Un modèle pour l'usage de l'hélium en thérapie hyperbare

A model of the evolution in time of the size of gas bubbles present in the body is established. Variable size bubbles are present in tissues as a consequence of decompression sickness or iatrogenic embolization. This model allows to estimate the disappearance time of bubbles during Hyperbaric Oxygen Therapy, optionaly with nitrogen or helium as inert gas. The phenomenon of isobaric counter diffusion is taken into account to show that the use of helium combined with high pressure at 6ATA is advantageous to accelerate the disappearance of bubbles

Modulating fusion in the McGurk effect by binding processes and contextual noise

International audienceIn a series of experiments we showed that the McGurk effect may be modulated by context: applying incoherent auditory and visual material before an audiovisual target made of an audio "ba" and a video "ga" significantly decreases the McGurk effect. We interpreted this as showing the existence of an audiovisual "binding" stage controlling the fusion process. Incoherence would produce "unbinding" and result in decreasing the weight of the visual input in the fusion process. In this study, we further explore this binding stage around two experiments. Firstly we test the "rebinding" process, by presenting a short period of either coherent material or silence after the incoherent "unbinding" context. We show that coherence provides "rebinding", resulting in a recovery of the McGurk effect. In contrary, silence provides no rebinding and hence "freezes" the unbinding process, resulting in no recovery of the McGurk effect. Capitalizing on this result, in a second experiment including an incoherent unbinding context followed by a coherent rebinding context before the target, we add noise all over the contextual period, though not in the McGurk target. It appears that noise uniformly increases the rate of McGurk responses compared to the silent condition. This suggests that contextual noise increases the weight of the visual input in fusion, even if there is no noise within the target stimulus where fusion is applied. We conclude on the role of audiovisual coherence and noise in the binding process, in the framework of audiovisual speech scene analysis and the cocktail party effect

A brief history of articulatory-acoustic vowel representation

International audienceThis paper aims at following the concept of vowel space across history. It shows that even with very poor experimental means, researchers from the 17 th century started to organize the vowel systems along perceptual dimensions, either articulatory, by means of proprioceptive introspection, or auditory. With the development of experimental devices, and the increasing knowledge in acoustic and articulatory theories in the 19 th century, it is shown how the relationship between the two dimensions tended to tighten. At the mid 20 th century, the link between articulatory parameters such as jaw opening, position of the constriction of the tongue, or lip rounding, and the acoustical values of formants was clear. At this period, with the increasing amount of phonological descriptions of the languages of the world, and the power of the computer database analysis allowing extracting universal tendencies, the question of how the vowel systems are organized arose. The paper discusses this important question, focusing on two points: (1) how the auditory constraints shape the positioning of a specific set of vowel within the acoustic space, and (2) how the articulatory constraints shape the maximal extension of the vowel systems, the so-called maximal vowel space (MVS)

Binding and unbinding the auditory and visual streams in the McGurk effect

International audienceSubjects presented with coherent auditory and visual streams generally fuse them into a single per- cept. This results in enhanced intelligibility in noise, or in visual modification of the auditory per- cept in the McGurk effect. It is classically considered that processing is done independently in the auditory and visual systems before interaction occurs at a certain representational stage, resulting in an integrated percept. However, some behavioral and neurophysiological data suggest the existence of a two-stage process. A first stage would involve binding together the appropriate pieces of audio and video information before fusion per se in a second stage. Then it should be possible to design experiments leading to unbinding . It is shown here that if a given McGurk stimulus is preceded by an incoherent audiovisual context, the amount of McGurk effect is largely reduced. Various kinds of incoherent contexts (acoustic syllables dubbed on video sentences or phonetic or temporal modi- fications of the acoustic content of a regular sequence of audiovisual syllables) can significantly reduce the McGurk effect even when they are short (less than 4s). The data are interpreted in the framework of a two-stage "binding and fusion" model for audiovisual speech perception

Effect of context, rebinding and noise, on audiovisual speech fusion

International audienceIn a previous set of experiments we showed that audio-visual fusion during the McGurk effect may be modulated by context. A short context (2 to 4 syllables) composed of incoherent auditory and visual material significantly decreases the McGurk effect. We interpreted this as showing the existence of an audiovisual "binding" stage controlling the fusion process, and we also showed the existence of a "rebinding" process when an incoherent material is followed by a short coherent material. In this work we evaluate the role of acoustic noise superimposed to the context and to the rebinding material. We use either a coherent or incoherent context, followed, if incoherent, by a variable amount of coherent "rebinding" material, with two conditions, either silent or with superimposed speech-shaped noise. The McGurk target is presented with no acoustic noise. We confirm the existence of unbinding (lower McGurk effect with incoherent context) and rebinding (the McGurk effect is recovered with coherent rebinding). Noise uniformly increases the rate of McGurk responses compared to the silent condition. We conclude on the role of audiovisual coherence and noise in the binding process, in the framework of audiovisual speech scene analysis and the cocktail party effect

A possible neurophysiological correlate of audiovisual binding and unbinding in speech perception

International audienceAudiovisual (AV) speech integration of auditory and visual streams generally ends up in a fusion into a single percept. One classical example is the McGurk effect in which incongruent auditory and visual speech signals may lead to a fused percept different from either visual or auditory inputs. In a previous set of experiments, we showed that if a McGurk stimulus is preceded by an incongruent AV context (composed of incongruent auditory and visual speech materials) the amount of McGurk fusion is largely decreased. We interpreted this result in the framework of a two-stage " binding and fusion " model of AV speech perception, with an early AV binding stage controlling the fusion/decision process and likely to produce " unbinding " with less fusion if the context is incoherent. In order to provide further electrophysiological evidence for this binding/unbinding stage, early auditory evoked N1/P2 responses were here compared during auditory, congruent and incongruent AV speech perception, according to either prior coherent or incoherent AV contexts. Following the coherent context, in line with previous electroencephalographic/magnetoencephalographic studies, visual information in the congruent AV condition was found to modify auditory evoked potentials, with a latency decrease of P2 responses compared to the auditory condition. Importantly, both P2 amplitude and latency in the congruent AV condition increased from the coherent to the incoherent context. Although potential contamination by visual responses from the visual cortex cannot be discarded, our results might provide a possible neurophysiological correlate of early binding/unbinding process applied on AV interactions

Suivi temporel de stimuli dynamiques interférants par marquage du plan temps-fréquence utilisant une statistique de passages par zéro

Dans un cadre d'Analyse de Scènes Auditives Computationnelle (CASA), ce papier présente un modèle de marquage du plan temps-fréquence par détection d'harmonicité. L'originalité du modèle tient à l'exploitation d'une statistique des passages par zéros du signal temporel pour le marquage, statistique qui fournit une mesure de la fiabilité du marquage par le biais de l'écart-type des longueurs d'intervalles inter-zéros du premier ordre. Après avoir présenté le modèle et son comportement, nous montrons que celui-ci peut-être utilisé pour le suivi de stimuli dynamiques présentant de fortes variations prosodiques