1. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 20021 Psychophysics of colour perception Neurophysiology, psychophysics, and magic (or you only though you knew what colour was…)

2. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 20022 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. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 20023 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. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 20024 Cone wavelength ranges SML Wavelength (nm) Relative absorption 400500600 700

5. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 20025 Cone Distributions Where is the fovea? Why is blue a “bad” colour?

6. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 20026 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. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 20027 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 orangebrown cyanyellow-greenbrown

8. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 20028 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. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 20029 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. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200210 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. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200211 Colour opponent channels achromatic: –M+L cone blue-yellow: –M+L versus S cone red-green: – L+S versus M cone SML 400500600 700 Relative efficiency

12. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200212 What is colour? Property of objects? Property of light? Property of our brain?

13. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200213 Physical dimension e.g. wavelength Psychological dimension e.g. colour ? Psychophysics of colour

14. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200214 Colour experiments determine number of distinguishable colours –JNDs determine number of “necessary colours” organize the colours according to similarity

15. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200215 Colour similarity resulting ordering seems to be cyclic where should white and black go? where is purple?

16. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200216 Colour similarity white and black correspond to saturation and brightness

17. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200217 HSV: Hue, Saturation and Value Hue: spectral hues + mixed colours like purple Saturation: purity of colour Value: brightness or intensity purple!

18. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200218 high low high low HSV: Hue, Saturation and Value Hue SaturationValue

19. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200219 hue HSV: a psychological colour space

20. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200220 saturation HSV: a psychological colour space

21. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200221 low high brightness medium HSV: a psychological colour space

22. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200222 white black HSV: a psychological colour space

23. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200223 Brightness high medium low high medium low white black

24. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200224 Brightness high medium low high medium low white black

25. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200225 Brightness high medium low high medium low white black

26. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200226 Brightness high medium low high medium low white black

27. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200227 Brightness high medium low high medium low white black

28. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200228 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

29. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200229 Colour constancy demo

30. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200230 Colour constancy demo

31. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200231 Colour constancy demo

32. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200232 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 SML

33. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200233 Colour vision tests

34. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200234 Colour vision tests

35. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200235 Normal colour vision

36. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200236 Protanopia L-cone, red/green deficient

37. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200237 Deuteranopia M-cone, red/green deficient

38. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200238 Tritanopia: S-cone, blue/yellow deficient

39. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200239 NormalTritanopia DeuteranopiaProtanopia Comparison

40. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200240 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

41. 2002/02/05PSYC202-005, Term 2, Copyright Jason Harrison, 200241 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”?