1. -perceptions not in agreement (“pure” blue?)
Perception of Colour
Defining colour:
”a quality such as red, blue, green, yellow, etc., that you see when you look at something” (Mirriam Webster)
-”perceptual attributes that correspond to differences in wavelengths of electromagnetic energy”?
Nanometre = billionth of a metre
Problems:
-perceptions not in agreement (“pure” blue?)
-no guarantee that the internal experience is similar between us
-colour perception is not in a 1:1 relationship with wavelength

3. Physical/psychological properties:
wavelength
colour
intensity
brightness
How many colours can we experience/see?
~200 jnds

4. The problem with that method:
Not all ‘colours’ are represented in the “visible spectrum”

7. Physical/psychological properties:
wavelength
colour
intensity
brightness
Amount of white light mixed in
Saturation

9. there are over 7 million distinguishable colours.
When you factor in variations in the intensity and purity of the light,
there are over 7 million distinguishable colours.

10. Colour-perception phenomena requiring an explanation:

11. Colour-perception phenomena requiring an explanation:
1) Complementary colours
A version of Newton’s Colour wheel
Generally speaking, Red-green and blue-yellow are the two basic complements

12. Subtractive mixing

13. Subtractive mixing

14. Subtractive mixing

15. Subtractive mixing

16. Subtractive mixing

17. Subtractive mixing

18. Subtractive mixing

19. Colour-perception phenomena requiring an explanation:
1) Complementary colours
2) Negative Afterimages x

20. Colour-perception phenomena requiring an explanation:
1) Complementary colours
2) Negative Afterimages
3) Colourblindness

21. Theories of Colour Vision
(Young/Helmholtz, circa 1800)

22. Colour-perception phenomena requiring an explanation:
1) Complementary colours
2) Negative Afterimages
3) Colourblindness

23. Theories of Colour Vision
(Young/Helmholtz, circa 1800)
(Hering/Hurvich, circa 1860)

24. Colour-perception phenomena requiring an explanation:
1) Complementary colours
2) Negative Afterimages
3) Colourblindness

25. Hurvich demarkates the opponent-process ‘mechanisms’ via psychophysics

26. 560+630: r/g cancels out, left with yellow

27. Early evidence: three cone types!

28. Colour-perception phenomena requiring an explanation:
1) Complementary colours
2) Negative Afterimages
3) Colourblindness
(red receptor deficit)
(green receptor deficit)
(blue receptor deficit)

29. Early evidence: three cone types!
Subsequent work: opponent-process cells in visual pathway (e.g. LGN and beyond)

30. Proposed neural wiring to go from trichromatic to opponent-processing codes:

31. But these two models can’t account for all of colour perception either.
Problem: both rely on the decoding of wavelength information.
In impoverished situations, they work just fine

32. Anomalous Colour Illusions

33. Anomalous Colour Illusions

34. Anomalous Colour Illusions

36. Edwin Land: “Mondrians”
But these two models can’t account for all of colour perception either.
Problem: both rely on the decoding of wavelength information.
In impoverished situations, they work just fine
Edwin Land: “Mondrians”

37. 100
100
100

38. Choice:
100
100
100

39. 100
100
100

40. 100 90
100 9
100 10

41. 100 90
100 9
100 10
90% 9%
10%

42. 100 90
100 9
100 10
90% 9%
10%

43. 100 90
100 9
100 10
90% 9% 10
10% 90 10

44. 100 90
100 9
100 10
90% 9% 10
10%
10%
90% 90
10% 10

45. 100 90
What if we make the “green” diamond reflect the same proportions as the red triangle?
100 9
100 10
90% 9% 10
10%
10%
90% 90
10% 10

46. 100 90
100 9
100 10
90% 9% 90
10%
10%
90% 9
10% 10

47. 900 90
100 9
100 10
90% 9% 90
10%
10%
90% 9
10% 10

48. 900 90 10 9
100 10
90% 9% 90
10%
10%
90% 9
10% 10

49. Choice:
Why?
The answer appears when we look at what the triangle is reflecting back under these illumination conditions
900 90 10 9
100 10
90% 9% 90
10%
10%
90% 9
10% 10

50. Choice:
900
810!!! 10
.9!!
100 10
90% 9% 90
10%
10%
90% 9
10% 10

51. A third alternative:
Land’s Retinex model
There are three ‘retinexes”, which examine how much red, green, and blue light is reflected off of all the surfaces relative to one another.

52. A third alternative:
Land’s Retinex model
There are three ‘retinexes”, which examine how much red, green, and blue light is reflected off of all the surfaces relative to one another.
Whichever retinex is ‘most predominant’ for an object, will be assigned that colour by the brain

53. A third alternative:
Land’s Retinex model
There are three ‘retinexes”, which examine how much red, green, and blue light is reflected off of all the surfaces relative to one another.
Whichever retinex is ‘most predominant’ for an object, will be assigned that colour by the brain

54. A third alternative: Land’s Retinex model
There are three ‘retinexes”, which examine how much red, green, and blue light is reflected off of all the surfaces relative to one another.
Whichever retinex is ‘most predominant’ for an object, will be assigned that colour by the brain
20%
90%
15%
90%
10%
10%
20%
80%

55. A third alternative: Land’s Retinex model
There are three ‘retinexes”, which examine how much red, green, and blue light is reflected off of all the surfaces relative to one another.
Whichever retinex is ‘most predominant’ for an object, will be assigned that colour by the brain
20%
90%
15% 2 2 1
90%
10% 3 3 1
10%
20%
80% 3 1 2

56. A third alternative: Land’s Retinex model
There are three ‘retinexes”, which examine how much red, green, and blue light is reflected off of all the surfaces relative to one another.
Whichever retinex is ‘most predominant’ for an object, will be assigned that colour by the brain
20%
90%
15%
“BLUE”! 2 2 1
90%
10% 3 3
“RED”! 1
10%
20%
80%
“GREEN”! 3 1 2

57. A third alternative: Land’s Retinex model Choice: 900 810!!! 10 .9!!
100 10
90% 9% 90
10%
10%
90% 9
10% 10

62. McCullough Effect