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Flashcards in Higher visual processing Deck (30)
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 What sort of visual information do M and P ganglion cells transmit?

M - motion

P - colour 


Where do M and P ganglion cells terminate in the primary visual cortex?

M cells - layer 4Ca

P cells - layer 4Cb


Which layer of the visual cortex is the input layer for sensory information?

Layer 4


How is information from M and P ganglion cells segregated?

Input to different regions of the visual cortex 

M - 4Ca

P - 4Cb


Where do cells in layer 4Ca of the visual cortex project to?

Layer 4B


Describe the characterisitcs of neurons in layer 4B of the visual cortex?

Directionally selective neurons

Only respond to stimuli moving in a certain direction

Allow us to encode motion 


How much of the brain is involved in vision?

Approximately 40%

V1 + extrastriate cortical areas


What are the two parallel visual streams of information that originate from the visual cortex?

Dorsal pathway: takes info from M cells, for 'where?'

Ventral pathway: takes info from P cells, for 'what?'


What is area MT?

What is its function?

Middle temporal lobe

Area specialised for processing object motion (objects moving beyond a certain speed)

Culmination of dorsal stream


Describe the inputs to area MT?

Receives retinotopic input from a number of cortical areas incl V2 and V3

Receives input from cells in Layer 4B of V1


Which cortical area is specialised for processing object motion?

Area MT


Describe the neurons in area MT?

Large receptive fields 

Respond to stimulus movement (respond to different types of motion)

Directionally selective



Describe how different colours a perceived?

Mixing of primary colours (blue, red and green)

Determined by how much each of the three colours signlas down to the ganglion cells (combination of all three cones)


Describe the receptive field of P ganglion cells?

Colour opponent centre-surround



How is comparison achieved in colour vision?

Comparison of what ganglion cells have been told comes from photoreceptors 

Depends on centre-surround receptive field of ganglion cells 

Comparisons: red and green, blue and yellow


Describe what happens when a red/green centre-surround ganglion cell is stimulated with red light in its centre?

PRs hyperpolarised by red light > BCs > ganglion cell is depolarised by light 


Describe what happens when a red/green centre-surround ganglion cell is stimulated by green light in the periphery?

Green cones stimulated in periphery > hyperpolarised > HCs hyperpolarised by light > singal back to red cone > maximally inhibited 


Describe what happens when a red/green centre-surround ganglion cell is stimulated by red light in both the centre and periphery?

Get an in between response > brain deletes it

Brain only wants maximal stimulation or maximal inhibition 


Describe what happens to information from the P ganglion cells?

Inputs into V1, then travels down ventral stream to Area V4/Area IT


Describe the properties of the neurons in Area V4/IT?

Large receptive fields

Both colour and orientation selective 


What is the function of Area V4?

Important for perception of shape and colour


What is the function of Area IT?

Important for object recognition, including faces

Neurons respond to wide variety of abstract shapes and colours 


What is blindsight?

Ability in some blind people for motion detection system to still work

Pathway from LGN to area MT 


What is the difference between colour vision deficiencies and colour blindness?

Colour vision deficiencies: unable to perceive some colours, confuse certain colours 

Colour blindness: inability to perceive any colour 


How may colour vision deficiencies arise?

Can be acquired or inherited

More commonly inherited 


Describe the three types of colour vision defects?

Which is most common?

Monochromacy: only have one type of cone

Dichromacy: have only two functional cones

Anomalous trichromacy: have all three cones, but one of them express abnormal pigment and doesn't work the same as normal cones (most common)


How are people that lack:

i) red cones 

ii) blue cones

iii) green cones described?

i) Protanope

ii) Deutanope

iii) Tritanope


How are people that have abnormal:

i) red cones

ii) green cones

iii) blue cones described?


i) Protanomal

ii) Deutanomal

iii) Tritanomal


What is the most common type of colour vision defetc?

Deutanomal: have green cone, but it doesn't work properly 


How is colour blindness tested?

Detection test (plates with numbers)

More than 6 wrong > other testing to determine which type