Chapter 5: The Perception of Color

Question 1

S-cone

Answer 1

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

Question 2

M-cone

Answer 2

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

Question 3

L-cone

Answer 3

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

Question 4

spectral sensitivity

Answer 4

Referring to the sensitivity of a cell or a device to different wavelengths on the electromagnetic spectrum.

Question 5

photopic

Answer 5

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 6

scotopic

Answer 6

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

Question 7

principle of univariance

Answer 7

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 8

trichromatic theory of color vision (trichromacy)

Answer 8

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.

Question 9

metamers

Answer 9

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

Question 10

additive color mixture

Answer 10

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.

Question 11

subtractive color mixture

Answer 11

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.

Question 12

lateral geniculate nucleus (LGN)

Answer 12

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 13

cone-opponent cell

Answer 13

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 14

koniocellular

Answer 14

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.

Question 15

parvocellular

Answer 15

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.

Question 16

circadian

Answer 16

Biological cycle that recurs approximately every 24 hours, even in the absence of cues to time of day (via light, clocks, etc.)

Question 17

melanopsin

Answer 17

A photopigment, found in a class of photoreceptive retinal ganglion cells.

Question 18

color space

Answer 18

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 19

opponent color theory

Answer 19

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 20

unique hue

Answer 20

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).

Question 21

double-opponent cell

Answer 21

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 22

single-opponent cell

Answer 22

Another way to refer to cone-opponent cells, in order to differentiate them from double-opponent cells.

Question 23

achromatopsia

Answer 23

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

Question 24

qualia

Answer 24

In philosophy, a private conscious experience of sensation or perception.

Question 25

basic color terms

Answer 25

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.

Question 26

cultural relativism

Answer 26

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

Question 27

deuteranope

Answer 27

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

Question 28

protanope

Answer 28

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

Question 29

tritanope

Answer 29

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

Question 30

color-anomalous

Answer 30

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.

Question 31

cone monochromat

Answer 31

An individual with only one cone type. Cone monochromats are truly color-blind.

Question 32

rod monochromat

Answer 32

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

Question 33

agnosia

Answer 33

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

Question 34

anomia

Answer 34

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.

Question 35

color contrast

Answer 35

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

Question 36

color assimilation

Answer 36

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

Question 37

unrelated color

Answer 37

A color that can be experience in isolation.

Question 38

related color

Answer 38

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 39

negative afterimage

Answer 39

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 40

adapting stimulus

Answer 40

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

Question 41

neutral point

Answer 41

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.)

Question 42

color constancy

Answer 42

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

Question 43

illuminant

Answer 43

The light that illuminates a surface.

Question 44

spectral reflectance function

Answer 44

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

Question 45

spectral power distribution

Answer 45

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

Question 46

reflectance

Answer 46

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.