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Psychology 333 Exam 2 > Chapter 5 Perceiving Color Pg. 153 > Flashcards

Chapter 5 Perceiving Color Pg. 153 Flashcards

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1
Q

Visible spectrum

A

Portion of the electromagnetic spectrum in the range of about 400-700nm; within this range, people with normal vision perceive differences in wavelength as differences in color

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2
Q

Spectral power distribution (SPD)

A

Intensity (power) of a light at each wavelength in the visible spectrum

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3
Q

Heterochromatic light

A

Light that consists of more than one wavelength
*White light = heterochromatic light that contains wavelengths from across the entire visible spectrum and has no really dominant wavelengths

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4
Q

Monochromatic light

A

Light that consists of only one wavelength-> vertical spike

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5
Q

Spectral reflectance

A

Proportion of light that a surface reflects at each wavelength
*Reflect and absorb light

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6
Q

Hue

A

Quality usually referred to as “color”- that is blue, green, yellow, red and so on, the perceptual characteristic most closely associated with the wavelength of light

  • Wavelength, vary wavelength peak
  • Strongest among CHROM processes (RGBY)
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7
Q

Saturation

A

Vividness (or purity or richness) of a hue

  • Purity, vary spectral purity
  • Strength of CHROM vs. ACHROM
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8
Q

Brightness

A

Intensity

  • Amount of light
  • Vary total energy intensity
  • Strength of ACHROM white vs. black
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9
Q

Color circle

A

2-D depiction in which hue varies around the circumference and saturation varies along any radius

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10
Q

Nonspectral color

A

only be created by mixing together two or more wavelengths

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11
Q

Color solid

A

3-D depiction in which hue varies around the circumference, saturation varies, along any radius and brightness varies vertically

  • Brightnesses increasing as you move up
  • Radius=saturation
  • Decrease (shrinking) radius -> smaller range -> either increase or decrease brightness from mid level so colors get very dim or very bright , they become less vivid
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12
Q

Subtractive color mixture

A

Mixture of different-colored substances, called “subtractive” because the light reflected from the mixture has certain wavelength subtracted (absorbed) by each substance in mixture
*Color printing, inkjet printers

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13
Q

Additive color mixture

A

Mixture of different-colored lights, called “additive” because the perceive color of the mixture is the result of adding together all the wavelengths in all the lights in the mixture

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14
Q

Complementary colors

A

Pairs of colors that combine in equal proportion to yield a shade of gray

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15
Q

Primary colors

A

Any three colors that can be combined in different proportions to produce a range of other colors (magenta, cyan, yellow/red, green, blue)
*TVs and computer monitors

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16
Q

Trichromatic color representation

A

Light evokes different responses from three different types of cone photoreceptors in retina

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17
Q

Opponent color representation

A

Responses from the cones are combined and processed by a subset of retinal ganglion cells and by color-selective neurons in the brain

  • 4 basic colors can be divided into 2 pairs of complementary colors: red, green, blue, yellow
  • Red-green, Blue-yellow
  • Color afterimages
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18
Q

Metameric color-matching experiments

A

Whether the right mixture of 3 monochromatic primary colors is perceived as identical in color to some other monochromatic light

  • Observers adjusted amounts of three wavelengths in a comparison field to match a test field of one wavelength
  • 420nm, 560nm, 640nm
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19
Q

Metamers

A

Any 2 stimuli that are physically different but are perceived as identical
*Adjust intensities so that the additive color mixture in comparison patch= color as test patch-> metameric color match

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20
Q

Spectral sensitivity function

A

Probability that a cone’s photopigment will absorb a photon of light of any given wavelength
*Overlap considerably

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21
Q

Principle of univariance

A

With regard to cones, the principle that absorption of a photon of light of any given wavelength

  • The strength of response generated by a cone when it traduces light depends only on the amount of light transduced, no on the wavelength of the light
  • A M-cone’s response o dim 543nm light and to a bright 450nm light could be identical, with right choice of intensities
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22
Q

If you had only one type of cone (or only rods)

A

A person with normal vision will perceive two lights of these wavelengths as the same if their intensities are equal
*Under equal illumination, green might look brighter than red/blue because the relative sensitivity of rods is higher in green than red/blue-but they will not look different in color

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23
Q

If you had only two types of cones

A

A person with 2 types or cones cannot adjust the intensity of a single arbitrary comparison light to match the color of a test light with different wavelength

  • People with 2 types of cones match a monochromatic test light of any wavelength if they have a mixture of 2 monochromatic comparison lights to work with instead of just 1
  • Only 2 primary colors needed to match any other color
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24
Q

Physiological evidence for Trichromacy

A

Retinal densitometry: produces high-resolution images of retina -> mosaic of 3 types of cones
Photocurrent measurements: directly measure an individual cone’s response to light

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25
Q

Hue cancellation

A

Experimental technique in which the person cancels out any perception of a particular color in test light by adding light of complementary color

  • Adding blue to cancel out yellowness
  • Adding red to cancel out greeness
  • “Unique blue” at zero between red and green and no yellow
  • “Perceive green” between “unique blue” and “unique yellow”
  • No trully unique red
  • Amount of a physical light needed to cancel a complementary hue percept is a measure of the strength of that original complementary hue percept
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26
Q

Physiological evidence for opponency

A
  • Introspection/ hue cancellation
  • Measurements of neurons in lateral geniculate nucleus that also responded to color in opponent fashion
  • Neural circuits supporting red-green, blue-yellow
  • 3 types of cones’ nerve impulse-> bipolar, horizontal + amacrine -> excitatory+ inhibitory inputs to retinal ganglion cells -> 4 different types of “opponent color circuits”
  • S= Short wavelength/ bluish-greenish; M=Medium wavelength/greenish-yellowish; L=Long wavelength/yellowish-reddish
  • +S-ML circuit: RGC fires above baseline in response to short-wavelength light and below baseline rate in response to medium and long wavelength; respond oppositely to blue and yellow
  • +ML-S circuit: Respond oppositely to blue and yellow
  • +L-M Circuit: Respond oppositely to red and green
  • +M-L Circuit: Respond oppositely to red and green
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27
Q

Color-opponent neurons

A
  • Color-selective neurons: RGCs, LGN cells, cortical cells have RFs that produce more elaborate patterns of response
  • V1: single opponent center-surround RF
  • Carry info about wavelength of light within uniformly colored regions of visual scene but don’t provide much info about color edges, locations, where adjacent regions are illuminated by different wavelengths
  • Double opponent center-surround RF: COLOR EDGES
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28
Q

Photopigment bleaching

A

Photopigment molecule’s loss of ability to absorb light for a period after undergoing photisomerization

29
Q

Chromatic adaptation

A

a kind of photopigment bleaching results from exposure to relatively intense light consisting of a narrow range of wavelengths-> color afterimages
*Not sensitive to M-cone, and look at white surface, L-cone is stronger than M-cone, +L-M -> red (opposed from green)

30
Q

Color constancy

A

Tendency to see a surface as having the same color under illumination by lights with very different spectral power distributions
*Our perception of color of surfaces corresponds to estimated reflectance of each surface, not to SPD of reflected light
*Fail if the illuminating light consists of only a narrow range of wavelengths
*Fail if just one surface is seen against a black and empty background; no way for system to know whether distribution of wavelengths is due to reflectance of a colored surface illuminated by a perfectly white light or perfectly white surface illuminated by colored light
Theory: Visual system automatically determines number of each wavelength reflected from all surfaces on average -> estimate of SPD f illuminant -> discounting illuminant

31
Q

Lightness constancy

A

See a surface as having same lightness under illumination by very different amounts of light
*Ratio principle: perceived lightness of a region is based on relative amount reflected from region and is surround

32
Q

Monochromy

A

See everything in shades of gray

33
Q

Rod monochromy

A

Must rely on rod vision all the time

*No color; hypersensitive to light, low acuity

34
Q

Cone monochromy

A

Less frequent than rod monochromy; have both rods and cones, but only one type of cone, which can be either S-, M- or L-cones

  • Lack color vision
  • Different wavelengths- different shades of gray
35
Q

Dichromacy

A

More common-but rare overalls; just one of three types of cone is missing

  • can discriminate between colors that a rod monochromat would see as equivalent
  • confuse some colors that a trichromat could tell apart
  • Person who needs only two wavelengths to match any color, confuses many hues seen by normal trichromats (has only 2 cone pigments)
36
Q

Protanopia

A

lacks L-cones

37
Q

Deuteranopia

A

Lacks M-cones

38
Q

Tritanopia

A

Lacks S-cones

39
Q

Ishihara color vision test

A

a test using configurations of multicolored disks with embedded symbols; the symbols can be seen by people with normal color vision but not by people with particular color vision deficiencies

40
Q

Achromatopsia

A

Loss of vision caused by brain damage

41
Q

Pointillist Painting

A

Additive color mixtures

42
Q

Digital color video displays

A

Use additive mixtures of 3 primary colors at each location on the screen to produce nearly the full gamut of colors you can see
*Taking advantage of ability of human eye-> distinguish dots that are sufficiently small and close together

43
Q

Pixels

A

picture elements, 3 subelements -> emit the light of one of three primary colors- red, green, blue

44
Q

Digital color printing

A
  • Applying tiny droplets of different color inks to a material
  • Cyan, magenta, yellow, black
  • Location and thickness -> light absorbs
  • Increase thickness, increase photo absorb
  • Subtractive effects when color on top of others
45
Q

Color vision

A

Ability to see differences between lights of different wavelengths

46
Q

What does a single photoreceptor type encode?

A

One receptor type cannot lead to color vision because:

  • Absorption of a photon causes the same effect in the cone, no matter what the wavelength is, because every absorbed photon causes the same isomerization of the photopigment molecule
  • This is termed the principle of univariance
  • There is no “memory” for the wavelength of an absorbed photon
  • Any two wavelengths can cause the same overall response by adjusting their relative intensities
  • Thus, there is no way to discriminate changes of wavelength from changes of intensity and, therefore, no color vision (rod vision)
47
Q

One non-spectrally opponent retinal output

A

Parasol ganglion cells

  • Sums L&M in both center & surround, both - and + center types
  • Could this be the black/white perceptual opponent process
48
Q

Two spectrally-opponent retinal outputs

A

Midget ganglion cells:
*Opposing M and L cones (M-L, L-M)
*Could this be the red/green perceptual opponent process?
Small bistratified ganglion cells:
*S cones opposed by L+ M
*Could this be the blue/yellow perceptual opponent process?

49
Q

What does cortex need to do to produce our actual opponent-hue perceptions?

A
  1. Add S-cone input to red-green opponent hue response, to produce short-wavelength red.
  2. Shift cone weights in opponent processes so that bbalance points fall at observed unique-hue wavelength
  3. Create a way of representing the thousands of binary hues we see.
50
Q

V1 response to color

A
  • Response in all hue directions of color circle
  • Reflects combination of signals from paravocellular and koniocellular pathways
  • Not biased perceptual unique-hue directions
  • Could be part of basis for representation of full range of binary hues
  • Show achromatic (black-white) response
51
Q

How is mutual exclusivity of opponent processing maintained in cortex?

A
  • Easy to see how LGN opponent cells can signal different hues by an increase or decrease from their baseline firing rate
  • Cortical cells have near-zero baseline firing rate
  • Cortical circuits create cells that only increase their firing rate to a narrow range of wavelengths
  • One way this could be accomplished is if cortical circuits create cells that only respond to increases (not decreases) of firing of LGN-like cells.
52
Q

Color processing in the Cortex

A
  • There is no single module for color perception
  • Cortical cells in V1, V2, V4 and beyond show differential response to wavelengths
  • These cells usually also respond to forms and orientations
  • Cortical cells that respond to color may also respond to brightness variations
  • Some evidence of focal centers for color processing-blobs in V1, thin stripes in V2, globs past V4-but still controversial
53
Q

What does Xiao study reveal about color in V2?

A
  • There may be clusters (“modules”) of color sensitive cells in or near thin stripes that display narrow color tuning and are arranged in a spatial pattern reflecting differences in hue.
  • Responses of cortical color cells are one-directional, not opponent.
  • The color patches indicate a dominant collective response of many cells but patches may overlap and show response to many different hues.
  • Neither optical imaging nor the the averaged electrophysiological recordings presented here tell what individual cells are doing (similar to comparison of fMRI and single-cell physiology).
  • No evidence of special status of unique hues.
54
Q

Conway study shows:

A
  • fMRI shows there are clumps (“globs”) of color-processing cells in V4 and PIT (posterior infratemporal cortex)
  • Single-unit electrophysiology shows that many cells in these areas have narrow hue tuning
  • Preferred axes are most commonly in general direction of unique-hue axes, not LGN axes
  • Globs may be first level we’ve seen in cortical processing that shows special status of unique hues
55
Q

Normal trichromat

A

*Person who needs three wavelengths to match any color (has 3 normal cone pigments)

56
Q

Anomalous trichromat

A
  • Needs three wavelengths in different proportions than normal trichromat and has reduced color discrimination ability (has 2 normal and one shifted cone pigment)
  • Need 3 wavelengths to match a 4th (thus, trichromatic), but in different proportions than normal trichromat
  • Has reduced color discrimination ability, can range from mild to severe deficiency
  • Modern color-vision genetics has revealed they have 2 normal and 1 shifted cone pigment
  • In deuteranomaly (most common of all inherited color deficiencies), M-cone pigment is shifted toward L-cone pigment In protanomaly, L-cone pigment is shifted toward M-cone pigment.
  • Result for both is that an L-M chromatic mechanism varies much less with wavelength change than for normals
57
Q

Monochromat

A

*Person who needs only one wavelength to match any color, no color vision (has only 1 or 0 cone pigments). Cone monochromats typically have only S cones. Rod monochromats have only rods.

58
Q

Sex-linked, “red-green” dichromacies

A

*Most common types; mostly males affected
*No red-green color discrimination (confuses color in normals’ green/yellow/red range and in normals’ aqua/blue/violet range)
*Deuteranope, missing cone M, remaining cones L and S
Protanope, missing cone L, remaining cones M and S

59
Q

Autosomal, “blue-yellow” dichromacy

A
  • Rare; males and females eqally affected
  • No-blue-yellow color discrimination (confuses colors in normals’ blue/aqua/green range and in normals’ orange/yellow/red)
  • Tritanope, miss cone S, remaining cones L and M
60
Q

Rod monochromats

A
  • Only rods and no functioning cones
  • True color blindness: Ability to perceive only in white, gray and black tones
  • Poor visual acuity
  • Eyes very sensitive to bright light
61
Q

S-cone monochromats

A
  • Have S-cones and rods only
  • True monochromat at bright and dim light levels when only S-cones or only rods function
  • At intermediate light levels, rods and S-cones can work together to permit wavelength discrimination
62
Q

Basic human genetics

A
  • 23 pairs of chromosomes (2 autosomal pairs, 1 sex pair)
  • Women have XX, men have XY (sex chromosomes)
  • L and M genes on X chromosome (sex linked)
  • S gene on autosome (not sex linked)
63
Q

Action of genes on photopigment molecules

A
  • Genes determine which amino acids end up in the protein part of the photopigment molecule (opsin)
  • Different amino acids have different effects on the pigment’s peak sensitivity, shifting it to longer or shorter wavelengths
  • 18 amino-acid dimorphisms in LM pigment molecule (one of two specific amino acids at each location) identified by number in the sequence of the opsin protein
64
Q

Spectral proximity principle

A

*Separation of anomalous and normal pigment determines severity of color vision impairment

65
Q

How can the brain set a consistent red-green balance across individuals with 30:1 differences in L:M ratios?

A
  • We think that, over time, the brain “averages” every day’s light exposure and adjusts its sensitivity so that there is a net balance of red and green. A similar sort of “normalization” is possible for blue-yellow but has not been demonstrated.
  • Evidence for normalization comes from long-term adaptation studies with subjects exposed to red or green light for several hours a day
66
Q

The job of the cortex: color and lightness constancy

A
  • Cortex needs to transform information about the wavelength distribution of light coming from an object (as represented by the pattern of cone excitations) into perceptions of color/lightness of that object.
  • The aim is to take the best inference about the state of the world. In this case, real objects don’t change under different illumination, so cortex assumes color/lightness stay constant.
  • The cortex will use anything it can get its hands on to make its inferences about the state of the world.
67
Q

Why Color Constancy?

A
  • In the real world, our views of objects and people always changing (amount and spectrum of illumination) yet the objects/people themselves don’t change
  • Visual system has evolved to provide representations of objects, not of actual pattern of light falling on the retina.
68
Q

What are the factors (cues) that influence the interpretation of color or lightness made by the visual system?

A
  • Shadows and perceived illumination gradients
  • Depth and size
  • Perceptual grouping (Gestalt principles)
  • Transparency/fog/filtering/atmosphere
  • Edges and junctions (local configurations)
69
Q

Brown and yellow

A
  • Both can be a red-green null or balance
  • Both are opponent to blue: blue cancels both yellow and brown
  • The properties of yellow don’t explain the properties of brown.
  • Different red-green balance- need more red for balanced brown, more green fro balanced yellow

Psychology 333 Exam 2 (3 decks)

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