Stimulus recognition Flashcards
What projects to the lateral geniculate nucleus?
BOTH the parvocellular and magnocellular ganglion cells
How many layers are there in the LGN?
6
How many layers of the LGN receive input from the P-ganglion cells?
4
How many layers of the LGN receive input from the M-ganglion cells?
2
What is received at each layer of the LGN?
Input from a single eye at each layer
Alternates between input from contralateral and ipsilateral eye
Where does the right LGN receive input from?
What is this seen by?
From the left visual field
Seen by the nasal left retina and the temporal right retina
Where does the left LGN receive input from?
What is this seen by?
From the right visual field
Seen by the right nasal retina and temporal left retina
How are the layers kept in the LGN?
Remain SEGREGATED
How is the LGN organised?
Retinotopically
Why can we not used imaging to find out some of the functions of the LGN?
It is located deep within the brain
What is a new way of imaging the LGN?
Insert a tiny microscope into the brain
How do the ganglion cells make connections with the neurons in the LGN?
One to one connection
What are the receptive fields of the LGN neurons similar to?
The receptive fields of the ganglion cells
What are the non-retinal inputs to the LGN?
Why?
- Neurons of the V1 cortex - to regulate the synaptic input to the LGN, for feedback
- Local interneurons in the LGN - to shape the activity of other neurons
Describe the ventral pathway
P-ganglion cells - input to the P-cell layers of the LGN
Input to the V1 cortex
To the V2 and V4 cortical areas
To the inferior temporal cortex
Describe the dorsal pathway
M-ganglion cells - input to the M-cell layers of the LGN
To the V1 cortex
To the V2 and V3 cortical area
To the posterior parietal cortex
The further along the dorsal or ventral pathways, what happens to the neurons?
What does this allow?
They become more complex
Allows them to respond to more complex shapes
Do the ventral and dorsal pathways interact with each other?
Yes
What is the ‘Jennifer Aniston’ theory?
What is the alternative to this theory?
Jennifer Aniston theory:
A single neuron responds to a specific object
Alternative theory:
Large number of neurons which respond to MANY objects, but each object in a DIFFERENT way
If the ‘Jennifer Aniston’ theory is true, what does stimulating a specific neuron lead to?
Perception of the specific object that it responds to
What 2 things can the visual system do, as well as recognise objects that are different to each other?
1) Recognise objects in any orientation
2) Recognise objects independantly of their size
What does the hierarchical model of object recognition state?
Along the ventral stream, neurons respond to more and more complex shapes
What are the different stimulus complexity that can be responded to at different stages the ventral stream? (in regards to the hierarchical model of object)
Detection of EDGES
Detection of a combination of EDGES and CONTOURS
Detection of object PARTS (eg. face)
Detection of object from one point of VIEW
View-invariant object detection (eg. rabbit, car)
Categorisation (eg. human, animal, vehicle)
How can we test the hierarchical model of object recognition?
What do these tests show? Why?
Lesions in the inferior temporal cortex
- Show a decrease in the ability to recognise objects
Modelling and electrophysiology studies
- DON’T prove the model, as need to be able to image the neurons
As well as increasing in complexity, what else increases along the ventral stream?
Increase in receptive field size of neurons
How many layers are there in the cortex?
6
What do different layers of the cortex contain?
What does this mean?
Some layers contain more cell bodies than other layers
Different layers contain different cells that perform different functions
Means that different layers of the cortex have different functions
Where do cells in the LGN send their axons?
What does this allow
Different types of cells from the LGN (from the different LGN layers) send their projections to different layers of the cortex
To keep segregation of inputs (from the different parts of the retina) that are already segregated in the LGN
What do interneurons in the cortex do?
Receive information from one layer and send projections to another layer
As well as specific inputs to the different cortical areas, what else is specfic?
Specific output from each layer to different areas of the brain
What are ‘columns’ in the cortex?
Where are they present?
Part of the brain which has very similar functions
Present in MANY cortical areas
What are the 3 columns in the cortex?
1) Ocular dominance column
2) Orientation column
3) Blobs
What do ocular dominance columns receive input from?
Only one eye (either the contralateral or ipsilateral eye)
Using proline, how were ocular dominance columns visualised?
- Inject radioactive proline into one eye
- Proline follows the pathway of information flow (from ganglion cells, to LGN, to V1 cortex)
- Optical methods show that the proline formed stripes in the V1 cortex - representing inputs from the eye where the proline was injected
Using radioactive glucose, how were ocular dominance visualised?
- Inject into the cortex
- Stimulate one eye with light
- As glucose is needed in neurons to produce energy, glucose will go into the active neurons
- See stripes of input, depending if input from ipsilateral or contralateral eye
What are orientation columns?
Neighbouring parts of the brain which respond to different orientations of bars of light/different orientation in motion
How are orientation columns different to each other?
They have different neurons with different properties
Where are orientation columns observed in the brain?
In many areas, including the LGN
What do blobs in the brain process?
Information about colour
What are hypercolumns?
Columns in some parts of the brain that have all 3 columns:
- Blobs
- Ocular dominance
- Orientation
And can process ANY type of information
What did Hubel and Wiesel do?
What did they discover?
Worked on the V1 cortex in cats
Discovered different orientations of light produces different responses in different neurons
Where do ocular dominance columns extend through?
The entire thickness of the cortex
For a particular neuron, when if the weakest response, when changing the orientation of the bars of light?
What graph does this produce
Weakest response when the orientation is PERPENDICULAR to optimum
Produces a bell shaped curve - where the most activity occurs when the bar of light is in the optimum orientation
What do simple cells of the cortex respond to?
Orientation but ONLY when the stimulus is in the CENTRE of the receptive field
Where are simple cells found in the V1 cortex?
In layers 4 and 6
How is the receptive field of the cortical simple cells different to the receptive field of the ganglion cells and LGN neurons?
Elongated vertically
Whereas in the ganglion cells and LGN - it is round
Why does the receptive field of the simple cells change from round shaped?
Several neurons in the LGN orientated in ONE LINE feed to the SAME neuron (simple cell) in the visual cortex
Receptive field of the neurons synapsing onto the simple cell are located in one line - simple cell then has an elongated receptive field
What layer of the cortex are orientation columns not present?
Layer I
What do complex cells of the cortex respond to?
Orientation presented ANYWHERE in the visual field
Where are complex cells found in the V1 cortex?
Found in layers 2,3,5
Where do complex cells in the V1 cortex receive input from?
MANY simple cells with SIMILAR orientation of receptive field
BUT in different POSITIONS in the receptive field
What is a ‘hypercomplex’
An END-STOPPED complex cell
What do hypercomplex cells respond to?
CHANGES in orientation that are produced by a right angle of stimulus (with combination of edges)
What are the inputs to the V1 cortex?
From M-cell and P-cell layers of the LGN
Where do outputs from the V1 cortex go to?
- Other cortical areas
- LGN and deep structures
What happens to the receptive fields downstream of V1?
Increase in size
Increase in complexity
Where are face sensitive neurons present?
In the inferior temporal cortex
What happens to face sensitive neurons when you start to remove features from a face?
Face sensitive neurons spike less
What do face sensitive neurons respond to?
Shapes that resemble faces
What happens to the face sensitive neurons when they are repeatedly shown the same ‘face’ or the ‘face’ stimulus is prolonged?
They undergo adaptation
What is present at the top of the heirarchical model?
What are these called?
Neurons which respond to VERY specific objects
Called the ‘grandmother cell’ or the ‘Jenifer Aniston’ neuron
What does particular Jenifer Aniston neurons respond to?
Why is it called this?
Responds specifically to presentation of PARTICULAR IMAGES
Found that a particular neuron responds to imges of JS but not of other people
What are the problems with the heirarchical model?
- It is a feedforward model and doesn’t take into account feedback from higher cortical areas
- Poor in scale and orientation invariance
What is top-down regulation?
Feedback from higher cortical areas
