Suppression Of Transient-evoked Otoacoustic Emissions Research Articles

Contralateral suppression of TEOAE in diabetic children. Effects of 1.0 kHz and 2.0 kHz pure tone stimulation--preliminary study.

The medial efferent system and its regulating outer hair cell function have not been previously studied in diabetic children. In this study, the group comprised 32 diabetic children, aged 6.0-16.0 years, with diabetes lasting 2.0-9.0 years, with normal tonal and impedance audiometry. A control group consisted of 30 healthy children with similar age and sex distribution. Contralateral stimulation (CS) was performed using 1.0 and 2.0 kHz pure tones on the level of 30 and 50 dB SL. Effects of CS on transient evoked otoacoustic emissions (TEOAE) elicited by click of a level equal to 70 and 60 dB SPL were investigated. Analysis included assessment of TEOAE amplitude and 0.8 kHz frequency bandwidth (0.8-FBW) amplitudes (signal/noise) centred at 1.0; 2.0; 3.0; 4.0; 5.0 kHz. TEOAE-RA recorded for stimulus 80, 70 and 60 dB SPL without CS were decreasing: average values respectively 7.3, 4.7 and 3.9 dB SPL. In the group of diabetic children TEOAE amplitudes, recorded for different click levels without CS, were similar to these recorded in healthy children. It suggested that normal function of the cochlea was preserved, mostly outer hair cells. However, the obtained effects of CS, in comparison with healthy children, were weaker and not so regular. Statistical analysis revealed that the reduction of TEOAE amplitudes for adequate 0.8-FBW in the control group was significantly higher, for both 1.0 kHz and 2.0 kHz CPTs of 30 dB SL and 50dB SL, in comparison with diabetic children. It is concluded that the suppressive effect on OAE in diabetic children is rather weak and seems to be associated with pathological changes in medial olivo-cochlear myelinated fibres.

Peripheral factors in loudness adaptation with OAE effects

Tone decay (TD), the ipsilateral comparison paradigm (ICP), and the monaural simple adaptation (SA) procedure assess loudness adaptation differently; this may all be peripheral but it has not been previously compared in one study. Transient evoked oto-acoustic emissions (TEOAE) have their source in the outer hair cells of the cochlear periphery. A significant correlation (r=−0.60) between contralateral suppression of transient evoked OAEs and tone decay adaptation (r=−0.60) has been reported [Collet et al., Audiology 31, 1–7 (1992)]. A significant correlation (r=−0.36) between ICP adaptation and contralateral suppression of TEOAEs has been found [Ernest M. Weiler, Hongwei Dou et al., J. Acoust. Soc. Am. 103, 3052 (1998)]. Comparison of TD, ICP, and SA with suppression of TEOAEs used repeated measures testing of 75 students (20–35 yrs) of mixed nationalities. Significant correlations were found, but not at all values, between TD, ICP, SA, and suppression of TEOAEs at 80, 60, and 70 dB. A principle components factor analysis found factor I based on suppression, and factor II based on monaural adaptation. It was concluded that the ICP, TD, and SA are primarily peripheral in origin. TD and ICP each include variation in stimulus intensity which may play a role in triggering perception of loudness adaptation.

Acoustically and electrically evoked contralateral suppression of otoacoustic emissions in guinea pigs

It is generally accepted that stimulation of the efferent auditory system results in changes of cochlear activity. A simple method of activating the olivocochlear pathway by contralateral electrical stimulation of the round window (ES-RW) was used in this study with the aim of comparing the efficacy of acoustically and/or electrically evoked contralateral suppression. The suppression of transient evoked otoacoustic emissions (TEOAEs) and distortion product otoacoustic emissions (DPOAEs) was elicited by contralateral acoustic stimulation (AS) (61 dB SPL continuous white noise), and/or by electrical stimulation of an electrode implanted at the contralateral round window (monopolar rectangular pulses 0.1 ms, repetition rate 300 Hz, intensity 50–100 μA) in 12 guinea pigs. The average value of contralateral suppression of TEOAEs amounted to 1.04±0.48 dB for acoustic stimulation and 0.97±0.53 dB for round window electrical stimulation. The simultaneous presentation of both acoustic and electrical stimulation had only a slight additive effect and resulted in 1.27±0.79 dB diminution of TEOAEs. The suppression of DPOAEs during contralateral acoustic and electrical stimulation was evident mainly at low and middle frequencies (1–4 kHz). In two guinea pigs the maximum DPOAE suppression was present at high frequencies. The average values of contralateral suppression measured at individual f2 frequencies of DPOAEs were similar to those calculated from 1/4 octave power spectrum analysis of the TEOAEs in half of the animals. The results demonstrated that contralateral ES-RW had a similar suppressive effect on TEOAEs and DPOAEs as did contralateral AS and simultaneous AS+(ES-RW). The results of spectral analysis suggested that both modes of contralateral stimulation excited similar sensory cochlear elements and induce comparable suppression of both TEOAEs and DPOAEs.

Development of human cochlear active mechanism asymmetry: involvement of the medial olivocochlear system?

To study the functional development of the medial olivocochlear system, transient-evoked otoacoustic emission suppression experiments were conducted in 73 ears of 38 pre-term and 11 full-term neonates. The continuous contralateral stimulation was a broad band white noise, presented at 70 dB SPL. Efferent suppression was determined by subtracting the without-contralateral stimulation condition from the with-contralateral stimulation condition. Across this population, a mean suppression effect of contralateral stimulation on transient-evoked otoacoustic emissions was found, with most of the suppression effect observed after 8 ms. The amount of suppression is linearly, positively correlated with the conceptional age. In the subgroup of bilaterally tested neonates, the suppression of transient-evoked otoacoustic emissions is similar in the right ear and the left ear in subjects whose conceptional age is less than 36 weeks and significantly higher in the right ear than in the left ear in older neonates. This last observation was seen at frequencies where transient-evoked otoacoustic emission amplitudes became higher in the right ear than in the left ear as the conceptional age increased, a finding already reported in adults. This study shows that the functional adult pattern of the medial efferent system, probably involved in the detection of signals in noise such as speech sounds, seems to appear gradually in neonates and represents one of the several arguments in favor of functional auditory lateralization in humans, with a right ear advantage

Peripheral auditory lateralization assessment using TEOAEs

Previous studies indicate a left-right asymmetry in the function of peripheral auditory system. Contralateral acoustic suppression of TEOAEs (transient evoked otoacoustic emissions) enables assessment of medial olivocochlear efferent system functioning, and has demonstrated that this system is more effective in the right than in the left ear. Moreover, TEOAE amplitudes are lower in the left than in the right ear. The aim of the present experiment was to verify firstly the absence of a relationship between medial efferent system asymmetry and TEOAE amplitude asymmetry, and secondly to study TEOAE input/output function slopes. There was no link between the asymmetries in TEOAE amplitude and in the medial efferent system functioning. Further, as previously shown, the medial olivocochlear system increased the TEOAE input/output function slopes. These TEOAE input/output function slopes seem to be consistent factors in peripheral asymmetry since the slope is lower in the right than in the left ear. Moreover, the lower the TEOAE amplitudes, the greater the TEOAE slopes. The slope asymmetry of the two ears could correspond to earlier saturation or a lower augmentation ability of the TEOAE response in the right ear, where the TEOAE amplitude is higher. This asymmetry in growth slopes reinforces the notion of peripheral auditory lateralization.

Evoked otoacoustic emissions, suppression and comparison to loudness constancy, at speech frequencies

Spontaneous otoacoustic emissions (SOAE) reflect spontaneous activity of the outer hair cells of the cochlea. Suppression of transient evoked otoacoustic emissions (TEOAE) bears operational similarity to loudness adaptation determined by the ipsilateral comparison paradigm (ICP). The present study gathered these measures from 41 normal hearing adults (5 male, 36 female, 20–45 years old). There was no significant relationship between spontaneous SOAE, but there was a significant relationship (r =−0.36, p<0.05) between ICP loudness adaptation and suppression of TEOAEs. The relationship between these two active measures has implications for failure of adaptation or the apparent loudness constancy in the speech range revealed by simple adaptation measures. It has been previously noted that the ICP technique yields adaptation in the speech frequencies between 40 and 80 dB, where the simple adaptation apparently does not [Weiler, Sandman, and Dou, program abstract 4pPPa10, J. Acoust. Soc. Am. 101, 3177 (1997)]. Implications will be discussed in terms of the results uncovered in this study.

Effects of interaural intensity and time disparity on transient evoked otoacoustic emissions

Monaural and binaural 11/s, 65 dB pe SPL clicks with interaural time and intensity disparities known to affect central auditory processing were used to study contralateral suppression of transient evoked otoacoustic emissions (TEOAEs) in 10 subjects (20 ears). Psychophysical assessment of sound lateralization induced by the same stimuli was also conducted. TEOAEs were recorded to monaural (ipsilateral to the OAE recording probe) and to binaural clicks when clicks to the contralateral ear were synchronous and symmetrical in intensity, or, in the binaural intensity disparity conditions, synchronous but 10 dB higher or 10 dB lower in the ear contralateral to the OAE recording probe. When interaural time disparities were studied, the clicks to the contralateral ear were of the same intensity throughout, but 400 μs earlier or 400 μs later than to the ear with the probe. The TEOAE components at 13–15.8 ms showed suppression, relative to monaural responses, under all binaural conditions. This contralateral suppression did not correlate with the psychophysical findings. Suppression effects were more pronounced with binaural disparity than with binaurally symmetrical clicks. Thus, although contralateral click intensity was the same with time disparities, suppression was paradoxically enhanced compared to the binaurally symmetrical stimulation. To explain these results we propose that two factors are involved in TEOAE suppression with binaural clicks: (1) contralateral intensity and (2) interaural disparity (time or intensity). The latency of the suppressions observed, the effect of interaural disparity on these suppressions, coupled with the anatomical origin of the crossed efferent fibers and the disparity sensitivity of the superior olivary complex (SOC), all suggest SOC involvement in these TEOAE suppressions.

Contralateral modification of transitory evoked otoacoustic emissions

In recent publications the influence of contralateral white noise on transient evoked otoacoustic emissions (TEOAE) is discussed with regard on contributions of the efferent auditory system. In the present study the effects have been investigated with regards to middle-ear muscles, efferents and cross hearing. TEOAE to monaural 40-80 dB SPL clicks were recorded in normal-hearing adults under simultaneous presentation of 20-60 dB SPL broadband noise to the contralateral ear. Control runs were performed before, during a short break of, and after contralateral stimulation. The control run before contralateral stimulation was used as a reference. Decrease in TEOAE, and increase in accompanying noise floor, were found to follow the contralateral stimulation. In particular a 1-3 dB decrease was found for contralateral noise levels of 40 and 60 dB SPL, even though the readings at 60 dB only were statistically significant (paired-samples t test, p = 0.05). For both TEOAE and noise floor no systematic dependence on click intensity was seen. The control runs during temporary break and after contralateral noise revealed an increase in both TEOAE and noise floor. As a rule, the TEOAE adapted to the reference within 2-3 min following the cessation of contralateral stimulation, whereas the increased noise floor level was still noted after 10 min. Traditionally, suppressing effects of contralateral stimulation on TEOAE have been attributed to cochlear efferents (CEs). Occasionally, the middle-ear muscle and cross hearing involvement have been considered as well. Substantially, the present results and findings of other workers are inconsistent with the basic knowledge of CE functioning: (I) The decrease in TEOAE under contralateral stimulation is in conflict with an increase in cochlear microphonics and summating potentials observed during activation of CEs: (II) contralateral suppression of TEOAE exhibited no significant dependence on the test-stimulus level while the CEs are known to be efficient in the range of the low signal intensities only, and (III) acoustic activation of the CEs can hardly be expected to reach levels sufficient to influence the TEOAE mechanism. The present findings, i.e. decrease in TEOAE and increase in noise floor level, can more reasonably be explained as being mainly attributable to activation of the middle-ear muscles.

The influence of evoking stimulus level on the neural suppression of transient evoked otoacoustic emissions

This study concerns the suppression of transient evoked otoacoustic emissions (TEOAEs) by contralateral noise. The suppression is interpreted as neurally induced changes in cochlear mechanics. The magnitude of TEOAE suppression is explored in response to a single level of contralateral noise, in 20 normal subjects, and as a function of TEOAE evoking stimulus power in 6 subjects. TEOAE were found to be relatively more susceptible to contralateral suppression when the TEOAE evoking stimulus was low. This suggests that saturation of the TEOAE generator by the evoking stimulus reduces the susceptibility of the generator to neural suppression. However, this relation did not hold between ears. Those ears in which the TEOAE seemed easier to saturate were easier to suppress by contralateral noise. We have concluded that TEOAE generators can differ in their susceptibility to neural suppression. Ears in which the TEOAE generating mechanism is less dependant on the ipsilateral evoking stimuli power level, are also naturally more susceptible to efferent suppression.

Ipsilateral suppression of transient evoked otoacoustic emission: role of the medial olivocochlear system.

Contralateral sound stimulation produces suppression of transient evoked otoacoustic emission (TEOAE), which is attributed to a reflex activation of the medial olivocochlear system. More pronounced suppression of TEOAE produced by ipsilateral masking could involve efferent-mediated effects along with effects of cochlear origin. However, this has not been investigated so far. Therefore, changes of click-evoked OAE under ipsi- and contralateral forward masking by clicks and noise-bursts were investigated in an extremely long-lasting experiment in one normal-hearing volunteer. The reduction of TEOAE under ipsilateral click-to-click forward masking was maximal during the first milliseconds after masker delivery implying that predominant role of the cochlear processes in TEOAE ipsilateral suppression. Ipsilateral forward masking by noise burst revealed additional TEOAE suppression with longer latency. Its time course was similar to that of the contralateral masking effect. The latter data suggest the involvement of the medial olivocochlear system in TEOAE ipsilateral suppression.

Contralateral suppression of TEOAE. Attempts to find a latency.

Latency of the contralateral suppression of transient-evoked otoacoustic emissions (TEOAE) has been investigated using the ILO88 system for ipsilateral stimulation and recording, and a laboratory computer interface producing contralateral noise bursts. Reduction of rms amplitude in the last 10.24 ms of the response was found to produce the most consistent indication of suppression. Onset latencies varied from less than 40 ms to 140 ms, offset latency from 20 ms to more than 80 ms. Acoustic reflex latencies have not been reported with such short latencies and this makes it unlikely that this reflex can be responsible for the contralateral suppression of TEOAE. This study used contralateral stimuli at 70 dB HL. Lower level stimuli may result in increased amplitude and it is also possible that the effect of contralateral stimulation may be frequency specific. The long offset latency necessitates long intervals between stimuli with an inherent risk of variation in stimulus and recording conditions. This makes an elaborate study of the latency difficult to perform in humans.