Here is a follow-up on Chris's response. It may be more than your students want to know, though. http://www.scientificamerican.com/article/seeing-forbidden-colors/
Carol On Mon, Nov 3, 2014 at 8:07 AM, Christopher Green <[email protected]> wrote: > > > > > > > What is the question, exactly? Yes, negative after images go to their > opposites — each primary becomes a secondary, and vice versa. When the > student says “the red-green opposite we were taught,” does s/he mean taught > in your class or just “taught” by her past. Lots of people say that red and > green are opposites, but it is important to remember that there is a lot of > “slippage” in color-naming. In particular, “magenta” and “cyan” are not > words commonly used in colloquial language and so nearby primary names are > often substituted. > > In addition, when kids are taught colour mixing, it is often with pigments > rather than light, and so it is subtractive mixing they are taught rather > than additive mixing (which is why “everyone” comes to perception class > thinking that mixing “blue” and “yellow” results in “green” — which they > do, subtractively). The additive primaries are identical to the subtractive > secondaries, and vice versa. BUT, no one ever calls the subtractive > primaries “cyan," “magenta," and “yellow." They are always called “blue," > “red," and “yellow." There is lots more to this topic, but I don’t want to > bore everyone here. Write me off line if you would like to not more about > the relation between additive and subtractive mixing. > > Images like the one above are rarely rendered exactly accurately. True > additive primary red is a little more orange than people expect it to be > (what North Americans think of a “pure” red actually has a bit of blue in > it, a cultural convention that caused Japanese car makers all kinds of > consternation when they first tried to sell red cars in the US). Also the > additive primary blue appears to North American to be closer to violet > (indeed, Helmholtz called it violet in his classic textbook on the topic). > > I hope this helps. > > Best, > Chris > ….. > Christopher D Green > Department of Psychology > York University > Toronto, ON M3J 1P3 > Canada > > [email protected] > http://www.yorku.ca/christo > ………………………………... > > On Nov 2, 2014, at 1:09 PM, Carla Grayson <[email protected]> wrote: > > > > > A student sent me this email and I don't have a response. Can somebody > help me? > > When you did the negative color afterimage demonstration in class on > Tuesday, I looked at the cross in the middle of the four eagles. The blue > and yellow swapped like I thought they would, but red became cyan and green > became magenta. They went to their color opposite instead of the "red > green" opposite we were taught. > > I also did a negative afterimage with this image > http://2.bp.blogspot.com/-bQvF9kxioDc/T-m6569bd6I/AAAAAAAADP4/9yl0NLP1G5Q/s400/red-green-blue-light-make-white.png > > Red, green, and blue turned into cyan, magenta, and yellow respectively > (on a white piece of paper) but the green was much stronger than the red, > which was stronger than blue. Is there a reason why some of these > afterimages show up more strongly? > > Lastly, by focusing on the boundaries of the images I can imagine that > there are only three circles, each with its own filter. When I do this, I > can no longer see the cyan, magenta, yellow, or white parts of the image > and this is easier to do when my eye is unfocused. Do you know the > cognitive explanation for this? > > Thanks, > Carla Grayson > ([email protected]) > University of Michigan > > --- > > You are currently subscribed to tips as: [email protected]. > > To unsubscribe click here: > http://fsulist.frostburg.edu/u?id=430248.781165b5ef80a3cd2b14721caf62bd92&n=T&l=tips&o=39798 > > (It may be necessary to cut and paste the above URL if the line is broken) > > or send a blank email to > leave-39798-430248.781165b5ef80a3cd2b14721caf62b...@fsulist.frostburg.edu > > > > > > --- > > You are currently subscribed to tips as: [email protected]. > > To unsubscribe click here: > http://fsulist.frostburg.edu/u?id=177920.a45340211ac7929163a0216244443341&n=T&l=tips&o=39816 > > (It may be necessary to cut and paste the above URL if the line is broken) > > or send a blank email to > leave-39816-177920.a45340211ac7929163a0216244443...@fsulist.frostburg.edu > > > > > -- Carol DeVolder, Ph.D. Professor of Psychology St. Ambrose University 518 West Locust Street Davenport, Iowa 52803 563-333-6482 --- You are currently subscribed to tips as: [email protected]. To unsubscribe click here: http://fsulist.frostburg.edu/u?id=13090.68da6e6e5325aa33287ff385b70df5d5&n=T&l=tips&o=39817 or send a blank email to leave-39817-13090.68da6e6e5325aa33287ff385b70df...@fsulist.frostburg.edu
