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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.
31

A philosophical investigation of Helmholtz' theory of perception

Windes, James Dudley, 1937- January 1963 (has links)
No description available.
32

Modelling of bio-inspired vision system for velocity estimation.

Rajesh, Sreeja January 2008 (has links)
Although motion processing in insects has been extensively studied for over almost 40 years, velocity detection in insects and how the insect brain computes the velocity of a moving feature, independent of its size or contrast, is a major enigma that remains unsolved. This study examines the accuracy of velocity estimation using two biologi-cally inspired models of motion detection, (i) the Horridge template model and (ii) the Reichardt correlator model. Various extensions and enhancements of these models are implemented with the goal of achieving robust velocity measurements. The template model is one of the prominant models of motion detection, which was proposed by Horridge in 1990. This Thesis further extends this model with the aim of improving accuracy in velocity detection using chrominance as well as luminance channels with various error checking mechanisms using different stimuli. Then the template model response is compared with Dror's elaborated Reichardt model and electro-physiological experimental results obtained from the fly visual system using similar stimuli in each case. A modified Reichardt model is shown to give a more similar response to that of fly neurons. In order to improve velocity performance of the Reichardt model, it is necessary to reduce contrast dependance of the correlator response as well as to make it independent of the structure of the visual stimuli. With this aim, the Reichardt model is then further elaborated to include contrast adaptation by a feedback adaptive mechanism and a clear reduction in contrast dependency is demonstrated. The deviation of the correlator response depending on the stimulus is termed as pattern noise. To reduce this pattern noise, the Reichardt correlator model is further extended to implement compressive non-linearity or saturation. It is seen that saturation has a profound effect on the shape of the pattern noise. Further studies on pattern noise is then performed in this Thesis using different stimuli at different speeds and contrasts. Work carried out in this Thesis on the affect of various receptive field shapes on the pattern noise reveals circular sampled arrays reduce pattern noise and hence, based on this result, a small 16 pixel yaw sensor using our elaborated model is built that shows promising performance with various potential applications. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1337180 / Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 2008
33

Measurement of the spectral and spatial responses of the human eye's blue sensitive system and the effects of lateral inhibition by the red and green sensitive systems /

Berg, Paul D. January 1986 (has links)
Thesis (M.S.)--Rochester Institute of Technology, 1986. / Typescript. Includes bibliographical references (leaves 63-64).
34

A study of the brain's transfer function for edge perception /

Fink, Charles G. January 1987 (has links)
Thesis (M.S.)--Rochester Institute of Technology, 1987. / Typescript. Includes bibliographical references (leaves 88-90).
35

Light interaction with human retinal photoreceptor finite-difference time-domain analysis /

Hajiaboli, Amir. January 1900 (has links)
Thesis (Ph.D.). / Written for the Dept. of Electrical & Computer Engineering. Title from title page of PDF (viewed 2009/06/08). Includes bibliographical references.
36

Contour integration and interpolation geometry, phenomenology, and multiple inputs /

Hilger, James Daniel, January 2009 (has links)
Thesis (Ph. D.)--UCLA, 2009. / Vita. Description based on print version record. Includes bibliographical references (leaves 300-309).
37

Quantitative analysis of the linear optical character of the anterior segment of the eye

Mathebula, Solani David 04 February 2014 (has links)
D.Phil. (Optometry) / An important issue in the quantitative analysis of optical systems is, for example, the question of how to calculate an average of a set of eyes. An average that also has an optical character as a whole and is representative or central to the optical characters of the eyes within that set of eyes. In the case of refraction, an average power is readily calculated as the arithmetic average of several dioptric power matrices. The question then is: How does one determine an average that represents the average optical character of a set of eyes, completely to first order? The exponential-mean-log transference has been proposed by Harris as the most promising solution to the question of the average eye. For such an average to be useful, it is necessary that the exponential-mean-log-transference satisfies conditions of existence, uniqueness and symplecticity, The first-order optical nature of a centred optical system (or eye) is completely characterized by the 4x4 ray transference. The augmented ray transference can be represented as a 5x5 matrix and is usually partitioned into 2x2 and 2x 1 submatrices. They are the dilation A, disjugacy B, divergence C, divarication D, transverse translation e and deflection 1t. These are the six fundamental first-orders optical properties of the system. Other optical properties, called derived properties, of the system can be obtained from them. Excluding decentred or tilted elements, everything that can happen to a ray is described by a 4x4 system matrix. The transference, then, defines the four A, B, C and D fundamental optical properties of the system…
38

Mach bands, Hermann grid, and lateral inhibition in the retina

Aktuna, Nuri 01 November 2008 (has links)
Literature about two illusions that are traditionally linked to lateral inhibitory processes in the retina is surveyed. Despite much research and a long history, the Mach bands illusion has not yet been very well-understood. Quantitative data is lacking, while qualitative data is controversial. The Hennann Grid illusion, equally old, has not yet been fully explored either. A critical and a comparative review of the experiments and the conclusions is carried out, noting common results as well as contradictory ones. New experiments and a different method of measurement are then proposed. Some preliminary experiments and their results are included in the appendix together with a review of recent knowledge about the primate retina and its functioning. / Master of Science
39

FURTHER STUDIES OF THE DETECTABILITY OF DEGRADED VISUAL SIGNALS

Wheeler, Lawrence 06 1900 (has links)
QC 351 A7 no. 78 / Observers responded to abstract forms (quadrigons) in six experiments, under a signal detection paradigm. Duration of stimulus exposure was shown to have strong effects upon detection accuracy (two studies); immediate feedback of accuracy information to observers affected performance chiefly by influencing guessing bias, not sensitivity (two studies); images that had been blurred and then deblurred by means of an analog device were compared with unblurred originals, and the effects of the retrieval process (deblurring) were characterized quantitatively by a signal detection index (one study); and electroencephalographic correlates of signal detection responses were found to vary with performance accuracy and observer confidence (one study). Discussions of the theory of signal detectability and of electroencephalography, as tools in the study of image quality and of observer sensitivity, are included in the report.
40

The Effects of Dichoptic and Isoluminant-Chromatic Stimuli on the Perception of Object and Objectless Motion

Unknown Date (has links)
Visual motion can be conveyed by a variety of information sources in the environment, and those types of information may be detected at various levels by different motion-perceiving mechanisms in the visual system. High-level visual information has been demonstrated to have 3rd order, or salience-based properties (Lu & Sperling, 1995). The perceptual system they describe that computes motion from these types of information shares several characteristics with Hock and colleagues' counterchange detection system, notably flexibility with respect to types of input from which motion can be computed, which comes at the cost of diminished processing speed. The mechanism of counterchange detection is well suited to processing visual features often present in environmental scenes, e.g., objects and surfaces, and may be a mechanism of 3rd order motion. Consistent with reported properties of 3rd order motion, the current experiments tested count erchange-, luminance-, and color-based motion stimuli with 3 objectives: to identify whether the 3 systems framework generalizes beyond the stimulus type with which it was defined, to test whether counterchange shares similarities with the 3rd order system with respect to dichoptic integration, and perception of isoluminant color-based motion, and to test subjectively objectless sources of motion-defining information (spreading luminance and hue) to see if they display properties of the 1st order system derived from sine wave gratings. Results indicate that counterchange-based stimuli displayed predicted properties of dichoptic integration, and perception at isoluminance, but putative 1st order (spreading) stimuli also displayed these properties. This may suggest that object-like surfaces, even when not directly the source of motion information, can contribute to computation of motion. Further, these results highlight the difficulty of generalizing from one theoretical framework to another, and specifically, of psychophysically testing high-level information while isolating contributions from low level information upon which high level visual stimuli are built. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection

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