The Visual System: The Structure of the Visual System

1
The Visual System The Structure of the Visual
System

• Module 9 Sensation

2
Cornea

• The clear bulge on the front of the eyeball
• Begins to focus the light by bending it toward a
  central focal point
• Protects the eye

3
Parts of the Eye Cornea
4
Iris

• A ring of muscle tissue that forms the colored
  portion of the eye creates a hole in the center
  of the iris (pupil)
• Regulates the size of the pupil by changing its
  size--allowing more or less light to enter the
  eye

5
Parts of the Eye - Iris
6
Pupil

• The adjustable opening in the center of the eye
  that controls the amount of light entering the
  eye (surrounded by the iris)
• In bright conditions the iris expands, making the
  pupil smaller.
• In dark conditions the iris contracts, making the
  pupil larger.

7
Parts of the Eye - Pupil
8
Lens

• A transparent structure behind the pupil focuses
  the image on the back of the eye (retina)
• Muscles that change the thickness of the lens
  change how the light is bent thereby focusing the
  image

• Glasses or contacts correct problems in the lens
  ability to focus.

9
Parts of the Eye - Lens
10
Nearsighted - Myopia
11
Farsighted - Hyperopia
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
Retina

• Light-sensitive surface with cells that convert
  light energy to nerve impulses
• At the back of the eyeball

16
Parts of the Eye - Retina
17
Receptor Cells

• These cells are present in every sensory system
  to change (transduce) some other form of energy
  into neural impulses.
• In sight they change light into neural impulses
  the brain can understand.
• Visual system has two types of receptor cells
  rods and cones

18
Rods

• Visual receptor cells located in the retina
• Can only detect black and white
• Respond to less light than do cones

19

• Visual receptor cells located in the retina
• Can detect sharp images and color
• Need more light than the rods
• Many cones are clustered in the fovea.

Cones
20
(No Transcript)
21
Fovea

• The central focal point of the retina
• The spot where vision is best (most detailed)

22
Parts of the Eye - Fovea
23
Visual Processing in the Retina
24
Optic Nerve

• The nerve that carries visual information from
  the eye to the occipital lobes of the brain

25
Parts of the Eye Optic Nerve
26
Blind Spot

• The point at which the optic nerve travels
  through the retina to exit the eye
• There are no rods and cones at this point, so
  there is a small blind spot in vision.

27
Parts of the Eye Blind Spot
28
(No Transcript)
29
The Visual System Color Vision

• Module 9 Sensation

30
Color Vision

• There are two theories of color vision
• Trichromatic Theory
• Opponent-Process Theory

31
Trichromatic (three-color) Theory

• Theory of color vision that says cones are
  tuned to be sensitive to red, green and blue
  light
• All the colors we see are a combination of these
  three colors.
• Similar to the design of a color TV

32
How do we see color?

• Trichromatic (three color) Theory
• three different retinal color receptors
• Red green blue

33
Can you see what is in the middle?
34
Color Deficient Vision

• People who lack one of the three types of cones
• Usually the red or green receptors are missing
• Usually referred to as color blindness
• In inherited and found more in males

35
Red-Green Color Blindness
36

• Opponent-Process Theory- Vision from opposing
  pairs of color receptors- only one side ON at a
  time

37
Opponent-Process Theory

• Sensory receptors in the retina come in pairs
• Red/Green
• Yellow/Blue
• Black/White
• Only one side is on at a time

38
Opponent Process Theory

• ON OFF
• red green
• green red
• blue yellow
• yellow blue
• black white
• white black

39
Afterimage Effect
40
(No Transcript)
41
(No Transcript)
42
(No Transcript)
43
(No Transcript)
44
(No Transcript)
45
Opponent-Process Theory

• If one sensor is stimulated, the other is
  inhibited
• If one sensor is over-stimulated, and fatigues,
  the paired sensor will be activated, causing an
  afterimage