Chapter 9

Question 1

Achromatic color

Answer 1

Color without hue. White, black, and all the grays between these two extremes are achromatic colors.

Question 2

Additive color mixture

Answer 2

The creation of colors that occurs when lights of different colors are superimposed.

Question 3

Anomalous trichromat

Answer 3

A person who needs to mix a minimum of three wavelengths to match any other wavelength in the spectrum but mixes these wavelengths in different proportions from a trichromat.

Question 4

Cerebral achromatopsia

Answer 4

A loss of color vision caused by damage to the cortex.

Question 5

Chromatic adaptation

Answer 5

Exposure to light in a specific part of the visible spectrum. This adaptation can cause a decrease in sensitivity to light from the area of the spectrum that was presented during adaptation.

Question 6

Chromatic color

Answer 6

Color with hue, such as blue, yellow, red, or green.

Question 7

Color blindness

Answer 7

A condition in which a person perceives no chromatic color. This can be caused by absent or malfunctioning cone receptors or by cortical damage.

Question 8

Color constancy

Answer 8

The effect in which the perception of an object’s hue remains constant even when the wavelength distribution of the illumination is changed. Partial color constancy occurs when our perception of hue changes a little when the illumination changes, though not as much as we might expect from the change in the wavelengths of light reaching the eye.

Question 9

Color deficiency

Answer 9

People with this condition (sometimes incorrectly called color blindness) see fewer colors than people with normal color vision and need to mix fewer wavelengths to match any other wavelength in the spectrum.

Question 10

Color-matching experiment

Answer 10

A procedure in which observers are asked to match the color in one field by mixing two or more lights in another field.

Question 11

Desaturated

Answer 11

Low saturation in chromatic colors as would occur when white is added to a color. For example, pink is not as saturated as red.

Question 12

Deuteranopia

Answer 12

A form of red–green color dichromatism caused by lack of the middle-wavelength cone pigment.

Question 13

Dichromat

Answer 13

A person who has a form of color deficiency. Dichromats can match any wavelength in the spectrum by mixing two other wavelengths. Deuteranopes, protanopes, and tritanopes are all dichromats.

Question 14

Double-opponent neurons

Answer 14

Neurons that have receptive fields in which stimulation of one part of the receptive field causes an excitatory response to wavelengths in one area of the spectrum and an inhibitory response to wavelengths in another area of the spectrum, and stimulation of an adjacent part of the receptive field causes the opposite response. An example of double-opponent responding is when the response of one part of a receptive field is L+ M- and the response of an adjacent part is L- M+.

Question 15

Hue

Answer 15

The experience of a chromatic color such as red, green, yellow, or blue or combinations of these colors.

Question 16

Illumination edge

Answer 16

The border between two areas created by different light intensities in the two areas.

Question 17

Ishihara plate

Answer 17

A display of colored dots used to test for the presence of color deficiency. The dots are colored so that people with normal (trichromatic) color vision can perceive numbers in the plate, but people with color deficiency cannot perceive these numbers or perceive different numbers than someone with trichromatic vision.

Question 18

Lightness

Answer 18

The perception of shades ranging from white to grey to black.

Question 19

Lightness constancy

Answer 19

The constancy of our perception of an object’s lightness under different intensities of illumination.

Question 20

Memory color

Answer 20

The idea that an object’s characteristic color influences our perception of that object’s color.

Question 21

Metamerism

Answer 21

The situation in which two physically different stimuli are perceptually identical. In vision, this refers to two lights with different wavelength distributions that are perceived as having the same color.

Question 22

Metamers

Answer 22

Two lights that have different wavelength distributions but are perceptually identical.

Question 23

Monochromat

Answer 23

A person who is completely color-blind and therefore sees everything as black, white, or shades of gray. A monochromat can match any wavelength in the spectrum by adjusting the intensity of any other wavelength. Monochromats generally have only one type of functioning receptors, usually rods.

Question 24

Neutral point

Answer 24

The wavelength at which a dichromat perceives gray.

Question 25

Opponent neuron

Answer 25

A neuron that has an excitatory response to wavelengths in one part of the spectrum and an inhibitory response to wavelengths in the other part of the spectrum.

Question 26

Opponent-process theory of color vision

Answer 26

A theory originally proposed by Hering, which claimed that our perception of color is determined by the activity of two opponent mechanisms: a blue–yellow mechanism and a red–green mechanism. The responses to the two colors in each mechanism oppose each other, one being an excitatory response and the other an inhibitory response. In addition, this theory also includes a black–white mechanism, which is concerned with the perception of brightness. See also opponent neuron.

Question 27

Partial color constancy

Answer 27

A type of color constancy that occurs when changing an object’s illumination causes a change in perception of the object’s hue, but less change than would be expected based on the change in the wavelengths of light reaching the eye. Note that in complete color constancy, changing an object’s illumination causes no change in the object’s hue.

Question 28

Penumbra

Answer 28

The fuzzy border at the edge of a shadow.

Question 29

Protanopia

Answer 29

A form of red–green dichromatism caused by a lack of the long-wavelength cone pigment.

Question 30

Ratio principle

Answer 30

A principle stating that two areas that reflect different amounts of light will have the same perceived lightness if the ratios of their intensities to the intensities of their surroundings are the same.

Question 31

Reflectance

Answer 31

The percentage of light reflected from a surface.

Question 32

Reflectance curve

Answer 32

A plot showing the percentage of light reflected from an object versus wavelength.

Question 33

Reflectance edge

Answer 33

An edge between two areas where the reflectance of two surfaces changes.

Question 34

Saturation (color)

Answer 34

The relative amount of whiteness in a chromatic color. The less whiteness a color contains, the more saturated it is.

Question 35

Selective reflection

Answer 35

When an object reflects some wavelengths of the spectrum more than others.

Question 36

Selective transmission

Answer 36

When some wavelengths pass through visually transparent objects or substances and others do not. Selective transmission is associated with the perception of chromatic color. See also selective reflection.

Question 37

Simultaneous color contrast

Answer 37

The effect that occurs when surrounding one color with another changes the appearance of the surrounded color. Occurs for chromatic and achromatic stimuli.

Question 38

Single-opponent neuron

Answer 38

Neurons that increase firing to long wavelengths presented to the center of the receptive field and decrease firing to short wavelengths presented to the surround (or vice versa).

Question 39

Subtractive color mixture

Answer 39

The creation of colors that occurs when paints of different colors are mixed together. (paint)

Question 40

Trichromat

Answer 40

A person with normal color vision. Trichromats can match any wavelength in the spectrum by mixing three other wavelengths in various proportions.

Question 41

Trichromatic theory of color vision/Young-Helmholtz theory of color vision

Answer 41

A theory proposing that our perception of color is determined by the ratio of activity in three receptor mechanisms with different spectral sensitivities. See also Young-Helmholtz theory of color vision.

Question 42

Tritanopia

Answer 42

A form of dichromatism thought to be caused by a lack of the short-wavelength cone pigment.

Question 43

Unilateral dichromat

Answer 43

A person who has dichromatic vision in one eye and trichromatic vision in the other eye. People with this condition (which is extremely rare) have been tested to determine what colors a dichromats perceive by asking them to compare the perceptions they experience with their dichromatic eye and their trichromatic eye.