vision

Question 1

DEFINE: orientation invariance

Answer 1

recognising objects in their natural orientation enables the brain to recognise objects in any orientation

Question 2

DEFINE: scale invariance

Answer 2

recognising objects in their natural size enables the brain to recognise objects at any size

Question 3

what do parvocellular ganglion cells process information about?

Answer 3

shape and colour

Question 4

what are blobs in the cortex?

Answer 4

parts of the brain processing colour

Question 5

what are the three types of columns in the cortex?

Answer 5

• ocular dominance
• orientation
• blobs

Question 6

what are the simple cells?

Answer 6

• elongated neurons in layers 4 and 6 of v1 cortex responding to a bar in a certain orientation in middle of receptive field

Question 7

what are complex cells?

Answer 7

• neurons in layers 2, 3 and 5 of v1 cortex responding to a bar in a certain orientation anywhere in the receptive field

Question 8

what is the grandmother cell/jennifer aniston neuron?

Answer 8

• neuron responding to very specific objects. at the top of the hierarchal model.

Question 9

ventral stream pathway?

Answer 9

parvocellular GCs –> LGN layers 3, 4, 5, 6 —-> v1 —-> v2 —> v4 –> inferior temporal cortex

Question 10

which part of the eye has the highest visual acuity?

Answer 10

fovea

Question 11

DEFINE: retinotopic map

Answer 11

neighbouring cells in the retina feed information to neighbouring cells in their targets

Question 12

DEFINE: foveation hypothesis

Answer 12

retinatopic map and topographic map matches up

Question 13

direction-selective neuron

Answer 13

neuron responds to motion in a particular direction

Question 14

what is the morphology of a direction sensitive cell

Answer 14

dendrites located in one particular direction

Question 15

when a stimulus moves in a null direction, what happens to the membrane potential of a direction selective ganglion cell?

Answer 15

excitatory input from bipolar cells = smaller and delayed
inhibitory input from amacrine cells = larger
neuron is still depolarised but does not reach threshold –> action potential does not fire

Question 16

what kind of photoreceptors does the fovea mostly contain?

Answer 16

cones

Question 17

DEFINE: visual acuity

Answer 17

the ability of the eye to distinguish 2 nearby points

Question 18

amacrine cells

Answer 18

receive input from bipolar cells

project laterally to inhibit ganglion cells

Question 19

horizontal cells

Answer 19

receive input from photoreceptors

project laterally to inhibit bipolar cells

Question 20

outer plexiform layer

Answer 20

where photoreceptors synapse with bipolar cells and horizontal cells

Question 21

inner plexiform layer

Answer 21

contains synapses between ganglion cells, bipolar cells and amacrine cells

Question 22

what are the layers of the retina (innermost to outermost)

Answer 22

1. ganglion cell layer
2. inner plexiform layer
3. inner nuclear layer - contains cell bodies of bipolar cells, ganglion cells and amacrine cells
4. outer plexiform layer
5. outer nuclear layer - contains cell bodies of photoreceptors
6. layer of photoreceptor outer segments embedded in pigmented epithelium

Question 23

when are rods active?

Answer 23

at dim light

Question 24

when are cones active?

Answer 24

at bright light

Question 25

how do photoreceptors respond in the dark

Answer 25

1. channels permeable to Na+ and Ca2+ open
2. depolarisation
   large concentration of cGMP in the cytoplasm

Question 26

how do photoreceptors respond to light

Answer 26

1. photoreceptor activated by light
2. g proteins activated
3. g proteins activate phosphodiesterase
4. phosphodiesterase converts cGMP to GMP
5. GMP causes ion channels to close
6. hyperpolarisation

Question 27

OFF bipolar cells

Answer 27

• hyperpolarise in response to light
  spot of light in centre of receptive field -> photoreceptor synapses directly onto bipolar cell -> hyperpolarise
  annulus of light -> horizontal cells synapse onto bipolar cell -> depolarise

Question 28

ON bipolar cells

Answer 28

• depolarise in response to light
  spot of light in centre of receptive field -> photoreceptor synapses directly onto bipolar cell -> depolarise
  annulus of light -> horizontal cells synapse onto bipolar cell -> hyperpolarise

Question 29

what would be observed in the ganglion cells if the whole receptive field is illuminated?

Answer 29

no change in spiking

GCs respond to differences in illumination within receptive field

Question 30

what % of ganglion cells do parvocellular GCs make up?

Answer 30

80%