The document discusses color vision and the theories behind how humans perceive color. It explains that humans have three types of cones in the retina that are sensitive to different wavelengths of light, allowing for trichromatic color vision. It describes how the opponent process theory proposes that the visual system processes color information by two opponent mechanisms - red versus green and blue versus yellow. It also discusses how color information is transmitted from the retina to the lateral geniculate nucleus and primary visual cortex in the brain.

2. Black and White vision is adequate for most purposes. Color vision is important in identifying ripeness, counteracting camouflage... Humans, Old World monkeys and apes each have 3 types of cones (3 iodopsins) providing the most elaborate color vision in the animal kingdom. COLOR VISION

3. Based on observation that any color of light can be attained by mixing various amounts of 3 colors of light. Proposed that humans have 3 kinds of photoreceptors that work together to give the sensation of hue. lights Photoreceptors: Trichromatic Theory of Color Vision

4. Due to in the color receptors (cones) in retina becoming "fatigued." When you then look a different background, the receptors that are tired do not work as well. Therefore, the information from all of the different color receptors is not in balance. Therefore, you see the color " afterimages." You can see that you vision quickly returns to normal. Photoreceptors: Trichromatic theory of color vision

7. Opponent Process Theory of Color Vision Based on idea that some colors don’t blend (e.g. reddish green), and on negative afterimages Trichromatic theory can’t explain these phenomena. lights Based on observation of negative afterimages .

9. 3 types of cones Note : All cones respond to a range of wavelengths, but their maximal response is at 440, 530, or 560 nm. This is determined by the type of iodopsin in the cone. 440 nm 530 nm 560 nm

13. 440 530 560 Red light “stimulates” red cone Red cone “stimulates” red/green ganglion cell cones signals red ganglion cells RETINAL COLOR CODING

14. 440 530 560 green light “stimulates” green cone green cone “inhibits” red/green ganglion cell cones signals green ganglion cells RETINAL COLOR CODING

15. 440 530 560 Red light “stimulates” red cone Red cone “inhibits” green/red ganglion cell cones signals red ganglion cells RETINAL COLOR CODING

16. 440 530 560 green light “stimulates” green cone green cone “stimulates” green/red ganglion cell cones signals green ganglion cells RETINAL COLOR CODING

17. 440 530 560 blue light “stimulates” blue cone blue cone “inhibits” yellow/blue ganglion cell cones signals blue ganglion cells RETINAL COLOR CODING

18. 440 530 560 yellow light “stimulates” red and green cones equally Red and green inputs to red/green cell cancel red and green sum to “ inhibit” blue/yellow cells cones ganglion cells signals yellow RETINAL COLOR CODING

19. 440 530 560 Accordingly, we can see reddish-yellow reddish-blue greenish-blue and greenish-yellow but we cannot see reddish-green or bluish-yellow cones ganglion cells orange purple turquoise lime RETINAL COLOR CODING

21. Visual Pathways The optic nerve has two principle branches