vision 3

Question 1

Retinal ganglion cells have donut-shaped receptive fields and come in two opposite types:

Answer 1

1. “ON” center ganglion cells

2. “OFF” center ganglion cells

Question 2

“ON” center ganglion cells –

Answer 2

excited by light shining in their centers and inhibited by light in the periphery

Question 3

“OFF” center ganglion cells

Answer 3

excited by light shining in their periphery and inhibited by light shining in their centers

Question 4

In the fovea, a ganglion cell receptive field center _____.

Answer 4

may be only as wide as a single cone, with an atagonistic surround not much bigger

Question 5

Receptive fields are larger _____

Answer 5

in the periphery of the retina.

Question 6

The receptive field surround is mediated by:

Answer 6

horizontal cells

Question 7

Horizontal cell function

Answer 7

1. behave as though they have excitatory receptors for glutamate released from photoreceptors
2. make inhibitory synapses on neighboring photoreceptors in the field center

Question 8

when horizontal cells are excited by glutamate, they

Answer 8

release GABA to inhibit neighboring photoreceptors in the receptive field

Question 9

The key determinant in the receptive field type of ganglion cells is ____

Answer 9

The type of receptor on bipolar cells.

Question 10

Light’s effect on photoreceptor cells

Answer 10

Light hyperpolarizes photoreceptor cells and leads to a decrease in NT release

Question 11

photoreceptor cells release

Answer 11

glutamate

Question 12

Bipolar cells can be:

Answer 12

1. excited (OFF-center)
2. inhibited (ON-center)

by glutamate, it just depends on the receptor type

Question 13

bipolar cells always make ____ on ganglion cells

Answer 13

excitatory synapses

Question 14

Ocular dominance is a

Answer 14

measure of the relative synaptic input to a cell from each eye

Question 15

Monocular deprivation:

Answer 15

1. kittens 1 eye closed for several days during critical period, lose all connections to deprived eye
2. the longer the deprivation, the worse the damage
3. even if eye is re-opened, damage doe not recover
4. once the connections are lost, they are gone for good.

Question 16

Monocular deprivation experiment illustrates that

Answer 16

While connections are genetically determined, they are not immutable, at least for a while after birth (sensitive period).

These results suggest the explanation known as “disuse” atrophy, or “use it or lose it”.

Question 17

Binocular deprivation:

Answer 17

1. deprive kitten of sign in both eyes
2. normal primary cortex
3. there were more non-responsive cells, but most cells could be driven, and most were binocular.
4. half of cells had normal receptive field
5. BUT cats were behaviorally blind with higher order visual cells completely disrupted

Question 18

Binocular deprivation experiment illustrates that

Answer 18

something is happening that involves an interaction—perhaps competition—between the two eyes.

Question 19

Alternating monocular deprivation:

Answer 19

1. One eye is deprived and then reopened
2. No cortical cells can be driven by the deprived eye
3. BUT if the other eye is then deprived, the re-opened eye recovers and the newly deprived eye loses its connection with the cortex

Question 20

Alternating monocular deprivation illustrates that

Answer 20

the competition—active suppression by the active eye—that occurs between converging inputs from each eye in the cortex.