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Sensation and Perception > Chapter 5: Color Perception > Flashcards

Chapter 5: Color Perception Flashcards

1
Q

Perceiving Color

A

Color is perceptual experience evoked by wavelengths of light reaching the eyes

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2
Q

Color Vision

A

Ability to see difference between light and different wavelengths

  • investigation of trichromacy and opponency, two psychological mechanisms that create our experience of color
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3
Q

Visible Spectrum

A

portion of electromagnetic spectrum in the range of 400-700 nm

  • people with normal vision perceive differences in wavelength as differences in color
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4
Q

Spectral Power Distribution (SPD)

A

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

  • perceived color depends on SPD of light and how things reflect light
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5
Q

Heterochromatic Light

A

Light that consists of more than 1 wavelength

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6
Q

Monochromatic Light

A

Consists of only one wavelength

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7
Q

Achromatic Light (white light)

A

Light containing wavelengths from across visible spectrum with no really dominant wavelengths

  • perceived as colorless
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8
Q

Spectral Reflectance

A

Proportion of light that a surface reflects at each wavelength

  • refers to the amount of light that is reflected back to our eyes from the object’s surface
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9
Q

Perceptual counterparts of color consist of three independent dimensions

A
  1. Hue- quality usually referred to as color; perceptual characteristic most closely associated with wavelength of light
  2. Saturation- vividness (or purity or richness) of hue
  3. Brightness- perceived amount of light
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10
Q

Color Circle

A

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

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11
Q

Nonspectral Purples

A

Where red and blue ends of spectrum meet

  • mixtures of shorted-wavelength violet and longest- wavelength red
  • don’t exist on visual spectrum as single wavelength
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12
Q

Red Wavelength

A

650 nm

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13
Q

Yellow Wavelength

A

600 nm

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14
Q

Green Wavelength

A

550 nm

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15
Q

Cyan Wavelength

A

500 nm

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16
Q

Blue Wavelength

A

450 nm

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17
Q

Color Solid

A

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

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18
Q

Subtractive Color Mixture

A

Primaries for subtractive color mixing= red, yellow, and blue

Light reflected by mixture has certain wavelengths subtracted (absorbed) by each substance in mixture

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19
Q

Additive Color Mixture

A

Primaries for additive mixing= red, green, and blue

Compositions of mixture is result of adding together all wavelengths in all lights in mixture

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20
Q

Complementary Colors

A

Hues that are opposite each other on color wheel

  • are pairs of colors that, when combined in equal proportion, are perceived as a shade of gray
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21
Q

Primary Color

A

Are any three color that can be combined in different proportions to produce a range of other colors

  • cyan, magenta, yellow
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22
Q

Trichromatic Color Representation

A

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

  • Young- Helmholtz trichromatic theory
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23
Q

Opponent Color Representation

A

Responses from cones are combined and processed in subset of RGCs and by color-selective neurons in brain

  • Hering opponent- process theory
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24
Q

Trichromatic color representation experiments

A

Use of metameric matching provided early evidence that there were three types of color receptors

  • Metamers- composed of different wavelengths of light but looking identical
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25
Q

Spectral Sensitivity of Photopigments

A
  • evidence for trichromatic theory
  • the spectral sensitivity function
  • photopigments in each type of cone are most responsive to a particular range of wavelength
    - spectral sensitivity functions may overlap considerably

*The principle of univariance means that means that color vision depends on crucially on the relative responses of multiple cone types

26
Q

Spectral Sensitivity Function

A

Probability that cone’s photopigment will absorb photon of any given wavelength

27
Q

Principle of Univariance

A

The charge in a cone cell’s firing rate does not depend on the wavelength of light

  • The absorption of photon of light causes fixed response by cone regardless of photon’s wavelength
  • also applies to rods and explains why night-vision is colorblind
28
Q

Physiological evidence for trichromacy emerged from the work of […]

A

George Wald

29
Q

Photocurrent measurements can be used as evidence for trichromacy

A
  • directly measures an individual cone’s response to light
  • produced three distinct patterns of sensitivity to light (spectral sensitivity curves of three different types of cones)
  • trichromatic representation of wavelength can be thought of as form of data compression
30
Q

Retinal Densitometry

A

High-resolution images of the retina

31
Q

Opponent color representation

A
  • at the level of the retina, most humans have three (some have four) types of cones
  • color-sorting tasks, after images, and hue cancellation tasks all support the idea that there are four primaries
  • there is evidence from the level of RGCs and beyond (LGN, visual cortex) that the visual system is organized in pairs of opposites
32
Q

Color Blindness

A

Dichromacy

  • two cones work properly, one doesn’t
  • could be S, M, or L cones
33
Q

Hue Cancellation

A

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

  • first physiological evidence for opponency: measurements of neurons in LGN of monkeys
34
Q

Color Afterimages

A

Result from photopigment bleaching known as chromatic adaptation

Ex. If you start at green square, photopigment molecules in M-cones will bleach more than those in L-cones
- M-cones will become less sensitive than L-cones

35
Q

Photopigment Bleaching

A

Lack of ability to absorption after phototransduction

36
Q

Chromatic Adaptation

A

There’s a lot of one color that a visual system needs to adapt to

  • kind of photopigment bleaching that results from exposure to relatively intense light consisting of narrow range of wavelengths
  • discounting the Illuminant- estimate illuminance and reflectance
  • adjusts cones to account for imbalance of wavelengths
37
Q

Hering (color afterimages)

A
  1. Human visual system operates as if there were four basic colors
  2. 4 colors can be divided into 2 pairs of colors: red-green and blue-yellow
38
Q

Physiological evidence for opponency

A
  • Until 1950s: support was psychophysical; based on hue cancellation experiments
  • Later research: existence of neural circuits underlying opponent color representations was confirmed
    - circuits supporting color vision with four basic colors groups in two pairs of opposites
  • explains color categorization, color afterimages, and results of hue-cancellation
39
Q

S cones

A

Bluish- greenish

40
Q

M cones

A

Greenish- yellowish

41
Q

L cones

A

Yellowish- reddish

42
Q

+S-ML

A

Responds to short wavelength light and below baseline rate in response to medium and long- wavelength light

43
Q

+ML-S

A

M and L cones respond above baseline and S cones respond below baseline

44
Q

+L-M

A

L cones respond above baseline and M cones respond below baseline

45
Q

+M-L

A

M cones respond above baseline and L cones respond below baseline

46
Q

Color-opponent neurons in the visual pathway

A
  • color-opponent RGCs
  • other color-selective neurons in the visual pathway- including RGCs, LGN cells, and cortical cells
  • double-opponent neurons: contributes of high acuity of color processing
47
Q

Color Contrast

A

Perception of surrounded color as shifted toward complement of surrounding color

48
Q

Color Assimilation

A

Perception of surrounded color as shifted toward non complementary surrounded color

aka “spreading effect”

49
Q

Single-Opponent Neuron

A

Provide info about wavelength of light within uniformly colored regions, but don’t have much info about visual edges

50
Q

Double-Opponent Neuron

A

Provide info about color edges

Suppressed response doesn’t go all the way down

51
Q

Color Constancy

A
  • tendency to see surface as having same color under illumination by lights with different SPD
  • color is perceived as constant under different types of light as long as enough wavelengths are available
  • visual system tends to achieve color constancy through chromatic adaptation
  • SPD of reflected lights is determined by multiplying intensity of illuminating light at each wavelength by reflectance of paper at each wavelength
  • wanting to see color how we know it
52
Q

Lightness Constancy

A
  • tendency to see surface as having same lightness under illumination by very different amounts of lights
  • suggests relative lightness (or darkness) of an object is perceived as consistent under different intensities of light
53
Q

Lightness

A

Perceived reflectance of a surface (proportion of illumination that surface appears to be reflecting)

54
Q

Ratio Principle

A

Perceived lightness of region is not based on absolute amount of light reflected from region, but on relative amounts reflected from region and its surround

55
Q

Color Blindness

A

Inherited deficiencies of color vision

  • genetic
  • sex-linked
  • other causes of color deficiency include diabetes, glaucoma, certain medications, and chemical exposure
56
Q

Rod Monochromacy

A

Only rods
Extremely sensitive to light
Low visual acuity

57
Q

Cone Monochromacy

A

Only one type of cone

Can process light with some acuity

58
Q

Dichromacy

A

Has two functional cones

- limited form of color vision

59
Q

Types of dichromacy

A
  • Protanopia: person lacks L-cones
  • Deuteranopia- person lacks M-cones
  • Tritanopia: person lacks S-cones
60
Q

Ishihara Color Vision Test

A

Symbols can be seen by people with normal color vision but not by people with particular color vision deficiencies

61
Q

Color Center in Brain

A

Area V4

- ventral pathway

62
Q

Cortical Achromatopsia

A

Color blindness from brain damage

  • rarer than color deficiencies and occurs when there’s damage to visual cortex

Sensation and Perception (14 decks)

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