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THE REPRESENTATION OF MEDIAL AXES
IN THE PERCEPTION OF SHAPE
by
Mark Daniel Lescroart
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
(NEUROSCIENCE)
May 2011
Copyright 2011 Mark Daniel Lescroart
Object Description
| Title | The representation of medial axes in the perception of shape |
| Author | Lescroart, Mark Daniel |
| Author email | mark.lescroart@usc.edu; marklescroart@gmail.com |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Neuroscience |
| School | College of Letters, Arts and Sciences |
| Date defended/completed | 2011-01-05 |
| Date submitted | 2011 |
| Restricted until | Unrestricted |
| Date published | 2011-02-14 |
| Advisor (committee chair) | Biederman, Irving |
| Advisor (committee member) |
Itti, Laurent McArdle, John Mel, Bartlett Tjan, Bosco |
| Abstract | Aristotle famously said that vision is “to know what is where, by looking”—but that is not the whole story. Vision is also to know what is where relative to everything else. We constantly make use of relative position information, when we draw, build, or read a map or diagram. How does our visual system divide up space, to let us know that one object is above another, or that one part of an object protrudes from the end of another part? Structural description theories of shape recognition hold that our visual system represents objects as collections of parts in particular relations.; The principal focus of this dissertation is to investigate one plausible scheme for the encoding of within-object (between-part) spatial relations: the encoding of medial-axis-relative relations. Medial axes are imaginary lines that pass through the central part of a volume, as a spit through a hot dog. Medial axes within each part of an object can define an invariant, stick-figure like structure of an object, in the sense that the points of attachment and relative angles between the axes (in rigid objects) will not change with the perspective from which the object is seen. A behavioral similarity rating experiment showed that naïve subjects spontaneously judge novel objects to be more similar if the objects share the same medial axis structure, in many cases even if the objects are composed of different-shaped parts and shown from different perspectives. When subjects were asked to distinguish (in a same/different task) categorically-different medial axis structures seen from different perspectives, they showed slower recognition times with greater differences in perspective (though the estimated rates of mental rotation were very fast).; Finally, evidence from a multi-voxel pattern classification fMRI study showed that medial axis structure—as distinct from simple retinotopic orientation—is encoded starting at a very early stage (V3) in the visual cortex. Patterns of activity in V3 were more similar in response to novel objects that shared the same medial axis structure than in response to novel objects that shared the same overall orientation. |
| Keyword | vision; medial axis; object recognition; fMRI; mental rotation; multi-voxel pattern classification |
| 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-m3655 |
| Rights | Lescroart, Mark Daniel |
| 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-Lescroart-4285 |
| Archival file | uscthesesreloadpub_Volume40/etd-Lescroart-4285.pdf |
Description
| Title | Page 1 |
| Full text | THE REPRESENTATION OF MEDIAL AXES IN THE PERCEPTION OF SHAPE by Mark Daniel Lescroart 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 (NEUROSCIENCE) May 2011 Copyright 2011 Mark Daniel Lescroart |
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