Spontaneous Otoacoustic Emissions Frequency Research Articles

Frequency Shifts in a Local Oscillator Model for the Generation of Spontaneous Otoacoustic Emissions by the Lizard Ear

Introduction: In order to understand human hearing, it helps to understand how the ears of lower vertebrates, like, for instance, lizards, function. A key feature in common is that the ears of both humans and lizards emit faint, pure tones known as spontaneous otoacoustic emissions (SOAEs). More than four decades after their discovery, the mechanism underlying these emissions is still imperfectly understood, although it is known that they are important for improving the sensitivity and sharpness of hearing. In both humans and lizards, the frequencies of SOAEs change by a few percent when static pressure is applied to the tympanic membrane. For the human ear, this observation is normally explained by a so-called global oscillator model (such as with Shera’s coherent reflection model), in which the emissions result from standing waves, and external pressure changes the boundary conditions – the stiffness of the oval and round windows – which then has a global effect on the SOAE frequencies. Methods: Here we investigate how changing parameters of an earlier developed local oscillator model for the lizard ear can change the frequencies of the SOAEs. A major feature of the model is that each oscillator is coupled only to its immediate neighbours. The oscillators then cluster into groups of identical frequency, and each of these so-called frequency plateaus can be taken to represent an SOAE. Results: Even though the natural (unperturbed) frequencies of all the oscillators remain fixed, here we find for several model parameters that by slightly changing their value the frequency plateaus – the SOAEs – shift by a few percent. Plots of how these changes alter SOAE frequencies are given, and their magnitude corresponds well with observations of SOAE changes in lizards. Discussion: Investigation of the influence of the change of parameters in an earlier developed local oscillator model for the lizard ear shows that a local oscillator model can explain small SOAE frequency changes as well as a global oscillator model.

The effects of mechanically gated ion channels of the inner ear on thermal sensitivity of spontaneous otoacoustic emissions

In quiet environments, the inner ears of vertebrates can produce low intensity sounds that are detectable in the ear canal, termed spontaneous otoacoustic emissions (SOAEs). This background activity of the inner ear has been regarded as an epiphenomenon of the active processes performed by hair cells – the sensory receptors of the auditory system. Experimental measurements of SOAEs from the ears of tokay geckos reveal a linear increase of SOAE frequency with body temperature, with the emission at higher frequencies displaying greater thermal sensitivity. In this work, we elucidated the cellular mechanism underlying the thermal sensitivity of SOAE frequency using a mathematical model of hair cell’s transduction process performed by mechanically gated ion channels. We employed the previously proposed gating-spring model which described an individual ion channel by a two-state system, whose activation energy associated with channel gating depended on the level of temperature. Our results from numerical simulations revealed that a rise in temperature elicited an increase in the frequency of spontaneous oscillations displayed by a single hair cell. The magnitude of the frequency shift increased with the oscillation frequency following a quadratic polynomial, a characteristic observed in the physiological recordings of SOAEs from tokay geckos. The model further suggested that the intrinsic energy difference between the open and closed state of the ion channels greatly controlled the temperature sensitivity of a hair bundle.

Carbamazepine induces upward frequency shifts of spontaneous otoacoustic emissions

In three subjects, we measured spontaneous otoacoustic emissions (SOAEs) when they were using carbamazepine (CBZ), and compared this to the SOAE measurement when they were not using CBZ. We observed 14 SOAEs showing a consistent upward shift of center frequency, related to CBZ intake. On average, the magnitude of the frequency shift increased with increasing frequency. The magnitude of the shift was 30–104 Hz, at frequencies ranging from 1.3 to 2.3 kHz, corresponding to a shift between 2.3 and 4.5%. Compared to other causes and manipulations known to change SOAE frequency, these shifts are relatively large. The underlying mechanism is most likely an increased stiffness of the cochlear partition. This would also explain the downward pitch shift due to CBZ, which has been reported by subjects with absolute pitch.

Comparing spontaneous and stimulus frequency otoacoustic emissions in mice with tectorial membrane defects

The global standing-wave model for generation of spontaneous otoacoustic emissions (SOAEs) suggests that they are amplitude-stabilized standing waves and that the spacing between SOAEs corresponds to the interval over which the phase changes by one cycle as determined from the phase-gradient delays of stimulus frequency otoacoustic emissions (SFOAEs). Because data characterizing the relationship between spontaneous and evoked emissions in nonhuman mammals are limited, we examined SOAEs and SFOAEs in tectorial membrane (TM) mutants and their controls. Computations indicate that the spacing between adjacent SOAEs is predicted by the SFOAE phase-gradient delays for TM mutants lacking Ceacam16, where SOAE frequencies are greater than ~20 kHz and the mutants retain near-normal hearing when young. Mice with a missense mutation in Tecta (TectaY1870C/+), as well as mice lacking Otoancorin (Otoa−/−), were also examined. Although these mutants exhibit hearing loss, they generate SOAEs with average frequencies of 11 kHz in TectaY1870C/+ and 6 kHz in Otoa−/−. In these animals, the spacing between adjacent SOAEs is larger than predicted by the SFOAE phase delays. It is also demonstrated that mice do not exhibit the strong frequency-dependence in signal coding that characterizes species with good low-frequency hearing. In fact, a transition occurs near the apical end of the mouse cochlea rather than at the mid-point along the cochlear partition. Hence, disagreements with the standing-wave model are not easily explained by a transition in tuning ratios between apical and basal regions of the cochlea, especially for SOAEs generated in TectaY1870C/+mice.

Suppression tuning of spontaneous otoacoustic emissions in the barn owl (Tyto alba)

Spontaneous otoacoustic emissions (SOAEs) have been observed in a variety of different vertebrates, including humans and barn owls (Tyto alba). The underlying mechanisms producing the SOAEs and the meaning of their characteristics regarding the frequency selectivity of an individual and species are, however, still under debate. In the present study, we measured SOAE spectra in lightly anesthetized barn owls and suppressed their amplitudes by presenting pure tones at different frequencies and sound levels. Suppression effects were quantified by deriving suppression tuning curves (STCs) with a criterion of 2 dB suppression. SOAEs were found in 100% of ears (n = 14), with an average of 12.7 SOAEs per ear. Across the whole SOAE frequency range of 3.4–10.2 kHz, the distances between neighboring SOAEs were relatively uniform, with a median distance of 430 Hz. The majority (87.6%) of SOAEs were recorded at frequencies that fall within the barn owl’s auditory fovea (5–10 kHz). The STCs were V-shaped and sharply tuned, similar to STCs from humans and other species. Between 5 and 10 kHz, the median Q10dB value of STC was 4.87 and was thus lower than that of owl single-unit neural data. There was no evidence for secondary STC side lobes, as seen in humans. The best thresholds of the STCs varied from 7.0 to 57.5 dB SPL and correlated with SOAE level, such that smaller SOAEs tended to require a higher sound level to be suppressed. While similar, the frequency-threshold curves of auditory-nerve fibers and STCs of SOAEs differ in some respects in their tuning characteristics indicating that SOAE suppression tuning in the barn owl may not directly reflect neural tuning in primary auditory nerve fibers.

Modulation of auditory percepts by transcutaneous electrical stimulation

Transcutaneous, electrical stimulation with electrodes placed on the mastoid processes represents a specific way to elicit vestibular reflexes in humans without active or passive subject movements, for which the term galvanic vestibular stimulation was coined. It has been suggested that galvanic vestibular stimulation mainly affects the vestibular periphery, but whether vestibular hair cells, vestibular afferents, or a combination of both are excited, is still a matter of debate. Galvanic vestibular stimulation has been in use since the late 18th century, but despite the long-known and well-documented effects on the vestibular system, reports of the effect of electrical stimulation on the adjacent cochlea or the ascending auditory pathway are surprisingly sparse.The present study examines the effect of transcutaneous, electrical stimulation of the human auditory periphery employing evoked and spontaneous otoacoustic emissions and several psychoacoustic measures. In particular, level growth functions of distortion product otoacoustic emissions were recorded during electrical stimulation with alternating currents (2 Hz, 1–4 mA in 1 mA-steps). In addition, the level and frequency of spontaneous otoacoustic emissions were followed before, during, and after electrical stimulation (2 Hz, 1–4 mA). To explore the effect of electrical stimulation on the retrocochlear level (i.e. on the ascending auditory pathway beyond the cochlea), psychoacoustic experiments were carried out. Specifically, participants indicated whether electrical stimulation (4 Hz, 2 and 3 mA) induced amplitude modulations of the perception of a pure tone, and of auditory illusions after presentation of either an intense, low-frequency sound (Bounce tinnitus) or a faint band-stop noise (Zwicker tone).These three psychoacoustic measures revealed significant perceived amplitude modulations during electrical stimulation in the majority of participants. However, no significant changes of evoked and spontaneous otoacoustic emissions could be detected during electrical stimulation relative to recordings without electrical stimulation.The present findings show that cochlear function, as assessed with spontaneous and evoked otoacoustic emissions, is not affected by transcutaneous electrical stimulation, at the currents used in this study. Psychoacoustic measures like pure tone perception, but also auditory illusions, are affected by electrical stimulation. This indicates that activity of the retrocochlear ascending auditory pathway is modulated during transcutaneous electrical stimulation.

Aftereffects of Intense Low-Frequency Sound on Spontaneous Otoacoustic Emissions: Effect of Frequency and Level.

The presentation of intense, low-frequency (LF) sound to the human ear can cause very slow, sinusoidal oscillations of cochlear sensitivity after LF sound offset, coined the "Bounce" phenomenon. Changes in level and frequency of spontaneous otoacoustic emissions (SOAEs) are a sensitive measure of the Bounce. Here, we investigated the effect of LF sound level and frequency on the Bounce. Specifically, the level of SOAEs was tracked for minutes before and after a 90-s LF sound exposure. Trials were carried out with several LF sound levels (93 to 108dB SPL corresponding to 47 to 75 phons at a fixed frequency of 30Hz) and different LF sound frequencies (30, 60, 120, 240 and 480Hz at a fixed loudness level of 80 phons). At an LF sound frequency of 30Hz, a minimal sound level of 102dB SPL (64 phons) was sufficient to elicit a significant Bounce. In some subjects, however, 93dB SPL (47 phons), the lowest level used, was sufficient to elicit the Bounce phenomenon and actual thresholds could have been even lower. Measurements with different LF sound frequencies showed a mild reduction of the Bounce phenomenon with increasing LF sound frequency. This indicates that the strength of the Bounce not only is a simple function of the spectral separation between SOAE and LF sound frequency but also depends on absolute LF sound frequency, possibly related to the magnitude of the AC component of the outer hair cell receptor potential.

Frequency selectivity of the human cochlea: Suppression tuning of spontaneous otoacoustic emissions

Frequency selectivity is a key functional property of the inner ear and since hearing research began, the frequency resolution of the human ear has been a central question. In contrast to animal studies, which permit invasive recording of neural activity, human studies must rely on indirect methods to determine hearing selectivity. Psychophysical studies, which used masking of a tone by other sounds, indicate a modest frequency selectivity in humans. By contrast, estimates using the phase delays of stimulus-frequency otoacoustic emissions (SFOAE) predict a remarkably high selectivity, unique among mammals. An alternative measure of cochlear frequency selectivity are suppression tuning curves of spontaneous otoacoustic emissions (SOAE). Several animal studies show that these measures are in excellent agreement with neural frequency selectivity. Here we contribute a large data set from normal-hearing young humans on suppression tuning curves (STC) of spontaneous otoacoustic emissions (SOAE). The frequency selectivities of human STC measured near threshold levels agree with the earlier, much lower, psychophysical estimates. They differ, however, from the typical patterns seen in animal auditory nerve data in that the selectivity is remarkably independent of frequency. In addition, SOAE are suppressed by higher-level tones in narrow frequency bands clearly above the main suppression frequencies. These narrow suppression bands suggest interactions between the suppressor tone and a cochlear standing wave corresponding to the SOAE frequency being suppressed. The data show that the relationship between pre-neural mechanical processing in the cochlea and neural coding at the hair-cell/auditory nerve synapse needs to be reconsidered.

Effects of spontaneous otoacoustic emissions on pure-tone frequency difference limens.

Pure-tone frequency difference limens (FDLs) have been shown to vary in the vicinity of spontaneous otoacoustic emissions (SOAEs). As lower FDLs have been observed near SOAEs when measured ipsi- and contralaterally to the emission ear, it has been proposed that prolonged ongoing stimulation of nerve cells tuned to the SOAE frequency could lead to a central oversensitivity to that frequency, hence a better frequency-discrimination ability. However, it is also known that tones close in frequency to an SOAE can "entrain" the emission to oscillate at their own frequency. This may instead explain the variations in FDL near SOAE frequencies as arising from peripheral interactions between SOAEs and external tones in the cochlea. To test these two hypotheses, SOAE entrainment patterns and FDLs were recorded in seven subjects with an ipsilateral SOAE and no neighboring contralateral SOAE. Ipsilateral FDLs were lowest in the SOAE entrainment region and worsened significantly when beating between the external tone and SOAE occurred. FDLs remained unaffected in the non-emission ear and did not alter with continuous ipsilateral or contralateral presentation of a pure tone aimed at emulating an SOAE. These findings suggest a mechanical rather than neural origin for the variations in FDL near SOAE frequencies.

Characterization of spontaneous otoacoustic emissions in full-term newborns

ObjectiveTo analyze the characteristics of spontaneous otoacoustic emissions (SOAEs) in full-term newborns. MethodsA total of 236 ears from 147 randomly selected full-term Chinese neonates (82 females and 65 males), who had passed the initial newborn hearing screening, were assessed for SOAEs using the Capella OAE equipment (Madsen, Denmark). The test was performed in a sound booth. Results(1) The overall prevalence of SOAE was 56.77% of the ears. The prevalence of SOAEs was significantly higher in females (69.23%) than in males (41.51%, p<0.01), as well as in the right ears (64.17%) than in the left ears (49.14%, p<0.05). (2) The overall mean level of SOAE was 11.78±8.36dB SPL, with no significant differences between males (11.73±8.25dB SPL) and females (11.81±8.43dB SPL) or between the left (11.97±8.56dB SPL) and the right ears (11.65±8.22dB SPL). (3) The 25th and 75th percentiles of SOAE frequencies were 2.31 and 4.36kHz in females and 1.93 and 3.94kHz in males, which were statistically significantly different (p<0.01). In contrast, the SOAE frequency was not significantly different between ears (2.22–4.18kHz in the left ears and 2.17–4.14kHz in right ears). (4) The overall mean number of SOAEs was 3.70±2.75, with no significant differences in females (3.62±2.70) and males (3.86±2.87) or in right (3.70±2.55) and left ears (3.70±3.02). ConclusionsThe prevalence rate of SOAE is significantly higher in females than in males and in the right ears than in the left ears in Chinese newborns. The frequencies of the SOAEs in newborns appeared to be higher than those reported in normal-hearing adults in the literature.

All that Jazz Coming Out of My Ears

All that Jazz Coming Out of My Ears

Spontaneous otoacoustic emissions, threshold microstructure, and psychophysical tuning over a wide frequency range in humans

Hearing thresholds have been shown to exhibit periodic minima and maxima, a pattern known as threshold microstructure. Microstructure has previously been linked to spontaneous otoacoustic emissions (SOAEs) and normal cochlear function. However, SOAEs at high frequencies (>4 kHz) have been associated with hearing loss or cochlear pathology in some reports. Microstructure would not be expected near these high-frequency SOAEs. Psychophysical tuning curves (PTCs), the expression of frequency selectivity, may also be altered by SOAEs. Prior comparisons of tuning between ears with and without SOAEs demonstrated sharper tuning in ears with emissions. Here, threshold microstructure and PTCs were compared at SOAE frequencies ranging between 1.2 and 13.9 kHz using subjects without SOAEs as controls. Results indicate: (1) Threshold microstructure is observable in the vicinity of SOAEs of all frequencies; (2) PTCs are influenced by SOAEs, resulting in shifted tuning curve tips, multiple tips, or inversion. High frequency SOAEs show a greater effect on PTC morphology. The influence of most SOAEs at high frequencies on threshold microstructure and PTCs is consistent with those at lower frequencies, suggesting that high-frequency SOAEs reflect the same cochlear processes that lead to SOAEs at lower frequencies.

THE NMDA DEFICIENCY HYPOTHESIS OF SCHIZOPHRENIA: EMERGING FROM PRECLINICAL CONCEPTS TO CLINICAL EVIDENCE

Spontaneous otoacoustic emissions (SOAEs) were measured in human monozygotic (MZ) and dizygotic (DZ) twins and in a sample of non-twins. The number of SOAEs exhibited was more highly correlated in MZ co-twins than in same-sex DZ co-twins. Model-fitting to the correlations suggested that about three-quarters of the individual variation in the expression of SOAEs is attributable to genes. There was no convincing evidence for the heritability of specific SOAE frequencies. In accord with past surveys, SOAEs were more numerous in right than left ears, and in female than male subjects. Also investigated were the numbers of SOAEs exhibited by dark- versus light-eyed people and by MZ versus DZ twins. Those differences in our data were small and not statistically significant, but they were in a direction consistent with other studies: more SOAEs in dark-eyed individuals and in MZ twins. The view presented here is that SOAEs themselves are unlikely objects for natural selection, and probably are epiphenomena resulting from selection for those cochlear mechanisms that contribute to good hearing sensitivity—which is related to SOAE expression. It is argued that, in addition to genetics, other factors have the potential to affect the specific numbers of SOAEs that are expressed. For example, some aspects of the complex prenatal process of producing a male fetus are presumed to be responsible for the smaller number of SOAEs seen in males than females.

Frequency tuning of the contralateral medial olivocochlear reflex in humans

Activation of the medial olivocochlear (MOC) efferents attenuates cochlear gain and reduces the amplitudes of mechanical, electrical, and neural cochlear outputs. The functional roles of the MOC efferents are not fully understood, especially in humans, despite postulations that they are involved in protection against acoustic trauma, facilitation of transient-sound perception, etc. Delineating the frequency tuning properties of the MOC efferents would provide critical evidence to support or refute these postulated functional roles. By utilizing spontaneous otoacoustic emissions (SOAEs), a cochlear measure sensitive to MOC modulation, we systematically demonstrate in humans that the contralateral MOC reflex is tuned to a fixed frequency band between 500 and 1,000 Hz independent of SOAE frequency. Our results question the role of the MOC reflex in protection against acoustic trauma or facilitation of transient-sound perception.

Fast and Slow Effects of Medial Olivocochlear Efferent Activity in Humans

BackgroundThe medial olivocochlear (MOC) pathway modulates basilar membrane motion and auditory nerve activity on both a fast (10–100 ms) and a slow (10–100 s) time scale in guinea pigs. The slow MOC modulation of cochlear activity is postulated to aide in protection against acoustic trauma. However in humans, the existence and functional roles of slow MOC effects remain unexplored.Methodology/Principal FindingsBy employing contralateral noise at moderate to high levels (68 and 83 dB SPL) as an MOC reflex elicitor, and spontaneous otoacoustic emissions (SOAEs) as a non-invasive probe of the cochlea, we demonstrated MOC modulation of human cochlear output both on a fast and a slow time scale, analogous to the fast and slow MOC efferent effects observed on basilar membrane vibration and auditory nerve activity in guinea pigs. The magnitude of slow effects was minimal compared with that of fast effects. Consistent with basilar membrane and auditory nerve activity data, SOAE level was reduced by both fast and slow MOC effects, whereas SOAE frequency was elevated by fast and reduced by slow MOC effects. The magnitudes of fast and slow effects on SOAE level were positively correlated.Conclusions/SignificanceContralateral noise up to 83 dB SPL elicited minimal yet significant changes in both SOAE level and frequency on a slow time scale, consistent with a high threshold or small magnitude of slow MOC effects in humans.

Effects of contralateral acoustic stimulation on hearing threshold fine structure and spontaneous otoacoustic emissions.

When plotted with fine frequency resolution, pure-tone thresholds often exhibit fine structure, a regular pattern of alternating minima and maxima. Spontaneous otoacoustic emissions (SOAEs) commonly occur at frequencies near those of threshold minima, and both phenomena are suggested to depend on active and vulnerable cochlear processes. The present study utilized contralateral acoustic stimulation (CAS), which modulates these processes via the medial olivocochlear efferent system, to further explore the relationship among SOAEs, threshold fine structure, and cochlear status. In normal-hearing individuals, thresholds and SOAEs were measured in quiet and with a 60 dB SPL broadband (0.1–10 kHz) noise presented to the contralateral ear. Thresholds were obtained in 1/500th–1/100th-octave steps at frequencies both near and far from those of SOAEs. Consistent with previous reports, CAS elevated SOAE frequency and reduced SOAE level. Threshold fine structure patterns were also shifted upward in frequency, though little reduction in the presence or depth of fine structure was observed. For frequency regions far from SOAEs, CAS elevated thresholds. However, at frequencies near SOAEs, where fine structure was more pronounced, thresholds often improved with CAS. Analysis of the relationships between concurrent changes in SOAE and thresholds will be presented.

Spontaneous otoacoustic emissions measured using an open ear-canal recording technique

Spontaneous otoacoustic emissions (SOAEs) and synchronized spontaneous otoacoustic emissions (SSOAEs) were recorded using both the standard closed-canal method of recording and a novel open-canal method which involved suspending the probe at the entrance to the ear canal with no occluding tip. In both conditions, a probe tube microphone was inserted down the ear canal to measure the acoustic pressure near the tympanic membrane. Open- and closed-canal recordings were obtained in twelve otologically normal ears, all of which exhibited SSOAEs, and 6 of which exhibited SOAEs. The results were analysed to identify any differences in response to frequency and amplitude. The different recording conditions appeared to have no significant effect on SOAE or SSOAE frequency, suggesting little effect on the SOAE generator within the cochlea. Below about 2 kHz, the amplitude for both types of emission was less for the open-canal recording when compared to the closed-canal recordings. Above 2 kHz, SSOAE amplitudes were greater in the open- than the closed-canal condition. Model stimulations of the ear canal and middle-ear acoustics are presented which were in qualitative agreement with the results shown for the effects on emission amplitudes.

The Effect of Contralateral Acoustic Stimulation on Spontaneous Otoacoustic Emissions

Evoked otoacoustic emissions are often used to study the medial olivocochlear (MOC) efferents in humans. There has been concern that the emission-evoking stimulus may itself elicit efferent activity and alter the evoked otoacoustic emission. Spontaneous otoacoustic emissions (SOAEs) are hence advantageous as no external stimulation is necessary to record the response in the test ear. Contralateral acoustic stimulation (CAS) has been shown to suppress SOAE level and elevate SOAE frequency, but the time course of these effects is largely unknown. By utilizing the Choi-Williams distribution, here we report a gradual adaptation during the presence of CAS and an overshoot following CAS offset in both SOAE magnitude and frequency from six normal-hearing female human subjects. Furthermore, we have quantified the time constants of both magnitude and frequency shifts at the onset, presence, and offset of four levels of CAS. Most studies using contralateral elicitors do not stringently control the middle-ear muscle (MEM) reflex, leaving the results difficult to interpret. In addition to clinically available measures of the MEM reflex, we have incorporated a sensitive laboratory technique to monitor the MEM reflex in our subjects, allowing us to interpret the results with greater confidence.

Long-term stability of spontaneous otoacoustic emissions.

Spontaneous otoacoustic emissions (SOAEs) were measured longitudinally for durations up to 19.5 years. Initial ages of the subjects ranged from 6 to 41 years. The most compelling finding was a decrease in frequency of all emissions in all subjects, which was approximately linear in %/year and averaged 0.25%/year. SOAE levels also tended to decrease with age, a trend that was significant, but not consistent across emissions, either within or across subjects. Levels of individual SOAEs might decrease, increase, or remain relatively constant with age. Several types of frequency/level instabilities were noted in which some SOAEs within an ear interacted such that their levels were negatively correlated. These instabilities often persisted for many years. SOAEs were also measured in two females over the course of their pregnancies. No changes in SOAE levels or frequencies were seen, that were larger than have been reported in females over a menstrual cycle, suggesting that levels of female gonadal hormones do not have a significant direct effect on SOAE frequencies or levels.

Effects of low-frequency biasing on spontaneous otoacoustic emissions: Frequency modulation

It was previously reported that low-frequency biasing of cochlear structures can suppress and modulate the amplitudes of spontaneous otoacoustic emissions (SOAEs) in humans [Bian, L. and Watts, K. L. (2008). "Effects of low-frequency biasing on spontaneous otoacoustic emissions: Amplitude modulation," J. Acoust. Soc. Am. 123, 887-898]. In addition to amplitude modulation, the bias tone produced an upward shift of the SOAE frequency and a frequency modulation. These frequency effects usually occurred prior to significant modifications of SOAE amplitudes and were dependent on the relative strength of the bias tone and a particular SOAE. The overall SOAE frequency shifts were usually less than 2%. A quasistatic modulation pattern showed that biasing in either positive or negative pressure direction increased SOAE frequency. The instantaneous SOAE frequency revealed a "W-shaped" modulation pattern within one biasing cycle. The SOAE frequency was maximal at the biasing extremes and minimized at the zero crossings of the bias tone. The temporal modulation of SOAE frequency occurred with a short delay. These static and dynamic effects indicate that modifications of the mechanical properties of the cochlear transducer could underlie the frequency shift and modulation. These biasing effects are consistent with the suppression and modulation of SOAE amplitude due to shifting of the cochlear transducer operating point.