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PSYCH 367 > Lecture 14 Colour > Flashcards

Lecture 14 Colour Flashcards

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1
Q

_______ was originally proposed as a sort of ‘colour centre’

A

V4

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2
Q

What is achromatopsia?

A
  • colour blindness
  • can co-occur with prosopagnosia, suggesting overlap between neural mechanisms for processing colour and other visual properties
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3
Q

Explain why so many people with achromatopsia also have prosopagnosia.

A

FFA and PPA are adjacent, so damage to that general region can overlap with both regions

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4
Q

What are monochromats?

A
  • have a very rare hereditary condition which could produce ‘true’ colour blindness
  • no functioning cones (only rods); perceived world in tones of white, grey, and black
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5
Q

Monochromats can match any wavelength in the spectrum by simply adjusting the _________________.

A

brightness

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6
Q

Describe the visual acuity and sensitivity to light in monochromats.

A
  • poor visual acuity (no cones)
  • very sensitive to bright light (all rods)
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7
Q

What are dichromats? What are the types?

A
  • missing one of the 3 types of cones
  • protanopia, deuteranopia, tritanopia
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8
Q

What are unilateral dichromats? What is unique about them?

A
  • trichromatic vision in one eye, and dichromatic in the other
  • unique opportunity to understand how dichromats ‘see’ colour b/c the same brain can interpret/describe perception of colour from both perspectives
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9
Q

What is protanopia? What percentage of males and females does it affect? what do they see short wavelengths as? What do they see above the neutral point?

A
  • affects 1% of males and 0.02% of females
  • missing the long-wavelength pigment
  • RED-GREEN COLOUR BLINDNESS (red looks more green and less bright)
  • short-wavelengths = blue
  • see yellow above the neutral point
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10
Q

What is the neutral point for protanopia?

A

492 nm

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11
Q

What is deuteranopia? What percentage of males and females does it affect? What does it see short-wavelengths as? What do they see about the neutral point?

A
  • affects 1% of males and 0.01% of females
  • missing the medium-wavelength pigment
  • RED-GREEN COLOUR BLINDNESS (green looks more red)
  • short-wavelengths = blue
  • see yellow above neutral point
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12
Q

What is the neutral point in deuteranopia?

A

498 nm

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13
Q

What is tritanopia? What percentage of males and females does it affect? What does it see short-wavelengths as? What do they see above the neutral point?

A
  • affects 0.002% of males and 0.001% of females
  • missing the short-wavelength pigment
  • BLUE-YELLOW COLOUR BLINDNESS (difficulty separating blue and green, red and yellow)
  • short-wavelengths = blue
  • see red above neutral point
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14
Q

What is the neutral point for tritanopia?

A

570 nm

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15
Q

How do colour-boosting glasses work?

A

filter out certain wavelengths that might produce an overlapping response across cone types, allowing for more contrast in the range of colours perceived

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16
Q

What are Hering’s primary colours? Describe where they are on the colour wheel.

A
  • top half = colours with redness
  • bottom half = colours with greeness
  • right half = colours with yellowness
  • left half = colours with blueness
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17
Q

What was Hering’s main finding based on the colour wheel? What does it imply?

A
  • ‘yellowish-reds’ and ‘bluish-greens’ possible, though cannot see ‘bluish-yellow’ or ‘reddish-green’
  • colour vision is built upon 4 primary chromatic colours, which are arranged in opposing pairs
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18
Q

What is the opponent process theory? Provide an example to illustrate the hypothesis.

A
  • colour vision arises from 3 primary mechanisms involving opponent-processes
  • white/black; red/green; yellow/blue
  • e.g. by increasing excitation in response to red, there is increasing inhibition in response to green
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19
Q

What is the hue cancellation method and what does it prove?

A
  • start with one colour (e.g. blue) and have participants ‘add’ light from the opposing pair (e.g. yellow) to see how taht changes the perception of colour
  • it proves that the opponent-process exists bc if true, we should be able to cancel out the perception of colour in one half of an opposing pair by adding wavelength from the part of the spectrum that correspond to its opposite
20
Q

TRUE or FALSE: at the midpoint between 2 opposing colours on the spectrum, both colours are perceived

A

FALSE: neither is perceived

21
Q

What are opponent neurons? Where are they located?

A
  • respond in an excitatory manner to one end of the spectrum and an inhibitory manner to the other
  • located in the retina and LGN
22
Q

What colour response is triggered by direct input from L cones?

A

red

23
Q

What colour response is triggered by direct input from M cones?

A

green

24
Q

What colour response is triggered by direct input from S cones?

A

blue

25
Q

Yellow is triggered by a combination of input from ________ and ________ cones.

A

M and L

26
Q

What is the difference between the trichromatic theory and the opponent-process theory?

A
  • trichromatic theory explains the responses of the CONES in the RETINA
  • opponent-process theory explains NEURAL RESPONSES for cells connected to the cones FURTHER IN THE BRAIN
    (i.e. trichromatic occurs before opponent-process in the visual system)
27
Q

What is colour constancy? Explain in detail.

A
  • perception of colours as relatively constant in spite of changing light sources
  • sunlight has ~equal amounts of energy at all visible wavelengths
  • tungsten lighting has more energy in the long wavelengths
  • ^objects reflect different wavelengths from these 2 sources
28
Q

review slide 21

A

slide 21

29
Q

what is chromatic adaptation? Explain the mechanism.

A
  • occurs with prolonged exposure to chromatic colours
  • when the stimulus colour selectively bleaches a specific cone pigment over an extended period of time, this results in a decrease in sensitivity to the associated colour
  • (this can occur in response to light sources, which contributes to colour constancy under different illuminations)
30
Q

Describe the Uchikawa et al (1989) experiment on colour constancy.

A
  • baseline: paper and observer in white light –> green paper seen as green
  • observer not (chromatically) adapted: paper illuminated by red light and observer by white –> green paper shifter to red
  • observer adapted: paper and observer both exposed to red light –> green paper only SLIGHTLY shifted toward red
31
Q

TRUE or FALSE: Colour constancy works best the surroundings are masked.

A

FALSE: colour constancy works best when an object is surrounded by many colours

(showing participants scenes with masked surroundings reduces ‘accuracy’ of colour perception reports)

32
Q

Review slide 28

A

slide 28

33
Q

What is lightness constancy?

A

achromatic colours are perceived as remaining relatively constant across different lighting conditions

34
Q

What is lightness?

A

the perception of the shade of achromatic colour

35
Q

Why does lightness constancy happen?

A

perception of lightness is not related to the TOTAL AMOUNT of light reflected by an object, but rather the PERCENTAGE

36
Q

What does the intensity of light reaching the eye from an object depend on?

A
  1. the intensity of illumination (total amount of light hitting the object)
  2. the object’s reflectance
37
Q

What is reflectance?

A

the proportion of light reflected back by the object

38
Q

TRUE or FALSE: lightness constancy is determined by intensity, not reflectance

A

FALSE: lightness constancy is determined by REFLECTANCE, not intensity

39
Q

What is the ratio principle?

A

2 areas reflecting different amounts of light look the same if the ratios of their intensities are the same (at least when evenly illuminated)

40
Q

When perceiving lightness under uneven illumination, the perceptual system must distinguish between___________ and _______________.

A

reflectance edges and illumination edges

41
Q

What are reflectance edges?

A

edges where the amount of light reflected changes between 2 surfaces (i.e. changes in material)

42
Q

What are illumination edges?

A

edges where lighting of 2 surfaces changes (i.e. changes in lighting)

43
Q

What are 2 dimensions that perception of light stimulus can depend on?

A
  1. chromatic colours
  2. brightness
44
Q

review slide 37

A
45
Q
A

PSYCH 367 (22 decks)

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