Neural Circuits of Object Recognition Flashcards
How do bats recognise water? (4)
- Echolocation
- Bats make a sound stimuli which reflects off the surface below
- If the surface is smooth, the sound is reflected directly back
- Bat recognises the smooth surface as water and tries to drink it
How do electric fish recognise objects? (3)
- Electroreception
- Electric fish creates an electric field around itself
- If the electric field is disrupted it tells the fish that something is nearby
What is orientation invariance?
Ability to recognise an object independent of the orientation
What is scale invariance?
Ability to recognise an object independent of the scale
What is the hierarchical model of object recognition? (6)
- Detection of edges
- Detection of combination of edges and contours
- Detection of object parts (e.g. face)
- Detection of objects from one POV
- View-invariant object detection (recognise despite variations)
- Categorisation
How is object recognition studied? (2)
- Lesions in the inferior temporal cortex decrease the ability to recognise objects
- Electrophysiology and mathematical modelling
What does the hierarchical model of object recognition demonstrate? (2)
- The responses of the neurons increase in complexity along the ventral stream
- The receptive field size of neurons increases along the ventral stream
What are the 2 types of ganglion cells?
- Parvocellular
- Magnocellular
Which ganglion cells are responsible for detection of motion?
Magnocellular
Which ganglion cells are responsible for object recognition?
Parvocellular
Where do the ganglion cells send their projections to?
Lateral geniculate nucleus
How many layers does the lateral geniculate nucleus have?
6
Which layers of the lateral geniculate nucleus do the parvocellular cells send their input to?
First 4 layers
Which layers of the lateral geniculate nucleus do the magnocellular cells send their input to?
Last 2 layers
How many eyes does each layer of the lateral geniculate nucleus receive input from? (2)
- Each layer receives input from one eye
- First layer receives from the contralateral eye, next layer from the ipsilateral eye and so on
What does the lateral geniculate nucleus (LGN) do? (5)
- Sends information to the primary visual cortex
- Ganglion cell axons make 1:1 connections with LGN projection neurons
- Receptive fields of of LGN neurons are similar to those of retinal ganglion cells so not much processing happening
- 60% of synaptic input to the LGN is from the cortex but mechanism unknown
- Local interneurons in LGN so some kind of modification happening
What are the 2 visual pathways in the cortex?
- Ventral ‘what’ stream
- Dorsal ‘where’ stream
What is the ventral stream? (2)
- ‘What’ pathway for object recognition
- Inferior temporal
What is the dorsal stream? (2)
- ‘Where’ pathway for object localisation/speed/movement etc.
- Posterior parietal
What is the ventral stream pathway for object recognition? (6)
- Parvocellular ganglion cells
- LGN
- V1 cortex
- V2 cortex
- V4 cortex
- Inferior temporal cortex
What are the 2 key features of the cortical structure?
- Layering
- Columns contain neurons of similar properties
How many layers are in the cortex?
6
What are the 3 main columns in the cortical structure?
- Ocular dominance (receives information from one eye)
- Orientation (direction)
- Blobs (colour)
How could you observe the ocular dominance columns in the cortex? (2)
- Inject radioactive proline into one eye and look at which columns are radioactive
- Inject radioactive glucose into the cortex and stimulate one eye with light
How could you observe the blob (colour) columns in the cortex?
Stain for cytochrome oxidase
What do the blobs do in the cortex? (3)
- Columns process information about colour
- Receive input from parvocellular cells from the LGN
- Not orientation selective
What does the orientation column do in the cortex?
Neurons are separated into columns depending on which orientation of stimulus they respond to
What does the ocular dominance column do in the cortex?
Neurons are separated into columns depending on which eye they receive input from (contralateral/ipsilateral)
What is a hypercolumn?
A section of the cortex containing all 3 columns which can process information about the entire stimulus
What is a simple cell?
A cell in the primary visual (V1) cortex which responds to bars of particular orientations
Who discovered simple cells?
Wiesel and Hubel
Where are simple cells located? (2)
- In layers 4 and 6 of the V1 cortex
- In the orientation columns depending on which orientation they respond to
Where is the lateral geniculate nucleus?
Thalamus
What are the receptive fields of the simple cells like? (3)
- Elongated oval shaped
- Larger than the receptive fields of the ganglion cells and LGN neurons
- Respond to a bar in a certain orientation in the centre of the receptive field
Why is the receptive field of the simple cell elongated? (2)
- Record from the simple cell and its presynaptic inputs
- The receptive fields of the presynaptic input neurons are all located on one line which causes the receptive field of the simple cell to be elongated
What is a complex cell?
Responds to bars of a particular orientation presented anywhere in the receptive field
What is the difference between simple and complex cells? (2)
- Simple cells respond to bars of a certain orientation but only when they are presented in the centre of its receptive field (centre-surround organisation, outside of the centre is inhibitory)
- Complex cells respond to bars of a certain orientation when they are presented anywhere in the receptive field
Where are complex cells located?
In layers 2, 3 and 5 of the V1 cortex
Why does the mechanism of complex cells differ from simple cells?
The idea is that complex cells receive inputs from many simple cells which respond to similar orientations but sample from different areas of the visual space
What is a hypercomplex/end-stopped complex cell? (2)
- Similar to complex cell but when the line extends beyond the receptive field the cell is inhibited
- However if the section of the line that extends beyond is at an angle the firing resumes
What does the hierarchical model say happens downstream of V1? (2)
- Increase in complexity of responses
- Increase in receptive field size
Where are face-sensitive neurons located?
Inferior temporal lobe
What is a ‘Jenifer Aniston’ neuron? (2)
- Neuron that specifically responds to images of Jenifer Aniston
- Demonstrates that 1 or few neurons recognise specific objects
What are the problems with the ‘Jenifer Aniston’ neuron evidence for the hierarchical model? (3)
- Doesn’t explain scale/orientation invariance
- Doesn’t take into account feedbacks from higher cortical areas
- Hard to replicate the experiment
