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Visual recognition : Study of the influence of peripheral vision in a predictive spatial frequency based model
No full textNous saisissons l’essentiel de notre environnement visuel en un seul coup d’œil, et ce indépendamment de sa complexité. Différentes propositions théoriques dans le domaine de la reconnaissance visuelle ont proposé que cette capacité reposerait sur l’extraction du 'gist' de la scène visuelle, une première représentation visuelle globale et rudimentaire. L’extraction du gist reposerait notamment sur l’analyse rapide des basses fréquences spatiales du signal visuel, qui permettrait une catégorisation assez grossière de la scène et des objets qui la composent. Cette première représentation de la scène permettrait par ailleurs de déclencher des mécanismes prédictifs qui guideraient dans un second temps une analyse visuelle plus minutieuse et détaillée. Ce cadre théorique, que nous avons formalisé dans cette thèse sous le nom de modèle fréquentiel prédictif, rend compte d’un grand nombre de résultats empiriques. Dans l’ensemble, les travaux à l’appui de ce modèle se sont concentrés sur la reconnaissance visuelle de petits stimuli présentés en vision centrale. Or, l’acuité visuelle diminue drastiquement avec l’excentricité rétinienne si bien qu’une grosse part du signal en basses fréquences spatiales provient de la vision périphérique. Dans ce travail de thèse, nous avons testé l’hypothèse selon laquelle l’information de basse résolution spatiale extraite en vision périphérique influence les traitements réalisés en vision centrale. Dans une première série d’expériences, nous avons observé que la catégorisation de stimuli visuels complexes (de type objets ou scènes) présentés en vision centrale peut être améliorée et/ou accélérée lorsque l’information visuelle périphérique est sémantiquement congruente par rapport à lorsqu’elle est incongruente. Dans une seconde série d’expériences, nous avons étudié les conséquences d’une perte de vision périphérique sur les traitements réalisés en vision centrale. Nous avons pour cela testé des patients atteints d'un glaucome. Cette pathologie ophtalmique affecte en particulier la rétine périphérique et représente ainsi un bon modèle pathologique d'un système dans lequel la vision périphérique a moins d'importance. Nous avons observé que ces patients présentaient un déficit pour catégoriser des petites scènes présentées en vision centrale, alors même que leur sensibilité rétinienne était préservée pour cette région du champ visuel. Ce dernier résultat suggère que la perte de vision périphérique causée par le glaucome désorganise les mécanismes prédictifs et perturberait ainsi la reconnaissance visuelle de manière globale, même en vision centrale. L’ensemble de ces travaux de thèse nous permettent de conforter et préciser le modèle fréquentiel prédictif tout en soulignant l’importance de considérer la vision périphérique dans les modèles de reconnaissance visuelle.We understand most of our visual environment at a glance, regardless of its complexity. Theories of visual recognition postulate that this ability is based on the extraction of the gist of the visual scene, a first global and coarse visual representation. Gist perception would be based on the rapid analysis of low spatial frequencies in the visual signal, and would allow a coarse categorization of the scene and the objects that compose it. This first representation of the scene would also trigger predictive mechanisms that guide a more detailed visual analysis. This theoretical framework, which we formalized in this thesis under the name of predictive frequency model, accounts for a large number of empirical results. Overall, work in support of this model has focused on the visual recognition of small stimuli presented in central vision. However, visual acuity decreases drastically with retinal eccentricity so that a large part of the signal at low spatial frequencies comes from peripheral vision. In this doctoral thesis, we tested the hypothesis that the low spatial resolution information extracted in peripheral vision would influence the processing of detailed information in central vision. In a first series of experiments, we observed that the categorization of complex visual stimuli (objects or scenes) presented in central vision can be improved and / or accelerated when information in peripheral vision is semantically congruent compared to when it is inconguent. In a second series of experiments, we studied the consequences of a peripheral vision loss onto visual recognition in central vision. We tested patients with glaucoma. This ophthalmological condition affects the peripheral retina, thus representing a good pathological model of a system in which peripheral vision is degraded. We observed that these patients presented a deficit to categorize small scenes presented in central vision, even though their retinal sensitivity was preserved for this region of the visual field. This last result suggests that the loss of peripheral vision disrupts the predictive visual system and would thus disturb visual recognition globally, even in central vision. Overall, the results allow consolidating and clarifying the predictive frequency model while emphasizing the relevance of considering peripheral vision in visual recognition models
Reconnaissance visuelle : Etude de l'influence de la vision périphérique dans le cadre d'un modèle fréquentiel prédictif
No full textWe understand most of our visual environment at a glance, regardless of its complexity. Theories of visual recognition postulate that this ability is based on the extraction of the gist of the visual scene, a first global and coarse visual representation. Gist perception would be based on the rapid analysis of low spatial frequencies in the visual signal, and would allow a coarse categorization of the scene and the objects that compose it. This first representation of the scene would also trigger predictive mechanisms that guide a more detailed visual analysis. This theoretical framework, which we formalized in this thesis under the name of predictive frequency model, accounts for a large number of empirical results. Overall, work in support of this model has focused on the visual recognition of small stimuli presented in central vision. However, visual acuity decreases drastically with retinal eccentricity so that a large part of the signal at low spatial frequencies comes from peripheral vision. In this doctoral thesis, we tested the hypothesis that the low spatial resolution information extracted in peripheral vision would influence the processing of detailed information in central vision. In a first series of experiments, we observed that the categorization of complex visual stimuli (objects or scenes) presented in central vision can be improved and / or accelerated when information in peripheral vision is semantically congruent compared to when it is inconguent. In a second series of experiments, we studied the consequences of a peripheral vision loss onto visual recognition in central vision. We tested patients with glaucoma. This ophthalmological condition affects the peripheral retina, thus representing a good pathological model of a system in which peripheral vision is degraded. We observed that these patients presented a deficit to categorize small scenes presented in central vision, even though their retinal sensitivity was preserved for this region of the visual field. This last result suggests that the loss of peripheral vision disrupts the predictive visual system and would thus disturb visual recognition globally, even in central vision. Overall, the results allow consolidating and clarifying the predictive frequency model while emphasizing the relevance of considering peripheral vision in visual recognition models.Nous saisissons l’essentiel de notre environnement visuel en un seul coup d’œil, et ce indépendamment de sa complexité. Différentes propositions théoriques dans le domaine de la reconnaissance visuelle ont proposé que cette capacité reposerait sur l’extraction du 'gist' de la scène visuelle, une première représentation visuelle globale et rudimentaire. L’extraction du gist reposerait notamment sur l’analyse rapide des basses fréquences spatiales du signal visuel, qui permettrait une catégorisation assez grossière de la scène et des objets qui la composent. Cette première représentation de la scène permettrait par ailleurs de déclencher des mécanismes prédictifs qui guideraient dans un second temps une analyse visuelle plus minutieuse et détaillée. Ce cadre théorique, que nous avons formalisé dans cette thèse sous le nom de modèle fréquentiel prédictif, rend compte d’un grand nombre de résultats empiriques. Dans l’ensemble, les travaux à l’appui de ce modèle se sont concentrés sur la reconnaissance visuelle de petits stimuli présentés en vision centrale. Or, l’acuité visuelle diminue drastiquement avec l’excentricité rétinienne si bien qu’une grosse part du signal en basses fréquences spatiales provient de la vision périphérique. Dans ce travail de thèse, nous avons testé l’hypothèse selon laquelle l’information de basse résolution spatiale extraite en vision périphérique influence les traitements réalisés en vision centrale. Dans une première série d’expériences, nous avons observé que la catégorisation de stimuli visuels complexes (de type objets ou scènes) présentés en vision centrale peut être améliorée et/ou accélérée lorsque l’information visuelle périphérique est sémantiquement congruente par rapport à lorsqu’elle est incongruente. Dans une seconde série d’expériences, nous avons étudié les conséquences d’une perte de vision périphérique sur les traitements réalisés en vision centrale. Nous avons pour cela testé des patients atteints d'un glaucome. Cette pathologie ophtalmique affecte en particulier la rétine périphérique et représente ainsi un bon modèle pathologique d'un système dans lequel la vision périphérique a moins d'importance. Nous avons observé que ces patients présentaient un déficit pour catégoriser des petites scènes présentées en vision centrale, alors même que leur sensibilité rétinienne était préservée pour cette région du champ visuel. Ce dernier résultat suggère que la perte de vision périphérique causée par le glaucome désorganise les mécanismes prédictifs et perturberait ainsi la reconnaissance visuelle de manière globale, même en vision centrale. L’ensemble de ces travaux de thèse nous permettent de conforter et préciser le modèle fréquentiel prédictif tout en soulignant l’importance de considérer la vision périphérique dans les modèles de reconnaissance visuelle
Horizontal face information is the main gateway to the shape and surface cues to familiar face identity
No full textInternational audienceHumans preferentially rely on horizontal cues when recognizing face identity. The reasons for this preference are largely elusive. Past research has proposed the existence of two main sources of face identity information: shape and surface reflectance. The access to surface and shape is disrupted by picture-plane inversion while contrast negation selectively impedes access to surface cues. Our objective was to characterize the shape versus surface nature of the face information conveyed by the horizontal range. To do this, we tracked the effects of inversion and negation in the orientation domain. Participants performed an identity recognition task using orientation-filtered (0° to 150°, 30° steps) pictures of familiar male actors presented either in a natural upright position and contrast polarity, inverted, or negated. We modelled the inversion and negation effects across orientations with a Gaussian function using a Bayesian nonlinear mixed-effects modelling approach. The effects of inversion and negation showed strikingly similar orientation tuning profiles, both peaking in the horizontal range, with a comparable tuning strength. These results suggest that the horizontal preference of human face recognition is due to this range yielding a privileged access to shape and surface cues, i.e. the two main sources of face identity information
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
It makes sense, so I see it better! Contextual information about the visual environment increases its perceived sharpness.
No full textInternational audiencePredictive coding theories of visual perception postulate that expectations based on prior knowledge modulate the processing of information by sharpening the representation of expected features of a stimulus in visual cortex but few studies directly investigated whether expectations qualitatively affect perception. Our study investigated the influence of expectations based on prior experience and contextual information on the perceived sharpness of objects and scenes. In Experiments 1 and 2, we used a perceptual matching task. Participants saw two blurred images depicting the same object or scene and had to adjust the blur level of the right image to match the blur level of the left one. We manipulated the availability of relevant information to form expectations about the image’s content: one of the two images contained predictable information while the other one unpredictable. At an equal level of blur, predictable objects and scenes were perceived as sharper than unpredictable ones. Experiment 3 involving explicit sharpness judgments confirmed these results. Our findings support the sharpening account of predictive coding theories by showing that expectations increase the perceived sharpness of the visual signal. Expectations about the visual environment help us understand it more easily, but also makes us perceive it better
Does radial bias contribute to fast saccades toward faces in the periphery?
No full textInternational audienceSaccadic choice studies have shown that humans initiate faster saccades toward faces than other visual categories. Here, we tested whether the saccadic advantage for faces observed in past studies is partly due to stimuli being typically presented along the horizontal meridian (HM). Our previous work suggests that the radial bias along the HM facilitates access to the horizontal structure of faces, which optimally drives human face-specialized processing. We expected to corroborate the saccadic advantage for faces along the HM, where the radial bias facilitates access to horizontal content, and to observe a reduction of this advantage along the vertical meridian (VM), especially in participants showing a strong horizontal tuning for face recognition. Fifty participants performed a saccadic choice task targeting faces or vehicles presented at 15°e ccentricity along the HM and VM. We also assessed the strength of the radial bias and the horizontal tuning for face identity recognition in each individual. As expected, saccades were faster and more accurate toward faces than vehicles; they were also faster along the HM than the VM. Contrary to our hypothesis, the saccadic face advantage did not differ between meridians, suggesting the robustness of face saccadic advantage. However, the saccadic face advantage along the VM correlated with the strength of the horizontal tuning of face identity recognition. Additionally, the radial bias predicted saccade latency toward faces along the HM. These findings indicate that low-level radial biases and high-level face-specialized mechanisms independently contribute to distinct functional aspects of the ultra-fast saccadic responses toward faces.</div
The neural basis of the paired-object affordance effect
No full textInternational audienceRecent behavioral studies indicate that right-handed individuals make faster action decisions on object pairs that appear in standard co-location for right-handed actions in comparison to object pairs that appear in a mirror location. In this fMRI study, we aimed to investigate the neural correlates of visual processing of thematic relations between co-acting objects (frying pan and spatula), depending of their co-location for right-handed actions. Fourteen right-handed participants made decisions about thematically related and unrelated object pairs. Pairs were either positioned in a standard location for a right-handed action (with the active object - spatula in the right visual hemifield, and the passive object - frying pan in the left visual hemifield), or in the reverse location. Behavioral results showed a benefit of positioning thematically related pairs in standard co-location when an action decision was made (deciding if the two objects are usually used together), but not when a more general contextual decision was made (deciding if the two object are typically found in the kitchen). Neuroimaging results showed that the left lateral occipital complex was more activated for standard than reverse locations. Our results provide novel evidence of close interrelations between thematic and action processing in the posterior semantic system
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