Sight and Visual Pathways wk2

Question 1

how can vision be experienced differently?

Answer 1

through
- motion
- 3D vision
- HD
- technicolour

Question 2

where does sensory processing start?

Answer 2

in the eye, as the retina is part of the brain

Question 3

how do retinal images begin?

Answer 3

the wrong way around and flipped side to side - variable resolution

Question 4

what part do axons play in processing information

Answer 4

• The axons of the retinal ganglion cells (that receive output from the photoreceptors ) are very sensitive to edge info
• e.g. contrast between objects excites retinal ganglion cells

Question 5

Why are edges important

Answer 5

• Not enough photo receptors to produce a more high res version of the world
• This is why edges are important

Question 6

how does the eye grab information?

Answer 6

through receptive fields

Question 7

receptive fields

Answer 7

• region in the sensory periphery within which stimuli influence the electrical activity of sensory cells
• e.g. excite/inhibit firing rate of a retinal ganglion cell
• this is because each photoreceptor receives a small part of info from the visual landscape

Question 8

How much space is a receptive field able to take in , what does this mean for the brain?

Answer 8

• only a small sample of sensory space is sampled, no one retinal ganglion cell can see the entire world
• So a single retinal ganglion cell will only respond to a single colour , they do not have access to everything we consciously see
• It shows how our brain has to pull together all of the output of many different ganglion cells to construct an image about the world

Question 9

When will photoreceptors respond

Answer 9

• when light falls on their receptive field
  -output takes form of AP in the retinal ganglion cells
  -their axons then form the optic nerve

Question 10

what happens to receptive fields as they get deeper into the brain?

Answer 10

get more structured and specific

Question 11

how are receptive fields organised?

Answer 11

to detect changes in vision, by having different regions which turn cells on and off

Question 12

where are retinal ganglion cells?

Answer 12

• on the inner surface of the retina
• at the bottom

Question 13

whats the pathway that leads us to retinal ganglion cells?

Answer 13

Photoreceptors+ rods+ cones –> bipolar cells –> retinal ganglion cells

Question 14

what function to retinal ganglion cells perform?

Answer 14

• lateral inhibition to cells that arent processing anything of interest
• this leads to compression

Question 15

types of ganglion cell receptive fields

Answer 15

• on centre and off surrround

Question 16

what are on center receptive feilds

Answer 16

• type of ganglion cell
• when receptive fields receive information from the bipolar cells, (like light)shines on the centre part of the receptive field
• it excites the firing rate of the retinal ganglion cell

Question 17

what are off surround receptive feilds

Answer 17

• info that shines on the surrounding part will inhibit/turn off the retinal ganglion cell
• So the on and off regions act as switches

Question 18

the consequence of centre-surround antagonism

Answer 18

“simultaneous contrast illusion”

Question 19

what do we see in a simultaneous contrast illusion

Answer 19

-The bar in the bottom is more darker on the right and lighter in the left
- in reality the lower bar is the same shade of grey all the way across

Question 20

“simultaneous contrast illusion”

Answer 20

1. on-centre receptive fields (on the darker background) are not inhibited, as there is less light to activate the off-surround, so the bar appears lighter= more info about light being sent to our brain tricking to us seeing brighter
2. on-centre cell (on the lighter background) is inhibited because there is more light to activate the off-surround, so the bar appears darker= less info about light being sent to our brain tricking to us seeing darker

Question 21

what do simultaneous contrast illusions show us

Answer 21

shows how background information plays a role in influencing what we see (because of our receptive fields )
- This is the same for colours (we see the opposite as consequence of receptive field )

Question 22

how is retinal output used to signal changes?

Answer 22

• by detecting edges over space,
• we break pictures apart in our brain into edges (colour comes later on)

Question 23

Our retinal ganglion cells and edges

Answer 23

• because of their sensitive nature , areas with changes would strongly excite our retinal ganglion cells = sharper edges
• no change= same static color
• so edges are enhance when changes occur

Question 24

What is the craik O’brien cornsweet illusion

Answer 24

tricks us into thinking the face we see is constructed of a brighter face and a darker hat + hair colour even though theyre the same

Question 25

craik o'brien cornsweet illusion is a consequence of...

Answer 25

seeing only edges, as images containing only edges pass through the retina unchanged, whereas normal images are converted into edges

Question 26

What is the end result of the Craik O'Brien -Cornsweet illusion

Answer 26

end result= retina output looks the same between both pictures, this means brain will interpret as the same and fill in the missing greys

Question 27

what are troxler fading and after-images?

Answer 27

Looking at the top cross for 10ish seconds--> moving eyes downwards you should see the opposite/complementary colour to the one you stared at initially ( at the bottom)

Question 28

how are after-images produced?

Answer 28

- Because there's no clear boundaries between the stimuli, there is little physical change taking place and so to save energy the brain inhibits activity of cells that receive info about luminance over time - so we opposite brightness youve adapted to because of time lag - Over a short period of time the blobs should fade because info about these colours is being inhibited/decreasing ( brain is receiving less info over time about what we are looking at)

Question 29

what does output from the retina reach?

Answer 29

the lateral geniculate nucleus

Question 30

what is the LGN?

Answer 30

- where information from the left and right VF combines in the brain, and RGC become specialised for motion or colour - so this happens before enters any of the V's

Question 31

Structure of the LGN

Answer 31

- Info starts to get separated in terms of color and motion so the LGN is constructed of different layers (6) - each layer has a complete retinotopic map of half the visual field - In between these layers we have certain types of cells

Question 32

LGN and how info is represented (retinotopic map)

Answer 32

The way which info is represented in the LGN has the same spatial relationship as info presented in the retina - So objects that appear side by side in the retina will activate activity that appears side by side in the brain (1:1 mapping from retina & LGN ) - However this is half the visual field because the left LGN only receives info from the right side of space (vice versa) - So there is no single cell within a layer of the LGN which has bionocular vision (both left and right side of space) - But each LGN receives input from both eyes

Question 33

what cells appear in the LGN?

Answer 33

koniocellular , parvocellular , magnocellular cells

Question 34

Koniocellular cells

Answer 34

K cells process info abour blue and yellow

Question 35

Magnocellular cells

Answer 35

- Large cell body - fast response -sensitive to motion/depth - clustered in the periphery (periphery is where we usually need to detect movement ) -course detail

Question 36

parvocellular cells

Answer 36

-small cell bodies - respond to red-green colour, - slow response to colour - closely concentrated in the fovea (part of the retina where there is high res vision, responding to more finer detailed info)

Question 37

the LGN is the main...

Answer 37

relay point from the optic nerve on the way to the cortex

Question 38

The visual pathway

Answer 38

info in the visual system is processed along to separate pathways , exciting different parts of the visual system

Question 39

division of visual pathways

Answer 39

dorsal stream ventral stream

Question 40

dorsal stream

Answer 40

where objects are processed in space, motion, and depth -helps motor cortex to helps us move our limbs V3, V5/MT, V6, V7

Question 41

ventral stream

Answer 41

recognising faces, places, and objects -what things are V1, V2, V4, V8, LOC, OFA, FFA, PPA

Question 42

The ventral system

Answer 42

Question 43

V1,2,3

Answer 43

-highly important in colour, deconstructing info into position and mapping out lines and spatial outlines of objects , info about motion -these are the first and main areas of our visual cortex

Question 44

The occipital facial area (OFA)

Answer 44

info about faces processed

Question 45

Fusiform facial area (FFA)

Answer 45

facial processing area

Question 46

Para hippocampal place area (PPA)

Answer 46

process info about places

Question 47

Lateral occipital cortex (LOC)

Answer 47

process objects

Question 48

Medial superior temporal cortex (MST)

Answer 48

processing advanced motion (e.g. rotation) + self movement

Question 49

Superior temporal sulcus (STS)

Answer 49

extracts info about emotions being expresses via face (this is separate from the area that recognises faces

Question 50

V5/MT

Answer 50

- motion

Question 51

How can we use a mathmatical model in relation to our vision?

Answer 51

- Using this model, they could represent how our brains see this illusion as its simply using knowledge of receptive fields - Supports the idea that many optical illusions are simply a consequence of the physiological behaviour of retinal ganglion cells - They did not need any higher order top down processing to explain visual illusions

Question 52

Why may mathematical models contradict the explanation

Answer 52

- Very lower order functions of retinal ganglion cells can contribute to this - But there is a more higher order mechanism (V4) with white balance correction (colour constancy )