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Updated: Jul 11, 2026

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Published on: April 11, 2025
Effects of contour proximity and lightness on Delboeuf illusions created by circumscribed letters
1Department of Psychology, 501 Westminster Avenue, Westminster College, Fulton, MO 65251, USA. JaegerT@westminster-mo.edu
Abstract:
32 observers judged the size of a letter, either an "A" or an "S," which was surrounded by a circle. Both letters were overestimated, but larger surrounding circles reduced the illusion. Decreasing the lightness contrast of the surrounding circle relative to the central letter diminished the illusion. The results suggest that, like the Delboeuf illusion, these circumscribed letters illusions are produced by interactions among size-coding neurons.
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