Remember that the colors we perceive depend on the color signal reaching the retina.

2. It is now possible, given the sequence of the L and M photopigment genes to predict the spectral sensitivity of the corresponding pigments.

3. Remember that the colors we perceive depend on the color signal reaching the retina.

4. Adding an oil droplet in the inner segment effectively narrows the overall relative spectral sensitivity of the cone relative to the pigment...

5. Human lens also acts as a chromatic filter Cuts out short wavelength light Increases with age (gets more dense) No change in color perception with age - demonstrates some degree of plasticity in the visual system

6. Common chromophores used in vision • 11-cis-Retinal - most widely used • 3-dehydroretinal - freshwater fishes, amphibians and reptiles • 3-hydroxyretinal - insects (moths, flies, butterflies)

7. 0.90 0.40 0.01 Increasing optical density broadens the absorbance spectrum

8. Processing of color signals

9. Neural color processing

10. Achromatic channel ? + + Red-green channel - - Blue-yellow channel L M S L M S L M S

11. The balance points of these chromatic channels have been demonstrated psychophysically as the unique hues A unique hue, by definition, cannot be described by any other unique-hue name(s) Red - neither blue nor yellow Green - neither blue nor yellow Blue - neither red nor green Yellow - neither red nor green

18. AP nasal BS Model for how L:M doesn’t affect color perception

19. Comparative color vision

27. 104 Would tetrachromacy add another dimension??

28. Variants of the L gene in individuals with normal color vision

29. Evolution of Trichromacy in mammals

30. Happened at least 4 times… OW NW Aloutta Marsupials

31. Duplication

32. Divergence

33. Selective expression • Neural circuitry already in place?

34. One Cell-Type Model Stochastic Pigment-Gene Choice random choice mechanism M L “L vs. M gene choice determines cell type” ? ? ? Second Order Neurons

35. X545 X560 X560 Y X560 X560 X545 Y X530 Y New World primates

36. Trichromacy in the Alouatta is similar to that found in OW primates - all animals are trichromats, not just females. It is not known how their trichromacy evolved, but it is believed to be a second duplication...

37. Recent work has shown 2 marsupials to have the requisite 3 cone types for trichromacy. As Jacobs (2002) points out, it is a nearly perfect correspondence between the number of cone types and the dimensionality of color vision. Thus, one can conclude that these marsupials represent a 4th independent evolution of trichromatic color vision.

38. Color Vision Defects in Humans

39. Many types of color vision “defects” Dichromacy Protan- Deutan- Tritan- Monochromacy (very rare) Blue cone monochromacy Rod monochromacy

40. *Tritan defects are extremely rare

41. Present at birth Type and severity is the same through life Type can be classified precisely Both eyes equally affected Visual acuity is often unaffected Predominantly protan or deutan Higher incidence in males Onset after birth Type and severity fluctuates Type may not be easily classified. Combined defects occur Monocular differences often occur Visual acuity is often reduced Predominantly tritan Equal incidence in males and females Characteristics of Color Vision Defects Congenital Acquired

42. X-linked defects

43. “Sir, When I had the pleasure of waiting on you last winter…I promised to procure you a written account from the person himself, but this I was unfortunately disappointed in, by his dying suddenly…” Joseph Huddart, 1777 First documented case of R/G defect