The tilted Hermann grid illusion: 'illusory spots' versus 'phantom bands'.
The Hermann grid illusion became a cause célèbre, when it was reported that small figural changes from straight to curved bars abolish the dark illusory spots. We demonstrate that this is not an all-or-none effect; rather, the visual system tolerates some tilt/curviness. We transformed straight and curved Hermann grids to rhombic Motokawa grids by gradually tilting the horizontal bars. Initially, we observed only dark illusory spots, then dark spots combined with phantom bands traversing the rhomb along the minor axis, and finally dark phantom bands only. This shows that two kinds of illusions can coexist in the same grid pattern.
Experimental Psychology and Cognitive Science, Justus Liebig University, Otto-Behaghel-Strasse 10F, 35394 Giessen, Germany.
Kai
K
Hamburger
Franziska
F
Baier
Lothar
L
Spillmann
D015350:Contrast Sensitivity; D006801:Humans; D009903:Optical Illusions; D009949:Orientation; D010364:Pattern Recognition, Visual; D011601:Psychophysics