Afterimages and Optical Illusions

posted by guy on 5 May 2014
last changed 31 May 2014

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ages: 10 yrs to 99 yrs

A sequence of lessons involving effects of visual desensitization. Focuses on several optical illusions. Occupies 1 to 2 hours of class time.

subjects: Biology, Psychology


titletypenotes
Yang and Yin - negative afterimageslessonUse this lesson to give the physiological explanation behind negative afterimages. Start with the Mona Lisa or the U.S. flag illusion to get students' attention and then follow with a discussion about visual desensitization to explain how it all works. Even very young students can enjoy these illusions.
Cheshire Cat IllusionslessonContinue with this lesson to show some dramatic disappearance effects. Point out that these illusions also depend on desensitization, but they need to be fuzzy-edged to avoid being counteracted by involuntary eye movements.
Seeing Blood Vessels in the EyelessonThis effect depends on thwarting the normal desensitization in the eye. If it's possible to get a very dark room, and there are enough small flashlights to go around, this is a good activity for 10 minutes.
Lilac Chaser IllusionlessonUse this illusion as a finale. It involves both disappearance and negative afterimages. Let the students explain it. 10 minutes worth.


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