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PSYCH 1XX3 (1,106)
Joe Kim (1,025)


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Joe Kim

COLOUR PERCEPTION Intro - The ability to see colour is not because the objects are colourful, but we see colours because the objects and surfaces we look at reflect certain wavelengths of visible spectrum and these trigger specific patterns of response in our brains - Colour is creation of our minds Who has colour vision - Birds, fish, reptiles and insects have excellent colour vision - Colour vision is limited to primates including humans among mammals - Dogs and cats can only see shades of grey Functions of colour vision in different species - Primates colour vision is especially well suited to distinguish red and yellow against green background - This adaptation helps foraging for fruit in the bushes and trees - One possible biological advantage of colour vision for primates is the ability to detect colour objects in the wild as well as predators or prey - Seeing the richness of soil, ripeness of fruit can predict weather - In birds, the colour of potential mates feathers provides signals to other birds about how healthy the bird is and can influence how likely that bird is chosen as a mate Colour mixing - Primary colours o The 3 colours can be combined in various proportions to make every colour in the spectrum o Are like base colours, cannot be reduced into other colours - There are types of colour mixing. Subtractive and additive Subtractive colour mixing - Applies to the mixing of pigments, dyes or paints and is called subtractive because every reflective surface absorbs or subtracts the colours that it does not reflect - Adding pigments to that surface alters the combination wavelengths subtracted - Eg. So blue objects looks blue to us because all wavelengths that are being absorbed by the object except short, blue waves which are being reflected back to our eye and making the object look blue - When 2 pigments are mixed, all wavelengths are being absorbed except those two pigments jointly reflect - If you shine a white light through both a yellow filter and the a blue one, the remaining colourwilll be green - This is because light hits yellow filter, all the short waves are being absorbed or subtracted out and only longer waves are allowed to pass through - When the longer waves hit blue filter, it absorbs the longest waves and what is left is the middle band of wavelengths that is transmitted by both pigments. - With subtractive colour mixing, the primary colours are red, yellow and blue because they can be mixed and make any colour - Opposite to primary colour is complementary colour. - When you mixed complementary colours you should get the colour brown. Additive mixing - Deals with mixing of coloured lights, where coloured lights add their dominant wavelength to the mixture as opposed to subtracting them out - With additive colour mixing the primary colours are red, green and blue because these colours can be added together in various proportions to make different colours we see. - The complementary colours are different from the ones in subtractive mixing - When you mix a primary colour with its complementary you get grey or white - When you have 2 white light going through, 1 going through blue filter other going through yellow , the lights become overlapped - Because each coloured light add its dominant wavelength to the mixture, you find that blue and yellow don’t make green but make grey - This is because grey light is the sum of complementary colours Trichromatic theory of colour vision - Proposes that the retina contains 3 different kinds of cones - Proposed by Thomas young and later modified by hermanovo helmhoitz - This theory follows from empirical observations about primary colours and colour mixing; that its possible to match all of the colours of the visible spectrum by mixing 3 primary colours - Thus you need 3 different receptors to discriminate all the colours of the visible spectrum - A given receptor will respond to other wavelengths just not as much as it would to its peak wavelength - When you perceive yellow, this is because red and green cones are equally stimulated - White is what you see when all 3 receptors are stimulated - Elegance with theory o Fits with additive colour mixing o Physiological evidence for three types of cones - Problems with theory o Yellow seems to be a primary colour and the mix of red and green o Why is yellow the after image o
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