Lecture 11

Question 1

REFER TO LECTURE 11 FOR SUMMARY OF VISUAL SYSTEM AND CELLS

Answer 1

NOTE

Question 2

Amblyopia

Answer 2

• occurs during development (before age 6) where it stops the two eyes working together
• anything that leads to imbalance or mis-integration of the signals from two eyes

Question 3

ocular dominance columns in V1

Answer 3

• alternate between left and right
• highlighted as alternating bars when injected with radioligand in V1

Question 4

effects of monocular deprivation on ocular dominance columns in V1

Answer 4

• V1 eyes deprived of light temporarily in development after birth blocks vision from that eye
• results in wider ocular dominance columns of the non-deprived eye even years after (permanent change the way the cortex is organised even if it happened during young age)

Question 5

timing of monocular deprivation is critical

Answer 5

• as you get older you need a longer period of monocular deprivation for the same effect / maybe no effect after adolescence
• better to do when younger

Question 6

Hubel and Wiesel ocular dominance scale

Answer 6

• quantifies electrophysiological responses of V1 cells to stimuli applied to left or right eye on a scale
• contralateral (!) –> ipsilateral (7)

Question 7

ocular dominance scale in monocular deprivation

Answer 7

• majority of cells are driven exclusively by non-deprived eye - more activity at 7 (ipsilateral)

Question 8

which eye was deprived ?

Answer 8

left eye

Question 9

developmental changes in V1

Answer 9

• axons of left and right eye become more separated and more branched
• to do with ocular dominance columns

Question 10

functional changes in V1 following monocular deprivation

Answer 10

signals from deprived eye are actively suppressed by local interneurons

Question 11

Stroke types that can causes vision problems

Answer 11

• occlusive
• hemorrhagic

Question 12

occlusive

Answer 12

• > 80% of strokes
• due to closure of a blood vessel
• blood clot, embolism
• atheroscelerosis

Question 13

hemorrhagic

Answer 13

• due to rupture of a blood vessel
• hypertension, aneurysm

Question 14

scotoma

Answer 14

‘a blind or partially blind spot in the visual field’

• occurs if stroke affects V1

Question 15

absolute scotoma

Answer 15

no remaining vision

Question 16

relative scotoma

Answer 16

some remaining vision

Question 17

hemianopic scotoma

Answer 17

one half of visual field gone

Question 18

facultative / suppression scotoma

Answer 18

in alternating foveation in squint conditions

Question 19

V1 blood supply

Answer 19

posterior cerebral artery

Question 20

what happens if artery is blocked

Answer 20

widespread loss of vision across one full hemisphere

Question 21

homoymous hemianopia

Answer 21

• loss of vision of the same side of the world on both eyes
• often as a result of V1 damage
• but are aware they can’t see that part of the world - ‘blindsight’

Question 22

blindsight

Answer 22

• when guessing is good / better than chance e.g. with orientation and colour
• result of extensive damage to striate cortex
• patient ‘unaware’of blind hemifield

Question 23

mechanisms of ‘blindsight’

Answer 23

• proportions of V1 remain intact and active
• residual vision in higher cortices
• can be tested by V1 lesions in monkeys

Question 24

role of V1 in blindsight

Answer 24

• removed V1 in 3 monkeys
• fixation task
• detection of targets in blind hemifield still much better than chance

but in another test
with probe trials where a target appears in the blind field but they are given an option to touch the rectangle if nothing appears, lesioned monkeys respond as if no target appears, showing blindsight

Question 25

Zihl's patient

Answer 25

had motion agnosia

Question 26

motion agnosia

Answer 26

- a patient with intact visual fields lost all perception of motion and could not distinguish between stationary and moving objects - loss of movement vision in all three dimensions e.g. fluid would appear as a glacier e.g. tea or coffee e.g. people are not seen moving e.g. unable to cross roads as can't see the speed of a vehicle

Question 27

what is motion agnosia due to

Answer 27

- bilateral damage to V5 (MT)

Question 28

parietal damage

Answer 28

- gives rise to errors in interpretation and interaction with objects in space - e.g. misses glass even though gaze is directed to it when pouring water

Question 29

neglect

Answer 29

- extreme parietal cortex damage - loss of one half of the world - different to scotoma, don't interact with things on other side of the world they can't see - arrangement of the world spatially is wrong - (supra-retinal reference frame)

Question 30

supra-retinal reference frame

Answer 30

more than what is immediately visible, it is the brain's map of the world

Question 31

where is neglect more often seen

Answer 31

damage to right parietal cortex (left side of the world)

Question 32

what may neglect may be due to

Answer 32

- competition or inability to disengage attention from one side of the brain

Question 33

prosopagnosia

Answer 33

- object agnosia - inability to recognize faces

Question 34

agnosia

Answer 34

loss of knowledge - Freud

Question 35

what is prosopagnosia due to

Answer 35

- damage to 'what' stream / inferior temporal cortex - can identify what a face is and things on a face and emotions, but not individual identities (maybe even own face) - identities not lost, only the connections between particular faces and identities

Question 36

V1 damage

Answer 36

scotoma, blindsight

Question 37

temporal damage

Answer 37

prosopagnosia

Question 38

V5/MT damage

Answer 38

motion agnosia

Question 39

parietal damage

Answer 39

spatial neglect