Open this image in full-size. Are those concentric circles, or one continuous spiral?

Let us revisit the Seemingly Bent category. We hadn’t had unique optical illusion that belongs to this section, in quite a while. To remind you once again, Seemingly Bent category consists of illusions that give you impression you are seeing slanted lines and shapes, while in fact they are perfectly straight (or mutually parallel). Most famous example to represent this category could be “Cafe Wall“, followed by both slanted square and slanted seesaw.

Now that we have repeated the matter, I can proceed explaining today’s two specimens. First one on the right is nothing new to be frank. It’s just a more recent version of “Circles or Spiral” illusion. You can open the image in full-size to see the full effect. In short: the image gives you impression you are seeing continuous spiral, while there are only 6 concentric (ones that share the same center) circles instead. The second image below is new work by Akiyoshi Kitaoka, and believe it or not – all of the lines in it (consisted of gray blocks) are placed perfectly horizontal. I’m not pretty sure why is that, and does the color combination help making the effect stronger.