Lecture 12 - Disorders of vision

Question 1

Blindness

Answer 1

Catastrophic but no mysterious

Question 2

Nasal retinas

Answer 2

Look out

Question 3

Temporal retinas

Answer 3

Look in

Question 4

2 parts to retinas

Answer 4

Temporal and nasal

Question 5

Left nasal retina

Answer 5

projects to the left visual field of the left eye

Question 6

Left temporal retina

Answer 6

Projects to the right visual field of the left eye

Question 7

Right monocular blindness

Answer 7

optic nerve from right eye is severed

Question 8

Bitemporal hemianopia

Answer 8

loss of peripheral vision, tumour that just damages the crossing fibres

Question 9

Left homonymous hemianopia

Answer 9

Left temporal and right nasal blindness

Question 10

Left homonymous hemianopia with macular sparing

Answer 10

Left homonymous hemianopia with macular sparing - Left temporal and right nasal blindness, damage to primary visual cortex, central vision is spared and this is known as macular sparing and this is because central vision is critical to us and is representing in multiple areas of the primary visual cortex

Question 11

Blindsight - Patient DB

Answer 11

Can localise objects that he swears he can not see
Intact field has nothing wrong so can see presented information in it, in the blindfold he can’t see anything but can point to where information is with good accuracy in the blind field
Present information in blind filed and move it a bit and then patient DB can localise it
Blind but some sort of conscious information must be getting through to the brain

Question 12

Blindsight pathway conclusion

Answer 12

Skipping V1 and going to V5 that then goes to the parietal lobe via the dorsal pathway accounts for 5% of visual pathways

If you do not go through V1 then you will not be able to see the object, but because it gets to the dorsal pathway, which only cares about where it is in space, people can know where it is

V1 taken out which is the basic building block of vision so the visual system cannot put together a representation of the object if you take away the part of the brain that is processing the lines and every object has some sort of link it. So DB is not able to tell you what something is but the information is still getting through the dorsal pathway.

Jiggling the object - V5 neurons care about movement, moving object in field causes DB to feel like there is an object moving but he cannot tell you what it is because it bypasses V1

Question 13

Achromatopsia

Answer 13

Achromatopsia = absence of colour vision

Damage to V4

V4 is the colour cortical area, it is part of the cortex that processes colour information, situated on the outside of the cortex rather than buried inside

It is rare to only get damage at V4

If damage occurs to V4, people see in shades of grey

Colour blindness does not mean that you have V4 damage, it usually missing cones in the cornea

Question 14

Akinetopsia

Answer 14

Akinetopsia = Absence of motion vision

Damage to V5 (VT)

People that have obtained damage to V5 cannot see the world when it is set in motion

Seeing the world in a freeze frame, don’t see the fluid motion in between

Difficult to pour tea into a cup for example because the fluid rising is motion and therefore they can not see it

Question 15

Apperceptive agnosia

Answer 15

Failure of object recognition due to a failure of visual perception - failure to identify an object due to the absence of perception, inability to describe something yet be able to see it

Preserved elementary visual function -patients can see colour and motion but cannot recognise

Poor matching and copying

Neuropathology - often a result of carbon monoxide poisoning, mercury poisoning, causes a small amount of damages at different places, not an overall damage

Question 16

Peppery mask hypothesis

Answer 16

Apperceptive agnosia - lots of blind spots in visual world

Damage to V1 therefore have this peppery mask vision, V1 has retinotopic mapping (point to point) therefore damaging this region causes a blindspot (scotoma), extensive V1 damage causes multiple blindspots in the visual field everywhere

The Peppery Mask account is a theory for apperceptive agnosia. In summary, the area of the visual cortices is covered or ‘peppered’ with multiple scotomas. Since they are scattered over the visual field, perception is degraded in that person (Gilds 567).

Question 17

Dorsal simultagnosia

Answer 17

Failure of object recognition due to a spacial perceptual impairment - failure of scene recognition

Preserved elementary visual function

Can recognise objects but no more than one at a time
Can’t recognise what is going on in the scene I.e. lack of integration of the objects, can name objects but can’t say what is happening as a scenario in an image

Neuropathology
Occipital-parietal area
‘Where’ pathway is damaged therefore parietal

Question 18

Ventral simultagnosia

Answer 18

Failure of object recognition due to a complex perceptual impairment

Preserved elementary visual function

Can recognise objects but not more than one at a time BUT… can see multiple objects

Neuropathology
Ventral stream damage (beyond V1, beyond primary visual cortex)

Question 19

Associative agnosia

Answer 19

Failure of object recognition due to a higher-order complex perceptual impairment

Preserved elementary visual function

Seemingly normal copying - cannot tell you what they copy

However, perception is not normal…Copying is accurate but slavish (lots of energy is required to get everything right)

Study
Control population would be able to identify occluded figures with high occlusion rates than the group that has sustained damage to the ventral system
Push the system then you will see that patients with associative agnosia will drop out quicker than the control population