Letteratura scientifica selezionata sul tema "Visuo-motor tracking"

Normal subjects were tested in short, repetitive trials of a tracking task, with an identical shape of target movement being used throughout one session. Analysis of the net error curves (pursuit minus target movement) revealed that subjects regularly exhibit a remoteness effect: neighbouring trials were more similar than distant ones. The effect is demonstrated to be stronger in the absence of visual cues, and was found to be absent in a patient with complete loss of proprioception when he was performing without visual feedback as well. The results are discussed in terms of a short term memory store contributing to unconscious movement habits in tracking. This may represent part of the motor learning process working together with conscious visuo-motor control mechanisms. Its function is probably related to the acquisition of automatic movements.

Keeping the finger pointing at an Earth-fixed object during body displacements can be achieved if compensatory arm movements counteract the effect of the rotation on the hand's position in space. Here we investigated the fusion of signals that originated from systems having different neurophysiological properties (i.e., the visuo-oculomotor and vestibular systems) in the production of such compensatory arm movements. To this end, we analyzed the subjects' performance in three conditions that differed according to the information they provided about relative target-body motion. This information originated either from the vestibular or visuo-oculomotor system, or from a combination of the two. To highlight the integration of visuo-oculomotor and vestibular signals, we compared the arm response to motion frequencies presumed to allow or not to allow optimal vestibular and oculomotor responses. When they could be used in isolation, the ocular signals allowed long-latency but precise kinematics control of the arm movement, whereas vestibular signals allowed accurate motor response early in the rotation but their contribution declined as body rotation developed. Optimal performance was obtained throughout the whole movement and for all rotation frequencies when the visuo-oculomotor and vestibular signals could be used together. This increase in hand-tracking performance could not be explained by a unimodal model or an additive model of vestibular and ocular cues, even when using weighted signals. Rather, the results supported a functional model in which vestibular and visuo-oculomotor signals have different influences on the temporal and spatial aspects of hand movement compensating for body motion.

AbstractSmooth pursuit eye movements allow primates to keep gaze pointed at small objects moving across stationary surroundings. In monkeys trained to track a small moving target, we have injected brief perturbations of target motion under different initial conditions as probes to read out the state of the visuo-motor pathways that guide pursuit. A large eye movement response was evoked if the perturbation was applied to a moving target the monkey was tracking. A small response was evoked if the same perturbation was applied to a stationary target the monkey was fixating. The gain of the response to the perturbation increased as a function of the initial speed of target motion and as a function of the interval from the onset of target motion to the time of the perturbation. The response to the perturbation also was direction selective. Gain was largest if the perturbation was along the axis of ongoing target motion and smallest if the perturbation was orthogonal to the axis of target motion. We suggest that two parallel sets of visual motion pathways through the extrastriate visual cortex may mediate, respectively, the visuo-motor processing for pursuit and the modulation of the gain of transmission through those pathways.

The aims of the current program of research were to examine the impact of anxiety on performance and attentional control during the execution of two far aiming tasks, and to examine the efficacy of gaze training interventions in mediating these effects. Attentional control theory (ACT), which suggests that anxious individuals have impaired goal-directed attentional control, was adopted as a theoretical framework, and the Quiet Eye, characterised by long final fixations on relevant locations, was adopted as an objective measure of overt attentional control. In Studies 1 and 2 increased pressure impaired goal directed attentional control (QE) at the expense of stimulus-driven control (more fixations of shorter duration to various targets). The aim of studies 3 and 4 was therefore to examine the efficacy of an intervention designed to train effective visual attentional control (QE training) for novices, and determine whether such training protected against attentional disruptions associated with performing under pressure. In both studies the QE trained group maintained more effective visual attentional control and performed significantly better in a subsequent pressure test compared to the Control group, providing support for the efficacy of attentional training for visuo-motor skills. The aim of study 5 was to examine the effectiveness of a brief QE training intervention for elite golfers and to examine if potential benefits shown for novices in studies 3 and 4 transferred to competitive play. The QE-trained group maintained their optimal QE and performance under pressure conditions, whereas the control group experienced reductions in QE and performance. Importantly, these advantages transferred to the golf course, where QE-trained golfers reduced their putts per round by 1.9 putts, compared to pre-training, whereas the control group showed no change in their putting statistics. This series of studies has therefore implicated the role of attention in the breakdown of performance under pressure, but has also suggested that visual attentional training regimes may be a useful technique for alleviating this problem.

In sports, one might wish to test new ideas regarding player movement, tactics, or strategy without subjecting the athletes to possibly wasteful or even harmful habit formations. If a method of simulation of the athlete can be devised, experiments might reasonably be conducted to evaluate the ideas independently of actual training or trial in the field. Simulation of a complex system generally begins with a long period of analysis. During this time there may be mathematical and programming explorations and constructions to sharpen and examine different approaches. Meetings are usually held by the participants to try to define the task and explore alternatives. Ideas are amplified, possibly discarded as not feasible, or incorporated into the system package. Gradually there evolves a tighter and more acceptable formulation using logical and mathematical expressions (Preface, p. vii)

L'effort cognitif est une sensation subjective qui pousse les individus à éviter les tâches coûteuses. D'un point de vue biologique et évolutif, il est considéré comme un mécanisme destiné à préserver les ressources cognitives. Cependant, aucun consensus n'a été établi sur la nature de ces ressources. Puisque le cerveau est un organe de traitement de l'information, la théorie du codage efficient suggère que les ressources cognitives—quelle que soit leur nature—sont optimisées et dépendent du gain d'information lors du traitement d'une tâche.Cette hypothèse repose sur certains principes concernant le codage neuronal et le traitement de l'information. Premièrement, nous partons du principe que le cerveau traite l'information de manière bayésienne, mettant à jour ses modèles internes par des inférences entre les entrées sensorielles et les estimations antérieures. Deuxièmement, si les stimuli sont familiers, le codage neuronal efficient optimise alors le traitement de l’information. Si ces conditions sont remplies, nous pouvons estimer l'information traitée par le cerveau comme étant l'entropie relative entre estimations antérieures et postérieures, ou gain d’information ; de plus, l'énergie nécessaire pour traiter cette information étant optimisée, l'énergie dépensée pour accomplir la tâche devrait être proportionnelle à cette même quantité.Des mesures indirectes de cette relation ont été validées par pupillométrie, puisque la taille de la pupille est corrélée au taux d'information traité lors des tâches cognitives. Dans cette thèse, nous avons conçu des expériences pour valider davantage ce cadre théorique, en utilisant des mesures comportementales et de neuro-imagerie complémentaires.Nous avons mené trois expériences principales : deux tâches de poursuite visuomotrice par joystick et oculométrie, en parallèle de la pupillométrie, ainsi qu'une tâche de réponse à un stimulus (Hick-Hyman) en IRMf.La première étude examine la relation entre l'effort cognitif, la taille de la pupille et la prédiction visuomotrice dans ce cadre. En contrôlant les composantes informationnelles, telles que la prédictibilité, le retard, la vitesse et l'accélération de la cible, nous validons l'origine informationnelle de l'effort cognitif (NASA-TLX) et sa corrélation avec la taille de la pupille.La deuxième expérience a testé l’apprentissage implicite de trajectoires de cibles par oculométrie et contrôle manuel. et leur consolidation. Avec le même design que dans la première expérience, nous avons réalisé quatre sessions expérimentales sur deux jours consécutifs. Les participants apprenaient implicitement à mieux prédire les parties répétitives de la trajectoire, entraînant de meilleures performances et une dilatation pupillaire réduite.La dernière étude explorait la relation entre traitement de l'information et dissipation énergétique, en quantifiant le taux de consommation cérébrale en oxygène (CMRO2) lors d'une tâche de réponse à stimuli en IRMf (BOLD-ASL). La tâche de Hick-Hyman attribue un nombre différent de stimuli, en fonction de la complexité (entropie) de l'essai ou du bloc, à leurs boutons respectifs. Comme il existe une relation linéaire entre la quantité d'information traitée (entropie) et la performance (temps de réponse), nous avons émis l'hypothèse qu'il devrait exister une relation similaire entre la quantité d'information nécessaire pour accomplir une tâche et l'énergie qui lui est allouée. Nous avons abordé plusieurs défis techniques liés au calcul du CMRO2 dans ce contexte. Bien que nous ayons amélioré et automatisé le traitement des données, nous avons rencontré des obstacles importants qui nous ont empêchés de tirer une conclusion définitive sur notre hypothèse initiale
Cognitive effort is a ubiquitous subjective feeling of exertion that pushes people to avoid demanding tasks. From a biological and evolutionary point of view, mental effort is thought to be a mechanism intended to preserve cognitive resources. However, so far, no consensus on the nature of these resources has been established. Since the brain functions as an information-processing organ, efficient coding theory suggests that cognitive resources—whatever their nature—are optimized and should depend on information gain.This hypothesis assumes certain principles about neural coding and information processing. Firstly, we frame our work in the premise that the brain is a Bayesian information-processing machine, that updates internal models through inferences between inputs and previous beliefs. If stimuli are familiar and naturalistic, efficient neural coding can take place to optimize information coding and processing. If these conditions are met, then we can estimate the quantity of information computed by the brain as the relative entropy between prior and posterior beliefs, or information gain; moreover the quantity of energy needed to compute information being optimized, energy spent on a task should be proportional to this same quantity.Indirect measures of this relationship have been validated through pupillometry, as pupil size correlates with information rate during cognitive tasks. In this thesis, we designed experiments to further validate this information-theoretical framework, using complementary behavioral and neuroimaging measures.To assess this hypothesis, we conducted three key experiments : two joystick visuo-motor and oculomotor tracking tasks with pupillometry, and a response-to-stimulus (Hick-Hyman) task in fMRI.The first study investigates the relation between cognitive effort, pupil size and continuous visual-motor prediction under this information framework. By controlling information components of the target, such as predictability, lag, speed and acceleration, we can validate the information origin of cognitive effort (NASA-TLX) and its correlation with pupil size .The second experiment was developed to test the overnight memorization and implicitness of eye and hand continuous tracking. Using the same design as in the first experiment, we ran four experimental sessions, divided in joystick and eye tracking, on two consecutive days. We showed that participants implicitly learned to better predict repeating parts of the trajectory, which resulted in better performance and smaller pupil dilation.The last study was designed to investigate the relationship between information processing and energy dissipation in the brain by quantifying the cerebral metabolic rate of oxygen (CMRO2) during a response to stimulus task in fMRI (BOLD-ASL sequence). Hick-Hyman task maps a different number of stimuli to their response buttons, depending on the complexity (entropy) of the trial or block. As a linear relationship exists between the quantity of information processed (entropy) and the performance (response time) during the task, we hypothesized that there should be a similar relation between the quantity of information needed to accomplish a task and the energy allocated to do so. We addressed multiple technical issues related to CMRO2 computation in a cognitive task context. While we have improved and automatized the data analysis pipeline, we faced significant challenges that prevented us to reach a final conclusion on our initial hypothesis

Robot therapy seems promising with stroke survivors, but it is unclear which exercises are most effective, and whether other pathologies may benefit from this technique. In general, exercises should exploit the adaptive nature of the nervous system, even in chronic patients. Ideally, exercise should involve multiple sensory modalities and, to promote active subject participation, the level of assistance should be kept to a minimum. Moreover, exercises should be tailored to the different degrees of impairment, and should adapt to changing performance. To this end, we designed three tasks: (i) a hitting task, aimed at improving the ability to perform extension movements; (ii) a tracking task, aimed at improving visuo-motor control; and (iii) a bimanual task, aimed at fostering inter-limb coordination. All exercises are conducted on a planar manipulandum with two degrees of freedom, and involve alternating blocks of exercises performed with and without vision. The degree of assistance is kept to a minimum, and adjusted to the changing subject's performance. All three exercises were tested on chronic stroke survivors with different levels of impairment. During the course of each exercise, movements became faster, smoother, more precise, and required decreasing levels of assistive force. These results point to the potential benefit of that assist-as-needed training with a proprioceptive component in a variety of clinical conditions.