The Perception of Color

Question 1

achromatopsia

Answer 1

An inability to perceive colors that is caused by damage to the central nervous system.

Question 2

spectral power distribution

Answer 2

The physical energy in a light as a function of wavelength.

Question 3

color constancy

Answer 3

The tendency of a surface to appear the same color under a fairly wide range of illuminants.

Question 4

achromatic

Answer 4

Referring to any color that lacks a chromatic (hue) component. Black, white, or gray.

Question 4

related color

Answer 4

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.

Question 5

adapting stimulus

Answer 5

A stimulus whose removal produces a change in visual perception or sensitivity.

Question 5

unrelated color

Answer 5

A color that can be experienced in isolation.

Question 6

illuminant

Answer 6

The light that illuminates a surface.

Question 6

problem of univariance

Answer 6

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.

Question 6

unique hue

Answer 6

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 (reddish blue, reddish yellow).

Question 7

spectral reflectance function

Answer 7

The percentage of a particular wavelength that is reflected from a surface.

Question 8

cone-opponent cell

Answer 8

A cell type—found in the retina, lateral geniculate nucleus, and visual cortex—that, in effect, subtracts one type of cone input from another.

Question 9

photopic

Answer 9

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).

Question 10

brightness

Answer 10

The perceptual consequence of the physical intensity of a light.

Question 11

agnosia

Answer 11

A failure to recognize objects in spite of the ability to see them, typically due to brain damage.

Question 11

protanope

Answer 11

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

Question 12

scotopic

Answer 12

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

Question 13

tritanope

Answer 13

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

Question 15

cone monochromat

Answer 15

An individual with only one cone type. Individual is truly color-blind.

Question 15

M-cone

Answer 15

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

Question 16

subtractive color mixture

Answer 16

A mixture of pigments. If pigments A and B mix, some of the light shining on the surface will be absorbed by A, and some by B. Only the remainder contributes to the perception of color.

Question 17

L-cone

Answer 17

A cone that is preferentially sensitive to long wavelengths; colloquially (but not entirely accurately) known as a “red cone.”

Question 18

trichromatic theory of color vision (or trichromacy)

Answer 18

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 known as the Young-Helmholtz theory.

Question 20

hue

Answer 20

The chromatic (colorful) aspect of color (red, blue, green, yellow, and so on).

Question 21

saturation

Answer 21

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

Question 22

reflectance

Answer 22

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.

Question 24

afterimage

Answer 24

A visual image seen after the stimulus has been removed.

Question 24

anomia

Answer 24

An inability to name objects in spite of the ability to see and recognize them (as shown by usage), typically due to brain damage.

Question 26

additive color mixture

Answer 26

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.

Question 26

rod monochromat

Answer 26

An individual with no cones of any type. In addition to being truly color-blind, these individuals are badly visually impaired in bright light.

Question 27

S-cone

Answer 27

A cone that is preferentially sensitive to short wavelengths; colloquially (but not entirely accurately) known as a “blue cone.”

Question 29

color space

Answer 29

The three-dimensional space, established because color perception is based on the outputs of three cone types, that describes the set of all colors.

Question 31

color assimilation

Answer 31

A color perception effect in which two colors bleed into each other, each taking on some of the chromatic quality of the other.

Question 33

opponent color theory

Answer 33

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.

Question 35

metamers

Answer 35

Different mixtures of wavelengths that look identical. More generally, any pair of stimuli that are perceived as identical in spite of physical differences.

Question 36

lateral geniculate nucleus (LGN)

Answer 36

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.

Question 37

deuteranope

Answer 37

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

Question 38

negative afterimage

Answer 38

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.

Question 39

neutral point

Answer 39

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.

Question 40

single-opponent cell

Answer 40

Another way to refer to cone-opponent cells.

Question 41

color contrast

Answer 41

A color perception effect in which the color of one region induces the opponent color in a neighboring region.

Question 42

double-opponent cell

Answer 42

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+).

Question 43

cultural relativism

Answer 43

In sensation and perception, the idea that basic perceptual experiences (e.g., color perception) may be determined in part by the cultural environment.

Question 44

color-anomalous

Answer 44

A better term for what is usually called “color-blind.” Most “color-blind” individuals can still make discriminations based on wavelength, but the discriminations are different from the norm.