This optical illusion experiment can be carried out by anyone. All you need is a pencil. Tell your students to take the pencil in between their thumb and forefinger and start to shake it up and down in a short motion of up to a few inches. The pencil should look like it is bending in the middle as if it is made from plastic. Of course it is not. It is merely an optical illusion.
Talk to the students about the history of optical illusions, pointing them back to the ancient Greeks. Epicharmus and Protagorus, who differed in their opinions on human senses. Epicharmus believed they could not be trusted making mistakes while Protagorus believed they could be. Give the students a copy of the psychologist J.J. Oppel's first optical illusions that date back to 1854. Hand the students some more recent examples and ask them what they see and why they think they see it. Ask them which of the two Greeks they think was correct in his opinion.
After giving students plenty of time to research and study the many examples of optical illusions, have your students create their own. This can involve illusions made from cards, crayons, pens, and string, or it can involve using design software on computers for those who are more technically minded. Once completed they should show their illusions to the rest of the class and explain the science behind them.
Split the class into two groups separated by gender and then give them all the same optical illusions to look at. They should be split into the categories of two pictures in one, one illusion in print, and geometric figures that come in two and three dimensions. Create questions to go with the illusions and see which gender has the better perception when it comes to optical illusions.