Les effets contextuels sur la perception de la brillance

Nous interagissons quotidiennement avec une multitude de matériaux et nous pouvons sans effort identifier les différents matériaux. Nous qualifions facilement des caractéristiques à des matériaux particuliers comme matte, doux, dur, lisse, brillant, par exemple. Ces caractéristiques sont basées sur l’aspect visuel du matériau et les estimations des propriétés physiques sous-jacentes du système visuel. Cependant, la perception est un problème mathématiquement sous-constraint. La quantité de lumière atteignant notre œil dépend des propriétés de réflectance de la matière, l’éclairage de la scène et la géométrie des objets. Estimer les propriétés intrinsèques des matériaux nécessite une clarification de ces différents éléments les uns des autres. Pour estimer propriétés, intrinsèques des matériaux, il faut les étudier indépendamment les uns des autres. Dans cette thèse, j’étudie l’influence d’une propriété intrinsèque particulière : les réflexions spéculaires. J’étudie l’influence du contexte sur la brillance perçue et le rôle des autres matériaux dans la scène observée. D’autres matériaux pourraient fournir des informations supplémentaires sur les caractéristiques de la scène qui guident et façonnent le percept final. Nos résultats expérimentaux confirment que : 1. La perception de la brillance est influencée par le point de vue et la direction d’illumination. La brillance perçue est bien corrélée avec les propriétés des réflexions spéculaires sur la surface. 2. La brillance perçue est largement affectée par d’autres matériaux sur la surface indiquant que les participants prennent les informations d’autres matériaux en compte. 3. La procédure d’estimation conjointe du maximum de vraisemblance peut être utilisées pour quantifier précisément les effets contextuels dans la perception matérielle. La luminance et interagissent brillant physique et en même temps une influence sur la perception de l’autre. En conclusion, cette thèse met en évidence l’importance du contexte sur la brillance perçue. Je soutiens que la définition de constance de brillance néglige largement l’influence du contexte. La capacité du système visuel pour récupérer la réflectance de surface a été largement testée et une absence de constance de brillance ont été trouvé. Cependant, le jugement d’une seule surface dans l’isolement ne correspond pas à une tâche naturelle. D’autres matériaux et objets de la scène apportent des informations supplémentaires sur l’environnement au système visuel. Le percept final de la brillance est formé par des informations disponibles à partir de ces matériaux dans la même scène.We interact with a multitude of different materials on a daily basis and we can effortless identify different materials. We easily add labels to particular materials like soft, hard, smooth, shiny, matte, for example. These labels are based on the visual appearances of the materials and the visual system's estimations of the underlying physical properties. However, mathematically material perception is an underconstrained problem. The light reaching our eye depends on the reflectance properties of the material, the illumination in the scene and the object's geometry. Estimating the intrinsic properties of materials requires to disambiguate these different factors from one another. In this thesis I will focus on one particular intrinsic property: Gloss. I will focus on the influence of the context onto perceived gloss and the role of other materials in the observed scene. Additional materials might provide supplementary information about the scene characteristics that guide and shape the final percept. Our experimental results confirm that: 1. Gloss perception is influenced by the viewpoint and the illumination direction. Perceived gloss correlates well with simple highlight properties on the surface. 2. Perceived gloss is largely influenced by other materials on the surface. Surfaces with two materials generate contrasting perceptual effects. 3. Maximum likelihood conjoint measurements can be used to precisely quantify contextual effects in material perception. Both, luminance and physical gloss interact and simultaneously influence each other. In conclusion, this thesis highlights the importance of the context onto perceived gloss. I argue that the definition of gloss constancy broadly neglects the influence of the context. The visual system's ability to recover the surface reflectance has extensively been tested and lacks of gloss constancy have been found. However, the judgement of a single surface in isolation does not correspond to a natural task. Other materials and objects in the scene provide the visual system with rich information about the environment (e.g. the illumination) and the final percept of the surface is formed by the additional information from these materials in the same scene

Dissociating implicit and explicit ensemble representations reveals the limits of visual perception and the richness of behavior

Contains fulltext : 232753.pdf (Publisher’s version ) (Open Access

Representing color and orientation ensembles: Can observers learn multiple feature distributions?

Contains fulltext : 207061.pdf (publisher's version ) (Open Access)Objects have a variety of different features that can be represented as probability distributions. Recent findings show that in addition to mean and variance, the visual system can also encode the shape of feature distributions for features like color or orientation. In an odd-one-out search task we investigated observers' ability to encode two feature distributions simultaneously. Our stimuli were defined by two distinct features (color and orientation) while only one was relevant to the search task. We investigated whether the irrelevant feature distribution influences learning of the task-relevant distribution and whether observers also encode the irrelevant distribution. Although considerable learning of feature distributions occurred, especially for color, our results also suggest that adding a second irrelevant feature distribution negatively affected the encoding of the relevant one and that little learning of the irrelevant distribution occurred. There was also an asymmetry between the two different features: Searching for the oddly oriented target was more difficult than searching for the oddly colored target, which was reflected in worse learning of the color distribution. Overall, the results demonstrate that it is possible to encode information about two feature distributions simultaneously but also reveal considerable limits to this encoding

The dress and individual differences in the perception of surface properties

This study investigates systematic individual differences in the way observers perceive different kinds of surface properties and their relationship to the dress, which shows striking individual differences in colour perception. We tested whether these individual differences have a common source, namely differences in perceptual strategies according to which observers attribute features in two-dimensional images to surfaces or to their illumination. First, we reanalysed data from two previous experiments on the dress and colour constancy. The comparison of the two experiments revealed that the colour perception of the dress is strongly related to individual differences in colour constancy. Second, two online surveys measured individual differences in the perception of colour-ambiguous images including the dress, in colour constancy, in gloss perception, in the subjective grey-point, in colour naming, and in the perception of an image with ambiguous shading. The results of the surveys replicated and extended previous findings according to which individual differences in the colour perception of the dress are due to implicit assumptions about the illumination. However, results also showed that the individual differences for other phenomena were independent of the dress and of each other. Overall, these results suggest that the striking individual differences in dress colour perception are due to individual differences in the interpretation of illumination cues to achieve colour constancy. At the same time, they undermine the idea of an overall perceptual strategy that encompasses other phenomena more generally related to the interpretation of illumination and surface properties

Publisher Correction : Dissociating implicit and explicit ensemble representations reveals the limits of visual perception and the richness of behaviour (Scientific Reports, (2021), 11, 1, (3899), 10.1038/s41598-021-83358-y)

Publisher Copyright: © 2021, The Author(s).The original version of this Article contained errors. Affiliation 2 was incorrectly given as “Sabrina Hansmann-Roth Univ. Lille, CNRS, UMR 9193 – SCALab – Sciences Cognitives et Sciences Affectives, Lille, France” rather than “Univ. Lille, CNRS, UMR 9193 – SCALab – Sciences Cognitives et Sciences Affectives, Lille, France”

The influence of the tested item on serial dependence in perceptual decisions

Serial dependence in vision reflects how perceptual decisions can be biased by what we have recently perceived. Serial dependence studies test single items' effects on perceptual decisions. However, our visual world contains multiple objects at any given moment, so it's important to understand how past experiences affect not only a single object but also perception in a more general sense. Here we asked the question: What effect does a single item have when there is more than one subsequently presented test item? We displayed a single line (inducer) at the screen center, then either a single test-line or two simultaneous test-lines, varying in orientation space to the inducer. Next, participants reported test-line orientation using a left or right located response circle (to indicate which test-line should be reported). The results demonstrated that the inducer influenced subsequent perceptual judgments of a test-line even when two test-lines were presented. Distant items caused repulsive serial dependence, while close items caused attractive serial dependence. This shows how a single inducer can influence test-line judgments, even when two test-lines are presented, and can produce attractive and repulsive serial dependence biases when the item to report is revealed after it has disappeared