Block 2- Motion perception

Question 1

Why is motion perception important?

Answer 1

-We need to continuously update our enviroment

-Also important for grouping and segmentation eg animal difficult to see in static image, but will see them when moving

Question 2

What are the two different ways to perceive motion?

Answer 2

• Real motion - A stimulus that really moves
• Illusionary motion- This is motion that is not real but we perceive motion

Question 3

What is the difference between real motion and ilusionary motion?

Answer 3

Illusionary motion does not produce retinal motion
Only real motion produces retinal motion

Question 4

What are the different types of illusionary motion?

Answer 4

• Apparent motion
  -Induced motion
  -Motion aftereffects
  -Visual illusions

Question 5

What is the illusionary motion of apparent motion?

Answer 5

Perceived motion in a static stimulus

Eg if you flick between two images, you will perceive motion

Which is how film works- series of static images

Question 6

What is the illusionary motion of induced motion?

Answer 6

Image -
Why- Neuronal adaption

Neurons adapt to the movement of the clouds

Therefore have induced feeling of movement of the moon despite looking at a stationary object

Question 7

What is the illusionary motion of motion after effects?

Answer 7

Question 8

What is the illusionary motion of visual illusions?

Answer 8

This works because the brighter and darker parts of the concentric circles and presented in a very clever way, so there is irritation from the brighter parts to the darker parts

That conflicts with the information from the next concentric circle

Question 9

What do we use to perceive real motion?

Answer 9

Motion direction selective neurons?

Question 10

What are the two pieces of evidence to support motion direction selective neurons?

Answer 10

1. Hubel and Wiesel single cell recoding - of motion direction neurons in V1 and cortical areas ( eg all the way to the Dorsal stream). Fire when stimulus matches the preferred direction
2. Newsome - Found that temporal area neuroms are highly specialised in motion direction - did this through presenting monkeys with moving dot displays and measured middle temporal neurons firing rate through single cell recording
   Wanted to know how the neurons respond when they increase or decrease the motion direction coherence
   With increasing motion direction coherence, the monkeys judged direction of the motion more accurately
   The MT neurons fired more rapidly

Question 11

Why are the motion-direction neurones so significant?

Answer 11

No neuron ever will cover the whole visual field

Every neuron ever will only cover part of the visual field ( the receptive field)

If no neuron ever responds to the whole visual field, how can we judge motion perception accurately

Question 12

What is the aperture problem?

Answer 12

The “aperture problem” describes how the small, finite receptive field of a neuron can make it difficult to correctly perceive the true direction of motion of a line, as it can only see a limited part of the line at a time.

The direction of a moving stimulus through an aperture (such as a receptive field) is ambigious

When the stimulus is larger than the receptive field, and possible direction is possible, your single neuron doesn’t know

Question 13

Why must we have a solution to the aperture problem?

Answer 13

As we are all able to judge the direction of movement

Question 14

What are two solutions to the aperture problem?

Answer 14

Solutions:

1. Pool the responses of multiple neurons ( Neuronal convergence)

So single neurons converge onto other neurons, and grouping together the information form other neurons helps to create the bigger picture

1. End stopped cells - Signal the end of a stimulus ( where the direction is unambiguous )- This is what we have referred to as object segmentation

So neurons seletivly respond to te end of a stimulus

Object segmentation is important - So we know what parts belong to an object, but we have a clear segregation of when one object ends and another starts - Helps us to decide where an object moves to

Question 15

where is there crosstalk between the dorsal and ventral stream?

Answer 15

One area in which this crosstalk happens is the

Superior temporal sulcus

This is inbetween the IT and MT

So, the superior temporal sulcus receives projections from the IT and the MT

Question 16

What is the consequence between the crosstalk between the two streams?

Answer 16

Makes us an expert in biological motion

Question 17

What is biological motion? What is an example that shows we are good at deicing it?

Answer 17

Biological motion - Is a certain kind of motion

Biolgical motion is self-produced motion of a biological being

So we are experts at perceiving and recognising biological motion

eg point-light walkers

Question 18

What is thecollonary discharge theory?

Answer 18

Motion perception depends on retinal motion and eye movement

Question 19

What do we need to know about eye movements?

Answer 19

• Each eye has 6 muscles, top, bottom, left, right and two wrapped around the eye
• With this, the eye can move in all directions

Question 20

According to the Collonary discharge theory, there are also 3 relevant signals to be taken into account, what are these?

Answer 20

1. Image displacement signal ( eqivalent of retinal motion)
2. Motor signal ( eye movement )
3. Collonary discharge signal

Question 21

What is the image displacement signal?

Answer 21

Equivalent to the retinal image - An image that moves across the retina, succesivley stimulates the receptors

Question 22

What is the motor singnal?

Answer 22

This is sent from the motor area of the brain, towards the eye, gives command to the eye to move in certain direction

Question 23

What is the collonary discharge signal?- What leads on from this

Answer 23

Copy of the motor signal ( so if there is a motor signal, there is automatically a collonary discharge signal )

Then copy of the motor signal, together with the Image displacement signal are then sent to the comparator. The comparator then compares these two signals ( the retinal image signal and the motor signal)

Depending on the outcomes of this comparison, signals back to the sensory area of the Brain that motion has either occurred or not occurred

Question 24

What does the collonary discharge theory cognitive model look like?
Draw this out and explain

Answer 24

Question 25

Why do we not perceive this dog to be moving even when we move our eyes side to side - Explain this using the collonary discharge Theory

Answer 25

-There is an image displacement signal - as the dog wanders across the retina ( hence the value of 1 in the image above) -There is a motor signal because we are moving our eyes -There is then a collonary discharge signal becsause whenever there is a motor signal, there must be a collonary discharge signal, because it is a copy -Then the comparator works out the difference between the two signals - which would be 0, there is no difference -This means that the brain will understand that no real motion has occurred The reason we see an image displacement signal, solely BECAUSE we moved our eye, not because the stimulus has moved

Question 26

What is the neuronal evidence of the collonary discharge theory?

Answer 26

-They put a monkey infront of moving bars, they measured the response of real motion neurons in the dorsal stream -So we have real motion neurons that will selectively respond to a moving object, as opposed to a static object -When the monkey was given the same scenario, and had to move eyes from one point to another, so a static image, the very same neuron did not fire So therefore, the neuron selectively responded to a moving bar, rather than an eyre movement that was made