neural circuits for visual perception

Question 1

what is the LGN and what are it’s components

Answer 1

lateral geniculate nucleus
6 layers - top 4 are parvocellular w info from midget ganglion cells
bottom 2 are megnocellular w info from parasol ganglion cells

Question 2

limitations of convergence of rods/cones

Answer 2

can only combine to measure size of neurons response, do not have info on edges, motion, colour or depth

Question 3

what are rgc and how do their receptive fields work

Answer 3

retinal ganglion cells
can either be off centre or on centre
on centre - fast firing middle with silent surround
outside rf is random firing

Question 4

how are receptive fields formed

Answer 4

by pulling responses of ganglion cells where the bipolar cells form the centre of the rf and the fovea feeds cones

Question 5

importance of retinal ganglion fields

Answer 5

all visual info encoded here is sent to the brain
they extract capture and enhance features of the retinal image
needed to understand colour, luminance contrast, edges light and dark

Question 6

perceiving luminance

Answer 6

using off and on centre surround cells
use the background for luminance contrast to see whether centre or surround is being activated

Question 7

how is colour represented using receptive fields

Answer 7

using opponent cells
signals of L M and S cones are compared
for example, red green opponent has L in centre, M in surround

Question 8

hypothesised purposes of the LGN

Answer 8

contralateral control representation - which helps to detect if a stimulus is lying behind one another if the L or R visual field
regulating and choosing stimuli to pay attention to and applying stored knowledge such as size constancy

Question 9

simple cells

Answer 9

excitatory and inhibitory are side by side and respond selectively to specific orientations

Question 10

complex cells

Answer 10

responds best to movement of correctly orientated bars across the RF, many cells have movement preference

Question 11

end stopped cells

Answer 11

respond to corners, angles or bars of certain (shorter) lengths moving in particular directions

Question 12

V1 perception

Answer 12

LGN sends most signals here, they rarely respond to spots of lights and prefer elongated contours and movement. it is most orientation specific and is in the occipital lobe

Question 13

functions of V2-5

Answer 13

2 - receives info from one and passes on
3 - depth
4 - colour
5 - motion

Question 14

disparity selective cell

Answer 14

how depth perception is mediated

Question 15

what is elaborate representation

Answer 15

orientation, motion direction, colour and binocular disparity has over 100% representation each across the first 5 cortical areas. this is because cells respond selectively to more than one stimulus