Diffusive model of current-in-plane-tunneling in double magnetic tunnel junctions

We propose a model that describes current-in-plane tunneling transport in double barrier magnetic tunnel junctions in diffusive regime. Our study shows that specific features appear in double junctions that are described by introducing two typical length scales. The model may be used to measure the magnetoresistance and the resistance area product of both barriers in unpatterned stacks of double barrier magnetic tunnel junctions.Comment: 4 pages, 3 figure

When One Size Does Not Fit All: A Simple Statistical Method to Deal with Across-Individual Variations of Effects

In science, it is a common experience to discover that although the investigated effect is very clear in some individuals, statistical tests are not significant because the effect is null or even opposite in other individuals. Indeed, t-tests, Anovas and linear regressions compare the average effect with respect to its inter-individual variability, so that they can fail to evidence a factor that has a high effect in many individuals (with respect to the intra-individual variability). In such paradoxical situations, statistical tools are at odds with the researcher’s aim to uncover any factor that affects individual behavior, and not only those with stereotypical effects. In order to go beyond the reductive and sometimes illusory description of the average behavior, we propose a simple statistical method: applying a Kolmogorov-Smirnov test to assess whether the distribution of p-values provided by individual tests is significantly biased towards zero. Using Monte-Carlo studies, we assess the power of this two-step procedure with respect to RM Anova and multilevel mixed-effect analyses, and probe its robustness when individual data violate the assumption of normality and homoscedasticity. We find that the method is powerful and robust even with small sample sizes for which multilevel methods reach their limits. In contrast to existing methods for combining p-values, the Kolmogorov-Smirnov test has unique resistance to outlier individuals: it cannot yield significance based on a high effect in one or two exceptional individuals, which allows drawing valid population inferences. The simplicity and ease of use of our method facilitates the identification of factors that would otherwise be overlooked because they affect individual behavior in significant but variable ways, and its power and reliability with small sample sizes (<30–50 individuals) suggest it as a tool of choice in exploratory studies

Retours acoustiques de la production de parole : caractérisation des différences informationnelles entre le son aérien et le son par conduction osseuse

International audienceDuring speech, the auditory feedback involves both an aerial component picked up by the external ear,and an internal vibration : the ‘bone conduction’ component. While a speaker hears both components, alistener only hears the aerial part. Although half of the cochlear signal comes from internal conduction,the information it conveys, and how it impacts oral motor control, is still unclear. In this study, weconsidered the sound emitted by the eardrum and ear canal during speech as a proxy for internalsound. After recording aerial and internal sound, we made use of a voice conversion method toevaluate their informational differences. As expected, nasal vowels and consonants correlate withstronger internal signal ; more surprisingly, we observe also more internal information during stop andfricative consonants. Overall, the summation of internal and aerial feedback leads to clearer formantictrajectories, which may facilitate speech motor control.Lorsqu'on parle, le retour auditif se décompose en une voie aérienne et une voie interne ou 'par conduction osseuse'. Un locuteur entend les deux composantes, contrairement au récepteur. Alors que la moitié du signal cochléaire est interne, on connaît mal l'information qu'il véhicule et comment elle impacte le contrôle moteur oral. Dans cette étude, nous considérons le son émis par le conduit auditif pendant la production de parole comme indicateur du signal interne. Après enregistrement des signaux internes et aériens, une méthode de conversion de voix nous permet d'évaluer leurs différences informationnelles. Comme anticipé, les voyelles et consonnes nasales corrèlent avec plus d'intensité et d'information osseuse ; de manière moins attendue, on observe également plus d'information osseuse pour les consonnes occlusives et fricatives. De façon globale, la somme des retours acoustiques aérien et osseux amène une lisibilité supérieure des trajectoires formantiques qui pourrait faciliter le contrôle de la production de parole

Tongue motor control stability: integrating feedback, dynamical internal representation and optimal planning

International audienc

Retours acoustiques de la production de parole : caractérisation des différences informationnelles entre le son aérien et le son par conduction osseuse

International audienceDuring speech, the auditory feedback involves both an aerial component picked up by the external ear,and an internal vibration : the ‘bone conduction’ component. While a speaker hears both components, alistener only hears the aerial part. Although half of the cochlear signal comes from internal conduction,the information it conveys, and how it impacts oral motor control, is still unclear. In this study, weconsidered the sound emitted by the eardrum and ear canal during speech as a proxy for internalsound. After recording aerial and internal sound, we made use of a voice conversion method toevaluate their informational differences. As expected, nasal vowels and consonants correlate withstronger internal signal ; more surprisingly, we observe also more internal information during stop andfricative consonants. Overall, the summation of internal and aerial feedback leads to clearer formantictrajectories, which may facilitate speech motor control.Lorsqu'on parle, le retour auditif se décompose en une voie aérienne et une voie interne ou 'par conduction osseuse'. Un locuteur entend les deux composantes, contrairement au récepteur. Alors que la moitié du signal cochléaire est interne, on connaît mal l'information qu'il véhicule et comment elle impacte le contrôle moteur oral. Dans cette étude, nous considérons le son émis par le conduit auditif pendant la production de parole comme indicateur du signal interne. Après enregistrement des signaux internes et aériens, une méthode de conversion de voix nous permet d'évaluer leurs différences informationnelles. Comme anticipé, les voyelles et consonnes nasales corrèlent avec plus d'intensité et d'information osseuse ; de manière moins attendue, on observe également plus d'information osseuse pour les consonnes occlusives et fricatives. De façon globale, la somme des retours acoustiques aérien et osseux amène une lisibilité supérieure des trajectoires formantiques qui pourrait faciliter le contrôle de la production de parole

L’orientation spatiale chez le primate

International audienc

Motor control of the tongue during speech: Predictions of an optimization policy under sensorimotor noise

International audienceSpeech production necessitates a high dexterity. Some sounds like /i/, /s/ or /l/ require every precise positioning of the tongue, while tasks constraints can vary widely (inertial perturbations in walking/running, vocal tract perturbations during eating...). Moreover, tongue movements are very rapid, on the order of some tenth of millisecond, while proprioceptive and auditory feedback latencies are longer. Last, sensory and motor signals have limited precision (they are 'noisy'). For all these reasons, it has been proposed that the central nervous system (CNS) rely on an optimal estimation system ('internal model') in order to adjust the trajectories in real time. Moreover, the CNS also seems to optimize some perceived cost, as suggested by the motor stereotypies observed in eye or arm movements. In particular, the hypothesis of the minimization of an internal measure of effort, or the minimization of the impact of motor noise on endpoint variance account for a large body of experimental observations. Here we test whether an effort optimization controller coupled to an optimal state estimator can account for the trajectories of the tongue when a subject produces the three vowels /i/, /a/ and /u/ from a neutral (schwa) initial posture. In a first step, we ran 20,000 simulations of a finite element model of the tongue in order to describe the effect of combinations of muscle activations ramps across six muscles of the tongue (3 intrinsic, 3 extrinsic). We then applied model identification techniques to obtain a computationally tractable dynamical model of the tongue in the sagittal plane. Assuming a fixed jaw position and a standard geometry for the rest of the vocal tract, we obtained a simplified model of the speech production system. We could then derive the first three formants of the voice from the instantaneous tongue position through a harmonic analysis. With the sensorimotor plant thus defined, we applied standard numerical techniques inside a time loop to simulate the function of an optimal estimator/controller subjected to sensory and motor uncertainty, and generated tongue trajectories from the initial posture to the final endpoints defined either in postural space or in acoustic (F1-F2) space. These simulations allow exploring how optimal control hypotheses can explain the average trajectories and the impact of sensorimotor noise on their variability

Retours acoustiques de la production de parole : caractérisation des différences informationnelles entre le son aérien et le son par conduction osseuse

International audienceDuring speech, the auditory feedback involves both an aerial component picked up by the external ear,and an internal vibration : the ‘bone conduction’ component. While a speaker hears both components, alistener only hears the aerial part. Although half of the cochlear signal comes from internal conduction,the information it conveys, and how it impacts oral motor control, is still unclear. In this study, weconsidered the sound emitted by the eardrum and ear canal during speech as a proxy for internalsound. After recording aerial and internal sound, we made use of a voice conversion method toevaluate their informational differences. As expected, nasal vowels and consonants correlate withstronger internal signal ; more surprisingly, we observe also more internal information during stop andfricative consonants. Overall, the summation of internal and aerial feedback leads to clearer formantictrajectories, which may facilitate speech motor control.Lorsqu'on parle, le retour auditif se décompose en une voie aérienne et une voie interne ou 'par conduction osseuse'. Un locuteur entend les deux composantes, contrairement au récepteur. Alors que la moitié du signal cochléaire est interne, on connaît mal l'information qu'il véhicule et comment elle impacte le contrôle moteur oral. Dans cette étude, nous considérons le son émis par le conduit auditif pendant la production de parole comme indicateur du signal interne. Après enregistrement des signaux internes et aériens, une méthode de conversion de voix nous permet d'évaluer leurs différences informationnelles. Comme anticipé, les voyelles et consonnes nasales corrèlent avec plus d'intensité et d'information osseuse ; de manière moins attendue, on observe également plus d'information osseuse pour les consonnes occlusives et fricatives. De façon globale, la somme des retours acoustiques aérien et osseux amène une lisibilité supérieure des trajectoires formantiques qui pourrait faciliter le contrôle de la production de parole