Sensation and perception Goldstein Chapter 9

Achromatic color

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

Additive color mixture

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

Anomalous trichromat

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.

Cerebral achromatopsia

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

Chromatic adaptation

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.

Chromatic color

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

Color blindness

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

Color constancy

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.

Color deficiency

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.

Color-matching experiment

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

Desaturated

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

Deuteranopia

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

Dichromat

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.

Double-opponent neurons

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+.

Hue

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

Illumination edge

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

Ishihara plate

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.

Lightness

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

Lightness constancy

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

Memory color

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

Metamerism

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.

Metamers

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

Monochromat

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.

Neutral point

The wavelength at which a dichromat perceives gray.

Opponent neuron

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.

Opponent-process theory of color vision

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.

Partial color constancy

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.

Penumbra

The fuzzy border at the edge of a shadow.

Protanopia

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

Ratio principle

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.

Reflectance

The percentage of light reflected from a surface.

Reflectance curve

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

Reflectance edge

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

Saturation (color)

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

Selective reflection

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

Selective transmission

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.

Simultaneous color contrast

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

Single-opponent neuron

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).

Subtractive color mixture

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

Trichromat

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

Trichromatic theory of color vision

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.

Tritanopia

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

Unilateral dichromat

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.

Young-Helmholtz theory of color vision

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 trochromatic theory of color vision.