Properties of color vision light waves electrical

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PROPERTIES OF COLOR Vision = light waves electrical signals Properties of a wave: Frequency, Amplitude Frequency (wavelength) Hue (color) violet, indigo, blue, green, yellow, orange, red Amplitude Color “Brightness” Many/Few wavelengths at once “Saturation” Frequency
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COLOR PERCEPTION Frequency (wavelength) Hue (color) violet, indigo, blue, green, yellow, orange, red Amplitude “Brightness” Many/Few wavelengths at once “Saturation” i.e. whether the color looks “washed out” or
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COLOR MIXING Colors of light add differently than colors of paint Primary colors of light: blue, green, and red Some combination of these can produce any hue in the visible spectrum “Additive Color Mixture” This is exactly how color TV works
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RODS, CONES, & COLOR Rods, 3 different types of cones Each has diff. sensitivity to certain wavelengths
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THEORIES OF COLOR VISION 1. Young-Helmholtz Trichromatic Theory : We have 3 types of cones, each maximally stimulated by either blue, green, or red light Each must send signals to the brain, depending on how much it is activated by a given wavelength The visual cortex could then “add up” the inputs and figure out the original ‘color’ of the light
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THEORIES OF COLOR VISION
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THEORIES OF COLOR VISION Problems with Trichromatic Theory: Says “Yellow” is based on red + green input But, people with red-green color blindness can still see yellow!! Caused by missing the red or green photopigment Color after-images
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THEORIES OF COLOR VISION 2. Opponent Process Theory : Thought each cone responded to 2 opposite colors Red/green, blue/yellow, black/white Opposite colors in a pair might be the result of 2 different types of chemical reactions Explanation of color after-images: After staring, receptors get “tired” (sensory adaptation) Then, when looking at white (all wavelengths), only the “red” half of the red-green cone, and the white half of the black-white cone was able to respond
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UNIFIED THEORY OF COLOR VISION Dual Process Theory : Currently the best understanding of color vision Turns out, both theories were partially correct Cones are sensitive to blue, green, red Combinations of activity seem to code hue Opponent processes do occur, just not at the level of cones Ganglion cells, and cells in visual cortex Code opposite colors by rate of firing (high/low)
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DUAL PROCESS THEORY
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COLORS IN LOW LIGHT Rods most sensitive to bluish-green light, not at all sensitive to red light Waking up in the middle of the night… WWII pilots and red sunglasses Overall, cones are most sensitive to yellow-green Some cities therefore changed from Red fire trucks (poor visibility in dark) to Yellow-Green X
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“COLOR BLINDNESS”
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“COLOR BLINDNESS” Most people have 3 types of cones (cone photopigments) normal color vision Called “trichromats” Some people have only 2 types
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