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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Motion perception: The effects of perceived three-dimensional distance.

Mowafy, Marilyn Kay. January 1988 (has links)
Contemporary computational models of motion perception assume that in processing continuous or near-continuous motion information, the visual system measures spatial displacement in retinal coordinates over a series of time-varying images. Additional three-dimensional information possessed by the system purportedly does not influence this low-level motion analysis. The present research investigated the influence of static three-dimensional distance information recovered from binocular disparity on the perceived direction of motion. It was assumed that if a stereoscopic display context influenced perceived motion direction, the apparent velocity of a moving element would increase in order to traverse the greater apparent distance. This would be reflected in a predictable pattern of errors when the true angular velocity was the same, slower or faster than that of the standard. The stimuli consisted of random-dot stereograms depicting surfaces at varying distances and orientations. In one stereoscopic display, the disparity information indicated a surface sloping smoothly in depth from crossed to uncrossed disparity. The second display contained two fronto-parallel planes at discrete distances from the observed. Motion stimuli were single element translating horizontally and presented monocularly to the observer's right eye. Experiment 1 compared differential velocity judgments in the contexts of the sloped surface and a control condition at zero disparity. The results indicated an overall increase in the perceived velocity of the element moving in the context of the sloped surface. The pattern of results was replicated in experiment 2, but an additional effect of the relative positions of the two surfaces also was obtained. Experiment 3 explored the case of two discrete fronto-parallel planes, one at crossed disparity and the other at uncrossed disparity. This experiment also produced a position effect, but indicated that the perceived distance of the two planes did not differentially affect observer's velocity judgments. It was concluded that in some cases, the metric of motion analysis could be affected by three-dimensional information recovered from binocular disparity. The particular case discovered in these experiments was a surface that appeared to slope smoothly in depth. Discrete depth planes produced no such effect.
22

Interaction of Different Modules in Depth Perception: Stereo and Shading

Bulthoff, Heinrich H., Mallot, Hanspeter A. 01 May 1987 (has links)
A method has been developed to measure the perceived depth of computer generated images of simple solid objects. Computer graphic techniques allow for independent control of different depth queues (stereo, shading, and texture) and enable the investigator thereby to study psychophysically the interaction of modules for depth perception. Accumulation of information from shading and stereo and vetoing of depth from shading by edge information have been found. Cooperativity and other types of interactions are discussed. If intensity edges are missing, as in a smooth-shaded surface, the image intensities themselves could be used for stereo matching. The results are compared with computer vision algorithms for both single modules and their integration for 3D vision.
23

Preference for phase-based disparity in a neuromorphic implementation of the binocular energy model /

Tsang, Kong Chau. January 2003 (has links)
Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 64-66). Also available in electronic version. Access restricted to campus users.
24

A PSYCHOPHYSICAL INVESTIGATION OF A DYNAMIC DEPTH PERCEPTION THRESHOLD IN THE HUMAN VISUAL SYSTEM USING ROTATING THREE-DIMENSIONAL LISSAJOUS PATTERNS

Gardner, Keith Leroy January 1980 (has links)
A tridimensional optical display is described which is capable of producing real images with no optics between the observer and the image. This display, which is called the Visually Integrated Volumetric Image (VIVID), was developed as a laboratory system designed to be used in vision research. Three dimensional Lissajous patterns were produced, whose rotational position and axial depth could be precisely controlled by a general purpose digital minicomputer. By reversing the direction of rotation of the pattern in a known manner, and recording a subject's ability to perceive the true rotational direction for various amounts of axial image depth, the transition between the kinetic depth effect and true depth perception could be investigated. This transition forms the basis for defining a depth perception threshold for this type of a dynamic three dimensional image. Two experiments were performed using this approach. In the first experiment, ten undergraduate and graduate students (both male and female) observed the pattern during 24 one-minute trials. Eight different axial depth values were used, with three trials at each depth. The patterns were made to reverse rotation direction in a pseudo-random manner which was different for each trial presented to a given subject. The subject indicated the perceived direction of rotation by controlling a two position rotary switch, which was monitored by the computer. The total time during which the subject correctly tracked the rotation was integrated by the computer. The ratio of this correct tracking time to the total trial time was taken as a measure of the subject's ability to perceive the axial depth of the image. Plots of this ratio as a function of image depth are presented and discussed. The results averaged over all subjects produce a remarkably smooth curve, yielding a depth perception threshold of 2 mm for the subject population under the given experimental conditions. The characteristics of the stimulus were: (a) 2 cm high by 2 cm wide pattern; (b) Lissajous pattern frequency ratio of 6:1; (c) Axial distance from observer of 55 cm; (d) Wavelength of 533 nm (green); (e) Horizontal rotation axis; (f) Rotation period of 7 seconds; (g) Neutral background field illumination over a 40° come angle; (h) Image line width of 0.5 mm. The second experiment was a pilot experiment designed to investigate the effect of wavelength variations on this form of depth perception. A single subject was presented with a total of 192 one-minute trials at four wavelengths spanning the visible region (i.e., 6 one-minute trials for each of eight depth values at each wavelength). No significant wavelength dependence was observed in this pilot experiment.
25

Feature-based stereo vision on a mobile platform

Huynh, Du Quan January 1994 (has links)
It is commonly known that stereopsis is the primary way for humans to perceive depth. Although, with one eye, we can still interact very well with our environment and do very highly skillful tasks by using other visual cues such as occlusion and motion, the resultant e ect of the absence of stereopsis is that the relative depth information between objects is essentially lost (Frisby,1979). While humans fuse the images seen by the left and right eyes in a seemingly easy way, the major problem - the correspondence of features - that needs to be solved in all binocular stereo systems of machine vision is not trivial. In this thesis, line segments and corners are chosen to be the features to be matched because they typically occur at object boundaries, surface discontinuities, and across surface markings. Polygonal regions are also selected since they are known to be well-configured and are, very often, associated with salient structures in the image. The use of these high level features, although helping to diminish matching ambiguities, does not completely resolve the matching problem when the scene contains repetitive structures. The spatial relationships between the feature matching pairs enforced in the stereo matching process, as proposed in this thesis, are found to provide even stronger support for correct feature matching pairs and, as a result, incorrect matching pairs can be largely eliminated. Getting global and salient 3D structures has been an important prerequisite for environmental modelling and understanding. While research on postprocessing the 3D information obtained from stereo has been attempted (Ayache and Faugeras, 1991), the strategy presented in this thesis for retrieving salient 3D descriptions is propagating the prominent information extracted from the 2D images to the 3D scene. Thus, the matching of two prominent 2D polygonal regions yields a prominent 3D region, and the inter-relation between two 2D region matching pairs is passed on and taken as a relationship between two 3D regions. Humans, when observing and interacting with the environment do not confine themselves to the observation and then the analysis of a single image. Similarly stereopsis can be vastly improved with the introduction of additional stereo image pairs. Eye, head, and body movements provide essential mobility for an active change of viewpoints, the disocclusion of occluded objects, the avoidance of obstacles, and the performance of any necessary tasks on hand. This thesis presents a mobile stereo vision system that has its eye movements provided by a binocular head support and stepper motors, and its body movements provided by a mobile platform, the Labmate. With a viewer centred coordinate system proposed in this thesis the computation of the 3D information observed at each individual viewpoint, the merging of the 3D in formation at consecutive viewpoints for environmental reconstruction, and strategies for movement control are discussed in detail.
26

Comparative study in stereographic reading

Santiago, Alberto E. January 1900 (has links)
Thesis (M.S.)--West Virginia University, 2007. / Title from document title page. Document formatted into pages; contains iv, 64 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 31-32).
27

First- and second-order binocular matching in stereopsis : psychophysics and modeling /

Buckthought, Athena Despina, January 1900 (has links)
Thesis (Ph. D.)--Carleton University, 2004. / Includes bibliographical references (p. 109-119). Also available in electronic format on the Internet.
28

Models of disparity gradient estimation in the visual cortex

Zotov, Alexander. January 2007 (has links) (PDF)
Thesis (M.S.)--University of Alabama at Birmingham, 2007. / Description based on contents viewed Oct. 6, 2008; title from PDF t.p. Includes bibliographical references (p. 51-52).
29

Psychophysical comparison of surface interpolation using motion and disparity defined depth

MacKenzie, Kevin J. January 2003 (has links)
Thesis (M.A.)--York University, 2003. Graduate Programme in Psychology. / Typescript. Includes bibliographical references (leaves 102-107). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://wwwlib.umi.com/cr/yorku/fullcit?pMQ82940.
30

Occlusion and the interpretation of visual motion : perceptual, oculomotor, and neuronal effects of context /

Duncan, Robert O. January 1999 (has links)
Thesis (Ph. D.)--University of California, San Diego, 1999. / Vita. Includes bibliographical references.

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