Primary Visual Pathways Flashcards
What are the stages of information processing in the primary visual pathway?
RETINA Photoreceptors-> bipolar cells-> retinal ganglion cells-> optic nerve -> LATERAL GENICULATE BODY -> VISUAL CORTEX
What happens to information as it passes through each stage of the primary visual pathway?
It becomes more elaborate and complex.
It starts by representing very simple features at the photoreceptors which show either the absence or presence of light.
How are visual responses of a neuron recorded along the visual pathway?
Present a stimulus on a projected to participants
Use micro electrodes to observe how the neurons respond to visual stimuli along the pathway
What are rods and cones?
They contain photopigments which change their confirmation in response to light.
This change is translated to intercellular signalling cascades which create a voltage change of the photoreceptors
What are the differences between rods and cones?
Rods are more abundant than cones - no colour discrimination
Cones have 3 different photopigments - short (blue), medium (green), long (red).
Rods are more sensitive in low light conditions and have a high density in the periphery.
Cones have a higher concentration in the fovea.
Rods can follow high rapid changes.
What is meant by the receptive field of a neuron?
The portion of the retina /visual field in which stimulation will evoke a change in the firing rate of a given visual neuron
What is the function of Retinal Ganglion Cells?
They receive input from multiple photoreceptors via bipolar cells.
What is meant by an ON/OFF centre-surround?
Light presented in ON regions excites the cell, light presented in OFF regions inhibits the cells.
What happens when a stimulus is no longer presented in the Retinal Ganglion Cells?
A rebound effect occurs.
- the neuron does the opposite action to when the stimulus was presented.
- this can explain visual after images.
What is the function of centre-surround fields.
They respond to changes changes in boundaries.
the luminance of a feature is represented relative to the surroundings - helps preserve the appearance of objects regardless of light levels in the environment.
What are the 2 main types of orientation-sensitive V1 neurons?
Simple cells - fields have inhibitory and excitatory regions. They can combine inputs from ON and OFF cells.
Complex cells - They have no discrete ON/OFF region and respond best to moving stimuli. They combine inputs from simple cells.
