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39 terms

Chapter 5 Color

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problem of univariance
the fact that an infinite set of different wavelength-intensity combinations can elicit exactly the same response from a single type of photoreceptor. One photoreceptor type cannot make color discriminations based on wavelength
scotopic
light intensities that are bright enough to stimulate the rod receptors but too dim to stimulate the cone receptors
photopic
light intensities that are bright enough to stimulate the cone receptors and bright enough to "saturate: the rod receptors
S-cone
a cone that is preferentially sensitive to short wavelenths; colloquially (but not entirely accurately) known as a "blue cone"
M-cone
A cone that is preferentially sensitive to middle wavelengths; colloquially (but not entirely accurately) known as "green cone"
L-cone
a cone that is preferentially sensitive to long wavelengths; colloquially (but not entirely accurately) known as a "red cone"
trichromatic theory of color vision (or trichromacy)
the theroy that the color of any light is defined in our visual system by the relationships of three numbers, the outputs of three receptors types now known to be the three cones
metamers
different mixtures of wavelengths that look identical. More generically any pair of stimuli that are perceived as identical in spite of physical differences
additive color mixture
a mixture of lights. If light A and light B are both reflected from a surface to the eye, in the perception of color the effects of those two lights add together
subtractive color mixture
a mixture of pigments. If pigments A and B mix, some of the light shining on the surface will be subtracted by A and some by B. Only the remainder contributes to the perception of color
color space
the three-dimensional space, established because color perception is based on the outputs of three cone types, that describes the set of all colors
hue
the chromatic (colorful) aspect of color
saturation
the chromatic strength of a hue. White has zero, pink is more, and red is fully
brightness
the distance from black (zero) in color space
lateral geniculate nucleus (LGN)
a structure in the thalamus, part of the midbrain, that receives input from the retinal ganglion cells and has input and output connections to the visual cortex
color-opponent cell
a neuron whose output is based on a difference between sets of cones
opponent color theory
the theory that perception of color is based on the output of three mechanisms, each of them based on an opponency between two colors: red--green, blue--yellow, and black--white
unique blue
a blue that has no red or green tint
unique hue
any of four colors that can be described with only a single color term (red, yellow, green, and blue)
afterimage
a visual image seen after the stimulus has been removed
adapting stimulus
a stimulus whose removal produces a change in visual perception or sensitivity
negative afterimage
an afterimage whose polarity is the opposite of the original stimulus. Light stimuli produce dark negative afterimages. Colors are complementary
neutral point
the point at which an opponent color mechanism is generating no signal
achromatopsia
an inability to perceive colors that is caused by damage to the ventral nervous system
deuteranope
an individual who suffers from color blindness that is due to the absence of M-cones
protanope
an individual who suffers from color blindness that is due to the absence of L-cones
tritanope
an individual who suffers from color blindness that is due to the absence of S-cones
color-anomalous
a better term for what is usually called "color-blind" most of these individuals can still make discriminations based on wavelength, those discriminations are different form the normal
cone monochromat
an individual with only one cone type; are truly color-blind
rod monochromat
an individual with no cones of any type. In addition to being truly color-blind; are badly visually impaired in bright light
agnosia
a failure to recognize objects in spite of the ability to see and recognize them, this is typically due to brain damage
cultural relativism
in sensation and perception, the idea that basic perceptual experiences may be determined in part by the cultural environment
unrelated color
a color that can be experienced in isolation
related color
a color, such as brown or gray, that is seen only in relation to other colors; a "gray" batch in complete darkness appears white
illuminant
the light that illuminates a surface
spectral reflectance function
the function relating the wavelength of light to the percentage of that wavelength that is reflected from a surface
spectral power distribution
the physical energy in a light as a function of wavelengths
color constancy
the tendency of a surface to appear the same color under a fairly wide range of illuminants
reflectance
the percentage of light hitting a surface that is reflected and not absorbed into the surface. Typically reflectance is given as a function of wavelength