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Neuroscience > Visual Perception > Flashcards

Visual Perception Flashcards

1
Q

What are photoreceptor cells?

A

The rods and cones in the eye.

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2
Q

How many rods are there in the human eye? And cones?

A

120 million. 6 million.

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3
Q

What purpose do rods and cones have?

A

They take light energy and turn it into electrochemical energy to be used in the nervous system.

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4
Q

What are the three main differences between rods and cones?

A
  1. They contain different pigments, which respond to light differently.
  2. The distribution of rods and cones across the retina differs.
  3. Multiple rods feed into each ganglion cell, whereas only a few cones feed into each ganglion cell.
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5
Q

Briefly explain rods’ pigmentation set up.

A

Rods have only one pigment: Rhodopsin. It is sensitive to very small amounts of light. It becomes saturated in daylight, causing the rods to cease functioning.

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6
Q

Briefly explain the cones’ pigmentation set up.

A

There are three different kind of cones, each with a different pigment. Each cone is sensitive to different wave lengths. (short, medium and long wave lengths)

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7
Q

What colours are each of the different cones sensitive to?

A

Short - blue
Medium - green
Long - red

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8
Q

Where are the cones densely packed?

A

In the Fovea - the centre of the retina.

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9
Q

What effect does the ratio of ganglion cells to rods have?

A

The higher number of rods, in the ratio, means that the registering of low light in each rod can accumulate, causing a response from the ganglion cell. However, it also means that there is less sensitivity to fine detail, because the large number of inputting cells means that detail is lost.

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10
Q

What effect does the ration of ganglion cells to cones have?

A

The lower number of cells means that the system preserves details. However, it also means that in low light conditions, there are not enough cones to provoke a reaction in the ganglion cell.

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11
Q

What do ganglion cells do?

A

They send information from the eye to the brain.

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12
Q

What is the optic nerve?

A

The ganglion cell bodies’ axons stretching from the retina toward the brain.

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13
Q

What are the two types of ganglion cells called?

A

M ganglion cells (Midget)

P ganglion cells (Parasol)

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14
Q

What do the M cells respond to?

A

Coarse patterns as well as detecting rapid movement.

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15
Q

What do the P cells generally do?

A

They preserve colour information.

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16
Q

What is the receptive field?

A

A specific region of space to which a particular cell responds.

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17
Q

What does it mean if a ganglion cell has a ‘centre-surround’ structure?

A

It means that although the cell is activated when light hits within its receptive field, light in the donut-shaped area around the cell will inhibit the cell. It’s called an ‘on-centre, off-surround’ cell.

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18
Q

What use does a centre-surround structure have?

A

It allows for the brain to process, and enhance, contrast.

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19
Q

What are the two main destinations for visual information, in the brain?

A

The superior colliculus and the lateral geniculate nucleus. (the LGN extends to the primary visual cortex)

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20
Q

What does the tectopulvinar path do?

A

It allows for rapid orientation to important visual information.

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21
Q

What is involved in the tectopulvinar pathway?

A

The information is sent from the eye to the midbrain, namely the superior colliculus. It makes use, primarily, on M ganglion cells as it is concerned with motion and not fine detail.

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22
Q

What happens once the tectopulvinar pathways has lead information into the superior colliculus?

A

It extends upstream, to the pulvinar nucleus in the thalamus, as well as the cortical areas that control head and eye movement. It also sends info to the brainstem areas that control eye muscles.

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23
Q

What happens once the brain has adjusted, by means of the tectopulvinar pathways, to put the source of visual stimulus in direct eye sight?

A

The brain adjusts to get a more detailed analysis of the object, via the Geniculostriate pathway.

24
Q

Approximately what percentage of the optic nerve fibres project to the geniculostriate pathway?

A

90%

25
Q

What does the geniculostriate pathway help us with?

A

Perceiving colour and fine grained textures.

26
Q

Where do the axons of the geniculostriate pathway terminate?

A

In a complex section of thalamus called the Lateral Geniculate Nucleus. From there, the info moves to the primary visual cortex.

27
Q

What is the optic chiasm?

A

It is the point in the brain where info from the right hand side of the left eye crosses over to reach the right side of the lateral geniculate nucleus.

28
Q

How is the lateral geniculate nucleus structured?

A

It consists of six layers, stacked on top of one another and folded in the shape of a knee.

29
Q

What cells lie between layers of the LGN?

A

K-cell layers or konicellular layers.

30
Q

What differs in each layer?

A

Each layer receives information from only one eye. Also, the bottom two layers receive info from M cells and the top four from P cells.

31
Q

What are the bottom two layers of the LGN called?

A

Magnocellular layers.

32
Q

What are the top four layers of the LGN called?

A

Parvocellular layers.

33
Q

Which three layers of the LGN receive input from the contralateral eye?

A

2, 3 and 5.

34
Q

Which three layers of the LGN receive input from the ipsilateral eye?

A

1, 4 and 6.

35
Q

What does each of the main layers of the LGN contain?

A

A retinotopic map of half of the visual world - a map that is laid out spatially in the same way that the retina is lain out.

36
Q

Where is the primary visual cortex?

A

In the occipital lobe.

37
Q

What is another name for the primary visual cortex?

A

The Straite Cortex

38
Q

What is the cortical magnification factor?

A

It describes the millimetres of cortical surface that are devoted to one degree of angle in the visual world.

39
Q

What are the three types of cells found in the striate cortex?

A

Simple, complex and hyper-complex.

40
Q

How do simple cells in the striate cortex work?

A

Their receptive fields are bar shaped, with an excitatory centre and inhibitory surround. The cell will only fire if the bar is orientated in a certain way.

41
Q

How do complex cells in the striate cortex work?

A

Their receptive fields are bar shaped, but they do not have on and off regions. They do show a preference for a particular orientation.

42
Q

How do hyper-complex cells in the striate cortex work/

A

They are much like simple cells, except they prefer lines of a certain length. As the line gets longer, at a certain point the cell will become less excited by it.

43
Q

What are orientation columns?

A

A structure formed when cells that prefer a certain orientation group together.

44
Q

What are ocular dominance columns?

A

Structures formed when when cells are segregated according to which eye sends them input.

45
Q

Briefly explain the structure of a hypercolumn.

A

Within a hypercolumn, there are subcolumns of cells that prefer particular orientations and receive input from particular eyes. There are also ‘blobs’ that run vertically through the hypercolumn.

46
Q

What are blobs?

A

Areas that contain cells that are involved with colour coding information.

47
Q

What is binocular disparity and why do we need it?

A

It is the fact that the image that falls on each retina is slightly different to one another because the eyes are in two different locations. We need this for depth perception.

48
Q

What is the figure-ground segregation phenomenon?

A

It is the fact that the cells fire faster when you are looking at stimuli in your receptive field that are part of a figure than when they are part of a background.

49
Q

What effect does contextual modulation have?

A

It makes the cells fire differently, at the same stimulus, depending on the context of the stimulus.

50
Q

What two kinds of cells contribute to the contextual modulation process?

A
  1. Neighbouring cells within the striate cortex that send lateral connections to one another.
  2. Feedback projections from higher levels of the visual system.
51
Q

What are the areas V2, V3 and V4?

A

They are extrastriate regions of the visual cortex. They’re all retinotopically mapped and generally the dorsal half of each region represents that lower visual field.

52
Q

What is V5 also called and what do we think it is connected to?

A

The MT, it’s linked to motion perception.

53
Q

What is V4 connected to?

A

Colour perception

54
Q

What is the label given to the visual pathway that works through the dorsal stream?

A

The ‘Where’ pathway - spatial understanding

55
Q

What is the label given to the visual pathways that works through the ventral stream?

A

The ‘What’ pathway - object recognition.

Neuroscience (9 decks)

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