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COPYRIGHTED MATERIAL Study Session: Learning to See 35 Optical Illusions Which of the horizontal lines in the image below are parallel? How do you know? Reproduced with permission. © Exploratorium® Do you see an old or a young woman in this picture? Both images are present if you look closely. With effort, you can switch back and forth from one image to another. Notice the slightly off-balance feeling that happens as you make the switch. Practice switching rapidly back and forth between each of the two images until you can do it comfortably. Reproduced with permission. © Exploratorium® COPYRIGHTED MATERIAL