1. The Visual System: The Nature of Light

2. Electromagnetic Energy
An energy spectrum that includes X-rays, radar, and radio waves
A small portion of the spectrum includes light visible to the human eye
Light can be described as both a particle and a wave

3. Electromagnetic Spectrum of Light
Gamma
rays
X-rays
Ultra-
violet
Infrared
Radar
Broadcast
bands AC
circuits
Visible light
Prism
White
light
400
500
600
700 10 -5 -3 -1 1 3 5 7 9 11 13 15 17
Wavelength in nanometers (billionths of a meter)
Hockenbury Powerpoint, slides (Schulman)

4. Hue
Hue is the color of light as determined by the wavelength of the light energy
Includes: red, orange, yellow, green, blue, indigo and violet (ROY G. BIV)
The eye can detect 7 million separate hues

5. Amplitude The brightness of light as determined by height of the wave
The taller the wave, the brighter the color

6. The Visual System: The Structure of the Visual System

7. Purpose of the visual system
Vision
Purpose of the visual system
Transduction: transform light energy into an electro-chemical neural response (action potential & synaptic transmission)
represent characteristics of objects in our environment such as size, color, shape, and location

8. Parts of the Eye – Cornea

9. 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

10. Parts of the Eye - Iris

11. 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

12. Parts of the Eye - Pupil

13. 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.

14. Parts of the Eye - Lens

15. 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 (Accommodation)
Glasses or contacts correct problems in the lens’ ability to focus.

16. The Cosmic Flower
Does this picture seem to pulsate? Because the lens of your eye is not perfectly round some parts of what you look at are blurry. Your eyes make micro movements to try to put this entire picture into focus and this creates the pulsation.

17. The lens correctly focuses the image onto the back of the eye (retina).

18. (Myopia)
The lens correctly focuses the image onto the back of the eye (retina).
Misshapen eye focuses light rays from a distant object in front of the retina. Can see near but not far.

19. The lens correctly focuses the image onto the back of the eye (retina).
(Myopia)
Misshapen eye focuses light rays from a distant object in front of the retina. Can see near but not far.
Misshapen eye focuses light rays from near objects past the retina. Can see far but not near.
(Hyperopia)

20. Other Causes of Poor Vision
Astigmatism – Uneven curvature of the cornea causes multiple focus points/images on the retina resulting in blurry vision.

21. Other Causes of Poor Vision
Presbyopia – form of farsightedness caused when lens becomes brittle & inflexible. Usually starts to happen in your early 40’s
Reading glasses will correct this.

22. Farsightedness
Nearsightedness
Astigmatism
Presbyopia

23. Parts of the Eye - Retina

24. Retina
Light-sensitive surface with cells that convert light energy to nerve impulses
At the back of the eyeball
Made up of three layers of cells
Receptor cells (Rods & Cones)
Bipolar cells
Ganglion cells

25. Parts of the Eye - Fovea

26. Fovea The central focal point of the retina
The spot where vision is best (most detailed – visual acuity)
Only cones are found in the Fovea

27. Receptor Cells (Rods & Cones)
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

28. Rods Visual receptor cells located in the retina
Can only detect black and white
Respond to less light than do cones
Located around the fovea. (remember pen-top demo from class)

29. Cones 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 at the center of the retina. (remember pen-top demo from class)

31. Watch Blue Man Group’s Rods & Cones Performance
Discovering PSY p 88 Photo at top of page

32. Distribution of Rods and Cones
Cones—concentrated in center of eye (fovea)
approx. 6 million
Rods—concentrated in periphery
approx. 120 million
Stare at a word and you’ll notice the others around it become blurred. (Clear word seen with cones, blurry area seen with Rods)
Blind spot—region with no rods or cones

33. The Hermann Grid
Are there gray dots between the squares? Rods in the periphery are responsible for this. When you look at an area directly there is no dot because you are using your cones but the periphery has dots because the rods are trying to do two things, show you there is a dark area and a light area.

34. Processing Visual Information
Rods & Cones transform light into action potential/synaptic transmission.
Bipolar cells—neurons that connect rods and cones to the ganglion cells
Ganglion cells—neurons that connect to the bipolar cells, their axons form the optic nerve
Optic chiasm—point in the brain where the optic nerves from each eye meet and partly crossover to opposite sides of the brain

35. Bipolar Cells Cells that form the middle layer in the retina
Gather information from the rods and cones and pass it on to the ganglion cells
Hundreds of Rods feed into 1 Bipolar Cell.
1 to 2 Cones feed into 1 Bipolar Cell.
This is why Cones have better visual acuity.

36. Ganglion Cells
Pass the information from the bipolar cells through their axons
Together these cells form the optic nerve.
The top layer of the cells in the retina

37. Receptive Fields and Rod vs. Cone Visual Acuity
Cones—in the fovea, one cone often synapse onto only a single ganglion cell
Rods—the axons of many rods synapse onto one ganglion cell
This allows rods to be more sensitive in dim light, but it also reduces visual acuity

38. Visual Processing in the Retina

39. Visual Processing in the Retina

40. Visual Processing in the Retina

41. Visual Processing in the Retina

42. Parts of the Eye – Optic Nerve

43. Optic Nerve
The nerve that carries visual information from the eye to the thalamus then on to the occipital lobes of the brain

44. Parts of the Eye – Blind Spot

45. Blind Spot
The point at which the optic nerve travels through the retina to exit the eye (Optic Disk)
There are no rods and cones at this point, so there is a small blind spot in vision. (do demo on page 98)
We don’t notice our blind spot because each eye compensates for the other or your brain “fills in” the missing background info. (Top-down process & Gestalt Theory)
Cover your right eye and stare at the can as you move closer to the screen. Notice the spider disappear in your peripheral vision?

46. Visual Pathway From the eye to the brain
Light travels through…
Cornea – Pupil – Lens – Fovea (retina) – Rods/Cones – Bipolar Cells – Ganglion cells (movement & light /color & detail) – Optic Nerve (blind spot) – Optic Chiasm (crossover point) – Thalamus – Occipital Lobe (Primary Visual Cortex)

47. How Can I Possibly Remember All of That in Order?
Cool = Cornea
People = Pupil
Like = Lens
Frosties = Fovea (Rods & Cones)
Because = Bipolar Cells
Gangsters = Ganglion Cells
Never = Optic Nerve
Cheat = Optic Chiasm
The = Thalamus
Officers = Occipital Lobe
Don’t like this one? Create Your Own!!!

48. Primary Visual Pathway: Thalamus processes info about form, color, brightness & depth
Secondary Visual Pathway: Midbrain processes info about the location of an object
Discovering PSY p 90 Fig 3.5
– feature detectors respond to things like angles, edges, lines & movement

49. Visual Adaptation
(a) A projector mounted on a contact lens makes the projected image move with the eye. (b) Initially the person sees the stabilized image, but soon she sees fragments fading and reappearing.

50. Visual Impairment
Play “Smart Glasses” (8:13) Segment #9 from Scientific American Frontiers: Video Collection for Introductory Psychology (2nd edition).
Watch in Class