Ch. 5-6 Flashcards
three steps to perceiving color
1) detection –> detecting wavelengths; photoreceptors convert light into signals in the nervous system
2) discrimination –> neurons compare inputs from different kinds of photoreceptors
3) appearance –> assign perceived colors to lights and surfaces in the world
three types of cone receptors
S-cone, M-cone, L-cone
S-cone
a cone that is preferentially sensitive to short wavelengths; blue cone
M-cone
a cone that is preferentially sensitive to middle wavelengths; green cone
L-cone
a cone that is preferentially sensitive to long wavelengths; red cone
spectral sensitivity
the sensitivity of a cell or a device to different wavelengths on the electromagnetic spectrum
photopic
referring to light intensities that are bright enough to stimulate the cone receptors and bright enough to “saturate” the rod receptors, that is, drive them to their maximum responses
scotopic
referring to light intensities that are bright enough to stimulate the rod receptors but too dim to stimulate the cone receptors
principle of univariance
the fact that an infinite set of different wavelength-intensity combinations can elicit exactly the same response from a single type of photoreceptor; one photoreceptor type cannot make color discriminations based on wavelength
trichromacy/trichromatic theory of color vision
the theory that the color of any light is defined in our visual system by the relationships of three numbers— the outputs of the three cones
metamers
different mixtures of wavelengths that look identical, or more generally, any pair of stimuli that are perceived as identical in spite of physical diffferences
example of metamers
single wavelength that produces equal M- and L-cone activity will look yellow and the correct mixture of longer- and shorter-wavelength lights will also look yellow
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
subtractive 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 will contribute to the perception of color
to tell the difference between lights…
the nervous system will look at differences in the activities of the three cone types
convert the three cone signals into three new signals
- L-M
- (L+M)-S
- L+M
cone-opponent cell
a cell type— found in the retinal, LGN, and visual cortex— that, in effect, subtracts one type of cone input from another
equiliminant
referring to stimuli that vary in color but not in luminance
mesopic
referring to the middle range of light intensities
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
because we have exactly three different types of cone photoreceptors…
the light reaching any part of the retina will be translated into three responses, one for each local population of cones
nonspectral hues
hues that can arise only from mixtures of wavelengths
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
hue cancellation
cancelling a color through their opposite; ex. finding out how much blue or yellow we need to cancel the yellow or blue in a light of that color
unique hue
in the context of opponent color theory, any of four colors that can be described with only a single color term: red, yellow, green, blue; other colors can also be described as compounds
achromatopsia
an inability to perceive colors that is caused by damage to the central nervous system
transformations that produce perceived color take place in…
visual cortex
basic color terms
color words that are single words are used with high frequency and have
cultural relativism
the idea that basic perceptual experiences may be determined in part by the cultural environment
number of basic color terms in English
11
tetrachromatic
referring to the rare situation where the color of any light is defined by the relationships of four numbers— the outputs of those four receptor types
determining factors of color blindness
- type of cone affected
- type of defect –> either the photopigment for that cone type is anomalous (different from the norm) or the cone type is missing altogether
most common defects in color blindness
M- and L-cone defects
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
most color-blind individuals can still make discriminations based on wavelength; those discriminations are different from the norm
cone monochromat
an individual with only one cone type; truly color-blind
rod monochromat
an individual with no cones of any type; in addition to being truly color-blind, they are badly visually impaired in bright light
agnosia
a failure to recognize objects in spite of the ability to see them; typically due to brain damage
anomia
an inability to name objects in spite of the ability to see and recognize them; typically due to brain damage
synesthesia
the perceptual experience (e.g., a color) elicited by a stimulus (e.g., a music note) that does not typically produce that experience while the stimulus (e.g., wavelength information) that does normally produce the experience is absent
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 than can be experienced in isolation
related color
a color, such as brown or gray, that is seen only in relation to other colors
negative afterimage
an afterimage whose polarity is the opposite of the original stimulus; light stimuli produce dark negative afterimages; colors are complementary
adapting stimulus
a stimulus whose removal produces a change in visual perception or sensitivity