To survive, organisms must be able to perceive stimuli in their environment, process what that stimuli means, and respond appropriately. The human visual perception system allows us to perform these three interrelated activities. Light enters the eye and passes through the cornea, iris, pupil, lens, vitreous body, and strikes the retina. The retina contains light-sensitive rods and cones that convert the image into neural signals sent to the brain for processing, allowing us to see. Proper functioning of all these eye structures enables humans to perceive the world visually.

1. PerceptionPerception

2. PerceptionPerception
• To survive, must be able to perform 3 interrelated activities:To survive, must be able to perform 3 interrelated activities:
– 1. Sensing stimuli1. Sensing stimuli
– 2. Processing stimuli (interpreting)2. Processing stimuli (interpreting)
– 3. Responding to stimuli (brain sends message to muscles)3. Responding to stimuli (brain sends message to muscles)
• Ex: Traffic lightEx: Traffic light
– 1. Sensing stimuli1. Sensing stimuli
• See red lightSee red light
– 2. Professing stimuli2. Professing stimuli
• Red means stopRed means stop
– 3. Responding to stimuli3. Responding to stimuli
• Putting foot on brakePutting foot on brake
Copyright © Prentice Hall 2007 2-2

3. PerceptionPerception
• The process of organizing andThe process of organizing and
making sense of sensorymaking sense of sensory
information.information.

4. PerceptionPerception
• Vision our most important sensoryVision our most important sensory
process?process?
• About 80% of the information weAbout 80% of the information we
receive about the world reaches usreceive about the world reaches us
through vision.through vision.
• We don’t have the top of the line eyeWe don’t have the top of the line eye
evolutionary speaking.evolutionary speaking.
– Antelope has 8 x’s magnification in it’sAntelope has 8 x’s magnification in it’s
lens.lens.

5. PerceptionPerception
• Visual perception is extremelyVisual perception is extremely
complicated.complicated.
• Either pick a partner and look at theirEither pick a partner and look at their
eye as we continue or look into a mirror.eye as we continue or look into a mirror.
• This simple clip made for childrenThis simple clip made for children
simplifies and clarifies the workings ofsimplifies and clarifies the workings of
the eyes.the eyes.
http://www.brainpop.com/health/bodysyhttp://www.brainpop.com/health/bodysy
stems/eyes/stems/eyes/

6. ProcessProcess
• CorneaCornea
• IrisIris
• PupilPupil
• LensLens
• RetinaRetina

7. Sclera or the White PartSclera or the White Part
• White part of theWhite part of the
eyeball is theeyeball is the
sclera (sklair-uh).sclera (sklair-uh).
• Made of a toughMade of a tough
material.material.
• Covers most of theCovers most of the
eyeball.eyeball.

8. Sclera or the White PartSclera or the White Part
• Think of theThink of the
sclera as yoursclera as your
eyeball's outereyeball's outer
coat.coat.

9. CorneaCornea
• Transparent dome.Transparent dome.
• In front of theIn front of the
colored part of thecolored part of the
eye.eye.
• Helps the eye focusHelps the eye focus
as light makes itsas light makes its
way through.way through.

10. CorneaCornea
• Made of clear tissue.Made of clear tissue.
• Like a windshield the itLike a windshield the it
gives your eye a cleargives your eye a clear
window to view thewindow to view the
world.world.
• No blood supply &No blood supply &
easily transplanted.easily transplanted.
• Shown is an artificialShown is an artificial
cornea but can comecornea but can come
from a cadaver.from a cadaver.

11. IrisIris
• Behind the cornea:Behind the cornea:
– IrisIris
– PupilPupil
– Anterior chamberAnterior chamber
• Iris the colorful partIris the colorful part
of the eyeof the eye

12. Iris Cont.Iris Cont.
• Muscles attachedMuscles attached
to it change itsto it change its
shape.shape.
• Controls howControls how
much light goesmuch light goes
through the pupilthrough the pupil
– Shutter on aShutter on a
cameracamera

13. PupilPupil
• Black circle inBlack circle in
the center of thethe center of the
IrisIris
• It is an openingIt is an opening
in the Iris.in the Iris.
• Lets light enterLets light enter
the eye.the eye.

14. PupilPupil
• When we say, “Your Pupil is dilated”, whatWhen we say, “Your Pupil is dilated”, what
are we really saying?are we really saying?
– Your Iris is expanding or contracting to let inYour Iris is expanding or contracting to let in
more or less light.more or less light.

15. Drug Overdose of UnconsciousDrug Overdose of Unconscious
PersonPerson
• Doctors can tell beforeDoctors can tell before
a toxicology report thata toxicology report that
someone has had a drugsomeone has had a drug
overdose.overdose.
• Narrow pinpoint pupilNarrow pinpoint pupil

16. Anterior ChamberAnterior Chamber
• Space between theSpace between the
cornea & Iriscornea & Iris
• Filled with aFilled with a
transparent fluidtransparent fluid
– Nourishes theNourishes the
eyeeye
– Keeps it healthyKeeps it healthy

17. LensLens
• Works like theWorks like the
lens of a movielens of a movie
projectorprojector
• You see a streamYou see a stream
of light comingof light coming
from thefrom the
projection boothprojection booth

18. LensLens
• Light goes through aLight goes through a
lens, which islens, which is
focusing the imagesfocusing the images
onto the screen, soonto the screen, so
you can see the movieyou can see the movie
clearly.clearly.
• In the eye's case, theIn the eye's case, the
film screen is yourfilm screen is your
retina.retina.

19. Ciliary MuscleCiliary Muscle
• The lens isThe lens is
suspended bysuspended by
fibersfibers
• These fibers areThese fibers are
attached to theattached to the
ciliary muscle.ciliary muscle.
• It changes theIt changes the
shape of the lensshape of the lens

20. Ciliary Muscle Cont.Ciliary Muscle Cont.
• It changes theIt changes the
shape of the lensshape of the lens
• Process calledProcess called
• AccommodationAccommodation

21. Ciliary Muscle Cont.Ciliary Muscle Cont.
• When you look atWhen you look at
things up close,things up close,
the lens becomesthe lens becomes
thicker to focusthicker to focus
the correct imagethe correct image
onto the retina.onto the retina.
• When you lookWhen you look
at things farat things far
away, the lensaway, the lens
becomes thinner.becomes thinner.

22. Vitreous Body (vih-tree-us)Vitreous Body (vih-tree-us)
• Biggest part of the eyeBiggest part of the eye
• Sits behind the lensSits behind the lens
Forms 2/3 of the eye'sForms 2/3 of the eye's
volumevolume
• Gives the eye its shape,Gives the eye its shape,
keeps the retina inkeeps the retina in
place.place.
• Filled with a clear,Filled with a clear,
jelly-like material but isjelly-like material but is
99% water99% water

23. Vitreous Body Cont.Vitreous Body Cont.
• Toy eyeballs areToy eyeballs are
sometimes squishysometimes squishy
because they're made tobecause they're made to
feel like they're filledfeel like they're filled
with vitreous humor.with vitreous humor.
• Light passes throughLight passes through
the lensthe lens
• It shines straightIt shines straight
through the vitreousthrough the vitreous
humor to the back ofhumor to the back of
the eye.the eye.

24. RetinaRetina
• Film that light hits.Film that light hits.
• The beginning of ourThe beginning of our
perception of light.perception of light.
• Very back of the eyeVery back of the eye
• It holds all theIt holds all the
receptors for vision.receptors for vision.

25. RetinaRetina
• Takes the light theTakes the light the
eye receives andeye receives and
changes it intochanges it into
nerve signals sonerve signals so
the brain canthe brain can
understand whatunderstand what
the eye is seeing.the eye is seeing.

26. DeathDeath
• When someone dies they get retinal bloodWhen someone dies they get retinal blood
columns called “boxcars”. They look like acolumns called “boxcars”. They look like a
little train.little train.
• This is why the doctor shines a light intoThis is why the doctor shines a light into
someone's eye to see if they are still alive.someone's eye to see if they are still alive.
• If dead the pupil will not contract and alsoIf dead the pupil will not contract and also
he/she will see the boxcars.he/she will see the boxcars.
• Pupil dilates at death, shine light in there isPupil dilates at death, shine light in there is
no reflex.no reflex.

27. Light Hitting The RetinaLight Hitting The Retina

28. Sensory CodingSensory Coding
• Activation of retinalActivation of retinal
cells by light resultscells by light results
in action potentialsin action potentials
that travel alongthat travel along
neurons that projectneurons that project
to the occipital cortexto the occipital cortex

29. Rods and ConesRods and Cones
• Retina uses cells toRetina uses cells to
process light.process light.
• In each eye:In each eye:
– RodsRods
• 120 million120 million
• PhotoreceptorsPhotoreceptors
– ConesCones
• 7 million7 million
• Color receptorsColor receptors

30. RodsRods
• Name: shapedName: shaped
like a column.like a column.
• See in black,See in black,
white, & shadeswhite, & shades
of grayof gray

31. Rods Cont.Rods Cont.
• Notice that we may think we are seeingNotice that we may think we are seeing
color because we expect something to becolor because we expect something to be
a certain color.a certain color.
• Tell us shape & movement of somethingTell us shape & movement of something
• Rods are super-sensitiveRods are super-sensitive
• Allow us to see in the dark for survival.Allow us to see in the dark for survival.

32. Periferal VisonPeriferal Vison
• Periferal field rods increase. Hunters knowPeriferal field rods increase. Hunters know
in dark settings to not look directly at yourin dark settings to not look directly at your
prey, better dark vision. I have personallyprey, better dark vision. I have personally
seen this with deers. They look at yourseen this with deers. They look at your
sideways.sideways.

33. ConesCones
• Color receptorsColor receptors
• SenseSense colorcolor
• Need more lightNeed more light
than rods to workthan rods to work
wellwell
• Work best in normalWork best in normal
or bright lightor bright light
• Retina has 3 types ofRetina has 3 types of
cones.cones.

34. Cones Cont.Cones Cont.
• The retina has 3The retina has 3
types of cones.types of cones.
• Each cone type isEach cone type is
sensitive to one ofsensitive to one of
three differentthree different
colors — red, green,colors — red, green,
or blue — to helpor blue — to help
you see differentyou see different
ranges of color.ranges of color.

35. Cones Cont.Cones Cont.
• Together, theseTogether, these
cones can sensecones can sense
combinations ofcombinations of
light waves thatlight waves that
enable our eyes toenable our eyes to
see millions ofsee millions of
colors.colors.

36. Feature DetectorsFeature Detectors
• Nerve cells that pick up specific featuresNerve cells that pick up specific features
– MovementMovement
– ShapeShape
– DepthDepth

37. Optic NerveOptic Nerve
• Messenger in back eye.Messenger in back eye.
• Rods & cones of retinaRods & cones of retina
– Change colors & shapes into millions of nerveChange colors & shapes into millions of nerve
messages.messages.
• Optic nerve carries those messages from eyeOptic nerve carries those messages from eye
> brain> brain
• Optic nerve serves as a high-speed telephoneOptic nerve serves as a high-speed telephone
line connecting eye > brain.line connecting eye > brain.

38. Optic NerveOptic Nerve
• When you see an image,When you see an image,
your eye "telephones"your eye "telephones"
your brain with ayour brain with a
report on what you arereport on what you are
seeing so the brain canseeing so the brain can
translate that reporttranslate that report
into "car," “person," orinto "car," “person," or
“Big Mac," or whatever“Big Mac," or whatever
the case may be.the case may be.

39. Optic NerveOptic Nerve
• Put an x on the wall and a dot on a card, closePut an x on the wall and a dot on a card, close
one eye, and the dot will disappear at yourone eye, and the dot will disappear at your
blind spot.blind spot.
• Blind spotBlind spot
– Where the Optic Nerve pierces the retinaWhere the Optic Nerve pierces the retina
• No receptor cells to pick up imagesNo receptor cells to pick up images
• Brain fills in the blankBrain fills in the blank

40. Eye TattooingEye Tattooing
• Some people have started gettingSome people have started getting
tattoos on their eyeballs. And we'retattoos on their eyeballs. And we're
not talking about permanentnot talking about permanent
makeup or anything else on themakeup or anything else on the
outsideoutside of the eye -- we're talkingof the eye -- we're talking
ink injected right into the cornea.ink injected right into the cornea.

41. Eye Tattooing Cont.Eye Tattooing Cont.
• Corneal tattooing is dangerous for aCorneal tattooing is dangerous for a
number of reasons, because in additionnumber of reasons, because in addition
to the usual risks the cornea versionto the usual risks the cornea version
can include infection, perforation,can include infection, perforation,
hemorrhage, scarring, and blindness. Ithemorrhage, scarring, and blindness. It
started as a means of repairing eyestarted as a means of repairing eye
damage and covering scarring, but it'sdamage and covering scarring, but it's
becoming a more and more popularbecoming a more and more popular
cosmetic procedure.cosmetic procedure.

42. Eye Tattooing Cont.Eye Tattooing Cont.
• IfIf you worry about regretting that yin-you worry about regretting that yin-
yang symbol on your ankle, just thinkyang symbol on your ankle, just think
how you'll feel with kaleidoscope eyes.how you'll feel with kaleidoscope eyes.
• So would you let a tattoo artist stick aSo would you let a tattoo artist stick a
needle in your eye? Talk about regret!needle in your eye? Talk about regret!