primary visual pathway Flashcards
What experimental strategy can be used to reveal mechanisms of visual perception?
-By studying the different neuronal responses at different stages of the visual pathway, we can gain understanding of different stages of visual information processing that mediate visual perception
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
