Illusion d'optique | EPFL Graph Search

On appelle illusion d'optique une perception visuelle qui s'oppose à l'expérience de la réalité qu'on peut avoir par ailleurs. Ces illusions liées au système visuel surviennent naturellement ou sont créées délibérément, soit pour la recherche, soit pour le spectacle. Parmi ces phénomènes, les erreurs d'appréciation nous laissent persuadés d'un état de chose qui ne correspond pas bien à la réalité. Les paradoxes visuels font douter de ce qu'on voit ou hésiter quant à l'interprétation. Les illusions visuelles sont les expériences dont les neurosciences disposent pour expliquer la vision. Depuis le , les chercheurs ont recherché les stimulus les plus simples ou qui produisent les résultats les plus curieux, pour établir un modèle des nombreux processus physiologiques et cognitifs qui concourrent à la vision. Les études sur la perception distinguent ce qui relève des limites du système visuel physiologique, les distorsions, les ambigüités ou l'instabilité d'interprétation et les paradoxe

Individual differences in visual (mis)perception: a multivariate statistical approach

Aline Françoise Cretenoud

Common factors are omnipresent in everyday life, e.g., people who do well in one cognitive test are likely to perform well in other cognitive tests as well, and vice versa. In vision, however, there seems to be a multitude of specific factors rather than a strong and unique common factor. For example, only weak correlations were observed between the susceptibility to different visual illusions, suggesting that the structure underlying visual illusions is multifactorial. In this thesis, I first examined the multidimensionality of the structure underlying visual illusions. To this aim, the susceptibility to various visual illusions was measured. In addition, subjects were tested with variants of the same illusion, which differed in spatial features, luminance, orientation, or contextual conditions. In line with previous work, only weak correlations were observed between the susceptibility to different visual illusions (i.e., between-illusion). An individual showing a strong susceptibility to one visual illusion does not necessarily show a strong susceptibility to other visual illusions. In contrast, there were strong correlations between the susceptibility to variants of the same illusion (i.e., within-illusion). Hence, factors seem to be illusion-specific but not feature-specific. In addition, the susceptibility to combinations of two illusions, which I call merged illusions, was measured to investigate how factors for illusions interact. The susceptibility to a merged illusion was strongly predicted from the susceptibility to the two illusions of which it was made, suggesting that factors for illusions combine independently to form complex illusory percepts. Second, I showed that individual differences in the perception of visual illusions are robust across the eye(s) to which the stimulus is presented, over a month, and when measured with an adjustment procedure or a method of constant stimuli. Last, I investigated whether a strong visual factor emerges in healthy elderly and patients with schizophrenia, which may be expected from the general decline in perceptual abilities usually reported in these two populations compared to healthy young adults. Similarly, a strong visual factor may emerge in action video gamers, who, contrary to healthy elderly and patients with schizophrenia, often show enhanced perceptual performance compared to non-video gamers. Hence, healthy elderly, patients with schizophrenia, and action video gamers were tested with a battery of visual tasks, such as a contrast detection and orientation discrimination task. As in control groups, between-task correlations were weak in general, which argues against the emergence of a strong common factor for vision in these populations. While similar tasks are usually assumed to rely on similar neural mechanisms, the performances in different visual tasks were only weakly related to each other, i.e., performance does not generalize across visual tasks. The results presented in this thesis highlight the relevance of an individual differences approach to unravel the multidimensionality of the visual structure.

EPFL2021

Anatomically plausible illusory posture affects mental rotation of body parts

Olaf Blanke, Mariko Funato, Silvio Ionta, Anna Sforza

During mental rotation (MR) of body parts, people internally simulate the movement of their corresponding body segments. These sensory-motor mechanisms render MR sensitive to proprioceptive information (e.g., posture). Similar mechanisms can alter illusory hand ownership following synchronous visuotactile stimulation (e.g., the rubber hand illusion [RHI]). In the present study, we first showed that illusory ownership for a fake hand can also be induced when the posture of the fake hand (palm-up) does not correspond with the subject's physical hand posture (palm-down). Then we tested whether illusory ownership for a fake hand in such a posture impacts the MR of hands carried out immediately and repeatedly after the RHI. The results showed that MR was altered for the view corresponding to the fake hand's posture, but not for other views. Additionally, these effects depended on illusory ownership, as only synchronous visuotactile stimulation was found to lead to these changes, characterized by a modulation of the rotation-dependent profile of MR response times. These findings show that similar sensory-motor mechanisms are recruited during the MR of hands and illusory hand ownership manipulated through multisensory mismatch, and that bottom-up visuotactile stimulation interferes with high-level imagery processes.

Springer2013

Belief as a Wise Wager

Leyla Loued-Khenissi

From the moment we wake up in the morning to the day's ebb when we settle in to sleep, we are bound to the task of decision-making. Some of these decisions barely register in our consciousness, if at all, while others, less shy, take a more prominent place at our mind's table. Regardless of the importance or difficulty of the decision, few, if any, are made with perfect information: being such a small of part of a large system, we can only know so much. Further, the system itself sends us noisy information for us to encode and decode as best we can. How do we do this? How do we continuously and, for the most part successfully, resolve uncertainty in order to survive and even flourish? We propose to define uncertainty in decision-making as a computational process, in line with information-processing theories of neural mechanisms. To that end, we investigate the neural correlates of uncertainty processing using functional magnetic resonance imaging (fMRI) in humans within a predictive coding framework. The field has already produced considerable evidence showing that decisions are made with the aim of maximizing utility, a process involving the dopaminergic reward system. We turn our focus to the uncertainty surrounding predictions and their concomitant errors by conducting a two-part fMRI experiment on 23 subjects. In the first session, we elicited objective, cognitive (financial) uncertainty in a gambling task. In the second session, we exposed individuals to subjective, perceptual uncertainty, in the form of visual illusions. Our fMRI results, modeled by computational definitions of surprise, confidence and information, show that 1) the brain employs computational principles to resolve uncertainty; 2) certain regions are consistently implicated in processing said uncertainty, notably insular cortex regions, across modalities (cognitive and perceptual), be it of a subjective or objective nature. These findings support the notion that the brain is an active inference machine, a paradigm within which further aspects of cognition can be investigated.

EPFL2018