Interfacing Brain and Body

Question 1

traditional sensory psychophysics

Answer 1

task complexity is found in varying the presented stimulus and recording different simple psychological responses

Question 2

motor psychophysics

Answer 2

the stimulus is very simple whereas the response looks for regular features of complex movements by varying the response parameters

Question 3

when planning movements, we must consider high-level choices such as:

Answer 3

duration (accuracy)
path (shortest, smoothest, minimising energy use)

Question 4

other lower-level parameters should also be considered:

Answer 4

velocity of movements
joint angles
coordinated muscle activity

Question 5

planning and complexity must occur somewhere…

Answer 5

in the CNS for even the simplest of movements to be produced
- this requires neural activity for muscles to contract

Question 6

what do motor invariants consider?

Answer 6

humans have highly stereotyped trajectories for eye and arm movements
- learn to perform actions through common mechanisms to maintain some unknown criteria

Question 7

path

Answer 7

sequence of positions of the hand in space

Question 8

velocity

Answer 8

time sequence of along a path

Question 9

explanations for motor invariants

Answer 9

• optimise smoothness of movement (minimum-jerk hypothesis)
• minimise forces around the joints (minimum torque-change model)
• minimise variance at endpoint of movements

Question 10

issues with motor invariant explanations

Answer 10

produce similar predictions for how movement should look, so difficult to establish whether one/all theories are true

Question 11

brain consists of…

Answer 11

100 billion neurones and 100 trillion synapses, which communicate to process sensory information

Question 12

dendrites

Answer 12

area where neurones receive information

Question 13

axons

Answer 13

output mechanism, which innervate and synapse onto dendrites of other neurones

Question 14

what is the NMJ?

Answer 14

the complex synapse between nerve and muscle, which contains specialised “alpha” motor neurones that connect to muscles

Question 15

how does NMJ provide basis for movement?

Answer 15

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

Question 16

why does the NMJ have a stronger response?

Answer 16

postsynaptic cell (muscle fibre) of NMJ has a convoluted SA which ensures more receptors are activated
- a single AP is enough to cause a contraction

Question 17

motor unit

Answer 17

signifies one motor neurone along with all the muscle fibres it innervates

Question 18

how are slow and fast twitch fibres recruited?

Answer 18

according to the size principle

Question 19

slow twitch

Answer 19

low levels of force for long periods of time, recruited at lower forces when muscles contract

Question 20

fast twitch

Answer 20

produce higher levels of force, maintained for much shorter periods of time

Question 21

how can different twitch fibres be developed?

Answer 21

regularly engaging in different force production activities can encourage muscles to develop different ones to support different activity

Question 22

why is it important to study vision?

Answer 22

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

Question 23

neural basis of vision

Answer 23

considers whether we are in command of our motor acts:

• as the popular belief is that our conscious decisions are the direct cause of our actions
• however, neuroscience demonstrates that actions are largely driven by brain processes outside of our consciousness

Question 24

how does the brain receive information?

Answer 24

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

Question 25

why must light shine through the retina?

Answer 25

to reach light-sensitive cells at the back of the eye, which detect light frequencies at particular wavelengths to provide information

Question 26

how does the structure of the retina provide insight into information processing?

Answer 26

as output is sent to fewer cells further back into the brain - suggests level of processing occurs before information reaches the brain structure comprising the visual system

Question 27

inference from the retina is...

Answer 27

actively reconstructed by the brain

Question 28

why do illusions occur?

Answer 28

because the brain makes mistakes in how real-world information is interpreted, due to not experiencing conscious perceptions of the world

Question 29

examples of illusions

Answer 29

- cannot be sure of colour - how big something is - direction, speed, and movement of an object - shape of an object - who someone is, facial expression, or their gender

Question 30

what does exploiting forced perspective lead to?

Answer 30

makes objects appear different size than they actually are, by employing optical illusions

Question 31

pareidolia example

Answer 31

recognising faces in collections of objects where there is none, due to the left and right fusiform gyrus

Question 32

reasons for illusions

Answer 32

1. resolution problem 2. energy problem

Question 33

resolution problem

Answer 33

amount of information the eyes and brain must capture is too vast

Question 34

energy problem

Answer 34

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

Question 35

how can illusions be solved?

Answer 35

compression: - transmitting only important information such as changes across space and time - some information is more important than others employed to save energy

Question 36

consequences of data compression

Answer 36

- 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 37

compression mechanism 1

Answer 37

spatial inhibiton → simultaneous contrast-type illusions

Question 38

1 how can encoding change over space and context?

Answer 38

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

Question 39

1 what does lateral inhibition cause spatial inhibitors to turn off?

Answer 39

cells when like-minded neighbours are active

Question 40

1 how can the brain compress signals?

Answer 40

since adaptation is fast. also allows greater facilitation of edge detection to allow contrast

Question 41

1 what does lateral inhibition disable?

Answer 41

the spreading of APs from excited cells to neighbouring cells

Question 42

what is lateral inhibition?

Answer 42

a sensory coding mechanism to facilitate representations of vision

Question 43

compression mechanism 2

Answer 43

temporal inhibiton → after-effect type illusions

Question 44

2 evidence of encoding changing over time?

Answer 44

temporal inhibition turns off RBG cells if they are active for a long time, since adaptation is slow

Question 45

2 stages of the brain compressing signals that stay the same

Answer 45

1. looking at R for a long time inhibits R cells 2. then looking at something white, BG cells will respond, but R will not 3. white will instead look more BG, explaining colour-after effects

Question 46

2 what does neural adaptation consider?

Answer 46

stimulus intensity determines size of AP, by their non-linear firing frequency

Question 47

2 how can stimulus intensity adapt?

Answer 47

in response to changes in the environment, to preserve sensitivity

Question 48

compression mechanism 3

Answer 48

filling in (craik o'brien cornsweet illusion)

Question 49

3 how does the illusion occur?

Answer 49

brain spreads excitation from edges to neighbouring cells, due to good edge detection

Question 50

3 what does good edge detection result in?

Answer 50

producing coherent but misleading image, which tricks brain into thinking certain parts are darker

Question 51

how does light enter the eye?

Answer 51

passing through the transparent cornea and aqueous humour

Question 52

what does the iris control?

Answer 52

the size of the pupil, which is the opening that allows light to enter the lens

Question 53

what is light focused by?

Answer 53

the lens, which goes through the vitreous humour to reach the retina

Question 54

rods and cones

Answer 54

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

Question 55

what do photoreceptors contain?

Answer 55

specialised outer segment that captures light to convert it into electrical signals for phototransduction

Question 56

what does the optic nerve initiate?

Answer 56

the journey of the eye to the cortex

Question 57

where do primary optic nerve pathways converge?

Answer 57

at the optic chiasm

Question 57

left-hand fibres convey information about...

Answer 57

right visual field vice versa

Question 57

what happens after the optic chiasm?

Answer 57

the optic nerve transforms into the optic tract