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The Oxford Compendium of Visual Illusions$
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Arthur G. Shapiro and Dejan Todorovic

Print publication date: 2017

Print ISBN-13: 9780199794607

Published to Oxford Scholarship Online: June 2017

DOI: 10.1093/acprof:oso/9780199794607.001.0001

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PRINTED FROM OXFORD SCHOLARSHIP ONLINE (oxford.universitypressscholarship.com). (c) Copyright Oxford University Press, 2021. All Rights Reserved. An individual user may print out a PDF of a single chapter of a monograph in OSO for personal use. date: 28 September 2021

Symmetry and Uprightness in Visually Perceived Forms

Symmetry and Uprightness in Visually Perceived Forms

(p.234) Chapter 23 Symmetry and Uprightness in Visually Perceived Forms
The Oxford Compendium of Visual Illusions

Lydia M. Maniatis

Oxford University Press

Why do some two-dimensional (2D) drawings look three-dimensional (3D)? The answer is because their projection on our retinas is consistent with a 3D percept that has a “better” shape and orientation than the 2D figure. Whenever a retinal projection is interpreted by the visual system as the projection of a surface that is not frontoparallel (i.e., not parallel to the retinal surface), then the retinal image will differ in shape from the source of the projection in (a) the sizes of its internal angles and/or (b) the relative extents of its surfaces. The latter differences arise because, when an extent is assumed to be receding, then it must also be assumed to have undergone foreshortening in the projection. Using pictures, we can show that the visual system likes more, rather than less, mirror symmetry and a vertical axis of symmetry more than a tilted one.

Keywords:   2D, 3D, orientation, retinal projection, shape, symmetry, precept

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