"Usually at first sight it seems it's a bunch of oddly shaped paralellograms; but once you realize it, it's actually one line."

stereogram 3D optical illusions.

You have to coordinate your two eyes and many parts of your brain in order to see 3D pictures. this is good exercise for your brain. 3D viewing stimulates many areas of the brain, so most people find it very pleasurable. The stimulation makes them feel alert, yet relaxed. It feels good!

The main trick to seeing stereograms is learning to de-couple your focus and eye positioning. You will need to position your eyes as though you were looking at an object about twice as far away, while focusing on the image.

try these.

helicopter



telephone

Can you perceive 6 triangles in this Kanisza-like figure?


Some regular concentric objects appear to rotate when we approach
or move back from them. Move your head backwards and forwards
keeping the focus on the central cross of the image, the
3 circular sets will counter-rotate!