The orientation dependence of the Hermann grid illusion
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Updated: Aug 30, 2026

Methods to Explore the Influence of Top-down Visual Processes on Motor Behavior
Published on: April 16, 2014
Victor De Lafuente1, Octavio Ruiz
1Departamento de Fisiologia, Biofisica y Neurociencias, Centro de Investigacion y de Estudios Avanzados del IPN, Av. IPN 2508 07360, Mexico DF, Mexico.
Abstract:
The Hermann grid illusion (HGI), elicited by a grid displayed as either horizontal-vertical (HV) or oblique (45 degrees ) configuration, was measured as the luminance necessary to cancel the illusory spots at the grid intersections. Overall, the HGI produced by the oblique grid was about one-third of that produced by the HV grid. The observers exhibited different sensitivities to the HGI orientation, and seemed to perceive the illusion in two manners: with moderate anisotropy (reduction of about 20%, three subjects) or large anisotropy (90% reduction, four subjects). The quantitative reduction of the HGI elicited by the oblique pattern tested and its reduction to almost zero in some subjects, constitute a benchmark for any model aimed at explaining the HGI on psychophysical grounds.
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