Oblique Grating – simplest

from Michael’s Visual Phenomena & Optical Illusions


What to see

Above are rows of disks and adjacent lines – are the rows parallel? For most people the rows seem oblique, slightly tilted relativ to each other.

What to do

If the rows look oblique to you, you can try to remedy this by using the slider (bottom, fairly right). Once you are fairly satisfied, click the Show button: now the elements building the lines change configuration (no more alternate colors) and you can see that your adjustment was not perfect :).

Lots of aspects can be tested for their effect: colors, blur, single/double rows…


The colors are not necessary, I chose yellow/blue because yellow is brighter than background, blue darker. This is, probably, the same mechanism underlying Skye’s Oblique Grating (a little stronger) and the Bulging Checkerboard, but different from the Café Wall Illusion or the Tilted Table. I have, however, currently no good idea about the underlying neuronal mechanisms. I created this version in a search for the “simplest possible” geometrical arrangement giving rise to this illusion, hoping to better understand what makes it tick. If this is really the simplest, remains open. More interesting examples can be found on David Flaieh’s site.