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quote:Originally posted by eric lI don't think you stand corrected, Neil.
quote:Originally posted by another_someoneI am not sure one can ask in any sensible way how the brain sees a colour, and whether one can modify the brain to see another colour.The only questions that I think are meaningful is whether the brain can see the difference between two things (i.e. whether one red looks the same, or different, from another red; whether a red looks different from a blue; whether a red looks different from a black?Once the brain/eye is able to distinguish two things, what label you apply to that thing is arbitrary. If someone looks to the sky, and is told that the colour he sees there is green, then to him the sky is green. The issue that matters is not whether the sky is blue or it is green, but whether one can distinguish between the colour of the sky and the colour of grass.George
quote:Originally posted by lightarrowYou can modify the brain to see colored numbers or to perceive a smell instead of an image! This happens in some people, according to neurophysiology. I wouldn't be much surprised if we could also see different colors.
quote:Superior marsupial eyes see more colourThey might spring from an ancient lineage and produce babies that look like peanuts, but marsupials have eyesight that is even better than ours, reseachers have found.The discovery by Dr Catherine Arrese from the University of Western Australia in Perth strikes another blow for those researchers challenging the view that marsupials, far from being primitive living fossils, are often superior placental mammals.Using a combination of behavioural studies and tissue analysis, Arrese found that two types of marsupial - honey possums and dunnarts - can see colours from red right through to ultraviolet, a colour outside detection by humans and most animals. This enables the creatures to pursue a lifestyle which spans both day and night activities.Arrese first suspected that sight is important to honey possums as she watched them scurry up banksia bushes to lap up the nectar of a particular flower. Banksia flowers turn from green to orange, and possums would always head for the brightest orange blossom - without being distracted by the fragrance coming from other flowers.Using microspectrophotometry - a delicate technique where a fine beam of coloured light is shone through a single eye cell - Arrese found that marsupials had numerous cones of at least three different types, enabling them to see a wide colour spectrum. Colour vision depends on cones - tiny cells in the retina which react to different wavelengths of light. Birds and reptiles have four types of cones in their eyes (ultraviolet, blue, green and red), while most placental mammals have only two (they've lost the blue and green), greatly limiting their colour vision.Humans and apes have two types of cones, but one of the cone types, SWS1 has a huge variation in spectral sensitivity, allowing primates - including humans - to see a wide range of colours.Some experts believe that placental mammals 'lost' the extra two cone types some time in their evolution, as they adapted to a nocturnal lifestyle. But primates re-acquired an extra cone type, enabling them to detect the reddish colour that fruit acquires as it ripens.Arrese believes that marsupials have kept their full colour vision throughout evolution, and were only thought not to have colour vision because most people thought they were nocturnal, she said: "Far from being typically nocturnal … the honey possum is actually crepuscular [active at dawn and dusk]."So far, three types of cones in dunnarts and honey possums have been found, but Arrese suspects a fourth type is also present in smaller concentrations.
quote:Primates swap smell for sightLike all primates, humans can distinguish all seven colours of the rainbow. But international research says they may have developed this sense of sight at the expense of a superior sense of smell.Dr Yoav Gilad and collegues at the Max Planck Institute for Evolutionary Anthropology in Germany and the Weizmann Institute of Science in Israel, showed that as primates evolved, so did the genes that controlled their senses. With time, they lost functional genes that controlled their sense of smell but gained a type of retinal protein that allowed full colour vision. The results appeared in the latest issue of the Public Library of Science Biology journal.Researchers know that people who are deaf or blind often have greater sensitivity in their remaining senses. Now Gilad and his team have shown that this greater sensitivity may also develop as species evolved. All 19 species of primates the researchers studied have about 1000 genes that control smell. These olfactory genes are the largest family of genes in mammals.But not all olfactory genes help us smell. Some are pseudogenes, genes that are thought to have once worked but as species evolved they lost their function due to mutations. The percentage of olfactory genes that are non-functional pseudogenes varies with each species. Primates with a greater proportion of pseudogenes genes can't smell so well.By correlating the proportion of olfactory pseudogenes with the number of different types of retinal proteins, Gilad and his team showed that humans and our closest relatives, the apes, traded our olfactory ability for a full set of retinal proteins that are are crucial to see things in colour.Common ancestorsAround 23 million year ago, humans and apes once shared a common ancestor with Old World monkeys, a group that includes the Rhesus monkey and the baboon. Old World monkeys, like apes, also have full colour vision and about 30% of their olfactory genes are the non-functioning pseudogenes. But they still out-sniff humans who have a greatly reduced sense of smell. Some 60% of humans' olfactory genes are pseudogenes. Humans share less in common with New World monkeys, such as spider monkeys and marmosets, than they do with Old World monkeys. This also holds true for sight and smell. Most New World monkeys have only two types of retinal proteins meaning they have limited colour vision. The compensation may be that New World monkeys generally have a more superior sense of smell with only 17% of their olfactory genes being pseudogenes.The exception is the howler monkey. Unlike other New World Monkeys, these have a full set of visual proteins, so can distinguish all colours in their environment. To achieve this full colour vision, the howler, like humans and apes, increased their proportion of olfactory pseudogenes and lost part of their keen sense of smell.Howlers underwent this evolutionary split with other New World monkeys between 7 and 16 million years ago.Gilad's research showed a swap in importance of sight and smell during primate evolution. Sight may have become more important than smell in finding food or the choosing a mate, the researchers said.
quote:Originally posted by eric lHello Boo,Apparantly I share that theatre experience with you, with the important difference that I acted as an amateur (sound and)light technician for an amateur theatre group. But things were done rather on a trial and error base there, and praying tha no bulbs would burn out during the show was as imortant as perfect colour rendition.I have learned about colours and colour perception mainly by expanding on my training in physical chemistry.Are you still involved in lighing stages ?
quote:Originally posted by Boowell... kinda.. at arizona state university there are only two lighting courses i could take and ive taken both already.. i have worked on lots of shows doing lights since high school but this semester i am taking a break and im stage manager for a mainstage performance but i love lights, i have a very visual memory and am a very visual person.. isnt it amazing how much science goes into things like theatre?
quote:Originally posted by eric lActually all cones react to all wavelengths ! The difference is that the S-cones react more (not exclussvely)to shorter wavelengths, while M and L cones react more to longer wavelengths.(See again http://en.wikipedia.org/wiki/Colour_perception)The primary colors for absorption are not linked to a specific wavelenght. If you would measure the spectrum refelected by the yellow, cyan or yellow ink in your printer, you would actually see a graph with a maximum, but with a multitude of small peaks and valleys.The so called primary colors are defined by centuries of experience from painters, printers, photographers... That is also the reason why the primary colours for your printer are not the same as the primary colours for your screen. The light emmited by the red, green and blue "guns" is closer to monochromatic light than the light reflected by a printed or painted surface with only one of the primary colors.
quote:Originally posted by bostjani beg to differ. you can start from any three colors 120 degrees apart on the color wheel and make any other color additively or subtractively, just as well. try it out if you don't believe me.
quote:...as far as the cones reacting to all wavelengths, this is not exactly clear. they do react to a range of wavelengths. obviously, they do not react to infrared or ultraviolet or anything beyond that. what i was referring to, was the maximum of each kind of cone. each one has a global maximum sensitivity correlated to a primary color. one of them (i forget which- violet, or maybe green) acts goofy with a couple of local maxima as well.
quote:Originally posted by bostjanYou saying you cannot subtract to yield red?! You have not tried enough, then. Surely, Yellow and Magenta subtracted yield red. To get any very bright colors subtractively is difficult, but try pale green and tiny bit of red. If you got brown, mix in white to lighten it up.There is nothing magical about any certain color, I assure you.And I never said that the sensitivity curve did not span the visible range, merely that it did not span outside this range. I stated this quite clearly in the first and second sentences you quoted.
quote:Originally posted by syhprumWhen I first joined the colour printing business the explanation I was given for subtractive colour generation was that white light passed through the printing ink removing some components, was reflected by the white paper and then passed out through the ink again and the normal additive process then took place