|MadSci Network: Physics|
Greetings, Max! I think what you've observed is closely related to what one sees in a darkened room where there is a fast strobe light flashing on and off. Your computer screen is like a strobe light! Your screen is not "displaying" continuously. Instead, it is actually re-drawing, or, "refreshing" the picture you look at many times a second. (Nowadays, most monitors do this at least 75 times each second. Their "refresh rate" is said to be 75 Hertz [Hz], or greater. Mine is set at a slower 60 Hz, because that's fast enough I don't personally notice any "flicker".Then again, I've always been a bit "slow"!) Your eyes and brain use something called "persistence of vision" to blend the individual pictures together into a coherent picture. Your brain doesn't usually notice the flashing. Try moving your hand in front of the monitor. If you move very slowly, you will not notice anything unusual. If you move more quickly, you will see "many images" of your hand as it moves. You may even notice some of these fleeting images seem "transparent". Try it away from the monitor, too. Use one finger. You won't see "many images", but you may see a "blur" depending on how fast your finger moves. I'm pretty sure what you are seeing is the same "blur" you see when you wave a finger very quickly under continuous lighting. The difference here is probably your monitor, which is "flashing" and "interrupting" the blur you'd normally perceive. In one sense, your monitor is flashing like a strobe light, "freezing" the movement of your hand. In another, your hand is moving in front of a flickering light source which otherwise seems continuous. Your brain notices something isn't quite "normal" about this! Our brains and eyes interpret this in the way which will give us the most possible information: we see a "divided blur", or, a set of semi-distinct "frozen" images in what we'd otherwise perceive as normal "motion blur". I've found this can be a fun thing to play with! Under continuous light sources you can wave a pencil loosely between your thumb and forefinger. It will appear to "bend" as you wave it more quickly. Now, try it in front of your monitor. The effect seems much more pronounced. ("Disco-bendy-pencil"! :) I hope I've helped with your question. If you wish to know more, please start with the links below. If you need more help, e-mail me at email@example.com, and I'll do my best to assist you! Your MadSci, -Matt firstname.lastname@example.org Links: Refresh Rate Defined: http://www.zdwebopedia.com/TERM/r/refresh.html Monitors (See Slide 4): http://nina.ecse.rpi.edu/shur/advanced/Notes/Noteshtm/Displays33/sld001.htm A whole Web-book about visual perception: http://www.yorku.ca/eye/
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