Lecture 6- Primary visual pathway Flashcards
What are the information processing stages?
Experimental strategy to reveal mechanisms of visual perception
Regarding info processing stages, why do we study different neuronal responses?
By studying the diff neuronal responses at different stages of the visual pathway, one may gain understanding of the diff stages of visual information processing that mediate visual perception.
What are the 2 types of photo receptors?
Rods and Cones
Describe Rods
(4 points)
-More abundant (120mill in human retina) -No colour (wave length) discrimination -Operate in low light levels -Higher density in periphery, track high-rate changes
Describe Cones
(5 points)
-Less abundant (6mill in human retina) -3 types discriminate diff wavelengths (S,M,L) -Operate in high light levels -Higher concentration in fovea -Cannot follow rapid changes
Are Rods or Cones more abundant?
Rods are w/ 120mill in human retina
Which photo receptor (rods/cones) can operate in either low or high light levels
(one for each)
Rods-operate in low light
Cones= operate in high light
What do photoreceptors and bipolar cells do regarding voltage?
They vary their voltage as they are stimulated whereas all subsequent cells vary spike rate.
What is photoreceptor detection of light translated into?
They are translated into excitation or inhibition of retinal ganglion cells via bipolar cells.
What are receptive fields of visual neurons?
The portion of retina/visual field in which visual stimulation will evoke a change in firing rate of a given neuron
What is the substructure of a receptive field of visual neuron?
A description of how visual stimuli need to be presented in the receptive field of a visual neuron in order to evoke firing rate changes.
What are retinal ganglion neurons?
Receive input from multiple photoreceptors via bipolar cells -On/Off centre-surround receptive fieldsW
What does light presented in ON regions do compared to light in OFF regions
ON= Excites the cell
OFF= Inhibits cell
How are ON/OFF regions organised?
Centre surround fashion
How is response rate of cell determined?
Based on the sum of stimulation in ON region minus stimulation in OFF region due to enhancement of contrast and boundaries.
How do neurons in lateral geniculate body respond to visual stimuli?
In a similar ways to retinal ganglion cells
What does the functional significance of centre-surround fields mean?
To be efficient we only need to respond to changes and boundaries (edges)
How is luminance of features represented?
The luminance of features is represented relative to their surround
What does luminance of features help preserve?
It helps preserve appearance of objects regardless of light levels in the environment
How do you determine colour sensitivity of retinal ganglion + LGN ?
Retinal ganglion and LGN cells receive inputs from cones (that are differentially sensitive to different wavelengths) and are sensitive to colour
Why are colour sensitive retinal ganglion and LGN neurons sensitive to colour?
Colour-sensitive retinal ganglion and LGN neurons have receptive fields that show centre-surround colour opponency
What explains negative after images?
Colour opponency, together with firing-rate adaptation (rebound effects), in retinal ganglion cells can explain negative afterimages.
How do most V1 neurons respond to elongated stimuli?
With specific orientation
What are the 2 types of orientation-sensitive V1 neurons?
Simple cells
Complex cells
What are simple cells?
-Fields have inhibitory and excitatory regions. -Can be thought of as combining inputs from ON and OFF cells
What are 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
How do you get perception and memory of holistic visual properties?
To result in perception and memory of the ‘holistic’ visual properties of whole objects and visuals scenes, the visual information from the modules in V1 needs to be combined and further processed
Where does the perception and memory further processing take place?
This processing takes place in the visual association cortices (V2-V5, inferior temporal cortex, posterior parietal cortex) and other regions.
What is blindsight?
Subjects w/ lesions to primary visual cortex and ‘blindness’ can show appropriate responses to visual stimuli of which they are not conscious.
Eg moving the eyes to look, pointing to visual stimuli
What does blindsight highlight?
(2 things)
Blindsight highlights that apart from the primary visual pathway that is critical for conscious vision, there are additional visual pathways.
-Blindsight’ also highlights that the brain can perform visual information processing which can guide subjects’ behaviour without their conscious awareness.
