Interfacing Brain and Body Flashcards
traditional sensory psychophysics
task complexity is found in varying the presented stimulus and recording different simple psychological responses
motor psychophysics
the stimulus is very simple whereas the response looks for regular features of complex movements by varying the response parameters
when planning movements, we must consider high-level choices such as:
duration (accuracy)
path (shortest, smoothest, minimising energy use)
other lower-level parameters should also be considered:
velocity of movements
joint angles
coordinated muscle activity
planning and complexity must occur somewhere…
in the CNS for even the simplest of movements to be produced
- this requires neural activity for muscles to contract
what do motor invariants consider?
humans have highly stereotyped trajectories for eye and arm movements
- learn to perform actions through common mechanisms to maintain some unknown criteria
path
sequence of positions of the hand in space
velocity
time sequence of along a path
explanations for motor invariants
- optimise smoothness of movement (minimum-jerk hypothesis)
- minimise forces around the joints (minimum torque-change model)
- minimise variance at endpoint of movements
issues with motor invariant explanations
produce similar predictions for how movement should look, so difficult to establish whether one/all theories are true
brain consists of…
100 billion neurones and 100 trillion synapses, which communicate to process sensory information
dendrites
area where neurones receive information
axons
output mechanism, which innervate and synapse onto dendrites of other neurones
what is the NMJ?
the complex synapse between nerve and muscle, which contains specialised “alpha” motor neurones that connect to muscles
how does NMJ provide basis for movement?
strong firing response of motor neurones at the NMJ causes muscle filaments to contract
why does the NMJ have a stronger response?
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
motor unit
signifies one motor neurone along with all the muscle fibres it innervates
how are slow and fast twitch fibres recruited?
according to the size principle
slow twitch
low levels of force for long periods of time, recruited at lower forces when muscles contract
fast twitch
produce higher levels of force, maintained for much shorter periods of time
how can different twitch fibres be developed?
regularly engaging in different force production activities can encourage muscles to develop different ones to support different activity
why is it important to study vision?
about 1/3 of the cortex is devoted to vision, and everything we do starts with sensation and vision
neural basis of vision
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
how does the brain receive information?
patterns of activity are projected onto the near surface of the eyeball, on the light-sensitive layer called the retina
why must light shine through the retina?
to reach light-sensitive cells at the back of the eye, which detect light frequencies at particular wavelengths to provide information
how does the structure of the retina provide insight into information processing?
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
inference from the retina is…
actively reconstructed by the brain
why do illusions occur?
because the brain makes mistakes in how real-world information is interpreted, due to not experiencing conscious perceptions of the world
examples of illusions
- 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
what does exploiting forced perspective lead to?
makes objects appear different size than they actually are, by employing optical illusions
pareidolia example
recognising faces in collections of objects where there is none, due to the left and right fusiform gyrus
reasons for illusions
- resolution problem
- energy problem
resolution problem
amount of information the eyes and brain must capture is too vast
energy problem
too much energy required to keep all cells in the retina active
how can illusions be solved?
compression:
- transmitting only important information such as changes across space and time
- some information is more important than others
employed to save energy
consequences of data compression
- 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
compression mechanism 1
spatial inhibiton → simultaneous contrast-type illusions
1 how can encoding change over space and context?
perceptions of colour are influenced by context, as cells in the retina are sensitive to particular colours
1 what does lateral inhibition cause spatial inhibitors to turn off?
cells when like-minded neighbours are active
1 how can the brain compress signals?
since adaptation is fast. also allows greater facilitation of edge detection to allow contrast
1 what does lateral inhibition disable?
the spreading of APs from excited cells to neighbouring cells
what is lateral inhibition?
a sensory coding mechanism to facilitate representations of vision
compression mechanism 2
temporal inhibiton → after-effect type illusions
2 evidence of encoding changing over time?
temporal inhibition turns off RBG cells if they are active for a long time, since adaptation is slow
2 stages of the brain compressing signals that stay the same
- looking at R for a long time inhibits R cells
- then looking at something white, BG cells will respond, but R will not
- white will instead look more BG, explaining colour-after effects
2 what does neural adaptation consider?
stimulus intensity determines size of AP, by their non-linear firing frequency
2 how can stimulus intensity adapt?
in response to changes in the environment, to preserve sensitivity
compression mechanism 3
filling in (craik o’brien cornsweet illusion)
3 how does the illusion occur?
brain spreads excitation from edges to neighbouring cells, due to good edge detection
3 what does good edge detection result in?
producing coherent but misleading image, which tricks brain into thinking certain parts are darker
how does light enter the eye?
passing through the transparent cornea and aqueous humour
what does the iris control?
the size of the pupil, which is the opening that allows light to enter the lens
what is light focused by?
the lens, which goes through the vitreous humour to reach the retina
rods and cones
rods - detect light and dark
cones - colour vision
translate light into electrical signal, which travels from the optic nerve to the brain
what do photoreceptors contain?
specialised outer segment that captures light to convert it into electrical signals for phototransduction
what does the optic nerve initiate?
the journey of the eye to the cortex
where do primary optic nerve pathways converge?
at the optic chiasm
left-hand fibres convey information about…
right visual field
vice versa
what happens after the optic chiasm?
the optic nerve transforms into the optic tract
