Primary Visual cortex REVISITED

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What are the 2 initial stages of the visual information processing?
The information from the left goes to the right primary visual cortex, whereas the information from the right goes to the left primary visual cortex
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What is the information processing stages in the primary visual pathway?
Retina --> Optic nerve --> Lateral geniculate body --> visual cortex
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What is an experimental strategy to reveal mechanisms of visual perception?
By studying the different neuronal responses at different stages of the visual cortex, for example, studying the optic nerve
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What are the two different types of photoreceptor?
Rods and Cones
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What are the rods used for?
More abundant, no colour discrimination, sensitive in low light levels, higher density in periphery and track high rate changes
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What are the characteristics of the cones?
Less abundant, colour discrimination, 3 types of different wavelengths, less sensitive to low light, higher concentration in the fovea, cannot follow rapid changes
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What can photoreceptors do?
Vary their voltage as they are stimulated whereas all subsequent cells vary spike rate
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What are photoreceptors detection of light translated into?
Excitation or inhibition of retinal ganglion cells
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What does the portion of the retina of visual neurons do?
Visual stimulation will evoke a change in the firing rate of a given visual neuron
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What is the substructure of the receptive field?
A description of how visual stimuli need to be presented in the receptive field of a visual neuron in order to evoke firing rate changes
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What do the retinal ganglion neurons receive input from?
Multiple photoreceptors
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Light presented in 'On' regions do what?
Excite cells
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Where as what do light in OFF cell regions do?
Inhibit celss
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How are ON and OFF regions organised?
In centre surround fashion
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ON centre/OFF surround cell: What happens?
Flashing small bright spots in the centre subregion increases the cell's response.
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What happens when you flash a bright annulus in the surround region?
This inhibits the cells response
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When is there little or no response?
To a full field spot of light that covers both the centre and the surround because the excitation in the centre cancels the inhibition from the surround
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What is this called?
lateral inhibition
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What arrangement does an OFF centre/ ON surround do?
Ganglion cell has the opposite arrangement. It gets inhibition from a small spot of light in the centre and excitation from an annulus in the surround
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What is the response rate of the cell?
Based on the sum of stimulation in ON region minus stimulation in the OFF region
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What does this enhance?
Contrast and boundaries
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Neurons in the lateral genticulate body respond to visual stimuli in what?
Similar ways to the retinal ganglion cells
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What are the functional significance of centre surround fields?
The world has a lot of things that stay constant, we don't need to keep responding to them, what counts the most are changes to boundaries, luminance of features is represented relative to surrounding, preserve appearance of objects regardless of lig
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What do retinal ganglion and LGN cells receive input from?
Cones and are sensitive to colour
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What do colour sensitive retinal ganglion and LGN neurons have?
receptive fields that show cell surround colour opponency
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For example?
Yellow On and Blue off
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Where is the primary visual cortex situated?
At the back of the brain near the occipital lobe
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What does V1 do?
Only gets activated with different orientations
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What is the first type of sensitive V1 neuron?
simple cells, Field have inhibitory and excitory regions, can be thought of as combining inputs from ON and OFF cells
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What is the second type of sensitive V1 neuron cell?
Complex cells
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What do complex cells do?
Fields have no discrete ON and OFF regions, best respond to moving stimuli, combine inputs from simple cells
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What is the retino topic map?
Orderly mapping of visual field on visual cortex
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What are modules
V1 is divided into small columnar modules that combine neurons sensitive to different aspects of stimuli presented in a small part of the visual cortex
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How do we result in perception and memory of holistic visual properties of whole objects and visual scenes?
The visual information from the modules of V1 need to be combined and further processed
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Where does this processing take place?
Visual association cortices (V2-V5)
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What is blind sight?
Subjects with lesions to primary visual cortex and apparent blindness can show appropriate responses to visual stimuli of which they are not conscious
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For example?
They can look or point toward visual stimuli: detection of movement, blindsight highlights that apart from primary visual pathway that is critical for conscious vision there are additional visual pathways
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Card 2

Front

What is the information processing stages in the primary visual pathway?

Back

Retina --> Optic nerve --> Lateral geniculate body --> visual cortex

Card 3

Front

What is an experimental strategy to reveal mechanisms of visual perception?

Back

Preview of the front of card 3

Card 4

Front

What are the two different types of photoreceptor?

Back

Preview of the front of card 4

Card 5

Front

What are the rods used for?

Back

Preview of the front of card 5
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