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CROWDING AND FORM VISION DEFICITS IN PERIPHERAL VISION
by
Anirvan S. Nandy
A Dissertation Presented to the
FACULTY OF THE USC GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
DOCTOR OF PHILOSOPHY
(PSYCHOLOGY)
August 2010
Copyright 2010 Anirvan S. Nandy
Object Description
| Title | Crowding and form vision deficits in peripheral vision |
| Author | Nandy, Anirvan S. |
| Author email | nandy@usc.edu; anirvan.nandy@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Psychology |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2010-04-23 |
| Date submitted | 2010 |
| Restricted until | Unrestricted |
| Date published | 2010-06-10 |
| Advisor (committee chair) | Tjan, Bosco S. |
| Advisor (committee member) |
Biederman, Irving Baker, Laura Itti, Laurent Grzywacz, Norberto M. |
| Abstract | Visual crowding is an ubiquitous limitation of peripheral vision and manifests itself as the marked inability to identify shapes when targets are flanked by other objects. It presents a fundamental bottleneck to object recognition in peripheral vision. Although the phenomenon has been widely studied over the last four decades, the neural mechanisms underlying crowding remain unsettled. Such an understanding is critical for the development of visual enhancement aids for patients with central field loss.; Here we first investigate the nature of form vision deficits in the periphery through a series of psychophysical experiments. We develop a novel method of classification images to overcome the intrinsic spatial uncertainty in the periphery (Tjan & Nandy, 2006), and show that the perceptual templates utilized in the periphery are undistorted. By using higher order reverse correlation analysis, we show that the form of flanking objects greatly influence target recognition errors under crowding and that crowding is associated with an inefficient selection and usage of low-level features (Nandy & Tjan,2007). We further show that feature integration across spatial frequency channels in optimal (for letter identification) in both central and peripheral vision (Nandy & Tjan, 2008).; We next develop a unified model of visual crowding. Our theory, guided by empirical findings, including the ones mentioned above, views crowding as a necessary consequence of gathering image statistics during eye movements. We show that any temporal overlap between spatial attention in the peripheral visual field that precedes a saccadic eye movement and the motion blur due to the subsequent saccade can cause a misrepresentation of image statistics in peripheral V1, where saccadic suppression is weak. We demonstrate with simulations that the strength and shape of long-range horizontal connections formed under such conditions quantitatively explain the three hallmark signatures of crowding: (a) the spatial extent of crowding scales linearly with eccentricity (Bouma, 1970); (b) crowding is asymmetric with respect to the target (Bouma, 1973; Petrov et al., 2007) and (c) the zone of crowding is anisotropic (Toet & Levi, 1992). The model provides a basis for understanding specific target-flanker interactions at the feature level and makes predictions about cortical reorganization in patients with central field loss. |
| Keyword | peripheral vision; crowding; form vision; computational modeling; visual psychophysics; AMD |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m3122 |
| Rights | Nandy, Anirvan S. |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | http://www.usc.edu/isd/libraries/services/ask_a_librarian/email/ |
| Filename | etd-Nandy-3824 |
| Archival file | uscthesesreloadpub_Volume23/etd-Nandy-3824.pdf |
Description
| Title | Page 1 |
| Full text | CROWDING AND FORM VISION DEFICITS IN PERIPHERAL VISION by Anirvan S. Nandy A Dissertation Presented to the FACULTY OF THE USC GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (PSYCHOLOGY) August 2010 Copyright 2010 Anirvan S. Nandy |
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