Module Seven - Color Flashcards
(127 cards)
1
Q
What is prosopagnosia as exhibited by Patient P.?
A
Prosopagnosia is the inability to recognize faces, demonstrated by Patient P.’s failure to identify even her husband visually while still recognizing voices.
2
Q
What is achromatopsia as seen in Patient P.?
A
Achromatopsia is a loss of color vision, causing Patient P. to see the world in grayscale and struggle to identify objects by color.
3
Q
How did Patient P. adapt to her achromatopsia when identifying foods?
A
Patient P. relied on the smell of foods to identify them, compensating for her inability to use color cues.
4
Q
What emotional impact did achromatopsia have on Patient P.?
A
Patient P. experienced depression and avoided visual experiences like viewing Impressionist art due to the drab, grayscale appearance.
5
Q
What defines color vision?
A
Color vision is the ability to distinguish lights of different wavelengths.
6
Q
How do surface reflections affect the spectral composition of light before it reaches the eye?
A
Surface reflections alter the spectral composition by absorbing some wavelengths and reflecting others, changing the distribution of wavelengths entering the eye.
7
Q
What is hue?
A
Hue is the quality corresponding to wavelength, what we ordinarily call “color” (e.g., blue, green, red).
8
Q
What is saturation?
A
Saturation is the purity or vividness of a color, indicating how much a color is mixed with white light.
9
Q
What is brightness?
A
Brightness is the perceived intensity or luminance of light.
10
Q
What is additive color mixing?
A
Additive mixing combines colored lights (e.g., red, green, blue) by overlapping their beams; combining all three at full brightness yields white.
11
Q
What is subtractive color mixing?
A
Subtractive mixing involves pigments that absorb certain wavelengths and reflect others; layering pigments (cyan, magenta, yellow) subtracts more wavelengths, making mixtures darker and potentially near black.
12
Q
What are the three types of cone photoreceptors in the retina?
A
The three cone types are S-cones (short-wavelength sensitive), M-cones (middle-wavelength sensitive), and L-cones (long-wavelength sensitive).
13
Q
How does trichromacy underlie human color perception?
A
Trichromacy means color perception arises from relative activation of the three cone types; comparing their response ratios allows discrimination of millions of hues.
14
Q
What are the three opponent channels in opponent processing?
A
The three opponent channels are the red–green channel (L vs. M cones), the blue–yellow channel (S vs. combined L+M cones), and the luminance channel (sum of L+M cones).
15
Q
What phenomenon do opponent channels explain?
A
Opponent channels explain color afterimages (e.g., staring at red yields green afterimage) and contextual color effects like color contrast and assimilation.
16
Q
What is color contrast?
A
Color contrast is when a central patch’s perceived hue shifts away from the color of its surround (e.g., red center looks redder when surrounded by green).
17
Q
What is color assimilation?
A
Color assimilation is when a central patch’s perceived hue shifts toward the hue of its surround (e.g., a blue square appears slightly red when surrounded by red).
18
Q
What is color constancy?
A
Color constancy is the tendency to perceive an object’s color as stable despite changes in the spectral power distribution of the illuminant.
19
Q
What is lightness constancy?
A
Lightness constancy is the phenomenon where the perceived reflectance (lightness) of a surface remains constant despite changes in illuminant intensity.
20
Q
What did Newton’s insight about color propose?
A
Newton proposed that color is not inherent in light or objects but arises from sensory processing; objects “dispose” certain wavelengths to evoke color sensations in observers.
21
Q
What is the visible spectrum range?
A
The visible spectrum ranges from approximately 400 nm (violet) to 700 nm (red).
22
Q
What does spectral power distribution (SPD) describe?
A
SPD describes a light source’s intensity (power) at each wavelength across the visible spectrum.
23
Q
How does heterochromatic light differ from monochromatic light in SPD?
A
Heterochromatic light contains many wavelengths, showing a broad SPD curve (e.g., sunlight), whereas monochromatic light consists of a single wavelength, appearing as a spike in SPD.
24
Q
What characteristic defines ideal white light’s SPD?
A
Ideal white light has a flat SPD—equal power at every wavelength—appearing colorless or gray.
25
How does the SPD of sunlight compare to an incandescent bulb?
Sunlight’s SPD approximates a flat white distribution, while an incandescent bulb’s SPD skews toward longer wavelengths (reds and yellows), giving a warm appearance.
26
How does the SPD of a fluorescent bulb differ from sunlight?
A fluorescent bulb’s SPD has distinct peaks in the blue and green regions, yielding a cooler, bluish tint, unlike the nearly uniform solar SPD.
27
What is spectral reflectance?
Spectral reflectance describes the percentage of incident light at each wavelength that a surface reflects versus absorbs.
28
How do colored surfaces’ reflectance curves relate to perceived color?
Colored surfaces reflect more strongly at wavelengths corresponding to their perceived color (e.g., a tomato reflects more long-wavelength red light).
29
What differentiates neutral surfaces’ reflectance curves?
Neutral surfaces (black, gray, white) have roughly flat reflectance curves, differing only in overall reflectance level (white reflects most, black absorbs most).
30
How is perceived color of an object determined?
Perceived color depends on the product of the source SPD (which wavelengths are present) and the surface reflectance (which wavelengths the object returns), determining which wavelengths reach the eye.
31
Contrast spectral power distribution vs. spectral reflectance.
SPD describes a light source’s absolute intensity at each wavelength; spectral reflectance describes a surface’s proportion of incident light reflected at each wavelength.
32
What are the three perceptual dimensions of color?
Hue, saturation, and brightness are the three independent dimensions describing color experience.
33
What does the color circle represent?
The color circle is a 2-D representation where hue varies around the circumference, saturation varies from center (unsaturated gray) to edge (fully saturated), and nonspectral purples bridge red and violet.
34
What does the color solid add to the color circle?
The color solid adds brightness as a vertical axis: black at the bottom, white at the top, with horizontal cross-sections showing color circles at fixed brightness levels.
35
How are subtractive color mixtures of pigments determined?
The mixture’s reflectance at each wavelength equals the product of individual pigments’ reflectances at that wavelength, so the mixture reflects only wavelengths both pigments reflect.
36
Explain how mixing blue and yellow paint yields green.
Blue paint reflects short (blue) and some medium (green) wavelengths; yellow paint reflects long (yellow-red) and some medium (green); their mixture reflects only medium (green) wavelengths both reflect.
37
Why do subtractive mixtures tend to appear darker?
Because pigments have reflectances below 100%, and multiplying their reflectance curves reduces overall reflectance, making mixtures darker than individual pigments.
38
What is additive color mixing on a white screen?
Additive mixing on a white screen combines the spectral power distributions of overlapping colored lights, with the screen reflecting the sum, producing hues based on combined wavelengths.
39
How can one predict the hue of an additive mixture using the color circle?
Draw a straight line between the two monochromatic hues on the color circle; the perceived hue lies along that line, closer to the hue of greater intensity (midpoint for equal intensity).
40
How does saturation change when mixing two fully saturated lights additively?
The resulting hue lies inside the circle, with saturation reduced compared to the fully saturated primaries.
41
What defines complementary colors?
Complementary colors are two hues exactly 180° apart on the color circle (e.g., red and cyan, yellow and blue).
42
What is the result of overlapping equal-intensity complementary lights additively?
The mixture falls at the center of the color circle’s chromaticity diagram on the achromatic axis, perceived as a shade of gray (black to white depending on intensity).
43
What are primary colors in additive mixing?
Primary colors are any three lights whose hues form the vertices of a triangle on the color circle; varying their intensities can produce every color inside that triangle (e.g., RGB).
44
Why is RGB chosen as primaries for additive displays?
RGB hues are spaced 120° apart, forming a maximally large triangle on the color circle, enclosing the largest gamut of colors achievable with three primaries.
45
Why can no set of three primaries produce all perceivable colors?
Because any three primaries form a triangle on the color circle; colors outside that triangle (e.g., highly saturated cyan) cannot be produced, so the triangle’s area limits the gamut.
46
What is the two-stage color vision process?
Stage 1: Trichromatic representation—three cone types encode spectral composition. Stage 2: Opponent representation—neurons recombine cone signals into red–green, blue–yellow, and luminance channels.
47
What do metameric color-matching experiments demonstrate?
They show that physically different stimuli can appear identical in color when three primaries are adjusted to match a test patch, validating that three cone types suffice for color matching.
48
In a metameric match, how is a 590 nm test light matched using three primaries?
An observer adjusts red, green, and blue primaries (e.g., at 645 nm, 526 nm, 444 nm) until the mixture appears identical to the 590 nm test light, demonstrating a metameric match.
49
What is a cone’s spectral sensitivity function?
It defines the probability that a photon at a given wavelength will be absorbed by a cone’s photopigment, showing each cone type’s relative response across wavelengths.
50
How do M- and L-cone sensitivities compare to S-cones?
M- and L-cones are much more sensitive at their peak wavelengths than S-cones, which have lower absolute sensitivity and peak around 443 nm.
51
What is the principle of univariance?
The principle states that a single cone’s response depends only on the number of absorbed photons, not their wavelengths, so one cone cannot distinguish wavelength vs. intensity alone.
52
What happens if only one cone type is present (single-receptor vision)?
The observer perceives lights achromatically (as varying gray intensities); different wavelength–intensity pairs can produce the same cone response, yielding true color-blindness.
53
Why is night vision monochromatic under scotopic conditions?
In low light, rods alone mediate vision; rods respond based on photon absorption without distinguishing wavelength, so vision is achromatic, perceiving only brightness variations.
54
If an observer had only M- and L-cones, what would their color vision be like?
They would need two primaries to match any test wavelength but could still perceive differences between wavelengths via distinct M,L response pairs, though with a reduced gamut compared to trichromacy.
55
What does the trichromacy principle state?
The minimum number of primaries required to match any visible color equals the number of cone types; since humans have three cones, three primaries are needed for universal matching.
56
How is trichromacy analogous to data compression?
Instead of encoding light intensity at every wavelength, the visual system uses three cone responses (three numbers), compressing vast spectral information into a low-dimensional encode.
57
What are metamers?
Metamers are physically different spectral distributions that evoke identical cone response triplets and thus appear the same color to an observer.
58
Why do metamers occur?
Because cone responses compress spectral information, different SPDs can yield the same three-cone response pattern, making them indistinguishable in color.
59
What evolutionary advantage does trichromacy provide?
Three broadly overlapping cone sensitivities provide fine color discrimination sufficient for tasks like identifying ripe fruits and edible plants in varied environments.
60
How do technologies exploit trichromacy?
Displays and printing use three primaries (e.g., RGB or CMY) to reproduce any target color by matching the same cone response pattern as the original light or object.
61
What physiological evidence supports trichromacy?
Color-matching psychophysics shows consistent three-primary matches across observers, and retinal densitometry directly images three spectrally distinct cone classes in the retina.
62
What was Hering’s argument against trichromacy?
Hering argued that certain phenomena (afterimages, color sorting into four categories, impossibility of certain mixtures) could not be explained by trichromacy alone, suggesting four basic colors.
63
What are Hering’s four basic hues and their opponent pairs?
Hering proposed four primitives—red, green, blue, yellow—grouped into two opponent pairs: red↔green and blue↔yellow.
64
What psychophysical observations support opponent theory?
Color sorting into four categories, complementary afterimages (e.g., red→green), and the impossibility of perceiving “reddish green” or “bluish yellow” support opponent opponencies.
65
Why are both trichromacy and opponent theory needed?
Trichromacy explains how cones encode spectral light; opponent theory explains perceptual phenomena (afterimages, hue cancellation, mixture restrictions) that trichromacy alone cannot.
66
What is hue-cancellation psychophysics?
A method where an observer adds light of the opponent hue (e.g., blue to cancel yellow) to a monochromatic test until one hue sensation is nullified, quantifying perceived amounts of the original hue.
67
What do hue-cancellation functions show?
They plot how much opponent light is needed to cancel perceived yellowness (blue–yellow axis) or greenness (red–green axis) across wavelengths, revealing unique hues where cancellation is zero.
68
What are unique hues and their approximate wavelengths?
Unique Blue (~464 nm), Unique Green (~489 nm), and Unique Yellow (~572 nm). There is no unique red, as the longest wavelengths still carry some yellowness.
69
What wavelength range appears as 'pure' blueness?
400–489 nm appears as pure blueness without perceived yellowness; observers can cancel blueness by adding yellow light.
70
What wavelength range appears as 'pure' greenness?
489–572 nm appears as pure greenness without perceived redness; observers can cancel greenness by adding red light.
71
What was the significance of Svaetichin & MacNichol’s fish retina recordings?
They were the first to record cones showing opposite responses to different wavelength bands, providing early evidence of opponency at the retinal level.
72
What did De Valois et al. find in monkey LGN recordings?
They found neurons exhibiting opponent responses to cone inputs (e.g., red–green or blue–yellow opponency), confirming opponent processing in early visual pathways.
73
What are the four types of retinal opponent-circuit RGCs?
1) +S − (M+L): excited by short (bluish), inhibited by medium/long (greenish-yellowish); 2) +(M+L) − S: opposite; 3) +L − M: excited by long (reddish), inhibited by medium (greenish); 4) +M − L: opposite of +L−M.
74
What are single-opponent neurons in V1?
Single-opponent neurons have a center–surround RF where the center is excited by one cone input (e.g., L) and the surround is inhibited by its opponent (e.g., M), encoding average hue over a region.
75
What are double-opponent neurons in V1?
Double-opponent neurons have center and surround regions each comparing cone inputs (e.g., center +L–M, surround +M–L), responding strongly at chromatic edges where hues change locally.
76
How do double-opponent cells detect colored edges?
When center sees red (L high, M low) and surround sees green (M high, L low), both center and surround fire, producing a strong response at red–green borders; reversed arrangement suppresses response.
77
What is photopigment bleaching?
Photopigment bleaching is the process where prolonged exposure to a narrow-band light reduces cone sensitivity temporarily by depleting photopigment in those cones.
78
How does a green afterimage arise after staring at a red patch?
Actually, staring at a green patch bleaches M-cones; looking at white then yields a red afterimage because L-cones respond more relative to desensitized M-cones, driving +L−M neurons toward 'red.'
79
What does the opponent representation add beyond trichromacy?
Opponent representation explains perceptual phenomena like afterimages, hue cancellation, and why certain mixtures (reddish green or bluish yellow) are never perceived, grounded in opponent neurons.
80
How does opponent subtraction create efficient coding?
Opponent circuits subtract overlapping cone signals (e.g., +L−M), reducing redundancy from heavily overlapping M and L cones, highlighting variations in spectral input, and aligning with natural scene color statistics.
81
What is color contrast and how is it mechanistically explained?
Color contrast is when a central patch’s perceived hue shifts away from its surround (e.g., red looks redder next to green). Mechanistically, opponent channels accentuate complementary opponencies between adjacent colors.
82
What is color assimilation and how does it differ from contrast?
Color assimilation is when a central patch’s perceived hue shifts toward its surround (e.g., blue appears redder when next to red), blending neighboring hues—contrast exaggerates differences, assimilation smooths them.
83
What is the ratio principle in lightness perception?
Under uniform illumination, perceived lightness is determined by the ratio of light reflected from a surface to that from its surroundings, not by absolute luminance.
84
How does the anchoring rule work in nonuniform scenes?
The region reflecting the most light in each illumination zone is perceived as white (global anchor for uniform scenes; local anchors for separate zones), and other regions’ lightnesses are judged relative to that anchor.
85
What was shown by Gilchrist’s depth-illusion experiment regarding anchoring?
When a target appears in a dimly lit near room, its local brightest patch anchors and appears white; if perceived as in the bright far room, the bright far-room target anchors, making the dim target appear dark gray.
86
What defines monochromacy in inherited color deficiencies?
Monochromacy is total color blindness: rod monochromacy (no functional cones, vision mediated by rods) or cone monochromacy (only one cone type plus rods), leading to no color discrimination.
87
What are the main types of inherited dichromacy?
Dichromacy is missing one cone type: protanopia (no L-cones), deuteranopia (no M-cones), and tritanopia (no S-cones).
88
What are the prevalence rates for protanopia, deuteranopia, and tritanopia?
Protanopia: ~1% of males, 0.02% of females; deuteranopia: ~1% of males, 0.01% of females; tritanopia: ~0.002% of the population.
89
What tool diagnoses dichromacy, and how does it work?
Ishihara plates are multicolored dot patterns encoding numerals visible only to trichromats; failure to see the numerals indicates dichromacy type.
90
What characterizes cortical achromatopsia?
Cortical achromatopsia is acquired color blindness due to damage to color-processing cortical areas (notably V4), resulting in loss of color perception despite intact cone function.
91
What evidence links V4 to color processing?
fMRI studies show greater activation in V4 and neighboring ventral-pathway regions when viewing color versus grayscale images, implicating V4 in cortical color processing.
92
What is pointillist painting and how does it approximate additive mixing?
Pointillist painting uses tiny dots of pure pigment placed closely; from a distance, these dots visually blend, approximating additive color mixing and producing high luminosity.
93
How do digital color video displays achieve additive mixing?
Displays have pixels with red, green, and blue subpixels; each subpixel’s intensity (0–255) combines to produce 256³ = 16,777,216 colors per pixel, blending perceptually at normal viewing distances.
94
How does digital color printing use subtractive CMYK mixing?
Printing uses cyan, magenta, yellow inks (each absorbing one primary region) plus black; overlapping inks absorb different wavelengths, subtractively mixing to reproduce a full gamut, with black ink providing neutral grays.
95
What is selective reflection and how does it make opaque surfaces appear colored?
Selective reflection is when opaque surfaces reflect some wavelengths more than others, causing them to appear chromatic (e.g., a tomato reflects red wavelengths).
96
What is selective transmission and how does it color transparent media?
Selective transmission is when transparent media transmit certain wavelength bands while absorbing others, making them appear colored (e.g., cranberry juice transmits red wavelengths).
97
How do achromatic surfaces reflect or transmit visible light?
Achromatic surfaces (white, gray, black) reflect or transmit uniformly across all visible wavelengths, without selective bias toward any particular band.
98
What do Ishihara plates test and how do they reveal red–green deficits?
Ishihara plates are dot-pattern tests embedding numbers in multicolored dots; normal trichromats see the intended numeral (e.g., “74”), while many red–green dichromats see no number, indicating a deficit.
99
How does the color-matching classification procedure categorize observers?
By determining the minimum number of primaries needed to match any test wavelength, observers are classified as monochromats (one primary → shades of gray), dichromats (two primaries → reduced gamut), or anomalous trichromats (three primaries mixed in shifted proportions with poorer discrimination).
100
What unique insight do unilateral dichromats provide about subjective color experience?
Unilateral dichromats have trichromatic vision in one eye and dichromatic vision in the other, allowing them to describe how a dichromatic eye perceives specific hues when swapping eyes.
101
What is monochromatism (rod-cone only vision) and its prevalence?
Monochromatism is total color blindness due to no functional cones, leaving only rod-mediated vision; it occurs in about ten per million individuals.
102
What are the main characteristics of rod-cone only vision (monochromatism)?
Individuals with monochromatism experience severe photophobia or glare in bright light (rod overload), have very low visual acuity, and typically must use dark filters outdoors.
103
What are Hering’s three opponent-process channels?
Hering’s opponent-process channels are Black (+)/White (–), Red (+)/Green (–), and Blue (–)/Yellow (+).
104
Why is opponency (e.g., L–M difference) considered an efficient coding strategy?
Opponent differences like L–M more sharply distinguish nearby wavelengths than raw L and M ratios, reducing redundancy and improving discrimination of similar colors.
105
Does the cortex have a single dedicated 'color module'?
No, cells selective for wavelength and form/orientation are distributed throughout V1 and ventral areas rather than localized in a single module.
106
What dissociation is observed in cerebral achromatopsia?
In cerebral achromatopsia, individuals (e.g., patient M.S.) can discriminate wavelength changes without conscious color experience, showing a dissociation between detection and subjective perception.
107
How is color represented in the cortex according to distributed representation?
Color processing involves multiple cortical regions contributing to transform wavelength signals into the percept of color, rather than relying on a single localized center.
108
What does 'percepts as neural constructions' imply about color?
It implies that color (and other sensory qualities like pitch or sweetness) are not inherent in stimuli but are created by how those stimuli activate neural circuits in the brain.
109
What is the 'qualia gap' between human and honeybee color perception?
Honeybees possess an extra UV-sensitive pigment peaking near 350 nm, allowing them to see ultraviolet; humans cannot experience UV, so we cannot know the bee’s subjective 'color' qualia in that range.
110
How does generalization across modalities relate to color perception?
Just as color is constructed by neural processing, other perceptual qualities—such as pitch in audition and odor qualities in smell—depend on how stimuli act on the nervous system, not on intrinsic physical features alone.
111
What are the three receptive-field types described by Conway et al. (2010)?
The three receptive-field types are circular single-opponent (e.g., +L –M center-surround), circular double-opponent (L vs. M opponency in both center and surround), and side-by-side double-opponent (responding to form-specific color borders).
112
What do single-cell recordings in fish retina and monkey LGN reveal about opponent neurons?
They reveal neurons that are excited by one wavelength band and inhibited by its opponent, providing direct physiological evidence for opponent processing at early visual stages.
113
Is there a single 'color center' in the cortex according to recent imaging?
No; while early fMRI work (Zeki) highlighted V4, high-resolution imaging shows multiple color-responsive patches scattered in ventral occipito-temporal cortex instead of a single center.
114
What is the 'sandwich' topology of color regions described by Lafer-Sousa et al. (2016)?
The 'sandwich' topology refers to color-responsive patches lying between face-selective (FFA) and place-selective (PPA) areas on the ventral occipito-temporal surface.
115
How do side-by-side double-opponent neurons integrate color with form in V1/V2?
Side-by-side double-opponent neurons respond selectively to purely chromatic edges, showing that color and form information are tightly coupled at early cortical stages to detect colored borders.
116
What does the corner-viewing demonstration illustrate about 3-D orientation and color constancy?
Viewing a folded card corner normally provides depth cues signaling a shadow; viewing through a small hole removes depth cues, making two faces merge perceptually and causing misperception of reflectance, demonstrating how 3-D orientation aids color constancy.
117
How does the penumbra-masking demonstration show the role of shadow cues in constancy?
Covering a shadow’s fuzzy border (penumbra) with an opaque line removes the cue that indicates an illumination edge, causing the shadowed area to appear as a reflectance change (grayer), illustrating the penumbra’s role in distinguishing lighting from material.
118
What cues help disambiguate reflectance edges from illumination edges?
Cues include penumbra (fuzzy shadow borders signaling illumination edges), surface orientation (knowledge of 3-D shape signaling when regions are in shadow), and shadow shape and context (natural contours guiding interpretation).
119
How is a reflectance edge defined compared to an illumination edge?
A reflectance edge is a change in surface material (e.g., brick versus metal), whereas an illumination edge is a change in lighting conditions (e.g., the boundary of a shadow).
120
When do infants develop appreciable trichromatic color vision?
Although cones are present at birth but immature, infants show appreciable, adult-like color vision by about 3–4 months of age.
121
Describe the habituation–dishabituation procedure used to assess infant color categorization.
Infants are habituated to a 510 nm (green) light until looking time decreases; on a test trial, they see either 480 nm (blue, across adult category boundary, eliciting renewed interest/dishabituation) or 540 nm (green, within category, no dishabituation), indicating categorical perception by 4 months.
122
What do habituation–dishabituation results by Bornstein et al. (1976) reveal about infant color categories?
They reveal that 4-month-old infants treat 480 nm versus 510 nm as different categories but 510 nm versus 540 nm as the same category, mirroring adult green/blue boundaries before infants learn color words.
123
Explain the novelty-preference procedure in infant color research.
After familiarizing infants (4–6 months) with two identical colored squares until looking times drop, one square is switched to a novel color; infants look longer at between-category changes (e.g., green to blue) about 70% of the time but show no preference for within-category changes.
124
What do Franklin & Davies’ (2004) novelty-preference findings indicate about infants?
They indicate that infants at 4–6 months demonstrate pre-linguistic categorical perception by preferring novel colors that cross adult-defined category boundaries but not within-category changes.
125
What does pre-linguistic color categorization in infants imply about the origins of color categories?
It implies that color categories emerge from low-level wiring of cone signals and perceptual mechanisms rather than from language or higher-level cognition.
126
What limitations remain in understanding how infants experience color?
Behavioral measures reveal discrimination and categorization but cannot determine subjective qualia; moreover, fine discrimination and higher-order color processing continue to mature into childhood and adolescence.
127
What is the developmental bottom line regarding infant color vision by 4 months?
By about 4 months, infants possess foundational trichromatic mechanisms and categorical boundaries of adult color vision well before they acquire color words, though their subjective experience and full maturation extend beyond infancy.
