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In this activity about light and perception, learners discover how a flash of light can create a lingering image called an "afterimage" on the retina of the eye.

In this activity about vision and optical illusions, learners conduct a simple test to demonstrate how our eyes create "afterimages." Learners stare at a black cardboard bat for at least 30 seconds an

In this activity (1st on the page), learners find their blind spot--the area on the retina without receptors that respond to light.

In this activity, learners calculate the width (horizontal diameter) of the blind spot on their retina. Learners make a blind spot tester using a piece of notebook paper.