar, but lacked the abrupt decrease. The variation of the even order (f2-f1) component was completely different, but appeared related to the odd order trajectories in a complex fashion. During the initial decrease for the vulnerable components, the decrease in emission amplitude (in dB) was found to be proportional to the square of the change in EP (in mV). The recovery with a subnormal EP was interpreted as an adaptive effect with a time constant of about 15 min.     

Effect of contralateral noise exposure on otoacoustic distortion product emissions in man

The influence of contralateral white noise with levels of 50 and 60 dBnHL on the amplitude of distortion-product otoacoustic emissions (DPOAE) was measured. Thirty ears of normally hearing adults (17 women, 13 men, mean age 26.5 +/- 5.3 years) were examined. Two representative DPOAE frequencies 2f1-f2 = 1342 Hz and 6341 Hz were compared. The lower DPOAE frequency was placed in the frequency region where middle-ear pressure has a strong influence on DPOAE amplitudes, the higher DPOAE frequency respectively in the region where lesser influence is exerted by middle-ear pressure. During the application of contralateral white noise a statistically significant total of 85% of DPOAE amplitudes was reduced, although there was some variation in the individual behaviour of DPOAE amplitudes. In general the higher DPOAE frequency (6341 Hz) was reduced distinctly less than the lower DPOAE frequency (1342 Hz). The reaction of DPOAE amplitude depended closely on the time course of the contralateral stimulus and amplitude reductions were present over 10 minutes without adaptation or fatigue. It is not possible to differentiate between middle-ear or inner-ear mediate effects but the middle ear is at least involved. Based on the presence of those DPOAE amplitude reductions over ten minutes without adaptation or fatigue and the fact that lower frequencies are influenced much more than higher frequencies a synergistic effect--middle-ear and efferent mediated--is suggested.     

Effect of temperature on the transient evoked and distortion product otoacoustic emissions in rats

In order to study the energy dependence of the cochlear amplifier, transient evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs) were recorded in rats during gradual cooling to 27 degrees C and heating to 40 degrees C. In the range 33-39 degrees C, the TEOAEs and DPOAEs were maximal in amplitude and almost insensitive to temperature. However, they were significantly depressed (reversibly) at higher and lower temperatures. Intensity functions were plotted at 37, 27 and 40 degrees C for both types of oto-acoustic emissions. At 37 degrees C intensity functions were nonlinear, with a notch at mid-intensity regions. At 27 degrees C, the magnitudes were depressed more at the lower intensities and threshold elevations were observed. As a result, the intensity functions were more linear and the notch was no longer seen. This result provides further evidence for a more active, energy-dependent component of the otoacoustic emissions at lower intensities for both TEOAEs and DPOAEs. The cooling probably affects the lower intensity otoacoustic emissions by inducing a depression in the endocochlear potential, by reducing the motility of the outer hair cells and by introducing a small conductive hearing loss.     

The effect of noise exposure on the details of distortion product otoacoustic emissions in humans

The effect of noise exposure on amplitude and phase of distortion product otoacoustic emissions (DPOAEs) was examined by five different paradigms: across a wideband of frequency, microstructure, input/output function, primary frequency ratio tuning curve, and group delay. The aim was to investigate the vulnerability of these different features to moderate levels of noise exposure. Nine subjects were exposed to third-octave-band noise. The DPOAE amplitude was reduced frequency specifically with the greatest reduction approximately half an octave above the frequency of the noise. The degree of amplitude reduction was greatest at low stimulus levels. There were no observed effects on the shape of the primary ratio tuning curve. A weak tendency to a decrease was seen in group delays. Distinct microstructure was seen in the amplitude against frequency of five out of seven subjects. The maximum to minimum ratio of the microstructure decreased, and the whole pattern shifted toward lower frequencies after noise exposure. Evidence of multiple internal reflection or interference was seen in the periodicity of the microstructure. Using a simple model of the microstructure based on multiple reflections, the noise-induced changes were reevaluated. A reduction in maximum to minimum microstructure ratio could be interpreted as a decrease in the internal reflection coefficient. The implications of these observations for the interpretation of the DPOAE measurements are considered.     

Electrophysiologic changes in preterm neonates: auditory brain stem response and distortion product otoacoustic emissions

The purposes of this investigation were to determine 1) if auditory peripheral maturity is present in the newborn; 2) if not, at what age maturational changes occur in the peripheral auditory system from preterm to full-term; and 3) how results of tests used to identify auditory dysfunction in neonates, such as distortion product otoacoustic emissions (DPEs) and auditory brain stem responses (ABRs), change during this period. Longitudinal DPE amplitude and ABR wave I latency measurements were obtained from a single ear of 18 preterm neonates. The DPEs were evoked at f2s of 2, 3, 4, and 5 kHz. The longitudinal data revealed that in general, DPE amplitude increased and ABR wave I latency decreased as a function of postconceptional age. These findings suggest that 1) the peripheral auditory system has not reached maturity in the preterm neonate; 2) maturational changes continue from preterm to full-term; and 3) these changes are reflected in ABR and DPE measurements.     

Comparison of distortion product otoacoustic emissions with auditory brain-stem response for clinical use in neonatal intensive care unit

PURPOSE: Kainic acid (KA) has long been used in experimental animals to induce status epilepticus (SE). A mechanistic implication of this is the association between excitotoxicity and brain damage during or after SE. We evaluated KA-induced metabolic impairment and the potential mitigating effects of GYKI 52466 [1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine] in superfused rat cerebral cortical slices. METHODS: Interleaved [31P]/[1H] magnetic resonance spectroscopy (MRS) was used to assess energy metabolism, intracellular pH (pHi), N-acetyl-L-aspartate (NAA) level, and lactate (Lac) formation before, during, and after a 56-min exposure to 4 mM KA in freshly oxygenated artificial cerebrospinal fluid (oxy-ACSF). RESULTS: In the absence of GYKI 52466 and during the KA exposure, NAA, PCr, and ATP levels were decreased to 91.1 +/- 0.8, 62.4 +/- 3.9, and 59.1 +/- 4.3% of the control, respectively; Lac was increased to 118.2 +/- 2.1 %, and pH, was reduced from 7.27 +/- 0.02 to 7.13 +/- 0.02. During 4-h recovery with KA-free ACSF, pHi rapidly and Lac gradually recovered, NAA decreased further to 85.5 +/- 0.3%, and PCr and ATP showed little recovery. Removal of Mg2+ from ACSF during KA exposure caused a more profound Lac increase (to 147.1 +/- 4.0%) during KA exposure and a further NAA decrease (to 80.4 +/- 0.5%) during reperfusion, but did not exacerbate PCr, ATP, and pHi changes. Inclusion of 100 microM GYKI 52466 during KA exposure significantly improved energy metabolism: the PCr and ATP levels were above 76.6 +/- 2.1 and 82.0 +/- 2.9% of the control, respectively, during KA exposure and recovered to 101.4 +/- 2.4 and 95.0 +/- 2.4%, respectively, during reperfusion. NAA level remained at 99.8 +/- 0.6% during exposure and decreased only slightly at a later stage of reperfusion. CONCLUSIONS: Our finding supports the notion that KA-induced SE causes metabolic disturbance and neuronal injury mainly by overexcitation through non-N-methyl-D-aspartate (NMDA) receptor functions.     

Distortion product otoacoustic emissions for the assessment of auditory sensitivity

Distortion product otoacoustic emissions (DPOAEs) were evaluated in 494 normal and 506 cochlear-impaired human ears, to determine whether DPOAEs depend on factors such as background noise, the shape of the pure tone audiogram, sex and aging, and whether a DPOAE test can perform well in distinguishing normal-hearing from hearing-impaired ears. The amplitudes of DPOAEs were measured at the frequency of 2f1-f2 (f1 < f2, f2/f1 = 1.22, f2 at 1, 2 and 4 kHz) using as stimuli two pure tones at level of 70 dB from an ILO92 Otoacoustic Emission Analyzer. The correlation coefficients between the DPOAE level and the auditory threshold decreased as the background noise levels at 1 kHz and 2 kHz increased. Therefore, it appeared that ears with large background noise levels would be inadequate for the study of DPOAEs predicting the hearing state. The sensitivity (normal-hearing ears identified as normal hearing) and the specificity (hearing-impaired ears identified as hearing impaired) at the equal-sensitivity-specificity condition were 80.7-86.7% at 1, 2 and 4 kHz, and the areas under the receiver operating characteristic (ROC) curves, which were used to estimate the test performance, were 0.88 for 1 kHz, 0.91 for 2 kHz and 0.92 for 4 kHz. Since these results suggest that a DPOAE can be used as a reliable technique for objective auditory tests, it is thought that actual values (DPOAE level: 4.3 dB at 1 kHz, 5.0 dB at 2 kHz and 2.9 dB at 4 kHz) of false-positive (hearing-impaired ears identified as normal hearing) rates corresponding to 5% can be used in clinical evaluation to separate normal hearing from hearing-impaired ears. There was, however, a significant age effect at 4 kHz on DPOAEs in the ears with the same pure tone hearing thresholds, and the areas of the ROC curves in subjects ranging from 10 to 29 years old were larger than in subjects over 50 years (1 kHz: 0.88 to 0.94 versus 0.83 to 0.84, 2 kHz: 0.95 versus 0.89, 4 kHz: 0.95 to 0.96 versus 0.88 to 0.89). Therefore, it is thought that age-adjusted norms may be necessary for the accurate interpretation of DPOAE results.     

Interrelations between transiently evoked otoacoustic emissions, spontaneous otoacoustic emissions and acoustic distortion products in normally hearing subjects

Active cochlear mechanisms and especially outer hair cells seem to be involved in oto-acoustic emissions (OAEs) genesis. This study sought to investigate basic characteristics of spontaneous otoacoustic emissions (SOAEs), click-evoked otoacoustic emissions (TOAEs) and interrelations between SOAEs, TOAEs and 2f1-f2 and 2f2-f1 distortion product OAEs (DPOAEs) in 135 normally hearing subjects. A gender effect was shown on TOAEs and DPOAEs amplitude, and is attributed to the higher incidence of SOAEs in women (58%) than in men (22%). Moreover, SOAEs presence seems to mask the age effect found, especially at high frequency components, on TOAEs amplitude. A general influence of SOAEs on TOAEs and DPOAEs is shown, especially at frequencies ranging from 1 kHz to 3 kHz, collecting more than 66% of the SOAEs peaks recorded. Lastly, correlations between TOAEs frequency band amplitude and 2f1-f2 DPOAEs amplitude, shows frequency specificity, at least at low frequencies (i.e., from 0.5 to 2 kHz) in agreement with previous works suggesting that the 2f1-f2 DPOAEs generation site is at the geometric mean of the primaries. The same correlations calculated with 2f2-f1 DPOAEs amplitude show frequency specificity at low frequencies i.e., at 800 Hz and 1600 Hz. 2f2-f1 DPOAEs in humans are shown to be generated near the 2f2-f1 frequency region on the cochlear partition.     

Distortion product otoacoustic emissions in healthy newborns: normative data

Distortion product otoacoustic emissions (DPOAE) offer an alternative to transiently evoked otoacoustic emissions (TEOAE) as an audiological test. The former can be used as a screening technique, and may also provide frequency-specific information about the functional state of the cochlea. We recorded DPOAE in a group of healthy newborns to establish the characteristics of a DPOAE "audiogram" (DP-gram) in this population. The DP-gram can be obtained with characteristics quite similar to those observed in adults, with two sharp peaks of maximum amplitude at F2 frequencies of 2 kHz and 5-6 kHz, and a decline in DPOAE amplitude in midfrequencies. The results confirm the limitations of DPOAE recording for testing parts of the basilar membrane where lower frequencies are coded.     

Transitory evoked and distortion products of otoacoustic emissions in absent auditory evoked potentials

Transient click-evoked otoacoustic emissions (TEOAE) and distortion-product otoacoustic emissions (DPOAE) are produced by an active biomechanical process in the cochlea, presumably related to outer hair-cell activity. Although it is generally accepted that in most cases of hearing loss with absent auditory evoked potentials neither TEOAE nor DPOAE can be found, some cases with such a constellation have been described. Here we report another four cases of children with severe to profound hearing loss where we discovered reproducible TEOAE and DPAOE, whereas auditory evoked potentials were missing. TEOAE and DPOAE recordings in these cases indicate substantially preserved outer hair-cell function independent of profound pre-sensineural hearing loss. Since the incidence of children with preserved otoacoustic emissions together with impairment of synaptic or postsynaptic function of the first neuron is not known, the unconditioned use of TEOAE nor DPOAE as a screening instrument must be seriously questioned. Secondly, in conjunction with subjective audiometry and brain-stem-evoked potentials, emission recordings is an indispensable measurement prior to cochlear implantation and use of high-power hearing aids.     

Interpretation of distortion product otoacoustic emission measurements. I. Two stimulus tones

The interpretation of common but poorly understood observed characteristics of distortion product emissions is assisted by the development of a simple model. This model essentially includes only saturation of the cochlear amplifier, with emissions arising naturally from the same nonlinear processes which cause the saturation. The model provides useful physical explanations of emission behaviour, particularly considered as a function of the stimulus intensities of the two primaries, i.e., behavior with fixed stimulus frequencies. It is assumed that emission generation consists of two main components which are always present in the total emission, but which most often have approximately opposite, i.e., canceling, phases. One component arises in a small region centered about the peak of the emission generation function, while the other arises from the region basal to this peak. At low stimulus levels with normal cochlear amplifier operation, the peak of the emission generation function is sharp, so the emission from the peak region dominates the total emission. This "peak" emission has typically been characterized as the "active" emission. At high stimulus levels where saturation is important, or at all levels when the gain of the cochlear amplifier is reduced, the summed "basal" component dominates the total emission. The characteristics of this basal emission are similar to, and continuous with, the characteristics of the truly "passive" emission, i.e., the emission observed when the cochlear amplifier gain is identically zero. Under circumstances when the emissions from the peak and basal components are approximately equal, there is seen a sharp "notch" characteristic of phase cancellation. The simple model produces emission distributions as a function of independent variation of the two stimulus amplitudes which are in good agreement with observation. It is shown that the furosemide assay provides a good estimate of cochlear amplifier gain when a correction factor of about 10 dB is added. However, when using two stimulus tones, neither absolute emission amplitudes, or emission input-output functions, or the furosemide assay can adequately distinguish between cases of moderate versus poor cochlear amplifier dysfunction when the cochlear amplifier gains are in the range from about half normal to zero.     

An optimal filtering technique to reduce the influence of low-frequency noise on click-evoked otoacoustic emissions

The aim of this paper was to study the physical performance, pain, pain behavior and disability in patients with subacute low back pain (LBP). The patients were blue-collar workers and had been sick-listed for 8 weeks due to subacute low back pain. A total of 103 patients were randomized, 51 of them to the intervention group and the other to a control group. Recordings of physical performance and complaints of LBP were done before and after treatment in the intervention group. The proportion of patients with no complaints of LBP was significantly greater in the intervention group than in the control group at the one-year follow-up. The patients who intra-individually improved their physical performance also intra-individually decreased their complaints of LBP. The intra-individual improvements were suggested to be important for the individual return to work.     

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.     

2f1-f2 distortion product otoacoustic emissions in White Leghorn chickens (Gallus domesticus): effects of frequency ratio and relative level

The effects of primary tone frequency ratio (f2/f1 ratio) and relative level (L2/L1) on the amplitude of the cubic difference tone (CDT: 2f1-f2) distortion product otoacoustic emissions (DPOAEs) were investigated in adult White Leghorn chickens (Gallus domesticus). In experiment 1, 9 f2/f1 ratios ranging from 1.05 to 1.8 were investigated. Measurements were obtained from both ears of 4 chickens at 7 f1 frequencies ranging from 0.8 to 4.0 kHz. The primary tones were equal in level, and varied from 20 to 80 dB SPL. The mean CDT amplitude increased with increasing primary tone level once the measurement noise floor was exceeded. The input/ output functions assumed one of two shapes: one in which there was a systematic increase in DPOAE amplitude with increasing primary tone level, and the other in which there was a plateau in the input/output function near 65-70 dB SPL. At the highest primary tone level (80 dB SPL), there was a decrease in the CDT amplitude with increasing f2/f1 ratio. At high primary tone levels, the f2/f1 ratio which produced the largest CDT was 1.05 or 1.1, while at lower primary tone levels the largest CDT occurred at f2/f1 ratios of 1.2-1.3. In experiment 2, L2 was held constant at 70 dB SPL, and L1 varied from 50 to 80 dB SPL. For f1 frequencies of 0.8 and 3.2 kHz, there was an increase in the CDT amplitude with increasing L1, followed by an asymptote at higher levels. In contrast, for 1.6 and 2.0 kHz f1 frequencies, the amplitude increased, plateaued and then increased again at higher levels. Informal measurements suggest that spontaneous otoacoustic emissions (SOAEs) are rarely seen in chickens. However, a reliable SOAE was observed in 1 chicken, which could be suppressed by external sounds and anoxia.     

Multi-variant analysis of otoacoustic emissions and estimation of hearing thresholds: transient evoked otoacoustic emissions

Evaluation of cochlear hearing loss by means of transiently evoked otoacoustic emissions is already established in clinical practice. However, accurate prediction of pure-tone thresholds is still questioned and is still regarded as troublesome. Both click- and tone-burst-evoked otoacoustic emissions at several intensity levels were measured and analysed in 157 ears from normally hearing and 432 ears from patients with different degrees of pure sensory hearing loss using the ILO88/92 equipment. Results of otoacoustic emissions (OAE), elicited by clicks and tone-bursts at centre frequencies from 1 to 5 kHz, were analysed using two different statistical methods. Both multivariate discriminant analysis and forward multiple regression analysis were used to determine which OAE variables were most discriminating and best at predicting hearing thresholds. We found that a limited set of variables obtained from both tone-burst and click measurements can accurately predict and categorize hearing loss levels up to a limit of 60 dB HL. We found correct classification scores of pure-tone thresholds between 500 and 4000 Hz up to 100 per cent when using combined click and tone-burst otoacoustic measurements. Prediction of pure-tone thresholds was correct with a maximum estimation error of 10 dB for audiometric octave frequencies between 500 and 4000 Hz. Measurements of multiple tone-bursts OAEs have a significant clinical advantage over the use of clicks alone for clinical applications, and a good classification and prediction of pure-tone thresholds with otoacoustic emissions is possible.     

Distortion product otoacoustic emissions in human newborns and adults. I. Frequency effects

This study varied stimulus frequency and recorded distortion product otoacoustic emissions (DPOAEs) in human newborns and adults. Because of outer and middle ear acoustics, the same auditory input resulted in higher newborn stimulus sound pressure levels across a broad frequency range in the occluded outer ear canal. Noise levels in the canal were 5-15 dB lower for adults at frequencies less than about 3 kHz. The 2 f1-f2 DPOAE was the most reliably recorded DPOAE except at the lowest frequencies assessed. At the lowest frequencies the 2 f2-f1 DPOAE was more frequently recorded than any other DPOAE. There were no striking developmental differences in the kinds of DPOAEs that were recorded. The amplitudes of consecutively recorded 2 f1-f2 DPOAEs were generally within 1.5 dB of each other for all age groups (slightly better reproducibility for adults than newborns). The phases of consecutively recorded 2 f1-f2 DPOAEs were generally within 15 degrees of each other (often less than 10 and 5 degrees for newborns and adults respectively). At the highest frequencies assessed (f2 = 4.2-9.9 kHz) all subjects had similar amplitude 2 f1-f2 DPOAEs. At lower frequencies adult 2 f1-f2 amplitudes were significantly less than those of newborns. At the lowest frequencies reliably assessed (f2 = 1.5-2.1 kHz) term newborns had significantly larger 2 f1-f2 DPOAEs than preterm newborns. Newborn and adult 2 f1-f2 DPOAE amplitude X f2/f1, functions were quite similar although there were reliable differences. Age related differences in the outer and middle ears may explain some of the differences in DPOAEs that were observed.     

Phenotypic patterns of distortion product otoacoustic emission in inbred and F1 hybrid hearing mouse strains

Distortion product otoacoustic emissions (DPOE) were obtained from five different hearing mouse groups: CBA/J, MOLF/Rk, ct (homozygous normal mice of the curly-tail stock), and the F1 hybrid offspring of the matings CBA/J x dn/dn and MOLF/Rk x dn/dn (dn/dn mice are the curly-tail stock with recessive deafness). The DPOE patterns of the CBA/J and ct strains were similar to each other and different from that of the MOLF/Rk. The two sets of F1 hybrid mice, (CBA/J x dn/dn)F1 and (MOLF/Rk x dn/dn)F1, were found to have significantly larger DPOE amplitudes than their hearing parent strains, MOLF/Rk and CBA/J, respectively. In addition, the DPOE amplitudes were greater for the offspring of the MOLF/Rk x dn/dn cross than for those of the CBA/J x dn/dn cross, even though they were lower for MOLF/Rk than for CBA/J. The distinct features of DPOE patterns among these five groups suggest that DPOE testing can be used for auditory phenotyping.