Biomedical subjects

C Micheyl

Publications and source records attributed to C Micheyl.

At least 19 recordsLinked to original sources

PubMed2000

An auditory negative after-image as a human model of tinnitus.

The Zwicker tone (ZT) is an auditory after-image, i.e. a tonal sensation that occurs following the presentation of notched noise. In the present study, the hypothesis that neural lateral inhibition is involved in the generation of this auditory illusion was investigated in humans through differences in perceptual detection thresholds measured following broadband noise, notched noise, and low-pass noise stimulation. The detection thresholds were measured using probe tones at several frequencies, within as well as outside the suppressed frequency range of the notched noise, and below as well as above the corner frequency of the low-pass noise. Thresholds measured after broadband noise using a sequence of four 130-ms probe tones (with a 130-ms inter-burst interval) proved to be significantly smaller that those measured using the same probe tones after notched noise at frequencies falling within the notch, but larger for frequencies on the outer edges of the noise. Thresholds measured following low-pass noise using the same sequence of probe tones were found to be smaller at frequencies slightly above the corner, but larger at lower, neighboring frequencies. This pattern of results is consistent with the hypothesis that the changes in auditory sensitivity induced by stimuli containing sharp spectral contrasts reflect lateral inhibition processes in the auditory system. The potential implications of these findings for the understanding of the mechanisms underlying the generation of auditory illusions like the ZT or tinnitus are discussed.

Acoustic Stimulation↗

PubMed2000

Activation of medial olivocochlear efferent system in humans: influence of stimulus bandwidth.

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.

Acoustic Impedance Tests↗

PubMed2000

Effect of frequency content on categorical loudness normalization.

In this study, increases in loudness with increases in bandwidth, termed loudness summation, were derived from loudness growth functions estimated using a loudness-scaling procedure. The results revealed that at equal loudness category, categorical loudness summation was generally larger in normal-hearing than in hearing-impaired subjects; furthermore, the increase in loudness summation at intermediate loudness levels observed in the former, was absent in the latter. These results, in broad agreement with recent data from the literature, can be explained in the light of physiological data on cochlear compression. One implication of these results regarding hearing aid fitting was that channel-by-channel loudness normalization was effective only when the incoming sound was closed in bandwidth to one of the test stimuli.

Adult↗

PubMed2000

Influence of peripheral resolvability on the perceptual segregation of harmonic complex tones differing in fundamental frequency.

Two experiments investigated the influence of resolvability on the perceptual organization of sequential harmonic complexes differing in fundamental frequency (F0). Using a constant-stimuli method, streaming scores for ABA-... sequences of harmonic complexes were measured as a function of the F0 difference between the A and B tones. In the first experiment, streaming scores were measured for harmonic complexes having two different nominal F0s (88 and 250 Hz) and filtered in three frequency regions (a LOW, a MID, and a HIGH region with corner frequencies of 125-625 Hz, 1375-1875 Hz, and 3900-5400 Hz, respectively). Some streaming was observed in the HIGH region (in which the harmonics were always unresolved) but streaming scores remained generally lower than in the LOW and MID regions. The second experiment verified that the streaming observed in the HIGH region was not due to the use of distortion products. Overall, the results indicated that although streaming can occur in the absence of spectral cues, the degree of resolvability of the harmonics has a significant influence.

Adult↗

PubMed2000

The effect of modulation rate on the detection of frequency modulation and mistuning of complex tones.

Experiment 1 measured frequency modulation detection thresholds (FMTs) for harmonic complex tones as a function of modulation rate. Six complexes were used, with fundamental frequencies (F0s) of either 88 or 250 Hz, bandpass filtered into a LOW (125-625 Hz), MID (1375-1875 Hz) or HIGH (3900-5400 Hz) frequency region. The FMTs were about an order of magnitude greater for the three complexes whose harmonics were unresolved by the peripheral auditory system (F0 = 88 Hz in the MID region and both F0s in the HIGH region) than for the other three complexes, which contained some resolved harmonics. Thresholds increased with increases in FM rate above 2 Hz for all conditions. The increase was larger when the F0 was 88 Hz than when it was 250 Hz, and was also larger in the LOW than in the MID and HIGH regions. Experiment 2 measured thresholds for detecting mistuning produced by modulating the F0s of two simultaneously presented complexes out of phase by 180 degrees. The size of the resulting mistuning oscillates at a rate equal to the rate of FM applied to the two carriers. At low FM rates, thresholds were lowest when the harmonics were either resolved for both complexes or unresolved for both complexes, and highest when resolvability differed across complexes. For pairs of complexes with resolved harmonics, mistuning thresholds increased dramatically as the FM rate was increased above 2-5 Hz, in a way which could not be accounted for by the effect of modulation rate on the FMTs for the individual complexes. A third experiment, in which listeners detected constant ("static") mistuning between pairs of frequency-modulated complexes, provided evidence that this deterioration was due the harmonics in one of the two "resolved" complexes becoming unresolved at high FM rates, when analyzed over some finite time window. It is concluded that the detection of time-varying mistuning between groups of harmonics is limited by factors that are not apparent in FM detection data.

Adult↗

PubMed2000

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.

Adolescent↗

PubMed1999

Stronger bilateral efferent influences on cochlear biomechanical activity in musicians than in non-musicians.

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.

Acoustic Stimulation↗

PubMed1999

Sinusoidal amplitude modulation alters contralateral noise suppression of evoked otoacoustic emissions in humans.

It is well established that low-level broad band noise can elicit an amplitude decrease in evoked otoacoustic emissions recorded in the opposite ear. However, the influence of the temporal characteristics of the contralateral stimulus on this effect remains largely unknown. In the present study, otoacoustic emissions evoked by 60 dB SPL clicks were recorded in 19 normal-hearing subjects using the Otodynamics IL088, successively in absence and presence of a contralateral noise that was either steady or modulated sinusoidally in amplitude at different depths (from 25% to 100% in 25 point steps) and rates (from 50 Hz to 800 Hz in half-octave steps). The energy was kept constant whatever the modulation depth. The results showed that the evoked otoacoustic-emission attenuation effect induced by contralateral stimulation varied depending on the modulation depth and frequency of the contralateral amplitude-modulated noise. The largest suppression effect was observed at the 100 Hz modulation frequency and the 100% modulation depth. The 50 Hz modulation resulted in less suppression than with unmodulated noise. An interpretation of these results in terms of the influence of temporal amplitude fluctuations falling within a certain range on medial olivocochlear bundle activity is discussed.

Acoustic Stimulation↗

PubMed1999

Temporal loudness integration and spectral loudness summation in normal-hearing and hearing-impaired listeners.

The aim of this study was to test for differences between normal-hearing and hearing-impaired listeners regarding two fundamental aspects of intensity perception: loudness integration and loudness summation. Loudness functions for three different stimuli were measured using categorical loudness scaling in 8 normal-hearing and 12 hearing-impaired subjects. The results indicated that temporal loudness integration, defined as the difference in SPL between 16.25-ms and 300-ms noise bursts of equal loudness, was larger in the hearing-impaired than in the normal-hearing listeners. Loudness summation, defined as the difference in SPL between a 300-ms, 1,600-Hz tone pip and a white noise burst of the same duration and loudness, did not differ between the two groups. Implications of these results for hearing aid fitting strategies based on loudness normalization are discussed.

Adult↗

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

Context dependence of fundamental-frequency discrimination: lateralized temporal fringes.

In a two-interval, two-alternative, forced-choice (2I-2AFC) adaptive procedure, listeners discriminated between the fundamental frequencies (F0s) of two 100-ms harmonic target complexes. This ability can be impaired substantially by the presence of another complex (the "fringe") immediately before and after each target complex. It has been shown that for the impairment to occur (i) target and fringes have to be in the same frequency region; (ii) if all harmonics of target and fringes are unresolved then they may differ in F0; otherwise, they have to be similar [C. Micheyl and R. P. Carlyon, J. Acoust. Soc. Am. 104, 3006-3018 (1998)]. These findings have been discussed in terms of information about the fringe's F0 being included in the estimate of the F0 of the target, and in terms of auditory streaming. The present study investigated the role of perceived location and ipsilateral versus contralateral presentation of the fringes on F0 discrimination of the target. Experiment 1 used interaural level differences (ILDs), and experiment 2 used interaural time differences (ITDs) to create a range of lateralized perceptions of the 200-ms harmonic fringes. Difference limens for the F0 of the monaural target complex were measured in the presence and absence of the fringes. The nominal F0 was 88 or 250 Hz and could be the same or different for target and fringes. Stimuli were bandpass filtered between 125-625, 1375-1875, or 3900-5400 Hz. In both experiments, the effect of the fringes was reduced when their subjective location differed from that of the target. This reduction depended on the resolvability of both the fringes and the target. The effect of the fringes was reduced most (but still present), when fringes were presented purely contralaterally to the target. The results are consistent with the idea that the fringes produce interference when the listeners have difficulty segregating the target from the fringes, and that a difference in perceived location enhances segregation of the sequentially presented stimuli.

Humans↗

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↗

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

Intensity discrimination and auditory brainstem responses in cochlear implant and normal-hearing listeners.

Intensity-discrimination limens (IDLs) and auditory brainstem responses (ABRs) were measured as a function of stimulus intensity in 6 cochlear implant (CI) and 8 normal-hearing (NH) listeners. Pulse-train stimuli were delivered electrically to the auditory nerve in CI listeners and acoustically in NH listeners. In CI listeners, the IDLs expressed as Weber fractions decreased monotonically with increasing intensity. In NH listeners, a nonmonotonic IDL function showing a peak a midintensities was observed. ABR wave amplitudes increased regularly with intensity only in CI listeners. Results support the notion that the slight decrease in Weber's fractions with increasing sound intensity--generally referred to as "the near-miss to Weber's law"--is subtended by retrocochlear processes, whereas the increase in Weber's fractions at midlevels--known as "the severe departure from Weber's law"--originates in cochlear mechanisms.

Acoustic Stimulation↗

PubMed1998

The role of excitation-pattern cues and temporal cues in the frequency and modulation-rate discrimination of amplitude-modulated tones.

These experiments examine the influence of excitation-pattern cues and temporal-fine-structure cues on frequency difference limens (FDLs) measured as a function of duration. In the first three conditions, listeners were required to detect a change in carrier frequency from a baseline of 250 or 2000 Hz, for stimuli with half-amplitude durations ranging from 5 to 320 ms. In the "steady" condition, duration was manipulated by increasing the steady-state portion of the envelope between two 5-ms linear onset and offset ramps. This resulted in spectra and excitation patterns that broadened with decreasing duration. In the "modulated" condition, the carrier was amplitude modulated with a triangle function (period 10 ms) and duration was manipulated by varying the number of cycles of the modulator. In this case, the spectral envelope did not vary with duration, but the width of individual spectral lobes broadened with decreasing duration. The "low-peak-constant" condition was similar to the modulated condition, except that an increase in carrier frequency was accompanied by a decrease in the period of the modulator, so as to hold constant the frequency of the spectral lobe located roughly 100 Hz below the carrier frequency. In this condition, changes in carrier frequency resulted in minimal changes in excitation level on the low-frequency side of the excitation pattern, but changes on the high-frequency side were larger than for the first two conditions. Both the values of the FDLs, and their variation with frequency and duration, were similar in these three conditions. The fourth, "modulator varying," condition differed in that the carrier frequency was held constant and listeners were required to detect a change in modulator frequency. Thresholds were expressed as the change in frequency of the spectral side lobes adjacent to the carrier frequency ("equivalent" FDLs). Excitation-pattern cues in this condition were at least as large as in the first three conditions. However, equivalent FDLs were significantly higher than for the other three conditions. The higher FDLs are attributed to the lack of temporal fine-structure cues related to the carrier frequency. Overall, the results suggest that FDLs in the first three conditions were determined by temporal cues rather than by excitation-pattern cues. The increase of the FDLs with decreasing duration did not arise from increasing spectral splatter.

Auditory Perception↗