Cite as:
Geier J, Sera L, Bernath L, 2004, "Stopping the Hermann grid illusion by simple sine distortion" Perception 33 ECVP Abstract Supplement

Stopping the Hermann grid illusion by simple sine distortion

J Geier, L Sera, L Bernath

Almost the only explanation of the Hermann grid illusion is the Baumgartner model: the effect is generated by the response of cells having concentric ON - OFF or OFF - ON receptive fields (ie a Mexican-hat weighting function). This model predicts that the illusion is independent from the relative directions of the right-angled intersections. Some authors (Wolfe, 1984 Perception 13 33 - 40; for a review see Ninio and Stevens, 2000 Perception 29 1209 - 1217) show that the magnitude -- not the existence -- of the illusion depends on certain geometrical properties. We made some simple distortions to the Hermann grid that make the illusion disappear totally while the Hermann-grid character remains. The most effective of these was to replace the straight lines with sine curves leaving the intersections right-angled. The illusion is found to disappear at a surprisingly small sine amplitude (amplitude/period < 1/10). We supported these results with psychophysical measurements (n = 29). Simple geometrical consideration shows that the distortions produced here do not change the weighted sum of the receptive field. We conclude that the Baumgartner model is not an adequate explanation of the Hermann grid illusion, because its prediction is contrary to the observations. The same distortions applied to the scintillating grid made the scintillations disappear.

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