1. Exam next week
Covers everything about all sensory modalities except hearing
This includes:
vision
balance/touch/taste/smell/ proprioception/theroception

2. COLOR VISION

3. Color Vision
Perceiving Color
Primary colors
Red Green Blue

4. Trichromatic Theory of Color Vision
Signal to Brain
Wavelength Input
Cone
“Blue”
Blue
“Green”
“Red”

5. Trichromatic Theory of Color Vision
Signal to Brain
Wavelength Input
Cone
“Blue”
“Green”
Green
“Red”

6. Trichromatic Theory of Color Vision
Signal to Brain
Wavelength Input
Cone
“Blue”
“Green”
“Red”
Red

7. Trichromatic Theory of Color Vision
Signal to Brain
Wavelength Input
Cone
“Blue”
Equal Parts Red and Green =
“Green”
Yellow
“Red”

8. Trichromatic Theory of Color Vision
Signal to Brain
Wavelength Input
Cone
“Blue”
Equal Parts Red and Green =
“Green”
Yellow
“Red”

9. Trichromatic Theory of Color Vision
Signal to Brain
Wavelength Input
Cone
“Blue”
Equal Parts Red and Green =
“Green”
Yellow
“Red”

10. Theories of Color Vision: Trichromatic Theory
Problem with Trichromatic Theory:
YELLOW

11. Theories of Color Vision: Opponent-Process Theory
color is determined by outputs of two different continuously variable channels:
red - green opponent channel
blue - yellow opponent channel

12. Theories of Color Vision: Opponent-Process Theory
Red opposes Green
(Red + Green) opposes Blue
Opponent-Process Theory explains color afterimages
because the “opposite” of blue is yellow, the “opposite” of green is red, etc.

13. Color is an illusion
Everything you’ve learned so far is wrong.

14. Color is an illusion Everything you’ve learned so far is wrong.
Well, not really wrong, just far from complete.

15. Everthing you thought you knew
L A N D
Everthing you thought you knew
about color is wrong...

16. What Newton Found (and everyone believed)
White light can be split into all wavelengths by a prism
According to previous theories: two wavelengths combine to yield intermediate color and no others
Red Light
Green Light
Red + Green = YELLOW

17. What Newton Found (and everyone believed)
White light can be split into all wavelengths by a prism
According to previous theories: two wavelengths combine to yield intermediate color and no others
Red + Green light can never yield blue
Blue + Green light can never yield red

18. What twist did Land do to this paradigm that confounds the conventional understanding of color mixing?

19. What Land found:
Two bands (colors) of the spectrum recombine to produce all the possible colors
provided the appropriate relative amount of each wavelength is projected
Red Light
Green Light
transparency slides

20. How did Land project the “appropriate” ratio of wavelengths?

21. Short- and Long- “record”
Camera
Capture two grey-scale images of the scene using filters that allow only the wavelengths you will project
“Long” filter
Object
“short” filter
film
Projector
Image
“Long” filter
“short” filter

22. Camera splits image into
maps of “longer” and “shorter”
wavelengths
long
filter
medium filter

23. Projector combines “longer” and “shorter” wavelengths
using the maps to get the appropriate amounts of each
long/“red”
light
medium/
“green” light
Viewer perceives
desaturated hues
including blues

24. What is Land’s interpretation? How do we perceive color?

25. Land’s interpretation:
perception of color is a weighing of the ratio of shorter and longer wavelengths

26. Land’s interpretation:
perception of color is a weighing of the ratio of shorter and longer wavelengths

27. Why would the visual system have evolved this way?

28. Why would the visual system have evolved this way?
Hint: “Within broad limits, the actual values of the wavelengths make no difference, nor does the over-all available brightness of each”

29. What is color for?
What is color vision used for?
Identification - what is this thing?
Discrimination - what other things is this thing like?
Communication - indicates this thing to others
But in each case color refers not to the illuminating light, but to the surface of the object itself

30. What is color for?
Does the color of an object remain constant under different lighting conditions?

31. Color Constancy
The “color” of objects is independent of the ambient light – even though light can vary dramatically
Sunlight
Incandescent Light
Relative Intensity
Relative Intensity
Wavelength

32. Color Constancy
Because of our mechanism of color constancy we can even use completely artificial spectra

33. Color Constancy
The “color” of objects is independent of the ambient light

34. Next Time
ATTENTION!