Trois expériences ont été menées dans le but de déterminer quels codes sous-tendant la représentation de l’organisation spatiale des composantes des formes complexes contribuent aux discriminations d’objets complexes. Les trois expériences ont utilisé une tâche d’appariement simultané d’objets complexes. Aux essais négatifs, les objets pouvaient avoir des différences catégorielles de configuration, des différences métriques de configuration, des différences métriques de configuration et du rôle des parties ou des différences du rôle des parties seulement. La distance angulaire 2D ou 3D entre les stimuli pouvait varier. À l’expérience 1, les stimuli étaient présentés avec stéréoscopie et avaient une surface avec un gradient de texture de haut contraste. L’expérience 2 constitue une réplication de l’expérience 1 hormis pour l’utilisation de stimuli dont le contraste était réduit. Le but de cette manipulation était de vérifier si les résultats de l’expérience 1 sont répliqués avec une tâche dont le niveau de difficulté est plus élevé. Les stimuli de la troisième expérience avaient une surface gris mat et étaient présentés sans stéréoscopie. Les trois expériences ont montré que des codes catégoriel et pertinent aux rôles des parties contribuent à la discrimination d’objets complexes. Toutefois, ces codes sont dépendants aux orientations 2D et 3D, et ce, peu importe la richesse de l’information de profondeur présente dans les stimuli. De plus, nos résultats démontrent une plus grande sensibilité aux différences catégorielles de configuration qu’aux différences métriques. Enfin, un code métrique contribue également aux discriminations. Toutefois, la contribution de ce code disparaît lorsque la quantité d’information de profondeur est réduite. / Tree experiments were conducted to determine which codes underlie the representation of the spatial organisation of the components of complex shapes. The tree experiments used a simultaneous matching task of complex objects. For the negative trials, the objects could have categorical differences of configuration, metric differences of configuration, metric difference along with differences in the role of parts, and differences in the role of parts only. The 2D or 3D angular distance between the stimuli could vary. In experiment 1, the stimuli were presented with stereopsis and had a surface with high contrast texture. Experiment 2 replicates the condition of experiment 1, except that the contrast of the stimuli was reduced. The goal of this manipulation was to verify if the results of experiment 1 were replicated if task difficulty is increased. In experiment 3, the stimuli were presented without stereopsis and without texture. The tree experiments showed that a categorical code, and a code relevant to the role of the parts contribute to the discrimination of complex objects and that these codes are dependent to 2D and 3D orientation, independently of depth cues. The results also show a greater sensitivity to categorical than to metric configuration differences. Finally, a metric code also contributes to complex shapes discrimination. However, the contribution of this code disappears when the quantity of depth cues is reduced.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

<div>In conventional computer graphics and visualization, images are synthesized following the planar pinhole camera (PPC) model. The PPC approximates physical imaging devices such as cameras and the human eye, which sample the scene with linear rays that originate from a single viewpoint, i.e. the pinhole. In addition, the PPC takes a snapshot of the scene, sampling it at a single instant in time, or timepoint, for each image. Images synthesized with these single viewpoint and single timepoint constraints are familiar to the user, as they emulate images captured with cameras or perceived by the human visual system. However, visualization using the PPC model suffers from the limitation of occlusion, when a region of interest (ROI) is not visible due to obstruction by other data. The conventional solution to the occlusion problem is to rely on the user to change the view interactively to gain line of sight to the scene ROIs. This approach of sequential navigation has the shortcomings of (1) inefficiency, as navigation is wasted when circumventing an occluder does not reveal an ROI, (2) inefficacy, as a moving or a transient ROI can hide or disappear before the user reaches it, or as scene understanding requires visualizing multiple distant ROIs in parallel, and (3) user confusion, as back-and-forth navigation for systematic scene exploration can hinder spatio-temporal awareness.</div><div><br></div><div>In this thesis we propose a novel paradigm for handling occlusions in visualization based on generalizing an image to incorporate samples from multiple viewpoints and multiple timepoints. The image generalization is implemented at camera model level, by removing the same timepoint restriction, and by removing the linear ray restriction, allowing for curved rays that are routed around occluders to reach distant ROIs. The paradigm offers the opportunity to greatly increase the information bandwidth of images, which we have explored in the context of both desktop and head-mounted display visualization, as needed in virtual and augmented reality applications. The challenges of multi-viewpoint multi-timepoint visualization are (1) routing the non-linear rays to find all ROIs or to reach all known ROIs, (2) making the generalized image easy to parse by enforcing spatial and temporal continuity and non-redundancy, (3) rendering the generalized images quickly as required by interactive applications, and (4) developing algorithms and user interfaces for the intuitive navigation of the compound cameras with tens of degrees of freedom. We have addressed these challenges (1) by developing a multiperspective visualization framework based on a hierarchical camera model with PPC and non-PPC leafs, (2) by routing multiple inflection point rays with direction coherence, which enforces visualization continuity, and without intersection, which enforces non-redundancy, (3) by designing our hierarchical camera model to provide closed-form projection, which enables porting generalized image rendering to the traditional and highly-efficient projection followed by rasterization pipeline implemented by graphics hardware, and (4) by devising naturalistic user interfaces based on tracked head-mounted displays that allow deploying and retracting the additional perspectives intuitively and without simulator sickness.</div>