primary visual pathway Flashcards
(16 cards)
What is the order of the primary visual pathway?
1: Retina (contains photoreceptors, bipolar cells and retinal ganglion cells)
2: Lateral geniculate body
3: Visual cortex
(R) Define transduction
-Energy from the environment is converted to a change in membrane potential in a neuron
-Converts external stimuli (light and sound) to internal stimuli (action potential)
Compare the abundance of rods and cones
-Rods = More abundant (120 million in human retina)
-Cones = Less abundant (6 million in human retina)
Compare the colour (wavelength) of rods and cones
-Rods = no colour
-Cones = 3 types discriminate different wavelengths (S is blue, M is green and L is red)
Compare the sensitivity of rods and cones
-Rods = operate in low light
-Cones = operate in high light
Compare the density/concentration of rods and cones
-Rods = High density in periphery
-Cones = High concentration in fovea
Compare the changes of rods and cones
-Rods = track high rate changes (seeing flicker of 60Hz monitor from corner of eyes)
-Cones = can’t follow rapid changes (can’t see 60Hz flicker when looking directly looking at monitor)
Describe the receptive fields of visual neurons
-The portion of retina in which visual stimulation will evoke a change in firing rate of a visual neuron
-Substructure of receptive field - a description of how visual stimuli need to be presented in a receptive field of a visual neuron in order to evoke firing rate changes
What occurs in Retinal Ganglion Neurons?
-Light presented in ‘ON’ regions excites cells
-Light in ‘OFF regions inhibit cell
-ON and OFF surround receptive fields, ‘centre-surround’ fashion
What is the functional significance of centre-surround fields?
-Responding to changes and boundaries is efficient
-Luminance if features is represented as relative to their surroundings
-Helps preserve appearance of objects regardless of light levels
-Can result in illusions
How does colour opponency occur?
-Can explain negative afterimages together with firing rate adaptation
-Retinal ganglion and LGN cells receive input from cones and are sensitive to colour
Describe simple cells
-Fields have inhibitory and excitatory regions
-Can be thought of as combining inputs from ON and OFF cells
Describe complex cells
-Fields have no discrete ON and OFF regions
-Best response to moving stimuli (reflecting response adaptation)
-Can be thought of as combining inputs from simple cells
What is the Lateral Geniculate Nucleus (LGN)?
-6 layers of neurons
-Each layer receives info from retinal ganglion cells in optic nerve of only one eye
Describe the processing of visual information
-To result in perception and memory of holistic visual properties of whole objects and visual scenes, visual info from modules in V1 need to be combined and further processes
-Processing takes place In visual association cortices
Describe ‘blindsight’
-Additional visual pathways as well as primary visual pathway that is critical for conscious vision
-Cortical regions involved in conscious perception are damaged, but other visual pathways that aren’t involved remain intact
