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what is the dorsal visual stream?
what information does it carry?
where is it?
what would a lesion to the pathway cause?

the dorsal visual stream is the ''where'' stream of vision
it carries information about the location of an image
this stream is from V1 --> parietal lobe

a lesion of this stream would cause optic ataxia


what is the ventral visual stream?
where is it?
what information does it carry?
what would a lesion to the pathway cause?

the ventral visual stream is the ''what'' stream of vision
it carries information about what an object is
this stream is from V1--> infratemporal lobe

a lesion to this stream would cause visual agnosia


where is the visual cortex located?
what broadman number is it?

located in the calcrine sulcus
broadman number 17


what are the specialisation of the Parvocellular layers in the LGN? where do they project to in the cortex?

the parvocellular layers are specialised in seeing red/green vision and they're specialised in for high acuity vision

P cells project to layer 4b of the visual cortex and from there to the blobs (to see colour vision) and to the inter-blobs (to see high acuity vision)

from the interblobs --> interstripes --> V3/V4 (Acuity)
from blobs --> thin stripes --> V4 (colour vision)
from 4b --> thick stripes --> V5 (motion)


where are the blobs and interblobs located?
where the thin and thick and interstripes located?

1. located in layer 2 and 3 of V1
2. located in V2


what is the optic nerve formed of?

formed of the axons of the retinal ganglion cells


what information does the optic nerve carry?

the optic nerve carries information from both visual fields of an eye


what information does the optic radiation, LGN and visual cortex receive?

receives input from the contralateral visual field


what is the optic tract? what information does it carry? what would a lesion to the optic tract cause?

the optic tract is the nerve fibres that emerge from the optic chiasm -- the optic nerve travels to the lateral geniculate nucleus of the thalamus
the optic tract carries information from:
- contralateral nasal hemi-field
- ipsilateral temporal hemi-field

a lesion to this tract would cause:
- homonymous hemianopia
loss of vision in the contralateral visual field


what would cause bitemporal hemianopia? what is it?

- optic chiasm lesion perhaps due to a pituatory gland tumor

what is it?
- damage of the decussating hemi-nasal fibres
- it is the loss of vision in the temporal field


what would cause monocular blindness?

damage to the optic nerve


what is superior quadranopia? what is caused by?

this is loss of vision in the superior upper quadrant of the visual field

caused by damage in Meyer's loop:
- this carries information from the superior visual field
- Meyer's loop terminates under the calcrine sulcus


would lesion would cause optic ataxia?

superior parietal lobe lesion, disruption of the dorsal/where stream of vision


what lesion would cause visual agnosia?

lateral occipital lobe lesion, disruption of the ventral/what stream of vision


what lesion would cause akinetopsia?

lesion to the V5 area - because this area is associated with the preception of motion


what lesion would cause prosopagnosia?

lesion of the fusiform gyrus, because it has the fusiform face area - which is used to recognise faces

prosopagnosia - is seen due to lesion on the right FFG


what lesion would cause topographagnosia?

lesion of the parahippocampal gyrus, would no longer be able to recognise places


what lesion would cause contralateral neglect?
where is it usually?

lesion to the right angular gryus, would cause left neglect syndrome

usually the lesion occur to the right hemisphere


what lesion would cause achromotopsia?

a lesion to V4v - this area is associated with processing of colour vision


what lesion is alexia associated with?

lesion to the word form area, which is located on the left fusiform gyrus


what is meant by the term magnification factor?

mm of visual cortex per degree of visual field - the fovea is disproportionately represented


what is Hebb's law?

Hebb's law states that if pre-synaptic activity frequently coincides with the formation of post-synpatic spikes - the synapse becomes stronger

if the activity does not coincide, a weak synapse is formed?


how does congenital cataracts affect the eyes? and how does the treatment affect the eyes?

in congenital cataracts - the non-affected eye ends up dominating in layer 4C (expanding in terriorties, while the affected eye has its terriorities shrunken)

in treating catarcts - fix the eye surgically, and then patch the good eye - and this allows the bad eye to 'catch up' on ocular dominance competition
- although good eye will have good acuity vision
but there will still by dipolpia and squinting

this is because the binocular hard-wiring in layer 3 of the visual cortex - outlasts the monocular dominance - this means biocular signals are not wired and stereopsis is not possible


how does strabismus affect central visual processing?

strabismus means the visual fields of both eyes do not correspond to each other - and so no binocular hard wiring occurs - and stereopsis is not possible


in the optic tract - the fibres have two main pathways, what are they?

medial fibres:
- retino--tecto-striate pathway
- those fibres go the midbrain tectum, specfically the prectal area- where they're involved in pupillary reflexes

lateral fibres:
- retino-geniculo-striate pathways
- those fibres go the visual cortex
- they're involved in seeing an image


what type of image is formed on the retina from the visual field?

one which is rotated laterally and vertically