To see the other types of publications on this topic, follow the link: Visual perception. Optical illusions.
Dissertations / Theses on the topic 'Visual perception. Optical illusions'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 37 dissertations / theses for your research on the topic 'Visual perception. Optical illusions.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Franceschiello, Benedetta. "Cortical based mathematical models of geometric optical illusions." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066131/document.
Full textAbstract:
Cette thèse présente des modèles mathématiques pour la perception visuelle et s'occupe des phénomènes où on reconnait une brèche entre ce qui est représenté et ce qui est perçu. La complétion amodale consiste en percevoir un complètement d'un object qui est partiellement occlus, en opposition avec la complétion modale, dans laquelle on perçoit un object même si ses contours ne sont pas présents dans l'image [Gestalt, 99]. Ces contours, appelés illusoires, sont reconstruits par notre système visuelle et ils sont traités par les cortex visuels primaires (V1/V2) [93]. Des modèles géométriques de l'architecture fonctionnelle de V1 on le retrouve dans le travail de Hoffman [86]. Dans [139] Petitot propose un modèle pour le complètement de contours, équivalent neurale du modèle proposé par Mumford [125]. Dans cet environnement Citti et Sarti introduisent un modèle basé sur l'architecture fonctionnelle de la cortex visuel [28], qui justifie les illusions à un niveau neurale et envisage un modèle neuro-géometrique pour V1. Une autre classe sont les illusions d'optique géométriques (GOI), découvertes dans le XIX siècle [83, 190], qui apparaissent en présence d'une incompatibilité entre ce qui est présent dans l'espace object et le percept. L'idée fondamentale développée ici est que les GOIs se produisent suite à une polarisation de la connectivité de V1/V2, responsable de l'illusion. A partir de [28], où la connectivité qui construit les contours en V1 est modelée avec une métrique sub-Riemannian, on étend cela en disant que pour le GOIs la réponse corticale du stimule initial module la connectivité, en devenant un coefficient pour la métrique. GOIs seront testés avec ce modèle<br>This thesis presents mathematical models for visual perception and deals with such phenomena in which there is a visible gap between what is represented and what we perceive. A phenomenon which drew the interest most is amodal completion, consisting in perceiving a completion of a partially occluded object, in contrast with the modal completion, where we perceive an object even though its boundaries are not present [Gestalt theory, 99]. Such boundaries reconstructed by our visual system are called illusory contours, and their neural processing is performed by the primary visual cortices (V1/V2), [93]. Geometric models of the functional architecture of primary visual areas date back to Hoffman [86]. In [139] Petitot proposed a model of single boundaries completion through constraint minimization, neural counterpart of the model of Mumford [125]. In this setting Citti and Sarti introduced a cortical based model [28], which justifies the illusions at a neural level and provides a neurogeometrical model for V1. Another class of phenomena are Geometric optical illusions (GOIs), discovered in the XIX century [83, 190], arising in presence of a mismatch of geometrical properties between an item in object space and its associated percept. The fundamental idea developed here is these phenomena arise due to a polarization of the connectivity of V1/V2, responsible for the misperception. Starting from [28] in which the connectivity building contours in V1 is modeled as a sub-Riemannian metric, we extend it claiming that in GOIs the cortical response to the stimulus modulates the connectivity of the cortex, becoming a coefficient for the metric. GOIs will be tested through this model
2
Elliott, David B., Anna Vale, David J. Whitaker, and John G. Buckley. "Does my step look big in this? A visual illusion leads to safer stepping behaviour." Public Library of Science, 2009. http://hdl.handle.net/10454/3265.
Full textAbstract:
Background.
Tripping is a common factor in falls and a typical safety strategy to avoid tripping on steps or stairs is to increase foot clearance over the step edge. In the present study we asked whether the perceived height of a step could be increased using a visual illusion and whether this would lead to the adoption of a safer stepping strategy, in terms of greater foot clearance over the step edge. The study also addressed the controversial question of whether motor actions are dissociated from visual perception.
Methodology/Principal Findings.
21 young, healthy subjects perceived the step to be higher in a configuration of the horizontal-vertical illusion compared to a reverse configuration (p = 0.01). During a simple stepping task, maximum toe elevation changed by an amount corresponding to the size of the visual illusion (p<0.001). Linear regression analyses showed highly significant associations between perceived step height and maximum toe elevation for all conditions.
Conclusions/Significance.
The perceived height of a step can be manipulated using a simple visual illusion, leading to the adoption of a safer stepping strategy in terms of greater foot clearance over a step edge. In addition, the strong link found between perception of a visual illusion and visuomotor action provides additional support to the view that the original, controversial proposal by Goodale and Milner (1992) of two separate and distinct visual streams for perception and visuomotor action should be re-evaluated.<br>College of Optometrists
3
Kabir, Fatema Q. "Phenomenon of Visual Perception Seen Over Wexner Center for Visual Arts and Knowlton School of Architecture." The Ohio State University, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=osu1229295464.
Full text
4
Hu, Gang. "Effect of visual and non-visual cues in the generation of reorientation illusions." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0020/MQ56182.pdf.
Full text
5
Dyde, Richard Thomas. "Illusions of visual orientation : comparisons between perceptual and visuo-motor tasks." Thesis, Durham University, 2001. http://etheses.dur.ac.uk/4265/.
Full textAbstract:
The Milner and Goodale (1995) model of dual cortical visual systems suggests that, in the primate cortex, separate neural substrates dominate the tasks of visual perception and visuo-motor control. This model derives from a number of independent sources of evidence: anatomical, physiological and behavioural. Neuropsychological evidence in humans suggests that visual perception and visuo-motor control can be selectively impaired through damage to the ventral and dorsal visual streams respectively. Evidence has emerged that in the healthy human visual cortex, differentiable effects of visual illusions can be found between the two measures of perception and visuo- motor control. This evidence has been cited to support the Milner and Goodale (1995) model. The series of studies reported in this dissertation used a similar, but methodologically revised application of the illusion paradigm in the novel domain of orientation. Using two types of visual illusions, the simultaneous tilt illusion (STI) and the rod-and-frame illusion (RFI), a series of studies found patterns of association, dissociation and interaction that strongly support the Mihier and Goodale model. The critical issue, in terms of predicting the pattern of effects across perception and visuo-motor control tasks, was found to be the siting of the causal mechanisms underlying the illusion employed.
6
Goebel, Rainer. "Visual illusions and auditory hallucinations scanning the neural correlates of perception /." Maastricht : Maastricht : Maastricht University ; University Library, Maastricht University [Host], 2000. http://arno.unimaas.nl/show.cgi?fid=12675.
Full text
7
Walter, Elizabeth Leigh. "Visuospatial contextual processing : illusions, hidden figures and autistic traits /." view abstract or download file of text, 2007. http://proquest.umi.com/pqdweb?did=1324388371&sid=3&Fmt=2&clientId=11238&RQT=309&VName=PQD.
Full textAbstract:
Thesis (Ph. D.)--University of Oregon, 2007.<br>Typescript. Includes vita and abstract. Includes bibliographical references (leaves 173-184). Also available for download via the World Wide Web; free to University of Oregon users.
8
Boe, Maria. "Utilizing Visual Illusions To Identify and Understand Perceptual Discrepancies in Product Design." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/35840.
Full textAbstract:
There are often discrepancies in how a product is perceived in different representation media employed in typical product development processes. The first goal of this research project was to determine how visual illusions influence a designer's perception of a product across three representations: industrial design sketches, computer aided design (CAD) models, and physical prototypes (FDM rapid prototyping). A visualization experiment was conducted in which participants were asked to report how they perceived the shape and size of certain features, representing two types of illusions across the three model representations. Their statements were analyzed to identify the trends of how these two illusions affect overall appearance, categorized by representation type and the users' backgrounds (i.e., specialization and years of experience). The participants included students and professionals with various levels of engineering and industrial design experience. The analysis shows that there are differences in how designers see models depending on the representation media, and to some degree depending on the participants' professional background. The second goal was to explore the process of identifying such illusions automatically during the design process. In this regard, a discussion on how to implement the results from the visualization experiment is presented. Emphasis is on the potential development of a tool in CAD systems that would identify illusory effects and subsequently suggest potential design solutions. The possibility of using spectral analysis (fast Fourier transform) for an automated shape recognition capability in CAD systems is discussed.<br>Master of Science
9
Knol, Hester. "Aiming for illusions : the perception of size and its influence on motor control." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4099.
Full textAbstract:
L’hypothèse des voies visuelles attribue des rôles fonctionnels spécifiques aux réseaux cérébraux ventral et dorsal du système visuel. Ce modèle émet l’hypothèse selon laquelle la voie ventrale sous-tend le traitement de l'information pour la perception (vision-for-perception), alors que la voie dorsale est impliquée dans le traitement de l'information pour l'action (vision-for-action). L'idée de deux réseaux visuels distincts dans le cerveau humain a fait l’objet de très nombreux travaux de recherche au cours des 20 dernières années, mais les résultats apparaissent contradictoires. Cette thèse vise à éclaircir une partie du mystère de la façon dont la perception et l'action s’articulent. La figure d’Ebbinghaus a été utilisée pour distinguer la fonction d’une vision pour la perception, sensible aux illusions visuelles (taille relative), de la fonction d’une vision pour l’action affectée par les propriétés physiques de l’objet. Dans une première étude, nous avons quantifié l’illusion d’Ebbinghaus. Après, une démarche comparable de caractérisation des mouvements visuomoteurs a été implémentée sous des contraintes de précision et de vitesse. La caractérisation des mouvements visuomoteurs et la quantification de la perception des configurations Ebbinghaus ont ensuite permis de concevoir une tâche visuomotrice dont les cibles étaient des figures d’Ebbinghaus.La thèse a démontré que les voies ventrale et dorsale ne sont pas strictement distinctes fonctionnellement. Différentes variables informationnelles sont potentiellement utilisées pour ‘la vision pour la perception’ et ‘la vision pour l’action’ indépendamment du fait que certaines variables causent des illusions<br>The influential two-visual streams hypothesis ascribes specific functional roles to the ventral and the dorsal network of the visual system. The ventral system has been hypothesized to process information for conscious perception (vision-for-perception), whereas the dorsal stream processes information for action (vision-for-action). The idea of two separate visual networks in the human brain inspired an enormous amount of research over the past 20 or so years. The results are conflicting and divisive about the idea, causing a seemingly insurmountable gap between supporters and opponents. This thesis aims to unravel a part of the jigsaw puzzle of how perception and action are functioning. The Ebbinghaus figure has been used to distinguish vision-for-perception that is susceptible to visual illusions (i.e., relative size) from vision-for-action that remain unaffected by perceptions of relative sizes. Therefore, we quantified the Ebbinghaus figure based on its geometry and systematically assessed its size illusion. Subsequently, a visuomotor task was implemented in which precision and speed of the voluntary movement were investigated. The description of the visuomotor task and of the perception of Ebbinghaus figures lead to combine both visuomotor task and Ebbinghaus figures. A dynamical model was fit to the experimental data to investigate the effect on the behavioral dynamics.This thesis demonstrated that the ventral stream and dorsal stream are not strictly functionally distinct, and that potentially different informational variables are used for ‘vision for perception’ and ‘vision for action’ irrespective of whether certain variables cause (perceptual) illusions
10
Perotti, Victor J. "The visual perception of surface orientation and structural rigidity from optical motion /." The Ohio State University, 1997. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487946776023705.
Full text
11
Henderson, A. Steven. "The effects of imposed image movement on visual disappearances /." Thesis, McGill University, 1987. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=63951.
Full text
12
Fink, Charles G. "A study of the brain's transfer function for edge perception /." Online version of thesis, 1987. http://hdl.handle.net/1850/11189.
Full text
13
Peng, Qinmu. "Visual attention: saliency detection and gaze estimation." HKBU Institutional Repository, 2015. https://repository.hkbu.edu.hk/etd_oa/207.
Full textAbstract:
Visual attention is an important characteristic in the human vision system, which is capable of allocating the cognitive resources to the selected information. Many researchers are attracted to the study of this mechanism in the human vision system and have achieved a wide range of successful applications. Generally, there are two tasks encountered in the visual attention research including visual saliency detection and gaze estimation. The former is normally described as distinctiveness or prominence as a result of a visual stimulus. Given images or videos as input, saliency detection methods try to simulate the mechanism of human vision system, predicting and locating the salient parts in them. While the later involves physical device to track the eye movement and estimate the gaze points. As for saliency detection, it is an effective technique for studying and mimicking the mechanism of the human vision system. Most of saliency models can predict the visual saliency with the boundary or the rough location of the true salient object, but miss the appearance or shape information. Besides, they pay little attention to the image quality problem such as low-resolution or noises. To handle these problems, in this thesis, we propose to model the visual saliency from local and global perspectives for better detection of the visual saliency. The combination of the local and global saliency scheme employing different visual cues can make fully use of their respective advantages to compute the saliency. Compared with existing models, the proposed method can provide better saliency with more appearance and shape information, and can work well even in the low-resolution or noisy images. The experimental results demonstrate the superiority of the proposed algorithm. Next, video saliency detection is another issue for the visual saliency computation. Numerous works have been proposed to extract the video saliency for the tasks of object detection. However, one might not be able to obtain desirable saliency for inferring the region of foreground objects when the video presents low contrast or complicated background. Thus, this thesis develops a salient object detection approach with less demanding assumption, which gives higher detection performance. The method computes the visual saliency in each frame using a weighted multiple manifold ranking algorithm. It then computes motion cues to estimate the motion saliency and localization prior. By adopting a new energy function, the data term depends on the visual saliency and localization prior; and the smoothness term depends on the constraint in time and space. Compared to existing methods, our approach automatically segments the persistent foreground object while preserving the potential shape. We apply our method to challenging benchmark videos, and show competitive or better results than the existing counterparts. Additionally, to address the problem of gaze estimation, we present a low cost and efficient approach to obtain the gaze point. As opposed to eye gaze estimation techniques requiring specific hardware, e.g. infrared high-resolution camera and infrared light sources, as well as a cumbersome calibration process. We concentrate on visible-imaging and present an approach for gaze estimation using a web camera in a desktop environment. We combine intensity energy and edge strength to locate the iris center and utilize the piecewise eye corner detector to detect the eye corner. To compensate for head movement causing gaze error, we adopt a sinusoidal head model (SHM) to simulate the 3D head shape, and propose an adaptive weighted facial features embedded in the pose from the orthography and scaling with iterations algorithm (AWPOSIT), whereby the head pose can be estimated. Consequently, the gaze estimation is obtained by the integration of the eye vector and head movement information. The proposed method is not sensitive to the light conditions, and the experimental results show the efficacy of the proposed approach
14
Ye, Ming. "Robust visual motion analysis : piecewise-smooth optical flow and motion-based detection and tracking /." Thesis, Connect to this title online; UW restricted, 2002. http://hdl.handle.net/1773/6077.
Full text
15
Corbo, Julien. "Des illusions tactiles à l’intégration spatiotemporelle dans le cortex somesthésique primaire : influence de la temporalité des stimuli cutanés sur leur représentation corticale." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0505.
Full textAbstract:
Plusieurs illusions tactiles suggèrent que la temporalité des stimulations cutanées dans une séquence modifie leur perception spatiale. S’ils sont assez proches dans l’espace, plus l’intervalle temporel entre deux stimuli est court, plus la distance perçue entre eux est courte. Lorsque les deux stimuli sont présentés simultanément, on observe une perception fusionnée, unique et centrée entre les positions réelles. Ainsi, le système de perception tactile semble utiliser le temps entre les stimuli pour estimer l’espace qui les sépare. Dans l’optique de comprendre comment cette règle perceptive est implémentée dans le système nerveux, nous avons étudié la représentation corticale des stimulations qui induisent ces illusions. Nous avons recherché les distorsions spatiales de la représentation somatotopique dans le cortex somesthésique primaire, à la suite de l’application séquentielle ou simultanée d’une paire de stimuli cutanés sur l’extrémité des phalanges distales de la patte antérieure chez le rat anesthésié. Avec des enregistrements électrophysiologiques et d’imagerie optique extrinsèque, nous avons mis en évidence un phénomène de fusion corticale des entrées sensorielles simultanées, avec un patron spatial d’activation unimodal, centré entre les représentations individuelles des doigts adjacents costimulés. Dans le cas de stimuli successifs, nous avons observé des modifications des réponses au deuxième stimulus dépendantes de l’intervalle inter stimuli. Cette intégration spatiotemporelle ne semble pas contribuer directement au raccourcissement des distances perçues, mais pourrait favoriser les erreurs de localisation constatées lors de la perception des illusions<br>Several tactile spatiotemporal illusions suggest that the timing of successive cutaneous stimulations modify the perception of their spatial location. If they are close enough in time and space, shorter inter-stimuli time intervals (ISI) lead to shorted perceived distances. To the extreme of this time-space relation, when the stimuli are simultaneous, subjects report the merged perception of a unique and centered point of stimulation. Therefore, the tactile perceptual system seems to use the time separating two stimuli to compute their spatial distance. To understand the implementation of this perceptual rule, one can investigate the neural representation of the stimuli that elicit the illusory percept, looking for spatial distortions and their underlying mechanisms. Studies based on the measure of the hemodynamic responses have shown such distortions of the somatotopic representations in the primary somatosensory cortex, for simultaneous and delayed stimulations. In order to enhance our understanding of the elementary phenomenon that underpins those spatial modifications of the sensory inputs, we investigated the cortical representation of pairs of simultaneous and delayed cutaneous stimuli in the S1 of anesthetized rats. Using electrophysiological recordings and extrinsic optical imaging, we revealed the cortical merging of inputs from simultaneous digits stimulation. When the stimuli were delayed, we observed ISI-dependent modulations of the responses to the second stimulus. This spatiotemporal integration, that didn’t seem to contribute directly to a distance contraction effect, could however favor the mislocalization observed in illusory perception
16
Pirrotta, Elizabeth. "Testing chromatic adaptation models using object colors /." Online version of thesis, 1994. http://hdl.handle.net/1850/11674.
Full text
17
Hilger, James Daniel. "Contour integration and interpolation geometry, phenomenology, and multiple inputs /." Diss., Restricted to subscribing institutions, 2009. http://proquest.umi.com/pqdweb?did=1973074431&sid=1&Fmt=2&clientId=1564&RQT=309&VName=PQD.
Full text
18
Surkys, Tadas. "Ryškio ir spalvos kontrasto įtaka stimulo geometrijos suvokimo iškraipymams." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2007. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2007~D_20070403_153129-87925.
Full textAbstract:
Distortions of perception of the Müller-Lyer, Delboeuf, Oppel-Kundt and Zöllner type have been studied in psychophysical experiments conducted under computer control with a program of our own design arranging the stimuli, presenting them on the monitor, introducing alterations according to the subject’s command, recording responses, and handling the results.
Our illusory figures designed by heteroluminant colours yielded the effects of perceived distortion qualitatively and quantitatively similar to the effects evoked by the white and black figures.
Variations of luminance of colours of the figures and backgrounds within a relatively wide interval of its values did not evoke a noticeable change in strength of the perceived distortions, but if the luminance of the stimulus colour approached the magnitude which was determined as isoluminant with the background colour, the strength of the distortions changed significantly; it increased for the Brentano figure and decreased for the Delboeuf, Oppel-Kundt and Zöllner figures. The curves obtained for different subjects with different colour combinations were similar in shape, though horizontal parts and peaks of the curve were not at the same level.
For isoluminant figures, the experimental curves demonstrating the strength variations of the perceived distortions in dependence of spatial parameters of the stimuli were similar in shape with the curves for heteroluminant figures, but lay above (Brentano) or below (Delboeuf... [to full text]
19
Rocha, Rafael Santos. "Influência do observador, do iluminante e do ângulo de visualização na perceptibilidade e aceitabilidade de diferenças de brilho superficial de resinas compostas." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/152401.
Full textAbstract:
Submitted by Rafael Santos Rocha null (rafaelrocha_ss@hotmail.com) on 2017-12-21T01:55:24Z
No. of bitstreams: 1
Dissertação mestrado - Rafael.pdf: 2092949 bytes, checksum: 7ff26a28718621a3aac72898b8ba2eb3 (MD5)<br>Submitted by Rafael Santos Rocha null (rafaelrocha_ss@hotmail.com) on 2017-12-21T12:31:26Z
No. of bitstreams: 1
Dissertação mestrado - Rafael.pdf: 2092949 bytes, checksum: 7ff26a28718621a3aac72898b8ba2eb3 (MD5)<br>Approved for entry into archive by Silvana Alvarez null (silvana@ict.unesp.br) on 2018-01-04T15:18:48Z (GMT) No. of bitstreams: 1
rocha_rs_me_sjc.pdf: 2002864 bytes, checksum: 354dae44b5fb5e16adc9be584300a8eb (MD5)<br>Made available in DSpace on 2018-01-04T15:18:48Z (GMT). No. of bitstreams: 1
rocha_rs_me_sjc.pdf: 2002864 bytes, checksum: 354dae44b5fb5e16adc9be584300a8eb (MD5)
Previous issue date: 2017-12-13<br>Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)<br>O objetivo deste trabalho foi avaliar a influência de observadores sobre a percepção e aceitabilidade de brilho superficial de resinas compostas, sob diferentes iluminantes, em angulação livre e pré-determina em 60°. E ainda, determinar o limite de perceptibilidade e aceitabilidade da variação de unidade de brilho (∆UB) entre os espécimes. Foram confeccionados 8 espécimes cilíndricos de 6 mm de diâmetro e 1,5 mm de espessura de resina composta, bem como um espécime padrão de dente humano, com 0,5 mm de espessura em esmalte e 1 mm em dentina. Os espécimes receberam polimento a fim de que se obtivesse ao final do processo amostras com 10 UB, 20 UB, 30 UB, 40 UB, 50 UB, 60 UB, 70 UB e 80 UB e um padrão de dente humano de 80 UB. Foram selecionados 60 observadores (20 leigos, 20 alunos de graduação e 20 cirurgiões-dentistas). O estudo foi submetido e aprovado pelo comitê de ética local. Os participantes fizeram a qualificação do brilho superficial de resina composta em cabine de luz (Gti – Newburgh,NJ). Para tanto, as amostras foram posicionadas no interior da cabine, duas a duas de forma aleatória, de forma com que a luz incidisse sua superfície em um ângulo de 60°. Os observadores responderam perguntas específicas para se determinar o nível e limite de perceptibilidade das variações de brilho. Todas as análises foram realizadas em duas condições de iluminação, com iluminantes D65 e luz fluorescente. Cinquenta por cento dos observadores iniciaram as análises com ângulo de visualização livre, seguido da qualificação em angulação pré-definida em 60° e, os demais observadores fizeram as observações de forma oposta. Para o nível e limite de aceitabilidade da variação do brilho, as amostras foram individualmente comparadas com o padrão de dente humano. Os dados foram analisados pelo teste Modelo Generalizado Linear/Não-Linear PROBIT e regressão não-linear PROBIT (5%). Para a perceptibilidade, foram encontradas diferenças significantes para a variação de brilho (Δ UB) (p<0,001), para os observadores (p=0,043) e para os iluminantes (p<0,001), no entanto, não houve diferença entre o ângulo de visualização livre e fixo em 60° (p=0,303). Em relação à aceitabilidade, foram observadas diferenças significantes para a variação de brilho (Δ UB) (p<0,001), para os observadores (p=0,003), para os iluminantes (p=0,045) e no ângulo de visualização livre e fixo em 60° (p<0,001). Os limites de perceptibilidade e aceitabilidade, levando em consideração todos os fatores foi de 6,4 UB e 35,7 UB, respectivamente. Conclui-se que fatores rotineiramente encontrados em situações clínicas influenciam a perceptibilidade e aceitabilidade de diferenças de brilho superficial de resinas compostas e que apesar de perceberem limites menores de diferença de brilho, os observadores aceitam clinicamente diferenças cinco vezes maiores.
20
Lindahl, Daniel, and Henric Stodell. "A Human Factors Analysis of Optical Distortion in Automotive Glazing." Thesis, Linköping University, Department of Management and Engineering, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-8709.
Full textAbstract:
<p>The glazing is today a part of the car design. The customer is more or less taking for granted that his or her view from inside the car is a direct mirror of the outside world. With more complex shapes, lower installation angles and thinner glass it is a great challenge to produce even better quality at a lower price. While the windscreen is regulated by law, the lack of well specified requirements for the optics in the backlight (rear window), together with the absence of direct customer complaints, is causing the optical quality of the backlight to decrease. The requirements and measuring methods used today are described in technical terms and do not correspond to the human perception of optical distortion.</p><p>This report is a first step towards new technical requirements, for the optics of backlights, based on the driver’s perception of optical distortion. The knowledge of how optical transmission distortion occurs, how it should be measured and how it affects the driver, is essential in order to control it.</p><p>Several databases were searched and contacts with experts were established, in order to gain knowledge. The connection between the technical requirements and the human perception of optical distortion in backlights was investigated by using psychophysical methods. A within factorial design was employed with two independent variables; viewing distance from backlight to tailing object and fixation time (viewing time). The result showed a significant difference in perception of optical distortion between 25 and 75 metres. Moreover, optical distortion is, according to the test, more disturbing during free fixation time than for fixation times of about one second.</p><p>The requirements often used for backlights today (12 ± 5 millimetres) allow distortions that 68 percent of the test subjects perceived as disturbing. In order to please the test driver from Volvo the requirements need to be as high as 12 ± 2 millimetres, which correspond to the 96th percentile. Furthermore, the result confirms that dynamic measurements are needed to find a connection to human perception of optical distortion. The principles of a new measuring method that measures the deformation and the dynamic distortion were developed to show the possibilities of measuring what the driver perceives.</p><p>Even if a good measuring method can help controlling the produced glazing it is not enough to optimize the quality of the production. More important is the choice of thickness and curvature of the glass, the installation angle and the manufacturing method. It is important to set about the origin of the problem and develop a good routine of how to work with optical distortions. Optical distortions in backlights, similar to the tested backlight, have a low probability to disturb the driver in such extent that it has an effect on the driving. Nevertheless, it is a source of irritation and discomfort, which do not belong in a premium car.</p><br>The video files are also clickable from the pdf file pages 29 and 56.
21
Tran, Minh Tue. "Pixel and patch based texture synthesis using image segmentation." University of Western Australia. School of Computer Science and Software Engineering, 2010. http://theses.library.uwa.edu.au/adt-WU2010.0030.
Full textAbstract:
[Truncated abstract] Texture exists all around us and serves as an important visual cue for the human visual system. Captured within an image, we identify texture by its recognisable visual pattern. It carries extensive information and plays an important role in our interpretation of a visual scene. The subject of this thesis is texture synthesis, which is de ned as the creation of a new texture that shares the fundamental visual characteristics of an existing texture such that the new image and the original are perceptually similar. Textures are used in computer graphics, computer-aided design, image processing and visualisation to produce realistic recreations of what we see in the world. For example, the texture on an object communicates its shape and surface properties in a 3D scene. Humans can discriminate between two textures and decide on their similarity in an instant, yet, achieving this algorithmically is not a simple process. Textures range in complexity and developing an approach that consistently synthe- sises this immense range is a dfficult problem to solve and motivates this research. Typically, texture synthesis methods aim to replicate texture by transferring the recognisable repeated patterns from the sample texture to synthesised output. Feature transferal can be achieved by matching pixels or patches from the sample to the output. As a result, two main approaches, pixel-based and patch-based, have es- tablished themselves in the active eld of texture synthesis. This thesis contributes to the present knowledge by introducing two novel texture synthesis methods. Both methods use image segmentation to improve synthesis results. ... The sample is segmented and the boundaries of the middle patch are confined to follow segment boundaries. This prevents texture features from being cut o prematurely, a common artifact of patch-based results, and eliminates the need for patch boundary comparisons that most other patch- based synthesis methods employ. Since no user input is required, this method is simple and straight-forward to run. The tiling of pre-computed tile pairs allows outputs that are relatively large to the sample size to be generated quickly. Output results show great success for textures with stochastic and semi-stochastic clustered features but future work is needed to suit more highly structured textures. Lastly these two texture synthesis methods are applied to the areas of image restoration and image replacement. These two areas of image processing involve replacing parts of an image with synthesised texture and are often referred to as constrained texture synthesis. Images can contain a large amount of complex information, therefore replacing parts of an image while maintaining image fidelity is a difficult problem to solve. The texture synthesis approaches and constrained synthesis implementations proposed in this thesis achieve successful results comparable with present methods.
22
Armstrong, Beth Diane. "Hippocampus: seahorse; brain-structure; spatial map; concept." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1002224.
Full textAbstract:
Through an exploration of both sculptural and thought processes undertaken in making my Masters exhibition, ‘Hippocampus’, I unpack some possibilities, instabilities, and limitations inherent in representation and visual perception. This thesis explores the Hippocampus as image (seahorse) and concept (brain-structure involved in cognitive mapping of space). Looking at Gilles Deleuze’s writings on representation, I will expand on the notion of the map as being that which does not define and fix a structure or meaning, but rather is open, extendable and experimental. I explore the becoming, rather than the being, of image and concept. The emphasis here is on process, non-representation, and fluidity of meaning. This is supportive of my personal affirmation of the practice and process of art-making as research. I will refer to the graphic prints of Maurits Cornelis Escher as a means to elucidate a visual contextualization of my practical work, particularly with regard to the play with two- and three-dimensional space perception. Through precisely calculated ‘experiments’ that show up the partiality of our visual perception of space, Escher alludes to things that either cannot actually exist as spatial objects or do exist, but resist representation. Similarly I will explore how my own sculptures, although existing in space resist a fixed representation and suggest ideas of other spaces, non-spaces; an in-between space that does not pin itself down and become fixed to any particular image, idea, objector representation.
23
Hill, Evelyn June. "Applying statistical and syntactic pattern recognition techniques to the detection of fish in digital images." University of Western Australia. School of Mathematics and Statistics, 2004. http://theses.library.uwa.edu.au/adt-WU2004.0070.
Full textAbstract:
This study is an attempt to simulate aspects of human visual perception by automating the detection of specific types of objects in digital images. The success of the methods attempted here was measured by how well results of experiments corresponded to what a typical human’s assessment of the data might be. The subject of the study was images of live fish taken underwater by digital video or digital still cameras. It is desirable to be able to automate the processing of such data for efficient stock assessment for fisheries management. In this study some well known statistical pattern classification techniques were tested and new syntactical/ structural pattern recognition techniques were developed. For testing of statistical pattern classification, the pixels belonging to fish were separated from the background pixels and the EM algorithm for Gaussian mixture models was used to locate clusters of pixels. The means and the covariance matrices for the components of the model were used to indicate the location, size and shape of the clusters. Because the number of components in the mixture is unknown, the EM algorithm has to be run a number of times with different numbers of components and then the best model chosen using a model selection criterion. The AIC (Akaike Information Criterion) and the MDL (Minimum Description Length) were tested.The MDL was found to estimate the numbers of clusters of pixels more accurately than the AIC, which tended to overestimate cluster numbers. In order to reduce problems caused by initialisation of the EM algorithm (i.e. starting positions of mixtures and number of mixtures), the Dynamic Cluster Finding algorithm (DCF) was developed (based on the Dog-Rabbit strategy). This algorithm can produce an estimate of the locations and numbers of clusters of pixels. The Dog-Rabbit strategy is based on early studies of learning behaviour in neurons. The main difference between Dog-Rabbit and DCF is that DCF is based on a toroidal topology which removes the tendency of cluster locators to migrate to the centre of mass of the data set and miss clusters near the edges of the image. In the second approach to the problem, data was extracted from the image using an edge detector. The edges from a reference object were compared with the edges from a new image to determine if the object occurred in the new image. In order to compare edges, the edge pixels were first assembled into curves using an UpWrite procedure; then the curves were smoothed by fitting parametric cubic polynomials. Finally the curves were converted to arrays of numbers which represented the signed curvature of the curves at regular intervals. Sets of curves from different images can be compared by comparing the arrays of signed curvature values, as well as the relative orientations and locations of the curves. Discrepancy values were calculated to indicate how well curves and sets of curves matched the reference object. The total length of all matched curves was used to indicate what fraction of the reference object was found in the new image. The curve matching procedure gave results which corresponded well with what a human being being might observe.
24
Li, Xingshan. "Perception of Kanizsa subjective contour requires attention." 2005. https://scholarworks.umass.edu/theses/2435.
Full text
25
Vuorre, Matti. "Using Visual Illusions to Examine Action-Related Perceptual Changes." Thesis, 2018. https://doi.org/10.7916/D8W39CRZ.
Full textAbstract:
Action has many influences on how and what we perceive. One robust example of the relationship between action and subsequent perception, which has recently received great attention in the cognitive sciences, is the “intentional binding” effect: When people estimate the timing of their actions and those actions’ effects, they judge the actions and effects as having occurred closer together in time than two events that do not involve voluntary action (Haggard, Clark, & Kalogeras, 2002). This dissertation examines the possible mechanisms and consequences of the intentional binding effect. First, in Chapter 1, I discuss previous literature on the relationships between experiences of time, action, and causality. Impressions of time and causality are psychologically related: The perceived timing of events impacts, and is impacted by, perceived causality. Similarly, one’s experience of causing and controlling events with voluntary action, sometimes called the sense of agency, shapes and is shaped by how those events’ timing is perceived—as shown by the intentional binding effect.
In Chapter 2 I present a series of experiments investigating a hypothesized mechanism underlying the intentional binding effect: Actions may lead to a slowing of subjective time, which would explain the intentional binding effect by postulating a shorter experienced duration between action and effect. This hypothesis predicts that, following action, durations separating any two stimuli would appear subjectively shorter. We tested this hypothesis in the context of visual motion illusions: Two visual stimuli are presented in short succession and if the duration between the stimuli (inter-stimulus interval; ISI) is short, participants tend to perceive motion such that the first stimulus appears to move to the position of the second stimulus. If actions shorten subjective durations, even in visual perception, people should observe motion at longer ISIs when the stimuli follow voluntary action because the two stimuli would be separated by less subjective time. Three experiments confirmed this prediction. An additional experiment showed that verbal estimates of the ISI are also shorter following action. A control experiment suggested that a shift in the ability to prepare for the stimuli, afforded by the participant initiating the stimuli, is an unlikely alternative explanation of the observed results. In Chapter 3 I further investigate whether temporal contiguity of actions and their effects, which is known to impact intentional binding, affects perceptions of visual motion illusions. Two experiments showed that temporal contiguity modulates perceptions of illusory motion in a manner similar to contiguity’s effect on intentional binding.
Together, these results show that actions impact perception of visual motion illusions and suggest that general slowing of subjective time is a plausible mechanism underlying the intentional binding effect.
26
Hui, Min. "Illusory contour processing in early visual areas a modeling approach /." Diss., 2007. http://etd.library.vanderbilt.edu/ETD-db/available/etd-09062007-082426/.
Full text
27
Bonfante, Mariana Costa. "Princípios de ilusão de ótica em medicina dentária." Master's thesis, 2017. http://hdl.handle.net/10284/6552.
Full textAbstract:
O rosto humano é um segmento extremamente importante na composição estética de
um individuo e a dentição assume um papel fundamental na estética da face. Segundo
Pilkington, a estética dentária é definida como “a ciência de copiar ou harmonizar o
nosso trabalho com a natureza tornando a nossa arte inconspícua.”
Recentemente os pacientes e mesmo os profissionais tem vindo a dar um maior
destaque ao ramo da estética em medicina dentária, em função da supervalorização da
aparência do individuo na sociedade, da influencia do sorriso na estética facial e como
um todo, e também da mudança de enfoque da pratica profissional, que passou do
tratamento restaurador de dentes cariados para o tratamento estético de dentes sãos.
A estética é algo muito pessoal; no entanto, existem normas que podem estar ao alcance
de todos para tornar o sorriso dos seus pacientes esteticamente mais agradáveis. Por
vezes, alguns pacientes apresentam situações estéticas bastante desfavoráveis e de
difícil correção.
Felizmente, o olho humano é suscetível a enganos, pelo que a utilização de efeitos de
ilusão de ótica pode ser muito útil para a resolução de problemas estéticos complexos.
Assim, a compreensão dos fenómenos de perceção visual e de ilusões de ótica assume
grande importância para o médico dentista que pretenda realizar um trabalho de estética
por excelência.
A presente monografia intitulada “Princípios de ilusões de Ótica na Estética Dentária”
tem como objetivo a elaboração de uma revisão bibliográfica que permita esclarecer
como as ilusões de ótica podem alterar a perceção visual e serem utilizadas pelo médico
dentista para proporcionar uma melhoria na estética dentária.<br>The human face is an extremely important segment in the aesthetic composition of an
individual and the dentition plays a fundamental role in the aesthetics of the face.
According to Pilkington, dental aesthetics is defined as "the science of copying or
harmonizing our work with nature making our art inconspicuous."
Recently, patients and even professionals have been giving a greater prominence to the
aesthetic branch in dental medicine, due to the overvaluation of the appearance of the
individual in society, the influence of the smile on the facial aesthetics and as a whole,
and also the change of focus of professional practice, which went from restorative
treatment of decayed teeth to the aesthetic treatment of healthy teeth.
Aesthetics is something very personal; However, there are standards that may be within
everyone's reach to make their patients smile more aesthetically pleasing. Sometimes,
some patients present esthetic situations that are very unfavorable and difficult to
correct.
Fortunately, the human eye is susceptible to misunderstanding, so the use of optical
illusion effects can be very useful for solving complex aesthetic problems. Thus, the
understanding of the phenomena of visual perception and optical illusions is of great
importance for the dentist who intends to perform excellent aesthetic work.
This thesis entitled "Principles of optical illusions in dental aesthetics" aims to elaborate
a bibliographical review to clarify how optical illusions can alter visual perception and
be used by the dentist to provide an improvement in dental aesthetics.
28
Hamburger, Kai [Verfasser]. "Visual illusions : perception of luminance, color, and motion in humans / vorgelegt von Kai Hamburger." 2007. http://d-nb.info/984203826/34.
Full text
29
Wu, Daw-An. "How Perception Adheres Color to Objects and Surfaces: Studies Using Visual Illusions and Transcranial Magnetic Stimulation." Thesis, 2006. https://thesis.library.caltech.edu/3809/1/Wu_DA_Thesis.pdf.
Full textAbstract:
<p>In early visual cortex, visual input is encoded primarily as edges. Information then flows into more specialized regions of the brain, which process visual features such as color, motion, etc. This encoding scheme poses some problems in explaining the experience of seeing. If the cortex processes various visual features separately, how do we see unified objects? What mechanisms bind the features together? If the cortex encodes the visual scene in terms of its edges, then how do we see solid surfaces? What mechanisms fill-in the map of outlines?</p>
<p>This thesis investigates the problems of binding and filling-in using the techniques of visual illusion psychophysics and transcranial magnetic stimulation (TMS). We find that TMS can cause an instant replay effect, whereby recently presented visual stimuli are seen again. When TMS induces an instant replay shortly after the presentation of Cai’s asynchronous binding illusion, some subjects see an image of the actual visual stimulus, undistorted. It appears that TMS can selectively activate a hidden, accurate representation of the stimulus, revealing it without the distortion caused by other processes.</p>
<p>We also find a number of cases in which visual features are decomposed and/or misbound. TMS-induced instant replay can cause the color of one object to be bound to the position and orientation of another. It can also separately replay the color and orientation of a grating. In a non-TMS experiment, we create a stimulus that induces a steady-state misbinding of color and motion—-a vivid, long-lasting misbinding effect ideal for neurophysiological investigation. These experiments confirm the separate encoding of visual features and the existence of an active binding mechanism.</p>
<p>Finally, we study filling-in by manipulating an effect distilled from the artwork of Julian Stanczak, in which color is perceived to spread discretely among segregated patches of space. We find that color-filling is dependent on perceptual surfaces, such that overlaid surfaces can support separate filling processes. It appears possible that the neural mechanisms of binding and filling-in might be intimately related, both of them highly integrated with the process of surface segregation.</p>
30
Boyraz, Pinar. "Perception of visual motion speed in human und monkey." Doctoral thesis, 2007. http://hdl.handle.net/11858/00-1735-0000-0006-B36C-D.
Full text
31
"Generalizing recognition from familiar to novel views." 2001. http://library.cuhk.edu.hk/record=b5890731.
Full text
32
Brooks, Anna. "The neural correlates of the jitter illusion." 2004. http://eprints.jcu.edu.au/1034/1/01front.pdf.
Full textAbstract:
The work that follows introduces a new visual illusion. The ‘jitter’ illusion arises in response to single brief presentations of stationary Glass patterns composed of decrement- and increment-defined dot-pairs. Remarkably, the perceptions that arise are of coherent global motion in trajectories that are consistent with the spatial configuration of the Glass patterns; patterns configured according to concentric functions give rise to perceptions of motion in concentric trajectories, those configured according to radial functions give rise to perceptions of motion in radial trajectories, and so on. The aim of the work that follows was to develop a model of the neural correlates of this illusion. An additional aim was to explore the implications of such a model for developing a broader understanding of the means by which coherent visual perceptions arise. Experiments were conducted under the working hypothesis that the jitter illusion is mediated by activity that arises within the magno-cellular (M-), and not the parvo-cellular (P-) pathway of the visual system. It is argued that a model based entirely on M-pathway activity can effectively account for the illusion if two critical conditions are met. The first is that the model must propose the mechanism by which presentations of stationary Glass patterns stimulate activity in the motion-sensitive cells of the M-pathway. The second is that it must propose plausible mechanism(s) by which the ensuing M-pathway activity gives rise to perceptions of coherent global motion. Experiments reported in chapters 3 and 4 address the first of these conditions. Data from these experiments suggest that abrupt changes in luminance introduced at the onset and offset of stationary Glass patterns (and not eye-movements) mediate the M-pathway activity on which the illusion is based. Experiments reported in chapters 5 through to 8 address the second condition. In chapters 5 and 6, the data suggest that the patterns of Off- and On-channel responses elicited by individual Glass pattern dot-pairs somehow stimulates cells that act as ‘local’ motion detectors. In chapters 7 and 8, models of the means by this occurs were tested. The resulting data rule out the possibility that the stimulation is a product of a processing asynchrony in the M-pathway Off- and On-channels. Instead, they are consistent with a model based on the diphasic temporal impulse-response functions attributed to cells that make up the M-pathway. Based on its ability to satisfy each of the stated conditions, the so-called diphasic TIRF model is presented as a plausible account of some of the neural correlates of the jitter illusion. The implications of the diphasic TIRF model are discussed in relation to both the jitter illusion and to visual processing more generally. One of the critical (and novel) implications of the model is that under some circumstances, M-pathway mechanisms ‘extract’ structural information from static visual images that P-pathway mechanisms cannot. On this basis, it is argued that both the jitter illusion and the diphasic TIRF model offer valuable insights into some of the means by which light-induced activity within the human visual system gives rise to coherent global perceptions.
33
Berg, Thomas. "High-level, part-based features for fine-grained visual categorization." Thesis, 2017. https://doi.org/10.7916/D8CF9VTF.
Full textAbstract:
Object recognition--"What is in this image?"--is one of the basic problems of computer vision. Most work in this area has been on finding basic-level object categories such as plant, car, and bird, but recently there has been an increasing amount of work in fine-grained visual categorization, in which the task is to recognize subcategories of a basic-level category, such as blue jay and bluebird.
Experimental psychology has found that while basic-level categories are distinguished by the presence or absence of parts (a bird has a beak but car does not), subcategories are more often distinguished by the characteristics of their parts (a starling has a narrow, yellow beak while a cardinal has a wide, red beak). In this thesis we tackle fine-grained visual categorization, guided by this observation. We develop alignment procedures that let us compare corresponding parts, build classifiers tailored to finding the interclass differences at each part, and then combine the per-part classifiers to build subcategory classifiers.
Using this approach, we outperform previous work in several fine-grained categorization settings: bird species identification, face recognition, and face attribute classification. In addition, the construction of subcategory classifiers from part classifiers allows us to automatically determine which parts are most relevant when distinguishing between any two subcategories. We can use this to generate illustrations of the differences between subcategories. To demonstrate this, we have built a digital field guide to North American birds which includes automatically generated images highlighting the key differences between visually similar species. This guide, "Birdsnap," also identifies bird species in users' uploaded photos using our subcategory classifiers. We have released Birdsnap as a web site and iPhone application.
34
Fylan, F., A. Hughes, J. M. Wood, and David B. Elliott. "Why do people drive when they can’t see clearly?" 2018. http://hdl.handle.net/10454/16123.
Full textAbstract:
Yes<br>Purpose
Refractive blur is associated with decreased hazard perception and impairments in driving performance, but little is known about why people who have spectacles to correct their distance vision drive with uncorrected vision.
Methods
We conducted six focus groups. Participants were 30 drivers (mean age 45) who reported having driven uncorrected at least twice in the past six months despite having spectacles to correct their distance vision. Focus groups were audio recorded, transcribed verbatim and analysed thematically.
Results
We identified three themes. 1. Responsibility: participants did not feel obliged to drive with optimal vision and believed that others have a responsibility to ensure drivers maintain clear vision. 2. Safe Enough: participants felt safe to drive uncorrected, did not believe they need to wear spectacles to see sufficiently clearly and that they would know if their uncorrected eyesight fails to meet minimum standards. 3. Situations: participants discussed how they would drive uncorrected for short and familiar journeys, when they feel alert, in daylight and in good weather.
Conclusions
Beliefs about the importance of driving with clear vision compete with the benefits of not wearing spectacles. Eyecare professionals should provide more direct advice to patients regarding the need to wear their visual correction for driving.
35
Rajabather, Harikrishna K. "An Adaptive Eye Gaze Tracking System Without Calibration for Use in an Automobile." 2011. http://hdl.handle.net/1805/2616.
Full textAbstract:
Indiana University-Purdue University Indianapolis (IUPUI)<br>One of the biggest hurdles to the development of an effective driver state monitor is the that there is no real-time eye-gaze detection. This is primarily due to the fact that such systems require calibration. In this thesis the various aspects that comprise an eye gaze tracker are investigated. From that we developed an eye gaze tracker for automobiles that does not require calibration. We used a monocular camera system with IR light sources placed in each of the three mirrors. The camera system created the bright-pupil effect for robust pupil detection and tracking. We developed an SVM based algorithm for initial eye candidate detection; after that the
eyes were tracked using a hybrid Kalman/Mean-shift algorithm. From the tracked pupils, various features such as the location of the glints (reflections in the pupil from the IR light sources) were extracted. This information is then fed into a Generalized Regression Neural Network (GRNN). The GRNN then maps this information into one of thirteen gaze regions in the vehicle.
36
Super, Selwyn. "Stereopsis and its educational significance." Thesis, 2014. http://hdl.handle.net/10210/11832.
Full textAbstract:
D.Ed.<br>Stereopsis -- binocular depth perception is a visual function which falls within the ambit of the hyperacuities. The term, Hyperacuity, is one coined by Westheimer (1976) to describe thresholds of discrimination which cannot be explained on the basis of the optical components or sensory elements of the eyes alone. By implication such levels of discrimination are effected by higher levels of brain function. It is reasoned that an individual's stereoscopic hyperacuity should in some way relate to other measures of higher sensory and motor brain functions. In a school situation hyperacuity should relate to measures of intelligence, as well as scholastic and sporting achievement. The design and implementation of an experiment to test this premise forms the basis of this thesis. A literature review is reported of current knowledge relevant to this study together with a description of the stereoscopic testing instruments commonly available in clinical practice. A rationale for modifying these instruments and testing methods to suit the needs of this study is also included. This study exposes new knowledge about the process of static nearpoint stereopsis. This stereopsis proves to be a complex of diverse skills, which are significantly age-related and developmental in nature. These skills are seen to influence and be influenced by educational interventions. It may be concluded from this study that there is value in measuring stereopsis in more depth than has been done previously and that it is crucial to measure the speed of stereo performance in its own right in addition to the measures of stereoacuity. The study reveals significant differences of performance which relate to stereopsis in front as opposed to behind the plane of regard and also related to figure/ground contrast differences. The two non-stereoscopic tests and the six different stereoscopic tests described in this thesis prove to be highly discriminative and diagnostic with respect to age, grade level, I.Q., scholastic achievement and sporting ability.
37
Nortmann, Nora. "Context Effects in Early Visual Processing and Eye Movement Control." Doctoral thesis, 2015. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-2015042913187.
Full textAbstract:
There is a difference between the raw sensory input to the brain and our stable perception of entities in the environment. A first approach to investigate perception is to study relationships between properties of currently presented stimuli and biological correlates of perceptual processes. However, it is known that such processes are not only dependent on the current stimulus. Sampling of information and the concurrent neuronal processing of stimulus content rely on contextual relationships in the environment, and between the environment and the body. Perceptual processes dynamically adjust to relevant context, such as the current task of the organism and its immediate history. To understand perception, we have to study how processing of current stimulus content is influenced by such contextual factors. This thesis investigates the influence of such factors on visual processing. In particular, it investigates effects of temporal context in early visual processing and the effect of task context in eye movement control. To investigate effects of contextual factors on early visual processing of current stimulus content, we study neuronal processing of visual information in the primary visual cortex. We use real-time optical imaging with voltage sensitive dyes to capture neuronal population activity in the millisecond range across several millimeters of cortical area. To characterize the cortical layout concerning the mapping of orientation, previous to further investigations, we use smoothly moving grating stimuli. Investigating responses to this stimulus type systematically, we find independent encoding of local contrast and orientation, and a direct mapping of current stimulus content onto cortical activity (Study 1). To investigate the influence of the previous stimulus as context on processing of current stimulus content, we use abrupt visual changes in sequences of modified natural images. In earlier studies, investigating relatively fast timescales, it was found that the primary visual cortex continuously represents current input (ongoing encoding), with little interference from past stimuli. We investigate whether this coding scheme generalizes to cases in which stimuli change more slowly, as frequently encountered in natural visual input. We use sequences of natural scene contours, comprised of vertically and horizontally filtered natural images, their superpositions, and a blank stimulus, presented with 10 or 33 Hz. We show that at the low temporal frequency, cortical activity patterns do not encode the present orientations but instead reflect their relative changes in time. For example, when a stimulus with horizontal orientation is followed by the superposition of both orientations, the pattern of cortical activity represents the newly added vertical orientations instead of the full sum of orientations. Correspondingly, contour removal from the superposition leads to the representation of orientations that have disappeared rather than those that remain. This is in sharp contrast to more rapid sequences for which we find an ongoing representation of present input, consistent with earlier studies. In summary, we find that for slow stimulus sequences, populations of neurons in the primary visual cortex are no longer tuned to orientations within individual stimuli but instead represent the difference between consecutive stimuli. Our results emphasize the influence of the temporal context on early visual processing and consequentially on information transmission to higher cortical areas (Study 2). To study effects of contextual factors on the sampling of visual information, we focus on human eye movement control. The eyes are actively moved to sample visual information from the environment. Some traditional approaches predict eye movements solely on simple stimulus properties, such as local contrasts (stimulus-driven factors). Recent arguments, however, emphasize the influence of tasks (task context) and bodily factors (spatial bias). To investigate how contextual factors affect eye movement control, we quantify the relative influences of the task context, spatial biases and stimulus-driven factors. Participants view and classify natural scenery and faces while their eye movements are recorded. The stimuli are composed of small image patches. For each of these patches we derive a measure that quantifies stimulus-driven factors, based on the image content of a patch, and spatial viewing biases, based on the location of the patch. Utilizing the participants’ classification responses, we additionally derive a measure, which reflects the information content of a patch in the context of a given task. We show that the effect of spatial biases is highest, that task context is a close runner-up, and that stimulus-driven factors have, on average, a smaller influence. Remarkably, all three factors make independent and significant contributions to the selection of viewed locations. Hence, in addition to stimulus-driven factors and spatial biases, the task context contributes to visual sampling behavior and has to be considered in a model of human eye movements.
Visual processing of current stimulus content, in particular visual sampling behavior and early processing, is inherently dependent on context. We show that already in the first cortical stage, temporal context strongly affects the processing of new visual information and that visual sampling by eye movements is significantly influenced by the task context, independently of spatial factors and stimulus-driven factors. The empirical results presented provide foundations for an improved theoretical understanding of the role of context in perceptual processes.