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F Berthommier

Publications and source records attributed to F Berthommier.

9 recordsLinked to original sources
PubMed1999

Effects of envelope expansion on speech recognition.

This study investigated the effects of expanding the gross time-amplitude variations of 'speech-envelope noise' stimuli on speech recognition. The initial stimuli were VCV logatomes presented in quiet or against a steady white noise with a 0-dB signal-to-noise ratio. Their low-frequency temporal modulations (<500 Hz) were extracted in broad frequency bands, and raised to the power 2. The resulting envelopes were then used to modulate a white noise, and combined to produce the 'speech-envelope noise' stimuli. As a consequence, listeners were forced to identify speech using primarily temporal envelope cues. The results obtained with four normal-hearing listeners show small decrements in recognition performance of 1-15% when expanding the envelope of the speech stimuli presented in quiet. The results also show a small but consistent improvement in performance of 6-14% when expanding the envelope of the speech stimuli presented in noise. These results are consistent with those obtained by Fu and Shannon (J. Acoust. Soc. Am. 104 (1998) 2570-2577) with speech presented in quiet. They also suggest that the reduction in the modulation depth of the speech envelope caused by noise or reverberation could be compensated by expanding low-frequency temporal modulations.

Adult↗
PubMed1997

Modulation masking in listeners with sensorineural hearing loss.

This study compares amplitude-modulation (AM) masking in listeners with normal hearing and in listeners with a hearing loss. To address this issue, we measured the detection of sinusoidal AM applied to a white noise carrier, as a function of the frequency of a masking sinusoidal AM applied to the same noise carrier. These input filter patterns were measured for four listeners with normal hearing and three listeners with moderate or mild-to-severe sensorineural hearing losses. Stimuli were presented at 50 dB SL for all listeners with normal hearing and for two of the three listeners with hearing loss. The third listener with hearing loss was tested at 25 dB SL. For the listeners with normal hearing, the input filter patterns obtained for 100-Hz signal modulation had a broad bandpass characteristic. All input filter patterns showed a primary masking peak at 100 Hz. A secondary masking peak was apparent also at 50 Hz. For the listeners with impaired hearing, the unmasked modulation thresholds were similar to those measured in the listeners with normal hearing. One listener with a moderate hearing loss exhibited a broadly tuned input filter pattern with a masking peak at 100 Hz, but no secondary peak. The two other listeners with moderate or mild-to-severe sensorineural hearing loss showed no main masking peak and increased thresholds at low masker modulation frequencies. These results suggest that cochlear damage may affect performance in a modulation masking task.

Adult↗
PubMed1996

Similarity of granular-induced inhibitory periods in pairs of neighboring mitral/tufted cells.

1. Neighboring mitral/tufted cells have been previously shown to present temporal correlations of their firings related to the respiratory rhythm, particularly under odor stimulation. This occurs despite the existence of a powerful inhibitory control exerted by granule cells onto mitral/tufted cells. In the present study, we hypothesized that neighboring mitral cells can present granular induced inhibitory periods with similar latencies and durations and that such a similarity would preserve them from a possible suppression of their temporal correlations. 2. To test this hypothesis, we analyzed the latencies and durations of the inhibitory periods induced by granular activation in pairs of simultaneously recorded neighboring mitral cells. The activation of granule cells was achieved by electrical stimulation of the different pathways known to directly activate granule cells [lateral olfactory tract (LOT), anterior limb of the anterior commissure (AC), and piriform cortex (PC)]. Data from this group were compared with those of a control group composed of distant cells also recorded simultaneously. 3. Results first show that the latencies to onset of inhibition or to recovery were more frequently similar in neighboring cells than in control cells and that this similarity was enhanced by odor stimulation. Second, the probability that two cells exhibit similar inhibitory periods (i.e., similar latencies to both onset and to recovery) in response to electrical stimulation of LOT, AC, or PC was significantly higher in neighboring than in control cells. Third, only neighboring cells were found to present similar inhibitory periods in response to the stimulation of all of the three structures. 4. Granular activation was also found to modify the temporal patterns of individual mitral cells. However, although these patterns were not systematically modified similarly in neighboring mitral cells, they remained perfectly synchronized with zero delay if they were already synchronous without electrical stimulation. On the contrary, if patterns were spontaneously uncorrelated, electrical stimulation never produced a synchronization of their firings, even if their temporal relationships could be profoundly modified. 5. These results show that neighboring mitral cells can receive granular-induced inhibition with similar latencies and durations with a probability much higher than control cells. Such similarities allow neighboring mitral cells to preserve their temporal correlation despite the powerful inhibitory input from granule cells. Functional hypotheses about the role of the cortical feedback projections onto the bulb are discussed.

Animals↗
PubMed1995

Neuronal correlates of perceptual amplitude-modulation detection.

The goal of the present paper is to relate the coding of amplitude modulation (AM) in the auditory pathway to the behavioral detection performance. To address this issue, the detectability of AM was estimated by modelling a single neuron located in the central nucleus of the inferior colliculus (IC). The computational model is based on cochlear nucleus responses and a coincidence detection mechanism. The model replicated the main feature of the neuronal AM transfer function, namely a bandpass function. The IC-unit model was initially tuned to a 200-Hz modulation frequency. A single neurometric function for AM detection at this modulation frequency was generated using a 2-interval, 2-alternative forced-choice paradigm. On each trial of the experiments, AM was taken to be correctly detected by the model if the number of spikes in response to the modulated signal exceeded the number of spikes in an otherwise identical interval that contained an unmodulated signal. Psychometric functions for 4 human subjects were also measured under the same stimulus conditions. Comparison of the simulated neurometric and psychometric functions suggested that there was sufficient information in the rate response of an IC neuron well-tuned in the modulation-frequency domain to support behavioral detection performance.

Acoustic Stimulation↗
PubMed1995

Interpretation of multimodal medical images using connectionist and variational methods.

Our medical objective is to match multimodal 3D medical images into a coherent model of the patient, from which diagnosis can be assessed and therapeutics guided. 3D image segmentation is absolutely necessary to reach this objective. We investigate two complementary approaches for segmenting 3D medical images. First we present some definitions, basic properties and recent theoretical results about formal neural networks, and show that these results can be applied to brain tumour segmentation. A variational approach (called the 'snake spline' method) is then detailed. We finally show how segmented 3D images can be used for multimodal image matching.

Algorithms↗
PubMed1992

Temporal pattern analyses in pairs of neighboring mitral cells.

1. Neighboring mitral cells in the rat olfactory bulb have been previously shown to give similar response profiles to a series of odorants. We now analyze their temporal patterns of activity before and during stimulation to evaluate to what extent soma proximity may act on their temporal correlation and to what extent olfactory stimulation may force two close cells to fire with similar patterns. 2. In anesthetized adult rats, we recorded simultaneously the extracellular single-unit activities of two mitral cells with the use of twin micropipettes with tips separated by less than 40 microns. These activities were recorded before and during stimulation by a series of five odorants. 3. Activities were classified into nine types according to their temporal pattern along the respiratory cycle. These types comprised nonrhythmic patterns and rhythmic ones, the latter being simple or complex. A phase parameter was also calculated to compare the positions of maximal activity within respiratory cycles of pairs of cells that had rhythmic activities. 4. All analyses were made by comparing data from pairs of close cells with data from pairs of control cells obtained by pairing each first cell of all recorded pairs with the second units of all other pairs. Results reveal a probability of similar activity types significantly higher in pairs of close cells than in control ones before stimulation. Odorant stimulation enhances this difference by reducing the probability of similar associations in control pairs. Close cells present similar patterns as frequently before, as during, stimulation; however, the probability of double nonrhythmic firings decreases whereas the probability of double rhythmic ones increases.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

[A model of the relation of tonotopy and synchronization in the auditory system].

Tonotopy and synchronization of spike discharges with the stimulus frequency are two modes of coding which are probably not independent. After defining an appropriate process of coding and a measure of temporal correlations between two neighbouring channels, we show that it is possible to build with these two fundamental features of the auditory system, a neurophysiologically plausible neural network which has properties of noise resistance and signal segmentation.

Action Potentials↗
PubMedDate not supplied

[Contrast sensitivity function. Results of an epidemiologic study].

The examination of contrast sensitive function partially tests the capabilities of ganglion cells. However, this method has not yet proven to be an unquestionable way of diagnosis, 108 Subjects with various pathological conditions were tested with this technique in order to confirm its value for ophthalmological pathology. The first epidemiological results show that there are changes in curves obtained for clinically sick patients, and that the currently used equipment is most sensitive of the 4 th frequency and high frequencies. Finally, each colored stimulation is very significant at low frequencies.

Contrast Sensitivity↗