Samenvatting Class notes - From Perception to Consciousness

- From Perception to Consciousness
- 2020 - 2021
- Universiteit van Amsterdam
- Psychologie
110 Flashcards en notities
1 Studenten
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Samenvatting - Class notes - From Perception to Consciousness

  • 1612220400 college 1

  • What are the main parts of the eye (involved in perceptions)?
    • The cornea
    • The pupil
    • The lens
    • The retina
    • The fovea
    • The macula
    • The blind spot
    • The optic nerves
  • What does the retina consist of?
    Rods and cones (visual cells)
  • What are the functions of rods and cones?
    They sample the image that is projected on the retina by the cornea and lens,
    this information is transported to the visual cortex by the optic nerves
  • The retina pre-processes the rod and cone signals, which cells in the retina are used for this?
    • Bipolar cells
    • horizontal cells
    • amacrine cells
    • ganglion cells
  • How does the retina pre-proces rod and cone signals?
    The bipolar-, horizontal- and amacrine cells pre-process the information they receive from the rods and cones. 
    the ganglion cells pass this pre-processed information onto the optic nerves
  • Rods and cones are sensitive to different wavelengths, which wavelengths are they sensitive to?
    • Short wavelength cones respond best to blue
    • medium wavelength cones respond best to green
    • long wavelength cones respond best to yellow or red
    • cones, are not responsible for processing colour, respond best to green
  • How do rods and cones translate light into a neural signal?
    • Rods and cones use a protein called Rhodopsin in rods and Photopsin in cones. (different versions of the same protein)
    • Light stimulation of Rhodopsin or Photopsin triggers a chain of events that leads to the closure of Na+ channels in the cell membrane.
    • this causes a hyperpolarisation of the cell, which is sent to the bipolar cells which pass it on to the ganglion cells.
  • Explain why different cones are sensitive to different wavelengths of light?
    • Different versions of Rhodopsin (or photopsin) are sensitive to different wavelengths.
    • Humans have 4 types (3 for cones, 1 for rods)
  • How is it possible that some animals are better or worse at discriminating colours?
    Some animals have more types of rhodopsin or photopsin in their retina, which enables them to discriminate better between colours.
    other animals have less thypes of rhodopsin or photopsin in their retina causing them to be worse at discriminating colours
  • What causes colour blindness in humans?
    • Retinal colour blindness is caused by the absence of a specific type of rhodopsin-protein.
    • this causes the inability to discriminate between different colours.
  • How are the cones and rodes divided over the retina?
    • The cones are mostly present in the fovea, the part of the retina directly behind the pupil. There are almost no rods there.
      • vision, and colour discrimination are optimal in this area
    • rods are mostly present in the rest of the retina, but the highest concentrations are in the areas right next to the fovea, the parafovea. 
    • The place where no rods and cones are found is the optic disk or blind spot, this is where the optic nerves come into the eye.
  • What is the fovea?
    • The cup-shaped place in the retina right behind the pupil
    • contains the highest concentration of photoreceptors, which are mostly cones
    • vision and colour discrimination are optimal in this spot
  • Fundoscopy (looking at your retina through the pupil) reveals that light has to pass a lot of obstacles to reach the photo-receptors: veins, vitreous body (liquid that fills the eye) particles (‘bugs’)
  • What is another word for fovea?
    The macular
  • What is wet or dry macular degeneration?
    • it is a disease of the fovea
    • proteins or fluids come into the retina causing to disturb the form of the fovea
    • this can cause blank spots or distortion in your central vision
    • interrupts the things you intentionally want to look at.
  • Next to blood vessels and objects in the vitreous body, the light also has to pass through the composition of ganglion cells and bipolar cells etc, to get to the photoreceptors. Why is the retina organized in this way?
    • Behind the photoreceptors there is a layer of cells called retina pigment epithelium (RPE)
    • These RPE cells absorb the light that is shined upon the retina
    • If it wasn't for these cells, the light would be reflected and scattered by the back of the retina.
    • This would cause other photoreceptors to receive light that would only be meant to be received by one specific photoreceptor causing a distorted image of the visual field.
    • The pigment epithelium prevents light scatter, so that sharper vision is possible
  • Cats have reflective pigment epithilium instead of absorbant, what are the advantages and disadvantages of this?
    • better low light vision (because same ray of light hits more photoreceptors)
    • but un sharper image (due to scatter)
  • What is the blind spot?
    • RGC (retina ganglion cells) fibers lying on top causes the blind spot: the place where all retinal ganglion cell fibers pass through the eye (optic disk), and no receptors are present.
    • The blind spot is also called the optic disk because you can see it as a disk where the blood vessels originate if you look into the eye through the pupil
  • What is glaucoma?
    • It's another disease of the fovea
    • It's caused by increase of pressure inside the eye, which causes oppression of the optic nerves
    • Damage of nerve fibers of the RGC’s: optic nerve
    • Loss of peripheral vision first (but may vary)
    • Treatment: eyedrops, surgery (but lost RGC’s are lost)
  • What is the reason cells in the retina preprocess information from the photoreceptors?
    You have 130 million photoreceptors and only 1 million nerves that pass through the optic nerve.
    so the data needs to be compressed to be transported.
  • How does compression of information work?
    • The photoreceptor responds to light by hyperpolarization (cell becomes more negative by closing of Na+ channels, Na+ out), to dark by depolarization (cell becomes more positive by opening of Na+ channels, Na+ in).
    • This is called a graded potential signal, the more light there is, the more hyperpolarised the cell becomes.
    • This hyperpolarisation or depolarisation is passed onto the bipolar cells which pass it onto the ganglion cells (NO action potential.)
    • if the bipolar cells pass on depolarisation to the ganglion cells, the depolarisation of gc's can result in an action potential sent to the brain.
    • each photoreceptors is connected to on and off bipolar cells

    in essence photoreceptors respond to degrees of darkness which is converted into de- or hyperpolarisation of ganglion cells through bipolar cells.
  • The bipolar cells in the retina can pass on hyperpolarisations and depolarisations onto the ganglion cells in two different ways, which are they and how do they work?
    • Through a sign conserving synapse
      • If a photoreceptor hyperpolarises, the bipolar cell also hyperpolarises.
      • the bipolar cell transmits this hyperpolarisation onto the ganglion cell which also hyperpolarises
      • same goes for depolarisation of photoreceptor
    • Through a sign inverting synapse
      • Hyperpolarisation of the photoreceptor causes bipolar cell to depolarise
      • depolarisation of the bipolar cell is passed onto the ganglion cell which also depolarises.
      • same goes for depolarisation of photoreceptor, causes bc and gc to hyperpolarise.
  • What is an on bipolar cell and what is an off bipolar cell?
    • Off bipolar cells hyperpolarise when the photoreceptor hyperpolarises (sign conversing synapses)
    • on bipolar cells depolarise when the photoreceptor hyperpolarises (sign inverting synapses)
  • How is the difference between on and off bipolar cells created?
    It is caused by differences in neurotransmitter receptor sites
  • What are the functions of the horizontal cell in visual processing?
    • Horizontal cells receive signals from widespread region of receptors. 
    • They provide negative feedback on the receptors they receive information from.
  • In the chain of visual processing, where are the horizontal cells?
    Between the photoreceptors and the bipolar cells. The photoreceptors are connected to the bipolar cells.
    the horizontal cells are connected to the photoreceptors, but not to the bipolar cells.
  • How exactly do the horizontal cells give feedback to the photoreceptors?
    • If there is a patch of light shining on the retina, there is central part of the receptive field and a peripheral part of the receptive field all connected to the same horizontal cell.
    • the signals of the peripheral visual field are negatively fed back to the centre visual field by the horizontal cells.
  • How do horizontal cells give feedback to the different parts of the retina with uniform (same shade) and biform (light circle, dark surrounding ring) patches of light?
    • With a uniform patch of light the entire visual field would hyperpolarise. The hyperpolarisation of the photoreceptors in the peripheral field are negatively fed back to the photoreceptors in the central visual field, in the form of depolarisation. So the hyperpolarisation and the depolarisation cancel eachother out, resulting in an absence of signal to the bipolar cells.
    • with a biform (light circle, dark surrounding ring) patch of light, the central visual field hyperpolarises, and the peripheral visual field depolarises. This depolarisation is negatively fed back to the visual field in the form of hyperpolarisation, so a stronger hyperpolarised signal is send out to the bipolar cells.
      • this also goes for dark in the middle and light surrounding.

    in essence, bipolar cells are sensitive to contrasts.
    Ganglion cells are also sensitive to contrasts since they simply do what the bipolar cells do.
  • What are off- and on-centre ganglion cells?
    • Off-centre ganglion cells are sensitive to dark in the centre visual field and light in the peripheral visual field
    • On-centre ganglion cells are sensitive to light in the centre visual field and dark in the peripheral visual field
  • Why does the horizontal cell gives the center-surround (‘Mexican Hat’) profile of the bipolar (and subsequently ganglion cell) receptive field?
    • Without the horizontal cell the bipolar cell would only be receptive to what the photoreceptor indicates. (spike)
    • because of the feedback of the horizontal cell to the photoreceptors, the bipolar cells become receptive to contrast (total line)
  • Describe the preprocessing network of the retina by celltype.
    The receptors are sensitive to light.
    the bipolar cells are receptive to contrast
    the ganglion cells send these graded potentials to the visual cortex in the form of action potentials.
  • Rods are primarily used for vision in the dark
  • How do rods connect to the ganglion cells?
    • Rods are connected to specific rod bipolar cells (RBC)
    • These RBC's are connected to amacrine cells
    • these amacrine cells are connected to cone driven bipolar cells (regular bc)
    • cone driven (on, off) bipolar cells are connected to ganglion cells.
    • Rods have the same mexican hat system with the horizontal cells as the cones do.
  • Why are rods mostly used for vision at night, also called scotopic vision?
    Rods are a hundred times more sensitive to light than cones are.
  • How does it work that rods are used mainly at night?
    • Because rods are so sensitive to light
    • the light during the day is so bright that all the rodhopsin proteins cause constant hyperpolarisation (bleaching)
    • only at night it becomes dark enough for the rods to become depolarised.
  • What is the difference between cone driven (on, off) bipolar cells and rod bipolar cells, what is the reason this difference exists?
    • The rod bipolar cells have a larger receptive field than cone driven on off bipolar cells
    • the reason for this is that rod bipolar cells are connected to multiple rods whereas cone driven bipolar cells are connected to one cone.
  • If you transition from a bright surrounding to a dark surrounding your vision adapts to this change in luminance, dark adaptation. What are the processes responsible for this dark adaptation?
    • Pupil dilation 
    • cone to rod transition
      • cones are less sensitive to light than rods, so the rods start to depolarise
    • bleaching of the rods becomes undone, the rods start to work more the longer you spend in the dark.
    • Less receptor signal causes less negative feedback from horizontal cells
  • What is Retinitis Pigmentosa?
    • It is a disease of the retina
    • the disease causes Progressive degeneration of receptors: rods first, followed by cones
    • it's caused by pigment deposits at the retina
    • the symtomps get worse over time:
      • Night Blindness* > loss of peripheral vision > tunnel vision > full blindness
    • no cure
  • Which types of ganglion cells are there?
    • Midget cells
    • parasol cells
  • What are the characteristics of a midget cell, and a parasol cell?
    Midget cells:
    • Small receptive field, due to small dendretic networks
    • receive input from one single cone in the center and single cone surrounding causing them to be color contrast selective
    • Slow sustained responses; as long as the stimulus is present, the midget cell will keep firing action potentials.
    Parasol cells:
    • Large receptive field, due to large dendretic networks
    • receive input from multiple cones in the center and multiple cone surrounding causing them to not be color selective
    • Fast transient response; it will fire an action potential when stimulus is presented, but doesn't repeat this even though the stimulus is still present.
  • To which type of contrasts are midget cells sensitive?
    • Green in the middle with red surroundings
      • or the other way around
    • blue in the middle and yellow (combination of red and green) in the surroundings
  • What is the reason we perceive green and red, and blue and yellow as opposite colours and we perceive afterimages of these contrasts?
    • Simply because our retina is encoded in that way. 
    • It responds to colour contrasts in those forms
  • What is spatial frequency?
    • Spatial frequency is the same concept as temporal frequency
    • low tones have a low frequency and high tones have a high frequency
    • high spatial frequencies convey rapid changing contrasts, whereas low spatial frequencies convey slow changing contrasts.
    • in spatial frequency detailed contours are conveyed by high spatial frequencys and general contours are conveyed by low spatial frequencys
  • What is spatial frequency decomposition?
    • Every image / contour can be decomposed into the spatial frequencies it contains, together they make the whole image
  • What is a factor in what spatial frequencies you can perceive?
    The amount of contrast, and brightness
  • Midget cells respond to high spatial frequencies 
    parasol cells respond to low spatial frequencies.
  • What is the reason midget cells respond to high spatial frequencies and parasol cells respond to low spatial frequencies?
    • Midget cells have a small receptive field so if the spatial frequency is higher, it 'fits' the receptive field better because the width of the contrast falls exactly on the central visual field and peripheral visual field
    • Parasol cells have a larger receptive field so if the spatial frequency is lower it 'fits' the receptive field better because the width of the contrast falls exactly on the central visual field and peripheral visual field
    • A midget cell will perceive a low spatial frequency as a uniform colour because the contrast is not narrow enough to trigger contrast between central and peripheral field, it will not fire.
    • a parasol cell will perceive a high spatial frequency as a uniform colour because the contrast is too narrow to trigger a contrast between central and peripheral field, it will not fire
  • How do ganglion cells connect to the brain?
    • Via the lgn
    • Midget cells connect to Parvocellular layers of the LGN (small RF, high SF’s)
    • Parasol cells connect to Magnocellular layers of the LGN (large RF’s, low SF’s)
    • M always connect to P
  • How do different spatial frequencies arrive in the brain?
    • Y-type (parasol) RGC axons have faster conduction velocities than X-type (midget)
    • Magnocellular fibers of LGN faster than parvocellular fibers

    thus, low spatial frequencies of an image arrive in the visual cortex earlier than high spatial frequencies.
  • What is the navon task?
    • A task where a bigger image is made out of smaller images.
    • Subjects have to detect either the global target (large letter or shape), or the local target (small items)
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Laatst toegevoegde flashcards

What causes a complex cell to be sensitive to direction and orientation?
  • Complex cells receive information from multiple simple cells with the same orientation.
  • these simple cells have the same orientation but different receptive fields
  • this causes the complex cells to be responsive to a specific orientation regardless of where this bar is presented because it combines information from multiple simple cells.
  • the complex cell is thus Orientation (and spatial frequency) selective but without clear ON and OFF zones
    • the on and off zones of the simple cells overlap so orientation only is left.
Within the category of simple cells, what distinction can be made?
  • Simple cells are ‘Gabor’ filters, tuned to orientation and spatial frequency, with ON and OFF zones
  • some simple cells respond to a high spatial frequency, and others to a low spatial frequency.
What is a gabor filter?
A 3d image of the receptive field of a simple cell.
What type of cortical cells are there in v1 and what causes their difference?
  • Simple cells; respond to a stimulus in a specific orientation
  • complex cells respond to stimuli of a specific orientation moving in a specific direction
  • hypercomplex cells respond to stimuli of a specific orientation with a specific width that moves in a certain direction.
The next question proposed was how do we go from circular, contrast selective visuals fields in the LGN to oriented spatial field in the primary visual cortex?
  • The basic function of a neuron is collect information at it's dendrites. 
  • If the neuron collects enough 'evidence' (depolarisation) the neuron will fire an action potential
  • So neurons at the LGN already have enough information to fire an action potential when they spot a contrast difference.
  • Apparently the orientated cells in v1 receive input from LGN cells that have receptive fields that lie along a specific orientation in the visual field.
  • this way the neuron in v1 will fire an action potential when it simultaneously receives information from the LGN cells along this specific orientation.
Now a problem is proposed; you have several different organizations of the v1.Orientation columnsOcular dominance columns CO blobs and stripeshow are all these organizations integrated?
  • They're integrated into the Hypercolumn (Hubel & Wiesel) which is the basic processing unit in V1
  • Within each hypercolumn you have two ocular dominance columns
  • within each ocular dominance columns you have a orientational column for each possible orientation
  • per ocular dominance column there're also CO blobs which are sensitive to colour (because they receive parvocellular information)
What is a way to visualize orientation columns and ocular dominance columns in humans?
  • Using 7 tesla fMRI, very strong fmri field
How are the orientation columns of the primary visual cortex visualized?
  • Through optical imaging.
  • you make a hole in the skull at the spot of the primary visual cortex. 
  • brain tissue that is active can be reflective, so you shine a bright light on v1
  • while you pick up any reflection of active brain tissue with a macrolens you present the animal with different orientated stimuli.
  • per orientation you see which brain parts become active.
How is the cortex ordered by orientation of stimuli?
  • If you go straight down through the cortex you'll find cells that are all responsive to the same orientation of stimuli
  • if you go sideways into the cortex you'll find cells that are responsive to orientations that shift with a certain degree per layer.
How was receptive field tuning discovered?
  • After finding out that contrasts is wat best activates the retina, two researchers put an elektrode under an angle in the primary visual cortex
  • They discovered that the further they put the elektrode in the orientation of the stimuli that would trigger the neuron would shift gradually
  • this led to the discovery that the cortex was highly ordered by orientation of stimuli