Chapter 5 Summary

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1.   Probably the most important fact to know about color vision is that lights and surfaces look colored because a particular distribution of ----- amplitudes wavelengths of light is being analyzed by a particular visual system. Color is a mental phenomenon, not a physical phenomenon. Many animal species have some form of color vision. It seems to be important for identifying possible mates, possible rivals, and good things to eat. Color vision has evolved several times in several different ways in the animal kingdom.
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2.   Rod photoreceptors are sensitive to ----- high low (scotopic) light levels. There is only one type of rod photoreceptor; it yields one “number” for each location in the visual field. Rods can support only a one-dimensional representation of color, from dark to light. Thus, scotopic vision is achromatic vision.
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3.   Humans have three types of cone photoreceptors, each having a different sensitivity to the wavelengths of light. Cones operate at brighter light levels than rods, producing three numbers at each location; the ----- pattern of activity over summed activity of the different cone types defines the color.
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4.   If two regions of an image produce the same response in the three cone types, they will look identical; that is, they will be . And they will look identical even if the physical wavelengths coming from the two regions are different.
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5.   In additive color mixture, two or more lights are mixed. Adding a light that looks blue to a light that looks yellow will produce a light that looks ----- green white (if we pick the right blue and yellow). In subtractive color mixture, the filters, paints, or other pigments that absorb some wavelengths and reflect others are mixed. Mixing a typical blue paint and a typical yellow paint will subtract most long and short wavelengths from the light reflected by the mixture, and the result will look ----- green white .
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6.   Color blindness is typically caused by the congenital absence or abnormality of one cone type—usually the L- or M-cones, usually in ----- females males . Most color-blind individuals are not blind to differences in wavelength. Rather, their color perception is based on the outputs of two cone types instead of the normal three.
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7.   A single type of cone cannot be used, by itself, to discriminate between wavelengths of light. To enable discrimination, information from the ----- one two three four cones is combined to form three cone-opponent processes. Cones sensitive to long wavelengths (L-cones) are pitted against medium-wavelength (M) cones to create an (L – M) process that is roughly sensitive to the redness or greenness of a region. (L + M) cones are pitted against short-wavelength (S) cones to create a process roughly sensitive to the blueness or yellowness of a region. The third process is sensitive to the overall brightness of a region.
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8.   Color appearance is arranged around opponent colors: red versus , and blue versus . This color opponency involves further reprocessing of the cone signals from cone-opponent processes into color-opponent processes.
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9.   The visual system tries to disentangle the properties of surfaces in the world (e.g., the “red” color of a strawberry) from the properties of the illuminants (e.g., the “golden” light of evening), even though surface and illuminant information are combined in the input to the eyes. Mechanisms of color use implicit knowledge about the world to correct for the influence of different illuminants and to keep that strawberry looking red under a wide range of conditions.
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