I use this Optical Illusions powerpoint as an introduction to the Nervous System for my Middle School students. It is a fun way to introduce this system! It would also be suitable for High School. The powerpoint explains optical illusions. There are some slides at the end that introduce the structure of the brain (the different lobes and hemispheres), and discuss how everyone's perception is different. It can be used as a lab (see my other documents to download the corresponding lab worksheet), or for an activity and note-taking. The kids love it. Enjoy!