Vision Flashcards
What does an ambiguous image lead too?
People not seeing the image, but once they’ve seen it, it will always be there - changed brain forever
What are the problems of vision?
Vision is hard to interpret - the eye has a 2D surface (receives things in 2D) but the world is 3D. The angle you look at something changes how you interpret it
The brain has an ambiguous signal, and needs to make sense of it, 2D projection needs to be unpacked and understood by the brain
What is computer vision?
Computer vision allows us to pick things out but this can go wrong, they can make more mistakes than we would
How does light enter the eye?
It has an opening to it, it comes in through the cornea
Where does light travel through?
Through the lens, the lens can be changed to focus on things
Where does light hit?
Retina - the back of the eye
What does the retina contain?
Cells sensitive to light - photoreceptors
What does light pass through before it gets to photoreceptors?
Cells
What do photoreceptors contain?
Photopigments - light sensitive molecules why change when light hits them
Why are photoreceptors on the edge?
Because they need good nutrients
What are the two types of photoreceptors?
Cones - 3 types, sensitive to different wavelengths, day time vision
Rods - contain rhodopsin, respond in dim light
What happens in the retinal ganglion cells?
This is the point that we start to process information that is coming in
What do retinal ganglion cells code for?
Different properties of the visual stimulus
Each one is responsible for coding something about one thing about the retina - taking input from loads, and processing it
What are the two channels of retinal ganglion cells?
Midgit ganglion - small, few connections
Parosol - large
Each project to parvocellular pathway
Cells have receptive fields, - the part of the retina the ganglion is connected too
What do single cell recordings on retinal ganglion cells show?
Shine light on receptor field and measure AP
no light - baseline activity
light fills RT - baseline activity
light fills centre - activity increases
light fills surround - activity decreases
What did the single cell recordings findings lead too?
On centre, off surround retail ganglion cells- lateral inhibition occurs where take input from a region of the retina, can code when light is specifically in the centre
What is lateral inhibition?
Ability of a neutron to reduce activity of its neighbours - disables the spreading of AP’s
What are retinal ganglion cells good at?
Detecting sharp edges, this is useful as edges contain a lot of information
What are retinal ganglion cells bad at?
Spotting gradual change
Perceptual effects
Illusory effect of grey patches, occurs due to an on centre off surround receptive field, inhibitory surround has more inhibition (more light)
Simultaneous contrasts
Perceiving 2 pics as different contrasts because of what is surrounding the image, e.g. less surrounding, less inhibition appears light, when more light, appears darer
brain uses contrasts to code and understand what is going on
What is the lateral geniculate nucleus?
It is in the thalamus, where all the senses go apart from smell
the gateway where we put mechanism and processes which are important for processing
organised into layers
What are the 3 layers of the lateral geniculate nucleus?
Midget - projects to the parvcallular, responsible for colour and detail - red/green differences, makes sense they are smaller as interested in colour
Parasol - projects to magnocellular layers, detection of movement and flicker. larger trying to detect movement so needs to be big so doesn’t go in and out too quick without seeing moevement
Konicellular cells - in between parvocellular and magnocellular layer, blue yellow discrimination
Where is the primary visual cortex?
At the back of the brain
What is the function of the visual cortex?
50% of dedicated to vision
lots of segments
What is the role of V1?
Retinotopic map - each point of visual field maps onto V1 so neighbouring neurons code for neighbouring parts - biased to representing the centre of visual field with more detail, when looking at nose, there will be more detail
What does retinotopic map refer too?
Maintaining a map of what is out there
What do cells in the visual cortex respond too?
For each given point in visual cortex, there are cells which respond to each orientation - retinotopically organised so neighbours represents orientation next to it
If a cat has lots of AP’s to vertical lines, what does it mean?
That this part of the cortex codes orientation
What is a critical period?
Kittens raised in tubes with vertical/horizontal stripes. No neurons responded to the orientation that they weren’t in - use it or lose it
Beyond V1
Doral pathway - at the back - where? projects to motor system
Ventral - front - what? projects to hippocampus, memories
processig hierarchy at V4, detects shapes
