wise@cal-unix.UUCP (12/09/83)
An interesting item appeared in the January, 1984 issue of the magazine "Family Circle" on page 110. The item was attributed to "The New England Journal of Medicine", Vol 309, page 315. The title in "Family Circle" was "Computer Aftereffect - Not to Worry". The text of the item follows. While it specifically mentions personal computers, it seems clear that it applies to any green on white VDU. A vivid visual illusion produced by working with a personal computer could be worrisome, but need not be. Northwestern University researchers, who experienced the illusion, relate what happened to them: After a session at the machine, which has a video display presenting luminous green characters on a dark backround, ordinary white letters and lines on contrasting backround appeared pink, and a pink fringe could be seen on sheets of white paper or white walls. Report Dr. Mark J. Greenwald and colleagues: "The pink aftereffect, which may persist for a day or longer, is a normal nervous system adaptation response. While the response is harmless and never permanent, it could alarm anyone who hasn't heard of it, and physicians who are unaware of it could mistake it for a hysterical symptom or manifestation of neurological disease." So now you know why the clothes you put on right after a session at the terminal don't match. I wonder if the reason that the color is pink is because green is yellow and blue combined, i.e. white minus red. Anyone out there know? I assume that this sort of problem has been encountered previously in some other situation. Rick Wise seismo!rlgvax!cal-unix!wise
akp@isrnix.UUCP (12/15/83)
#R:cal-unix:-15300:isrnix:6500006:000:1119 isrnix!akp Dec 14 04:45:00 1983 /./ Okay... Psych 101 was not so long ago for me, so here goes: Your eye works by inhibiting itself. If a cone is hit by light, it "fires" more rapidly, sending a "light" message to the Optic Nerve (indirectly). As a side-effect, the firing is building up some waste material, which in turn inhibits the cone which is firing AND THOSE AROUND IT. If you look at the sun (on the right kind of day), you'll start seeing a bluish disk blocking it; that's the result of the yellow-sensing cones being inhibited; you sense more blue. Same thing goes for green screens: the green receptors are busy inhibiting each other, and when you look away it takes a bit for them to recover. During that time, the red sensors are still as active as normal, and the green ones are inhibited, so you see "extra" red on everything (relatively speaking), especially light-colored (white) things. The above is a simplification. The "yellow" sensors are actually a combination of the blue and the green, and all that inhibiting is more complex than that, really. But you get the idea. -- Allan Pratt ...decvax!ihnp4!iuvax!isrnix!akp
rpw3@fortune.UUCP (12/16/83)
#R:cal-unix:-15300:fortune:14500012:000:375 fortune!rpw3 Dec 15 22:16:00 1983 The complementary colors stuff is all o.k., except... If you look at the "Land effect" reports, it is not clear that there are specifically red, green, blue, or any other color cones. SOMETHING is going on, and the inhibitory neuro-physiology sounds right, but just because we chose to build T.V.'s with triple dots, don't assume that's the way the eye works. -Rob Warnock
norskog@fortune.UUCP (12/16/83)
#R:cal-unix:-15300:fortune:14500013:000:289 fortune!norskog Dec 16 11:47:00 1983 The inhibition mechanism serves as a "contrast gain". Has this technique ever been used in the low-level analog parts of a digital camera system? Lance Norskog Fortune Systems hpda!fortune!norskog harpo!... sri-unix!... amd70!... ihnp4!... allegra!...