colour perception Flashcards

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1
Q

why is colour important?

A
  • We could operate without colour, but most people wouldn’t want to live without colour.
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2
Q

what do we use colour for?

A
  • Decoration - as we like looking at colour/certain pattern of colours
    • Distinguishing food between good and bad
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3
Q

where does colour come from?

A
  • Electromagnetic spectrum spans from cosmic and gamma rays to radio waves and theres this little slice in the middle which we call visible light and it so happens that there’s a little slight of electromagnetic spectrum which are eyes are sensitive to.
    • If you take white light, you can split it with a prism and you will get lights of lots of different wavelengths.
    • The brain is doing a lot of work, so interprets those signals from the outside world and turn it into a full colour experience.
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4
Q

cone photoreceptors

A
  • Human trichromacy - three cone types, maximally sensitive at short (s), middle (m), and long (l) wavelengths
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5
Q

evolution of cone types

A
  • Trichromacy evolution related to foraging for ripe fruit/berries
    • E.g., Regan, Julliot, Simman, Vienot, Charles-Dominique and Mollon, 2001
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6
Q

bare skin - socio-sexual signals from blood oxygenation

A
  • monochromatic primates (one cone type)
  • dichromatic primates (two cone types: ‘short’ and ‘medium’)
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7
Q

genetic colour vision deficiency

A
  • Monochromats:
    • Only one cone (or no cones, only rods)
      · Dichromats:
    • Protanopia - lack L cone i.e., long wavelength
    • Deuteranopia - lack M cone i.e., medium wavelength
    • Tritanopa - lack s cone i.e., short wavelength
      · Anomolous trichromats:
    • Deuteranomoly (M cone shifted towards L)
    • Protanomoly (L cone shifted to M)
      · Overall 8% men, <1% women gentic deficiency
  • Also acquired colour vision deficiency (ageing, drugs, hormones)
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8
Q

a cure for colour vision deficiency?

A

· Gene therapy turns dichromat into trichromat!
· Dichromatic male squirrel monkeys
· Red opsin gene, virus & DNA injected into some cones
· Can see colours previously not seen!
· Brain able to use new signal even though circuitry not in use early on in life
· (Mancuso et al., 2009 – the Neitz’s lab)

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9
Q

human tetrachromacy

A

· Some women have four cone types!
· Usual 3 cone types & shifted red or green cone type
· Does an extra cone mean they can see more colours?
· Psychophysical tests & genetic analysis
· Only one woman behaviourally tetrachromatic
· Still need cortical processing of extra signal
· (Jordan, Deeb, Bosten & Mollon, 2010)

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10
Q

cone opponency

A

· Output from three cones combined & contrasted to give three cone-opponent channels:
- L/(L+M): “red-green”
- S/(L+M): “blue-yellow”
- L+M: “black-white”
· They are more accurately expressed as:
- L/(L+M): “cherry-teal”
- S/(L+M): “violet-lime”
- L+M: achromatic (or luminance axis

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11
Q

colour-opponent cells in the LGN

A

· Parvocellular = L/(L+M) (cherry-teal)
· Koniocellular = S/(L+M) (violet-lime)
- Magnocellular = luminance (black-white

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12
Q

lilac chaser illusion

A

· Adaptation - prolonged exposure to a sensory stimulus reduces sensitivity.
· Opponent coding - After a short period of staring at the central cross the gap from the missing magenta spot is replaced by its opponent colour – green.

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13
Q

colour at the cortex

A

· Patches of cells (“blobs”) responsive to colour at primary visual cortex (V1)
· Other areas of visual cortex process colour (e.g., V2,V4/V8)
· Sent to temporal cortex (ventral processing stream –“what” pathway)

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14
Q

central achromatopsia

A

· Damage to small cortical region, loss of colour perception
· Humans with lesions in extrastriate visual cortex (e.g., V4/V8)
· Functioning cones, can record activation at V1 in response to colour
· BUT, things don’t appear coloured
· Can affect one visual field
· Illustrates importance of cortical processing
· e.g., see Cowey & Heywood, 1997

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15
Q

memory colour

A

· Some objects have a typical colour (e.g. banana) that we learn from experience and therefore expect.
· Bananas are typically yellow, so to make a banana look grey it is necessary to add a little extra blue, to counteract the memory colour.
· The error is not present for a simple circle of colour
· Hansen, Olkkonen, Walter & Gegenfurtner (2006) Nature Neuroscience

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16
Q

aesthetic response to colour

A

· Why do we prefer some colours more than other?:
- Biological components theory (Hulbert and Ling, 2007)
- Ecological valence theory (Palmer and Schloss, 2010)

17
Q

ecological valence theory

A

· Colour preference due to colour-object associations
· WAVE (how good/bad objects associated with that colour are)
· Palmer and Schloss, 2010

18
Q

aesthetic preference for colour patterns

A

· Colour in natural scenes tends to be dominated by blue-yellow variation
· This is also the type of colour pattern which people like the most.