Higher visual processing Flashcards
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
