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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


light intensities that are bright enough to stimulate the rod receptors but too dim to stimulate the cone receptors


light intensities that are bright enough to stimulate the cone receptors and bright enough to "saturate: the rod receptors


a cone that is preferentially sensitive to short wavelenths; colloquially (but not entirely accurately) known as a "blue cone"


A cone that is preferentially sensitive to middle wavelengths; colloquially (but not entirely accurately) known as "green 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


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


the chromatic (colorful) aspect of color


the chromatic strength of a hue. White has zero, pink is more, and red is fully


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)


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


an inability to perceive colors that is caused by damage to the ventral nervous system


an individual who suffers from color blindness that is due to the absence of M-cones


an individual who suffers from color blindness that is due to the absence of L-cones


an individual who suffers from color blindness that is due to the absence of S-cones


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


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


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


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

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