Task 3 Flashcards
True Colors (25 cards)
Basics of color perception
- color as result of interaction of a physical stimulus with a particular nervous system
- three steps:
1: Detection -> detection of wavelengths
2: Discrimination -> tell difference between one wavelength and another
3: Appearance -> assign perceived colors to lights and surfaces in the world
Step 1: Detection
- three types of cone photoreceptors: differ in photopigment they carry -> differ in sensitivity to light of different wavelengths
- S-Cones: 420 nm
- M-Cones: 535 nm
- L-Cones: 565 nm
- their spectral sensitivities overlap
Step 2: Color Discrimination
- principle of univariance
- cone-opponent cell
- principle of univariance: an infinite set of different wavelength-intensity combinations can elicit exactly the same response from a single type of photoreceptor -> one photoreceptor cannot make color discriminations based on wavelength
- cone-opponent cell: cell type that subtracts one type of cone input from another
Step 3: Color Appearance
- color space
- color space: three-dimensional space, established because color perception is based on the outputs of three cone types, that describes a set of all colors
Color Blindness:
- determining factors
- type of cone affected
- type of defect (photopigment for cone missing or anomalous)
- mostly: M- and L-cone defects
Color Blindness:
- Types
- Protanope: absence of L-cones
- Deutanope: absence of M-cones
- Tritanope: absence of S-cones
- Cone monochromat: only one cone type; truly color-blind
- Rod monochromat: no cones; truly color-blind; badly visually impaired in bright light
- Cerebral achromatopsia: total color blindness
Color Blindness:
- Anemia
inability to name objects in spite of the ability to see and recognize them
- typically due to brain damage
Color Blindness:
- Agnosia
failure to recognize objects in spite of the ability to see them
- typically due to brain damage
Adaptation and Afterimages:
- negative afterimages
- adapting stimulus
- neutral point
- negative afterimages: afterimages whose polarity is the opposite of the original stimulus; light stimuli produce dark negative afterimages; colors are complementary
- adapting stimulus: stimulus whose removal produces a change in visual perception or sensitivity
- neutral point: point at which an opponent color mechanism is generating no signal
Color Constancy
= tendency of a surface to appear the same color under a fairly wide range of illuminants
Light Constancy
= fact that we see whites, grays, and blacks as staying about the same shape under different illuminations
- information of shadows: shadow’s meaningful shape must be taken into account
Selective Reflection
= process in which some wavelengths are reflected more than others -> leads to occurrence of chromatic colors (blue, green, and red)
- achromatic colors = white, gray, and black
Selective Transmission
= only some wavelengths pass through the object or substance -> color of things that are transparent (liquids, plastics, and glass)
Color Mixing
- Paints -> subtractive color mixture
- both paints still absorb same wavelengths they absorbed when alone -> only wavelengths selected are those selected by both paints common –> subtractive color mixture
Color Mixing
- Lights -> 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
Perceptual Dimensions of Colors
- spectral colors: colors in spectrum
- nonspectral colors: colors that do not appear in the spectrum because they are mixtures of other colors (e.g. magenta -> red and blue)
Trichromatic Theory of Color Vision
- in general
= theory that the color of any light is defined in our visual system by the relationships of three numbers - outputs of three cones
- Young-Helmholtz theory
Trichromatic Theory of Color Vision
- Color-Matching Evidence
- color matching
- light of a particular wavelength stimulates each receptor mechanism to different degrees -> pattern of activity in three mechanisms result in the perception of a color
Trichromatic Theory of Color Vision
- Physiological Evidence
- metamerism
- cone pigments (S-, M-, and L-cones)
- metamerism: two physically different stimuli are perceptually identical
Trichromatic Theory of Color Vision
- three receptor mechanisms
- monochromat:
- principle of univariance
- dichromat:
- color perception depends on the pattern of activity in three receptor mechanisms
Opponent-Process Theory of Color Vision
- in general
= color vision is caused by opposing physiological responses generated y blue and yellow, red and green, and black and white
- evidence:
- color circle -> all colors fall in four different categories
Opponent-Process Theory of Color Vision
- psychophysical measurements
- hue cancellation
- discovery of opponent neurons
Opponent-Process Theory of Color Vision
- physiological evidence
- opponent neurons
- BUT:
- both theories correct –> each describes neural processes that take place in different parts of the visual system
Article: #thedress
- color constancy –> perception of the dress is based on individual differences
- people either correct for “cool illumination” (white and gold) or “warm illumination” (blue and black)
