Week of April 25, 2004

Fix-a-Knee

Scrub up as lead surgeon for an exciting, interactive Virtual Knee Surgery at www.livingchildren.com/ knee. Start by studying patient vitals, X-rays and anesthesia procedures before giving the final OK for surgery. To remove damaged bone, you will use tools such as the rongeur, drill and bonesaw. Artificial knee parts replace the bone tissue. When the surgery is complete, secure the skin around the knee. If your stomach can handle the sight of blood, check out photos of a real-life knee surgery. (This site is no longer available.)

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Get a Spark in Your Top

SparkTop at www.sparktop.org/ intro.html will fire you up with zany features that are updated regularly. Check out Totally Hidden Audio and help computer geeks Zack and Zoey as they help someone who is in a predicament. You can create a funky masterpiece by arranging random tunes, voices and sound effects. Or make a Spark2Spark personal profile. Just answer four simple questions about your awesome self, and you’re set. SparkTop has so many options that you might spontaneously combust.

Where Your Dollars Go

Friends lend each other a few bucks all the time, but how do banks lend people and other banks money? Fed101 will teach you about big-time money lending at www.kc.frb.org/ fed101. Explore the relationship between the Federal Reserve and everyday money spending in five interactive sections. For example, follow the life of a check from when you sign it to when the money leaves your account. Or play the role of an examiner and determine whether Judy, a bookstore owner, should get a loan. (This site is no longer available.)

	Dear Amy: In some optical illusions, why is it that when you look at something you don’t see it, but when you look away you do? — Angela, Sacramento, Calif. Dear Angela: The Hermann Grid Illusion does just what you’ve described. You’ll find an example of it at www.yorku.ca/eye/ hermann.htm. When you look at the grid of black squares, gray dots appear at the intersections of the white lines between the squares. But when you look at a dot, it disappears. This is due to lateral inhibition, which affects the amount of light reflecting to your eye. A large amount of light reflects from the point of focus while less light reaches the eye from other points. When you focus on a spot that is very bright, such as an intersection, the bright light entering your eye from that point is more intense than the darkness from the black squares, so you don’t see a gray dot. However, when you look at a dark place on the grid, less light reflects to your eye from that point, and due to lateral inhibition, less light enters your eye from the area surrounding the point of focus as well. Because such a small amount of light reflects to your eye from the white lines, you perceive gray dots instead of white. Ask Amy a Question

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