1. Psychology 210
Lecture 4
Kevin R Smith

2. Vision Sensory System Perceptual System The eye
Exactly what we sense from our environment
Perceptual System
The brain
How we put together what we sense into a visual picture

3. The brain constructs our environment

4. Multiple experiences of an item lead to different interpretations

7. The Visual Sensory System
Light is made of waves
Wavelength
Different colors have different wavelengths
Amplitude
Different amplitudes lead to differences in brightness
Visible spectrum
400nm to 750nm
ROY G BIV
Short wavelengths are near blue and violet
Long wavelengths are near red and orange

8. Properties of Light and Waves
The color of an object is determined by its abilities across two dimensions
Absorption
Reflection
Colors that are reflected are the colors that we see
A red sweater is red because it reflects wavelengths that we perceive as red
Other wavelengths would be absorbed and NOT visible as a color for this sweater

9. Properties of Light and Waves
Black is a color that absorbs all other colors
ie. It is the absence of reflected color
White is a color that reflects all other colors
ie. It is the presence of all colors
prisms
White object

10. Properties of Light and Waves
Refraction
The change of direction of the waves
Occurs in water
Different substances refract light differently

11. The eye Sclera Outer covering that protects the eye and gives it shape
Cornea
Protective covering for the eye
Begins to bend the light waves and focus them
Aqueous humor
Fluid filled area behind the cornea
Provides nutrients to the cornea and lens

12. Parts of the eye Pupil Lens Vitreous humor
Area in the center of the eye
Controls the amount of light that enters
Iris
The muscle that controls the widening or narrowing of the pupil
Lens
Bend to focus light onto the retina
Accommodation
The process of the bending of the lens to properly focus the image on our retina
Vitreous humor
Gives the eye its shape
Does not regenerate
The vitreous humor your born with is what you still have
Floaters
Debris that gathers in the vitreous humor and casts shadows onto the retina

14. Retina
Translates light waves into an electrical signal our brain can process
Concave
Object on retina is translated upside-down
Photoreceptors
Rods and cones
Optic Disk/ Optic Nerve
Area in the retina where nerves and blood vessels exit the eye
Forms a blind spot
Fovea
Area in center of retina

15. Layers of the Retina Four main types of visual processing neurons
Ganglion cell layer
Amacrine and bipolar cell layer
Horizontal cells
Visual Sensory Neurons
Photoreceptors
Rods
Cones

16. Rods and Cones
Where a sensory signal (light waves) gets changed into electrical energy
Process called transduction
Rods
Sensitive to black and white
Most of them in periphery
Cones
Sensitive to color
Most of them in fovea

17. Rods Contain rhodopsin 120 million in a human eye
Responsible for night vision
Very sensitive to light
Very poor clarity

18. Cones 6 million in the human eye
Responsible for vision in bright light
Excellent clarity
3 different types with different pigments

19. Cones
Three different types
Blue, short
Green, medium
Red, long

21. Horizontal Cells Integrate information from the photoreceptors
Transfer that information to bipolar cells

22. Bipolar cells Receive input from horizontal cells and photoreceptors
Amacrine Cells
Bipolar cells
Receive input from horizontal cells and photoreceptors
Transmit information to amacrine cells
Contain receptive fields
Antagonistic center-surround organization
Horizontal cells
photoreceptors

24. Amacrine Cells Respond to changes in the visual environment
Connect bipolar cells, ganglion cells, and other amacrine cells

25. Ganglion cells Receive input from bipolar and amacrine cells
Same center-surround receptive fields found in bipolar cells
On-center bipolar fields connect to on-center ganglion cells
Off-center bipolar fields connect to off-center ganglion cells

27. What do receptive fields do?
On-center and off-center fields provide for greater acuity
Large unchanged surfaces don’t activate the neurons as well as changing surfaces with lines, cracks, and ends

29. Types of Ganglion cells
Three types
P cells: Parvocellular
M cells: Magnocellular
Non P or M cells

30. Pathway to the Brain Optic nerve
Group of ganglion axons exit the eye
Superior Colliculus (part of the tectum)
Thalamus- Lateral Geniculate Nucleus
Visual cortex- V1, V2, V3, V5 (MT)

31. Contralateral organization
Visual hemifields in space are contralaterally organized
Not the contralaterally organized by the eyes

32. The Thalamus The lateral geniculate nucleus (LGN)
6 Layers: Keep much of the information seperated
Parvocellular and Magnocellular information go to different layers
Non P and M projections go between the other layers
Information from each eye goes to different layers
Displays retinotopy

33. What is retinotopy?
A B C D E F G H I J K L

34. Primary Visual Cortex Located in the Calcarine Sulcus (Occipital Lobe)
Also referred to as
Striate cortex
Brodmann Area 17 V1

35. Cortical organization of V1
Cells don’t like spots!
They like lines/edges
Retinotopically organized
Simple cortical cells
Respond to edges from a specific location
Complex cortical cells
Respond to edges from a larger area than simple cells
Orientation selective
Often movement direction selective

36. Other properties of V1
Cortical magnification (half of V1 is devoted to fovea)
Cells often respond to input from either eye, but with a preferred eye (“ocular dominance”)
Ocular dominance columns
M & P pathways project to different layers
Response preferences are organized into columns (ocular dominance, orientation, visual field location)

37. Organization in V1

38. Other Visual Areas: V2, V3…
Also retinotopically organized
V3 encodes colors

39. Visual Pathways 2 Main pathways Dorsal stream Ventral Stream
Also called the “where” stream
Processes where things are in space
Ventral Stream
Also called the “what” stream
Processes what things are

40. The “Where” Stream Contains MT (area V5) Visual motion area
Integrates with the “where stream of the auditory system in the parietal lobe to construct a full picture of the environment

41. The “What” Stream Contains the Fusiform Face Area (FFA)
Responsible for recognition of faces
Much debated

42. The FFA debate

43. The FFA debate Expert vs face area
Scientists argue that the FFA is not sensitive to faces, but instead is sensitive to identification of things that we can expertly identify
We’ve all seen so many faces that we are effectively “face experts”
Bird watchers show increased activation when identifying various types of birds

44. Greebles
Face-like
Train people about the different types and check their activation
The debate is still going on whether a face area exists
Nancy Kanwisher
Isabel Gautier

45. Problems of the visual system
Nearsightedness
Focuses image before retina
Can see close, not far
Farsightedness
Focuses image beyond retina
Can see far, not close
Astigmatism
Aspherical cornea

46. Color processing theories
Young-Helmholtz theory
Trichromacy
Found in the retina
Opponent process theory
Red-green, blue-yellow, and black-white
Input from one color inhibits the other color
Found beyond the retina
Evidence from afterimages