problem 2 - the visual brain

Question 1

the lateral geniculate nucleus (LGN)

Answer 1

• in the thalamus
• regulates info coming from the retina to the visual cortex
• for every 10 nerve impulses the LGN sends back 4 to the cortex
• LGN neurons have the same center-surround configuration as retinal ganglion cells = respond best to small spots of light on the retina

Question 2

layers of the LGN

Answer 2

LGN is organized into 6 layers
* each layer receives signals from only one eye
* 1, 4 & 6 = contralateral eye
* 2, 3 & 5 = ipsilateral eye
* each eye sends half of the information to the LGN in left hemisphere and half to LGN in right

Question 3

magnocellular cells (LGN)

Answer 3

size: large

location: layers 1 & 2

function: for dynamic visual properties like movements

Question 4

parvocellular cells (LGN)

Answer 4

size: small

location: layers 3, 4, 5 & 6

function: for texture & color

Question 5

koniocellular cells (LGN)

Answer 5

size: very small cell bodies

location: between each layer of M & P cells

function: for color

Question 6

super colliculus

Answer 6

an area involved in controlling eye movements & other visual behaviors that receives about 10% of the fibers from the optic nerve

Question 7

striate cortex (aka primary visual receiving area)

Answer 7

in the occipital lobe

3 types of cells: simple cortical, complex & end-stopped

neurons respond to some patterns of light & not to others

Question 8

simple cortical cells (striate cortex)

Answer 8

• have excitatory & inhibitory areas
• arranged side by side
• respond best to bars of a particular orientation (specific orientation)

Question 9

complex cells (striate cortex)

Answer 9

• respond best to movement of a correctly oriented bar across the receptive field
• respond best to a particular direction of movement

Question 10

end-stopped cells (striate cortex)

Answer 10

• fire to moving lines of a specific length or to moving corners or angles
• respond best when the corner moves upward

Question 11

orientation tuning curve

Answer 11

indicates the relationship between orientation and firing

determined by measuring the responses of a simple cortical cell to bars with different orientations

Question 12

selective adaptation

Answer 12

if neurons fire for long enough, they become fatigued, or adapt - this adaptation causes 2 physiological effects:
1. The neuron’s firing rate decreases
2. The neuron fires less when stimulus is immediately presented again

Adaptation is selective because only the neurons that respond to verticals or near-verticals adapt, and other neurons do not

Question 13

selective rearing

Answer 13

if an animal is reared in an environment that contains only certain types of stimuli, then neurons that respond to these stimuli will become more prevalent

use it or lose it principle

Question 14

retinotopic map

Answer 14

a map in which each point on the LGN corresponds to a point on the retina

occur in each of the 6 layers and the maps of each of the layers line up with one another

Question 15

maps in the striate cortex

Answer 15

Similar to retinotopic maps: nearby points in the striate cortex receive signals from nearby locations on the retina

Cortical magnification factor: apportioning the small fovea with a large area on the cortex

Question 16

location columns (striate cortex)

Answer 16

are perpendicular to the surface of the cortex so that all of the neurons within a location column have their receptive fields at the same location on the retina

Question 17

orientation columns (striate cortex)

Answer 17

each column contains cells that respond best to a particular orientation

orientation of columns depends on the orientation that they respond to

Question 18

ocular dominance columns (striate cortex)

Answer 18

neurons in the cortex are also organized with respect to the eye to which they respond best = each neuron encountered along a perpendicular electrode track responds best to the same eye

Most neurons respond better to one eye than to the other = ocular dominance

Question 19

hypercolumns (striate cortex)

Answer 19

all 3 types of columns can be combined into this larger unit
* has many columns that all together are responsible for all functions
* is like an idea (not real)

Question 20

the what pathway (vision)

Answer 20

ventral pathway - temporal lobe
* associated with object discrimination

Question 21

the where pathway (vision)

Answer 21

dorsal pathway - parietal lobe
* associated with landmark discrimination
* is for taking action & knowing the location of the object (where)
* also involves physical interaction with the object (how)

Question 22

single dissociation

Answer 22

2 groups are tested on 2 tasks and between group difference is apparent only in one task

Used to know if a certain brain area is involved in a certain function
* Group 1 would be control, group 2 would be people with brain damage for example
* Both groups do the same 2 tasks - one task they would both perform the same and in the other task the experimental group would perform worse

Question 23

double dissociation

Answer 23

Has 3 groups
1. group impaired with area A
2. group impaired with area B
3. group with no impairements
* Performances can be compared to each other
* stronger evidence - can see exactly where the impairment comes from

solves problem w single dissociation: no longer reasonable to argue that a difference in performance results merely from the unequal sensitivity of the two tasks

Question 24

achromatopsia

Answer 24

dont see colors
* disturbance in the CNS
* seeing in shades of gray (depth and texture remain intact)
* associated with lesions encompassing V4 and region anterior to V4 (ventral pathway)

Question 25

akinetopsia

Answer 25

not seeing movement / loss of motion perceptin
* Seeing moving objects as snapshots → one position and suddenly another
* Lesion at V5/MT – middle temporal area
* Only when lesion is bilateral = akinetopsia, people can perceive motion as long as V5 is intact in at least one hemisphere