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PL3232 > Week 6: Vision Part II Central Processing > Flashcards

Week 6: Vision Part II Central Processing Flashcards

1
Q

What is the optic nerve composed of?

A

Composed of axons of retinal ganglion cells, which exit the eye through the optic disc. Eventually enters the brain.

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2
Q

Where is the suprachiasmatic nucleus located?

A

Hypothalamus

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3
Q

How much axons does the suprachiasmatic nucleus receive from the retina

A

A small number

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4
Q

What is the suprachiasmatic nucleus involved in?

A

Controlling circadian rhythms

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5
Q

What does the pretactal nuclei consist of? And where is it located?

A

Cluster of small nuclei

Midbrain

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6
Q

What is the pretactal nuclei involved in?

A

Controls visual reflexes

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7
Q

What are the 3 types of visual reflexes controlled by the pretactal nuclei?

A

1) optokinetic nystagmus - observed when a repetitive visual stimulus moves fast in 1 direction
2) pupilary light reflex - pupil becomes larger or smaller in response to intensity of light reaching the eye. More light, pupil contracts, allowing less light to enter. Dark, pupil relaxes (larger), allowing more light to enter.
3) Vestibule-ocular reflex

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8
Q

Where is the superior colliculus located?

A

Midbrain

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9
Q

How much axons does the superior colliculus receive from the retina?

A

Large number

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10
Q

What is the superior colliculus essential for? What could it be involved in?

A 
Visuomotor transformations (eg. fixing on a visual item)
May play a role in visual processing. Believed to underlie newborns' visual capacities. Primary target of retina in many mammals.
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11
Q

Where is the lateral geniculate nucleus (LGN) located?

A

Thalamus

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12
Q

_____ is the primary retinal target in primates.

A

Lateral Geniculate Nucleus (LGN)

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13
Q

What is the LGN essential for?

A

Conscious vision

It is the primary input to the visual cortex

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14
Q

There are 6 layers in the LGN.
Layers 1-2 are the _____ layers.
Layers 3-6 are the _____ layers.

A

Magno

Parvo

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15
Q

Where do the parvocellular layers of the LGN receive input from?

A

Midget cells in the retina

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16
Q

What are midget cells characterised by?

A
  • very small dendritic trees
  • largest population of retinal ganglion cells
  • small receptive fields
  • slow at propagating action potentials
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17
Q

Where do magnocellular layers of the retina receive input from?

A

Parasol cells in the retina

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18
Q

What are parasol cells characterised by?

A
  • large dendritic trees
  • larger receptive fields
  • small proportion of retinal ganglion cells
  • fast transmission of information, action potentials move faster down axons
19
Q

What does fixating on an object mean?

A

Positioning both eyes such that the object is located right in the center of your fovea.

20
Q

Why does the fovea have the highest resolution for vision?

A

It has the highest density of photoreceptors

21
Q

Light from the right visual field falls on the ___ side of the left eye and ___ side of the right eye.

A

temporal; nasal

22
Q

Light from the left visual field falls on the ___ side of the left eye and ___ side of the right eye.

A

nasal; temporal

23
Q

What is the optic chiasm?

A

The point where fibres in the optic nerve cross over the other hemisphere of the brain.
right hemifield –> left thalamus (LGN)
left hemifield –> right thalamus (LGN)

24
Q

Layers 1, 4, 6 of the LGN receive _____ projections.

Layers 2, 3, 5 of the LGN receive ______ projections.

A

contralateral (left eye, right thalamus etc.)

ipsilateral (left eye, left thalamus etc.)

25
Q

LGN is often considered a relay station between ___ and ____?

A

retina ; visual cortex

26
Q

Why is the LGN often considered a relay station between retina and visual cortex?

A

Because the response properties of its neurons are similar to those found in the eye.

27
Q

The LGN projects to V1, where they are processed in different “columns”, what are they called?

A

Ocular dominance columns

28
Q

What is the difference between an orientation selective complex cell vs simple cell?

A

Complex cell has no inhibitory cell unlike the simple cell. Complex cells also tend to have larger receptive fields.

29
Q

What will evoke an activity in a complex cell?

A

A bar located anywhere in the receptive field in the right orientation will evoke an activity

30
Q

simple cells and complex cells are neurons found in ____?

A

V1

31
Q

Besides orientation selectivity, what other property do complex cells possibly have?

A

direction-selectivity

32
Q

The dorsal (where) /magnocellular pathway spans which part of the brain?

A

posterior parietal cortex

33
Q

The ventral (what) / parvocellular pathway spans which part of the brain?

A

temporal lobe

34
Q

What is the magnocellular pathway involved in?

A

involved in processing spatial information (where things are)

35
Q

What is the parvocellular pathway involved in?

A

Involved in processing object identity (what they are)

36
Q

What is the input to magnocellular layers in the magnocellular pathway?

A

parasol cells, characterised by very fast transmission speed

dorsal pathway processes motion, which require very fast responses

37
Q

What is the input to parvocellular layers in the parvocellular pathway?

A

midget cells. characterised by smaller receptive fields, which is important for shape perception, since we need high resolution to determine identity of objects.

38
Q

Where does the neurons in the dorsal pathway project to?

A

Area MT (middle temporal area)

39
Q

What do neurons in the dorsal pathway consist of?

A

complex direction-selective cells with very large receptive fields

40
Q

What condition arises from the damage of MT area?

A

Akinetopsia – the inability to perceive motion. person only sees flashes of stationary stimuli, very disturbing since motion is an important dimension of vision.

41
Q

What condition results from damage to dorsal parietal visual areas?

A

visuospatial neglect – inability to pay attention to a part of space when another competing stimulus is present on the other hemisphere.
right parietal damage –> hemineglect of left visual field
vice versa

42
Q

Which two conditions can arise from damage to the inferior temporal area?

A

1) agnosia – inability to recognise objects

2) prosopagnosia – inability to recognise faces

43
Q

What is agnosia characterised by?

A

Can recognise borders and maybe shape, but unable to link these visual features with the identity of objects he has learned throughout his life. can recognise faces!

44
Q

What is prosopagnosia characterised by?

A

inability to recognise faces, including own face :(

can learn to cope by using other visual cues, like smile, hair colour etc.

PL3232 (11 decks)

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