Chapter 9 Color blindness caused by cortical injury after a lifetime of experiencing injury after a lifetime of experiencing color Total color blindness occurs at birth bc of genetic absence of one or more cone receptors Color Helps facilitate perceptual organization small elements become grouped perceptually into larger objects enhances the contrast of objects that if didn t appear colored would appear more similar ability to tell one object from another and pick out objects in a scene helps detect objects that might be otherwise obscured by their surroundings helps recognize and identify things we can see easily recognize appropriately colored objects more rapidly and accurately visual spectrum red yellow green blue basic colors short wavelength medium WL long WL yellow red green blue color circle and color wheel extraspectral colors brown and purple bc they do not appear in spectrum but on color wheel saturation the relative amount of whiteness in a chromatic color purity less whiteness color contains more saturated adding white decreases saturation desaturated a less saturated form of a chromatic color assed white colors related to wavelength of light organizing scheme for psychological properties of color brightness intensity color and wavelength perception of color associated w physical property of wavelength short 400 nm long 700 nm bands in b w associated with different colors reflectance and transmission colors of light in spectrum related to wavelength colors of objects are largely determined by WL of light that is reflected from object into eyes reflectance curve plots of the of light reflected vs WL for the of objects chromatic color color w hue hue some wavelengths are reflected more than others experience of chromatic color or combinations of color selective reflection property of reflecting some wavelengths more than others characteristic of chromatic colors achromatic colors when light reflection is similar across the full spectrum selective transmission only some wavelengths pass through the object or substance creates chromatic color contains no hue white black and all grays b w 2 things are transparent mixing lights when colored LIGHTS are superimposed all of the light reflected from the surface by each light when alone is also reflected when the lights are superimposed combined if added together light superimposed has S M L wavelengths perception of white additive color mixture adding up the wavelengths of each light in a mixture when mixing lights term for mixing lights pointillism additive color mixing the mix is in the mind Mixing paints when colored PAINTS are mixed together both paints still absorb the same WL they absorb alone so reflected WL is one reflected by both paints subtractive color mixture mixing paints bc paint absorbs WL alone and in mixture if mixed paints don t overlap in a reflected wavelength no color in common reflected would result in little or no reflection across spectrum mixture appears black if blue only reflected shot and yellow only reflected medium and long connection b w wavelength and color 1 colors of light are associated w WL in visible spectrum 2 colors of objects associated w which WL are reflected opaque objects or transmitted transparent objects 3 mixing colors the colors that occur are associated w WL reflected into eye causes more WL to be reflected each light ADDS wavelengths to mixture mixing paints causes fewer WL to be reflected each paint SUBTRACTS WL from mixture Newton colors we see in response to diff wavelengths are not contained in the rays of light themselves colors are created by perceptual system the connection b w WL and the experience color is arbitrary people who see no colors their nervous system processes WL info differently and doesn t transform WL info into perception of color trichromatic theory of color vision color vision depends on the activity of three different receptor mechanisms Helmholtz based theory color matching behavioral evidence color matching experiments observers adjusted the amounts of 3 diff wavelengths of light mixed together in a comparison field until the color of this mixture matched the color of a single wavelength in the test field any 3 wavelengths can be used as long as any of them can t be matched by mixing other 2 1 by correctly adjusting proportions of 3 wavelengths in comparison field possible to match any wavelength in test field 2 people w normal color vision cannot match all wavelengths in spectrum with only 2 wavelengths people who are color deficient can t perceive all colors in spectrum can match colors of all wavelengths in spectrum by mixing only 2 other wavelengths metamerism two physically different stimuli are perceptually identical color of one wavelength is the same color as adding 3 wavelengths metamers two identical fields in a color matching experiment theory based on finding that people with normal color vision need at least 3 WL to match any wavelength in test field later termed Young Helmholtz theory of color vision color vision depends on 3 receptor mechanisms each with diff spectral sensitivities spectral sensitivity indicates the sensitivity to wavelengths across the visible spectrum light of particular wavelength stimulates the 3 receptor mechanisms to different degrees and pattern of activity in 3 mechanisms results in perception of color each wavelength represented in nervous system by its own pattern of activity in the 3 receptor mechanisms physiology evidence cone pigments made up of large protein component opsin and small light sensitive component retinal differences in structure of long opsin part of the pigment are responsible for the 3 diff absorption spectra 3 cone types S M L white signaled by activity in all the receptors perception of color is determined by the pattern of activity in different receptors photon small packet of light energy visual pigment molecule is activated if absorbs one photon trichromats people with 3 visual pigments monkeys and goldfish dichromats people with just 2 types of cone pigment see color but see fewer colors than trichromats dichromats color deficiency a problem with color vision that involves only a partial loss of color perception associated with problems with the receptors in the retina daltonism describes color deficiency ishihara plates color vision tests inherited color deficits trichromatic theory can t explain photopigments defective or absent 1 monochromat can match many wavelength in the