Original (sent) abstract to ECVP2004  (abstract deadline: March 09, 2004)

Title: Stopping the Hermann grid illusion by simple sine distortion

J Geier, L Sera, and L Bernath (Eötvös Loránd University, Psychology department, H1046, Budapest, Izabella u. 46, geier@izabell.elte.hu)

Almost the single explanation of the Hermann grid illusion is the Baumgartner’s model. In this way the effect is generated by the response of cells having concentric on-off or off-on receptive fields (i.e. 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; Ninio and Stevens, 2000, Perception, 29, 1209-1217, review) shows that the magnitude – not the existence - of the illusion depends from certain geometrical properties. We made some simple distortions on the Hermann grid, where the illusion disappears totally while the „Hermann–grid-character” remains. The most effective was to change the straight lines with sine curves while the intersections remain right-angled. Results: the illusion disappears at a surprising small sine amplitude (amplitude/period < 1/10). We supported these results with psychophysical measurements (29 peoples).Simple geometrical consideration shows that the used distortions don’t change the weighted sum of the receptive field. Consequence: the Baumgartner’s model is not adequate for the Hermann grid illusion, because its prediction is in contrary with the observations. By using the same distortions at scintillating grid the results was similar: scintillation disappeared.

Accepted (final) abstract (Perceptionweb)