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Visual pathway Flashcards

1
Q

What is 50% of the cerebral cortex?

A

Visual

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2
Q

What are examples of the large no. of submodalities in vision?

A
  1. Colour
  2. Depth
  3. Motion
  4. Spatial localisation
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3
Q

What are the properties of visual acuity?

A
  1. Minimum separable images
  2. Depends on cone density in photopic vision
  3. Falls of with increasing eccentricity from fovea
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4
Q

What is used for acuity in central vision?

A

Letter or other symbol

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5
Q

What is most commonly used to assess peripheral vision?

A

Sensitivity to spots of light

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6
Q

Define retinal eccentricity?

A

When objects are projected directly onto fovea are the sharpest

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7
Q

How is visual acuity measured?

A

Smallest letters that can be distinguished on a chart and is governed by anatomical spacing of mosaic of sensory elements on retina

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8
Q

What is found only in the fovea?

A

Cone photoreceptors

Photoreceptors that deal with higher light levels, non-functioning at low light level - subserve colour

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9
Q

What is found at the periphery retina?

A
  1. Cones

2. Rods taking over at low light levels

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10
Q

What does visual acuity use?

A

Fovea

Width of 2 foveal cones = 1 arc minute

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11
Q

What is 360 degrees in vision?

A

Entire visual world around the subject

Divide into 60 arc/minute

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12
Q

What is the resolution limit of visual acuity?

A

60c/deg or a line resolution of 30 arc seconds

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13
Q

What is hyperacuity measured in and what does it detect?

A

3 arc seconds

Detect displacement of 2 light: Higher processing

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14
Q

Define visual acuity

A

The ability to read a standard test pattern at a certain distance, usually measured in terms of a ratio to ‘‘normal’’ vision

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15
Q

What is the test of foveal vision based on?

A

Gaps that are used by humans to identify those letters

  1. same no. of letters on each line
  2. Same level of difficulty
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16
Q

Where is fovea located?

A

Optical centre of eye

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17
Q

What is found at the optic nerve?

A

Physiological blindspot

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18
Q

What is not present in the fovea?

A

Rods

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19
Q

What is Perimetry?

A

A test of the entire visual field

Central 30 degrees

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20
Q

What does perimetry measure?

A

All areas of your eyesight, including your side, or peripheral vision

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21
Q

Where are Rods and cones found?

A

Rods: Periphery of the eye
Cones: Throughout the fovea [high concentration]

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22
Q

What happens at high light levels?

A

Rods doesn’t function

23
Q

What happens at low light levels?

A

Cones doesnt function

24
Q

What does numbers in perimetry represent?

A

Threshold detecting a bright spot on the background

25
What is visual world created from?
Electromagnetic radiation falling on the retina
26
What is Kanizsa triangle?
illusory contours A white equilateral triangle can be clearly be perceived even though there are no explicit lines or enclosed spaces to indicate such a triangle
27
What does visual perception do?
Takes the information and does Bayesian probability prediction as to find the appropriate physical explanation for the image that is falling on the retina
28
What is perception thought to be?
Dynamic
29
What is filling in?
An empty region of visual space appears to be filled with colour, brightness or texture of its surround
30
What is the brain capable of filling in?
The blindspot, borders, surfaces and objects
31
What is fading?
When one fixates on a particular point for even a short period of time, an unchanging stimulus away from the fixation point will fade away and dissapear [peripheral fading]
32
What are photoreceptors?
Analysis of colour
33
What are the spectral responsitivites of 3 cone types?
1. Blue, green or red | 2. Short, medium and long wavelength photoreceptors
34
What can we not discriminate?
Any colour that cannot be created by different outputs from those 3 cone types
35
Why does retina have to be transparent?
Photoreceptors are at the back of retina therefore requires high energy requirements
36
What varies with eccentricity?
Dendritic spread and cell body size and cell type
37
What is the basic arrangement of RGC called?
Centre-surround | simplest form of receptive field
38
What are all RGC divided into?
50% on centre and 50% off centre
39
What is on-centre?
Light falling on centre
40
What is off-centre?
Light falling on surrounding regions
41
What is magno, parvo and Konzo?
A neuron with a small cell body that is located in koniocellular layer of LGN in primates, including humans
42
What does magno subserve?
Detection of high temporal frequencies - motion high contrast sensitivity Chromatic information does not contribute to hue discrimination
43
What does parvo subserve?
slower temporal response - low contrast sensitivity but with spectral opponency High acuity foveal cone system
44
What does konzo subserve?
Sluggish temporal response - variable morphology and response function coneo-cellular pathway
45
What are the properties of magnocellular system?
Large RGCs include parasol ganglion cells 30 micrometre dendritic spread at Fovea axonal diamater large 10% total population projects to layer 4c alpha of V1 high contrast sensitivity Chromatic information present but would not contribute to hue discrimination
46
What are the properties of Parvocellular system?
Small RGC include foveal midget ganglion cells 5-10 micrometre dendritic spread at fovea Axonal diameter small 80% total population Projects to layer 4cB 'interblob' and 'blob' regions of VI Low contrast sensitivity spectral opponency
47
What is the property of koniocellular system?
Small dendritic spread, varied morphology Axonal diameter small 10% total population Projects to layer interlaminar region of LGN+ to midbrain Projects to layer 3 and 'blob' regions of VI Intermediate constrast sensitivity Variable spectral opponency
48
What are the properties of Intrinsically photosensitive RGCs?
``` 3rd photoreceptor Large dendritic spread Axonal diameter small 1% total population Project to midbrain light sensors Input from rods and cones aswell as intrinsic sensitivity to light ```
49
What is the role of IPRGCs?
Circadian rhythms, pupil light reflex
50
What is optic nerve surrounded by?
cranial meninges
51
Chiasm
All information coming from one hemi-field is going to contralateral side of brain
52
How are magnocellular and parvocellular arranged in the optic nerve?
Magnocellular are ventral Parvocellular are dorsal that go into LGN also crossing over where fibres are coming from retina - move to opposite optic tract in chiasm
53
What does visual input remain?
Monocular
54
How were blobs discovered?
Cytochrome oxidase staining of the visual cortex | higher metabolic activity

C1 Modules (20 decks)

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