vision from retina to cortex

Question 1

what is the “the problem of vision”

Answer 1

there is inherent ambiguity is the visual signals our eyes receive e.g. in shape

we have a 2d perception of a 3d world - leading to 2 different shapes being reflected on the retina in the same way

also courses a issue with distance

Question 2

elements of an eye

Answer 2

retina, pupil, cornea and lens, iris, ciliary muscles

Question 3

pupil

Answer 3

where light enters eye

Question 4

iris

Answer 4

adjustable aperture, constricts in bright light to make pupil smaller

Question 5

cornea and lens

Answer 5

focuses light on retina

Question 6

accommodation in the eye

Answer 6

an ability to change the shape of the lens to bring objects into focus at different distances

this process involves changes in the ciliary muscles

Question 7

Fovea

Answer 7

allows for our vision to be sharpened

is an indentation in the center of the macula and is the area with the greatest concentration of cones

Question 8

photo-receptors

Answer 8

cells with light sensitive photopigments in outer segments

detect light

Question 9

rods

Answer 9

contain rhodopsin, respond in dim light, none in the fovea

Question 10

cones

Answer 10

3 types with photopigments sensitive to different wavebands (long, medium and short) - daytime vision

Question 11

retinal ganglion cells

Answer 11

are positioned downstream of the retina

have a critical role in processing

there are 2 board types =
1. midget (parvocellular)
2. parasol (magnocellular)

Question 12

large parasol ganglion cells

Answer 12

connect to a larger number of photoreceptors
connects to the magnocelluar system

Question 13

small midget ganglion cells

Answer 13

connect to a smaller number of photoreceptors

connect to the parvocelluar system

Question 14

kuffler (1953)

Answer 14

single cell recording from retinal ganglion cells

Question 15

single cell recording from retinal ganglion cells

Answer 15

kuffler 1953
measured the action potential (clicks) of the retinal ganglion cells

took a baseline activity in a condition of no light
then filled the receptor field with light to take another baseline measurement

found that when center of the Receptive field was filled with light there was an increase in activity but when the off-surround retinal ganglion cell’s RF was filled with light activity decreased

meaning that we are efficient at finding centers

Question 16

lateral inhibition

Answer 16

the phenomena where in which a neuron’s response to a stimulus is inhibited by the excitation of a neighboring neuron. Lateral inhibition has been experimentally observed in the retina.

links to kuffler 1953 research into the single cell recording from retinal ganglion cells

Question 17

retinal ganglion processing

Answer 17

poor at spotting gradual change
good at picking out sharp edges
filters the input for useful information

Question 18

hermann grid

Answer 18

Baumgarter 1960

when looking at a black and white grid there appears to be dots at the intersections
this believed to because of on center off surround cells
however it is because they are more active in these sections

Question 19

Baumgarter 1960

Answer 19

hermann gird

when looking at a black and white grid there appears to be dots at the intersections
this believed to because of on center off surround cells
however it is because they are more active in these sections

Question 20

limitation of the hermann grid

Answer 20

wiggly version of the illusion courses the dots to go away
showing that illusion doesn’t happen due to activity in the retinal ganglion cells

Question 21

perceptual effects of retinal ganglion cells - simultaneous contrast

Answer 21

illusion
shows a grey square in the center of a black square and white square
even though the square is the same shade of grey in both situations
it appears darker on the darker background as this is the less surround inhibition
this means that what we are actually seeing is more contrast that in the more surround inhibition situation

Question 22

lateral Geniculate nucleus

Answer 22

located in the thalamus
is formed like a club sandwich - is layered with parvocelluar cells and magnocellular cells with koniocellular cells in between the layers

Question 23

mag/no/cell/u/lar - magnocellular cells

Answer 23

parasol - large
involved with movement and flickers

Question 24

par/vo/cell/u/lar - parvocellular cells

Answer 24

midget / small cells

colour and detail

Question 25

kon/io/cell/u/lar - koniocellular cells

Answer 25

blue - yellow cones

Question 26

visual cortex

Answer 26

occipital lobe
>50% of cortex dedicated to vision - visual cortex and beyond
primary visual cortex - V1 - striate cortex

Question 27

V1

Answer 27

contain the retina representation map
all the points in our visual field