W7: Motion Perception

Question 1

How is a Reichardt Detector used to determine speed and direction of motion?

Answer 1

2 spatially separated zones, 1 with a temporally delayed response.
Cell body is maximally excited when signals arrive simultaneously

Question 2

Describe the experiment which proved motion selectivity of MT cells

Answer 2

Newsome and colleagues trained monkeys to perfom difficult discrimination tasks judging the direction of noisy, non-coherent dot stimuli and deciding which direction they’re moving
Increased coherence meant increased MT cell response activity

Question 3

State the Aperture problem

Answer 3

Cell can tell an edge is moving through it’s receptive field but can’t tell it’s direction (Assumed perpendicular to edge)

Question 4

Describe biological motion perception

Answer 4

Distinguish animate from inanimate objects using patterns of movement

Question 5

Explain structure from motion and bi-stable perception

Answer 5

When an object’s part moves it reveals 3D form and if object is ambiguous; direction of motion interchangeable

Question 6

Define optic flow and its processing in MST

Answer 6

Flow of visual scene across retina
MST neurons respond to expansions/contractions in flow field (centre focus of which defines heading)

Question 7

Explain looming

Answer 7

When approaching stimulus, it’s size increases rapidly just before reaching it; rapid increase calculates arrival time

Question 8

Explain apparent motion

Answer 8

Stimulus flashed in 2 nearby locations to an observer in quick succession so it appears stimulus has moved smoothly to 2nd position

Only possible if inter-stimulus interval is 60-200ms

Question 9

Describe the temporal correspondence problem and wagon wheel effect

Answer 9

In apparent motion, visual system can struggle to match parts of 1st and 2nd frame.

Nearest neighbour matching results in wheels appearing to rotate opposite to direction of motion