ND - Motion Perception - Week 1

Question 1

Distinguish between simple and apparent motion using examples of each.

Answer 1

Simple - a ball being thrown

Apparent - a sequence of lights in a neon sign

Question 2

List three natural reasons why motion perception is important.

Answer 2

Navigation
Hazard avoidance
Segmentation of objects

Question 3

Define optic flow.

Answer 3

Movement of the world

Question 4

Describe the motion pathway in the brain. Describe where both parvocellular and magnocellular signalling goes to.

Answer 4

Parvocellular - Retina - LGN - V1 - V4 - Ventral temporal pathway
Magnocellular - Retina - LGN - V1 - MT - Dorsal parietal pathway

Question 5

Which cells are responsible for parvocellular and magnocellular signalling?

Answer 5

Parvocellular - midget ganglion cells

Magnocellular - parasol ganglion cells

Question 6

Do V1 cells show direction selectivity?

Answer 6

Yesd

Question 7

What does the directional selectivity of a neuron depend on? Briefly describe what this means using a set of 5 neurons labelled a-e.

Answer 7

The response latency of the presynaptic neurons
Consider a series of neurons, a-e. Consider them to be directionally sensitive to left-right movement.
They are connected to the target cell such that they will fire sequentially from a-e, if a leftward movement occurs, and this is because their signals arrive simultaneously and sum, reaching threshold.
If a rightward movement occurs, then d/e will fire first, followed by c, b, and a. This results in insufficient summation and threshold is not reached.

Question 8

Are directionally selective cells distributed evenly throughout V1?

Answer 8

No, the proportion of cells that are direction-selective varies according to V1 layers

Question 9

Where does MST lie in humans?

Answer 9

Adjacent to MT (also known as V5)

Question 10

Do M- and P-systems follow completely separate pathways or is there crosstalk?

Answer 10

Not completely separate, there is crosstalk between dorsal and ventral streams

Question 11

Define akinetopsia.

Answer 11

Visual motion blindness

Question 12

Is the M-system the only motion pathway in the human system?

Answer 12

No, there is also the colliculo-cortical pathway

Retina - superior colliculus - V5

Question 13

What do the following areas of the brain process?
V1
V5/MT
MST

Answer 13

V1 - direction selectivity
V5/MT - global motion integration
MST - optic flow