Anxiety can be advantageous in terms of survival and well-being, yet atypically high levels may be maladaptive and result in the clinical diagnosis of an anxiety disorder. Several risk factors have been implicated in the manifestation of clinical anxiety, including cognitive biases. In recent years, a plethora of research has emerged demonstrating that anxious adults exhibit biases of attention for threatening stimuli, especially that which is biologically relevant (e.g., facial expressions). Specific components of attentional bias have also been identified, namely facilitated engagement, impaired disengagement, and avoidance. However, the majority of studies have focused on the spatial domain of attention. Furthermore, the area is under-researched in children, despite research demonstrating that symptoms relating to clinical and non-clinical anxiety follow a stable course from childhood through to adolescence and adulthood. Consequently, the aim of this thesis was to investigate how anxiety affects children’s visual attention for emotive, particularly angry, faces. In order to provide a more comprehensive understanding, the current research involved examining the role of temporal and spatial attention utilising rapid serial visual presentation with the attentional blink, and the visual probe paradigm, respectively. The main hypothesis was that high state and/or trait anxiety would be associated with an attentional bias for angry, relative to positive or neutral faces in both the temporal and spatial domains. In relation to the temporal domain, key findings demonstrated that high levels of trait anxiety were associated with facilitated engagement towards both angry and neutral faces. It was further found that all children rapidly disengaged attention away from angry faces. Findings related to the processing of angry faces accorded with the main hypothesis stated in this thesis, as well as research and theory in the area. The finding that anxious children preferentially processed neutral faces in an attentional blink investigation was unexpected. This was argued to potentially reflect this stimulus type being interpreted as threatening. Key findings regarding the spatial domain were that high trait anxious children displayed an early covert bias of attention away from happy faces and a later, overt bias of attention away from angry faces. The finding that high trait anxiety was linked to an attentional bias away from happy faces in a visual probe task was also unexpected. This was argued to potentially reflect smiling faces being interpreted as signifying social dominance, thus resulting in the viewer experiencing feelings of subordination and becoming avoidant and/or submissive. To conclude, this thesis has enhanced current knowledge of attentional bias in both the temporal and spatial domains for emotive stimuli in anxious children. It has demonstrated that higher levels of trait anxiety moderate children’s allocation of attentional resources to different stimulus types, whether these are threatening, positive, or neutral. This has important implications for evaluating past research in adults and children, and for further developing theoretical models of attentional bias and anxiety. It also offers important clinical implications, since attending towards or away from specific stimuli may affect the development and maintenance of anxiety disorders. Recently, a treatment that aims to modify attentional bias in anxious individuals has begun to be developed. In light of the present findings, it may be necessary to review this treatment so that anxious children are re-trained in the specific biases of attention demonstrated here.

La mémoire à court terme visuelle (MCTv) est un système qui permet le maintien temporaire de l’information visuelle en mémoire. La capacité en mémoire à court terme se définit par le nombre d’items qu’un individu peut maintenir en mémoire sur une courte période de temps et est limitée à environ quatre items. Il a été démontré que la capacité en MCTv et les habiletés mathématiques sont étroitement liées. La MCTv est utile dans beaucoup de composantes liées aux mathématiques, comme la résolution de problèmes, la visualisation mentale et l’arithmétique. En outre, la MCTv et le raisonnement mathématique font appel à des régions similaires du cerveau, notamment dans le cortex pariétal. Le sillon intrapariétal (SIP) semble être particulièrement important, autant dans la réalisation de tâches liées à la MCTv qu’aux habiletés mathématiques. Nous avons créé une tâche de MCTv que 15 participants adultes en santé ont réalisée pendant que nous enregistrions leur activité cérébrale à l’aide de la magnétoencéphalographie (MEG). Nous nous sommes intéressés principalement à la composante SPCM. Une évaluation neuropsychologique a également été administrée aux participants. Nous souhaitions tester l’hypothèse selon laquelle l’activité cérébrale aux capteurs pariéto-occipitaux pendant la tâche de MCTv en MEG sera liée à la performance en mathématiques. Les résultats indiquent que l’amplitude de l’activité pariéto-occipitale pendant la tâche de MCTv permet de prédire les habiletés mathématiques ainsi que la performance dans une tâche de raisonnement perceptif. Ces résultats permettent de confirmer le lien existant entre les habiletés mathématiques et le fonctionnement sous-jacent à la MCTv. / Visual short-term memory (VSTM) is a memory system that permits the temporary retention of visual information. Short-term memory capacity can be defined by the amount of information that an individual can remember over a short period of time and is limited to about four items. It was shown that VSTM capacity and mathematical abilities are closely related. VSTM is useful for a lot of components linked to mathematical skills like word problem solving, mental visualisation and arithmetic. Moreover, VSTM and mathematical reasoning activate similar brain regions, mainly within the parietal cortex. The intraparietal sulcus (IPS) appears to be particularly important both in the realization of VSTM tasks and mathematical reasoning tasks. We created a VSTM task which 15 healthy adult participants completed while we recorded their brain activity using magnetoencephalography (MEG). We were mainly interested in the SPCM component. A neuropsychological assessment was also administrated to the participants. We wanted to verify the hypothesis stipulating that cerebral activity recorded at parieto-occipital sensors during the VSTM task should be linked to performance in mathematics. The results indicate that parieto-occipital activity during the VSTM tasks predicted mathematical abilities as well as performance on a perceptive reasoning task. These results confirmed the link existing between mathematical abilities and VSTM functioning.

Uma das tarefas básicas dos mecanismos atencionais é decidir qual a localização dentro do campo visual, em que devemos prestar atenção primeiro. Um objeto que contenha características distintas, tais como orientação, forma, cor, tamanho, brilho, textura, etc. diferentes, pode atrair a atenção de uma maneira \"bottom-up\". A informação \"top-down\" baseia-se no conhecimento prévio e tem uma grande influência nas localizações atendidas. Inspirado nos mecanismos da Atenção Visual Humana, embora sem a pretensão de simulá-la, este trabalho prevê o desenvolvimento de uma nova metodologia que integra os dois tipos de informações: \"bottom-up\" e \"top-down\". Características \"bottom-up\" são geradas a partir de Momentos e essas informações são utilizadas em mapas de saliência, enquanto que um conhecimento prévio é utilizado para gerar pistas \"top-down\". Neste trabalho, desenvolveu-se uma metodologia específica para a busca e o reconhecimento visual em cenas com múltiplos objetos, utilizando para isso uma rede \"fuzzy\" contendo três subsistemas \"fuzzy\". Dada uma imagem de entrada, o objetivo consiste em se detectar regiões que possam conter informações mais significativas, a fim de que se possa guiar e restringir processamentos mais complexos. A inclusão de mecanismos de atenção (seleção de uma região de interesse dentro da imagem) é de fundamental importância pois os resultados obtidos pelo método podem ser usados para controlar a aquisição da imagem de uma maneira dinâmica. O modelo proposto está estruturado em três estágios principais: O primeiro estágio consiste em se segmentar os objetos e extrair características globais dos mesmos baseadas principalmente na teoria dos momentos, tais como tamanho, orientação, formato e distância e também média de nível de cinza. Por intermédio da comparação de um objeto com os outros presentes na cena, características \"bottom-up\" de conspicuidade são usadas para guiar a atenção ao objeto mais diferente. Por intermédio do uso da lógica \"fuzzy\" é possível inferir com grande flexibilidade algumas regras de decisão baseadas nos princípios de percepção visual tais como as leis Gestalt. O segundo estágio consiste de um subsistema \"fuzzy top-down\" que combina diferentes características de acordo com a relevância das mesmas em diferentes tarefas. Finalmente, o terceiro estágio consiste de um subsistema \"fuzzy\" que integra as informações obtidas dos subsistemas anteriores e fornece um índice geral de saliência, e indica a provável localização do objeto a ser reconhecido. A nova abordagem foi testada com objetos geométricos levando-se em consideração as características que atraem a atenção dos serem humanos / One of the basic tasks assigned to the human attentional mechanisms is to decide which location in the visual field we must pay attention first. An object containing distinctive features (such as different orientation, shape, color, size, shine, texture, etc.) can attract attention in a bottom-up way. Top-down information is based on the previous knowledge and has a large influence on the attended locations. Inspired on human visual attention mechanisms, although it doesn\'t want simulate it, this work presents a new methodology to integrate two different kind of information: bottom-up and top-down. Bottom-up features are obtained from Moment Theory and this information is used in salience maps, while a previous knowledge is used to create top-down hints. In this work, an specific methodology to visual search and recognition was developed to be applied to scenes containing multiple objects by a fuzzy net with three fuzzy subsystems. The aim of this methodology is to detect regions that may contain the most significant information, in order to guide and to restrict most complex processing. The inclusion of attentional mechanisms (the selection of a region of interest in the image) is fundamental and can be used to control the image acquisition in a dynamic way. The proposed model is structured in three main stages. The first stage segments the objects and extracts global features of them, based on the Moment Theory such as size, orientation, shape and distance and gray level average. By comparing one object with the other ones present in the scene, bottom-up features of conspicuity are used to guide the attention to the most different object. The Fuzzy Logic allows us to infer with great flexibility some of decision rules based on the visual perception principles such as the Gestalt Laws. The second stage is a top-down fuzzy subsystem that combines different features according to the relevance of them in different tasks. Finally, the third stage is a fuzzy subsystem that integrates the information obtained from the previous sub-systems and gives us a general salience index. The new methodology was tested in geometrical objects considering the feature that attracts attention to human beings

Die Erforschung visueller Aufmerksamkeit beruht auf verdeckter Aufmerksamkeit; das heißt, wenn der Fokus der Aufmerksamkeit trotz strikter Fixation ausgerichtet wird ohne größere Sakkaden auszuführen. EEG-Studien haben das neuronale Netzwerk identifiziert, dass verdeckte Aufmerksamkeit steuert. Diese Studien ignorieren jedoch unwillkürliche kleine Sakkaden während der Fixation - Mikrosakkaden (MS) genannt. Blickbewegungsstudien hingegen belegen einen Zusammenhang zwischen Aufmerksamkeit und diesen MS, beziehen ihre Resultate jedoch nicht auf etablierte EEG-Befunde. Um diese Forschungslücke zu schließen, zielt diese Dissertation darauf, den Zusammenhang zwischen Ereignis-korrelierten Potentialen (EKP) endogener Aufmerksamkeit und MS zu untersuchen. Folglich wurden drei Studien mit gleichzeitiger Erfassung von EEG und Blickbewegungen durchgeführt. In den Studien haben die Probanden ein „Posner Spatial-Cueing-Paradigma“ absolviert mit einem endogenen Hinweisreiz. Wir zeigen deutliche Zusammenhänge zwischen MS und neuronalen Korrelaten visueller Aufmerksamkeit. Erstens, MS und ein posteriores EKP reflektierten die Selektion visueller Reize basierend auf deren Merkmale. Dieses Ergebnis stärkt die Idee eines Netzwerkes, dass relevante Reize unter Distraktoren selektiert und zielgerichtetes Verhalten initiiert. Zweitens, MS erzeugten ein visuelles Potential, das verstärkte Potentialkomponenten für Reize zeigte, die im Aufmerksamkeitsfokus lagen. Dieses MS-evozierte Potential stellte einen zeitlich gut aufgelösten Aufmerksamkeitsindex dar. Drittens, MS erzeugten zudem ein in früheren Studien übersehenes, korneoretinales Artefakt. Dieses Artefakt kontaminierte die Messung eines frontalen EKPs, dass zuvor mit der Kontrolle von Aufmerksamkeit assoziiert war. Zusammenfassend zeigt diese Dissertation, dass die gleichzeitige Erfassung von EEG und Blickbewegungen bedeutsame Einblicke in den Zusammenhang von MS und visueller Aufmerksamkeit erlaubt. / Research on visual attention focusses on covert attention; that is, when attention is directed during fixation periods in the absence of larger saccades. While previous EEG research has provided insights into the neural network that controls covert attention, this field fails to account for the inevitable occurrence of miniature fixational saccades - called microsaccades (MS). In contrast, previous eye-tracking research has established links between MSs and covert attention, but has not directly related their findings to seminal EEG results. This thesis bridges this research gap by investigating the link between event-related potentials (ERPs) of endogenous attention and MSs. To this end, three studies were conducted with concomitant ERP and high-resolution eye-tracking recordings while participants performed a Posner spatial cueing task with an endogenous cue. Crucially, we show that MSs relate to neural correlates of visual attention. First, MS and an early posterior ERP reflected the top-down selection of a visual stimulus based on its features. This finding is consistent with the notion of a neural network that selects relevant stimuli from distracting ones and initiates goal-directed behavior toward selected stimuli. Second, gaze shifts from MSs evoked a visual potential in the EEG that was enhanced for stimuli in the focus of attention; a finding well-known for the visual potential measured after presenting a stimulus. Importantly, these MS-related potentials provided a fine-grained temporal index of the subject’s attentional state. Finally, MSs further evoked a corneoretinal artifact overlooked in previous EEG studies. This artifact contaminated the measurement of a frontal ERP previously associated with preparatory attentional control. In sum, this thesis provides first evidence for the benefits of using concomitant ERP and eye-tracking recordings to examine the link between MSs and visual attention.

Die Reaktionsauswahl und die visuelle Aufmerksamkeit sind kapazitätslimitiert. In Doppelaufgaben des Paradigmas der Psychologischen Refraktärperiode (PRP) wird angenommen, dass die Reaktionsauswahlstufen in Aufgabe 1 und Aufgabe 2 sequentiell verarbeitet werden. Für Konjunktionssuchaufgaben wird angenommen, dass die visuelle Aufmerksamkeit Objekte selektiert und Objektmerkmale zusammen bindet, was zu einem seriellen Suchprozess führt. In der vorliegenden Dissertation wurde untersucht, ob die visuelle Aufmerksamkeit (d.h. Merkmalsbindung) demselben zentralen Verarbeitungsengpass wie die Reaktionsauswahl in Doppelaufgaben unterliegt. Sequentielle Verarbeitung von Reaktionsauswahl und visueller Aufmerksamkeit würde Evidenz dafür zeigen, dass beide Prozesse derselben Kapazitätslimitation unterliegen, während parallele Verarbeitung Evidenz dafür zeigen würde, dass beide Prozesse unterschiedlichen Kapazitätslimitationen unterliegen. Um diese Frage zu untersuchen, wurden Reaktionszeitmaße (locus-of-slack Methode), Targetdetektionsmaße (d’) und Ereigniskorrelierte Potentiale (EKPs; N2pc (N2 posterior contralateral)) gemessen. Schwerpunkt aller Analysen war der visuelle Aufmerksamkeitsprozess in einer Konjunktionssuche, die als Aufgabe 2 in Doppelaufgaben implementiert wurde. Aufgabe 1 war stets eine Wahlunterscheidungsaufgabe. Die Verhaltens- und elektrophysiologischen Ergebnisse zeigten, dass die Reaktionsauswahl in Aufgabe 1 und die visuelle Aufmerksamkeit (d.h. Merkmalsbindung) in Aufgabe 2 parallel verarbeitet wurden unabhängig von der Stimulusmodalität in Aufgabe 1, der Schwierigkeit der Reaktionsauswahl in Aufgabe 1 und der Darbietungsform des Stimulusdisplays in Aufgabe 2. Außerdem wurde eine Methode entwickelt, um die Anzahl der Objekte zu berechnen, die parallel zur Reaktionsauswahl verarbeitet wurden. Die Berechnungen stützten die Konklusion, dass die Reaktionsauswahl und die visuelle Aufmerksamkeit unterschiedlichen Kapazitätslimitationen unterliegen. / Response selection and visual attention are limited in capacity. Concerning dual-tasks of the Psychological Refractory Period (PRP) paradigm, it is assumed that response selection of Task 1 and Task 2 are processed sequentially. On the other hand, concerning conjunction search, it is assumed that visual attention selects the items and binds the item features resulting in a serial search process. In the present dissertation I investigated whether visual attention (i.e., feature binding) is subject to the same bottleneck mechanism as response selection in dual-tasks. Sequential processing of response selection and visual attention would provide evidence that both processes rely on a common capacity limitation, whereas concurrent processing would provide evidence that they rely on distinct capacity limitations. Reaction time (RT) measures based on the locus-of-slack method, target detectability measures based on d’, and the event-related potential (ERP) technique to measure the N2pc (N2 posterior contralateral) were combined to investigate this question. Analyses focused on visual attention deployment in a conjunction search task, which was implemented as Task 2 in dual-task situations. Task 1 was a choice discrimination task. Both tasks were presented at variable temporal overlap (Stimulus Onset Asynchrony, SOA). The behavioral and N2pc results showed that response selection in Task 1 and visual attention (i.e., feature binding) in Task 2 operated concurrently irrespective of the stimulus modality in Task 1, the response selection difficulty in Task 1 and the type of presentation of the search display in Task 2. Based on a method that was developed in the present dissertation, it was possible to calculate how many items of the search display were processed in parallel to response selection. The results supported the conclusion that response selection and visual attention rely on distinct capacity limitations.

Decision making for fast-moving consumer goods involves a choice between numerous similar alternatives. Under such demanding circumstances, a decision is made for one product. The decision is dependent on the interaction between the environment and the mind of the consumer, both of which are filled with information that can influence the outcome. The aim of this dissertation is to explore how the mind and the environment guides attention towards considered and chosen products in consumer decision making at the point-of-purchase. Consumers are equipped with several effort reduction strategies to simplify complex decision making. The selection of strategies can be conscious or automatic and driven by information in the environment or the mind of the decision maker. The selected decision strategy reduces the set of options to one alternative in an iterative process of comparisons that are fast and rely on perceptual cues to quickly exclude irrelevant products. This thesis uses eye-tracking to explore this rapid processing that lacks conscious access or control. The purpose is to explore how product packaging and placement (as in-store factors), and recognition, preferences, and choice task (as out-of-store factors) influence the decision-making process through visual attention. The results of the 10 experiments in the five papers that comprise this thesis shed new light on the role of visual attention in the interaction between the environment and the mind, and its influence on the consumer. It is said that consumers choose with their eyes, which means that unseen is unsold. The results of this thesis show that it is just as important to be comprehended as it is to be seen. In split-second decision making, the ability to recognize and comprehend a product can significantly impact preferences. Comprehension stretches beyond perception as consumers infer value from memory structures that influence attention. Hence, the eye truly sees what the mind is prepared to comprehend.

Summaries in Afrikaans and English / Text in Afrikaans / Die waarde van visueel-perseptuele skoling of terapie vir visueel-perseptueel gestremde leerlinge as 'n subgroep van leergestremdheid, is reeds vir dekades 'n omstrede aangeleentheid. Hierdie omstredenheid is ondersoek aan die hand van sewe internasionaal erkende psigometriese toetse. Die interne konsekwentheidskoeffisiente van hierdie toetse het vir die huidige studie van 0,62 tot 0,95 gestrek. 'n Faktorontleding van die toetsinterkorrelasies het 'n gemeenskaplike faktor blootgele. Ses toetse was primer visueel-perseptueel, en Goodenough <1926> se skaal is vir die bepaling van intelligensie gebruik. Bykomend hiertoe, is leerlinge se prestasies in hul eerste taal, wiskunde en skrif gebruik om die effek van terapie te bepaal. Proefpersone is as visueel-perseptueel gestremd gediagnoseer deur 'n opvoedkundige sielkundige en 'n visuele skolingsentrum in Pretoria, waar eksper imentele leerlinge terapie ontvang het. Hierdie diagnoses is deur die Test for Visual Analysis Skills wat beduidend tussen normale en visueelperseptueel gestremdes onderskei, bevestig. Die toets se geldigheid vir Suid-Afrikaanse omstandighede is in 'n voorstudie bepaal. Honderd en ses, ses- tot negejarige proefpersone (82 seuns en 24 dogters>, van normale intelligensie, gesigskerpte en gehoor, is betrek. Drie en vyftig het die eksperimentele groep gevorm wat onderverdeel is in 32 wat terapie voltooi het, en 21 wat nie het nie. Hierdie leerlinge is individueel afgepaar met kontroleleerlinge van dieselfde geslag, ouderdom, huistaal, sosio-ekonomiese status en skoolstanderd. Eksperimentele leerlinge het visuele terapie in n breer groepsverband vir een uur per week ontvang. Terapieperiodes het van 4 tot 15 maande gewissel. Die eksperimentele ontwerp was 'n voortoets-natoets-tweegroepontwerp. t-Toetse vir afhanklike (afgepaarde) groepe is uitgevoer op die verskille tussen voor- en natoetstellings, asook tussen die eksperimentele en kontrolegroepe. Geeneen van die primer visueel-oerseptuele meettegnieke het beduidende resultate opgelewer nie. Dit is aanduidend van die ondoeltreffendheid van visueel-perseptuele terapie om die tekorte waarop dit gemik is, reg te stel. Die waarde van visueel-perseptueie terapie is inteendeel beperk tot 'n oorhoofse verbetering in konseptualisering en intellektuele ryping by die groep wat terapie voltooi het. Skrif was die enigste vak wat by dieselfde groep beduidend verbeter het. Hierdie resultaat is egter twyfelagtig vanwee beoordelingstekorte. / The value of visual perceptual training or therapy, to visually perceptually impaired pupils as a subgroup of the learning disabled, has been a controversy far decades. This controversy was investigated by means of seven internationally recognised psychometric tests. The internal consistency coefficients of these tests for the present study ranged from 0,62 to 0,95. A factor analysis of test intercorrelations revealed a common factor. Six tests were primarily visual perceptual, whilst the Goodenough (1926) scale determined intelligence. Additionally, pupils' performance in their first language, mathematics and writing, was used to assess the therapeutic effect. Subjects were diagnosed as visually perceptually impaired by an educational psychologist and a visual training centre in Pretoria where experimental pupils received therapy. These diagnoses were confirmed by the Test for Visual Analysis Skills, which significantly differentiates between the normal and visually perceptually impaired. This test's validity for South African circumstances was determined in a prestudy. One hundred and six, six to nine year old subjects <82 boys and 24 girls>, of normal intelligence, visual acuity and hearing, were involved. Fifty three formed the experimental group which was subdivided in 32 who completed therapy, and 21 who did not. These pupils were individualiy matched with controls of similar sex, age, home language, socio economic status and school standard. Experimental pupils received visual therapy within a broader group context for one hour per week. Therapy periods fluctuated between 4 and 15 months. The experimental design was a pretest-posttest two group design. t-Tests for dependant <matched) groups were conducted on the differences between pre and oosttest scores, as well as between the experimental and control groups. None of the primarily visual perceptual tests revealed significant results. This signifies the inefficiency of visual perceptual therapy to rectify the deficits at which it is directed. The value of visual perceptual therapy is, on the contrary, restricted to an overall improvement in conceptualization and intellectual maturation within the group which completed therapy. Writing was the only subject which improved significantly within the same group. However, this result is dubious, due to evaluation deficits. / Psychology / D.Litt. et Phil. (Psychology)

Uma das tarefas básicas dos mecanismos atencionais é decidir qual a localização dentro do campo visual, em que devemos prestar atenção primeiro. Um objeto que contenha características distintas, tais como orientação, forma, cor, tamanho, brilho, textura, etc. diferentes, pode atrair a atenção de uma maneira \"bottom-up\". A informação \"top-down\" baseia-se no conhecimento prévio e tem uma grande influência nas localizações atendidas. Inspirado nos mecanismos da Atenção Visual Humana, embora sem a pretensão de simulá-la, este trabalho prevê o desenvolvimento de uma nova metodologia que integra os dois tipos de informações: \"bottom-up\" e \"top-down\". Características \"bottom-up\" são geradas a partir de Momentos e essas informações são utilizadas em mapas de saliência, enquanto que um conhecimento prévio é utilizado para gerar pistas \"top-down\". Neste trabalho, desenvolveu-se uma metodologia específica para a busca e o reconhecimento visual em cenas com múltiplos objetos, utilizando para isso uma rede \"fuzzy\" contendo três subsistemas \"fuzzy\". Dada uma imagem de entrada, o objetivo consiste em se detectar regiões que possam conter informações mais significativas, a fim de que se possa guiar e restringir processamentos mais complexos. A inclusão de mecanismos de atenção (seleção de uma região de interesse dentro da imagem) é de fundamental importância pois os resultados obtidos pelo método podem ser usados para controlar a aquisição da imagem de uma maneira dinâmica. O modelo proposto está estruturado em três estágios principais: O primeiro estágio consiste em se segmentar os objetos e extrair características globais dos mesmos baseadas principalmente na teoria dos momentos, tais como tamanho, orientação, formato e distância e também média de nível de cinza. Por intermédio da comparação de um objeto com os outros presentes na cena, características \"bottom-up\" de conspicuidade são usadas para guiar a atenção ao objeto mais diferente. Por intermédio do uso da lógica \"fuzzy\" é possível inferir com grande flexibilidade algumas regras de decisão baseadas nos princípios de percepção visual tais como as leis Gestalt. O segundo estágio consiste de um subsistema \"fuzzy top-down\" que combina diferentes características de acordo com a relevância das mesmas em diferentes tarefas. Finalmente, o terceiro estágio consiste de um subsistema \"fuzzy\" que integra as informações obtidas dos subsistemas anteriores e fornece um índice geral de saliência, e indica a provável localização do objeto a ser reconhecido. A nova abordagem foi testada com objetos geométricos levando-se em consideração as características que atraem a atenção dos serem humanos / One of the basic tasks assigned to the human attentional mechanisms is to decide which location in the visual field we must pay attention first. An object containing distinctive features (such as different orientation, shape, color, size, shine, texture, etc.) can attract attention in a bottom-up way. Top-down information is based on the previous knowledge and has a large influence on the attended locations. Inspired on human visual attention mechanisms, although it doesn\'t want simulate it, this work presents a new methodology to integrate two different kind of information: bottom-up and top-down. Bottom-up features are obtained from Moment Theory and this information is used in salience maps, while a previous knowledge is used to create top-down hints. In this work, an specific methodology to visual search and recognition was developed to be applied to scenes containing multiple objects by a fuzzy net with three fuzzy subsystems. The aim of this methodology is to detect regions that may contain the most significant information, in order to guide and to restrict most complex processing. The inclusion of attentional mechanisms (the selection of a region of interest in the image) is fundamental and can be used to control the image acquisition in a dynamic way. The proposed model is structured in three main stages. The first stage segments the objects and extracts global features of them, based on the Moment Theory such as size, orientation, shape and distance and gray level average. By comparing one object with the other ones present in the scene, bottom-up features of conspicuity are used to guide the attention to the most different object. The Fuzzy Logic allows us to infer with great flexibility some of decision rules based on the visual perception principles such as the Gestalt Laws. The second stage is a top-down fuzzy subsystem that combines different features according to the relevance of them in different tasks. Finally, the third stage is a fuzzy subsystem that integrates the information obtained from the previous sub-systems and gives us a general salience index. The new methodology was tested in geometrical objects considering the feature that attracts attention to human beings

Le niveau d'exigence minimum pour tout système 3D (images stéréoscopiques) est de garantir le confort visuel des utilisateurs. Le confort visuel est un des trois axes perceptuels de la qualité d'expérience (QoE) 3D qui peut être directement lié aux paramètres techniques du système 3D. Par conséquent, le but de cette thèse est de caractériser objectivement l'impact de ces paramètres sur la perception humaine afin de contrôler la qualité stéréoscopique. La première partie de la thèse examine l'intérêt de prendre en compte l'attention visuelle des spectateurs dans la conception d'une mesure objective de qualité 3D. Premièrement, l'attention visuelle en 2D et 3D sont comparées en utilisant des stimuli simples. Les conclusions de cette première expérience sont validées en utilisant des scènes complexes avec des disparités croisées et décroisées. De plus, nous explorons l'impact de l'inconfort visuel causé par des disparités excessives sur l'attention visuelle. La seconde partie de la thèse est dédiée à la conception d'un modèle objectif de QoE pour des vidéos 3D, basé sur les seuils perceptuels humains et le niveau d'acceptabilité. De plus nous explorons la possibilité d'utiliser la modèle proposé comme une nouvelle échelle subjective. Pour la validation de ce modèle, des expériences subjectives sont conduites présentant aux sujets des images stéréoscopiques fixes et animées avec différents niveaux d'asymétrie. La performance est évaluée en comparant des prédictions objectives avec des notes subjectives pour différents niveaux d'asymétrie qui pourraient provoquer un inconfort visuel. / The minimum requirement for any 3D (stereoscopic images) system is to guarantee visual comfort of viewers. Visual comfort is one of the three primary perceptual attributes of 3D QoE, which can be linked directly with technical parameters of a 3D system. Therefore, the goal of this thesis is to characterize objectively the impact of these parameters on human perception for stereoscopic quality monitoring. The first part of the thesis investigates whether visual attention of the viewers should be considered when designing an objective 3D quality metrics. First, the visual attention in 2D and 3D is compared using simple test patterns. The conclusions of this first experiment are validated using complex stimuli with crossed and uncrossed disparities. In addition, we explore the impact of visual discomfort caused by excessive disparities on visual attention. The second part of the thesis is dedicated to the design of an objective model of 3D video QoE, which is based on human perceptual thresholds and acceptability level. Additionally we explore the possibility to use the proposed model as a new subjective scale. For the validation of proposed model, subjective experiments with fully controlled still and moving stereoscopic images with different types of view asymmetries are conducted. The performance is evaluated by comparing objective predictions with subjective scores for various levels of view discrepancies which might provoke visual discomfort.

Lorsque le système visuel est confronté à un nouvel environnement, un nombre trop important d’informations lui parvient en même temps. De façon précoce, avant tout mouvement oculaire, l’attention explore automatiquement la scène pour sélectionner les éléments d’intérêt. Des recherches récentes ont montré que cette exploration du champ visuel ne se faisait pas aléatoirement, mais se basait sur la saillance des éléments visuels. La saillance est une caractéristique qui émerge de la comparaison des éléments visuels entre eux, par exemple une fleur jaune dans un jardin de fleurs rouges va être considérée comme plus saillante que son voisinage. En permanence et de façon continue, une hiérarchie des éléments est établie à un niveau préattentif ; ils sont triés du plus au moins saillant, et l’attention se base sur cet organisation pour progresser dans le champ visuel. Les recherches présentées dans ce document avaient pour objectif d’investiguer les mécanismes de ce phénomène : quels sont les mécanismes cognitifs impliqués dans la progression de l’attention sur la base de la hiérarchie de la saillance ? Le présent document regroupe des articles qui cherchent à répondre à cette question grâce à des travaux en Psychologie expérimentale. Par ailleurs, de nombreux travaux de Psychologie, Neurophysiologie et Neuroimagerie se sont penchés sur le substrat neural de l’attention visuelle et ont révélé un ensemble de structures clés qui sous-tendraient les mécanismes responsables des fonctions attentionnelles. Cependant, vis-à-vis de la progression de l’attention sur la base de la saillance, seule une étude récente a pu apporter des indices quant au rôle de certaines voies visuelles. Les recherches présentées ici avaient donc également pour objectif de définir ces voies visuelles et les structures corticales et sous-corticales qui les composent, pour investiguer leurs rôles dans la hiérarchie de la saillance et la progression de l’attention. Le présent document regroupe des travaux qui ont exploré ces aspects par le biais de l’approche Psychophysique et Electroencéphalographique. / When confronted to a new environment, the visual system faces too much information intake and cannot process it all at once. Before any eye movement, early automatic attention explores the visual scene in order to select relevant items.Recent research revealed that the exploration of the visual scene is not a random process, but is based on the respective saliency of the items in the field. Salience is not a characteristic of an item per se but is emerging as a result of the comparison between an item and its visual neighborhood. For instance, a yellow flower in a garden of red flowers will be considered as more salient than the others in its visual neighborhood. Thus, a hierarchical ordering of the items is continuously established in a preattentive stage, and consists in a sorting of every element from the most to the least salient. Attention, then, relies on this hierarchy to progress in the visual field. The present dissertation had for objective to investigate the cognitive mechanisms involved in this phenomenon: what mechanisms support the salience-based progression of visual attention? Several papers are reported here and explored this question with experimental Psychology.Moreover, numerous works in Psychology, Neurophysiology and Neuroimaging took interest in the neural substrate of visual attention and revealed several key-structures that would subtend the mechanisms involved in attentional functions. However, when it comes to the salience-based progression of attention, only one study could bring cues of the involvement of certain visual pathways in this phenomenon. Another objective of the present dissertation was to define the cortical and sub-cortical structures that constitute those pathways, in order to explore their roles in the salience-base progression of attention. Several papers in the present report are investigating this aspect through Psychophysics and Electroencephalography studies.