A laminar cortical model of stereopsis and 3D surface perception: Closure and da Vinci stereopsis

A laminar cortical model of stereopsis and 3D surface perception is developed and simulated. The model describes how monocular and binocular oriented filtering interact with later stages of 3D boundary formation and surface filling-in in the LGN and cortical areas VI, V2, and V 4. It proposes how interactions between layers 4, 3B, and 2/3 in V 1 and V2 contribute to stereopsis, and how binocular and monocular information combine to form 3D boundary and surface representations. The model includes two main new developments: (1) It clarifies how surface-toboundary feedback from V2 thin stripes to pale stripes helps to explain data about stereopsis. This feedback has previously been used to explain data about 3D figure-ground perception. (2) It proposes that the binocular false match problem is subsumed under the Gestalt grouping problem. In particular, the disparity filter, which helps to solve the correspondence problem by eliminating false matches, is realized using inhibitory intemeurons as part of the perceptual grouping process by horizontal connections in layer 2/3 of cortical area V2. The enhanced model explains all the psychophysical data previously simulated by Grossberg and Howe (2003), such as contrast variations of dichoptic masking and the correspondence problem, the effect of interocular contrast differences on stereoacuity, Panum's limiting case, the Venetian blind illusion, stereopsis with polarity-reversed stereograms, and da Vinci stereopsis. It also explains psychophysical data about perceptual closure and variations of da Vinci stereopsis that previous models cannot yet explain

Psychophysical investigations of inverse cyclopean texture segmentation

Inverse cyclopean texture segmentation is segmentation based on monocular boundaries which are absent in the binocularly fused percept. Texture segmentation based on the monocular image does occur, even though texture segmentation is impossible in the optically fused image (Kolb & Braun, 1995). On the other hand, orientation defined, inverse cyclopean visual search is impossible (Wolfe & Franzel, 1988). The purpose of the present study was therefore to investigate these apparent contradictions in the literature. Orientation-defined texture elements within Kolb and Braun’s stimulus occupied positions on a 20 x 20 notional grid. For Wolfe and Franzel’s stimulus, 8 texture elements were spaced evenly on a circle. The purpose of Experiments 1.1 and 3 was to determine whether the critical variable for the difference between Kolb and Braun’s and Wolfe and Franzel’s results was texture density i.e. the number of elements within the display area. We found that orientation-defined, inverse cyclopean texture segmentation was better when texture elements were dense (12 x 12) than when those elements were sparse (8 x 8) and covered the same area (Exp. 1.1 & 3). The purpose of Experiment 4 was to determine whether texture segmentation depended on orientation-defined texture boundaries that were closer together. Texture segmentation improved when the number of texture elements within the sparse grid (8 x 8) used in Experiment 3 was held constant and texture boundaries were closer together (Exp. 4). This implies that the critical difference between Kolb and Braun’s and Wolfe and Franzel’s experiments is the proximity of orientation-defined, texture boundaries. The purpose of Experiment 2 was to investigate the possibility that, if there were an effective contrast imbalance between the two eyes, the texture boundary within an inverse cyclopean stimulus might be visible in the optically fused percept and be detected by mechanisms at a binocular stage of processing. An imbalance in sensory input from the two eyes does affect orientation-defined, inverse cyclopean texture segmentation (Exp. 2). Therefore, the purpose of Experiment 7 was to determine whether effective contrast imbalance between the two eyes was responsible for high performances for texture segmentation when texture elements were dense (Exp. 1.1 & 3) and when texture boundaries were closer together (Exp. 4). Performances for orientation-defined, inverse cyclopean texture segmentation were >80% when the balance-point was used to equalise a difference in effective contrast between the two eyes (Exp. 7.2). This implies that monocular input is available to texture segmentation mechanisms

The spatial averaging of disparities in brief, static random-dot stereograms

Visual images from the two eyes are transmitted to the brain. Because the eyes are horizontally separated, there is a horizontal disparity between the two images. The amount of disparity between the images of a given point depends on the distance of that point from the viewer's point of fixation. A natural visual environment contains surfaces at many different depths. Therefore, the brain must process a spatial distribution of disparities. How are these disparities spatially put together? Brief (about 200 msec) static Cyclopean random-dot stereograms were used as stimuli for vergence and depth discrimination to answer this question. The results indicated a large averaging region for vergence, and a smaller pooling region for depth discrimination. Vergence responded to the mean disparity of two transparent planes. When a disparate target was present in a fixation plane surround, vergence improved as target size was increased, with a saturation at 3-6 degrees. Depth discrimination thresholds improved with target size, reaching a minimum at 1-3 degrees, but increased for larger targets. Depth discrimination showed a dependence on the extent of a disparity pedestal surrounding the target, consistent with vergence facilitation. Vergence might, therefore, implement a coarse-to-fine reduction in binocular matching noise. Interocular decorrelation can be considered as multiple chance matches at different disparities. The spatial pooling limits found for disparity were replicated when interocular decorrelation was discriminated. The disparity of the random dots also influenced the apparent horizontal. alignment of neighbouring monocular lines. This finding suggests that disparity averaging takes place at an early stage of visual processing. The following possible explanations were considered: 1) Disparities are detected in different spatial frequency channels (Marr and Poggio, 1979). 2) Second-order luminance patterns are matched between the two eyes using non-linear channels. 3) Secondary disparity filters process disparities extracted from linear filters

Displacement and disparity representations in early vision

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1992.Includes bibliographical references (p. 211-220).by Steven James White.Ph.D

Exploring the optical perception of image within glass

Within the contemporary world, 3D film and television imagery is at the cutting edge of visual technology, but for centuries we have been captivated by the creation of visual illusions/allusions that play with our perception of the world, from the auto-stereoscopic barrier methods pioneered in the late 17th century by the French painter G. A. Bois-Clair to the ‘Op’ art movement of the 1960s and, more recently, Patrick Hughes’ ‘reverse perspective’ paintings. By building on these new and old technologies I have extended my own practice, which engages with the 2D image as a 3D allusion/illusion in glass, by examining how this type of image can be created and perceived within glass. I have explored theories of optical perception in connection with the binocular recognition of depth and space, as well as kinetic clues to distance through motion parallax monitoring and assumptions about default linear perspective, light and inference within our personal schemata. - ‘Optical illusion’ is used to mean an instance of a wrong or misinterpreted perception of a sensory experience; the distortion of senses revealing how the brain organises and interprets visual information; an individual’s ability to perceive depth, 3D form and motion. - ‘Allusion’ is used to imply a symbolic or covert reference. My practical research focuses on the perceived creation of the 3D image within glass and explores the notion of glass as a facilitator in working with and challenging the themes of 3D image perception. I have particularly addressed artistic spatial illusionary methods, reverse perspective techniques, auto-stereoscopic image-based systems, parallax stereograms and lenticular print and lens technology. Through building on my previous practice of working with multiple-layered images within cast glass, combined with more complex and scientific optical methods, I have explored the perception of the image by working with new and old 3D technologies in order to produce a body of work which examines this perception within glass. During my research I have developed an original casting process, a vacuum-casting lost wax process for glass, in addition to producing an accurate industry standard lenticular glass lens. This research intends to provide a theoretical basis for new glass working techniques, both within the glass artist’s studio and in the commercial world of print, towards applications within architectural design, installation art and image-based artwork in general. This thesis is therefore a summation of the research that I have undertaken over the past six years and an attempt to give substance to the ideas and references that have preoccupied my own investigations over that period. I have structured the thesis into three themes: perspective; perception; and process but those three elements were never separate from each other and not only do they depend on each other, their purpose is, in some way, to combine in the creation of my finished pieces

Binocular strategies in reading and non-reading visual tasks: from oculomotor behaviours to higher cognition

Humans use two eyes to extract selected information from the real world and deliver it to the human brain for higher cognition and the perceptual system. However, the two eyes are not always aligned. Eye movements are produced and the eyes accommodate in response to different visual stimuli. Studies on binocularity have reported its importance in accord with specific visual processing requirements. The main aim of this thesis is: how does binocular performance correspond to higher cognition in visual perception? This thesis explores how the two eyes coordinate their efforts to respond and adapt to cognitive activity, through oculomotor behaviours. The physical disposition of the eyes can be a part of cognitive processing, as an ‘embodied’ process of visual perception, that facilitates visual information processing. Therefore, we investigate binocular strategies in both reading and non-reading visual tasks, from oculomotor behaviours to higher cognition, to understand its implications for systematic and strategic processing in visual perception. In the reading part, we first investigate the two left-to-right orthographies, English and Chinese. We analyse small temporal non-alignments between the two eyes’ with nine patterns of temporal disjugacy and find that the distribution of small asynchronies of binocular fixation accord with ocular prevalence (Chapter 2). Such asynchronies are predictive of ocular prevalence, in which input to the left eye is prioritised in conscious perception of a fused visual stimulus for targets in the left visual field and right-eye input is prioritised for targets in the right visual field. Then, this typology is further explored in two right-to-left orthographies, Arabic and Hebrew (Chapter 3). We found reading behaviours of these Semitic languages resemble this advantageous switching of ocular prevalence, but mirror the pattern of left-to-right orthographies due to the change of reading direction. In the non-reading tasks, we first investigate binocular adaptive behaviours in two reading-like tasks (i.e. reading lines of numbers). We specifically explore how the visual system reacts and adapts to continuous text-background contrast (chapter 4) and how the visual system reacts and adapts to the level of faintness of the stimulus (chapter 5). In the contrast experiment (chapter 4), we found systematic adaptation of binocular vision in response to the contrast change, with an overall crossed tendency of binocular fixations (i.e. right eye’s fixation to the left of the left eye’s), as well as disparity-related behaviours as the contrast became lower and reading difficulty increased. On the other hand, in the experiment with variation of the level of faintness of the stimulus (chapter 5), we also found systematic adaptive binocular behaviours with an overall crossed tendency of fixations, but with increasing distribution of uncrossed fixation pairs (i.e. right eye’s fixation to the right of the left eye’s) as the level of blurriness of the text stimulus increases and reading difficulty increases. Our findings are consistent with previous research but reveal that the adaptation is a strategy rather than the effect of fatigue, and that this strategy operates very flexibly and specifically with respect to location. The overall effect of the visually adaptive behaviours in these two experiments suggests that the two eyes coordinate to adjust through very peripheral muscle-driven movements of the eyes and all the way to higher cognitive processing, in response to contrast change and blurring of the stimuli, for better visual quality and performance in different conditions for visual perception. Finally, we conducted two illusion-related experiments, including a visual illusion created by depth information (chapter 6) and a motion-based illusion with Plateau’s Spiral (chapter 7). We replicated Murray et al.’s (2006) experiment with far and near spheres and investigated how the visual system reacts and responds to a visual illusion created by depth information as a cue for judgement of perceived size (chapter 6). Our results support Murray et al.’s (2006) interpretation of their data only partially and suggest an alternative interpretation to their influential experiment: Murray et al.’s apparent VI correlate of the size illusion may be partially attributable to larger binocular fixation disparities on the back sphere (i.e. sizeable non-overlap between the retinotopic mappings from the left and right eye). In another visual illusion experiment, we investigate how the two eyes would respond to stimuli that produce a motion-based illusion of depth, given that such stimuli produce not just an aftereffect but different perceptions during the stimulus. We found general similarities in processing clockwise and anticlockwise spinning spirals, in terms of vergence movements. However, our experiment shows a remarkable difference in the binocular strategies in processing at different spatial locations. It indicated hemispheric specialisation and projection during viewing an illusional stimulus, and corresponding binocular strategies for visual processing. Perception can be manipulated by hemisphere-based higher cognition controlling the oculomotor musculature, allowing the hemispheres to generate their own most appropriate input, when viewing a visually challenging stimulus, Plateau’s Spiral. In summary, this thesis investigates binocular strategies in visual perception in response to different stimuli and conditions in both reading and non-reading tasks. We found systematic and harmonious behaviours from peripheral muscle-driven movements of the eyes that correspond to the cortical processing that contributes to cognition, showing the flexibility of the visual system in different modes of operation, from peripheral binocular movement all the way to higher cognitive processing

Une méthode pour l'évaluation de la qualité des images 3D stéréoscopiques.

Dans le contexte d'un intérêt grandissant pour les systèmes stéréoscopiques, mais sans méthodes reproductible pour estimer leur qualité, notre travail propose une contribution à la meilleure compréhension des mécanismes de perception et de jugement humains relatifs au concept multi-dimensionnel de qualité d'image stéréoscopique. Dans cette optique, notre démarche s'est basée sur un certain nombre d'outils : nous avons proposé un cadre adapté afin de structurer le processus d'analyse de la qualité des images stéréoscopiques, nous avons implémenté dans notre laboratoire un système expérimental afin de conduire plusieurs tests, nous avons crée trois bases de données d'images stéréoscopiques contenant des configurations précises et enfin nous avons conduit plusieurs expériences basées sur ces collections d'images. La grande quantité d'information obtenue par l'intermédiaire de ces expérimentations a été utilisée afin de construire un premier modèle mathématique permettant d'expliquer la perception globale de la qualité de la stéréoscopie en fonction des paramètres physiques des images étudiée.In a context of ever-growing interest in stereoscopic systems, but where no standardized algorithmic methods of stereoscopic quality assessment exist, our work stands as a step forward in the understanding of the human perception and judgment mechanisms related to the multidimensional concept of stereoscopic image quality. We used a series of tools in order to perform in-depth investigations in this direction: we proposed an adapted framework to structure the process of stereoscopic quality assessment, we implemented a stereoscopic system in our laboratory for performing various tests, we created three stereoscopic datasets with precise structures, and we performed several experimental studies using these datasets. The numerous experimental data obtained were used in order to propose a first mathematical framework for explaining the overall percept of stereoscopic quality in function of the physical parameters of the stereoscopic images under study.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

How sketches work: a cognitive theory for improved system design

Evidence is presented that in the early stages of design or composition the mental processes used by artists for visual invention require a different type of support from those used for visualising a nearly complete object. Most research into machine visualisation has as its goal the production of realistic images which simulate the light pattern presented to the retina by real objects. In contrast sketch attributes preserve the results of cognitive processing which can be used interactively to amplify visual thought. The traditional attributes of sketches include many types of indeterminacy which may reflect the artist's need to be "vague". Drawing on contemporary theories of visual cognition and neuroscience this study discusses in detail the evidence for the following functions which are better served by rough sketches than by the very realistic imagery favoured in machine visualising systems. 1. Sketches are intermediate representational types which facilitate the mental translation between descriptive and depictive modes of representing visual thought. 2. Sketch attributes exploit automatic processes of perceptual retrieval and object recognition to improve the availability of tacit knowledge for visual invention. 3. Sketches are percept-image hybrids. The incomplete physical attributes of sketches elicit and stabilise a stream of super-imposed mental images which amplify inventive thought. 4. By segregating and isolating meaningful components of visual experience, sketches may assist the user to attend selectively to a limited part of a visual task, freeing otherwise over-loaded cognitive resources for visual thought. 5. Sequences of sketches and sketching acts support the short term episodic memory for cognitive actions. This assists creativity, providing voluntary control over highly practised mental processes which can otherwise become stereotyped. An attempt is made to unite the five hypothetical functions. Drawing on the Baddeley and Hitch model of working memory, it is speculated that the five functions may be related to a limited capacity monitoring mechanism which makes tacit visual knowledge explicitly available for conscious control and manipulation. It is suggested that the resources available to the human brain for imagining nonexistent objects are a cultural adaptation of visual mechanisms which evolved in early hominids for responding to confusing or incomplete stimuli from immediately present objects and events. Sketches are cultural inventions which artificially mimic aspects of such stimuli in order to capture these shared resources for the different purpose of imagining objects which do not yet exist. Finally the implications of the theory for the design of improved machine systems is discussed. The untidy attributes of traditional sketches are revealed to include cultural inventions which serve subtle cognitive functions. However traditional media have many short-comings which it should be possible to correct with new technology. Existing machine systems for sketching tend to imitate nonselectively the media bound properties of sketches without regard to the functions they serve. This may prove to be a mistake. It is concluded that new system designs are needed in which meaningfully structured data and specialised imagery amplify without interference or replacement the impressive but limited creative resources of the visual brain

The Victorian Naturalist

v.114 (1997