Régine Le Bouquin Jeannès

Scalp localization of human auditory cortical activity modified by GSM electromagnetic fields

Purpose: This study attempted to determine whether there is a localized effect of GSM (Global System for Mobile communications) microwaves by studying the Auditory Evoked Potentials (AEP) recorded at the scalp of nine healthy subjects and six epileptic patients. Materials and methods: We determined the influence of GSM RadioFrequency (RF) on parameters characterizing the AEP in time or/and frequency domains. A parameter selection method using SVM (Support Vector Machines)-based criteria allowed us to estimate those most altered by the radiofrequencies. The topography of the parameter modifications was computed to determine the localization of the radiofrequency influence. A statistical test was conducted for selected scalp areas, in order to determine whether there were significant localized alterations due to the RF. Results: The epileptic patients showed a lengthening of the scalp component N100 (100 ms latency) in the frontal area contralateral to the radiation, which may be due to an afferent tract alteration. For the healthy subjects, an amplitude increase of the P200 wave (200 ms latency) was identified in the frontal area. Conclusions: The present study suggests that radiofrequency fields emitted by mobile phones modify the AEP. Nevertheless, no direct link between these findings and RF-induced damages in brain function was established.

Evaluation of two computational models of amplitude modulation coding in the inferior colliculus

Two computational models replicating amplitude-modulation encoding in the inferior colliculus (IC) are presented and compared. Neurons in this nucleus are modeled as point neurons using Mc Gregor equations, and receive depolarizing currents from action potentials delivered by stellate cells (chopper units) in the cochlear nucleus (CN). Stellate cells are modeled using modified Hodgkin-Huxley equations and receive inputs from a peripheral auditory model. The CN models of the two proposed architectures are characterized by an important dispersion of cellular characteristics, and therefore by various cellular best modulation frequencies (BMFs) ranging from 60 to 300 Hz. In contrast with the previous model proposed by [M.J. Hewitt, R. Meddis, A computer model of amplitude-modulation sensitivity of single units in the inferior colliculus, J. Acoust. Soc. Am. 95 (1994) 2145], each IC cell model receives convergent input from stellate cells with various BMFs. This approach assumes therefore minimal constraints on the model architecture and cell characteristics. The two models differ in terms of the neuronal structure of the IC, composed of 1 or 2 layers of point neurons acting as coincidence detectors. Each model is evaluated using two metrics: mean firing rate and modulation gain. Rate and temporal modulation transfer functions (r-MTFs and t-MTFs, respectively) are simulated and compared with physiological data. Simulations reveal that (i) an important dispersion of BMFs in the CN cells providing input to IC cells yields plausible IC cells responses to AM stimuli, (ii) the 2-layer IC structure yields the best approximation of IC responses measured in vivo.

Fast communication: Detecting information flow direction in multivariate linear and nonlinear models

In this paper we present an approach to analyze the direction of information flow between time series involving bidirectional relations. The intuitive idea comes from a first study dedicated to the so-called phase slope index, which is a measure originally developed to detect unidirectional relations and is based on the complex coherence function. In order to detect bidirectional flows, we propose two new causality indices supplying the previous index with two other functions, the directed coherence function and the directed transfer function. Moreover, to cope with the inability of the approaches based on coherence (ordinary or directed) or on directed transfer function to distinguish between direct and indirect relations, we propose another causality index based on the partial directed coherence to identify only direct relations. Experimental results show that some challenges have promising solutions through the use of this new indicator dealing with both linear and nonlinear multivariate models.

Proposal of a speech detector based on eigenspectra

This letter deals with the problem of speech detection in the context of hands-free telecommunications. The principle of the detectors studied is based on the coherence function (ordinary or partial coherence), which is usually computed from the periodogram (first approach). The present work is aimed at proposing a new approach to compute the coherence from the eigenspectra with a view to reduce the bias. A statistical analysis is carried out to estimate the bias of both coherence estimators. Both approaches are compared experimentally, and results show the superiority of the new estimator.

Optimization of a cascaded structure for noise and echo cancellation using a noise filtering preprocessing

This paper deals with speech enhancement in hands-free telecommunication systems. The two major problems encountered in such contexts - noise reduction and acoustic echo cancellation - are addressed. After the presentation of the two basic cascaded structures found in the literature, we propose a new promising technique which takes advantage of the previous ones. The main objective is to get a near-end speech signal with low levels of distortion, echo and noise. The structure is tested in a real mobile environment and compared with the two others. An objective evaluation shows the improvement provided by this structure.RésuméCet article traite de l’amélioration des télécommunications mains-libres. Les deux problèmes majeurs rencontrés dans de tels contextes à savoir la réduction du bruit et l’annulation d’écho acoustique sont appréhendés. Après avoir présenté les deux structures de base qui consistent à la mise en cascade des deux opérations précédentes, une nouvelle technique prometteuse visant à obtenir un signal utile le moins distordu possible et le mieux nettoyé est présentée. Cette structure est évaluée dans des conditions réelles et comparée aux deux techniques de base. Une quantification objective permet d’attester les bonnes performances de cette technique.

Proposal of a health monitoring system for continuous care

Internet of Things is a growing market. Given the keen interest wide public is showing, manufacturers keep launching new models and types each day, trying to connect the real world to Internet. However, while trying to connect everything in our life, manufacturers are facing new challenges that may impact this market growth. In this work, we tackle these challenges and how we can face them by proposing a health monitoring system able to ensure a continuity of care between the home and the hospital in spite of sensors heterogeneity.

Synthèse sur la réduction conjointe de bruit et d’écho pour lés systèmes mains-libres

RésuméLes télécommunications modernes s’éprennent de liberté et, dans ce paysage, les systèmes mains-libres proposent aux abounés de converser de manière plus naturelle, sans avoir à tenir un combiné. Ce nouvel usage entraîne des problèmes jusqu ’alors négligeables en téléphonie classique : la superposition de bruit et d’écho, souvent très énergétiques, sur le signal de parole. Afin de pallier ces problèmes et de fournir une qualité suffisante aux télécommunications, une réduction conjointe des perturbations, bruit et écho, est nécessaire. Cet article présente une synthèse des solutions retenues pour cette double réduction dans le cadre déééééééééé’une prise de son mono-capteur et bi-capteurs.AbstractIn the context of modern telecommunications, hands-free systems allow to talk in a more natural way, without handling a telephone. This leads to new problems which were negligible in classical telephony: the superposition of energetic noise and echo on the speech signal. To solve these problems and to provide a sufficient speech quality, a joint reduction of these perturbations is needed. This paper presents a synthesis of solutions retained to achieve this reduction in the context of mono-channel and two-channel observations.