Page 1Color VisionJanuary 30, 2001Color is an ExperienceAn Important Experience:– The Colorblind Painter– Functions“…And please let Mom, Dad, Rex, Ginger, Tucker, me and all of the rest of the family see color.”Three DimensionsHue– Associated with color namesSaturation– Inversely related to the amount of whiteBrightness– Appearance of how light or dark100% 50%Isaac Newton’s ExperimentSpectral (Basic) Colors Non-spectral colorsThose colors that can only be experienced when 2 or more wavelengths are combined(some purples, browns)Page 2Color and WavelengthColor MixingPaint PaintSubtractiveLight LightAdditivePredicting Additive MixturesPredicting Additive MixturesPredicting Additive MixturesColor Mixing– We can see the same color when presented with a single wavelength or a mix of two.– There are colors that we can only see by mixing.– Combine 2 complementary lights and get white.Page 3How Does Color Vision Work?RetinaOptic NerveLightPhotoreceptorsBipolar cellsGanglion cellsHorizontal cellAmacrine cellHow Does Color Vision Work?Rods– outnumber cones 20 to 1– very sensitive to light– distributed throughout retina; none in foveaCones = Color– only effective in bright illumination– 3 kinds of photopigments– fovea and peripheryTwo theories that complement each other-Young-Helmholtz Trichromatic Theory-Opponent-Process TheoryHow Does Color Vision Work?How Does Color Vision Work?Young-Helmholtz Trichromatic Theory– Cones = color vision– 3 Types of cones– All cones are active, but to different levels3 Types of ConesS M LFor Example:Blue:– High activity in Blue– Minimal in Green– Minimal in RedPurple:– High activity in Blue– Minimal in Green– High in RedPage 4How Does Color Vision Work? How Does Color Vision Work?Imagine colors:– Red– Yellowish-red– Greenish-red??How Does Color Vision Work?Opponent-Process Theory– Three mechanismsB+W-R+G-B+Y-Color Deficiencies: Retinal Level• Monochromatism• DichromatismMonochromatism-very rare-no functioning cones; only shades of lightness-Poor visual acuityColor Deficiencies: Retinal Level Color Deficiencies: Retinal LevelDichromatism– More common in males– One photopigment missing– Red-green color blindness is most common• M or L cones absentPage 5Ishihara platesCan you read this number?Color Perception Deficits: CorticalAchromatopsia– Case of the colorblind painterColor anomia– Deficits in naming colorsImpaired color-object associations– A banana is