Visual Perception of Elliptic movements in 7- to-11-year-old children : Influence of Motor Rules

Cette recherche porte sur la perception visuelle des mouvements humains chez l’enfant. Le but est de vérifier si le principe d’isochronie (tendance à maintenir le temps de mouvement constant quelle que soit son amplitude) que l’on observe sur le plan moteur est également présent sur le plan perceptif. On présentait sur un écran un point décrivant une trajectoire elliptique. La taille de l’ellipse variait de 2.94 à 53 cm. Des enfants âgés de 7 à 11 ans devaient ajuster selon leur préférence la vitesse (période) du mouvement. Les résultats montrent que la relation ente la période choisie et la taille de l’ellipse correspond à celle observée lors de la réalisation du mouvement (Viviani et Schneider, 1991) : dès 7 ans les ajustements perceptifs sont conformes au principe d’isochronie. Ces résultats permettent de discuter les liens motricité-perception.The aim of the present study is to analyse the visual perception of human movements in children. We evaluated whether the isochrony motor principle (that is the tendency to maintain constant the duration of movement across change of movement amplitude) is at work in a perceptive task. Children, aged 7 to 11 years, had to adjust the velocity (the period) of a dot depicting an elliptic motion. The size of the ellipse varied from 2.94 to 53 cm. Results showed that the relation between the chosen period and the size of the ellipse corresponded to that observed in motor production (Viviani & Schneider, 1991) : From 7-year-old perceptual adjustments were in agreement with the isochrony principle. The results are discussed in terms of motor-perception relationships

Seeing two faces together: preference formation in humans and rhesus macaques

Humans, great apes and old world monkeys show selective attention to faces depending on conspecificity, familiarity, and social status supporting the view that primates share similar face processing mechanisms. Although many studies have been done on face scanning strategy in monkeys and humans, the mechanisms influencing viewing preference have received little attention. To determine how face categories influence viewing preference in humans and rhesus macaques (Macaca mulatta), we performed two eye-tracking experiments using a visual preference task whereby pairs of faces from different species were presented simultaneously. The results indicated that viewing time was significantly influenced by the pairing of the face categories. Humans showed a strong bias towards an own-race face in an Asian–Caucasian condition. Rhesus macaques directed more attention towards non-human primate faces when they were paired with human faces, regardless of the species. When rhesus faces were paired with faces from Barbary macaques (Macaca sylvanus) or chimpanzees (Pan troglodytes), the novel species’ faces attracted more attention. These results indicate that monkeys’ viewing preferences, as assessed by a visual preference task, are modulated by several factors, species and dominance being the most influential

Four-Day-Old Human Neonates Look Longer at Non-Biological Motions of a Single Point-of-Light

BACKGROUND: Biological motions, that is, the movements of humans and other vertebrates, are characterized by dynamic regularities that reflect the structure and the control schemes of the musculo-skeletal system. Early studies on the development of the visual perception of biological motion showed that infants after three months of age distinguished between biological and non-biological locomotion. METHODOLOGY/PRINCIPAL FINDINGS: Using single point-light motions that varied with respect to the “two-third-power law” of motion generation and perception, we observed that four-day-old human neonates looked longer at non-biological motions than at biological motions when these were simultaneously presented in a standard preferential looking paradigm. CONCLUSION/SIGNIFICANCE: This result can be interpreted within the “violation of expectation” framework and can indicate that neonates' motion perception — like adults'—is attuned to biological kinematics

Perception visuelle des mouvements humains : Analyse comportementale, neuroimagerie et neuropathologie.

This dissertation concerns the visual perception of human motions. The aim was to demonstrate the functional relations between perception and action using evidences from a neuroimaging study, the study of clinical cases (Parkinson's disease), and the analysis of adults and children behavior. Firstly, the research focuses on the identification of the structure that enables these functional relations. The positron emission tomography was used to reveal the neural network involved in the visual perception of writing and pointing movements. The results show that the perception of these two categories of movements activate distinct neural networks that also participate in the planning and the implementation of these movements. Secondly, the researches outline the role of these relations between perception and action. We focus on a phenomenon of perceptual preference for the velocity of drawing and pointing movements. After a demonstration and an analysis of this phenomenon, we study the way these preferences are modulated by the subject's representation of the motion, the length of the motion's trajectory and the category of the movement. The roles of the level of the subject's motor development and of the state of the subject's motor system (Parkinson's disease) are also tested. The main results show that : 1) the distribution of the favorite periods indicate a central tendency in the choices ; 2) favorite periods and imagined actions duration are comparable ; 3) as for real movements, the modulation of the perceptual preferences depends on a baseline tempo and a scaling factor ; 4) the values of the above mentioned parameters depend on the category of the movement as for perception and action. Taken together, the results suggest that perceptual preferences rely on an implicit motor simulation of the perceived movement. The perceptual preference for movement velocity could reflect a natural tendency of the observer to prefer dynamic events that are compatible with its own motor system.Cette thèse est consacrée à la perception visuelle des mouvements humains. L'objectif est de démontrer l'existence de liaisons fonctionnelles entre la perception et la motricité en utilisant des données issues de l'imagerie cérébrale, de l'étude de cas clinique (maladie de Parkinson) et de l'analyse comportementale de sujets adultes et d'enfants. Dans un premier temps, les recherches ont consisté à identifier les structures assurant ces liaisons fonctionnelles. La tomographie par émission de positon est utilisée pour révéler les réseaux neuronaux activés lors de la perception visuelle des mouvements d'écriture et de pointage. Les résultats indiquent que la perception de ces deux catégories de mouvements implique des structures distinctes ayants un rôle dans la planification et l'exécution de ces mouvements. Dans un second temps, les recherches ont consisté à préciser le rôle de ces liens entre perception et motricité. Dans ce but, nous nous sommes plus particulièrement intéressés à un phénomène de préférence perceptive pour la vitesse, dans le cas des mouvements de traçage et de pointage. Après avoir démontré et analysé en détail ce phénomène de préférence perceptive, nous avons étudié la façon dont ces préférences sont modulées en fonction de la représentation que le sujet a du mouvement, de la longueur de la trajectoire, du type de mouvement, du niveau de développement moteur, et de l'état du système moteur des sujets (maladie de Parkinson). Les résultats principaux montrent que : 1) les valeurs des périodes préférées pour un cycle du mouvement révèlent l'existence d'une tendance centrale dans les choix ; 2) les périodes préférées sont comparables aux périodes des mouvements imaginés ; 3) la modulation de la période de référence du sujet dépend, comme dans le cas de l'exécution des mouvements, d'un tempo et d'un paramètre d'échelle ; 4) les valeurs de ces paramètres dépendent du type de mouvement, pour la perception comme pour l'action. Cet ensemble de données permet de penser que la préférence perceptive s'appuie sur un processus de simulation motrice intériorisée du mouvement perçu se déroulant à un niveau implicite. La préférence perceptive pour la vitesse serait la manifestation d'une tendance naturelle du sujet à préférer des stimuli dynamiques conformes à sa propre motricité

Measurement of Individual Color Space using Luminous Vector Field

International audienceA luminous vector field is a set of couples (x,v) where x is a point in the computer display color space and v the direction of observer’s dependent achromatic luminosity change from x. That vector field is the set of orthogonal vectors to iso-luminous surfaces considering each vector v locally orthogonal to one surface passing through x. If the set of surfaces covering individual color space by stacking are considered quadratic and proportional, iso-luminous surfaces can be reconstructed from vector field.Hypothesis: If, like luminance in colorimetry, luminosity vectors are parallels for the whole color space, iso-luminous surfaces were planes. Otherwise, iso-luminous surface can be ellipsoid or hyperboloid depending on the vector field divergence or convergence. Method: We embedded computer display color space into a Euclidean space for enabling orthogonality. We choose two orthogonal planes passing through x where we measure luminous vector by heterochromatic photometry using minimum motion stimulus contrasts around x. Two sessions of minimum motion in either plane determines the three coordinates of luminous vector v attached to x. We repeat the measurement for several points placed on spheres of different radii. Fifteen points on five different radii for the two authors and six points for three different radii for twenty naïve observers. We estimate an affine model v = Ax+a0 for each observer. From observer’s data A and a0 we deduced the quadratic form of the surface (x-x0)tH(x-x0) = k2. Where x0 is the origin for the visual system, k is the level of the surface passing through x and H the surface metric for the observer’s color space. Results: All the iso-luminous surfaces we estimated were hyperboloids with a metric tensor H having one or two negative eigenvalues. This suggests that observer’s color space is a stack of iso-luminous hyperboloid sheets. All hyperboloids are included into a cone, the spectral cone for the observer of equation (x-x0)tH(x-x0)=0. From the spectral cone three vectors LMS are extracted, composing with the visual origin x0 and the metric H, a frame for the observer hyperbolic color space

Objective evaluation of motor outcomes in deep brain stimulation of the STN: Beyond patient's self-report

International audienceOver the last decades, deep brain stimulation (DBS) of the subthalamic nucleus (STN) has developed as a surgical alternative to levodopa medication in Parkinson's disease (PD). DBS is also used as a treatment for essential tremor or dystonia and is now moving toward psychiatric disorders (depression, obsessive compulsive disorder). New approaches for Parkinson disease, including gene therapy and multiple target DBS, are likely to develop in the future and raise issues concerning the objective evaluation of treatment outcomes. Outcome following DBS is typically assessed using the Unified Parkinson Disease Rating Scale (UPDRS-III) and the Parkinson Disease Quality of Life Measure (PDQ-39). Although efficient and widely used these measures focuses on overt, and often self-reported, aspects of motor behavior such as rigidity, tremor, fine motor control, posture, locomotion and bradykinesia. Starting from published results in the field of motor control and rehabilitation we propose that evaluation should be made more objective by using known principles of motor behavior to assess the current state of the patient's motor system. Results from a follow up study on a group of 7 patients with Parkinson disease treated with DBS of the STN are used to illustrate the power of the motor principles approach for detecting changes in fine motor control. We conclude that objective motor assessment could be used both for precisely estimating the outcomes of DBS of the STN and for finding the best site location for the electrodes during surgery

Mesure de l'espace couleur individuel par un champ de vecteur lumineux

International audienceThis study is intended to measure the geometry of the observer's color space when viewing a computer screen and to define individual variations from this data. A CIE photometric standard observer assumes that the eye's spectral efficiency function is constant, and photometry measurements correspond to vectors with fixed directions. By definition, the standard observer decomposes color space into planar surfaces of constant luminance. Using heterochromatic photometry with a minimum motion stimulus, we systematically measure the direction of luminous vectors for many observers and many color points. During the measurement process, the background and stimulus modulation averages are fixed to the given points in order to ensure that the observer is in a fixed adaptation mode. Our measurements result in a vector field or set of vectors (x, v), where x is the point's color space position, and v is the observer's luminousity vector. In order to estimate surfaces from vector fields, two mathematical hypotheses were used: (1) that surfaces are quadratic or equivalently that the vector field model is affine, and (2) that the metric of surfaces is proportional to a visual origin. Across twenty-four observers, we found that vector fields are convergent and the corresponding surfaces are hyperbolic. The equation of the surface in the display's color space coordinate system, and in particular the axis of symmetry, varied systematically from individual to individual. A hyperbolic geometry is compatible with studies that emphasize a modification of the photometric vector with changing adaptations

Vers des afficheurs individualisés, le rôle de la vision des couleurs

International audienceIn order to reduce fatigue and pain caused by prolonged use of a computer screen, visual displays can be adapted to the individual. According to the ecological theory of vision, human bodies have adapted to natural circumstances for vision. Tiredness is the consequence of the unnatural viewing that the visual system is optimized for. Through the prism of human color vision, we examined this question. What does the knowledge of color vision tell us about the inadequacy of displays to reproduce natural viewing conditions? To argue, we will discuss some recent results on human color vision geometry obtained by the authors a few months ago. In a preceding experiment we show that the human visual system operates a decomposition of the display color space into a stack of hyperboloid sheets of different photometrical levels. We will discuss the consequences of this hyperbolic geometry in color vision for the human computer interface.Afin de réduire la fatigue et la douleur causées par l'utilisation prolongée d'un écran d'ordinateur, les affichages visuels peuvent être adaptés à chaque individu. Selon la théorie écologique de la vision, le corps humain s’est adapté aux circonstances naturelles pour la vision. La fatigue est la conséquence d’une vision non naturelle pour laquelle le système visuel est optimisé. À travers le prisme de la vision humaine des couleurs, nous avons examiné cette question. Que nous apprend la connaissance de la vision des couleurs sur l’incapacité des écrans à reproduire les conditions naturelles de visualisation ? Pour argumenter, nous discuterons de quelques résultats récents sur la géométrie de la vision humaine des couleurs obtenus par les auteurs il y a quelques mois. Dans une expérience précédente, nous montrons que le système visuel humain opère une décomposition de l'espace colorimétrique d'affichage en un empilement de feuilles hyperboloïdes de différents niveaux photométriques. Nous discuterons des conséquences de cette géométrie hyperbolique dans la vision des couleurs pour l'interface homme-machine

Neurogeometry of color vision

International audienceIn neurogeometry, principles of differential geometry and neuron dynamics are used to model the representation of forms in the primary visual cortex, V1. This approach is well-suited for explaining the perception of illusory contours such as Kanizsa's figure (see Petitot (2008) for a review). In its current version, neurogeometry uses achromatic inputs to the visual system as the starting-point for form estimation. Here we ask how neurogeometry operates when the input is chromatic as in color vision. We propose that even when considering only the perception of form, the random nature of the cone mosaic must be taken into account. The main challenge for neurogeometry is to explain how achromatic information could be estimated from the sparse chromatic sampling provided by the cone mosaic. This article also discusses the non-linearity involved in a neural geometry for chromatic processing. We present empirical results on color discrimination to illustrate the geometric complexity for the discrimination contour when the adaptation state of the observer is not conditioned. The underlying non-linear geometry must conciliate both mosaic sampling and regulation of visual information in the visual system

Toward a robot-assisted assessment of the control processes of the motor system

International audienceWe present a visuo-haptic display and a set of tasks aimed at evaluating upper-limb sensory-motor functions. The visual and force feedbacks were manipulated to assess the functioning of different feedforward and feedback elements of movement control. We report the results of healthy adults who performed these tasks with both hands over two different experimental sessions. Results reproduced known effects related to motor learning and handedness. The whole procedure lasted about 15 minutes per hand so as to be potentially usable with patients in clinic. Such evaluation routine could improve the detection of age- or disease-related changes in motor behavior, and the assessment of the outcomes of rehabilitation methods