Samenvatting
samenvatting sensation and perception deeltt 2
- Instelling
- Universiteit Utrecht (UU)
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Voorbeeld van de inhoud
COLLEGE 8Motion processing: color, stereo depth, form
Robust a lot of area’s process motion. You need to destroy a lot to tackle the motion
system.
Different (anatomical) mechanisms in different animals
Retinal motion processing= process motion on the retina,
rabbit/frogs/turtle/birds
Non retinal motion processing= human
Motion= a chance in position of an object. You can see objects because of
movement, shapes of objects are divined by motion. So, motion is not
necessary based on objects.
Bilocal correlator= 2 positions and their correlation.
- Velocity= span/delay. De dot is moving so the cells are not activated at the same time.
But the left cell is delayed so the information of both comes at the same time on X.
- They need to come in at the same time to reach a threshold.
Reichart detector= signal cancels out due to inhibition when the stimulus
doesn’t move/ flicker.
Detector failure= the failure to see motion suggests we actually use a
mechanism like reichart detector.
The ability to see this kind of motion suggests we use additional mechanisms
beyond the reichart detector.
Luminance based: first order.
Temporal texture: texture changes trough space and time
Spatial frequency texture: size of objects is different.
Motion based motion: changes in space and time, also in object moves.
1st order motion based on luminance that is a first order attribute. They don’t need to be
reconstructed into other things.
2nd order motion not based on (completely) luminance.
- Double dissociation between first and second order motion
- More interocular transfer of the second order compared to first.
- Later brain structures show more interocular transfer.
- Different mechanisms with second order processing originating later in the visual
hierarchy.
- Many different types of motion and all require different types of receptive fields.
Local motion= within a persiculair position there is a black dot making a jump. The dots are
not doing anything together, but they have the direction or speed.
Triggered in V1: To detect local things you have to gather information from a small part of
space small receptive fields.
V1
- V2 sends information to V1.
- Orientation selectivity
, - 20% direction selectivity
V2/V3
- Many directions selective responses
- Receive much input from V1.
- Direction selective properties similar to V1, so inherits.
Aperture problem= viewed through a small aperture, motion signals can be ambiguous.
Local vs global. Small receptive fields provide local information. Large receptive fields
capture global motion signal. You need the bigger picture.
Global motion= MT, large receptive fields,
High convergence loose information on specific spatial location of inputs
More sensitive when detecting.
Low convergence information on exact location maintained.
Less sensitive when detecting receptive fields.
MT
- Input from superior colliculus
- 90% direction selective
- Motion processing cells
- Large receptive fields
- Associated with perception of motion.
Complex motion= MST combines local and global motion signals/information from MT,
expands/contract, optic flow, where are you heading, rotation.
Biological motion= helps with object recognition/identiy activity/species/gender/emotional
state/identity. A spontaneous and universal perceptual ability, both inside and outside
traditional laboratory environments.
Objects need to be learned sensitivity to motion-defined from and biological motion may take
years.
Motion perception= MT crucial for global motion perception
Microstimulation stimulate cells of MT. the shifting point/threshold
moves to the left; you are earlier to say it’s moving to the right.
Motion after effect= a powerful illusion of motion in the visual image caused by prior
exposure to motion in the opposite direction
Waterfall illusion= when one looks at the rocks beside a waterfall, they may appear to drift
upwards after one has viewed the flowing water
Ratio model= After adaptation, decreased responsiveness of cells coding the
adaptors’ direction would change the spiking ratios in favor of the opposite direction
when viewing a stationary pattern. Note that in this explanation, none of the direction
selective cells are active above baseline. Up has a stronger signal than down, relative
activity, combine motion opponency.
- MT cells tuned to the direction of the adaptor show a decrease in activity but
oppositely tuned cell do not show an increase in activity!
, Disinhibition model=integrating 2 cells with opposite directions, 2 cells inhibit each
other, when 1 gets active it pushes the other one down, absolute increase
- In V1, cells tuned to an adaptor also show a decrease in response after adaptation,
Direction Selective cells tuned to the anti-preferred stimulus become depolarised.
❖ Only the disinhibition model includes inhibition between motion cells with opposing
direction preferences
❖ Ratio model does not require output to be above baseline (only relative increase over
opposite motion signal), disinhibition model does (absolute increase over baseline)
❖ Both integrate (combine) motion signals from
opposite directions (motion opponent)
Distribution-shift model= not only opposites but take all into account at the same
time. Fits ratio model better.
Population coding:
COLLEGE 9
Eye movements: influenced by external events, (Exogenously/endogenously generated)
Superior colliculus= controlling eye movements,
Upper layer sensory map
Middle layer motor map
Voluntary eye movements: posterior parietal cortex, supplementary eye fields, frontal eye
fields
- Supplementary motor cortex was discovered later because you can’t make animals
make endogenously generated eye movements.
- All movements have a component of endogenous and exogenous.
Eye muscles
Oculomotor nucleus: up and down, move towards the nose.
Trochlear nucleas: rotate eye in skull
Abducens nucleus: away from nose, lateral muscles
When you make an eye movement you are blind visual system turns itself of when making
an eye movement, flash, blurry.
Smooth pursuit eye movements= slow, following a moving object, extern,
Saccadic eye movements= fast, short, attention
- It is impossible to have smooth eye movements, except when you look at a moving
object.
- If your eyes are moving along the retina, you do not perceive moving.
Corollary discharge= compare retinal motion and eye movements the brain can remove the
motion component in the image that comes from the eye movements and were left with a
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