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PS262 CH9.docx

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Wilfrid Laurier University
Elizabeth Olds

What Are some Functions of Color Vision  serves important signaling functions both natural and contrived by humans  helps facilitate perceptual organization  proposal that colour vision may have evolved to determine different fruits for humans and monkeys What colours do we perceive  we can describe all the colours we perceive by using the terms red, yellow, green, blue and their combinations.  humans can discriminate between about 200 different colours across the length of the visible spectrum  we can create even more colours by changing the intensity to make colours brighter or dimmer by adding white to change the saturation  perception of white is equal amounts of all wavelenghts across the spectrum  by changing wavelength, intensity and saturation we can create a million discriminable colours Colour and Wavelength  colour spectrum stretches from 400nm to 700nm  400nm-450nm appear violet  450-490nm blue  500-575nm green  575-590nm yellow  590-620nm orange  620-700nm red  reflectance curves: plots of the % of light reflected vs wavelengths  mixing lights does not give the same effect as mixing paint  mixing blue and yellow light gives white light because of the mixes of wavelenghts  mixing lights is called addictive color mixture  when paints mix both colours are still reflecting the same wavelengths so the wavelengths that are reflected are the ones both colours have in common  mixing paints is called subtractive color mixture Wavelengths Do not have Colour  light rays are simply energy, colours are created by our perceptual system  colours are how our brain tells us what wavelengths are being presented to us Thrichromatic Theory of Color Vision  states that color depends on the activity of three different receptor mechanisms  was proposed by Thomas Young and Hermann von Helmoltz  color matching experiments found that it is possible to match any wavelength in the testfield by adjusting proportions of three wavelengths in the comparison field and people with normal vision cannot match all wavelengths in the spectrum with only two wavelengths Colour Deficiencies  associated with problems in receptors of the retina  Daltonism: early term used to describe colour deficiencies, named after John Dalton, who experienced deficiencies  monochromat: only sees shades of grey, so they can match any wavelength by adjusting intensity of one not three wavelengths, hereditary  dichromat: needs only two wavelengths to match any wavelength; three major forms: protanopia, deuteranopia (recessive; inherited through the X chromosome)and tritanopia (less common)  anamalous trichomat: needs three wavelengths li
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