Vision

1. Vision By: Rachel, Tina, Lisa, Yingjie, Ashar

2. Essential Questions • How does vision work? • What are the major components of the visual system and the function of each?

3. Transduction • The eye transduces light characteristics into neural signals the brain can process. • Photons pass through ganglion cells and bipolar cells first. • Then it strikes photoreceptors. • Once stimulated, rods and cones transmit info to bipolar cells, which transmit neural impulses to ganglion cells. • These travel from ganglia to the brain via the optic nerve.

4. Eye anatomy • retina: light sensitive layer at back of eyeball, has photoreceptors • photoreceptors: neurons in retinas that convert light energy to neural impulses • rods: photoreceptors sensitive to dim light • cones: photoreceptors sensitive to colors • bipolar cells: transmit signals from photoreceptors to ganglion cells • ganglion cells: transmit signals from axon to brain • fovea: tiny area of sharpest vision in retina • optic nerve: neuron bundle carrying visual info from retina to brain • choroid: provides oxygen to retina

5. More eye anatomy • cornea: clear white covering over the outside of the eye. It helps the eye focus like a lens on a camera • iris: part of your eye that has color, gets bigger and smaller to let in different amounts of light • sclera: white of the eye • pupil: black opening in the middle of the eye • aqueous humor: clear water-like substance that keeps your eye clean, provides nutrition • lens: bends light, helps the eye see close up and far away things • vitreous humor: the vitreous humor is clear water-like substance in the back of your eye

9. Even more eye anatomy • blind spot: where optic nerve exits each eye • color: psychological sensation created in brain from eye info from wavelengths of visible light • afterimages: negative afterimages • colorblindness: genetics disorder preventing person from discriminating certain colors; red/green

10. How you see images • Visual cortex in brain turns the incoming neural impulses into visual sensations of color, form, boundary, and movement • Depth perception is a result of the brain combing 2D patterns from each eye • Retinal disparity: difference between the visual images that each eye perceives because of the different angles in which each eye views the world

11. How you see brightness • Depends on light intensity/amplitude • Bright light = intense stimulation to retina • Brain sense brightness by level of activity in retina passed though optic pathways

12. How you see color • Color is a sensation that only exists in the mind – a psychological aspect of sensation • Color(hue)is based on the wavelength of light striking the eyes • Saturation: intensity of a color, expressed as the degree to which it differs from white • The eyes detect visible light, which is pure energy • Electromagnetic spectrum: entire range of EM energy , including radio waves, x rays, microwaves, and visible light • The visible spectrum is a small segment on the EM spectrum • Left part of brain see’s the right half • Right part of the brain see’s the left half.

14. Theories on how sight works • trichromatic theory: colors sensed by three different types of cones sensitive to light in red/blue/green wavelengths; explains earliest stage of color sensation • opponent process theory: eye cells process colors in complementary pairs like red/green or yellow/blue; explains color sensation from bipolar cells onward • dark adaptation: the way the eye adjusts to the dark and detects faint traces of light

15. Cool stuff • Accommodation is the process by which the vertebrate eye changes optical power to maintain a clear image (focus) on an object as its distance varies. • Parallel processing is the ability of the brain to simultaneously process incoming stimuli of differing quality • Radiant light is light straight from the source • Reflected light is light reflected off a surface; not directly from the source

16. Imperfect Eyesight:Near-sighted and Farsighted Not all people have perfect vision. Acuity: acuteness or clearness of vision People who can see things up close, but not far away are considered to be near-sighted. This happens when the light entering the eye focuses on a point in front of the retina.

17. On the other hand, people who can see far away objects but not those that are up close are farsighted. Farsightedness occurs when the light that enters the eye focuses on a point behind the retina.

18. 2 cues • Binocular cues - Humans are able to see things that are both far and near, and can actually identify where those objects are in space (meaning, they can determine if those objects are close or far away) • Monocular cues -is the visual ability to perceive the world in three dimensions (3D) and the distance of an object

19. Color • Color does not exist outside the brain because color is a sensation that the brain creates based on the wavelength of light striking our eye. • The eye detect the special form of energy called visible light. The electromagnetic waves differ in their wavelengths, the distance they travel in making one wave cycle.

20. Color blindness • Inability to distinguish colors • Color weakness: can’t distinguish colors under low light • Most color blindness involves a problems in distinguishing red from green • More rare: confusing yellows and blues • Total color blindness: see no color at all, only variation in brightness

21. The Ishihani Blindness Test

22. Eye Fun Facts • Most people blink every 2-10 seconds.Each time you blink, you shut your eyes for 0.3 seconds, which means your eyes are closed at least 30 minutes a day just from blinking. • If you only had one eye, everything would appear two-dimensional. (This does not work just by closing one eye.)‏ • Owls can see a mouse moving over 150 feet away with light no brighter than a candle. • The reason cat's and dog's eyes glow at night is because of silver mirrors in the back of their eyes called the tapetum. This makes it easier for them to see at night. • An ostrich has eyes that are two inches across. Each eye weighs more than their brain. • A chameleon's eyes can look in opposite directions at the same time. • A newborn baby sees the world upside down because it takes some time for the baby's brain to learn to turn the picture right-side up. • One in every twelve males is color blind