This online exhibit contains five interactive visual illusions. They demonstrate how hard it is to be sure that one's perceptions are accurate. These visual illusions challenge students to analyze what they are seeing. The visual paradoxes they find are used to study visual perception and the workings of the brain. The exhibit points out that scientists are fascinated by illusions because, by figuring out how the eye and brain can be tricked, they can better understand the normal workings of the visual system.