Motion wk4

Question 1

where does motion processing begin?

Answer 1

• in the retina, into the LGN, and then into the primary visual cortex (V1,2,3)
• also a direct projection from LGN–> V5/MT

Question 2

Motion sensation in the retina

Answer 2

• we dont have this, only in the cortex
• animals have this though

Question 3

Blindsight

Answer 3

• Damage to the primary visual cortex (V1)
• Happens from stroke/brain trauma
• Causes blindness
• You can still detect/sense motion, this is because of the direction projection of LGN-> V5

Question 4

motion processing in V1/2

Answer 4

small receptive fields.
cells respond to simple stimuli and linear motion, but are not tuned or specialised for motion

Question 5

motion processing in V3

Answer 5

larger receptive fields and specialised for motion of complex stimuli, e.g., texture.

Question 6

motion processing in V5/MT

Answer 6

• large receptive fields that respond to motion of anything
• tuned for complex direction and speed
• respond to simple patterns of motion and static images that imply motion
• have motion contrast cells

Question 7

motion processing in MST

Answer 7

identical to V5, but also respond to vestibular cues (self motion) and complex motion patterns
- mostly contribute to motion processing but not as critical as V5

Question 8

motion processing in V6

Answer 8

responds to self induced motion

Question 9

What are the two ways we can sense motion

Answer 9

1. When our eyes are static+ something moves across our retina
2. When our eyes are dynamic (move) and the image on our retina is static

Question 10

what does differentiating between static and moving objects suggest?

Answer 10

• we can incorporate information about our own movements (self motion) when interpreting information in the environment

led to two theories generated to explain how we interpret the info we get from our retina

Question 11

sherrington’s eye muscle signal theory (inflow)

Answer 11

• taking the signal from our eye muscles
• When our eye moves, our muscles contract
• We get signals from these muscles to interpret the signal we get l from the retina

Question 12

helmholtz’s brain signal theory (outflow)

Answer 12

• suggested EMS theory of waiting for the signal from the muscle was far too slow of a process
• Instead, we take the intention signals from the higher part of the brain
• Intention to move our eyes is the signal we actually take to compare what’s happening in the retina

Question 13

whats in our retina in order to detect motion?

Answer 13

• we have two receptive fields (eye A->B )
• motion is detected and will start in eye A
• moving towards eye B, it will trigger
• time delay is used to combine the two eyes together for comparison

Question 14

what are time delays required for?

Answer 14

to detect motion happening at the same time, signals will then fire at the same time

Question 15

what does combining information between areas allow?

Answer 15

for a sense of relative motion – this is called an opponent-motion circuit

Question 16

Whats an opponent motion cell

Answer 16

• This is an opponent motion cell, tuning towards its preferred direction with inhibition happening in the opposite
• We have a lot of these cells in area MT

Question 17

what do opponent-motion detectors respond to?

Answer 17

the balance between motion cells preferring opposite directions

Question 18

apparent motion

Answer 18

• interpreting a set of still images as smooth motion, as long as the time interval and physical displacement are not too large between points A and B
• e.g. the functions of a speed detector

Question 19

wagon wheel illusion demonstrates…

Answer 19

-a series of static images at slightly different orientations
- shows how increases in speed cause changes in the perception of repetitive motion, as larger displacements between faster movements make them harder to link

Question 20

what is the result of the wagon wheel illusion

Answer 20

This results in movements being connected to the closest one, which can generate counterclockwise

Question 21

When do problems arise with apparent motion

Answer 21

• when the delay between images interacts with the speed of object
• especially with repetitive patterns such as wheel spokes

Question 22

when does motion sensitivity develop?

Answer 22

• 10-12 weeks, however certain types of motion,
• e.g., looming stimuli (things that might collide with the child) are detected even earlier around birth
• these may be later lost and have to be relearnt

Question 23

damage to MT

Answer 23

• akinetopsia (motion blindness)
• we can see but we cannot sense motion
• integration of smooth motion breaks down and we see the world as still photographs

Question 24

MT neurons ,motion blindness and motion coherance tests

Answer 24

• MT neurons are sensitive to specific direction so things cannot be moving in mismatch directions at all during these tests otherwise patients will fail if below 80% coherence

Question 25

damage to V1

Answer 25

functionally blind, can still respond to movement

Question 26

damage to V3

Answer 26

impedes motion perception, not destroy

Question 27

damage to MST/V6

Answer 27

inhibits navigation, can still see motion

Question 28

MT and speed

Answer 28

MT has specific speed-sensitive neurons, excited for different degrees of speed

Question 29

what can affect estimates of speed?

Answer 29

physical distance from the object being recorded

Question 30

how do neurons measure speed?

Answer 30

- degrees per second - this is because the same speed will vary on our retina depending on actual distance

Question 31

what is the waterfall illusion

Answer 31

- a motion after effect Looking at the cross in the middle whilst the peripheral moves downwards - -When we avert our gaze to another image we should see it expanding even though its stationary - We don’t sense that the picture is moving or displaces

Question 32

waterfall illusion (addams, 1834) suggests...

Answer 32

- Suggesting that motion sensation or processing is independent from place processing

Question 33

how do motion after-effects work?

Answer 33

1. perceived motion is encoded by a population of cells to generate a neural code 2. after prolonged adaptation to a certain direction, these cells reduce their output 3. the neural code for a subsequent static stimulus will be biased in favour of cells that normally respond to the opposite direction of that movement

Question 34

evidence of adaptation in perceptions of speed over time within the RGC

Answer 34

Retinal Ganglion Cell neurons increase dramatically when motion first occurs, but then drops down in excitement once motion is finished, the neuron inhibits below initial baseline activity

Question 35

evidence of adaptation in perceptions of speed over space within the fovea

Answer 35

- fovea is sensitive to changes in speed – important for processing information - however after 10s of movement in the periphery, we stop seeing this motion entirely

Question 36

when are speed judgements more accurate?

Answer 36

before adaptation, than afterwards

Question 37

what happens to motion in the periphery?

Answer 37

fades over time until change

Question 38

principle of univariance

Answer 38

cells cannot differentiate between speed and contrast (or frequency and intensity) motion cells can be driven by different things but can only have one output, they cannot signal two different things, e.g., contrast and motion

Question 39

how can PoU affect perceptions of speed?

Answer 39

- If you show participants moving objects under conditions of low contrast they may perceive them as slower than the same movements under high contrast - e.g. driving in fog (low contrast) will make us perceive speed as slower than it actually is

Question 40

motion contrast cell structure in MT

Answer 40

- their centre-surround cells activate to motion in the centre, but are inhibited if the same motion occurs in the periphery - also excited when surround is in the oppisite motion - allows for us to distinguish between motion

Question 41

snow blind illusion

Answer 41

-shows how motion-contrast cells can affect speed and motion perception, - as motionless stripes expand, covering background excite the motion-contrast cells and suggest higher speed

Question 42

when is induced motion and vection common?

Answer 42

- when motion is slight and acceleration is smooth we get no vestibular cues - uncertainty as to whether it is us moving or the environment

Question 43

illusory motion (leviant, 1981)

Answer 43

- the sensation of motion in a static stimulus even without adaptation

Question 44

Illusionary motion explanation

Answer 44

Illusion over-excites the orientation cells in V1,2,3 as its high in contrast and spatial frequency - cells are also motion sensitive so pass a motion signal to MT when over excited - so we see motion

Question 45

aperture problem

Answer 45

involves only seeing motion at right angles to the edge, when viewing a moving stimulus through a small window (aperture) distorts the true direction of motion perception

Question 46

Why does the aperture problem occur

Answer 46

- we have very small receptive fields in V1 , responding to only short edges - we need cells in area MT to combine these receptive fields to derive the true motion

Question 47

Pinna illusion

Answer 47

- Fixating on the black spot, then move forward and back to sense sensation - product of the aperture problem

Question 48

Where is visual speech processed

Answer 48

- the movement of faces - STS, specifically the temporal visual speech area (TVSA) m

Question 49

Autism and visual speech processing

Answer 49

- reduced activation in the TVSA and MT (motion processing) where task requires visual speech processing - shows it is motion processing responsible for speech processing rather than motor porcessing