Lecture 11 - detecting motion 1 Flashcards
1
Q
Where is motion processed?
A
- Pathway from LGN going straight from V5/MT, bypassing v1 = where motion is consciously perceived = needed to move and react to moving objects in environment = survival
- Route through dorsal processing stream = able to act upon where objects are in space
- Pathway from V5/MT to STS = not traditionally part of visual processing stream but important for temporal ordering of sequences
2
Q
V1 and V2
A
- Small receptive fields
- Cells respond to simple stimuli
- Respond to linear motion
- Not tuned for speed
- Not specialised for motion
3
Q
V5/MT
A
- Large receptive fields
- Responds to motion of anything, including random dots
- Direction and speed tuned
- Simple patterns of motion
- Motion contrast cells
- Responds to static images that imply motion
4
Q
V3
A
- Larger respective fields
- Specialised for motion of complex stimuli (texture)
5
Q
MST (medial superior temporal)
A
- Very large receptive fields
- Responds to motion of anything, including random dots
- Direction and speed tuned
- Complex motion patterns
- Static images that imply motion
- Responds to vestibular cues
6
Q
V6
A
Responds to self-induced motion
7
Q
Two ways to see motion
A
- Whether world is moving and head is fixed = motion on retina
- Or head moving when tracking moving object = motion of retina
- Brain knows when you move your eyes or head intentionally and codes all movement relevant to this
8
Q
Eye muscle signal theory
A
- Sherrington
- Inflow theory
- Idea the ability to work out whether the world is moving when we move our eyes is based upon signal coming from eye muscles = info compared with motion taking place on back of retina
- Hypothetical part of brain which compares output signal from muscle to output signal from retina
9
Q
Brain signal theory
A
- Helmholtz
- Outflow theory
- Actual signal that goes to muscle to make it move = efferent copy of motor command sent to comparative part of brain where it compares signal from retina about motion
- Faster route to work out if motion coming from eye or world as dont have to wait for signal to come from muscle
- Efferent copy = signal for intention to move
-Look at G’s notes for examples and further explanations = read before exam
10
Q
How do we detect motion?
A
Look to notes
11
Q
Motion selectivity in area MT
A
- Cells identified through single cell recordings in visual area V5/MT = specifically tuned to detect motion in particular direction and speed
- Needs time and distance to detect motion
12
Q
Apparent motion
A
- If object appears in position A at time 1 and position B at time 2 is has moved from A to B, even if it didn’t appear at all the points in between them
- If time delay between time 1 and 2 is too long or physical gap is too large then won’t see motion, just displacement
- If both time delay and distance travelled are sufficiently short will see motion
- This is basis for seeing motion in movies, TV, animations
13
Q
Movies designed around human vision
A
-One image displayed every 40ms = falls brain into session motion
14
Q
Wagon wheel illusion
A
- Western movies = people saw spokes on wheel moving in backwards direction even though horse pulling wagon forward
- Occurred due to conflict between speed and frame rate
- In slow moving wheels possible to work out correct direction of motion if distance between frames is small enough for brain to work out that position of spoke is same as time 1 and 2 etc.
- Optimal frame needs to be adopted and displacement must be kept normal to see motion in correct direction
15
Q
Development of motion perception
A
-Sensitivity to motion seems to develop around 10-12 weeks
