Primary visual pathway Flashcards
What is the sequence of seeing something?
Eyes > optic nerve > optic chiasm > lateral geniculate nucleus > primary visual cortex
Where is the primary visual cortex?
Striate cortex, V1 of the occipital lobe
What are the 3 information stages?
- Retina
- Later geniculate nucleus
- Visual cortex
What is the sequence at retinal level?
Photoreceptors > bipolar cells > retinal ganglion cells
Facts about rods (5)
Abundant (120million) No colour discrimination Sensitive in low light fields Higher density in pheriphery Track high rate changes
Facts about cones (5)
Less abundant than rods (6million) 3 types discriminate different wavelengths Less sensitive to low lights High concentration in fovea Cannot follow rapid changes
What do photoreceptors and bipolar cells vary?
Voltage
What kind of signal do photoceptors and bipolar cells emit?
Analogue
What do all other cells vary?
Spike rate
What is a receptive field?
The portion of th retina/visual field in which stimulation will evoke a change in the firing rate of a given visual neuron
Define substructure of a receptive field
A description of how visual stimuli needs to be presented in the receptive field of a visual neuron in order to evoke firing-rate changes
What do ON-OFF centre-surround receptive fields enchance?
Contrast and boundaries
Which two regions respond to centre-surround receptive fields?
Retinal ganglion
Geniculate body
Why are centre-surround fields important? (4)
They’re efficient
- Changes and boundaries matter the most
The luminance of features is represented relative to their surround
Help preserve appearance regardless of light levels
Can cause illusions
What are the 4 colours that have receptors in retinal ganglion and lateral geniculate cells?
Blue, yellow, red and green
What is the functional significance of centre-surround colour opposites?
It’s unclear except they can explain negative after images when accompanied by firing-rate adaptation
Simple cells (2)
Fields have inhibitory and excitatory regions
Can be thought of as combining inputs from ON and OFF regions
Complex cells (3)
Fields have no discrete ON/OFF regions
Best response to moving stimuli (reflecting response adaptation)
Can be thought of as combining inputs from simple cells
What is blindsight?
Appropriate responses to visual simuli of which someone is not conscious
What causes blindsight?
Lesions to primary visual cortex
How is blindisight possible?
There must be additional visual pathways
