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VisionBy: Rachel, Tina, Lisa, Yingjie, Ashar

+Essential Questions

How does vision work?

What are the major components of the visual system and the function of each?

+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.

+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

+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

+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

+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

+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

+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.

+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

+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

+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.

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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.

+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

+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.

+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

The Ishihani Blindness Test

+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

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