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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.
11

Interocular transfer in the pigeon

Graves, Jefferson A. January 1980 (has links)
The interocular transfer of simultaneously presented visual discriminations was examined in the pigeon (Columba livia) in several experimental situations. When trained monocularly on a jumping stand, there was no evidence of transfer to the other eye-hemisphere system of either pattern or colour discriminations using retraining and reversal learning measures as well as testing. This failure was not due to any obscuring of transfer consequent upon switching the occluder from one eye to the other, nor was there any suggestion of even a small amount of transfer of information from the trained eye to the untrained eye with extensive overtraining and decoupling trials. Binocular training on the jumping stand also revealed that some of the pigeons were learning a discrimination with only one eye in spite of the opportunity to learn with both eyes. When trained in a key pecking task, pigeons demonstrate perfect transfer. Testing revealed that this discrepancy in results is not due to the number of trials given in the two situations, to separation of the stimuli over a greater distance or by a partition, nor to the distance at which the pigeon makes a decision about which stimulus to approach. When the function of the retinal locus of the stimuli was examined, evidence was found in the literature and in my observations that the pigeons were using a different part of the retina when scanning the stimulus display in a key pecking task than on the jumping stand, even though the stimuli in the two situations were located in the same position relative to the bird's head. Specifically, in the key pecking tasks the red area of the retina, which serves the lower binocular portion of the retina, is used. On the jumping stand this area is not used to scan the stimuli. It was then possible to demonstrate a failure of transfer in a key pecking task and successful transfer on the jumping stand by simply manipulating whether the red area was used in scanning the stimuli. The results are discussed in terms of a consequence of binocular convergence from the red area, and when there is a failure of transfer, when the red area is not used, or prevented from being used, the stimuli fall within the monocular field where there is no necessity of later convergence from the two inputs. Active inhibition mechanisms also might serve to lateralize input to one hemisphere.
12

The Effect of an Occluder on the Accuracy of Depth Perception in Optical See-Through Augmented Reality

Hua, Chunya 15 August 2014 (has links)
Three experiments were conducted to study the effect of an occluder on the accuracy of nearield depth perception in optical-see-through augmented reality (AR). The first experiment was a duplicate experiment of the one in Edwards et al. [2004]. We found more accurate results than Edwards et al.’s work and did not find the occluder’s main effect or its two-way interaction effect with distance on the accuracy of observers’ depth matching. The second experiment was an updated version of the first one using a within-subject design and a more accurate calibration method. The results were that errors ranged from –5 to 3 mm when the occluder was present, –3 to 2 mm when the occluder was absent, and observers judged the virtual object to be closer after the presentation of the occluder. The third experiment was conducted on three subjects who were depth perception researchers. The result showed significant individual effects.
13

Neural computation of depth from binocular disparity

Reis Goncalves, Nuno January 2018 (has links)
Stereopsis is a par excellence demonstration of the computational power that neural systems can encapsulate. How is the brain capable of swiftly transforming a stream of binocular two-dimensional signals into a cohesive three-dimensional percept? Many brain regions have been implicated in stereoscopic processing, but their roles remain poorly understood. This dissertation focuses on the contributions of primary and dorsomedial visual cortex. Using convolutional neural networks, we found that disparity encoding in primary visual cortex can be explained by shallow, feed-forward networks optimized to extract absolute depth from naturalistic images. These networks develop physiologically plausible receptive fields, and predict neural responses to highly unnatural stimuli commonly used in the laboratory. They do not necessarily relate to our experience of depth, but seem to act as a bottleneck for depth perception. Conversely, neural activity in downstream specialized areas is likely to be a more faithful correlate of depth perception. Using ultra-high field functional magnetic resonance imaging in humans, we revealed systematic and reproducible cortical organization for stereoscopic depth in dorsal visual areas V3A and V3B/KO. Within these regions, depth selectivity was inversely related to depth magnitude — a key characteristic of stereoscopic perception. Finally, we report evidence for a differential contribution of cortical layers in stereoscopic depth perception.
14

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

Popple, Ariella Vered January 1999 (has links)
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.
15

Attending to pictorial depth electrophysiological and behavioral evidence of visuospatial attention in apparent depth /

Parks, Nathan A. January 2005 (has links) (PDF)
Thesis (M. S.)--Psychology, Georgia Institute of Technology, 2005. / Randall W. Engle, Ph.D., Committee Member ; Paul M. Corballis, Ph.D., Committee Chair ; Daniel H. Spieler, Ph.D., Committee Member. Includes bibliographical references.
16

Effects of display contrast and field of view on distance perception /

Helbing, Katrin G., January 1992 (has links)
Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1992. / Vita. Abstract. Includes bibliographical references (leaves 106-108). Also available via the Internet.
17

Disparity contingent high spatial frequency constraints on the upper velocity limit of steropsis /

Lee, Stan S., January 1900 (has links)
Thesis (Ph. D.)--Carleton University, 2001. / Includes bibliographical references (p. 119-125). Also available in electronic format on the Internet.
18

Integration of motion and disparity cues in the recovery of three-dimensional shape /

Mackenzie, Kevin James. January 2009 (has links)
Thesis (Ph.D.)--York University, 2009. Graduate Programme in Psychology. / Typescript. Includes bibliographical references (leaves 181-198). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR51739
19

A Study of Depth Perception Among Brain-injured, Familial and Idiopathic Mentally Retarded Subjects

Wright, Ronald W. 01 1900 (has links)
In light of the conflicting data regarding depth perception and the retardate, it was the purpose of this study to reinvestigate whether or not significant differences exist in depth perceptual abilities among mental retardates. A standard depth perception apparatus was utilized to test the groups of brain-injured, familial and idiopathic subjects.
20

Surface lightness and size and distance effects

Viswanathan, Ramkumar. January 1978 (has links)
Call number: LD2668 .T4 1978 V58 / Master of Science

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