Amplitude Of Spontaneous Otoacoustic Emissions Research Articles

Top-Down Cognitive and Linguistic Influences on the Suppression of Spontaneous Otoacoustic Emissions.

Auditory sensation is often thought of as a bottom-up process, yet the brain exerts top-down control to affect how and what we hear. We report the discovery that the magnitude of top-down influence varies across individuals as a result of differences in linguistic background and executive function. Participants were 32 normal-hearing individuals (23 female) varying in language background (11 English monolinguals, 10 Korean-English late bilinguals, and 11 Korean-English early bilinguals), as well as cognitive abilities (working memory, cognitive control). To assess efferent control over inner ear function, participants were presented with speech-sounds (e.g., /ba/, /pa/) in one ear while spontaneous otoacoustic emissions (SOAEs) were measured in the contralateral ear. SOAEs are associated with the amplification of sound in the cochlea, and can be used as an index of top-down efferent activity. Individuals with bilingual experience and those with better cognitive control experienced larger reductions in the amplitude of SOAEs in response to speech stimuli, likely as a result of greater efferent suppression of amplification in the cochlea. This suppression may aid in the critical task of speech perception by minimizing the disruptive effects of noise. In contrast, individuals with better working memory exert less control over the cochlea, possibly due to a greater capacity to process complex stimuli at later stages. These findings demonstrate that even peripheral mechanics of auditory perception are shaped by top-down cognitive and linguistic influences.

Otoacoustic emissions and auditory brain stem responses in hearing-impaired Saudi diabetic patients

Objective: To compare otoacoustic emissions and auditory brain stem responses in hearing-impaired diabetic patients and matched controls in order to determine the lesion site for hearing loss in diabetic patients.Subjects and Methods: This matched case-control study compared 88 hearing-impaired type 2 diabetic patients with 63 age- and gender-matched controls. Cochlear function was evaluated on the basis of otoacoustic emissions. The presence and amplitude of spontaneous otoacoustic emissions, distortion product amplitudes and latencies were recorded. Retrocochlear function was evaluated on the basis of auditory brainstem response. Absolute latencies of waves I, III, and V and inter-peak latencies of I–III, III–V, and I–V of the auditory brainstem were compared.Results: In the case of diabetic patients, no spontaneous otoacoustic emissions were produced, suggesting cochlear damage. Distortion product otoacoustic emission amplitudes at 1, 2, 4, and 6 kHz, but not the latencies, were significantly different between diabetic and control patients. Wave V latency was also significantly different between the 2 groups while the values of all other auditory brainstem parameters were similar.Conclusion: Cochlear damage may be one of the causes of hearing loss in diabetic patients. Distortion product otoacoustic emission amplitude may be used for assessment of hearing loss in diabetic patients.

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.

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

The dynamic effects of low-frequency biasing on spontaneous otoacoustic emissions (SOAEs) were studied in human subjects under various signal conditions. Results showed a combined suppression and modulation of the SOAE amplitudes at high bias tone levels. Ear-canal acoustic spectra demonstrated a reduction in SOAE amplitude and growths of sidebands while increasing the bias tone level. These effects varied depending on the relative strength of the bias tone to a particular SOAE. The SOAE magnitudes were suppressed when the cochlear partition was biased in both directions. This quasi-static modulation pattern showed a shape consistent with the first derivative of a sigmoid-shaped nonlinear function. In the time domain, the SOAE amplitudes were modulated with the instantaneous phase of the bias tone. For each biasing cycle, the SOAE envelope showed two peaks each corresponded to a zero crossing of the bias tone. The temporal modulation patterns varied systematically with the level and frequency of the bias tone. These dynamic behaviors of the SOAEs are consistent with the shifting of the operating point along the nonlinear transducer function of the cochlea. The results suggest that the nonlinearity in cochlear hair cell transduction may be involved in the generation of SOAEs.

Evaluation of Cochlear Function in Patients with Tinnitus Using Spontaneous and Transitory Evoked Otoacoustic Emissions

The aim of this paper has been to investigate the cochlear function and the basic properties of otoacoustic emissions (OAEs) in patients with tinnitus using Spontaneous Otoacoustic Emissions (SOAEs) and Transitory Evoked Otoacoustic Emissions (TEOAEs). We have analyzed the incidence, amplitude and spectral content of hearing thresholds, SOAEs and TEOAEs in a sample of 44 ears. We have measured incidence, intensity, frequency, number of peaks and amplitude of emission and their variability across frequency range from 500 to 5000 Hz. A correlation was determined between the OAEs results and the results obtained using hearing thresholds. We have not found statistically significant differences at 500, 1000, 2000, 4000 and 8000 Hz frequencies neither at mean hearing thresholds between the sample of ears with tinnitus and the sample of ears without tinnitus. SOAEs were only present in 1 of the 44 ears tested (2.27%) and it was a 17 dB SPL amplitude peak at 2770 Hz frequency. TEOAEs, however, were displayed in some frequency in all the ears. We have compared TEOAEs parameters between the sample of ears with tinnitus and the sample of ears without tinnitus in 500, 1000, 2000, 4000 and 5000 Hz frequencies, and we have only found statistically significant differences at 4000 Hz, p = 0.02. Comparison of TEOAEs parameters between ears with tinnitus and ears without tinnitus in the same patient have only found statistically significant differences at 4000 Hz frequency, p = 0.011. In both cases there were not statistically significant differences at 500, 1000, 2000 and 5000 Hz frequencies nor at mean TEOAEs amplitudes for every group. We have not found significant relations between tinnitus and OAEs registration.

A retrospective study of the spectral probability of spontaneous otoacoustic emissions: Rise of octave shifted second mode after infancy

The recording of otoacoustic emissions (OAEs) is today a widely used tool in medical diagnosis. The mechanisms of OAE generation in the cochlea and their transmission to the external ear canal, however, are not well understood and a matter of long-standing debates. Here, the frequency distribution of 1660 spontaneous otoacoustic emissions (SOAEs) from three surveys, covering 296 human subjects, is analyzed. Neonates show a monomodal distribution with a peak at 4 kHz, but both children (5–11y) and adults show an identical bimodal distribution, with two peaks in an octave distance (1.5 and 3 kHz). For the combined children and adult data, distribution density at the two peak tops is 2.8 and 2.7 times as high as at the low between them. Mean SOAE amplitudes are unrelated to the two peaks, but show a significant narrow-band dip precisely at the low in between at 2140 Hz ( P < 0.008). External ear canal resonance can explain the single 4 kHz mode at birth and the 3 kHz mode in children and adults. The octave shifted 1.5 kHz mode remains without mechanical explanation. It may reflect descending neural influence from central octave band processing. The results are relevant for the interpretation of OAE levels in medical diagnosis.

Calcium Modulates the Frequency and Amplitude of Spontaneous Otoacoustic Emissions in the Bobtail Skink

Active processes in the inner ear of lizards can be monitored using spontaneous otoacoustic emissions (SOAE) measured outside the eardrum. In the Australian bobtail lizard, SOAE are generated by an active motility process in the hair-cell bundle. This mechanism has been shown to be sensitive to the calcium-chelating agent 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid and is presumed to be related to the calcium-sensitive transduction-channel motor implicated in other nonmammalian hair cell systems. In studies of frog saccular and turtle auditory papillar hair cells in vitro, the frequency and amplitude of bundle oscillations depend on the concentration of calcium in the bathing solutions. In the present study, the calcium concentration in the endolymph was changed in vivo in the Australian bobtail lizard Tiliqua rugosa, and SOAE were monitored. Glass pipettes with large tips and containing different calcium concentrations in their fluids were introduced into scala media, and their contents were allowed to passively flow into the endolymph. Low calcium concentrations resulted in a downward shift in the frequency of SOAE spectral peaks and generally an increase in their amplitudes. Calcium concentrations > 2 mM resulted in increases in frequency of SOAE peaks and generally a loss in amplitude. These frequency shifts were consistent with in vitro data on the frequencies and amplitudes of spontaneous oscillation of hair cell bundles and thus also implicate calcium ions in the generation of active motility in nonmammalian hair cells. The data also suggest that in this lizard species, the ionic calcium concentration in the cochlear endolymph is > or = 1 mM.

Effects of AC and DC stimulation on chinchilla SOAE amplitude and frequency

The effects of AC and DC current on spontaneous otoacoustic emissions (SOAEs) were studied in normal chinchillas and chinchillas with selective inner hair cell (IHC) loss. Electrical stimulation was delivered through an electrode on the round window or through an electrode in scala media. SOAE frequencies ranged from 4 to 11 kHz and amplitudes ranged from 13 to 51 dB SPL. AC simulation suppressed SOAE amplitude. The suppression contours had a narrowly tuned, low-threshold tip located above the frequency of the SOAE. AC suppression contours were similar to acoustic suppression contours except that the AC suppression contours lacked a high-threshold, low frequency tail. The lowest threshold of the AC suppression contour was 3.9 μA rms whereas the lowest acoustic suppression threshold was 19 dB SPL. AC stimulation, which induced an electrically evoked otoacoustic emission, interacted with the SOAE to generate distortion product otoacoustic emissions (DPOAEs) of up to 26 dB SPL at 2 f S− f AC ( f S=SOAE). DPOAE amplitude increased with AC current, but saturated at high levels. DC current steps affected both SOAE frequency and amplitude. Positive current at the round window decreased SOAE amplitude and frequency whereas negative current increased SOAE frequency, but had little effect on amplitude. The effects of AC and DC current on SOAEs in animals with IHC loss were similar to those in normal chinchillas.

Efferent adaptation and fatigue: The effect of contralateral noise on spontaneous otoacoustic emissions

Mott etal. [Hear. Res. 38, 229–242 (1989)] have shown that both frequency and amplitude of spontaneous otoacoustic emissions (SOAEs) can be modulated by contralateral acoustic stimulation. They also examined the effects of stimulus durations up to 4 min in search of long-term adaptation, but none was found. Because the driven rate of efferent fibers declines by only about one spike per second per minute [M. C. Liberman and M. C. Brown, Hear. Res. 24, 17–36 (1986)], longer durations might be necessary to observe efferent adaptation/fatigue. In the present study, SOAEs of three subjects were measured in the presence of contralateral narrow-band noises with various frequency characteristics and with durations of up to 60 min. The hypothesized effect—an initial decline in SOAEs amplitude under contralateral stimulation followed by a return to preexposure levels with the onset of efferent adaptation—was not consistently observed. While seen in some sessions for some subjects, it could not be brought under experimental control. Thus these results were in approximate agreement with the findings of Mott etal. Some methodological and functional implications of these findings will be discussed. [Work supported by a NIDCD grant to D. McFadden.]

Differential effects of visual attention on spontaneous and evoked otoacoustic emissions

A visual task decreases evoked otoacoustic emisions (TEOAE) to an interindividually variable degree. The aim of these two studies was to assess whether the presence or absence of spontaneous otoacoustic emissions (SOAE) is involved in this variability. The first experiment investigated spontaneous otoacoustic emission (SOAE) frequency shifts during a visual attention task with a Fast Fourier Transform analysis, and found no attention effect on SOAEs. Using a larger subject pool, the second experiment concerned the attention effect on transiently evoked otoacoustic emissions and SOAE amplitude, using different measurement methods with the same visual task. The sample was composed of two groups of subjects: group A comprising subjects presenting SOAEs and group B subjects without SOAEs. A decrease in EOAE amplitude for group B during attention was observed and seems to confirm a possible influence of attention on the cochlea via the medial olivocochlear efferent system (MOES). The TEOAE amplitude of group A did not vary during attention, showing the peculiarity of this population of subjects and suggesting a different cochlear functioning.

Spontaneous otoacoustic emissions in the bobtail lizard. III: Temperature effects

Spontaneous otoacoustic emissions (SOAE) in the ear canal of the Australian bobtail lizard are temperature sensitive. They shift their frequency up with an increase in temperature, an effect that is fully reversible. The degree of shift is dependent not only on the center frequency of the SOAE (lower-frequency SOAE show a smaller shift) but also on the temperature range in question. Rates of change of frequency are 0.014 to 0.04 oct/°C at 30°C, and twice that at 22°C. There was no strong and consistent effect of temperature on SOAE amplitudes. The above findings are very similar to those on the effect of temperature on SOAE of frogs and mammals. Suppression tuning curves of SOAE shifted with temperature, the largest effects being near the center frequency in the tuning-curve's tip region.

Effects of contralateral acoustic stimulation on spontaneous otoacoustic emissionsa)

Spontaneous otoacoustic emissions (SOAEs) were measured in the ear canal of adult humans prior to, during, and following presentation of tonal and broadband stimuli to the contralateral ear. Tones were presented at a fixed level at ten frequencies relative to the SOAE. Broadband noise was presented at eight levels, from 6 to 76 dB SPL. Shifts in SOAE frequency and amplitude were observed for some subjects, for some tone conditions. Frequency shifts were always positive, whereas amplitude shifts were variable. No apparent pattern of tuning was seen, such that tones with a particular frequency relationship to the SOAEs induced greater changes in the SOAEs. Systematic changes in frequency and amplitude of SOAEs were observed for increasing level of broadband noise for all subjects. Results are discussed with respect to possible mechanism(s) responsible for the alterations in SOAEs: Transcranial conduction; the olivocochlear system; and/or the middle-ear reflex arc.

Relaxation time constants for the suppression of spontaneous otoacoustic emissions by multiple ipsilateral tones.

Previous investigations of the time constants associated with suppression and recovery from suppression of spontaneous otoacoustic emissions (SOAEs) by pulsed external tones have shown that limit-cycle-oscillator models of SOAEs provide a basis for qualitative and quantitative interpretation of SOAE behavior [Talmadge etal., MechanicsandBiophysicsofHearing, edited by P. Dallos etal., pp. 235–242 (1990)]. The Van der Pol limit-cycle oscillator model is generalized to the case of two external driving tones, one continuous and the other pulsed. The continuous tone introduces a suppressed SOAE amplitude that is further modulated by the pulsed suppressor component. The model predicts that suppression onset and recovery times will increase with increases in the amount of suppression from the continuous suppressor tone. Preliminary data indicate that the onset and recovery times are affected in the manner implied by the model. [Work supported by NIH-NIDCD Grant No. DC 00307.]

Manifestations of intense noise stimulation on spontaneous otoacoustic emission and threshold microstructure: experiment and model.

Comparison between changes that occur simultaneously on spontaneous otoacoustic emissions (SOAEs) and on other cochlear origin phenomena can contribute to the understanding of cochlear micromechanical activity. The temporary changes that arise after short noise exposure are investigated in the following paper. The effects of noise exposure on the threshold microstructure near an SOAE and on the amplitude and frequency of the SOAE were measured. These experimental results indicate the following: (1) exposure to wideband noise for a short time causes a temporary reduction in the SOAE frequency and amplitude, and alters reversibly the threshold microstructure in the vicinity of the SOAE. The difference between the minimum and maximum in the threshold microstructure is reduced, and the frequency that yields the minimum threshold decreases; (2) the threshold at the SOAE frequency is most sensitive to noise exposure; (3) intense stimulation causes a relatively small increase, or even a decrease, in threshold at frequencies near the SOAE. The experimental results are interpreted in terms of a nonlinear transmission line model which includes nonlinear amplifiers. The effect of the noise exposure is modeled by reduction in the cochlear partition amplification term. Most of the experimental results are predicted by this model.

Changes in spontaneous otoacoustic emissions produced by acoustic stimulation of the contralateral ear

Spontaneous otoacoustic emissions (SOAEs) were measured in human ear canals before, during and after presentation of tonal stimuli to the contralateral ear. Stimuli were presented in 1 8 octave steps from 2 octaves below to 1 octave above the SOAE frequency at sound levels below the observed contralateral acoustic reflex threshold. For certain conditions there was an abrupt upward frequency shift at stimulus onset. For a fixed level the effect was frequency selective; the maximum frequency shift was obtained with tones approximately 1 2 octave below the SOAE. SOAE amplitude usually decreased but in some cases increased or remained unchanged. When amplitude changes were observed, the maximum shifts were observed for tones at or near the SOAE frequency. Changes in SOAEs were not observed for stimulus levels below 60 dB SPL. The effect is believed to be mediated by medial efferent neurons of the uncrossed olivocochlear bundle which arise in the medial region of the superior olivary complex and terminate on outer hair cells (OHCs). These results support those models which attribute SOAE generation to OHCs, and are indicative of an efferent influence on cochlear mechanics. A simple model is presented that proposes that efferent activity alters the tuning of the emission generator by causing changes in OHC membrane conductance.

Production of inner ear fluids.

Production of inner ear fluids.

Effects of intense sound exposure on spontaneous otoacoustic emissions

The effects of intense sound exposure on spontaneous otoacoustic emissions (SOAE) were measured in normally hearing human subjects as a function of exposure duration and frequency region. Consistent with the TTS literature, exposures one‐half to one‐quarter oct below the SOAE frequency have the largest effect. A 30‐s, 105‐dB SPL exposure shifts the SOAE frequency downward, while having little effect on SOAE amplitude. Recovery is biphasic: In the first minute post‐exposure, the SOAE frequency changes rapidly; over the next 20 to 30 min, the SOAE slowly returns to pre‐exposure values. Exposures of 15 and 60 s have similar effects. These results suggest that alterations in cochlear mechanics can be produced by stimuli that do not typically produce TTS. [Work supported by NINCDS grants R15 NS23202‐01 (SJN & CAC) and T‐32‐NS07257 (JBM).]