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The outer hair cells of the organ of Corti are the target of abundant efferent projections from the olivocochlear system. This peripheral efferent auditory subsystem is currently thought to be modulated by central activity via corticofugal descending auditory system, and to modulate active cochlear micromechanics. Although the function of this efferent subsystem remains unclear, physiological, psychophysical, and modeling data suggest that it may be involved in ear protection against noise damage and auditory perception, especially in the presence of background noise. Moreover, there is mounting evidence that its activity is modulated by auditory and visual attention. A commonly used approach to measure olivocochlear activity noninvasively in humans relies on the suppression of otoacoustic emissions by contralateral noise. Previous studies have found substantial interindividual variability in this effect, and statistical differences have been observed between professional musicians and non-musicians, with stronger bilateral suppression effects in the former. In this paper, we review these studies and discuss various possible interpretations for these findings, including experience-dependent neuroplasticity. We ask whether differences in olivocochlear function between musicians and non-musicians reflect differences in peripheral auditory function or in more central factors, such as top-down attentional modulation., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Cochlear damages have been shown to induce changes in tonotopic maps in the central auditory system of animals; neurons deprived from peripheral inputs start to respond to stimuli with frequencies close to the cutoff frequency (Fc) or "edge" of the hearing loss, which then become over-represented at the neural level. Here, we review findings, which reveal a possible psychophysical correlate of such central over-representation in human listeners with sensorineural hearing loss. These findings concur to demonstrate a local improvement in difference limens for frequency (DLFs) at or near Fc. This effect has now been observed in several studies and subjects with varied audiometric characteristics, including high- and low-frequency, and symmetric and asymmetric hearing losses. The presence of cochlear dead region or a steeply sloping hearing loss appear as a necessary condition for its occurrence. The effect cannot be explained simply by more prominent loudness cues or spontaneous otoacoustic emissions (SOAEs) near the audiogram edge. Overall, the data are consistent with local changes in pitch discrimination performance near the hearing-loss cutoff frequency being a result of the neural over-representation of that frequency region in the central auditory system. Further work is needed to confirm this hypothesis, and investigate other possible perceptual correlates of injury-related cortical plasticity in both humans and animals.

Benzodiazepines (Bzd) are known to interact with GABAergic inhibitory neurotransmission. Previous research on their effect on human auditory efferent pathways--through evoked otoacoustic emissions suppression by contralateral acoustic stimulation (CAS)--indicated a decrease in medial olivocochlear (MOC) efferent system inhibitory activity, after oral intake of oxazepam--representative of the Bzd drug class. To date, this pharmacological effect was only assessed in the right ear. Since a leftward asymmetry of Bzd receptors localization in human auditory cortex has been described recently, we explored in this study the hypothesis of an asymmetrical action of Bzd on MOC efferent functioning. The results revealed a significant difference of Bzd effect probing the right ear versus the left ear, with CAS-induced suppression being less effective in the right than left ear after oxazepam intake. This finding raises the question of possible neurochemical left-right asymmetry in the descending auditory pathways. The potential localization of this asymmetry is discussed.

This study was conducted to investigate maturation of the medial olivocochlear efferent system (MOCS) in pre- and full-term neonates using Quickscreen (Otodynamics Ltd) and to confirm previous findings on transient otoacoustic emission (TEOAE) suppression in neonates. MOCS maturation was investigated in 46 neonates born at the Chaim Sheba Medical Center, Tel Hashomer, Israel, using Quickscreen. All neonates were normal with no family history of general or auditory disease and no risk factors for hearing impairment. MOCS function appears gradually in human pre-term neonates and is considered to reach maturity shortly after term birth. The clinical value of MOCS testing in specific populations of newborns at risk for hearing and/or brainstem function can be legitimately raised as activation of the MOCS clearly alters cochlear output. The present results can be interpreted to support the testing of infants at risk of developing abnormal MOCS function using a commercially available rapid TEOAE measurement system.

Patients with steeply sloping hearing losses of cochlear origin may exhibit enhanced difference limens for frequency (DLFs) near the cut-off frequency (Fc) of their hearing loss. This effect has been related to observations in deafened animals of an over-representation of Fc in the primary auditory cortex. However, alternative interpretations in terms of peripheral mechanisms have not been eliminated. In the present study, we assessed the possible role of two peripheral mechanisms [loudness cues and spontaneous otoacoustic emissions (SOAEs)] in a group of patients with high-frequency hearing loss. We tested first whether the DLF enhancement effect was still observed under conditions where subjects could not rely on loudness cues to perform the frequency discrimination task. To achieve this, we adjusted the nominal level of each stimulus so that it fell on an equal loudness contour measured at very fine (1/8 octave) frequency intervals, and we roved the level of each stimulus over a large range (12 dB). Under these conditions, the DLF enhancement was still observed in all patients; this demonstrates that the effect cannot be explained simply by loudness cues. We then screened the patients for SOAEs to test whether the DLF enhancement effect could be explained by the presence of such emissions in the vicinity of the Fc. None of the patients exhibited SOAEs. Finally, we tested whether the patients had cochlear dead regions, i.e. regions lacking functional inner hair cells and/or auditory nerve fibres. Using a refined version of a non-invasive clinical test for the identification of dead regions, we assessed the presence of such regions in fine frequency steps (1/4 octave) up to very high frequencies. All of the patients had cochlear dead regions. The first two findings support the hypothesis that DLF enhancement is due to injury-induced central reorganization in the auditory system. The last one is consistent with neurophysiological data in animals, which suggest that complete deprivation from auditory input at certain cochlear sites may be a necessary condition for the occurrence of injury-induced cortical reorganization.

In order to test the hypothesis of a role of cochlear efferent activity in intensity perception in humans, loudness functions, loudness integration, and loudness summation were measured in the absence and in the presence of contralateral noise in normal-hearing subjects. Additionally, relationships with the effect of the noise on evoked otoacoustic emissions (EOAEs) were tested, and comparisons with vestibular neurotomy patients were performed. Overall, the results failed to demonstrate significant effects of contralateral noise stimulation on loudness functions and loudness integration. Furthermore, no significant differences were found in vestibular neurotomy patients. A significant effect of contralateral noise on loudness summation was noted, but was not related to the effect on otoacoustic emissions. The present results fail to support the notion that efferent influences onto the cochlear compression have a significant perceptual effect.

Earlier data in the literature have shown local improvements in frequency discrimination performance near the cut-off frequency of steeply sloping, high-frequency hearing loss in subjects with cochlear damage. The general objective of the present study was to characterize further the relationships between this effect and various audiometric variables: namely, the slope, extent and shape of the hearing loss. In particular, we were interested in determining whether the effect was present in subjects with more moderately sloping hearing loss and/or other patterns of loss. Frequency difference limens (DLFs) were measured in 20 subjects (eight female, 12 male, median age 55.5 years) with high-frequency hearing loss. At least 12 frequencies were tested at intervals of 1/8 octave over a range of 1.5 octaves around the cut-off frequency for hearing loss (Fc). The Fc corresponded to the audiogram edge frequency and was defined as the highest test frequency, at the beginning of the slope, with a hearing threshold of no more than 5 dB HL above that of the best hearing frequency. The level of the test tones was randomized over a range of 6 dB around a nominal level, following an equal-loudness contour curve measured at 1/2-octave intervals. Results showed that DLFs were significantly smaller in a frequency band 1/4 octave wide centred on Fc than in the other bands. Furthermore, the average DLF measured in this band proved to be negatively correlated with the slope of hearing loss. No such significant relationship was found with the other audiometric indices considered, namely, the extent and maximum amount of hearing loss and the log-transformed cut-off frequency. The 20 subjects were divided into three groups according to the slope of their hearing loss relative to Fc (steep, >25 dB/1/2 octave; medium, between 12 and 25 dB/1/2 octave; and shallow, <12 dB/1/2 octave). A local improvement in DLF around Fc was observed in the steep- and medium-slope groups and was confirmed statistically in the steep-slope group. Similar measurements in subjects with low-frequency or notched hearing loss allowed us to establish the presence of similar local improvements in DLFs around audiogram edges. These results, which suggest the slope of the hearing loss to be the most important factor for the occurrence of local DLF improvements, are consistent with both an interpretation in terms of peripheral mechanisms and one in terms of central mechanisms, i.e. injury-induced neural reorganization.

Objective: Contralateral suppression of the transient-evoked otoacoustic emissions (TEOAEs) provides a means of studying auditory efferent function, but the temporal dynamics of the reflex are not fully understood. The most fundamental parameter is the time-course of activation of contralateral suppression. The stimulus parameters are likely to be important; this may include temporal dynamics of the suppressor itself. This investigation thus was devoted to the further study of 1) delay of contralateral suppression of TEOAEs-effect of delay of the ipsilateral probe-and 2) temporal variation of the suppressor-effect of amplitude modulation of the contralateral noise stimulus., Design: Measurements were made in three samples of normal-hearing subjects (N(total) = 71), employing well-established methods of TEOAE assessment., Results: Statistically significant contralateral suppression occurred some 60 msec after onset of the contralateral noise; thereafter, the effect was essentially constant (i.e., to >180 msec). The results for click delays less than 60 msec, nevertheless, were systematic and readily fitted by a sloping straight line (dB suppression versus time) reminiscent of the concept of threshold power integration. The onset of suppression may thus be characterized by a time constant. The delay of suppression also was found to be reduced by contralateral amplitude-modulated noise., Conclusions: These findings reinforce a growing consensus in the literature that, despite initiation perhaps some milliseconds after onset of the contralateral stimulus, there is a substantial delay, i.e., in the tens of milliseconds, before maximal suppression is achieved. The exact time constant of this effect appears to depend upon the combination of probe and suppressor levels, including the temporality of the suppressor. These factors are likely to delimit the role/influence of this reflex in real-world function, favoring perhaps more-or-less sustained suppression that is activated in a time-varying sound environment.

At the auditory periphery, the medial olivocochlear system is assumed to be involved in complex sound processing and may be influenced by feedback from higher auditory nuclei. Indeed, the descending auditory pathway includes fibers coming from the auditory cortex that are anatomically well positioned to influence the superior olivary complex, and thus the medial efferent system. The aim of the present study was to verify the hypothesis of an implied influence of the auditory cortex on the peripheral auditory system. In three rare cases of patients presenting with intractable temporal lobe epilepsy, Heschl's gyrus (i.e. the temporal superior gyrus) was surgically removed in the right hemisphere in two patients and in the left hemisphere in a third patient, in order to minimize epilepsy attacks, as preoperative stereoencephalography had shown the epileptic focus or tumor to be situated in those locations. In all three cases, several weeks after the operation the medial olivocochlear system was clearly less functional on both sides, but especially on the side contralateral to the resection. In healthy controls, no such pattern was obtained. In four other epileptic patients, who were operated unilaterally at the anterior temporal pole, amygdala and hippocampus with the temporal gyrus partially spared, efferent suppression grew stronger in the ear ipsilateral to surgery. These results revealed that, in humans, the primary and secondary auditory cortex play a role in modulating auditory periphery activity through direct or indirect efferent fibers. In accordance with previous findings, this descending influence may improve the auditory afferent message by adapting the hearing function according to cortical analysis of the ascending input.

The mammalian auditory system contains descending pathways that originate in the cortex and relay at various intermediate levels before reaching the peripheral sensory organ of Corti. The last link in this chain consists of the olivocochlear bundle. The activity of this bundle can be measured through otoacoustic emissions, which are acoustic signatures of the cochlear biomechanical activity. In the present study, it was hypothesized that frequency-specific activation of the olivocochlear bundle in the contralateral ear would show up as frequency-specific variations in otoacoustic emission amplitude in the ipsilateral ear. Two groups of young adult subjects participated in this experiment. Evoked otoacoustic emissions were recorded in the ipsilateral ear at two test frequencies (1 and 2 kHz). Subjects had to detect probe tones at a given frequency in background noise in the contralateral ear. Larger efferent activation was measured at test frequencies on which attention is focused. This result provides evidence for an influence of attention on the auditory periphery via descending projections.

The activity of the medial olivocochlear bundle (MOCB) can be studied in humans through variations in the level of evoked otoacoustic emissions (EOAEs) elicited by contralateral acoustic stimuli (CAS). The present study sought to investigate how the activity of the MOC system at a given frequency, as measured through the contralateral suppression of tone-pip EOAEs, depends on the bandwidth of the contralateral stimulus. EOAEs were recorded in 155 normal-hearing subjects, successively with and without contralateral stimuli whose bandwidth, center frequency and level were systematically varied. We showed a clear dependence of contralateral EOAE suppression on bandwidth demonstrating increased suppression with increased bandwidth over about two octaves around the center frequency of the noise. This effect was obtained irrespective of whether contralateral noise energy was kept constant independently of bandwidth or not, which indicates a role of bandwidth per se in contralateral EOAE suppression. Results are interpreted in terms of a simple model of MOCB activation mechanisms including peripheral bandpass filtering, within-channel compression and across-channel spatial summation by the afferent paths. Complementary experiments suggested a greater effectiveness of increases in bandwidth on the upper than on the lower side and of frequency components akin to or remote from the test frequency than of intermediate bands. Finally, these results were complemented by detailed spectrum analyses of the EOAE level variations induced by the different noises, which revealed that whilst noise components close to or remote from the center frequency generally attenuated EOAE level, intermediate components could in some cases lead to a relative increase in EOAE level. These results can further be explained by assuming different positive and negative weights on the inputs to the spatial summation process depending on their position relative to the center frequency.

The auditory sensory end organ is under the control of the central nervous system via efferent projections. Contralateral suppression of otoacoustic emissions (acoustic signatures of the cochlear biomechanical activity) provides a non-invasive approach to assess olivocochlear efferent activity in humans. Using this approach, the present study compared professional musicians with musically-inexperienced subjects. The results revealed stronger bilateral cochlear suppression, suggesting larger efferent influences in both ears, in musicians. Furthermore, in indicating no difference in left/right asymmetry of efferent-mediated suppression between the two groups, the present findings suggest that the observed differences in olivocochlear activity reflect bilaterally-enhanced activity of the cortical auditory structures in musicians rather than differences in cerebral hemispheric asymmetry between the two groups.

Variations in the amplitude of transiently evoked otoacoustic emissions (TEOAEs) produced by a contralateral complex tone were measured in 26 normal-hearing human subjects. TEOAEs were evoked using a 1-kHz tone pip at 60 dB SPL. The contralateral complex consisted of harmonic components with frequencies between 400 and 2000 Hz; it was presented at levels ranging from 40 to 50 dB SL and its fundamental frequency (F0) was varied. In experiment 1, the dependence of TEOAE amplitude variations on the F0 of the contralateral complex was measured by varying the F0 from 50 to 400 Hz in octave steps. The results revealed a nonmonotonic dependence of TEOAE amplitude variations on contralateral F0, with significantly larger TEOAE suppression for F0's of 100 and 200 Hz than for F0's of 50 and 400 Hz. Experiment 2, in which the harmonics were summed in alternating sine-cosine phase instead of constant sine phase, showed a shift of the function relating TEOAE attenuation to F0 towards lower F0's, indicating that the waveform repetition rate, rather than harmonic spacing, was the actual factor of the dependence of contralateral TEOAE attenuation on F0. Furthermore, significantly smaller suppression was observed with the alternating-phase complexes than with the sine-phase complexes, suggesting an influence of the waveform crest factor. Experiment 3 showed no difference between the contralateral TEOAE attenuation effects produced by positive and negative Schroeder-phase complexes. Overall, these results bring further arguments for the notion that contralaterally induced medial olivocochlear bundle (MOCB) activity, as measured through the contralateral suppression of TEOAEs in humans, is sensitive to the rate of temporal envelope fluctuations of the contralateral stimulus, with preferential rates around 100-200 Hz.

In a previous study, a peripheral auditory asymmetry in right-handers was found. The activity of the uncrossed medial olivocochlear efferent pathway has been shown to be more effective in the right than in the left ear. Our aim was to compare right and left medial olivocochlear inhibition during contralateral, ipsilateral and binaural ear stimulation with a broad band noise, in order to better localize this asymmetry. Uncrossed pathway asymmetry was confirmed and the crossed pathway showed a reverse asymmetry: a left ear advantage. These results are in accordance with the assumption that the medial superior olivary complex is the locus of the asymmetry observed. As this nuclear complex receives central efferents, the peripheral auditory asymmetry may be related to the well-known cortical asymmetry.

Neuropsychological studies have demonstrated that language perception is lateralized at the hemispheric level. There is also much evidence for a peripheral lateralization of the auditory system in humans. Spontaneous otoacoustic emissions are more frequent in the right than in the left ear. The medial olivo-cochlear system is also more functional in the right than in the left ear in normal subjects. The study of specific samples shows that this asymmetry is found in professional musicians which have more functional efferent system in both ears. A link is hypothesized between peripheral and central laterality because of a dysfunctional peripheral asymmetry in pathological cases which show hemispheric lateralization disorders. Consequences of those pathological data will be discussed.

To investigate the involvement of the medial olivocochlear system (MOCS) in outer hair cell (OHC) motility stabilization, evoked otoacoustic emissions (EOAEs) were recorded in 20 normal-hearing subjects and in eight vestibular-neurotomized subjects, successively in the presence and absence of low-intensity contralateral acoustic stimulation. Intrasubject EOAE amplitude variability was assessed as the standard deviation computed over several successive recordings. In normal-hearing subjects, a significantly lower EOAE amplitude variability with contralateral acoustic stimulation (CAS) was observed in subjects in whom the CAS induced the greatest EOAE amplitude reduction. This result could not be attributed to the EOAE amplitude reduction itself, since variability was otherwise found to increase when EOAE amplitude decreased. Moreover, statistically significant correlations between EOAE amplitude attenuation and EOAE amplitude variability under CAS were observed. In the eight subjects operated for vestibular neurotomy, no such effect was found. Being sectioned in vestibular-neurotomized subjects, the MOCS can no longer exert its effects. These results strongly support the notion that MOCS activity, as induced by CAS, elicits a reduction in EOAE amplitude variability in normal-hearing subjects. This finding and some of its possible implications for understanding the role of the MOCS in hearing in humans are discussed.

To test the hypothesis of temporal modifications of cochlear responses when medial efferents are activated, otoacoustic emission latencies were estimated in 16 normal human subjects, in the presence and absence of a contralateral broadband noise, using measurements of the phase of the 2f1-f2 distortion product (group latency method). Significant decrease in the latency of lower frequency (0.8-2.7 kHz) emissions was found in the presence of increasing levels of contralateral sound, and this effect disappeared when the primary-tone levels increased to 60 dB SPL. To ensure that effects were not attributable to mechanisms involving middle ear structures, susceptible to activation by contralateral sound, latency measures were performed in seven subjects whose efferents were severed during a vestibular neurotomy and in two subjects with paralyzed stapedial muscle. Results in patients were compared to those obtained in three surgical control patients with intact efferent bundle, and in eight other normal subjects. All the subject groups exhibited a decrease in latency under contralateral sound except the patients with the severed efferent system who showed increased latencies.

The influence of variable durations of contralateral acoustic stimulation on the suppression of click-evoked otoacoustic emissions was investigated in order to determine whether olivocochlear efferent fibers are equally effective whatever the acoustical stimulation duration or if they show fatigue. The suppression effect was measured for contralateral stimulus durations ranging from 10 to 180 s prior to the onset of otoacoustic emission recording, and continuing throughout the recording time (60 s). No significant stimulus duration effect was found.

Evoked otoacoustic emissions (EOAEs) are assumed to be generated by outer hair cells (OHCs). It is now generally accepted that EOAEs represent a means of functional exploration of the active micromechanical properties of OHCs. Efferent fibers of the medial olivocochlear system (MOCS) are connected along the sides and the bases of OHCs. Some studies have shown that a suppression effect on EOAE amplitude is induced by the MOCS neurons during contralateral stimulation, presumably by modification of OHC motility. The contralateral acoustic stimuli used in experiments on the EOAE suppression effect have consisted mainly of sounds without a slow temporal fluctuation in their envelopes (broad-band noise, narrow-band noise, pure tones, or clicks). To elucidate further the parameters of MOCS activation, in the present study we looked at the contralateral suppression effect of amplitude-modulated (AM) tones. The results showed that EOAE amplitude was reduced with AM tones compared with no contralateral acoustic stimulation. The suppression effect mainly depended on three parameters. 1) Contralateral stimulation intensity: EOAE suppression occurred only with intensities > or = 40 dB SL. 2) The greater the modulation depth, the greater the suppression effect: statistical analysis showed a significant effect for 75 and 100% modulation depth. 3) The 100- and 140-Hz modulation frequencies gave the greatest suppression effect for 100 and 75% modulation depths. The suppression effect was frequency specific. The greatest decreases were observed when the carrier frequency of the contralateral AM tone was close to the frequency of the EOAE under study, i.e., 1 and 2 kHz. Acoustic cross talk and middle ear effects, which cannot be completely excluded, are discussed. However, the demonstrated frequency specificity of the EOAE suppression effect, together with observed presence of contralateral EOAE suppression in patients without stapedial reflex and the very weak intensities used (i.e., below acoustic reflex threshold), suggested that it was unlikely that the observed effects were due merely to middle ear reflexes. Our results confirm further the contralateral suppression effect on human cochlea mechanisms and show that the suppression effect can be influenced by amplitude modulations of the suppressor, characteristic of sounds in the environment.

The present study aimed to confirm and extend the finding, suggested by the results of a previous study, of different auditory neural efferent functioning in musicians compared with non-musicians. The activity of the medial olivocochlear bundle (MOCB), an auditory efferent subsystem, was measured through the contralaterally induced attenuation of the amplitude of evoked otoacoustic emissions (EOAEs) in two groups, one of musicians and one of non-musicians, paired for age and sex. The results indicated a statistically significant difference between the two groups, with the musicians showing greater amplitude reduction upon contralateral noise stimulation than non-musicians (U-test, U = 204, p < 0.025, n = 32). These results indicate greater MOCB activity in musicians than in non-musicians. The possible origins and implications of this finding are discussed.

Distortion product otoacoustic emissions (DPOAEs) provide a non-invasive and relatively direct method for evaluating cochlear travel time in humans. In the present study, the 2f1-f2 DPOAE latency was deduced from DPOAE phase shift according to f2 frequency shift, with f1 being fixed, using the ILO92 system. Latencies of 2f1-f2 DPOAEs were recorded at various primary frequencies and levels. Results were not wholly consistent with previous latency estimates. This study showed that the functions describing both 2f1-f2 DPOAE latency decrease with primary frequency increase, at several primary-tone levels, and 2f1-f2 DPOAE latency decrease with primary-level increase, at various frequencies, are best fit by exponential equations. The results of the evaluation of the latency-frequency-level relationship indicated the possibility of linking these three variables by the following expression: Latency = 68.30 exp (-0.027I -0.000434 f)+1.13.

The aim of the present experiment was to investigate the influence of hypothermia on transient evoked otoacoustic emissions (TEOAEs) in humans. Hypothermic alterations were brought about directly by cooling the cardiovascular system of young children during open heart bypass surgery. This condition caused TEOAE levels to decrease with a significant positive correlation between total and frequency band TEOAE amplitudes during cooling. TEOAEs were totally abolished at tympanic temperatures around 30 degrees C, without it being possible to find differences in TEOAE alteration among the frequency components. During rewarming, the changes reversed and TEOAEs returned to their initial prehypothermia status, although sometimes only partially. Despite large possible metabolic changes caused by this hypothermic condition at various levels, it is concluded that the motile properties of outer hair cells (OHCs), that are related to TEOAEs, are temperature-sensitive. The total suppression found in deep hypothermia (above 30 degrees C) could conceivably be attributable to a process involving a temperature-dependent energy source.

Despite onset of function early during the third term of gestation, the human auditory system demonstrates continued maturation, thought previously to occur primarily at the neural level. The electromotile properties of outer hair cells appear to contribute substantially to hearing sensitivity and frequency selectivity and lead to the generation of otoacoustic emissions (OAEs). This report demonstrates continued development of cochlear active mechanisms (i.e. end-organ level) after onset of cochlear function, as reflected by OAEs. Significant gender differences also are reported, corresponding to recently observed intersex differences in cochlear length and precursory to gender differences observed in the adult.

The present study used distortion product otoacoustic emission (DPOAE) latency as a tool to provide information about the generation sites of 2f1-f2 and 2f2-f1 DPOAEs in humans. The DPOAE 2f1-f2 is supposed to be generated near the f2 site, but little is known about the 2f2-f1 DPOAE processing in humans. The present work sought to test several hypotheses as to the possible generation of 2f1-f2 at the f2 site and of 2f2-f1 at the 2f2-f1 site as well as their backward reflection site, by comparing latencies of the two DPOAEs, under appropriate frequency manipulation. The effect of stimulus level was also studied. The latency values were calculated as the phase-lag related to the frequency shift, using the ILO92 software. Amplitudes were lower and latencies shorter for 2f2-f1 than for 2f1-f2. As expected, 2f1-f2 and 2f2-f1 DPOAE latency decreased with increasing stimulus level and frequency. At 70 dB SPL, latencies of DPOAEs with primaries f1 and f2 or f*1 and f*2, chosen so as to obtain 2f*1-f*2 = 2f2 - f1, were identical, whereas at 55 dB SPL the similarities were less obvious, suggesting two different generation processes. The present study suggests that the comparison of several DPOAE components may produce useful information about their processing within the cochlea.

Recording electrical auditory brainstem responses (EABR) provides clinical insight about responses of the residual post-cochlear neural system to electrical stimulation in profoundly deaf patients. A new strategy is presented for stimulating patients already implanted with a 15-electrode cochlear implant. Since the device is fully re-programmable via a RS-232 PC interface, it was possible to load a specific stimulating strategy designed to improve the spatial locus and the temporal structure of the impulse stimulation. Waves III to V emerge more clearly when this method is applied.

The aim of this study was to investigate the human peripheral auditory system in either ear to allow comparison of right and left medial olivocochlear inhibition during contralateral ear stimulation with a broad band noise. The efferent system showed a statistically significant greater right-side activity among 44 young subjects. This laterality appeared to be related to the presence of spontaneous otoacoustic emission but not to gender. This efferent asymmetry and the parallel spontaneous otoacoustic emission asymmetry could explain the lateralization of auditory sensitivity, temporary threshold shift and tinnitus.

To investigate the involvement of auditory efferents in hearing-in-noise in humans, olivocochlear bundle (OCB) functioning and detection-in-noise abilities were compared in 30 subjects. OCB function was assessed in terms of contralateral attenuation of evoked otoacoustic emissions (EOAE): i.e., the reduction in EOAE amplitude elicited by a 30-dB SL contralateral broadband noise. Correspondingly, the detection thresholds for 1- and 2-kHz tone pips embedded in 50-dB SPL broadband noise were measured in the same ear as the EOAEs, successively in the presence and in the absence of a 30-dB SL broadband noise in the opposite ear. The shifts in detection threshold induced by the contralateral stimulation could thus be compared to those in EOAEs. The results indicated significant statistical correlations between the contralateral attenuation of EOAEs and (1) the detection threshold of the 2-kHz signal and (2) the contralaterally induced shift in the 1- and 2-kHz thresholds. Furthermore, the correlation between contralaterally induced reduction of EOAE amplitude and contralaterally induced threshold shift was observed only in the group of subjects who had first performed the detection task in the presence of contralateral stimulation. These results, which suggest that OCB is involved in detection of tones in noise in humans, are discussed in relation to previous physiological and behavioral studies of OCB function.

Simple loudness adaptation and crossed olivocochlear feedback were investigated--through the Tone Decay Test (TDT) and Transiently Evoked Otoacoustic Emission (TEOAE) recording, respectively--in a sample of normal-hearing subjects including both musicians and non-musicians. The results for musicians and non-musicians differed statistically: the musicians showed on average less loudness adaptation and a greater reduction in TEOAE amplitude under contralateral acoustic stimulation, suggesting a stronger medial efferent feedback on the auditory periphery in these subjects. This finding, that not only psychoacoustic performance but also the physiological mechanism is different in musicians, strongly suggests that the latter should, like the former, be influenced by auditory "training" such as music studies. This perspective is discussed in detail in the text, since it raises puzzling questions and outlined promising issues in the field of auditory psychophysiology.

We investigated the effect of body temperature on transient evoked otoacoustic emissions (TEOAEs) in humans. Hyperthermic conditions were obtained in adults in a climatic chamber. During hyperthermia up to an average temperature of 38.4 degrees C, significant falls were found in total amplitude and peak values of TEOAEs: by 1.3 dB SPL/degree C and 2.3 dB/degree C, respectively. This inhibition affected all spectrum components equally. These findings indicate that the outer hair cell micromechanical activity that is presumed to be measured by TEOAEs is not independent of variations in body temperature. The reduction found in hyperthermia suggests that temperature-dependent mechanisms are involved in the generation of TEOAEs.

In neonates and infants, hearing impairment leads to impaired language and cognitive development. For that reason, early detection of this sensory deficit is of outstanding importance, particularly in pre-term neonates, who constitute a high risk population in regard to very early acquired hearing loss. Evoked (EOAE) and spontaneous otoacoustic emission (SOAE) recording in 93 pre-term and full-term neonates revealed that this technique is potentially useful for auditory screening in neonatology units. EOAEs and SOAEs can be recorded successfully from 30 weeks of conceptional age. SOAEs were found to be prevalent in females and presented higher peak numbers in right than in left ears. Furthermore, SOAE incidence in pre-term and full-term neonates was found to be high in EOAE positive ears, associated with strong and robust EOAEs.

A number of lines of evidence indicate that the human cochlea is fully functional as a mature sound transducer by 6 months of age. However, information about the development of the active cochlear mechanisms and notably the development of outer hair cell (OHC) activity is yet incomplete. Recording and analysis of otoacoustic emissions (OAEs), probably generated by the OHCs of the organ of Corti, have led to a better understanding, in humans, of how sounds are analysed in the cochlea by means of active mechanisms. Evoked OAEs (EOAEs) and spontaneous OAEs (SOAEs), when they can be recorded in full-term and preterm neonates, show different characteristics from those in adults, suggesting that maturation of the peripheral auditory system is incomplete at birth. To learn more about this maturation, using the best-established facts concerning SOAEs in adults, such as their greater prevalence in females and also in right ears, SOAEs were studied in more detail in 81 preterm neonates, from 30 to 40 weeks of conceptional age, all presenting bilateral EOAEs according to objective criteria. The first finding of this study was that SOAEs existed and could be recorded as of 30 weeks of conceptional age in humans. Some SOAE characteristics in preterm neonates, such as prevalence, peak number and acoustic frequencies, showed similarity with full-term neonates. Comparison of other criteria between the two populations, such as greater SOAE prevalence in right ears and higher SOAE peak number in females, suggested that these developmental factors emerge around term in humans. Comparison of SOAE characteristics between male and female preterms suggested that male preterms were less advanced in peripheral auditory development than were female preterms.

Although some findings suggest that auditory efferent fibers are involved in perception in noise, their function remains controversial. The contralateral suppression of evoked otoacoustic emissions (EOAEs) has recently provided a means of exploring the medial olivocochlear system (MOCS) in humans. In an experiment based on this paradigm, the present study examined the relationships between variations of both EOAEs and detection-in-noise thresholds, induced in the same subjects by a contralateral 50-dB-SPL broad-band noise masker. EOAEs were recorded in response to a burst of a multitone complex composed of 1, 1.5 and 2-kHz components. The detection thresholds of this 3-component complex were measured at 2 ipsilateral noise levels: 50 and 70 dB SPL. The main finding was a significant correlation between EOAE suppression and threshold variations under contralateral masking. A relationship was also found between the contralateral suppression of EOAEs and threshold variation induced by the increase in ipsilateral noise level. These findings support the notion that the MOCS is involved in the detection of multicomponent stimuli in noise.

The influence of contralateral auditory stimulation on otoacoustic emissions (OAE), spontaneous OAE, evoked OAE and acoustic distortion products, can be summarized as follows: (1) alteration (mainly a decrease) of OAE amplitude; (2) alteration of response spectrum (upward shift frequency of SOAE); (3) alteration of phase; (4) effect dependent on intensity of contralateral stimulation; (5) effect inversely dependent on intensity of ipsilateral stimulation; (6) frequency specificity of the suppressive effect. Involvement of the medial olivocochlear bundle is highly probable but one cannot exclude a double pathway including also the acoustic reflex.

Transiently evoked otoacoustic emissions (TEOAEs) without and with contralateral acoustic stimulation (CAS), as well as distortion product otoacoustic emissions (DPOAEs), were recorded on 60 subjects divided into 2 groups, the first constituted by 38 normally hearing young subjects and the second by 22 subjects aged from 70 to 88 years and with normal hearing levels in view of their age. TEOAEs and DPOAE 'audiograms' were recorded in a third group constituted by 15 subjects with ages ranging from 6 to 57 years and with hearing levels not significantly different from those of the second group for frequencies above 500 Hz. TEOAEs were present in 100% of the subjects in the first group and in 91% in the second group, although with smaller amplitude. The fall in TEOAE amplitude under CAS was smaller in the second group. Concerning DPOAE audiograms, in the first group, a response was found in 71 to 95% of cases for frequencies ranging from 1 to 6.35 kHz, and in 7 to 37% of cases in the second group. Mean amplitudes were significantly lower in the second group for frequencies ranging from 2.83 to 5.04 kHz. group for frequencies ranging from 2.83 to 5.04 kHz. Mean 'thresholds' ranged from 38.55 to 43.57 dB SPL for frequencies ranging from 1 to 6 kHz in the first group and from 50 to 58 dB SPL in the second group. No significant difference was found between the second and third groups concerning the amplitude and spectrum of the TEOAEs and DPOAE audiograms. Thus, age influences TEOAEs, DPOAEs and the effect of CAS on TEOAEs.(ABSTRACT TRUNCATED AT 250 WORDS)

The possible existence of an attention effect on the peripheral auditory system remains a controversial issue. The aim of the present study is to show the possible contribution of otoacoustic emissions towards demonstrating cognitive control of peripheral auditory processes via the auditory efferent fibers. This measurement technique allows investigation of a further part of the peripheral auditory pathways and of whether efferent fibers, presumably involved in cochlear neurosensory activity, could mediate an attention effect by the selection of auditory information.

A young patient with normal pure-tone thresholds in both ears underwent a unilateral vestibular neurotomy in January 1992 to relieve severe vertigo ascribed to Ménière's disease. Evidence is provided that the whole vestibular nerve including the olivocochlear bundle (OCB) was sectioned. Just prior to the surgery, the patient was examined in several psychoacoustic tests involving mainly signal detection and selective attention. Over the next 20 months, he was reexamined in those same tests. The patient's ability to detect expected tones in the quiet (including audiograms) or in noise was the same as before the surgery. The one change was a marked improvement in the detection of unexpected signals in noise, which appears to reflect impaired selective attention. During those 20 months, new tests were also performed on discrimination, loudness, pitch, lateralization, and temporary threshold shift. On these tests, the only differences between the operated and unoperated ears concerned binaural diplacusis and loudness adaptation close to threshold, but these differences may well have been present prior to the surgery. Except with respect to what is probably selective attention, we uncovered no other clear role for the OCB in hearing. This outcome agrees with limited measurements on other patients, with their subjective reports, and with a number of published neurophysiological observations.

According to current theories, auditory selective attention alters the sensory analysis of acoustic inputs only in the central auditory system. Despite numerous attempts, no evidence of attentional selection has been found in the auditory periphery. Measurements of evoked otoacoustic emissions (EOAEs) during a selective dichotic listening task showed that the EOAEs to tones in one ear had larger amplitude when attention was directed to this ear than when attention was directed to the opposite ear. The results indicate that genuine effects of auditory selective attention can be observed at the cochlear receptor.

With the hypothesis that cochlear active mechanisms are the origin of otoacoustic emissions (OAEs) and of the high frequency selectivity exhibited by the ear, psychoacoustical tuning curves (PTCs), transiently evoked otoacoustic emissions (TEOAEs), and spontaneous otoacoustic emissions (SOAEs) have been examined in 50 normal hearing subjects. Using a clinical simplified method, PTCs were successively assessed at three frequencies--1, 2 and 4 kHz--in each subject. The results showed the existence of significant differences in the quality of tuning (Q10dB) of the PTCs between, first, subjects having SOAEs and subjects having no SOAEs (Student's t-test; p < 0.05; df = 35) and, second, subjects having large TEOAEs and subjects having small TEOAEs (Student's t-test; p < 0.05; df = 14). Nevertheless, these significant differences did not appear for all the frequencies studied: the frequency selective relationship between PTCs and OAEs mainly involved the 2 kHz zone. Such results are discussed according to the specificities of the clinical method used for PTC measurement as well as to the spectral characteristics of OAEs.

This study compared the influence of an auditory attention task and of repetitive measures on the peripheral auditory system, using evoked otoacoustic emissions (EOAEs). The experimental task protocol comprised three sessions (pre-control, attention and post-control conditions) with, in each session, six measurements of EOAEs, at intervals of about 60 seconds, while the other ear was receiving two pure tones of 2,500 and 750 Hz, with a probability of appearance of 20% and 80%, respectively. In the contralateral attention condition, the subject had to count the number of the less frequent high pitched sounds. A long duration protocol (20 min for the total experiment) was used in order to examine a possible time-effect on EOAEs. An increase in EOAE amplitude during the second and third sessions, with linear saturation around the last measurements, was observed. While no attention effect could be identified, a time-effect seemed to be present. Possible explanations for the influence of repeated measurements on EOAEs are discussed. Moreover, EOAE amplitudes of subjects presenting spontaneous otoacoustic emissions were compared to those of subjects without SOAEs: significant differences were found, showing the particularity of cochleas emitting SOAEs.

The aim of this study was to investigate the functional development of cochlear active mechanisms and of the medial efferent olivocochlear system. Otoacoustic emissions (evoked and spontaneous) were recorded in 42 preterm neonates (conceptional age ranging form 33 to 39 weeks) and a control group of 20 young normal-hearing adults. Medial olivocochlear system activity was examined by coupling evoked otoacoustic emission recording to a contralateral stimulation. Otoacoustic emission recordings were carried out using the Otodynamic ILO88 software and hardware. The stimuli were unfiltered clicks and the contralateral stimulation was broad band noise of 50 and 70 dBSPL delivered by an Adam generator. The results revealed the presence of EOAEs and SOAEs from at least 33 weeks in humans, suggesting that the functional maturation of the outer hair cells is nearly complete at that age. The study further revealed that the contralateral stimulation had no effect on evoked otoacoustic emissions in preterm neonates. The lack of activity observed in medial olivocochlear system indicated functional immaturity here, at least before full-term birth.

A possible role of the efferent system in the mechanisms of tinnitus generation has been put forward by several authors. A simple method for studying the functioning of this system is to compare the amplitudes of otoemissions with and without mild contralateral stimulation. In a recent communication, Veuillet et al. (1991) reported that, on the side of tinnitus, the efferent system of patients suffering from unilateral tinnitus seems to be less efficient than on the other side. The results presented here correspond to those obtained in the very first tinnitus patients submitted to a research protocol exploring systematically the efferent system. When possible, the effectiveness was tested in two ways: globally, using evoked otoacoustic emissions (EOAEs) and, very precisely in the frequency zone of the tinnitus, using cubic distortion product 2f1-f2. Preliminary results obtained in bilateral and unilateral tinnitus sufferers show that a majority of them exhibits, at least in the proximity of the tinnitus, a lack of effectiveness of the efferent system. In some of them, instead of the suppressive effect, an increasing one was even observed.

The association between contralateral stimulation and otoacoustic emissions makes it possible to study the medial olivocochlear system in humans. Characterization of this functional exploration and clinical applications are discussed.

The influence of hearing loss on the click-evoked otoacoustic emissions (EOAE) were studied in 931 ears. The EOAEs were never found when hearing loss on the best hearing frequency was above 40 dB HL. The presence of EOAEs reflects the hearing threshold at the best hearing frequency, not only at the middle frequencies.

In this paper the effect of sleep on the cochlea is studied by transiently evoked otoacoustic emissions (TEOAEs). Amplitude increases considerably (e.g., 4 dB) and the effect of a contralateral noise on the TEOAEs decreases during the night. These modifications can be related to sleep, although there is no link to electroencephalographic sleep stage. During sleep onset, the effect of contralateral noise disappears: this could correspond to a functional rest of the auditory pathway during that period.

Since 1989, the exploration of the medial efferent system has been possible in human by using a non-invasive technique consisting in the association of the contralateral acoustic stimulation and the evoked otoacoustic emissions (EOAEs). This exploration presents a great interest for fundamental auditory research because it is the sole means of exploring in human these cochlear efferent neurons synapsing at the base of the outer hair cells. The function of this system is still unknown. The interest of such an exploration in clinical research is now becoming obvious such that it would be not only useful but also necessary to establish a precise diagnosis in particular pathologies. The aim of the present paper is to expose basic results obtained on the medial efferent system in normal subjects and above all to present findings for pathological ears, among which figure in particular: retrocochlear pathologies, hyperacousia, noise-induced hearing loss, tinnitus. In addition to the diagnostic interest of the exploration of the medial efferent system, a knowledge of its functioning will probably allow its role in audition to be determined.

The effect of ear canal pressure variation (ECPV) on click evoked otoacoustic emissions (EOAEs) was compared to the suppressive effect observed with contralateral acoustic stimulation (CAS) in 11 healthy subjects. Both total EOAE amplitude and amplitude of 200 Hz frequency bands (22) were analyzed. Our results revealed that the ECPV as the CAS induced a decrease of the total EOAE amplitude; these two factors showed an additive effect when they are conjoint. The study of the EOAE frequency bands showed that the majority of them decreased under CAS and ECPV; however, a few bands are not affected. Moreover, it appeared that amplitude of the EOAE frequency bands were not modified in a similar way between the two factors: indeed some bands around 4.1 kHz did not decrease either by CAS or ECPV. These results suggest that these applied factors exert different actions on EOAEs. Moreover, the lack of a decrease effect for the same bands, both with CAS and ECPV, may explain the vulnerability of some cochlear locations.

The influence of age, sex and of hearing loss on the EOAEs were studied in 140 subjects. The EOAEs were never found when hearing loss on the best hearing frequency was above 40 dB HL and when the threshold of intelligibility was above 45 dB HL. The presence of EOAEs therefore does not only give specific information on the midfrequencies, but also shows a hearing loss below or equal to 40 dB HL on at least one frequency. In addition, there is a relation between the audiometric curve and the spectrum analysis of EOAEs. These seem to be promising results for clinical applications.

The authors report their exploration's test of efferent pathway through the BERA with the wave one's surface... Thirty one subjects have been tested. If we can deduce through this study the interaction of the two cochlea by efferent pathway.

1. Outer hair cells (OHCs) have active micromechanical properties that are thought to be the origin of evoked otoacoustic emissions (EOAEs). In the present study, click-evoked otoacoustic emissions were recorded in humans with or without various contralateral acoustic stimulations. A previous study, concentrating on contralateral stimulation with broadband noise, had shown a decrease of the EOAE amplitude in humans. Results support a role for the efferent system in cochlear mechanics; indeed, medial efferent neurons of the olivocochlear bundle terminate on the OHCs. To obtain a better understanding of the medial efferent system functioning in humans, the present study looked at the contralateral suppressive effect as a function of stimulus parameters. 2. The study of the input-output function of the EOAE amplitude with and without a 50-dB SPL contralateral broadband noise showed that the suppressive effect was equivalent to a mean reduction of 3.77 dB. 3. For the EOAEs to tone pips, the contralateral suppressive effect was strongest when the contralateral ear stimuli were narrow bands that were centered around the central EOAE frequency. This frequency specificity disappeared for contralateral narrow band noise levels greater than 50 dB SPL. 4. The contralateral suppressive effect was also observed with transient contralateral sounds (nonfiltered clicks). Significant reductions of the EOAE amplitude were seen with contralateral click levels as low as 17.5 dB SL. Above this level, the EOAE amplitude decreased as the contralateral stimulus level increased. This effect was still present in subjects without any stapedial reflex, but absent in total unilateral hearing-loss subjects. Therefore this suppressive effect is unlikely to be due to alteration of the middle ear function or to transcranially conducted sound. 5. When the contralateral interclick interval exceeded 14.2 ms. the suppressive effect was smaller. With contralateral stimulus level maintained subjectively constant, the effect was found to disappear when the interclick interval was greater than 49.9 ms. A saturation of the contralateral suppressive effect was observed for click rates greater than 70/s (interclick interval less than 14.2 ms). 6. Our study confirms and specifies the contralateral sound suppression effect on cochlear mechanisms in humans, assessing the equivalent reduction, showing a frequency specificity and extending these findings to contralateral transient sounds. Any influence of the acoustic crosstalk was eliminated. A role played by middle ear muscles cannot be absolutely ruled out but is not necessary to produce such a contralateral suppressive effect (the effect being found in subjects after surgical removal of the stapedius muscle) and could not explain the frequency specificity.(ABSTRACT TRUNCATED AT 400 WORDS)

Evoked otoacoustic emissions (EOAE) and sound evoked olivocochlear feedback were performed in 200 subjects (noise induced hearing loss (NIHL), n = 109; sensori-neural hearing loss (SNHL), n = 91). Intensity of EOAE is greater in NIHL than in SNHL. This result does not seem to be related to the medial olivocochlear system since sound olivocochlear feedback was not significantly different between the two groups. No correlations were seen between temporary threshold shifts (TTS) and sound-olivocochlear feedback in the NIHL group.