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NEURAL BASIS OF VISION > Interfacing Brain and Body > Flashcards

Interfacing Brain and Body Flashcards

1
Q

traditional sensory psychophysics

A

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

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2
Q

motor psychophysics

A

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

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3
Q

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

A

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

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4
Q

other lower-level parameters should also be considered:

A

velocity of movements
joint angles
coordinated muscle activity

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5
Q

planning and complexity must occur somewhere…

A

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

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6
Q

what do motor invariants consider?

A

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

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7
Q

path

A

sequence of positions of the hand in space

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8
Q

velocity

A

time sequence of along a path

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9
Q

explanations for motor invariants

A
  • optimise smoothness of movement (minimum-jerk hypothesis)
  • minimise forces around the joints (minimum torque-change model)
  • minimise variance at endpoint of movements
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10
Q

issues with motor invariant explanations

A

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

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11
Q

brain consists of…

A

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

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12
Q

dendrites

A

area where neurones receive information

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13
Q

axons

A

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

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14
Q

what is the NMJ?

A

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

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15
Q

how does NMJ provide basis for movement?

A

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

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16
Q

why does the NMJ have a stronger response?

A

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

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17
Q

motor unit

A

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

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18
Q

how are slow and fast twitch fibres recruited?

A

according to the size principle

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19
Q

slow twitch

A

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

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20
Q

fast twitch

A

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

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21
Q

how can different twitch fibres be developed?

A

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

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22
Q

why is it important to study vision?

A

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

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23
Q

neural basis of vision

A

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
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24
Q

how does the brain receive information?

A

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

25
Q

why must light shine through the retina?

A

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

26
Q

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

A

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

27
Q

inference from the retina is…

A

actively reconstructed by the brain

28
Q

why do illusions occur?

A

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

29
Q

examples of illusions

A
  • 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
30
Q

what does exploiting forced perspective lead to?

A

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

31
Q

pareidolia example

A

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

32
Q

reasons for illusions

A
  1. resolution problem
  2. energy problem
33
Q

resolution problem

A

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

34
Q

energy problem

A

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

35
Q

how can illusions be solved?

A

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

employed to save energy

36
Q

consequences of data compression

A
  • 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
37
Q

compression mechanism 1

A

spatial inhibiton → simultaneous contrast-type illusions

38
Q

1 how can encoding change over space and context?

A

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

39
Q

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

A

cells when like-minded neighbours are active

40
Q

1 how can the brain compress signals?

A

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

41
Q

1 what does lateral inhibition disable?

A

the spreading of APs from excited cells to neighbouring cells

42
Q

what is lateral inhibition?

A

a sensory coding mechanism to facilitate representations of vision

43
Q

compression mechanism 2

A

temporal inhibiton → after-effect type illusions

44
Q

2 evidence of encoding changing over time?

A

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

45
Q

2 stages of the brain compressing signals that stay the same

A
  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
46
Q

2 what does neural adaptation consider?

A

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

47
Q

2 how can stimulus intensity adapt?

A

in response to changes in the environment, to preserve sensitivity

48
Q

compression mechanism 3

A

filling in (craik o’brien cornsweet illusion)

49
Q

3 how does the illusion occur?

A

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

50
Q

3 what does good edge detection result in?

A

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

51
Q

how does light enter the eye?

A

passing through the transparent cornea and aqueous humour

52
Q

what does the iris control?

A

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

53
Q

what is light focused by?

A

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

54
Q

rods and cones

A

rods - detect light and dark
cones - colour vision

translate light into electrical signal, which travels from the optic nerve to the brain

55
Q

what do photoreceptors contain?

A

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

56
Q

what does the optic nerve initiate?

A

the journey of the eye to the cortex

57
Q

where do primary optic nerve pathways converge?

A

at the optic chiasm

57
Q

left-hand fibres convey information about…

A

right visual field

vice versa

57
Q

what happens after the optic chiasm?

A

the optic nerve transforms into the optic tract

NEURAL BASIS OF VISION (10 decks)

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