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SEM 2 Sensation & Perception > Receptive Fields > Flashcards

Receptive Fields Flashcards

1
Q

Which parts of the eye are responsible for focusing light on the retina?

A

Cornea and Lens

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2
Q

How do the cornea and lens help to focus light on the retina?

A

Bending the light so that it falls on the retina

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3
Q

Why does visual perception rely on rods at night?

A

Cones don’t work at night due to lower sensitivity

We only rely on the rods because it has very high sensitivity

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4
Q

Why do cones enable higher acuity vision?

A

Because there is less neural convergence and is able to pick up on the fine details

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5
Q

What is the ratio between retinal ganglion cells and photoreceptors?

A

1:126 (1 million : 126 million)

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6
Q

Are there more or fewer ganglion cells than photoreceptors?

A

Fewer

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7
Q

Because there are fewer ganglion cells, what do they do?

A

Ganglion cells must condense raw information from the photoreceptors

They aim to extract only important information from the retinal image

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8
Q

What happens in single-cell recording?

A
  • Physiological approach
  • An electrode is inserted into a neuron and it measures the electrical activity
  • It measures the activity of a SINGLE neuron
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9
Q

How do neurons communicate with one another?

A

By sending electrical impulses that travel down the axon

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10
Q

What does single-cell recording measure?

A

It measures the activity of a SINGLE neuron
(change in voltage as the action potential/nerve impulse passes by)

As action potential passes down the neuron, there is a spike in voltage

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11
Q

True or False?

As action potential passes down the neuron, there is a drop in voltage

A

False

As action potential passes down the neuron, there is a spike (sudden increase) in voltage

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12
Q

The more excited the neuron is, what happens to the action potential?

A

The more the action potential will fire

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13
Q

What does the rate of firing neurons indicate?

A

How active that neuron is

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14
Q

True or False?

If you excite a neuron more, it increases the size of the action potential

A

False

If you excite a neuron more, it DOES NOT increase the size of the action potential

Instead, it fires more action potential (rate of firing AP increases)

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15
Q

Increased rate of action potentials indicates ….

A

Increased activity of the neuron

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16
Q

Often single cell recording from ganglion cells is performed on cats. Describe how the activity of the cells is measured

A

1) Electrode is inserted into the retina to measure the ganglion cell

2) Experimenters present different stimuli to the cat

3) Experimenters observe what effect each stimulus has on the activity of the ganglion cell

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17
Q

Before you present any stimuli, the ganglion cell is already active. What term is used to describe this cell activity?

A

Baseline activity from the cell

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18
Q

Through single-cell recording and presenting different stimuli, what do experimenters aim to measure?

A

Experimenters try to find a stimulus that changes the activity of that ganglion cell

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19
Q

How is ganglion cell response measured? List 9 steps

A

1) Present spots of light onto the retina

2) Observe whether the ganglion cells respond (through the rate of firing AP)

3) Find the spot of light that increases the activity of the ganglion cells

4) Map out an area on the retina where any light within that area causes an increase in the activity of the ganglion cell

5) Fill that area with light (this will increase AP)

6) Observe what happens when you place the light just outside that area

7) If the light is just outside, the ganglion cell activity will decrease in response relative to the baseline level

8) Map out a 2nd (larger) area that surrounds the 1st area where light within that outer region causes an inhibitory response

9) If you present a bigger spot of light in the 2nd area, you’ll get an even bigger decrease in response

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20
Q

What is an inhibitory response?

A

Hyperpolarisation

When the ganglion cell is responding less than it would be if there was nothing presented to the retina

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21
Q

When the ganglion cell is responding less than it would be if there was nothing presented to the retina

This is known as…?

A

Inhibitory response

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22
Q

The area on the retina which, when stimulated by light, elicits a change in the firing rate of the cell

This is known as…?

A

Receptive field of a cell

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23
Q

Define receptive field

A

The area on the retina which, when stimulated by light, elicits a change in the firing rate of the cell

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24
Q

When there is an increase in the ganglion cell’s response rate, this is known as…?

A

Excitatory response (depolarisation)

Higher rate of firing action potential per/sec

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25
Q

When there is a decrease in the ganglion cell’s response rate, this is known as…?

A

Inhibitory response (hyperpolarisation)

Lower rate of firing action potential per/sec

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26
Q

There are 2 types of regions for measuring ganglion cell activity. What are they?

A

1) Excitatory response region
2) Inhibitory response region

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27
Q

Why are ganglion cells influenced by a region on the retina?

A

Convergence

On the retina, there is a group of photoreceptors whose responses converge to a single ganglion cell

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28
Q

How can convergence create 2 types of region (excitatory and inhibitory)?

A

Lateral inhibition

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29
Q

Inhibition that is transmitted across the retina by horizontal and amacrine cells is known as…?

A

Lateral inhibition

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30
Q

What is lateral inhibition?

A

Inhibition that is transmitted across the retina by horizontal and amacrine cells

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31
Q

What do amacrine and horizontal cells do in lateral inhibition?

A

These cells send messages across the retina

They transmit inhibition across the retina which causes inhibitory areas

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32
Q

What are the 2 types of cells involved in lateral inhibition?

A

1) Amacrine cells
2) Horizontal cells

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33
Q

What happens when photoreceptors send signals directly through the ganglion cell?

A

Excitatory response (increase the firing rate of AP)

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34
Q

What happens when photoreceptors send signals through intermediate neurons (horizontal or amacrine cells) which then send them to the ganglion cell?

A

Inhibitory response (decrease the firing rate of AP)

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35
Q

Why does lateral inhibition lead to an inhibitory response?

A

Because when photoreceptors send signals to intermediate neurons first, they will excite horizontal and/or amacrine cells (which are inhibitory cells)

This causes the (inhibitory) horizontal and/or amacrine cells to fire which causes a decrease in response/ rate of firing AP

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36
Q

What is Centre-surround antagonism?

A

Areas of excitation and inhibition due to intermediate neurons

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37
Q

Areas of excitation and inhibition due to intermediate neurons

This is known as…?

A

Centre-surround antagonism

38
Q

What happens in a centre-surround antagonism?

A

Area in the little circle has the opposite charge/effect and work antagonistically to the area outside of the little circle (but within the bigger circle)

e.g. Inner area = excitatory (+)
Outer area = inhibitory (-)

39
Q

What is ON-centre OFF-surround?

A

Inner area = Excitatory (+)
Outer area = Inhibitory (-)

40
Q

What is OFF-centre ON-surround

A

Inner area = Inhibitory (-)
Outer area = Excitatory (+)

41
Q

Inner area = Inhibitory (-)
Outer area = Excitatory (+)

This is known as…?

A

OFF-centre ON-surround (antagonism)

42
Q

Inner area = Excitatory (+)
Outer area = Inhibitory (-)

This is known as…?

A

ON-centre OFF-surround (antagonism)

43
Q

A region of the retina that affects the response of the ganglion cell is known as…?

A

Receptive field

44
Q

Stimulation of the receptive field can have (…………) effect on ganglion cell response

A

Inhibitory or excitatory

45
Q

What is a receptive field?

A

A region of the retina that affects the response of the ganglion cell

46
Q

In ON centre–OFF surround (antagonism), what happens when there’s no spot of light presented?

A

Ganglion cells respond at the baseline level

47
Q

In ON centre–OFF surround (antagonism), what happens when there’s a spot of light presented only on the inner area (centre receptors)?

A

Ganglions produce an excitatory response

48
Q

In ON centre–OFF surround (antagonism), what happens when there’s a spot of light presented only on the outer area (outer receptors)?

A

Ganglions produce an inhibitory response

49
Q

In ON centre–OFF surround (antagonism), what happens when there’s a spot of light presented on all areas (all receptors)?

A

Ganglions produce an inhibitory and excitatory response which cancel each other out

Thus, the cells respond at the baseline level

50
Q

In ON centre–OFF surround (antagonism), what happens when there’s a small spot of light presented on the inner area (centre receptors)?

A

Ganglions produce a WEAK excitatory response

51
Q

In ON centre–OFF surround (antagonism), what happens when there’s a large spot of light presented on the inner area (centre receptors)?

A

Ganglions produce a STRONG excitatory response

52
Q

In ON centre–OFF surround (antagonism), what happens when there’s a large spot of light presented on the inner area (centre receptors) but the light also seeps through onto a small area of the outer receptors?

A

Ganglions produce a WEAK excitatory response

53
Q

In OFF centre–ON surround (antagonism), what happens when there’s a spot of light presented on the inner area (centre receptors)?

A

Ganglions produce an inhibitory response

54
Q

In OFF centre–ON surround (antagonism), what happens when there’s a spot of light presented on the outer area (outer receptors)?

A

Ganglions produce an excitatory response

55
Q

In OFF centre–ON surround (antagonism), what happens when there’s a spot of light presented on all areas (all receptors)?

A

Ganglions produce an inhibitory and excitatory response which cancel each other out

Thus, the cells respond at the baseline level

56
Q

In OFF centre–ON surround (antagonism), what happens when there’s no spot of light presented on all areas (all receptors)?

A

Ganglions respond at the baseline level

57
Q

In OFF centre–ON surround (antagonism), what happens when there’s a large spot of light presented on the inner area (centre receptors) but the light also seeps through onto a small area of the outer receptors?

A

Ganglions produce a WEAK inhibitory response

58
Q

In OFF centre–ON surround (antagonism), what happens when there’s a large spot of light presented on the inner area (centre receptors)?

A

Ganglions produce a STRONG inhibitory response

59
Q

In OFF centre–ON surround (antagonism), what happens when there’s a small spot of light presented on the inner area (centre receptors)?

A

Ganglions produce a WEAK inhibitory response

60
Q

In OFF centre–ON surround (antagonism), what happens when there’s a small spot of light presented on the outer area (outer receptors)?

A

Ganglions produce a WEAK excitatory response

61
Q

In OFF centre–ON surround (antagonism), what happens when there’s a large spot of light presented on the outer area (outer receptors)?

A

Ganglions produce a STRONG excitatory response

62
Q

True or False?

Each photoreceptor is part of the receptive field of only one ganglion cell

A

False

Each photoreceptor is part of the receptive field of more than one ganglion cell

63
Q

Receptive fields of neighbouring ganglion cells overlap

Why?

A

Because they share photoreceptors

64
Q

True or False?

Receptive fields of neighbouring ganglion cells overlap

A

True

65
Q

True or False?

Receptive fields of all ganglion cells together cover the whole visual field

A

True

66
Q

If light falling on a region of the retina causes an increase in the response of a ganglion cell – what type of region is this?

A

Excitatory region

67
Q

What term describes the organisation of the receptive field of a ganglion cell?

A

Centre surround antagonism

68
Q

What pattern of activity do you get if the whole receptive field is illuminated?

A

Baseline level reponse

69
Q

How is it possible for a single ganglion cell to be influenced by a large number of photoreceptors?

A

Convergence

Lots of photoreceptors converge on a single ganglion cell

70
Q

True or False?

Ganglion cells respond to changes in light falling within the receptive field

A

True

71
Q

Why do ganglion cells have their particular organisation?

A
  • Ideal for detecting spots of light & edges
  • NOT able to detect the orientation of bars
72
Q

Why are ganglion cell organisations ideal for detecting spots of light & edges?

A

Because when there is light on the lines and edges, there will always be some areas of light and some areas of dark within the receptive field

73
Q

True or False?

Ganglion cells only detect which area in the receptive field is illuminated, regardless of orientation

A

True

74
Q

Ganglion cells have no response to changes in the overall level of illumination

What does this tell us?

A

Ganglion cells indicate that there are boundaries in the receptive field but do not indicate (overall) how much light is falling within the receptive field

75
Q

If you make the light darker, what happens to the ganglion cell response?

A

Gives the same response

76
Q

If you make the light brighter, what happens to the ganglion cell response?

A

Gives the same response

77
Q

What do ganglion cells do?

A

Respond to changes in the pattern of light within the receptive field

(and respond to some areas of light and dark)

78
Q

Respond to changes in the pattern of light within the receptive field

(and respond to some areas of light and dark)

What cell does this?

A

Ganglion cells

79
Q

Ganglion cells respond to changes in the pattern of light within the receptive field

(and respond to some areas of light and dark)

Why?

A

Because ganglion cells have to condense down the amount of information received from photoreceptors

The changes in the pattern of light carry the most important information

So ganglion cells only take the most important info by having boundaries that indicate light and dark

80
Q

True or False?

Ganglion cells increase the amount of information in a stimulus by finding contours and boundaries

A

False

Ganglion cells reduce the amount of information in a stimulus by finding contours and boundaries

81
Q

Why are line drawings effective (based on what we know of ganglion cells)?

A

The importance of boundaries between areas of light and dark explains why line drawings are so effective

82
Q

Hermann Grid can be explained by…?

A

Lateral inhibition

83
Q

What is the Hermann grid?

A

A grid with white lines and black squares

But the illusion is = you can see a grey dot in the intersections of white lines

84
Q

How can receptive fields explain the Hermann Grid illusion?

A

Because there are 2 ON-centre-OFF-surround cells centred on light regions of the grid

Because the inner area already has a lot more light than the outer area, it produces an excitatory response

At the intersection, more light falls on the surround area (OFF region) so it receives more inhibition and the cell fires less action potential

Overall, this produces a weak excitatory response and less firing of AP is interpreted as less bright so we perceive a dark grey spot

85
Q

Why do grey illusory spots reduce/disappear when we look directly at (fixate) them in the Hermann grid?

A

Neural convergence and receptive field sizes relative to eccentricity

120 rods send signals to 1 ganglion cell
6 cones send signals to 1 ganglion cell

When we look directly at the intersection between white lines on the Hermann grid, the image is projected onto our fovea (centre of eye)

Fovea contains high concentrations of cones (which has less convergence) which produces higher acuity vision. Fovea also has a small field of perception

In the periphery of the retina, acuity is poorer (because there are more rods in the periphery areas of the retina and rods have more convergence) so the illusion is stronger

86
Q

As retinal eccentricity increases (going from the fovea to peripheral areas of the retina), what happens to the receptive field size?

A

The more eccentric, the larger the receptive field

SImply = Fovea has a small receptive field and peripheral areas of the retina have a large receptive field

87
Q

True or False?

According to our centre-surround antagonism & receptive field explanation, we should get the same illusion in grids with wave lines as well. And we do.

A

False

According to our centre-surround antagonism & receptive field explanation, we should get the same illusion in grids with wave lines as well. But we don’t.

88
Q

The Hermann Grid illusion can be explained in terms of …? (List 2 ways)

A
  1. Centre-surround antagonism
  2. Varying receptive field sizes (and the illusion reduces when you look directly at it)
89
Q

What is simultaneous contrast illusion?

A

When you are presented with the same square of the same shade of colour but each square is placed inside a bigger square with different shades of a colour (different background)

Simply = There are 4 small squares of the same shade of grey but we think they look different (because of their background)

90
Q

Why is an inner square with a light background perceived as darker than an inner square with a darker background?

A

The brighter outer square causes a lot of inhibition around the edge of the inner square (because there’s less darkness falling within the receptive fields)

So the ganglion cells fire less AP and the inner square appears darker

91
Q

Why is an inner square with a darker background perceived as lighter than an inner square with a lighter background?

A

The darker outer square causes weak inhibition around the edge of the inner square (because there’s more darkness falling within the receptive fields)

So ganglion cells fire more AP and the inner square appears brighter

SEM 2 Sensation & Perception (12 decks)

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