Visual System

Question 1

Visual Agnosia

Answer 1

problems in perception (not sensation)

Question 2

Visual Perception: Light

Answer 2

range of electromagnetic radiation (particles and waves)
- particles are photons
- waves of various lengths
(we don’t see all waves)

Question 3

the eye

Answer 3

the light has to go through a lot of tissue before reaching the retina all the way back where it get perceived

Question 4

Retina

Answer 4

photoreceptions absorb the light
rods and cones

Question 5

rods

Answer 5

responsible for low levels of stimulation (e.g. night vision or dim lighting)
- 120 million
CLOSER TO PERIPHERY

Question 6

cones

Answer 6

responsible for intense light (day vision)
- 6 million
- red, gree, and blue
-gives visual resolution/acuity
CLOSER TO FOVEA

Question 7

optic nerve

Answer 7

axons of the cells that have collected information in the retina and sends it to the brain

Question 8

optic chiasm

Answer 8

where the brain separates information to get the LGN (lateral geniculate nucleus)

Question 9

ipsilateral

Answer 9

same side

Question 10

contralateral

Answer 10

opposite side

Question 11

blind spot

Answer 11

• at 17 degrees
• the other eye is functioning for you
• we mentally reconstruct the blindspot
• blindspot is created because the axons of the retinal ganglion cells are coming out

Question 12

first synapse in the LGN

Answer 12

3 layers receive information from one eye
3 layers receive information from the other eye

Question 13

LGN to V1

Answer 13

• many LGN cells synapse onto one V1 Cell
• receptive field of the LGN combine to make a larger receptive field in the V1 cells

Question 14

V1

Answer 14

• organized into cortical modules (like little slices of cubes)
• cortical module holds the color and orientation
• helps make up the map of the “pixels” you can see

Question 15

orientation

Answer 15

shapes, angles, size, edges → how something is composed

Question 16

blind sight

Answer 16

never synapses onto the LGN, it goes to the superior colliculus and goes directly to the parietal cortex (bypasses LGN and goes to parietal)

Question 17

LGN

Answer 17

• retinotopically organized –> spatial map

Question 18

Top 4 Layers - Parvo (slow)

Answer 18

-larger cells
- color orientation
- ventral pathway
- had the fovea which has cones, which do color

Question 19

Bottom 2 - Magno (fast)

Answer 19

• smaller cells
  -input from the periphery
  gives motion

Question 20

10%

Answer 20

of information goes directly to the parietal cortex

Question 21

left visual field

Answer 21

nasal (inner left eye)
temporal (outer right eye)

Question 22

right visual field

Answer 22

nasal (right inner eye)
temporal (left outer eye)

Question 23

preferences of photoreceptors

Answer 23

short, medium, long waves
high intensity lights (cones)
low intensity (rodes

Question 24

Visual Cortex (V1)

Answer 24

• organizes color and orientation into cortical modules
• if damage to entire V1 in left hemisphere –> then you cannot see anything in right eye
  = damage = completely bling

Question 25

V2

Answer 25

detects corners (not just edges)

Question 26

V4

Answer 26

• detects curvature and actual computation of color occurs here
• if someone has damage –> color blind
• color processing
• blindness = grayscale

Question 27

cortical visual areas

Answer 27

• optimal stimulus
• more complex along route
• bidirectional connectivity

Question 28

Retinotopic mapping

Answer 28

• put someone in MRI and show them a rotating checkerboard on a circle
• can identify the regions in the cortex and ask questions about what the groups of cells are doing

Question 29

Hierarchy

Answer 29

Retina → points of light, very small
LGN → On/off cells, bit larger
V1 → larger RFs, orientation selectivity
V2-4 → larger Rfs, edges, T-junctions, curvature (early stages of visual processing; the cells have preferences)

Question 30

Rods → LGN M cells → V1

Answer 30

Movement and contrast sensitive
Color and location insensitive

Question 31

Cones → LGN P cells → V1

Answer 31

Color and orientation selective
Contrast insensitive