Chapter 5: The Perception of Color Flashcards
Three steps to color perception
- Detection - Wavelengths must be detected
- Discrimination - Must be able to tell difference between wavelengths.
- Appearance - Assign perceived colors to lights and surfaces in world.
S-cone
A cone that is preferentially sensitive to short wavelengths; colloquially (but not entirely accurately known as a “blue cone.”
M-cone
A cone that is preferentially sensitive to middle wavelengths (but not entirely accurately known as a “green cone.”
L-cone
A cone that is preferentially sensitive to long wavelengths; colloquially (but not entirely accurately known as a “red cone.”
Photopic
Referring to light intensities that are bright enough to stimulate the cone receptors and bright enough to “saturate” the rod receptors.
Scotopic
Referring to light intensities that are bright enough to stimulate the rod receptors but too dim to stimulate cone receptors.
Problem of Univariance
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.
Trichromatic theory of color vision (trichromacy)
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.
Metamers
Different mixtures of wavelengths that looks identical. More generally, any pair of stimuli that are perceived as identical in spit of physical differences.
Additive color mixture
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.
Subractive color mixture
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.
LGN
structure in thalamus, receives input from ganglion cells and outputs to V1
cone-opponent cells
A cell type-found in the retina, LGN, and V1,-that in effect, subtracts one type of cone input from another.
Color space
The three-dimensional space, established because color perception is based on the outputs of three cone types, that describes the set of all colors.
achromatic
Referring to any color that lacks a chromatic(hue) component. Black, white, or gray.
hue
the chromatic (colorful) aspect of color (red, blue, green, yellow…)
saturation
The chromatic strength of a hue. White has zero saturation, pink is more saturated, and red is fully saturated.
brightness
The perceptual consequence of the physical intensity of a light.
opponent color theory
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.
unique hue
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).
double-opponent cell
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.
single-opponent cells
Another way to refer to cone-opponent cells, in order to differentiate them from double-opponent cells.
achromatopsia
An inability to perceive colors that is caused by damage to the CNS
afterimage
A visual image seen after the stimulus has been removed.
adapting stimulus
A stimulus whose removal produces a change in visual perception or sensitivity.
negative afterimage
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.
neutral point
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.)
deuteranope
an individual who suffers from color blindness that is due to the absence of M-cones.
protanope
an individual who suffers from color blindness that is due to the absence of L-cones.
tritanope
an individual who suffers from color blindness that is due to the absence of S-cones.
color-anomalous
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.
cone monochromat
An individual with only one cone type. Cone monochromat are truly color blind.
rod monochromat
An individual with no cones of any type. In addition to being truly colorblind, that are visually impaired in bright light.
agnosia
A failure to recognize objects in spite of the ability to see them. Agnosia is typically due to brain damage.
anomia
An inability to name objects in spit of the ability to see and recognize them.
cultural relativism
In sensation and perception, the idea that basic perceptual experiences (color perception) may be determined in part by cultural environment.
color contrast
A color perception effect in which the color of one region induces the opponent color in a neighboring region.
color assimilation
A color perception effect in which two colors bleed into each other, each taking on some of the chromatic quality of the other.
unrelated color
a color that ca be experienced in isolation
related color
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.
color constacnty
The tendency of a surface to appear the same color under a fairly wide range of illuminants
illuminant
The light that illuminates a surface
spectral reflectance function
The percentage pf a [articular wavelength that is reflected from a surface.
spectral power distribution
The physical energy in a light as a function of wavelength.
reflectance
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.
