Many years ago as an undergraduate student, I was fascinated by some of my psychology classes. I’ve forgotten most of what I learned, but one thing stuck with me. It was an experiment done with kittens where half were put in a room with images that horizontal lines only. The other half were put in a room with images that had vertical images only. This was done shortly after birth to determine what affect environment would have on their vision.
As it turned out, their vision developed based on what they saw. So kittens in the horizontal room only would walk into chair legs because they literally couldn’t see them.
I think of that experiment whenever I see optical illusions because it makes me wonder how much of the world we simply can’t experience. Click on this image to get a larger picture: