Sensation And Perception Ch.7

Front 1

Achromatic color

Back 1

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

Front 2

Anomalous trichromat

Back 2

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.

Front 3

Cerebral achromatopsia

Back 3

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

Front 4

Chromatic adaptation

Back 4

Prolonged exposure to light in a specific part of the visible spectrum, which adapts receptors that fire to these wavelengths by selectively bleaching a specific visual pigment. For example, adaptation to a long-wavelength light selectively bleaches the long-wavelength pigment. The perceptual effect of adapting to long-wavelength light is a decrease in sensitivity to these wavelengths. Chromatic adaptation has been proposed as one of the mechanisms responsible for color constancy.

Front 5

Chromatic color

Back 5

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

Front 6

Color constancy

Back 6

The effect in which the perception of an object’s hue remains constant even when the wavelength distribution of the illumination is changed. Approximate color constancy means that our perception of hue usually 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.

Front 7

Color deficiency

Back 7

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.

Front 8

Color mixture, additive

Back 8

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

Front 9

Color mixture, subtractive

Back 9

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

Front 10

Color-blindness

Back 10

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

Front 11

Color-matching experiment

Back 11

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

Front 12

Desaturated

Back 12

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

Front 13

Deuteranopia

Back 13

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

Front 14

Dichromat

Back 14

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.

Front 15

Hue

Back 15

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

Front 16

Illumination edge

Back 16

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

Front 17

Ishihara plate

Back 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.

Front 18

Lightness

Back 18

Perception of reflectance. Usually objects with high reflectance are perceived as white and objects with low reflectance are perceived as gray or black.

Front 19

Lightness constancy

Back 19

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

Front 20

Memory color

Back 20

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

Front 21

Metamerism

Back 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.

Front 22

Metamers

Back 22

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

Front 23

Monochromat

Back 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.

Front 24

Neutral point

Back 24

The wavelength at which a dichromat perceives gray.

Front 25

Opponent neuron

Back 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.

Front 26

Opponent-process theory of color vision

Back 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 neurons.

Front 27

Penumbra

Back 27

The fuzzy border at the edge of a shadow.

Front 28

Protanopia

Back 28

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

Front 29

Ratio principle

Back 29

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

Front 30

Reflectance

Back 30

The percentage of light reflected from a surface.

Front 31

Reflectance curve

Back 31

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

Front 32

Reflectance edge

Back 32

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

Front 33

Saturation (color)

Back 33

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

Front 34

Selective reflection

Back 34

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

Front 35

Selective transmission

Back 35

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.

Front 36

Simultaneous contrast

Back 36

The effect that occurs when surrounding one color with another changes the appearance of the surrounded color.

Front 37

Trichromatic theory of color vision

Back 37

A theory proposing that our perception of color is determined by the ratio of activity in three receptor mechanisms with different spectral sensitivities.

Front 38

Tritanopia

Back 38

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

Front 39

Unilateral dichromat

Back 39

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 dichromat perceives by asking them to compare the perceptions they experience with their dichromatic eye and their trichromatic eye.

Front 40

Univariance, principle of

Back 40

Absorption of a photon by a visual pigment molecule causes the same effect no matter what the wavelength.