Though human visual system is far the best among the artificial visual systems humans ever were able to make it still sometimes confuses us. The reasons are sometimes well known and easily explainabla, sometimes we can say just really handwaving reasons of these ambiguities. Psychologyst know a lot about this topic but it is interesting to see these contradictory pictures, because we can get closer to understand how human brain works. I just show here some examples.

Let me start with illusions at low level of out visual system.

This is the so called Hermann illusion. If You move back and forth there must be a point, where You see black blobs at the white intersections. , but as soon as You concentrate on a certain intersection You would not see this dark circle. This is a fairly well understood illusion based on the on/off cells of the human visual cortex.

There are some illusions that hard to explain. One of these is the Fraser Spiral. No matter we can explain or not this is my favorite.

What You actually see is some concentric circle, If Yoo do not believe follw the line and You will be amazed not converging to the centre.

The next is an architectural design. But are You sure it is possible to build?

Or try to climb this stair:

Weired paralell lines: