7&8 - Stimulus Recognition I&II Flashcards
What must we do in order to understand visual recognition?
- Find single neurones that specifically respond to presentation of specific objects and understand their pre-synaptic neuronal circuits.
What is orientation invariance?
Being able to recognise an object regardless of the orientation.
What is scale invariance?
Being able to recognise an object regardless of size.
What can lesion in the inferior temporal cortex cause?
A decrease in the ability to recognise objects
How are lesions in the temporal cortex studied?
By modelling and electrophysiology.
What is the lateral geniculate nucleus (LGN)?
- A thalamic relay station
- Has 6 layers which alternate input from each eye.
- Parvo and magnocellular cells input here
How are cells in the LGN organised?
Retinopically
What are receptive fields of the LGN similar to?
The receptive fields of retinal ganglion cells.
What is back propagation?
60% of the synaptic input from the cortex going to the LGN.
What are 2 key features of the cortical structure?
- Layering
- Columns - ocular dominance, orientation, direction and Blobs
Where do the ocular dominance columns receive their input from?
From either an ipsilateral or contralateral eye.
What are blobs responsible for?
The processing of colour, they are not orientation selective.
Where do blobs receive their input from?
Parvocellular cells of the lateral geniculate nucleus.
Where are simple cells localised?
In layers 4-6
When do simple cells respond to a stimulus?
When it hits the middle of the receptive field
When do complex cells respond to a stimulus?
If the stimulus is anywhere in the cell.
Where are complex cells localised?
In layers 2,3 & 5
How do complex cells collect their info?
from simple cells with similar orientation.
What are hyper-complex cells?
End-stopped complex cells that can respond to the stimulus is any orientation not just outside the receptive field.
How does info move through the V1 cortex?
They send projections to subsequent brain areas from processing, the fields downstream of V1 increase in complexity and the receptive fields increase in size.
What kind of neurons does the temporal lobe contain?
Face sensitive neurons.
What kind of stimuli do neurons in the temporal lobe respond to?
Complex shapes such as faces.
What are some problems with the neurons in the temporal lobe?
- they are poor in scale
- doesn’t take feedback from higher cortical cells
- Needs some experimental validation.
What are some examples of object localisation in the visual system?
- Orienting reflex (orientation of the head and eyes to focus stimulus on the fovea)
- Smooth pursuit (Following a moving object)
- Motion anticipation (prediction of motion during prey capture)
- Saccadic movements during object inspection
What are some areas involved in stimulus localisation?
- The retina
- Superior & Inferior colliculus
- The dorsal stream in the cortex
What is the function of the superior colliculus?
- It receives input from the ganglion cells, auditory system and the somatosensory system.
- Helps us orient ourselves towards a stimulus
What happens in the dorsal stream?
Info from the stimulus is coded, mainly motion info
How is direction selectivity evident in the retina?
The retina can predict the location of a moving object counteracting the delay due to phototransduction.
What kind of responses come from bipolar cells?
Excitiation
What kind of responses come from amacrine cells?
Inhibitory
In preferred direction what is the size of excitatory and inhibitory responses?
Excitatory responses are larger and inhibitory responses are smaller and delayed.
