2. COLOR VISION After Stephen E. Palmer, 2002

3. COLOR VISION “The Color Story” is a prototype for Cognitive Science Contributions from: Physics (Newton) Philosophy (Locke) Art (Munsell) Psychophysics (Maxwell) Physiology (De Valois) Cognitive Psychology (Rosch) Neurology (Zeki) Linguistics (Lakoff) Cognitive Anthropology (Berlin & Kay) Computer Science (Zadeh) © Stephen E. Palmer, 2002

4. COLOR VISION “The Color Story” is a prototype for Cognitive Science Contributions from: * Berkeley faculty Physics (Newton) Philosophy (Locke) Art (Munsell) Psychophysics (Maxwell) Physiology (De Valois) Cognitive Psychology (Rosch) Neurology (Zeki) Linguistics (Lakoff) Cognitive Anthropology (Berlin & Kay) Computer Science (Zadeh) © Stephen E. Palmer, 2002

5. The Physics of Light Light: Electromagnetic energy whose wavelength is between 400 nm and 700 nm. (1 nm = 10 meter) -6 © Stephen E. Palmer, 2002

6. The Physics of Light Some examples of the spectra of light sources © Stephen E. Palmer, 2002

7. The Physics of Light Some examples of the reflectance spectra of surfaces Wavelength (nm) % Photons Reflected Red 400 700 Yellow 400 700 Blue 400 700 Purple 400 700 © Stephen E. Palmer, 2002

8. The Psychophysical Correspondence There is no simple functional description for the perceived color of all lights under all viewing conditions, but …... A helpful constraint: Consider only physical spectra with normal distributions area mean variance © Stephen E. Palmer, 2002

9. The Psychophysical Correspondence MeanHue # Photons Wavelength © Stephen E. Palmer, 2002

10. The Psychophysical Correspondence VarianceSaturation Wavelength # Photons © Stephen E. Palmer, 2002

11. The Psychophysical Correspondence AreaBrightness # Photons Wavelength © Stephen E. Palmer, 2002

12. Overview of the Visual System

13. Physiology of Color Vision © Stephen E. Palmer, 2002 Cones cone-shaped less sensitive operate in high light color vision Rods rod-shaped highly sensitive operate at night gray-scale vision Two types of light-sensitive receptors

14. The Microscopic View

15. http://www.iit.edu/~npr/DrJennifer/visual/retina.html Rods and Cones in the Retina

16. What Rods and Cones Detect Notice how they aren’t distributed evenly, and the rod is more sensitive to shorter wavelengths

17. How They Fire No stimuli: –both fire at base rate Stimuli in center: –ON-center-OFF-surround fires rapidly –OFF-center-ON-surround doesn’t fire Stimuli in surround: –OFF-center-ON-surround fires rapidly –ON-center-OFF-surround doesn’t fire Stimuli in both regions: –both fire slowly

18. Center / Surround Strong activation in center, inhibition on surround The effect you get using these center / surround cells is enhanced edges top: the stimuli itself middle: brightness of the stimuli bottom: response of the retina You’ll see this idea get used in Regier’s model http://www-psych.stanford.edu/~lera/psych115s/notes/lecture3/figures1.html

19. Theories of Color Vision Two main algorithmic theories of color vision: © Stephen E. Palmer, 2002 Trichromatic Theory (Palmer/Young/Helmholtz) Hermann von Helmholtz Opponent Process Theory (Hering) Ewald Hering

20. © Stephen E. Palmer, 2002 Three kinds of cones: Absorption spectra Implementation of Trichromatic theory Physiology of Color Vision Opponent Processes: R/G = L-M G/R = M-L B/Y = S-(M+L) Y/B = (M+L)-S

21. © Stephen E. Palmer, 2002 Opponent-Process Cells in LGN (De Valois) Physiology of Color Vision Implementation of opponent process theory (Similar color behavior in retinal ganglion cells)

22. © Stephen E. Palmer, 2002 Double Opponent Cells in V1 Physiology of Color Vision G+R-G+R- G+R-G+R- R+G-R+G- R+G-R+G- Red/Green Y+B-Y+B- Y+B-Y+B- B+Y-B+Y- B+Y-B+Y- Blue/Yellow

23. Color Blindness Not everybody perceives colors in the same way! What numbers do you see in these displays? © Stephen E. Palmer, 2002

24. Color Blindness There are several forms of inherited variations of color vision. Trichromatic (“normal”) color vision Dichromatic color vision 2 forms of red-green color blindness 1 form of yellow-blue color blindness Monochromatic color vision 4 forms Various forms of “color weakness” © Stephen E. Palmer, 2002

25. Color Blindness What does the world look like to a color blind person? Normal Trichromat ProtanopeDeuteranopeTritanope © Stephen E. Palmer, 2002

26. Theories of Color Vision Opponent Process theory (Hering): All colors are combinations of responses in three underlying bipolar systems (Red/Green, Blue/Yellow, Black/White). © Stephen E. Palmer, 2002

27. Theories of Color Vision Dual Process Theory (Hurvich & Jameson): The color vision system contains two stages: an initial trichromatic stage and a later opponent-process stage. © Stephen E. Palmer, 2002 Trichromatic stage Opponent- Process stage Dual Process Theory

28. Theories of Color Vision A Dual Process Wiring Diagram © Stephen E. Palmer, 2002 Trichromatic Stage Opponent Process Stage

29. COLOR VISION: Part 4 © Stephen E. Palmer, 2002 1. Color Constancy: Surface-based processing 2. Color Naming: Category-based processing

30. Color Constancy © Stephen E. Palmer, 2002 Color Constancy: the ability to perceive the invariant color of a surface despite ecological Variations in the conditions of observation. Another inverse problem: Physics of light emission and surface reflection underdetermine perception of surface color

31. Color Constancy © Stephen E. Palmer, 2002 RwRw IwIw LwLw

32. Color Constancy © Stephen E. Palmer, 2002

33. Color Constancy © Stephen E. Palmer, 2002 Two approaches to lightness constancy Unconscious Inference (Helmholtz) Luminance = Intensity * Reflectance If you know L and I, you can solve for R! Invariant Relations (Hering) Luminance ratios are invariant with illumination

34. Color Constancy © Stephen E. Palmer, 2002 Luminance ratio is invariant over illumination: Luminance Ratio = 9:1

35. Color Constancy © Stephen E. Palmer, 2002 What about absolute lightness? How do we know what is white? (How big is the anchor???) The anchoring problem:

36. Anchoring heuristic: The lightest region is taken as white

37. COLOR VISION: © Stephen E. Palmer, 2002 Color Naming: Category-based processing Big Questions for Cognitive Science 1)Are Words Arbitrary? 2)Does Language Influence Thought? (Whorf Hypothesis)

38. Color Naming © Stephen E. Palmer, 2002 Basic Color Terms (Berlin & Kay) Criteria: 1. Single words -- not “light-blue” or “blue-green” 2. Frequently used -- not “mauve” or “cyan” 3. Refer primarily to colors -- not “lime” or “gold” 4. Apply to any object -- not “roan” or “blond”

39. Color Naming © Stephen E. Palmer, 2002 BCTs in English Red Green Blue Yellow Black White Gray Brown Purple Orange* Pink

40. Color Naming © Stephen E. Palmer, 2002 Five more BCTs in a study of 98 languages Light-Blue Warm Cool Light-Warm Dark-Cool

41. Color Naming © Stephen E. Palmer, 2002 Studied color categories in two ways Boundaries Best examples (Berlin & Kay)

42. Color Naming © Stephen E. Palmer, 2002 MEMORY : Focal colors are remembered better than nonfocal colors. LEARNING: New color categories centered on focal colors are learned faster. Categorization: Focal colors are categorized more quickly than nonfocal colors. (Rosch)

43. Color Naming Degree of Membership Fuzzy set theory (Zadeh) A fuzzy logical model of color naming (Kay & Mc Daniel) © Stephen E. Palmer, 2002

44. Color Naming © Stephen E. Palmer, 2002 “Primary” color categories

45. Color Naming © Stephen E. Palmer, 2002 “Primary” color categories Red Green Blue Yellow Black White

46. Color Naming © Stephen E. Palmer, 2002 “Derived” color categories Fuzzy logical “AND f ”

47. Color Naming © Stephen E. Palmer, 2002 “Derived” color categories Orange = Red AND f Yellow Purple = Red AND f Blue Gray = Black AND f White Pink = Red AND f White Brown = Yellow AND f Black (Goluboi = Blue AND f White)

48. Color Naming © Stephen E. Palmer, 2002 “Composite” color categories Fuzzy logical “OR f ” Warm = Red Or f Yellow Cool = Blue Or f Green Light-warm = White Or f Warm Dark-cool = Black Or f Cool

49. Color Naming © Stephen E. Palmer, 2002

50. The WCS Color Chips Basic color terms: –Single word (not blue-green) –Frequently used (not mauve) –Refers primarily to colors (not lime) –Applies to any object (not blonde) FYI: English has 11 basic color terms

51. Color Naming © Stephen E. Palmer, 2002 Five more BCTs in a study of 98 languages Light-Blue Warm Cool Light-Warm Dark-Cool

52. Results of Kay’s Color Study If you group languages into the number of basic color terms they have, as the number of color terms increases, additional terms specify focal colors Stage IIIIIIa / IIIbIVVVIVII W or R or YWWWWWW Bk or G or BuR or Y RRRR Bk or G or BuG or BuYYYY BkG or BuGGG BkBu WBk RY+Bk (Brown) YR+W (Pink) Bk or G or BuR + Bu (Purple) R+Y (Orange) B+W (Grey)

53. Color Naming © Stephen E. Palmer, 2002 Typical “developmental” sequence of BCTs

54. COLOR VISION: © Stephen E. Palmer, 2002 Color Naming: Category-based processing Big Questions for Cognitive Science 1)Are Words Arbitrary? 2)Does Language Influence Thought? (Whorf Hypothesis)

55. Overview of the Visual System

58. Same paradigm with dogs vs. cats

60. Verbal interference caused RVF reversal as with color Animal mismatch task, with verbal and non verbal masks.

61. Aphasic patients on visual search task w/o interference