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© Van Lier & Vergeer, 2006

Visual Illusion Contest 2006. Catching Patches. Rob van Lier & Mark Vergeer NICI, Radboud University Nijmegen, The Netherlands. © Van Lier & Vergeer, 2006. A fuzzy grid. © Van Lier & Vergeer, 2006. A fuzzy grid . Dark background  no patches. © Van Lier & Vergeer, 2006.

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© Van Lier & Vergeer, 2006

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  1. Visual Illusion Contest 2006 Catching Patches Rob van Lier & Mark Vergeer NICI, Radboud University Nijmegen, The Netherlands © Van Lier & Vergeer, 2006

  2. A fuzzy grid... © Van Lier & Vergeer, 2006

  3. A fuzzy grid. Dark background  no patches © Van Lier & Vergeer, 2006

  4. With luminance edges however... © Van Lier & Vergeer, 2006

  5. A fuzzy grid. Dark background, light edges  dark patches © Van Lier & Vergeer, 2006

  6. A fuzzy grid. Dark background, dark edges  dark patches (weak) © Van Lier & Vergeer, 2006

  7. A fuzzy grid. Light background  no patches © Van Lier & Vergeer, 2006

  8. A fuzzy grid. Light background, dark edges  light patches © Van Lier & Vergeer, 2006

  9. A fuzzy grid. Light background, light edges  light patches (weak) © Van Lier & Vergeer, 2006

  10. Another grid, but now with thicker fuzzy bars... © Van Lier & Vergeer, 2006

  11. A fuzzy grid. Dark background  no patches © Van Lier & Vergeer, 2006

  12. A fuzzy grid. Dark background, light edges  dark patches © Van Lier & Vergeer, 2006

  13. A fuzzy grid. Dark background, dark edges  dark patches (weak) © Van Lier & Vergeer, 2006

  14. A fuzzy grid. Light background  no patches © Van Lier & Vergeer, 2006

  15. A fuzzy grid. Light background, dark edges  light patches © Van Lier & Vergeer, 2006

  16. A fuzzy grid. Light background, light edges  light patches (weak) © Van Lier & Vergeer, 2006

  17. Patches follow random changes of the edges at the crossings... © Van Lier & Vergeer, 2006

  18. Random edges at intersections – 1 © Van Lier & Vergeer, 2006

  19. Random edges at intersections – 2 © Van Lier & Vergeer, 2006

  20. ..and using a ‘Geier pattern‘... © Van Lier & Vergeer, 2006

  21. A Geier-modified Hermann grid – no patches © Van Lier & Vergeer, 2006

  22. The return of the patches... © Van Lier & Vergeer, 2006

  23. ..catched between the edges! © Van Lier & Vergeer, 2006

  24. The patches that appear at the crossings in the Hermann grid are known to disappear when the straight contours in the grid are distorted, e.g. by curvature (Geier, 2004). Here, we present an illusion based on Hermann-grid like gratings in which the contours are quite randomly distorted. These distortions guarantee a severe reduction or complete disappearance of the visibility of the patches. Starting with these gratings we show that the patches at the crossings return when luminance edges are introduced and extended at the intersections. The ‘returned’ patches have the same relative lightness properties as they would have in a regular Herman grid (dark patches when the crossing bands are relatively light, and light patches when the crossing bands are relatively dark). In addition, the polarity of the perceived lightness difference does not depend on the lightness of the edges (i.e., whether they are dark or light). A remarkable effect here is that at the crossings the whole area between the edges is perceived to have a different lightness, irrespective of the shape of that area (i.e., whether the edges bend inward or outward etc.). Measurements on perceived lightness differences confirmed the above observations (and also for observations on various other edge manipulations). A manuscript is currently in preparation (Van Lier & Vergeer). © Van Lier & Vergeer, 2006

  25. The end Thanks! © Van Lier & Vergeer, 2006

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