Exploratorium
Depth Spinner
Put a new twist on your collection of optical illusion activities. Affix the linked printable spiral to a drill, record player, or some other rotating tool. Have learners stare at the spinning disk for only 15 seconds and then look away....
National Institutes of Health
National Eye Institute: Optical Illusions
Visit this site for some optical illusions for you to have fun with! Click on the "optical illusions" page in this PDF format for a printable version of these four illusions.