Chapter 5: The Perception of Color Flashcards
S-cone
A cone that is preferentially sensitive to short wavelengths; 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 a “green cone.”
L-cone
A cone that is preferentially sensitive to long wavelengths; colloquially (but not entirely accurately) known as a “red cone.”
spectral sensitivity
Referring to the sensitivity of a cell or a device to different wavelengths on the electromagnetic spectrum.
photopic
Referring to light intensities that are bright enough to stimulate the cone receptors and bright enough to “saturate” the rod receptors (that is, drive them to their maximum responses).
scotopic
Referring to light intensities that are bright enough to stimulate the rod receptors but too dim to stimulate the cone receptors.
principle 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.
trichromatic theory of color vision (trichromacy)
The theory that the color of any light is defined in our visual system by the relationships of three numbers–the outputs of three receptor types now known to be the three cones. Also called the Young-Helmholtz theory.
metamers
Different mixtures of wavelengths that look identical. More generally, 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 they 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 perceptions of color.
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.
cone-opponent cell
A cell type–found in the retina, lateral geniculate nucleus, and visual cortex–that, in effect, subtracts one type of cone input from another.
koniocellular
Referring to cells in the koniocellular layer of the lateral geniculate nucleus of the thalamus. Konio from the Greek for “dust” referring to the appearance of the cells.
parvocellular
Referring to cells in the parvocellular layers of the lateral geniculate nucleus of the thalamus. Parvo from the Greek for “small” referring to the size of the cells.
circadian
Biological cycle that recurs approximately every 24 hours, even in the absence of cues to time of day (via light, clocks, etc.)
melanopsin
A photopigment, found in a class of photoreceptive retinal ganglion cells.
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.
opponent color theory
The theory that perception of color is based on the output of three mechanisms, each of them resulting from an opponency between two colors: red-green, blue-yellow, and black-white.
unique hue
Any of four colors that can be described with only a single color term: red, yellow, green, blue. Other colors (e.g., purple or orange) can be described as compounds (red-dish blue, reddish yellow).
double-opponent cell
A cell type, found in the visual cortex, in which one region is excited by one cone type, combination of cones, or color and inhibited by the opponent cones or color (e.g., R+/G-). Another adjacent region would be inhibited by the first input and excited by the second (thus, in this example, R-/G+).
single-opponent cell
Another way to refer to cone-opponent cells, in order to differentiate them from double-opponent cells.
achromatopsia
An inability to perceive colors that is caused by damage to the central nervous system.
qualia
In philosophy, a private conscious experience of sensation or perception.
basic color terms
Color words that are monolexemic (single words “blue” not, “sky blue”), used with high frequency, and have meanings that are agreed upon by speakers of a language.
cultural relativism
In sensation and perception, the idea that basic perceptual experiences (e.g., color perception) may be determined in part by the cultural environment.
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 “color-blind” individuals can still make discriminations based on wavelength. Those discriminations are different from the norm–that is, anomalous.
cone monochromat
An individual with only one cone type. Cone monochromats are truly color-blind.
rod monochromat
An individual with no cones of any type. In addition to being truly color-blind, rod monochromats are badly visually impaired in bright light.
agnosia
A failure to recognize objects in spite of the ability to see them. Agnosia is typically due to brain damage.
anomia
An inability to name objects in spite of the ability to see and recognize them (as shown by usage). Anomia is typically due to brain damage.
color contrast
A color perception effect in which the color of one region induces the opponent color in a neighboring region.
color assimilation
A color perception effect in which two colors bleed into each other, each taking on some of the chromatic quality of the other.
unrelated color
A color that can be experience in isolation.
related color
A color, such as brown or gray, that is seen only in relation to other colors. For example, a “gray” patch in complete darkness appears white.
negative afterimage
An afterimage whose polarity is the opposite of the original stimulus. Light stimuli produce dark negative afterimages. Colors are complementary; for example, red produces green, and yellow produces blue.
adapting stimulus
A stimulus whose removal produces a change in visual perception or sensitivity.
neutral point
The point at which an opponent color mechanism is generating no signal. If red-green and blue-yellow mechanisms are at their neutral points, a stimulus will appear achromatic. (The black-white process has no neutral point.)
color constancy
The tendency of a surface to appear the same color under a fairly wide range of illuminants.
illuminant
The light that illuminates a surface.
spectral reflectance function
The percentage of a particular wavelength that is reflected from a surface.
spectral power distribution
The physical energy in a light as a function of wavelength.
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.
