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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

The Curved Grid Non-Illusions

The Curved Grid Non-Illusions

Eliminating Hermann’s Spots and Lingelbach’s Scintillation

(p.362) Chapter 45 The Curved Grid Non-Illusions
The Oxford Compendium of Visual Illusions

János Geier

Mariann Hudák

Oxford University Press

The generally accepted explanation of the Hermann grid illusion is Baumgartner’s hypothesis that the illusory effect is generated by the response of retinal ganglion cells with concentric ON-OFF or OFF-ON receptive fields. To challenge this explanation, some simple distortions to the grid lines were introduced that make the illusion disappear totally, while all preconditions of Baumgartner’s hypothesis remained unchanged. Psychophysical experiments in which the distortion tolerance was measured showed the level of distortion at which the illusion disappears at a given type of distortion for a given subject. Statistical analysis shows that the distortion tolerance is independent of grid-line width within a wide range and of the type of distortion, except when one side of each line remains straight. The conclusion is the main cause of the Hermann grid illusion is the straightness of the edges of the grid lines. Similar results have been obtained in the scintillating grid.

Keywords:   curved grid non-illusions, Hermann grid illusion, Lingelbach, scintillation, distortion tolerance

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