Topic 9: Color Perception Flashcards
Cerebral Achromatopsia
a loss of color vision caused by damage to the cortex
Color Deficiency
condition (sometimes incorrectly called color blindness) in which people see fewer colors than people with normal color vision and need to mix fewer wavelengths to match any other wavelength in the spectrum
Chromatic Colors
color with hue, such as blue, yellow, red, or green
Selective Reflection
when an object reflects some wavelengths of the spectrum more than others
Reflectance Curves
a plot showing the percentage of light reflected from an object versus wavelength
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
Transmission Curves
plots of the percentage of light transmitted through a liquid or object at each wavelength
Subtractive Color Mixture
both paints still absorb the same wavelengths they absorbed when alone, so the only wavelengths reflected are those that are reflected by both paints in common
Additive Color Mixture
all of the light that is reflected from the surface by each light when alone is also reflected when the lights are superimposed
Spectral Colors
colors that appear in the visible spectrum
Non-spectral Colors
colors that do not appear in the spectrum because they are mixtures of other colors
an example is magenta, which is a mixture of red and blue
Hues
the experience of a chromatic color, such as red, green, or yellow, or blue, or combinations of these colors
Saturation
the relative amount of whiteness in a chromatic color
the less whiteness a color contains, the more saturated it is
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
Value
the light-or-dark dimension of color
Lightness
the perception of shades ranging from white to gray to black
Color Solid
a solid in which colors are arranged in an orderly way based on their hue, saturation, and value
Munsell Color System
depiction of hue, saturation, and value developed by Albert Munsell in the early 1900s in which different hues are arranged around the circumstance of a cylinder with perceptually similar hues placed next to each other
Trichromacy of Color Vision
the idea that our perception of color is determined by the ratio of activity in three receptor mechanisms with different spectral sensitivities
also known as the Young-Helmholtz theory
Color Matching
a procedure in which observers are asked to match the color in one field by mixing to or more lights in another field
Microspectrophotometry
a technique in which a narrow beam of light is directed into a single visual receptor
this technique makes it possible to determine the pigment absorption spectra of single receptors
Adaptive Optical Imaging
a technique that makes it possible to look into a person’s eye and take pictures of the receptor array in the retina
Aberrations
imperfections on the eye’s cornea and lens that distort light on its way to the retina
Cone Mosaic
arrangement of short-, medium-, and long-wavelength cones in a particular part of the retina
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
Monochromatism
rare form of color blindness in which the absence of cone receptors results in perception only of shades of lightness (white, gray and black), with no chromatic color present
Monochromats
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
Color Blind
a condition in which a person perceives no chromatic color
this can be caused by absent or malfunctioning cone receptors or by cortical damage
Dichromats
a person who has a form of color deficiency
dichromats can match any wavelength in the spectrum by mixing two other wavelength
Trichromats
a person with normal color vision
trichromats can match any wavelength in the spectrum by mixing three other wavelengths in various proportions
Ishihara Plates
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 on the plate, but people with color deficiency cannot perceive these numbers or perceive different numbers than someone with trichromatic vision
Unilateral Dicrhomat
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 dichromats perceive by asking them to compare the perceptions they experience with their dichromatic eye and their trichromatic eye
Dichromatism
a form of color deficiency in which a person has just two types of cone pigment and so can see chromatic colors but confuse some colors that trichromats can distinguish
Protanopia
a form of dichromatism in which a protanope is missing the long-wavelength pigment, and perceives short-wavelength light as blue and long-wavelength light as yellow
Neutral Point
the wavelength at which a dichromat perceives gray
Deuteranopia
a form of dichromatism in which a person is missing the medium-wavelength pigment
a deuteranope perceives turquoise at short wavelengths, sees yellow at long wavelengths, and has a neutral point at about 498 nm
Tritanopia
a form of dichromatism in which a person is missing the short-wavelength pigment
a tritanope sees blue at short wavelengths, red at long wavelengths
Anomalous Trichromatism
a type of color deficiency in which a person needs to mix a minimum of three wavelengths to match any other wavelength in the spectrum but mixes these wavelengths in different proportions than a trichromat
Opponent-Process Theory of Color Vision
a theory originally proposed by Hering, which claimed that our perception of color 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
Color Circle
perceptually similar colors located next to each other an arranged in a circle
Hue Scaling
procedure in which participants are given colors from around the hue circle and told to indicate the proportions of red, yellow, blue, and green that they perceive in each color
Unique Hues
name given by Ewald Hering to what he proposed were the primary colors: red, yellow, green, and blue
Hue Cancellation
procedure in which a subject is shown a monochromatic reference light and is asked to remove, or “cancel”, the one of the colors in the reference light by adding a second wavelength
this procedure was used by Hurvich and Jameson in their research on opponent-process theory
Opponent Neurons
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
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
Chromatic Adapatation
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
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
Memory Color
the idea that an object’s characteristic color influences our perception of that objects’ color
Lightness Constancy
the constancy of our perception of an object’s lightness under different intensities of illumination
Reflectance
the percentage of light reflected from a surface
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 Edge
an edge between two areas where the reflectance of two surfaces changes
Illumination Edge
the border between two areas created by different light intensities in the two areas
Habituation Procedure
procedure in which a person pays less attention when the same stimulus is presented repeatedly
for example, infants look at a stimulus less and less on each successive trial
Dishabituation
an increase in responding that occurs when a stimulus is changed
this response is used in testing infants to see whether they can differentiate two stimuli
Novelty-Preference Procedure
a procedure used to study infant color vision in which two side-by-side squares of different colors are presented and the infant’s looking time to the two squares is measured to determine whether they can tell the difference between them
What is perceptual segregation?
aids in discriminating objects from background
What is crypsis?
camouflage, concealment, or disruption with respect to the surrounding environment
concealing coloration, disruptive coloration
What is concealing coloration?
animal has same color as its environment
e.g., snowy owl
What is disruptive coloration?
pattern breaks up outline so one individual doesn’t stand out
may also produce “motion dazzle”
e.g., zebras
What is mimesis?
camouflage or concealment by imitation of another object
disguise, mimicry
What is disguise?
animal looks like another, unimportant object to predator or prey
e.g., walking stick
What is mimicry?
animal looks like other distasteful or dangerous animal
e.g., scarlet king snake
How did Sir Isaac Newton describe color?
split sunlight into component colors using a prism
wavelength correspond to (most) colors
spectral colors: those found in the rainbow
what about purple?
What are the three physical and psychological dimensions of color?
wavelength / hue
purity / saturation
intensity / brightness
What is the color spindle?
describes all colors we can see
slice = color circle
problem: some hues saturate before others
How are color terms separated differently in different languages?
if a language includes only 2 color terms, they represent light and dark
if there are three color terms, vocabulary is equivalent to light (white), warm (red, yellow, brown) and dark (including black, green & blue, or grue)
warm is always split into red and yellow before grue is split into green and blue
basic hues (black, white, red, yellow, green, and blue) named before color terms
if there are 7 or more color concepts, the words for brown, orange, pink, purple, and grey are added before green or blue are subdivided
concluded there are 11 basic color terms
What is the invariant sequence in which color names emerge in language?
- black, white
- red
- green or yellow
- blue
- brown
- orange, pink, purple, grey
What are metamers?
two lights with different wavelength distribution, but appearing identical in color
metamers must produce identical neural activation
What is an additive color mixture?
mix light of different wavelengths
mix red and green = yellow
mix all colors = white
e.g., computer or TV screen pixels
What is a subtractive color mixture?
mix paint (or ink) of different pigments
mix red and green = grey-brown
mix all colors = black
e.g., inkjet pigments (usually yellow, magenta, & cyan)
paint absorbs (subtracts) wavelengths except the one you perceive it having
What are complementary colors?
colors on opposite sides of the color circle which, when added, produce greyish-white
What are primaries?
three wavelengths that, when mixed in certain proportions, can match any other hue
any primary cannot be matchable by mixing the other two (i.e., use monochromatic lights, not metamers)
believed to be basic units of color sensation
primaries define the “color triangle”
problem: some test colors are not matchable (spectral yellow requires a negative primary)
What is the “gamut”?
defined bigger, imaginary triangle (“gamut”) encompassing all spectral hues to overcome problem of negative primaries
CIE chromaticity space: hues defined by two numbers; proportion of G and R
add another dimension for brightness
any hue may be specified in terms of these primaries
What is scotopic vision?
only rods function; no color
thus cones are responsible for color vision, but how?
What is the Young-Helmholtz Trichromatic Theory?
Thomas Young (1802): proposed that only three different types of receptors are needed, each sensitive to a different wavelength
Hermann von Helmholtz (1806): provided evidence that mixing three primary colors would match any given color
What is the evidence for the Young-Helmholtz Trichromatic Theory?
color-matching experiments: observers can match a given color by combining proportions of three primaries together
physiological evidence: measure wavelength of light absorbed by cones using microspectrophotometer, different wavelengths produce different activations in each receptor type
What is opponent-process theory?
Ewald Hering (1878)
phenomenological observation led to questions: how many primary colors do there seem to be? can all colors be combined the same way?
proposed that basic colors come in opposing pairs
What is the evidence for the opponent-process theory?
afterimage: visual sensation appearing after adapting to a stimulus; produces opposite color
simultaneous color contrast: surrounding an area with a color changes the appearance of the surrounded area
habituation: infants get bored of looking at the same thing
physiological evidence: centre-surround cells have opposing receptive field regions of bright and dark
How are color-opponent cells neurally wired?
opponent process obtains a difference function for the associated pair of wavelengths
What is the cortical coding of color perception?
color-opponent cells found in blobs (V1 layers 2 & 3)
V1 layer 4 and V4 have double color-opponent cells
What is rod monochromacy?
no cones
incidence: 1 per 100,000
What is cone monochromacy?
one type of cone only
blue-cone monochromats: more common
What is dicrhomacy?
two types of cones only
What is protanopia?
long wavelength cone deficient
perceives spectrum as blue-yellow
impaired in ability to distinguish red/green
What is deuteranopia?
medium wavelength cone deficient
perceives spectrum as blue-yellow
impaired ability to distinguish red / green
What is tritanopia?
short wavelength cone deficient, very rare
perceives spectrum as turquoise-red
impaired ability to perceive blue and yellow
What is anomalous trichromacy?
have all types of cones, but one type is abnormal
are poor at discriminating hues
What is color constancy?
perception of an object’s color remains constant, despite variations in the quality of illumination
What is chromatic adaptation?
prolonged exposure to a particular wavelength causes cones to be less sensitive to it
What is memory color?
characteristic color of a familiar object may influence color perception
What proportion of people thought #TheDress was different colors?
blue/black: 57%
white/gold: 30%
blue/brown: 11%
~10% of people report seeing it switch colors
What are the possible interpretations for why people saw the dress differently?
white/gold dress seen under “cool” bluish illumination (or due to camera’s white balance, shifting whites to blue)
blue/black dress in “warm” yellowish illumination, overexposed in photo
What was the Wallisch (2017) study on the effects of chronotype on how people perceived the dress?
“larks” are people to tend to get up early and go to bed early, whereas “owls” get up late and stay up later
larks are exposed to more (bluish) sunlight than owls, who are exposed to more (yellowish) incandescent light
chronotype accounts for experience of the dress: larks are more likely to see it as white/gold; owls are more likely to see it as blue/black
What is lightness (whiteness) constancy?
perception of an object’s lightness (inherent white/grey/black-ness) remains constant, despite changes in illumination
illumination (light falling on surface) x reflectance (proportion of light reflected from a surface) = retinal luminance (amount of light on retina)
What is the ratio principle?
percentage of light reflected from an object (compared to illumination) determines perception of lightness
What is the McCollough effect (1965)?
- look at vertical black & green striped for 5 sec. each, alternately looking at horizontal red & black stripes, for a total of 5 minutes
- then look at a pattern of horizontal and vertical black & white stripes
vertical whites appear reddish; horizontal whites look greenish (but no afterimages on blank white paper)
due to fatigue of cortical (not retinal) colored-line detecting cells?
aftereffects may last for weeks
duration can be changed by consumptions of coffee and some psychoactive drugs
stronger in extroverts than introverts, and might be a reliable test for extroversion
What is absolute identification?
it is difficult to identify (or categorize) unidimensional stimuli (whereas it is easy to identify complex stimuli like faces)
e.g., poor performance on color recognition task
What is relative information?
the task is easier if a comparison scale is provided
e.g., good performance identifying temperature on color-coded map
