Lecture 1 Flashcards
what is anticipatory control?
an important process which takes place in the brain to help us interact with the world in a way that our movements are smooth and executed on time
why is anticipatory control a necessary brain function?
because there is quite a long delay between the brain generating a motor command and sending it to the muscles to activate the limbs for movement, we need to anticipate in advance where our lives need to be so that our movements are smooth and on time as delays can be quite dangerous
what is the cerebellum and how is it related to anticipatory control?
the cerebellum, back of the brain, plays a really important function in making decisions outside of conscious awareness, so that you can make movements in a timely manner
it only knows that you’re doing eight seconds before you’re consciously aware of it
what occurs when a motor command comes from the brain?
when a motor command comes from the brain to activate muscles its characterised by changes in what are called action potentials, which activate your muscles
stronger forces = faster rate of ap = less intense movement
describe planning choices?
e.g. duration, path, velocity, joint angles, muscle activity, and neural firing pattern
We carry out normal daily movements in a very stereotypical manner, the same way time and time again
The type of decision the brain needs to make might be E.g. so which path. I’m going to take to pick up an object, how fast I’m going to move my limbs, what kind of angles my joints are going to bend to execute that action
what are motor invariants?
regularities in movement that control and perceive actions to save energy and reduce the amount of information that needs to be sent from the eye to the brain
what is a velocity profile?
a graph that shows the velocity and time of a movement, this often resembles a bell curve because movement they speed up and then slow down once they reached the target
many of our movements are characterised by parameters that stay the same, what are these?
velocity, duration, smoothness/jerk of movements, time, deviations of the position that you’re taking
what does NMJ stand for and what is it?
Neuro-muscular junction
the connection between the brain and our limbs
describe the process of an ap being sent to the limbs
the action potential is sent to the pre-synaptic axon & terminal (from the brain) to then be received via the acetylcholine receptors across the post synaptic membrane to the muscles/limbs
what are the features of the eye?
pupil
lens
iris
cornea
cilliary body
sclera
choroid
retina
blind spot
fovea
optic nerve
photoreceptors
(within the retina)
how is the retina the connection between the eyes and the brain?
the retina contains light sensitive cells which detect sensory information from the visual world
optic nerve -> brain
what is an example of proof that we don’t see thing the way they are?
the strawberry cyan picture
Because the berries are in a scene where everything is cyan - the visual system discounts the cyan (like ignores it)
The “opposite” of cyan is red - meaning it lies opposite red on the colour wheel which is why we see it
what is the resolution problem?
if your eyes were video cameras and your brain simply recorded everything the amount of data to be captured and recorded would be vast (it has to reduce the amount of information it sends to the brain in order for it to be processed)
what is the energy problem?
if all of the cells in the retina were active all of the time the amount of energy (and therefore blood vessels/blind spot) required would be huge
what is the solution to both the resolution and energy problems?
Compression
what is compression?
- Only transmits important information
- Don’t transmit things humans don’t need to react to
- Changes are more important than the stuff that stays the same
- Changes across space = only detect edges
- Changes over time = only detect things that move (new objects)
- Thus, some kinds of information are more important than others
what is the first compression mechanism?
inhibition over space
describe the compression mechanism 1
spatial inhibition -> simultaneous contrast-type illusions
One colour influences your perception of another colour
Aka a surrounding colour can influence ones perceptions of the true colour making it appear different
For example an orange line surrounded by a deeper orangey-red vs that same orange line surrounded by a bright yellowy shade of green
explain changes over space
G cells detect green at different (nearby) locations (visually)
Spatial inhibitors turn off cells if their like-minded neighbours are active (i.e., lateral inhibition)
Every ‘G’ cell has a spatial inhibitor cell linked to it
Adaptation is fast (it comes on quickly and disappears quickly)
Thus, the brain compresses signals that stay the same over space
describe how context affects perception
e.g you would get activity of red and green photoreceptors
But all the neighbouring cells also have a cell that can switch them off (the small s cells)
To reduce how much info the brain sends from the eye to the brain, the red cell in the centre is inhibited or reduced to save energy
But the consequence of that is that the green photoreceptor has not been reduced which tricks us into thinking that centre square is more green than what it actually is
do photoreceptors work in pairs or singles?
Pairs - red + green, blue + yellow
often works in opposites or complimentary pairs
what is lateral inhibition?
- Lateral inhibition disables the spreading of action potentials from excited cells to neighbouring cells
- It enhances the contrast between stronger and weaker signals
- Spatial enhancement of contrast improves the localisation of objects
- Same process for retina and in skin (motor systems)
- Each receptive field (see next week lecture) inhibits its neighbour
*Tactile inhibition actually occurs “upstream” in the spinal cord
what is the second compression mechanism?
inhibition over time
describe compression mechanism 2
If you stare at something for a long time, you adapt to it so the cells which are active reduce their activity to save energy
For example
The picture above is comprised of colours which are the opposite or complementary of the real world colours in the image
But because a person will stare at those particular colours for a long period of time, the photoreceptors that are sensitive to those colours have adapted and reduced their activity
But the cells which are the opposite of those colours were not inhibited
So now their output is greater than the cells that were inhibited
So the only information left aside from the eyes and brain is about the opposite or complementary colours which explains why you briefly see the image in positive real world colours
explain encoding changes over time
- R cells detect red things, g cells green things and B cells blue things
- Temporal inhibitors turn off cells if they are active for a long time
- Adaptation is slow. It takes time to build up and takes time to fade away
- Thus, the brain compresses signals that stay the same over time
In the retina you have your red green and blue photoreceptors
We also have a temporal inhibitor cells which can turn off a cell if it’s active for a long period of time simple to save energy
how does the brain compress signals that stay the same over time?
- White = Red + Green + Blue (additive colour mixing)
- If we look at red for a long time our ‘R’ cells will be inhibited
- If we then look at something white the green and blue cells respond, but the red cells don’t
- So, white now looks blue/green
leads to colour after-effects
what is neural adaptation?
Neural adaptation occurs to ensure our neurones can adapt and change to changes in the environment
stimulus intensity determines size of action potentials
firing frequency codes for intensity (“rate codes”)
very non-linear
usually codes for intensity of contrast between two levels
describe stimulus intensity
- Senses can adapt in response to changes in the environment
- Dynamic range of neurons is quite low
- Dynamic range of stimuli can be huge
- Sensory adaptation useful to preserve adequate sensitivity across a wide range of input intensities
- Fast or slow time courses of adaptation
- May reflect neural changes, mechanical relaxation or both
why is it better to have stimulus adaptation?
It is better to have a single cell which can change or adapt to a wide range of intensities than having certain cells that respond to fixed amounts of intensities as you would need a lot of them to detect a range of light and heavy objects
what is the third compression mechanism?
filling-in (Craik-O’Brien-Cornsweet illusion)
describe the compression mechanism 3
aim is to fill in missing information as a way of reducing how much information is sent from the eye to the brain
In the image above we are ticked into believing the face is a lighter colour than the hair (on the right side that is grey and covered by the blue square)
When in actuality they’re the same colour
The reason for this is if you look closely at the edges, because the brain is sensitive to edges, at the boundary when there’s contrast, it’s actually lighter on one side of the line and darker on the other side of the line
So what the brain is actually doing is only using information at the boundary and using that information to fill in
explain how the brain spreads excitation from edges to neighbouring cells
There are black and white photoreceptors
Information about white would be active on the right hand side of the stimuli
Information about blackness would also be active because it corresponds to that, the left side of that stimuli
So info about the boundary where there is contrast is strongly active, this info is then sent from the eye to the brain
But the brain then uses the information from those two centre photoreceptors and spreads their activity to neighbouring cells
And the consequence of that is the brain is filling in missing information
what is special about the compression mechanism 3?
This is the only mechanism which actually requires energy to spread information from neighbouring cells
summarise this lecture
brain integrates sensory info from the world & body to control muscles and joints for action (planning choices)
neuro-muscular junction is the interface between brain & limbs
brain adapts to sensory info to enable animals to adjust to changing environments
retina is the interface between eyes and brain
brain compresses signals that stay the same over space and time via inhibition
