Chapter 5: The Perception of Color

Question 1

Three steps to color perception

Answer 1

1. Detection - Wavelengths must be detected
2. Discrimination - Must be able to tell difference between wavelengths.
3. Appearance - Assign perceived colors to lights and surfaces in world.

Question 2

S-cone

Answer 2

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

Question 3

M-cone

Answer 3

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

Question 4

L-cone

Answer 4

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

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.

Question 6

Scotopic

Answer 6

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

Question 7

Problem of Univariance

Answer 7

The fact that an infinite set of different wave length-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 defines in our visual system by the relationships of three numbers - the outputs of three receptor types known to be the three cones.

Question 9

Metamers

Answer 9

Different mixtures of wavelengths that looks identical. More generally, any pair of stimuli that are perceived as identical in spit 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

Subractive 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 perception of color.

Question 12

LGN

Answer 12

structure in thalamus, receives input from ganglion cells and outputs to V1

Question 13

cone-opponent cells

Answer 13

A cell type-found in the retina, LGN, and V1,-that in effect, subtracts one type of cone input from another.

Question 14

Color space

Answer 14

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 15

achromatic

Answer 15

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

Question 16

hue

Answer 16

the chromatic (colorful) aspect of color (red, blue, green, yellow…)

Question 17

saturation

Answer 17

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

Question 18

brightness

Answer 18

The perceptual consequence of the physical intensity of a light.

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 (purple/oragne) can be described as compounds (reddish blue, reddish yellow).

Question 21

double-opponent cell

Answer 21

A cell type, found in the V1, in which one region is excited by one cone type, combination of cones, or color and inhibited by the opponent cones or color. Another adjacent region would be inhibited by the first input and excited by the second.

Question 22

single-opponent cells

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 CNS

Question 24

afterimage

Answer 24

A visual image seen after the stimulus has been removed.

Question 25

adapting stimulus

Answer 25

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

Question 26

negative afterimage

Answer 26

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 27

neutral point

Answer 27

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. (black-white process has no neutral point.)

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 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 32

cone monochromat

Answer 32

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

Question 33

rod monochromat

Answer 33

An individual with no cones of any type. In addition to being truly colorblind, that are 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 spit of the ability to see and recognize them.

Question 36

cultural relativism

Answer 36

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

Question 37

color contrast

Answer 37

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

Question 38

color assimilation

Answer 38

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

Question 39

unrelated color

Answer 39

a color that ca be experienced in isolation

Question 40

related color

Answer 40

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 41

color constacnty

Answer 41

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

Question 42

illuminant

Answer 42

The light that illuminates a surface

Question 43

spectral reflectance function

Answer 43

The percentage pf a [articular wavelength that is reflected from a surface.

Question 44

spectral power distribution

Answer 44

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

Question 45

reflectance

Answer 45

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.