The Influence of Fog on Motion Discrimination Thresholds in Car Following

A possible explanation for close following in fog is that it would allow drivers to control headway more precisely by reducing motion perception thresholds. The purpose of our experiments was to determine the motion discrimination thresholds for closing and receding under normal and foggy conditions. An experiment and a pilot study were conducted on a driving simulator in which subjects were presented with a car following situation. Subjects had to press a button as soon as they detected that the lead vehicle was closing or receding, and their choice response time was recorded. Several visibility conditions were tested corresponding to different contrasts between the lead vehicle outline and the background, ranging from clear weather conditions to foggy conditions in which the vehicle could only be seen by its rear lights. Initial headway and lead vehicle acceleration were also varied. As expected, response times were longest with small accelerations and long headways. There was also an effect of visibility conditions with longer response times when the contrast between the vehicle outline and the background was 5% or less. Moreover, the reduction of response time corresponding to a reduction of headway was greater in fog than in clear conditions, at least in the given range of distances. This suggests that driving closer in fog may have a perceptual-control benefit in terms of a reduction in response times that partially offsets the reduction in timeheadway. Driving closer may also benefit lateral trajectory control because the lead vehicle is less likely to be lost in fog

A statistical mixture method to reveal bottom-up and top-down factors guiding the eye-movements

When people gaze at real scenes, their visual attention is driven both by a set of bottom-up processes coming from the signal properties of the scene and also from top-down effects such as the task, the affective state, prior knowledge, or the semantic context. The context of this study is an assessment of manufactured objects (here car cab interior). From this dedicated context, this work describes a set of methods to analyze the eye-movements during the visual scene evaluation. But these methods can be adapted to more general contexts. We define a statistical model to explain the eye fixations measured experimentally by eye-tracking even when the ratio signal/noise is bad or lacking of raw data. One of the novelties of the approach is to use complementary experimental data obtained with the “Bubbles” paradigm. The proposed model is an additive mixture of several a priori spatial density distributions of factors guiding visual attention. The “Bubbles” paradigm is adapted here to reveal the semantic density distribution which represents here the cumulative effects of the top-down factors. Then, the contribution of each factor is compared depending on the product and on the task, in order to highlight the properties of the visual attention and the cognitive activity in each situation

Mapping dynamical properties of cortical microcircuits using robotized TMS and EEG: Towards functional cytoarchitectonics

International audienceBrain dynamics at rest depend on the large-scale interactions between oscillating cortical microcircuits arranged into macrocolumns. Cytoarchitectonic studies have shown that the structure of those microcircuits differs between cortical regions, but very little is known about interregional differences of their intrinsic dynamics at a macro-scale in human. We developed here a new method aiming at mapping the dynamical properties of cortical microcircuits non-invasively using the coupling between robotized transcranial magnetic stimulation and elec-troencephalography. We recorded the responses evoked by the stimulation of 18 cortical targets largely covering the accessible neocortex in 22 healthy volunteers. Specific data processing methods were developed to map the local source activity of each cortical target, which showed interregional differences with very good interhemi-spheric reproducibility. Functional signatures of cortical microcircuits were further studied using spatio-temporal decomposition of local source activities in order to highlight principal brain modes. The identified brain modes revealed that cortical areas with similar intrinsic dynamical properties could be distributed either locally or not, with a spatial signature that was somewhat reminiscent of resting state networks. Our results provide the proof of concept of " functional cytoarchitectonics " , that would guide the parcellation of the human cortex using not only its cytoarchitecture but also its intrinsic responses to local perturbations. This opens new avenues for brain modelling and physiopathology readouts

CortExTool: a toolbox for processing motor cortical excitability measurements by transcranial magnetic stimulation

Assessing motor cortical excitability (CE) is essential in transcranial magnetic stimulation (TMS) in order to ensure both safe and normalised stimulation power across subjects or patients. However, there is still a lack of automatic and easy-to-use tools for analysing the electromyographic (EMG) signal features that are relevant for CE assessment, such as the amplitude of motor evoked potentials (MEPs) or the duration of cortical silent periods (CSPs). Here, we describe CortExTool, a signal processing toolbox we developed to fulfil these needs. The toolbox, developed in the Matlab programming language, is open-source and freely accessible to the TMS community. CortExTool provides all the standard functionalities required to automatically process EMG signals recorded during a CE experiment, on both individual and group levels. Its use should allow to standardize and to facilitate the processing of CE measurements by TMS

Dépendance-indépendance à l'égard du champ, activités opératoires et sénescence

Summary : Field dependence-independence, cognitive operations and senescence. In order to study the inter-individual and intra-individual variability of operatory activities in elderly subjects in relation to cognitive style, 120 intellectual men : 40 active young men and 80 retired, were tested with four Piagetian tasks and the Rod-and-Frame test. The experiment shows : 1) A wide intra-individual dispersion of operatory level especially because of certain cognitive attitudes proper to old age ; 2) Field dependence vs independence associated : a) to the inter-individual variability of senescents1 operatory level : field independency limits the lowering of efficiency in infralogical tasks; b) to the inter-tasks intra-individual variability : the dependent senescents are more dispersed than the independent ones and for certain pairs of tests show different patterns of variability. Key-words : senescence, cognitive operations, field dependence-independence.Résumé Afin d'étudier la variabilité interindividuelle et intra-individuelle des activités opératoires des sujets âgés en fonction des styles cognitifs, 120 hommes de profession intellectuelle : 40 actifs jeunes et 80 retraités, sont examinés à l'aide de 4 épreuves opératoires et du RFT. L'expérience montre : 1) une forte dispersion intrasujet du niveau opératoire des sénes-cents du fait notamment de certaines attitudes cognitives spécifiques au vieil âge ; 2) La dépendance-indépendance à l'égard du champ est associée : a) à la variabilité interindividuelle du niveau opératoire des sujets âgés : l'indépendance du champ limite la baisse d'efficience dans les épreuves infralogiques ; b) à la variabilité intra-individuelle interépreuves : les sénescents dépendants sont plus dispersés que les indépendants et, pour certaines paires d'épreuves, présentent des patrons de décalage différents. Mots clefs : sénescence, activités opératoires, dépendance-indépendance à l'égard du champ.Marendaz Christian. Dépendance-indépendance à l'égard du champ, activités opératoires et sénescence. In: L'année psychologique. 1984 vol. 84, n°2. pp. 185-205

Attraction de l'attention par des différences relatives de familiarité (étude expérimentale de la dynamique des processus précoces)

GRENOBLE2/3-BU Droit/Lettres (384212101) / SudocSudocFranceF

Modélisation de l'interaction perception mémoire à travers l'étude de l'amorçage par répétition sur des items illégaux (systèmes de représentations perceptives versus systèmes non abstractifs)

GRENOBLE2/3-BU Droit/Lettres (384212101) / SudocSudocFranceF

Perception et contrôle de la distance intervéhiculaire en condition de brouillard (étude sur simulateur)

GRENOBLE2/3-BU Droit/Lettres (384212101) / SudocSudocFranceF

Recherche visuelle (intégration des informations visuo-posturales et mnésiques en vision de bas niveau)

Ce travail porte sur la pénétrabilité de la vision de bas niveau opérationnalisée par la recherche visuelle. Sur la base des variations de l'anisotropie qui caractérise le codage des orientations en vision de bas niveau. La première série d'expériences montre que l'effet d'un cadre incliné sur l'anisotropie est préalable à l'activité de recherche et sensible aux indices de surface en favorisant les informations les plus éloignées. Confortant l'idée d'une interprétation visuo-posturale de l'effet cadre, la deuxième série d'expériences met en évidence des différences inter-individuelles reliées à la dépendance-indépendance à l'égard du champ visuel. La troisième série d'expériences montre l'intervention des représentations mnésiques, par le biais de l'orientation canonique, sur l'anisotropie. Cet ensemble de recherches, conforté par des données neuropsychologiques, met en évidence l'intégration précoce des informations visuo-posturales et mnésiques lors du traitement visuel.GRENOBLE2/3-BU Droit/Lettres (384212101) / SudocSudocFranceF