Add Yahoo as a preferred source to see more of our stories on Google. A supposedly 3D optical illusion has been posted online and is possibly the most divisive I've ever seen on the optical illusion.

Optical illusions are older than you think. The first optical illusions date back to 20,000 BC and were seen in caves. Nowadays they are found all over the place – on screens, in books and even in ...

So I've read in more than a few places that color doesn't exist outside our heads, it's just wavelengths of light. That our brains are the things that make color, same with sound (which is just ...