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L Collet

Publications and source records attributed to L Collet.

At least 37 records · Page 2Linked to original sources
PubMed1999

Loudness growth functions and EABR characteristics in Digisonic cochlear implantees.

Electrically evoked auditory brainstem responses (EABRs) and loudness functions were measured in 14 subjects equipped with an MXM Digisonic cochlear implant. EABRs were evoked by 75-Hz pulse trains presented on the apical electrode. Loudness functions at the same rate and at a rate more conventional for psychoacoustic measurements (300 Hz) were measured using a categorical loudness-scaling procedure. The results revealed a significant difference in the loudness functions measured at 75 and 300 Hz, loudness increasing more steeply with stimulus intensity for the latter rate. Significant correlations between EABR wave V thresholds and perceptual thresholds measured at both 75 and 300 Hz were observed. Furthermore, in 8 out of the 14 patients, EABR wave V saturated at a stimulus level corresponding precisely to the loudest bearable, i.e. "Too loud" level for the 300-Hz stimulation rate; this same level corresponded to the "Comfortable" loudness level for the 75-Hz stimulation rate. On average, an almost linear relationship was observed over the first half of the loudness range between the stimulus intensity, expressed as a pulse duration in log units, and wave V amplitude in dB. Although further investigation is required before maximum comfort levels can be predicted reliably from EABR measures in individual subjects, these results indicate new directions regarding the estimation of perceptual dynamic range limits on the basis of EABR measures in cochlear implantees.

Adult↗
PubMed1999

Contralateral suppression of transiently evoked otoacoustic emissions by harmonic complex tones in humans.

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.

Acoustic Stimulation↗
PubMed1999

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.

Adult↗
PubMed1999

The medial olivocochlear efferent system in humans: structure and function.

The mammalian cochlea receives innervation from the central nervous system via two efferent systems: the lateral and the medial olivocochlear bundles. Advances in cochlear physiology have clarified the origins and terminations of these fibers. However, to date, while the functional significance of lateral efferents remains totally unknown, that of medial efferents is still controversial. The peripheral effects of medial olivocochlear system activation have been described, but the role of this inhibitory feedback onto the cochlea is still unclear. This overview summarizes the main results of several psychophysiological studies performed in humans dealing with the functional significance of medial olivocochlear efferents in hearing.

Auditory Pathways↗
PubMed1999

[Doppler tissue imaging: a new method in the study of diastolic function in left ventricular hypertrophy].

BACKGROUND: Many factors influence diastolic function indexes obtained by monitoring left ventricular filling. Recent reports suggest that the study of myocardial wall velocity with Doppler tissue imaging (DTI) can give diastolic function parameters that are less affected by the same factors. An altered diastolic function has been demonstrated with invasive methods in patients with left ventricular hypertrophy (LVH). The aims of this study were 1) to compare a group of healthy subjects with a group of patients with LVH and presumably affected by diastolic dysfunction, to try to demonstrate if DTI could give new indexes to discriminate between the two groups; 2) to compare the indexes obtained with DTI against the ones given by Doppler study of left ventricular filling in the two populations. MATERIALS AND METHODS: Forty-two patients with LVH were compared to forty normal subjects. We studied the posterior wall velocity with pulsed DTI from parasternal view, measuring the early diastolic velocity (E'), the late diastolic velocity (A') and the E'/A' ratio. In addition, we estimated the usual ventricular filling parameters and the time interval between R wave of ECG and the peaks of E' and E waves. RESULTS: At left ventricular filling, patients with LVH showed an increase in A-wave peak velocity (mean 75.3 cm/s versus 66.4 cm/s; p < 0.05) and prolonged deceleration time (mean 216 ms versus 181 ms; p < 0.05), as compared to normal reference subjects. E-wave peak velocity and E/A ratio did not differ between the two groups. At DTI, patients with LVH had decreased early diastolic velocity (E') (mean 9 cm/s versus 12 cm/s; p < 0.05) and E'/A' ratio (mean 1.53 versus 1.91; p < 0.05) as compared to the control group. We observed an inverse correlation between E' wave and age in normal subjects. There was no correlation between the early diastolic myocardial velocity (E') and early inflow velocity (E) in both groups. A correlation was found between A and A' waves in normal subjects, but not in hypertrophic ones. The E'-wave peak always preceded the E-wave peak in all the subjects. CONCLUSION: Diastolic function indexes achieved by DTI can offer additional information that is independent of the data derived from left ventricular filling.

Adult↗
PubMed1998

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.

Acoustic Stimulation↗
PubMed1998

Cochlear implant performance and electrically-evoked auditory brain-stem response characteristics.

OBJECTIVES: The purpose of this study was to find a correlation between cochlear implant performances in phoneme discrimination and activity of the brain-stem. METHODS: Electrically-evoked auditory brain-stem responses (EABRs) and speech recognition performances were measured in 17 patients implanted with an MXM Digisonic DX10 cochlear implant. Speech recognition performances without lip-reading were tested using lists of isolated French words containing 3 phonemes. RESULTS: The results indicated statistically significant correlations between phoneme correct-identification scores and the following EABR variables: wave V latency, wave II-V latency interval and wave III-V latency interval. These results, indicate that up to about 48% of the variance in isolated word recognition without lip-reading can be accounted for by EABR variables. CONCLUSION: The quality of brain-stem functioning influences central processes in phoneme discrimination.

Adult↗
PubMed1998

Contralateral frequency-modulated tones suppress transient-evoked otoacoustic emissions in humans.

In order to test the sensitivity of the human medial olivocochlear bundle (MOCB) to stimulus frequency fluctuations, changes in transient-evoked otoacoustic emission (TEOAE) amplitude induced by frequency modulated (FM) tones were measured in 18 normal-hearing subjects. The results revealed that TEOAE amplitude was reduced by contralateral FM tones at 40 dB above pure-tone threshold, with significant influences of both modulation rate (MR) and modulation depth (MD). This finding is discussed in the light of other recent results indicating amplitude fluctuation and frequency bandwidth effects in MOCB activation in humans.

Acoustic Stimulation↗
PubMed1998

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.

Acoustic Stimulation↗
PubMed1998

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.

Administration, Oral↗
PubMed1998

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.

Acoustic Stimulation↗
PubMed1998

Correlation between electrical auditory brainstem response and perceptual thresholds in Digisonic cochlear implant users.

OBJECTIVES: To examine the relationships between psychophysical perceptions and the electrically evoked auditory brainstem responses (EABRs) in multichannel cochlear implant (CI) users and to determine the effectiveness of EABRs in electrode failure. DESIGN: A descriptive study reported the EABR characteristics while the different electrodes were activated. Characteristics of the EABR and of the perceptual measures served as compared variables in a correlational study. SETTING: The study was carried out in the audiology clinic of an otolaryngology department at a university hospital. PATIENTS: The subjects consisted of nine consecutively selected habitual Digisonic DX1OR multichannel CI users. Seven patients were postlinguistically deafened adult patients; two were congenitally deaf children. MAIN OUTCOME MEASURES: Ipsilateral recordings were performed using a previously published method. Morphology, latency, and amplitude measures of the EABR recordings were described, computed, and compared with the literature data for EABRs obtained while activating other types of CI and for acoustically evoked ABRs. Correlations between EABRs and behavioral perception thresholds were analyzed using the parametric Pearson's correlation test. RESULTS: EABRs allowed the authors to detect failure of no. 10 electrode integrity in one child. Perceptual threshold measures were found to be highly significantly related to the EABR threshold across subjects and electrode position (n = 31, r = 0.98; P < 0.001; linear regression equation: perceptual threshold = 1.06 EABR threshold + 0.76). The latencies and amplitudes were found to be similar to those described in the literature. CONCLUSIONS: EABRs may be used to estimate settings for the Digisonic DX10 CI even in a pediatric population, although they cannot entirely replace behavioral measurements, especially in children. The EABR can be employed for electrode dysfunction diagnosis. Further studies are needed to determine whether recordings of EABR quality could contribute to the evaluation of functional prognosis during the rehabilitation.

Adult↗
PubMed1998

[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.

Adolescent↗
PubMed1997

Difference in cochlear efferent activity between musicians and non-musicians.

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.

Acoustic Stimulation↗
PubMed1997

Acoustical recognition of laryngeal pathology using the fundamental frequency and the first three formants of vowels.

The recognition of laryngeal pathology by analysis of the voice is investigated. The fundamental frequency and the first three formants are considered. The recognition strategy is based on comparison with normal ranges calculated over 200 ordinary voices, grouped in ten age classes ranging from 20 to 70 years, for males and females. 220 test voices are studied divided into four groups: normal voices, functional dysphonia, nodules and recurrent nerve palsy. Each subject is marked according to his/her normal range. Parameters (or items) are calculated on the Interactive Laboratory System workstation. The vocalic material is composed of 11 vowels taken from a sentence. Results are given in terms of the number of values out of the normal ranges. Statistical analysis considers both parameter ability and error rates in pathology recognition. Pathology recognition shows the following error percentages: 23% for dysphonia, 14% for nodules and 33% for recurrent nerve palsy. Parameters do not show the same efficiency for voice pathology characterisation. Formants appear to be better than the fundamental frequency.

Adult↗
PubMed1997

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.

Auditory Threshold↗
PubMed1997

Contralateral suppression and stimulus rate effects on evoked otoacoustic emissions.

Transiently evoked otoacoustic emissions (EOAE) were recorded in normal-hearing humans using pseudorandom pulse trains. This allowed the effect of increasing stimulus rate to be studied on EOAE amplitudes, input-output (I/O) functions and suppression by contralateral stimulation. EOAEs are very probably due to micromechanical properties of cochlear outer hair cells, and contralateral suppression is considered to result from olivo-cochlear efferent activation. EOAEs at various stimulus rates showed excellent reproducibility. Total EOAE amplitude diminished as interstimulus interval (ISI) decreased from 20 to 3 ms, but not for ISIs under 3 ms. The amplitude reduction was significant only on EOAE spectrum bands below 3.4 kHz. I/O functions, which kept a linear pattern, were steeper, and contralateral suppression was lower, with the highest stimulus rate (1111 c/s) relative to other rates. The EOAE decline with increasing stimulus rate might be due to incomplete recovery after adaptation of outer hair cells. The lower contralateral suppression at high stimulus rates suggests that crossed olivo-cochlear bundle action is lessened when outer hair cells are responding to a high-rate stimulus. An explanation may be that contralateral stimulation and a high-rate ipsilateral stimulus act via the same mechanisms, i.e., that high-rate stimulation activates an ipsilateral efferent loop.

Acoustic Stimulation↗