Chapter 5

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

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

trichromacy or trichromatic theory of color vision

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 the 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 will contribute to the perception 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 LGN 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 LGN of the thalamus. Parvo from the Greek for “small” referring to the size of the cells.

Question 16

equiluminant

Answer 16

Referring to stimuli that vary in color but not in luminance.

Question 17

circadian

Answer 17

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

Question 18

melanopsin

Answer 18

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

Question 19

mesopic

Answer 19

Referring to the middle range of light intensities.

Question 20

color space

Answer 20

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 21

opponent color theory

Answer 21

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 22

unique hue

Answer 22

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 also be described as compounds (reddish blue, reddish yellow).

Question 23

achromatopsia

Answer 23

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

Question 24

basis color terms

Answer 24

Color words that are single words (like “blue,” not “sky blue”), are used with high frequency, and have meanings that are agreed upon by speakers of a language.

Question 25

cultural relativism

Answer 25

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

Question 26

qualia

Answer 26

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

Question 27

tetrachromatic

Answer 27

Referring to the rare situation (in humans, at least) where the color of any light is defined by the relationships of four numbers—the outputs of those four receptor types.

Question 28

deuteranope

Answer 28

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

Question 29

protanope

Answer 29

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

Question 30

tritanope

Answer 30

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

Question 31

color-anomalous

Answer 31

A better term for the commonly used term color-blind. Most “color-blind” individuals can still make discriminations based on wavelength. Those discriminations are different from the norm—that is, anomalous.

Question 32

cone monochromat

Answer 32

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

Question 33

rod monochromat

Answer 33

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 34

agnosia

Answer 34

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

Question 35

anomia

Answer 35

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 36

color contrast

Answer 36

A color perception effect in which the color of one region

induces the opponent color in a neighboring region.

Question 37

color assimilation

Answer 37

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

Question 38

unrelated color

Answer 38

A color that can be experienced in isolation.

Question 39

related color

Answer 39

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 40

negative afterimage

Answer 40

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 41

adapting stimulus

Answer 41

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

Question 42

neutral point

Answer 42

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 43

color constancy

Answer 43

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

Question 44

illuminant

Answer 44

The light that illuminates a surface.

Question 45

spectral reflectance function

Answer 45

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

Question 46

spectral power distribution

Answer 46

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

Question 47

reflectance

Answer 47

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.