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Exam next week

Exam next week. Covers everything about all sensory modalities except hearing This includes: vision balance/touch/taste/smell/ proprioception/theroception. COLOR VISION. Color Vision. Perceiving Color. Primary colors. Red Green Blue. Color Vision.

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Exam next week

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  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 RedGreenBlue

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

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

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

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

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

  9. Color Vision 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 • 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 • 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. 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!

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