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By: 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?
 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
Eye anatomy
retina: light sensitive layer at back of eyeball, has
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
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
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
 colorblindness: genetics
disorder preventing
person from discriminating certain colors;
+ 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
 Bright
 Brain
on light intensity/amplitude
light = intense stimulation to retina
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
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
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.
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
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)
cues - is the visual ability to
perceive the world in three dimensions (3D) and the distance
of an object
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
The Ishihani Blindness Test
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