Guidelines of the French Society of Otorhinolaryngology-Head and Neck Surgery (SFORL) and the French Society of Audiology (SFA) for Speech-in-Noise Testing in Adults

OBJECTIVES

This document presents the fundamentals of speech audiometry in noise, general requirements for implementation and criteria for choice among the tests available in French according to the health-professional's needs.

MATERIAL AND METHODS

The recommendations are based on a systematic analysis of the literature carried out by a multidisciplinary group of doctors, audiologists and audioprosthetists from all over France. They are graded A, B, C or expert opinion according to decreasing level of scientific evidence.

RESULTS

Eight tests of speech audiometry in noise can be used in France.

CONCLUSION

To be complete, evaluation of hearing status requires testing understanding of speech in noise. The examination must begin with a minimum of two measurements familiarizing the subject with the test procedure. For initial diagnosis, adaptive procedures establishing the 50% speech reception threshold (SRT50) in noise are to be preferred in order to obtain a rapid and standardized measurement of perception of speech in noise. When the aim is to measure real-life speech comprehension, tests based on sentences, cocktail-party noise and free-field stimulation are to be preferred. Prosthetic gain is evaluated exclusively in free field. This is the only way to evaluate the contribution of binaurality and to measure perception in noise in an environment as close as possible to real life. In order to avoid acoustic interference in free field, at least five loudspeakers should be used, in particular for evaluating the effectiveness of directional microphones, CROS devices enabling sounds picked up in the damaged ear to be rerouted to the functional ear, or bimodal fitting (i.e., when hearing is enabled by two modalities: for example, hearing aid for one ear, cochlear implant for the other).

A new genetic variant causing auditory neuropathy: A CARE case report

INTRODUCTION

Auditory neuropathy refers to impaired synchronization of the auditory signal along the cochlear nerve. The present study, following CARE case report guidelines, describes a case of auditory neuropathy secondary to a genetic variant not previously described.

OBSERVATION

An 18-year-old patient was followed for multiple learning disorder. His main complaint was speech comprehension, especially in noise. Auditory neuropathy was diagnosed on electrophysiological criteria, linked to a 2.66Mb deletion on the short arm of chromosome 16, at 16p13.11p12.3 (15,492,317-18,162,167, according to the hg19 version of the human reference genome). Adapted speech therapy sessions with auditory training for intelligibility in noise and a hearing aid with high-frequency microphone were prescribed. At 6months, the patient reported improvement in understanding speech in noise.

CONCLUSION

The involvement of this 16p13.11 deletion in the patient's symptomatology was not obvious, in a probable context of incomplete penetrance and variable expression. Early diagnosis of auditory neuropathy allowed implementation of better adapted multidisciplinary specialized management.

Contribution of bone conduction click-evoked auditory brainstem responses to diagnosis of hearing loss in infants in France

INTRODUCTION

Neonatal hearing screening in France involves confirmation by a childhood hearing expert centre in case of suspected hearing loss. Although click-evoked air-conduction auditory brainstem responses (AC-ABR) are the gold standard in France, there are no guidelines for bone-conduction ABRs (BC-ABR). The present study assessed the interest of associating click-evoked BC- and AC-ABRs for diagnostic confirmation in neonatal hearing screening.

MATERIALS AND METHODS

A retrospective study included 59 infant ears with conductive hearing loss referred to the centre of Lyon, France. Objective hearing thresholds were compared between click-evoked BC- and AC-ABRs on a method previously validated in a normal-hearing population.

RESULTS

There was a significant difference in mean threshold between AC-ABR (53.27±1.189 dBnHL) and BC-ABR (28.1±0.935 dBnHL) (P<0.001). AC thresholds ranged from 40 to 60 dBnHL while BC thresholds exceeded 40 dBnHL in only 9 ears.

CONCLUSION

Using BC-ABRs could reduce the false-positive rate in neonatal bilateral permanent hearing loss screening, in complement to AC-ABRs using the same stimulus. Click-evoked BC-ABR could be contributive whenever conductive hearing loss is suspected, in complement to AC-ABR, without unreasonably increasing examination time.

The temporal relationship between speech auditory brainstem responses and the acoustic pattern of the phoneme /ba/ in normal-hearing adults

OBJECTIVE

To investigate the temporal relationship between speech auditory brainstem responses and acoustic pattern of the phoneme /ba/.

METHODS

Speech elicited auditory brainstem responses (Speech ABR) to /ba/ were recorded in 23 normal-hearing subjects. Effect of stimulus intensity was assessed on Speech ABR components latencies in 11 subjects. The effect of different transducers on electromagnetic leakage was also measured.

RESULTS

Speech ABR showed a reproducible onset response (OR) 6ms after stimulus onset. The frequency following response (FFR) waveform mimicked the 500Hz low pass filtered temporal waveform of phoneme /ba/ with a latency shift of 14.6ms. In addition, the OR and FFR latencies decreased with increasing stimulus intensity, with a greater rate for FFR (-1.4ms/10dB) than for OR (-0.6ms/10dB).

CONCLUSIONS

A close relationship was found between the pattern of the acoustic stimulus and the FFR temporal structure. Furthermore, differences in latency behaviour suggest different generation mechanisms for FFR and OR.

SIGNIFICANCE

The results provided further insight into the temporal encoding of basic speech stimulus at the brainstem level in humans.

Cochlear implantation in 3 adults with auditory neuropathy/auditory dys-synchrony

We describe 3 adult patients with auditory neuropathy/auditory dys-synchrony (AN/AD) who underwent cochlear implantation. All patients had absent or poorly formed auditory brainstem responses (ABRs) in combination with preserved otoacoustic emissions (OAEs). They exhibited various aetiologies and a large variation in clinical features known to be consistent with AN/AD. Cochlear implantation was successful in 2 out of 3 cases. We conclude that AN/AD implantee candidates should be counselled with care.

Rehabilitation plasticity: influence of hearing aid fitting on frequency discrimination performance near the hearing-loss cut-off

Several studies have already demonstrated that patients with steeply sloping hearing loss of cochlear origin exhibit an improvement in frequency discrimination performance at or around the cut-off frequency. This enhancement cannot be explained in terms of peripheral mechanisms and should rather be interpreted in terms of central reorganization: i.e., injury-induced cortical plasticity. However, the reversibility and time course of such reorganization has not yet been described. The main goal of the present study was therefore to investigate the occurrence of rehabilitation plasticity associated with hearing-aid fitting in human subjects. Nine subjects with steeply sloping hearing loss and who were candidates for auditory rehabilitation were tested. Discrimination-limen-for-frequency (DLF) enhancement was investigated at the frequency with the best DLF (bDLF) for each individual subject before and during auditory rehabilitation (at 1 month, 3 months and 6 months). From 1 month on, frequency discrimination performance decreased significantly at the bDLF frequency, while remaining stable at other frequencies. This normalization may reflect a new central reorganization reversing the initial injury-induced changes in the cortical map. A correlation between subject's age and alteration in DLF at 1 month was also found, suggesting that plasticity operates faster in younger patients.

Simple reaction times in subjects with steeply sloping hearing loss: Is there an alteration at the edge of the loss?

The aim of the present study was to investigate the simple reaction time (RT) performance of patients with steeply sloping sensorineural hearing loss. This kind of hearing loss has the particularity of inducing a reorganization of the primary auditory cortex (Dietrich et al, 2001), the edge frequency of the loss being over-represented. It is assumed that a consequence of this plasticity could be reflected in an improvement in frequency discrimination performances around the edge of the loss (McDermott et al, 1998). In the present study we used pure tones equalized in loudness to investigate whether RT might be altered at the cut-off frequency (Fc) of the loss, or at the frequency that presented the best discrimination-limen-for-frequency (bDLF). The effect of auditory rehabilitation on RT was also studied. A great variability in RT was noted in all our subjects. Our results demonstrated that RT was unmodified at Fc or bDLF, be it before or after hearing aid fitting. However, an improvement in the correlation between RT and frequency discrimination performance was observed at three months post-rehabilitation.

Lateralization of the effects of the benzodiazepine drug oxazepam on medial olivocochlear system activity in humans

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.

The auditory acclimatization effect in sensorineural hearing-impaired listeners: Evidence for functional plasticity

The present study provides new data on perceptual and physiological modifications associated with hearing aid (HA) fitting. Eight sensorineural hearing-impaired (SNHI) listeners participated. They had symmetrical hearing loss and were being fitted with binaural HAs for the first time. Perceptual performances were measured four times during auditory rehabilitation, using an intensity discrimination task and a loudness-scaling task. Pure tones of two different frequencies were used, one well amplified by HAs and the other weakly amplified. Two intensity levels were also tested, one rated 'soft' by SNHI listeners and the other 'loud'. Auditory brainstem responses (ABRs) to click stimulation were recorded. All measures were performed without HA. Results were consistent with the auditory acclimatization effect: most modifications induced by HA fitting were found at loud intensity levels and at high frequency, i.e., for acoustic information that was newly available to the listener. While both ears had similar hearing loss and aided gains, some differences between ears appeared in both perceptual tasks and in ABRs. In the right ear, a shortening of wave V latency paralleled perceptual modifications. The present results suggest that HA-fitting induces functional plasticity at the peripheral level of the auditory system.

Effect of stimulus frequency and stimulation site on the N1m response of the human auditory cortex

The aim of the present study was to investigate the functional organization of the auditory cortex for pure tones of 1, 2, 4, 6, 8 and 12 kHz. Ten subjects were tested with a whole-head magnetometer (151 channels). The location, latency and amplitude of the generators of the N1m (the main component of the response, peaking approximately at 100 ms) were explored simultaneously in the right and left hemispheres under monaural stimulation. Our results revealed that tonotopy is a rather complex functional organization of the auditory cortex. From 1 to 12 kHz, tonotopic maps were found for contralateral as well as for ipsilateral stimulation: N1m generators were found to be tonotopically organized mainly in an anterior-posterior direction in both hemispheres, whatever the stimulated ear, but also in an inferior-superior direction in the right hemisphere. Furthermore, latencies were longer in the left than in the right hemisphere. Two different representations of spectral distribution were found in the right auditory cortex: one for ipsilateral and one for contralateral stimulation.

Influence of benzodiazepines on auditory perception

The aim of this study was to test for an influence of benzodiazepine (BZD) on various perceptual and/or cognitive auditory processes. Loudness, auditory selective attention, and the ability of subjects to form perceptual streams out of alternating tone sequences were tested. Nine subjects were tested before, 1, 3, 7, and 24 h after a single-dose oxazepam vs placebo administration in a crossover design. A sample of blood allows us to measure plasma oxazepam concentration. The results revealed a significant reduction in stream segregation expressed as d' scores 1 h after oxazepam intake in the test subjects. No significant change occurred across time in the same subjects when they were administrated a placebo in another session. Furthermore, oxazepam had no substantial and systematic influence either on auditory selective attention or on loudness perception. Altogether, these results suggest that the perceptual organization of sound sequences involves inhibitory neural mechanisms, which can be affected by BZDs. This outcome is consistent with existing models of auditory stream segregation and may be paralleled with earlier findings on the effect of BZDs on perceptual binding in the visual modality.

Auditory rehabilitation effects on speech lateralization in hearing-impaired listeners

OBJECTIVE

Previous studies reported that the consequences of auditory rehabilitation were lateralized, with the right ear (RE) showing more improvement than the left ear (LE) over the time course of hearing aid (HA) use in elderly patients with symmetrical presbyacusis. It has been suggested that this asymmetry is linked to a change in speech lateralization. The aim of this study was to explore the consequences of HA use on interaural asymmetry in symmetrical sensorineural hearing impairment patients before and 4 months after binaural HA fitting.

MATERIAL AND METHODS

Two types of perceptual task were chosen in order to measure speech lateralization: two dichotic listening tasks; and an identification task for a voice onset time continuum. Seven elderly, right-handed patients suffering from symmetrical presbyacusis were selected and tested before HA fitting and 4 months after. All measurements were made without the use of the HA, and the listeners were all first-time HA wearers.

RESULTS

Dichotic listening scores for words improved significantly over the course of HA use. Moreover, the dichotic listening task for syllables revealed an increase in auditory asymmetry after 4 months of HA use. Concerning the identification task, a significant difference between ears was found, with only the R E showing significant improvement with HA use.

CONCLUSION

These results suggest that auditory rehabilitation is lateralized, with greater change as a result of HA use occurring in the RE than the LE in right-handed patients.

Medial olivocochlear bundle activation and perceived auditory intensity in humans

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.

Psychometric normalization of a hyperacusis questionnaire

Clinical hyperacusis consists of a marked intolerance to ordinary environmental sounds, while hearing thresholds are quite often normal. Hyperacusis appears to be a subjective phenomenon, which is not easily defined or quantified by objective measurements. In order to create a tool suitable to quantify and evaluate various hyperacusis symptoms, a questionnaire screening several aspects of auditory symptomatology has been constructed. Two hundred and one subjects (who were either hyperacusic or not), randomly selected from the general population, were tested. A principal component analysis performed on the correlation matrix of the 14 items of the questionnaire isolated three dimensions: attentional, social, and emotional. The three dimensions had satisfactory internal consistency reliability. The mean +/- SD total score was 15 +/- 6.7 out of 42 (maximum of hyperacusis) and a score greater than 28 seems to represent a strong auditory hypersensitivity. This new psychometric tool should further be tested on hyperacusic patients to verify its relevance in pathology and define the involvement of the three dimensions statistically obtained on the hyperacusis symptomatology.

Intensity-related performances are modified by long-term hearing aid use: a functional plasticity?

It is now well established that the adult central nervous system can reorganize following various environmental changes. In particular, it has been hypothesized that auditory rehabilitation of sensorineural hearing-impaired adults may involve functional plasticity. The present study sought to compare intensity-related performance between two groups of subjects paired for age, gender and absolute thresholds in both ears. One group comprised long-term binaural hearing aid (HA) users and the other non-HA users. The effect of HA use was measured in two intensity tasks, a discrimination-limen-for-intensity task (DLI) and a loudness-scaling task. Results indicated that significant differences exist in loudness perception between long-term HA users and non-HA users, the latter rating intensity as louder than the former. Concerning intensity discrimination performance, a statistical tendency to lower, i.e. better, DLIs in long-term than in non-HA users was revealed. Moreover, significant differences between ears were observed in the loudness-scaling task, with the right ear showing greater inter-group difference than the left ear. This additional result points to a lateralization of the acclimatization effect. Finally, this study suggests significant perceptual modification and thus a possible functional plasticity entailed by HA use.

Evidence of peripheral auditory activity modulation by the auditory cortex in humans

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.

Relationship between NRT measurements and behavioral levels in children with the Nucleus 24 cochlear implant may change over time: preliminary report

OBJECTIVE

Response from spiral ganglion cells to electrical stimulation via the Nucleus 24 cochlear implant can be measured using the neural response telemetry system. The purpose of this study was to assess, in children, the correlation between the neural response threshold and the behavioral levels used for cochlear implant programming process.

METHODS

The neural response telemetry test was administered to 23 children (mean age at implantation: 4 years) with the Nucleus 24 cochlear implant. Four intra-cochlear electrodes (electrodes 5, 10, 15 and 20) were tested. The neural response threshold at 3, 6, 9 and 12 months post-implantation was compared with the behavioral threshold and the maximum comfort level estimated during the same periods: a Pearson's correlation test was performed for each tested electrode.

RESULTS

On apical electrodes, the correlation with the behavioral threshold remained significant from 3 to 12 months post-implantation (r ranging from 0.696 to 0.909, P<0.05), and the correlation with the maximum comfort level was also significant throughout the study period, except on electrode 15 at 9 months (tendency to significance). On basal and intermediate electrodes, statistical correlations were found only at some points of time; nonetheless, at 12 months post-implantation, a significant correlation with behavioral levels could be clearly demonstrated both on electrode 15 (r=0.914--0.778, P<0.05) and on electrode 10 (r=0.845--0.720, P<0.05).

CONCLUSIONS

This preliminary study suggests that the correlation between the neural response threshold and behavioral levels may improve from the base towards the apex of the cochlea. However, a significant correlation can be demonstrated for all tested electrodes at 12 months post-implantation. During the first months post-implantation care must be exercised when interpreting neural response telemetry measurements: a positive test does not necessarily mean that the stimulus delivered to the acoustic nerve will be centrally processed with the result of an auditory perception.

Peripheral auditory asymmetry in infantile autism

Difficulty in filtering relevant auditory information in background noise is one of the features of autism. Auditory filtering processes can be investigated at the peripheral level as they are hypothesized to involve active cochlear mechanisms which are regulated by the efferent activity of the medial olivocochlear (MOC) system. The aim of the present work was therefore to assess these peripheral auditory processes in 22 children and adolescents with autism compared with age- and gender-matched normal controls. Active cochlear mechanisms were evaluated with transiently evoked otoacoustic emissions (TEOAEs) and MOC system efficiency was assessed via TEOAEs which are decreased when stimulating the contralateral ear with noise. The MOC system evaluation was performed on 18 of the 22 children. In both studies, results were analysed according to age (from 4 to 10 years and from 11 to 20 years). The main result concerns the asymmetry of the efferent system which differs in individuals with autism. Several neural processes might be hypothesized as involved in the results obtained as the MOC system which originates in the brainstem received regulating controls from upper brain structures including auditory cortex. Lateralization abnormalities at the auditory periphery may reflect indirectly a problem at a higher level of auditory processing. A second important result shows a decrease in TEOAE amplitude with age, in patients, that may correspond to a decrease in hearing sensitivity.

Asymmetrical localization of benzodiazepine receptors in the human auditory cortex

In humans, administration of benzodiazepines (BZD) has been shown to have an asymmetrical effect on the medial olivocochlear system. Indeed, a decrease of evoked otoacoustic emission suppression by contralateral acoustic stimulation, which explores the medial olivocochlear efferent system, was observed in the right ear, with no left ear effect. This result suggests a possible left-right auditory pathway BZD receptor asymmetry. Given the anatomical link between auditory centers and the medial olivocochlear system, the existence of a larger volume of cortical connecting fibers in the left hemisphere, and the possible link between BZD receptor density and neuronal density, we tested the hypothesis of an asymmetrical localization of BZD receptors in the auditory system in 10 right-handed subjects using [11C]flumazenil positron emission tomography. Semi-quantitative measurements of flumazenil binding were evaluated in Heschl's gyrus showing a left-right asymmetry in favor of left auditory cortex. This result indicates a higher density of neurons in left auditory cortex. The possible link between neurochemical asymmetry and functional asymmetry, and the perceptual outcome of BZD administration, will be discussed.

Otoacoustic emissions and medial olivocochlear suppression during auditory recovery from acoustic trauma in humans

It is well known that the large inter-individual susceptibility to noise exposure makes it impossible to predict the degree of hearing loss which will develop after any given intense noise exposure. The acoustic trauma which sometimes occurs affects cochlear mechanisms, the damage being most probably due to deactivation of the active processes of the outer hair cells (OHCs), which receive direct efferent innervation. The present report is of a follow-up study involving young military personnel recovering auditively from impulse noise exposure, and seeks to assess changes in cochlear status by means of otoacoustic emissions (OAEs) and their modulation by the medial olivocochlear (MOC) system. The study investigated the relationship between recovery of cochlear function and variables that could serve as predictors of vulnerability to noise-induced hearing loss (NIHL). Thirty-six subjects with unilateral NHIL above 4 kHz were included. Normal and affected ears were compared with respect to click-evoked and spontaneous OAEs (CEOAEs and SOAEs, respectively) and for contralateral CEOAE suppression. Measurements were obtained: (i) just after the traumatic exposure (D0); (ii) 3 days after this first measurement (D3); and (iii) 30 days after (D30). Significant improvement in the 4, 6 and 8 kHz thresholds was observed for the affected ear, with large inter-subject variability. No significant change was observed in CEOAE amplitude or MOC suppression, whereas incidence of SOAE was found to increase in the affected ear, leading to higher SOAE prevalence on this side I month after the intense noise exposure. There was no significant correlation between NIHL at 4, 6 and 8 kHz and MOC functioning on D0, but significant correlations were obtained between audiometric threshold improvement by D3 and contralateral CEOAE suppression, with better recovery in subjects with greater MOC suppressive action. The MOC system could be an underlying mechanism in post-traumatic auditory threshold recovery.

Abnormal peripheral auditory asymmetry in schizophrenia

OBJECTIVE

Auditory processing difficulties have been reported in schizophrenia. This study explores peripheral auditory function in patients with schizophrenia in whom certain early disturbances of auditory message filtering have been found and may be associated with certain abnormalities which are particularly localised in the left temporal lobe.

METHODS

Otoacoustic emissions, including click evoked and spontaneous emissions and measurements of functioning of the medial olivocochlear efferent system were obtained from 12 chronic schizophrenic patients and compared with normative data recorded from 12 normal controls.

RESULTS

Otoacoustic emission amplitudes and medial olivocochlear functioning were similar between the normal controls and schizophrenic patients; the schizophrenic patients did, however, differ from the normal controls in otoacoustic emission intensity and in medial olivocochlear asymmetry. A tendency to a higher number of spontaneous peaks, and a significantly higher click evoked otoacoustic emission response amplitude were found in the right ear compared with the left ear of schizophrenic patients. For the medial olivocochlear system, whereas normal controls showed greater attenuation in the right than in the left ear, schizophrenic patients lacked such an asymmetry.

CONCLUSION

In the absence of any attention task, the findings show disturbed peripheral lateralisation in schizophrenia of mechanisms involved in auditory information filtering. Such a lack of right ear advantage in medial olivocochlear functioning may thus be a peripheral reflection of central lateralisation anomalies.

Clinical relevance of medial efferent auditory pathways

Evoked otoacoustic emissions have been shown to be suppressed by sounds applied in the contralateral ear and this effect can be largely explained by the involvement of medial olivocochlear efferent fibers. Thus, EOAE recording during contralateral stimulation provides a non-invasive means of investigating auditory efferent system functioning in humans. The question remains, however, as to whether this test provides a tool, which could be useful in a variety of clinical applications. This review describes current clinical applications for this test, showing that it may prove useful for improving identification of retrocochlear pathologies. Some new areas are also identified. Methodological topics are discussed and suggestions for maximizing the value of this test are proposed.

Frequency and temporal analysis of contralateral acoustic stimulation on evoked otoacoustic emissions in humans

Previous studies have shown that the effect of contralateral acoustic stimulation (CAS) on ipsilateral evoked otoacoustic emissions (EOAE) depends somewhat upon the spectrum of the eliciting stimulus. The latency of the EOAE, however, is itself frequency-dependent. Consequently, two general ways of analyzing the effects of CAS may be considered: by frequency band or by temporal segment. In this study, we analyzed the effects of CAS both ways in the same subjects, essentially simultaneously. The frequency analysis of the EOAE derived from the wavelet transform (WT). The WT is known to provide a robust approach to the analysis of non-stationary signals and was anticipated to avoid possible time-frequency confounds of the cochlear mechanical system. For comparison, a more basic analysis - using a temporal moving window - was employed. The results largely support earlier findings and confirm that in humans the greatest suppression of EOAEs by CAS is obtained for lower frequency and/or longer latency EOAE components. Despite expectations for the WT analysis, the more basic, temporal, analysis tended to yield the clearer results.

Tones disappear faster in the right ear than in the left

In order to gain further information on the characteristics and physiological correlates of tone decay in humans, the tone decay test was administered to 58 normal-hearing subjects, successively in the left and right ears and in absence and presence of a contralateral noise. The results revealed that tone decay was greater in the right than in the left ear and was increased by contralateral noise. The contralateral effect of this noise on cochlear biomechanisms was then estimated by measuring contralaterally induced variations in the amplitude of click-evoked otoacoustic emissions in the same subjects. In the right ear, the increase in tone decay and the decrease in otoacoustic emission amplitude--both induced by contralateral noise--were positively correlated (r = .315, p = .016). Furthermore, the contralateral changes in otoacoustic emission amplitude were found to be on average larger in the right than in the left ear, this asymmetry being correlated with that observed for the tone decay. These findings are discussed in relation to previous results on simple and induced loudness adaptation in the vicinity of threshold, on contralateral attenuation of otoacoustic emissions and on the influence of the auditory efferents on cochlear biomechanisms.

Functional asymmetries of crossed and uncrossed medial olivocochlear efferent pathways in humans

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.

Influence of handedness on peripheral auditory asymmetry

It is well established that in humans many differences between right- and left-handers, anatomical, physiological and functional, exist. Left- and mixed-handedness is associated with greater bihemispheric representation of cognitive functions than in right-handers. Several studies indicate a left-right asymmetry in the function of hearing pathways between cochlea and auditory cortex, and furthermore, that this asymmetry is associated with handedness. Our investigation focuses on the medial olivo-cochlear system, which has been demonstrated to be more effective in the right than left ear in right-handers. The aim of the study was to investigate this auditory efferent system asymmetry according to handedness, gender, eyedness, footedness and the presence of spontaneous otoacoustic emissions. The medial efferent system has been found to be more effective in the right than left ear in right-handers, while functioning symmetrically in left-handers. Furthermore, the olivo-cochlear system, assumed to be involved in basic language processing, shows an asymmetrical pattern of functioning influenced by handedness as well as by hemispheric language representation. Reverse medial efferent system asymmetry was observed in left-handers compared to that in right-handers, on condition that only left-handed males were considered, or that the left-handers were also left-eyed, or that spontaneous otoacoustic emissions were present in the left ear of the left-handers, or when only left-handers without mixed-handers were considered.

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.

Benzodiazepines alter cochleo-cochlear loop in humans

By using otoacoustic emission, we looked for change in outer hair cell (OHC) motile activity and medial olivocochlear (MOC) system inhibition due to benzodiazepine administration, a drug that is known to produce a pharmacological effect by interacting with GABAergic inhibitory neurotransmission. No effect was observed on OHC motile activity, in contrast benzodiazepines decreased MOC system effectiveness suggesting the existence of GABAergic fibers projecting onto the MOC system.

[Peripheral auditory lateralization]

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.

Effects of hypothermia on cochlear micromechanical properties in humans

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.

Effect of contralateral acoustic stimulation on the growth of click-evoked otoacoustic emissions in humans

Input-output (I/O) functions of click-evoked otoacoustic emissions (CEOAEs) were obtained over a 12 dB range for 64 normally hearing adult listeners with and without contralateral broadband noise (BBN). Contralateral acoustic stimulation (CAS) is a convenient way of suppressing responses to ipsilateral stimuli, probably acting via the medial olivocochlear system (MOCS). The present study shows that this contralateral sound suppression of CEOAEs is largest at low stimulus levels. In fact, the curves obtained under CAS approach the curves obtained without CAS as stimulus level rises. I/O slope analysis for the whole study population (n = 64) showed a slight but significant rise in slope with BBN, which may be interpreted as I/O function decompression. A loss of contralateral suppression effect at high ipsilateral stimulus levels was found in both very low and very high amplitude CEOAE subjects, despite the fact that I/O slopes differed between these two groups, whereas rise in slope under contralateral stimulation failed to be found for these same 2 groups of 16 subjects each. These findings clearly indicate that the MOCS is mostly functional at low sound levels, and suggest that the study of CEOAE I/O slope alteration under CAS may help specify one form of MOCS action on cochlear functioning.

Contralateral auditory stimulation and otoacoustic emissions: a review of basic data in humans

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.

Influence of aging on active cochlear micromechanical properties and on the medial olivocochlear system in humans

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)

Characteristics of transient otoacoustic emissions in patients with sudden idiopathic hearing loss

In a prospective study of 24 patients hospitalized with sudden idiopathic hearing loss syndrome (SIHLS), tonal audiometry was conducted first at an early stage after onset (Day O), again a second time (Day A, mean = 4.12 days), and again a third time (Day B, mean = 8.71 days). Transient evoked otoacoustic emissions (TEOAE) were recorded on Days O and A elicited by click stimulation. The question under investigation was whether TEOAE presence, TEOAE amplitude or peak amplitudes for the various 200-Hz-wide bands on Day O could be exploited to assess cochlear function, as indicated by pure-tone audiometry on Days A and B. The TEOAE amplitude on Day O was found to be correlated with improvement in tone threshold on Day B at 2 kHz. One significant correlation emerged between the band amplitude on Day O and the audiometric frequency improvement: on Day B between peak amplitude at 1.2 kHz and 1 kHz frequency improvement. From these results, TEOAE could theoretically be a means to assess cochlear functioning during SIHLS for 1 and 2 kHz frequencies. However, correlations are too weak to form the basis of any predictive test that could be clinically useful.

Evoked and spontaneous otoacoustic emissions. A comparison of neonates and adults

Evoked otoacoustic emissions (EOAEs) and spontaneous otoacoustic emissions (SOAEs) were compared between neonates and adults. Several differences were seen for EOAEs: (i) the occurrence of EOAEs was significantly greater in adults than in neonates, and in neonates it increased with extra-uterine age; (ii) the high frequency EOAE intensity was greater in neonates than in adults; (iii) the EOAE intensity was significantly greater in neonates than in adults. No age-related differences for SOAEs were found: (i) age was not significantly related to the presence/absence of SOAEs in neonates or adults; (ii) the occurrence of SOAEs was, however, significantly greater in females than in males in both neonates and adults.

Click-evoked otoacoustic emissions and hearing threshold in sensorineural hearing loss

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.

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

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

[Study of the ototoxicity of amikacin and netilmicin using provoked acoustic oto-emissions and high-frequency audiometry]

To compare the ototoxicity of amikacin and netilmicin, tone audiometry, high-frequency audiometry, early auditory evoked potentials, and evoked otoacoustic emission testing were used to evaluate 30 patients (15 under amikacin and 15 under netilmicin). Ototoxicity was not significantly different in the two groups.

Differential effects of ear-canal pressure and contralateral acoustic stimulation on evoked otoacoustic emissions in humans

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.

Effects of contralateral white noise on click-evoked emissions in normal and sensorineural ears: towards an exploration of the medial olivocochlear system

The association between contralateral stimulation and evoked otoacoustic emissions (EOAEs) allows study of sound-evoked olivocochlear feedback and then of the medial olivocochlear system. A method allowing quantification of sound-evoked olivocochlear feedback is proposed. The feedback is present in almost all normal-hearing subjects, but with great interindividual variability. In sensorineural hearing loss, the feedback is present in 20 out of 21 subjects. One paradoxical clinical case is described with a unilateral increase of EOAE intensity during contralateral stimulation.

Evoked otoacoustic emissions: relative importance of age, sex and sensorineural hearing-loss using a mathematical model of the audiogram

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.

Effect of contralateral acoustic stimulation on active cochlear micromechanical properties in human subjects: dependence on stimulus variables

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)

Noise and medial olivocochlear system in humans

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.

Evoked otoacoustic emissions: correlates between spectrum analysis and audiogram

Correlations between spectrum analysis of evoked otoacoustic emissions (EOAEs) and hearing losses have been calculated in 150 patients with pure sensorineural hearing loss. Significant correlations were found. The greater the high-frequency spectral components of the EOAE, the better the high-frequency hearing. However the relationship is complex, and it does not seem possible to establish an audiogram knowing only the spectrum analysis of EOAEs.

Effect of contralateral auditory stimuli on active cochlear micro-mechanical properties in human subjects

The present study investigates the possibility that contralateral auditory stimulation along medial efferent system pathways may alter active cochlear micromechanics and hence affect evoked oto-acoustic emissions in humans. A first experiment, involving 21 healthy subjects showed reduction of oto-acoustic emission amplitude under low intensity contralateral white noise (from 30 dB SPL, 10 dB SL, upwards). The effect is found for intensities below the acoustic reflex threshold (85.2 dB HL). A second experiment, involving 10 of the above 21 subjects, sought to rule out any technical artefact. Recording was again carried out, but after sealing of the contralateral ear with a silicon putty plug. No contralateral intensity effect on oto-acoustic emission amplitude was found for contralateral intensities below 65 dB SPL. In subjective perception terms (dB SL) an effect was found under sealing when the sound reached or passed above the 10 dB SL level. These two findings confirm the preceding experiment. The third experiment investigated the role of transcranial transmission of the contralateral auditory stimulus. 16 subjects having total unilateral deafness and one healthy ear were tested by the same procedure as above. No fall-off in oto-acoustic emission amplitude was found for contralateral stimuli equal to or less than 80 dB SPL. There is thus a contralateral auditory stimulus effect on active cochlear micromechanics. The most appropriate explanation involves the medial cochlear efferent system, excited at brainstem level via the afferent auditory pathways. Alteration of active cochlear micromechanics seems promising at a basic level, pointing, as it does, to an interactive cochlear functioning which can be investigated by simple, non-intrusive, objective techniques which can be used with human subjects. We have here a model for functional exploration of the medial olivocochlear efferent system.

A simple electromagnetic mechanical stimulator for electrophysiological recording in man

In order to study peripheral nervous signals in response to a noxious or innocuous mechanical cutaneous stimulus we deviced an electromechanical stimulator of which stimulus duration, response frequency and delay are perfectly controlled. Using this device, stimulation of the finger has allowed us to record electrophysiological responses over the course of the median nerve.