An optical illusion happens when visually perceived images differ from objective reality. We see what really isn’t there. What’s going on in our brain?
Optical illusions reveal to us the way our photo receptors and brain assemble visual information into the 3D world we see around us. A white grid on a black background creates “dancing” intersections, because our retinal cells are organized to increase contrast with lateral inhibition. Edges of pictures get extra attention, because the edges in the real world can either help or hurt you. Furthermore, your brain’s visual cortex operates on assumptions about the lighting of an image. It expects light to come from a single source. That’s why 3D concave or convex shapes on a piece of paper can be confused when flipped. The brain uses assumptions of visual information to create a tailored, edited version of the world.