The present thesis reports psychophysical and modeling studies on the spatial properties of visual mechanisms mediating the perception of mirror symmetry in human vision. In a first set of experiments, patterns were filtered for power spectra that decayed with spatial frequency according to variable slopes. Results revealed that symmetry detection is optimal if contrast energy is roughly equated across log-frequency bands (i.e. 1/f2) and that, under such conditions, spatial scales contribute equally and independently to symmetry perception. In a second study, random-noise patterns were filtered for various orientation bands. Results showed that symmetry perception is possible at all orientations, is mediated by oriented mechanisms, and is computed independently in different orientation channels. Data also revealed that the dimensions of the spatial integration region (IR) for symmetry vary with orientation in a way that approximately matches the spatial distribution of information in the stimulus. Finally, symmetry detection was measured for bandpass textures of variable spatial density and variable contrast polarity. For such patterns, it was found that symmetry is computed at a spatial scale proportional to stimulus density and that mechanisms insensitive to contrast polarity (i.e. second-order) are involved in the scale-selection process. / Overall, results from empirical and modeling work revealed an intimate link between symmetry perception and the properties of spatial filters. In particular, I argue that the size of the IR tends to vary such that a fixed amount of information is integrated irrespective of the spatial properties of the stimulus. Implications for the functional architecture of symmetry perception are discussed, and a paradigm for future research in symmetry perception is proposed in which spatial filtering is extended to higher orders of spatial complexity.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.36688 |
| Date | January 1999 |
| Creators | Rainville, Stéphane Jean Michel. |
| Contributors | Kingdom, Frederick A. A. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Psychology.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001747184, proquestno: NQ64650, Theses scanned by UMI/ProQuest. |
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