4 Primary Visual Pathway Flashcards
What is the primary visual pathway
The processing of visual information from the retina to the primary visual cortex (V1)
Which side of the primary visual cortex controls the right eye
The left side
What are the processing stages involved in vision?
Photoreceptors Bipolar cells Retinal ganglion cells Optic nerve Lateral geniculate body Visual cortex
Where can you find photoreceptors
In the retina
What are the two types of photoreceptors?
Rods and cones
What are the features of rods?
More abundant No colour discrimination Sensitive in low light Higher density in periphery Track high rate changes
What are the features of rods
Less abundant Discriminates between colours Less sensitive in low light Higher concentration in fovea Can’t follow rapid changes
Which type of cells vary their voltage as they are stimulated rather than varying their spike rate?
Photoreceptors and bipolar cells
What is photoreceptor detection of light translated into?
Excitation or inhibition of retinal ganglion cells via bipolar cells
Receptive fields of visual neurons
The portion of the retina/ visual field in which visual stimulation will evoke a change in the firing rate of a given visual neuron
Substructure of a receptive field
Provide a description of how visual stimuli needs to be presented in the receptive field of a visual field in order to evoke firing rate changes
Where are the receptive fields of visual neurons found?
In the retina
Where are the retinal ganglion neurons found?
In the retina
Where do the retinal ganglion neurons receive input from?
Photoreceptors via bipolar cells
Describe the ON-OFF structure of receptive fields
Light presented in ‘ON’ regions excite the cells. Light in ‘OFF’ region inhibits the cells. Response rate of the cell is based on the sum of stimulation in ON regions minus stimulation in OFF regions
We what does the ON-OFF centre surround structure allow?
Us to only respond to changes in surrounding and allows us to preserve the appearance of objects regardless of light levels
How are the retinal ganglion and LGN neurons structured?
They have receptive fields that show centre surround colour opponency
What can explain negative after images
Centre surround colour opponency of receptive fields along with the firing rate adaption (rebound effect)
Simple cells
Fields have inhibitory and excitatory regions. Can be thought of as combining inputs from ON and OFF cells.
Complex cells
Fields have no discrete on and off regions. Best response to moving stimuli. Can be thought of as combining the inputs of simple cells
Retino topic map
The mapping of retina onto the visual cortex
Modules
V1 is divided into small column like modules that combine neurons sensitive to different aspects of stimuli presented in a small part of the visual field
Blindsight
Where blind people can show appropriate responses to visual stimuli of which they are not conscious
What does blindsight tell us?
There are additional visual pathways, as well as the fact that the brain can perform visual information processing which can guide subjects’ behaviour without their conscious awareness
