A new statistical test based on the wavelet cross-spectrum to detect time–frequency dependence between non-stationary signals: Application to the analysis of cortico-muscular interactions

The study of the correlations that may exist between neurophysiological signals is at the heart of modern techniques for data analysis in neuroscience. Wavelet coherence is a popular method to construct a time-frequency map that can be used to analyze the time-frequency correlations be- tween two time series. Coherence is a normalized measure of dependence, for which it is possible to construct confidence intervals, and that is commonly considered as being more interpretable than the wavelet cross-spectrum (WCS). In this paper, we provide empirical and theoretical arguments to show that a significant level of wavelet coherence does not necessarily correspond to a significant level of dependence between random signals, especially when the number of trials is small. In such cases, we demonstrate that the WCS is a much better measure of statistical dependence, and a new statistical test to detect significant values of the cross-spectrum is proposed. This test clearly outperforms the limitations of coherence analysis while still allowing a consistent estimation of the time-frequency correlations between two non-stationary stochastic processes. Simulated data are used to investigate the advantages of this new approach over coherence analysis. The method is also applied to experimental data sets to analyze the time-frequency correlations that may exist between electroencephalogram (EEG) and surface electromyogram (EMG)

“Biological Geometry Perception”: Visual Discrimination of Eccentricity Is Related to Individual Motor Preferences

In the continuum between a stroke and a circle including all possible ellipses, some eccentricities seem more “biologically preferred” than others by the motor system, probably because they imply less demanding coordination patterns. Based on the idea that biological motion perception relies on knowledge of the laws that govern the motor system, we investigated whether motorically preferential and non-preferential eccentricities are visually discriminated differently. In contrast with previous studies that were interested in the effect of kinematic/time features of movements on their visual perception, we focused on geometric/spatial features, and therefore used a static visual display.In a dual-task paradigm, participants visually discriminated 13 static ellipses of various eccentricities while performing a finger-thumb opposition sequence with either the dominant or the non-dominant hand. Our assumption was that because the movements used to trace ellipses are strongly lateralized, a motor task performed with the dominant hand should affect the simultaneous visual discrimination more strongly. We found that visual discrimination was not affected when the motor task was performed by the non-dominant hand. Conversely, it was impaired when the motor task was performed with the dominant hand, but only for the ellipses that we defined as preferred by the motor system, based on an assessment of individual preferences during an independent graphomotor task.Visual discrimination of ellipses depends on the state of the motor neural networks controlling the dominant hand, but only when their eccentricity is “biologically preferred”. Importantly, this effect emerges on the basis of a static display, suggesting that what we call “biological geometry”, i.e., geometric features resulting from preferential movements is relevant information for the visual processing of bidimensional shapes

Etude comportementale et Neurofonctionnelle des interactions perceptivo-motrices dans la perception visuelle de lettres.<br />Notre manière d'écrire influence-t-elle notre manière de lire?

we have to do itwe have to do itLa lecture et l'écriture sont traditionnellement considérées comme deux objets d'études distincts par les Neurosciences Cognitives. Pourtant, ces deux habiletés sont étroitement mises en relation au cours de leur apprentissage initial. Dans ce travail, nous avons tenté de mettre en évidence des interactions perceptivo-motrices dans l'écrit, c'est à dire de montrer que lorsque nous reconnaissons les lettres qui forment les mots, nous nous référons implicitement aux mouvements que nous produirions pour écrire ces mêmes lettres. Pour cela, nous avons adopté deux approches. La première a consisté à mesurer, par Imagerie par Résonance Magnétique fonctionnelle (IRMf), l'activité cérébrale de sujets adultes qui lisaient ou qui écrivaient des lettres ou des symboles graphiques inconnus. Nous avons observé qu'une zone corticale prémotrice qui est activée pendant l'écriture, l'est aussi pendant la lecture de lettres, alors que les sujets sont immobiles. Un certain nombre d'arguments nous ont permis d'avancer l'idée que cette zone spécifique serait impliquée dans la représentation des mouvements nécessaires à écrire chaque lettre.La seconde a consisté en une étude comportementale en école maternelle, auprès d'enfants qui ne savaient pas encore lire et écrire (3-5 ans). Nous avons comparé, chez ces enfants, l'apprentissage traditionnel de la lecture/écriture et l'apprentissage avec un clavier, dans le but de mesurer l'effet de ces deux méthodes sur les capacités subséquentes de reconnaissance visuelle des lettres. Après l'apprentissage, les enfants qui avaient appris à la main discriminaient mieux les lettres de leurs images en miroir que ceux qui avaient appris au clavier. Cet avantage de l'écriture manuscrite n'apparaissait qu'après une semaine et uniquement chez les enfants les plus âgés. Ces données indiquent que les mouvements d'écriture participent à la mémorisation de l'orientation des lettres.L'ensemble de ces résultats, discutés dans le cadre de la théorie motrice de la perception, suggère un couplage fonctionnel entre les versants perceptif et productif du langage écrit. Parce que nous apprenons simultanément à lire et à former les lettres en les traçant, nos aptitudes à la lecture pourraient en partie dépendre de notre manière d'écrire

Corrélats cérébraux de l'écriture

International audienc

Clavier ou stylo: comment apprendre à écrire?

article de vulgarisation sur l'impact de l'apprentissage de l'écriture au clavier et à la,mai

Clavier ou stylo: comment apprendre à écrire?

article de vulgarisation sur l'impact de l'apprentissage de l'écriture au clavier et à la,mai

Two thumbs and one index: A comparison of manual coordination in touch-typing and mobile-typing

International audienceno abstrac

The Serial Order of Response Units in Word Production: The Case of Typing.

International audienceThe selection and ordering of response units (phonemes, letters, keystrokes) represents a transversal issue across different modalities of language production. Here, the issue of serial order was investigated with respect to typewriting. Following seminal investigations in the spoken modality, we conducted an experiment where participants typed as many times as possible a pair of words during a fixed time-window. The two words either shared their first two keystrokes, the last two ones, all the keystrokes, or were unrelated. Fine-grained performance measures were recorded at the level of individual keystrokes. In contrast with previous results from the spoken modality, we observed an overall facilitation for words sharing the initial keystrokes. In addition, the initial overlap briefly delayed the execution of the following keystroke. The results are discussed with reference to different theoretical perspectives on serial order, with a particular attention to the competing accounts offered by position coding models and chaining models. Our findings point to potential major differences between the speaking and typing modalities in terms of interactive activation between lexical and response units processing levels

Training-related decrease in antagonist muscles activation is associated with increased motor cortex activation: evidence of central mechanisms for control of antagonist muscles

International audienceno abstrac

Quel est le rôle fonctionnel du cortex moteur primaire dans la perception visuelle de traces graphiques ? (études comportementale et neurophysiologique)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF