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2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002

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  • 1. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2002 1 Psychophysics of colour perception Neurophysiology, psychophysics, and magic (or you only though you knew what colour was…)
  • 2. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 202 Why have colour vision? • Why don’t other mammals have colour vision? • Why do bees have colour vision? • Is hue or luminance more useful? • Is hue or luminance more accurate?
  • 3. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 203 The neurophysiology of colour vision • Rods and cones – Rods are inhibited during day light – Cones are “blind” during night light • Three different types of cones, each optimally responsive to a different wavelength 1. L-Cone: long wavelength, red 2. M-Cone: medium wavelength, green 3. S-Cone: short wavelength, blue • Each type responds to a range of wavelengths
  • 4. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 204 Cone wavelength ranges S M L Wavelength (nm) Relativeabsorption 400 500 600 700
  • 5. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 205 Cone Distributions • Where is the fovea? • Why is blue a “bad” colour?
  • 6. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 206 Young-Helmholtz theory of colour • 3 primaries needed to produce any spectral colour • 3 cones found in the retina • simplest colour vision theory: – cones transduce light and send signals directly to brain
  • 7. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 207 Weaknesses of the YH colour theory• red-green are mutually exclusive (opponency): – a red light can have a blue or yellow tint but not a green tint – a green light can have a blue or yellow tint but not a red tint purple orange brown cyan yellow-green brown
  • 8. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 208 Weaknesses of the YH colour theory• blue-yellow are mutually exclusive (opponency): – a blue light can have a red or green tint but not a yellow tint – a yellow light can have a red or green tint but not a blue tint purple orangegrey cyan yellow-green grey
  • 9. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 209 Patching up the YH colour theory • Hering theorized opponent channels – one type of colour receptor – three colour channels: • Red/Green, Yellow/Blue, White/Black – also explains coloured afterimages – does not explain colour matching • (requires 3 types of colour receptor) • Modern opponent process theory: – combine Young-Helmholtz and Hering
  • 10. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2010 Modern opponent process theory • different combinations of three cone types are fed into the channels: – achromatic: M+L cone responses – blue-yellow: M+L versus S cone responses – red-green: L+S versus M cone responses • chromatic channels are weighted so that they give a zero response to white
  • 11. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2011 Colour opponent channels • achromatic: – M+L cone • blue-yellow: – M+L versus S cone • red-green: – L+S versus M cone S M L 400 500 600 700 Relativeefficiency
  • 12. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2012 What is colour? • Property of objects? • Property of light? • Property of our brain?
  • 13. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2013 Physical dimension e.g. wavelength Psychologicaldimension e.g.colour ? Psychophysics of colour
  • 14. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2014 Colour experiments • determine number of distinguishable colours – JNDs • determine number of “necessary colours” • organize the colours according to similarity
  • 15. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2015 Colour similarity • resulting ordering seems to be cyclic • where should white and black go? • where is purple?
  • 16. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2016 Colour similarity • white and black correspond to saturation and brightness
  • 17. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2017 HSV: Hue, Saturation and Value • Hue: spectral hues + mixed colours like purple • Saturation: purity of colour • Value: brightness or intensity purple!
  • 18. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2018 high low high low HSV: Hue, Saturation and Value Hue Saturation Value
  • 19. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2019 hue HSV: a psychological colour space
  • 20. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2020 saturation HSV: a psychological colour space
  • 21. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2021 low high brightness medium HSV: a psychological colour space
  • 22. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2022 white black HSV: a psychological colour space
  • 23. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2028 Colour constancy • Discounting the spectral distribution of the light source – Incandescent lights are reddish – Sun is yellowish – Sun setting is orange • Similar to lightness constancy
  • 24. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2029
  • 25. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2030
  • 26. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2031
  • 27. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2032 Congenital colour deficiency • Approximately 8% of the population (1 in 12) • Sex linked genes on X-chromosome – mostly men (women possibly tetrachromats) • Three types: missing or abnormal 1. protanopia/protoanomaly: L-cones 2. deuteranopia/deuteranomaly: M-cones 3. tritanopia: missing S-cones S M L
  • 28. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2033 Colour vision tests
  • 29. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2034 Colour vision tests
  • 30. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2035 Normal colour vision
  • 31. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2036 Protanopia L-cone, red/green deficient
  • 32. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2037 Deuteranopia M-cone, red/green deficient
  • 33. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2038 Tritanopia: S-cone, blue/yellow deficient
  • 34. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2039 Normal Tritanopia DeuteranopiaProtanopia
  • 35. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2040 • Bilateral damage to V4 results in achromatopsia • “she looked like a rat”, Rama p. 73 • Neurons in V4 respond to colours (not wavelengths) Cerebral Achromatopsia
  • 36. 2002/02/05 PSYC202-005, Term 2, Copyright Jason Harrison, 2041 Benham, Fechner disks • Black and white patterns that produce colours – flickering monochromatic light below 40Hz • Colour is sensation NOT just physics • Does colour exist “out there”? Or “up here”?