Interfacing Brain and Body wk 1

Question 1

how do we carry out a certain movement?

Answer 1

• in a stereotypical manner, even between individuals

-different amounts of muscle activity prompts different neural firing patterns (action potentials)

Question 2

why do we experience illusions?

Answer 2

• because the brain has a preferred way in processing the world around us
• mostly to save energy + reduce amount of info that’s needed to be sent from the eye to the brain (compression)

Question 3

what are motor invariants

Answer 3

humans have highly stereotyped trajectories for eye and arm movements

Question 4

Name 2 Motor invariants

Answer 4

• Path
• Velocity

Question 5

path

Answer 5

sequence of positions of the hand in space

Question 6

velocity

Answer 6

time sequence of along a path

Question 7

what is the NMJ?

Answer 7

-the complex synapse between nerve and muscle
- the connection between brain and limbs

Question 8

how does NMJ provide basis for movement?

Answer 8

strong excitatory firing response of motor neurones at the NMJ causes muscle to contract

Question 9

why does the NMJ have a stronger response?

Answer 9

postsynaptic cell (muscle fibre) of NMJ has a convoluted surface area which ensures more receptors are activated

Question 10

What gets released in NMJ

Answer 10

Acetylcholine then gets released to activate a muscle

Question 11

why is it important to study vision?

Answer 11

about 1/3 of the cortex is devoted to vision, and everything we do starts with sensation and vision

Question 12

how does the brain receive information?

Answer 12

patterns of activity are projected onto the near surface of the eyeball, on the light-sensitive layer called the retina

Question 13

what does the retina contain

Answer 13

sensory cells that detect sensory info from the visual nerve

Question 14

how is the optic nerve formed

Answer 14

The output from the colour sensitive cells form the optic nerve this then sends info from the eye to the brain

Question 15

How is the world around us reconstructed in the retina

Answer 15

• the further along the visual pathway = more reconstructed
• so how reality looks like at the level of the retina is very different to how we consciously experience it

Question 16

what mechanism causes illusions to occur?

Answer 16

• the compression system doesn’t always work correctly
• it becomes too efficient where we see things that aren’t really there

Question 17

Strawberries illusion and how it works

Answer 17

• we perceive the strawberries as red but theyre actually grey
• this is because the fruit is in a scene where everything is cyan so visual system discounts this colour
• we process colours in pairs-> opposite of cyan = red
• as red cells arent adapted, we see red

Question 18

reasons for illusions

Answer 18

1. resolution problem
2. energy problem

Question 19

resolution problem

Answer 19

• amount of information the eyes and brain must capture is too vast
• so there must be a reduction in the amount of info sent from the ey to the brain

Question 20

energy problem

Answer 20

too much energy required to keep all cells in the retina active

Question 21

what would happen if we used up all of our energy?

Answer 21

• The optic nerve must be fatter to carry all the info, overriding the eye
• This causes blind spots–> blindness

Question 22

how can illusions be solved?

Answer 22

compression:
- transmitting only important information such as changes across space and time
- changes across space= edges+ contrast
- changes over time= new objects/ movement

employed to save energy/cells that are all responding to e.g. the same colour

Question 23

consequences of data compression

Answer 23

• sensitive to sudden changes, and poor at detecting slow changes
• poor colour resolution
• poor absolute judgements at different times, compared to side-by-side ones
• past events and context affect perceptions

Question 24

compression mechanism 1

Answer 24

spatial inhibiton → simultaneous contrast-type illusions

Question 25

1 how can encoding change over space and context?

Answer 25

perceptions of colour are influenced by context/surrounding colours , as cells in the retina are sensitive to particular colours

Question 26

1 what is lateral inhibition

Answer 26

- when spatial inhibitors turn off cells if their like minded neighbors are active - each receptive feild inhibits its neighbour

Question 27

1 Why can colour be affected by a neighboring colour?

Answer 27

- In the retina there are a bunch of cells that respond to the colour e.g. green - Associated to every one of these cells are another type of cells that play a role in inhibiting/turning off the cells (spatial inhibitors) - So, they turn off the cell, if their neighbour is also active

Question 28

1 how can the brain compress signals?

Answer 28

since adaptation is fast, it compresses the signals to stay the same over time

Question 29

1 explain whats happening in the spatial inhibition illusion

Answer 29

- block in the middle (red-green) could activate red and green cells - neighbouring cells can switch this off (spatial inhibition) - surrounding colour of red cause red cells to be active for processing - contrast (block in the middle) causes inhibition as we want to reduce the amount of red cells being used - so green receptor is more active= we see a more greenish colour to whats reality

Question 30

1 what does lateral inhibition disable?

Answer 30

- the spreading of APs from excited cells to neighbouring cells

Question 31

what is a consequence of lateral inhibition

Answer 31

enhances the contrast between stronger and weaker signals - this improves the localization of objects - e.g. pen resting on our palm this would activate all touch receptors directly underneath it but also it would inhibit the activity of neighbouring cells in order to enhance the contrast been the cells that are and aren't active

Question 32

compression mechanism 2

Answer 32

temporal inhibiton → after-effect type illusions

Question 33

2. explain an after effect type illusion

Answer 33

looking at the girls nose then flashing a white screen we should still be able to see the image in (the actual) colour rather than the colours in the picture

Question 34

2 why do after effect illusions happen

Answer 34

temporal inhibition turns off cell if they are active for a long time, since adaptation is slow it takes time to build this illusion up and takes time to fade away (due to compression)

Question 35

2 stages of the brain compressing signals that stay the same

Answer 35

White= a mix of red green blue 1. looking at R for a long time inhibits R cells AS weve become sensitive to it 2. then looking at something white, BG cells will respond, but R will not (complementary colours to R) 3. white will instead look more BG, explaining colour-after effects

Question 36

2 what does neural adaptation consider?

Answer 36

- stimulus intensity determines size of Action potential , by their non-linear firing frequency - lifting up a heavy object you would see a more frequent firing rate of action potential - this is called a rate code

Question 37

2 What is the problem with rate codes

Answer 37

- assumes the brain is capable of processing an infinite no. of AP (it cannot) - We cannot process AP that quickly, with a small period of time between them - AP decreases as intensity of stimulus we interacted with increases

Question 38

2 how can stimulus intensity adapt?

Answer 38

- in response to changes in the environment - sensory adaptation is useful to preserve sensitivity across a wide range of input intensities

Question 39

compression mechanism 3

Answer 39

filling in (craik o'brien cornsweet illusion)

Question 40

3 what is the craik o'brien cornweet illusion

Answer 40

- When comparing the left picture with a grey scale version on the right we are tricked into thinking the face is a lighter colour than the hair and beret, this is wrong - The hair and face are the same colour with slight variance

Question 41

3 Why does this illusion occur

Answer 41

- our visual system fills in missing info as a way to reduce how much info is sent from the eye to the brain

Question 42

3 how does the illusion occur?

Answer 42

- If we look at the edges, at the boundary where there's contrast it is lighter on one side of the line and darker on the other side - cells responding to the face don't need to be active, only at the boundary - The brain is sensitive to edges, so it spreads excitation to neighboring neurons , using this info at the boundary to fill in the missing info

Question 43

3 what does good edge detection result in?

Answer 43

- only info from the contrast between light and dark is being used to tell us what colour we are looking at - producing coherent but misleading image, which tricks brain into thinking certain parts are darker

Question 44

rods and cones

Answer 44

rods - detect light and dark cones - colour vision translate light into electrical signal, which travels from the optic nerve to the brain

Question 45

left-hand fibres convey information about...

Answer 45

right visual field vice versa