Midterm 2: Chapter 9 Flashcards
a rare brain disorder that causes partial or total loss of color vision
Cerebral achromatopsia
What does color vision enhance?
The contrast of objects that, if they didn’t appear colored, would be more difficult to perceive.
What does our ability to perceive color help us with?
- detect objects that might otherwise be obscured by their surroundings
- helps us recognize and identify things we can see easily.
- can be a cue to emotional signals by facial expressions.
Wavelengths from about 400 to 450 nm appear __________
Violet
Wavelengths from about 450 to 490 nm appear __________
Blue
Wavelengths from about 500 to 575 nm appear __________
Green
Wavelengths from about 575 to 590 nm appear __________
Yellow
Wavelengths from about 590 to 620 nm appear __________
Orange
Wavelengths from about 620 to 700 nm appear __________
Red
colors that have a dominant hue or wavelength, and include shades and tints of colors like red, orange, yellow, green, blue, indigo, and violet
Chromatic Colors
When a surface reflects waves of different lengths with varying intensity.
Selective Reflection
colors that lack hue or saturation, and are limited to white, black, and gray
Achromatic Colors
only some wavelengths pass through the object or substance
Selective Transmission
Plots of the percentage of light transmitted at each wavelength
Transmission curves
What is the key to understanding what happens when colored paints are mixed together?
Both paints still absorb the same wavelengths they absorb when alone, so the only wavelengths reflected are those that are reflected by both paints in common.
a process that involves the selective absorption and transmission of light to create colors
Subtractive color mixture
A process that combines light from different wavelengths to create a range of colors, including white.
Additive Color Mixture
What are colors of light associated with?
Wavelengths in the visible spectrum
What are colors of objects associated with?
Which wavelengths are reflected or transmitted
The colors that occur when we mix colors are associated with?
which wavelengths are reflected into the eye
True or false: mixing paints causes fewer wavelengths to be reflected
TRUE because each paint subtracts wavelengths from the mixture
True or false: mixing lights causes fewer wavelengths to be reflected
FALSE because each light adds wavelengths to the mixture.
colors that make up the visible light spectrum and each have their own wavelength
Spectral Colors
colors that do not appear in the spectrum because they are mixtures of other colors
Nonspectral colors
a color or shade/ chromatic colors
Hues
Intensity of color
Saturation
The light-to-dark dimension of color
Value/ lightness
3D color space that specifies colors based on three properties of color: hue (basic color), value (lightness), and chroma (color intensity).
Munsell color system
Theory that color vision is based on three principal colors
Trichromacy of color vision
the cones are sensitive to three different colors: green, blue, and red. When these colors are combined, eyes can tell a difference between millions of colors.
Young-Helmholtz Theory
What was the key finding from Maxwell’s color-matching experiment?
Any reference color could be matched, provided that observers were able to adjust the proportions of three wavelengths in the comparison field.
What were Maxwell’s color-matching experiences?
a series of tests conducted by physicist James Clerk Maxwell where he demonstrated that by mixing different proportions of just three primary colors (red, green, and blue), almost any other visible color could be created
Light of a particular wavelength stimulates each receptor mechanism to different degrees, and the pattern of activity in the three mechanisms results in the perception of a color.
Trichromatic Theory
The short-wavelength pigment (S) is absorbed maximally at _________.
419 nm
The medium-wavelength pigment (M) is absorbed maximally at _________.
531 nm
The long-wavelength pigment (L) is absorbed maximally at _________.
558 nm
Imperfections in the eye’s cornea and lens that distort the light on its way to the retina
Aberrations
What is the order of the eye?
- Light enters the eye through the CORNEA. This is the clear, dome-shaped surface that covers the front of the eye.
- From the cornea, the light passes through the PUPIL. The IRIS, or the colored part of your eye, controls the amount of light passing through.
- From there, it then hits the LENS. This is the clear structure inside the eye that focuses light rays onto the RETINA.
- Next, light passes through the VITREOUS humor. This is the clear, jelly-like substance that fills the center of the eye. It helps to keep the eye round in shape.
- Finally, the light reaches the RETINA. This is the light-sensitive nerve layer that lines the back of the eye. Here the image is inverted.
- The OPTIC NERVE is then responsible for carrying the signals to the visual cortex of the brain. The visual cortex turns the signals into images (for example, our vision).
Two physically different stimuli are perceptually identical
Metamerism
A rare form of color blindness that is usually hereditary. Individuals usually have no functioning cones, so their vision is created only by the rods
Monochromatism
How can a person with normal vision experience Monochromatism?
By sitting in the dark for several minutes. Dark adaption occurs; vision will be controlled by rods, and you’ll see the world as gray.
_________ perceive all wavelengths as shades of gray.
Monochromats
When do visual pigment molecules isomerize?
When the molecule absorbs one photon of light
Once a photon of light is absorbed by a visual pigment molecule, the identity of the light’s wavelength is lost.
Principle of Unvariance
People with just two types of cone pigment can see chromatic colors, but because they only have two types of cones, they confuse some colors that trichromats can distinguish.
Dichromats/ people with Dichromacy
a person with normal color vision, meaning they can see the three primary colors and mix them to match a perceived spectrum
Trichromats
What are ways to determine the presence of color deficiency?
- The color-matching procedure is used to determine the minimum number of wavelengths needed to match any other wavelengths in the spectrum.
- A color vision test that uses Ishihara plates.
A person with trichromatic vision in one eye and dichromatic vision in the other.
Unilateral dichromat
How are protanopia and deuteranopia (types of dichromatism) inherited?
Through the gene on the X chromosome.
Why are males more likely to have color deficiency?
Males only have one X chromosome, while females have two X chromosomes making them less likely to have color deficiency.
Why are females less likely to have color deficiency?
Females have two X chromosomes, and only one normal gene is required for normal color vision.
Missing the long-wavelength pigment; As a result, a protanope perceives short-wavelength light as blue, and as the wavelength is increased, the blue becomes less and less saturated until, at 492 nm, the protanope perceives gray
Protanopia
Missing the medium- wavelength pigment. A deuteranope perceives blue at short wavelengths, sees yellow at long wavelengths, and has a neutral point at about 498 nm
Deuteranopia
Needs three wavelengths to match any wavelength, just as a normal trichromat does
Anomalous Trichromatism
There are two pairs of chromatic colors; red-green and blue-yellow
Opponent-Process Theory
Arranges perceptually similar colors next to each other around its perimeter
Color circle
What did Hering propose?
Our color experience is built from the 4 primary chromatic colors arranged into two opponent pairs: yellow-blue and red-green.
Why wasn’t Hering’s opponent mechanism proposal accepted?
1) its main competition, trichromatic theory, was champi- oned by Helmholtz, who had great prestige in the scientific community
(2) Hering’s phenomenological evidence, which was based on describing the appearance of colors, could not compete with Maxwell’s quantitative color mixing data
(3) there was no neural mechanism known at that time that could respond in opposite ways.
What was the purpose of hue cancellation experiments?
to provide quantitative measurements of the strengths of the B–Y and R–G components of the opponent mechanisms.
Responded with an excitatory response to light from one part of the spectrum and an inhibitory response to light from another.
Opponent Neurons
Why are opponent neurons important for color perception?
Opponent responding is how color is represented in the cortex
What do opponent neurons indicate?
The difference in response of pairs of cones
Where do many neurons respond to color?
V4
a cortical area in the ventral visual pathway that plays a key role in visual object recognition
V4
Why do some researchers reject the idea of a “color center”?
They favor the idea that color processing is distributed across a number of cortical areas.
What did a double dissociation prove?
Color and form are processed independently
We perceive the colors of objects as being relatively constant even under changing illumination
Color constancy
______________ contains approximately equal amounts of energy at all wavelengths, which is a characteristic of white light.
Sunlight
Why does an incandescent bulb appear yellow?
It contains more energy at long wavelengths.
Why does an LED bulb appear blue?
They emit light at substantially shorter wavelengths
How do we determine the wavelengths that are actually reflected from the sweater?
we multiply the sweater’s reflectance curve at each wavelength by the amount of illumination at each wavelength.
Prolonged exposure to chromatic color
Chromatic Adaption
What was Uchikawa’s experiment?
At baseline, the paper is green and illuminated by white light
When the observer is not adapted, the paper is illuminated by red light and observer by white light
When the observer adapted to red, both the paper and the observer are illuminated by red light, making the paper appear more yellowish.
The perception of the object is shifted after adaption, but not as much as when there was no adaptation.
Partial Color Constancy
Effect on perception of prior knowledge of the typical colors of objects.
Memory color
How was memory of objects affect one’s perception?
Colors of familiar objects are judged to have richer, more saturated colors than unfamiliar objects that reflect
When is color constancy better?
When viewed with two eyes, and when an object is observed in a 3D scene.
Refers to our ability to perceive the relative reflectance of objects despite changes in illumination.
Lightness constancy
What is the visual system’s problem?
The intensity of light reaching the eye from an object depends on two things: the illumination and the object’s reflectance
The total amount of light that is striking the object’s surface
Illumination
The proportion of this light that the object reflects into our eyes.
Object’s reflectance
What is our perception of an object’s lightness related to?
the percentage of light reflected from the object, which remains the same no matter what the illumination.
As long as this ratio remains the same, the perceived lightness will remain the same.
Ratio principle
An edge where the reflectance of two surfaces changes
Reflectance Edge
An edge where the lighting changes.
Illumination Edge
In order for lightness constancy to work, the visual system needs to be able to take WHAT into account?
The uneven illumination created by shadows
