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.