The Hollow Mask Optical Illusion Explained

In a fascinating educational video by the Royal Institution, mathematician and host Rachel Dorris explained the disarming optical illusion created by a hollow mask to her two children, Eva and Daniel. Once they understood the concept behind the illusion, she then enlisted the kids to create a hollow mask of their own.

We make a lot of assumptions about the world around us, often based on experience. These assumptions help us make judgments and decisions quickly, but they’re not always correct. …This is the ‘hollow mask illusion’. Although the mask is actually concave, bending inwards, it sometime looks like it is sticking forwards out of the base. This is partly because we expect faces to be convex, curving out towards us, and make assumptions about what we’re seeing based on our past experience. You probably won’t have one of these at home,