14 - Vision 2 Flashcards
What does lateral inhibition allow the detection of?
allows the detection of edges and contrasts
How does lateral inhibition work in ommatidia receptors in horseshoe crabs?
as light intensity/brightness increases, ommatidia receptors firing rate increases -> thus causing more inhibition of neighboring receptors
How does lateral inhibition work to show contrast between an object that is one part dark and one part light?
at the edge of the light part: receptor is inhibited less (as its next to ‘dark’ neuron)
at the edge of the dark part: receptor is inhibted more (by ‘bright’ neuron)
What happens when you foveate on an intersection in the Hermann grid?
Why does this happen?
-grey blobs disappear (no lateral inhibition effect
-you position image on a part of the retina cells with much smaller receptive fields (than periphery-> no later inhibition
What does lateral inhibition do to relative difference between low and bright light?
What cell is responsible for this?
-lateral inhibition amplifies relative difference between transitioning from high to low light intensity (changes from 5:11 normal to 11:1)
-horizontal cells
What is the optic chiasm?
(nasal temporal optic nerves)
Where do the optic nerves project to?
Crossing over of L and R nasal optic nerves so that information projects contralaterally toV1
What is unique about the pupillary reflex due to light?
when light is shone exclusively in one eye, still both L and R eye reflex pathways are activated and BOTH pupils constrict
Where do visual reflexes eg. pupillary dilation project to ?
What pathway ?
accessory optic and pre-tectal nuclei in brain stem
retino-tectal
What are the visual reflexes? list them
accomodation, pupillary dilation, vergence
What is the purpose of the retino-tectal pathway?
Where does this pathway project?
-survival: orientate the head and eye movement towards unexpected events
(gaze-shift/foveation)
-superior colliculus (midbrain SC)
What is the largest visual pathway?
What does this pathway project to?
Where does it pass via?
-retino-geniculate-striate pathway
–takes info from retina to medial surface of primary visual cortex (V1) via the lateral geniculate nuclei (LGN) of thalamus
What is the function of the retino-geniculate-striate pathway?
scene analysis and object identification
What does it mean when the retino-geniculate-striate pathway is retinotopic?
Thus two stimuli presented to adjacent regions of the retina excite adjacent neurons at all levels of the system (there is a retinotopic map at V1)
Where are the nasal hemiretina located?
Do they project ipsilaterally or contralaterally?
inside half of retina
contralaterally
What is the function of the binocular overlap?
depth perception
What are the layers in the Lateral Geniculate Nucleus (LGN)?
What pathway is the LGN in?
-parvocellular p-layers
magnocellular m-layers
-retino-geniculate-striate pathway
What is the difference in appearance and function of the P-layer and M-layer cells in the Lateral geniculate nucleus?
Which photoreceptors do p and m receive input from?
-p are small and m are large
p layers are responsive to inputs of color, fine detail, stationary/slow moving objects (scene analysis/object identification
m layers are responsive to inputs to luminance charge
-p cones
m rods
What is a receptive field of a neuron?
an area within a visual field which can change the firing of a specific neuron
What are the four commonalities observed by Wiesel and Hubel about the receptive fields across the retino-geniculate-striate pawthays (but not at V1)?
- The receptive fields of the neurons representing the foveal area were smaller than those in the periphery
- circular
- monocular – from one eye only
- RFs have excitatory area and inhibitory area
How are the RF in neurons in the V1 different from others area of the retino-geniculate-striate pathway?
V1 have specific RFs: simple cells and complex cells
(other RFs are all the same)
What do V1 neuron RFs respond to?
Which cell type makes up 75% of V1?
-bars of light and their orientations
-75% - complex cells
What do simple cells respond to V1? why?
What to complex cells respond to V1? why?
-bars of light in a specific orientation at a specific location because simple cells have straight line borders between antagonistic on off regions in RF
-straight-edge stimulus of a particular orientation REGARDLESS of its position because complex cells do not have static on off regions
How are neurons functionally grouped in V1? (+ in relation to receptive fields)
-vertical columns - all cells in column have have receptive field (in visual field)
where does neural information go if you want to pass forward through the visual hierarchy?
-towards other parts of the cortex in which the neural processing complexifies
