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understanding the brain > Vision > Flashcards

Vision Flashcards

Week 9

1
Q

what is the unit of light?

A

nanometers (nm)

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2
Q

what is the light spectrum?

A

380-760 nm

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3
Q

what is electromagnetic radiation defined by?

A

its frequency/ wavelength and ampitude

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4
Q

what are light rays emitted by?

A

a luminous object can be reflected, absorbed and/or refracted
light source bounces off the object

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5
Q

what is the speed of light?

A

300 thousand km/hour

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6
Q

where is light processed/ projected onto?

A

retina

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7
Q

what kind of light is most prominent to bees?

A

UV light

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8
Q

what does dichromatic mean?

A

pick up 2 different colours only.

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9
Q

what does light enter the eye from?

A

through the cornea (clear dome)

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10
Q

where is light processed?

A

the pupil (centre of the iris)

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11
Q

where in the eye does light bend?

A

the lens (image reversed and inverted)

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12
Q

what does light continue through the eye?

A

the vitreous humour (clear gel)

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13
Q

what is the role of the fovea?

A

picks up detail of an image (high acutany)

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14
Q

what is lens accommodation?

A

when the optical power of the eyes curvature changes to focus on objects at a range of distances

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15
Q

describe the change in curvature for short focal distances?

A

when ciliary muscles contract, zonules loosen creating a rounder shaped lens & higher refractive power- see at shorter focal distances

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16
Q

describe the change in curvature for far focal distances?

A

When ciliary muscles relax, zonules increase in tension, creating a flattening of the lens- increase in further focal distances.

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17
Q

what is presbyopia?

A

As we get older, objects that are close tend to become harder to focus on
○ As we age lens becomes stiffer- harder for ciliary muscles to change the lens shape
§ Full accommodation range becomes narrowed
§ Gradually starts in 20s but is very subtle so don’t notice until 40-50s.
§ Can be treated through glasses, contact lenses or laser eye surgery.

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18
Q

what are photoreceptors?

A

convert light energy into neural activity
Have photopigment in cells

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19
Q

what are bipolar cells?

A

transmit information to ganglion cells
○ Hyperpolarisation of rods and cones, depolarises the bipolar cells

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20
Q

what are ganglion cells?

A

integrate information and send APs to brain
○ Interpret the message: intensity of firing

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21
Q

what are horizontal and amacrine cells?

A

ateral neurites influence cells close by
○ Communicate with the bipolar cells- what is firing and at what intensity
* Occipital lobe transduces the message
* Light travels through all the cells

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22
Q

how many rods are there in the body?

A

92 million

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23
Q

where are rods found?

A

retinal periphrey (not in the fovea)

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24
Q

are rods sesnsitive to light?

A

yes- very

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25
Q

what is the function of rods?

A

identifying light or dark

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26
Q

are rods sensitive to colour?

A

no- balck and white info only
(monochromatic information)

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27
Q

what type of acuity do rods have?

A

poor- not sensitive to sahrpness/form of objects

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28
Q

how many cones are there in the eye?

A

4.6 million

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29
Q

where are cones found?

A

mainly in the fovea

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30
Q

how sensitive to light are cones?

A

less sensitive than rods

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31
Q

what type of information do cones provide us with?

A

info about the hue (colour/wavelength of light)

32
Q

what type of acuity do cones have?

A

high- can detectr shape, form, colour

33
Q

what is an optic disk?

A

where all axons from the ganglion cells accumulate together to form optic nerve

34
Q

what is transduction?

A
  • A process that converts an external stimulus to an internal stimulus
  • Transduction of light energy into changes in membrane potential
35
Q

what are receptive fields?

A

The area of the visual space in which a stimulus must be presented to change the activity of a neuron

36
Q

what does the size of a neuron’s receptive fiel determine?

A

its acuity (smaller the better) and sensitivity (larger is better)

37
Q

what is the fovea?

A

small as few photoreceptors converge on ganglion cell (parvocellular ganglion cells)
Small receptive field- sharper image

38
Q

what is the periphery?

A

large as many receptors converge (magnocellular ganglion cells)
○ Large receptive field- better location of image
○ Lot more ganglion in receptive field- more rods and cones
§ Has boundaries (can be wide or small- according to where ganglions are on the retina)
Provoke action potential or non action potential

39
Q

where do the rigth and left visual fields cross?

A

Optic Chiasma

40
Q

what does ipsilateral mean?

A

opposite side

41
Q

what does contralateral mean?

A

same side

42
Q

what is binocular vision?

A

both right and left eye are working together

43
Q

what happens in the nasal side of the eye?

A

they cross to the opposite hemisphere of the brain

44
Q

what happens to the vision in the temproal/lateral side of the eye?

A

stays on the same side of the hemisphere

45
Q

what is the role of the LATERAL GENICULARE NUCLEUS (LGN)?

A

relay information to make it easier to be processed further down

46
Q

What is the process called through which external sensory stimuli (e.g., light) is transferred into neural activity?

A

transduction

47
Q

Where do the axons from each optic nerve meet and cross over (depending on if they are nasal or lateral)?

A

optic chiasm

48
Q

what is the LGN part of?

A

thalamus

49
Q

what does each LGN recieve?

A

info from both eyes but only about the contralateral visual field

50
Q

how many layers of LGN are there?

A

6 layers

51
Q

what are the 6 layers of LGN innervated by?

A

the contralateral (layers 1, 4 and 6) and ipsilateral eye (layers 2, 3 and 5)

52
Q

what is the magnocellualr layer of LGN?

A

layers 1 & 2: relay information about form, movement, depth, light-dark contrast, basics of information
○ Pick up the rods that provide magnocellular layer info

53
Q

what is the parvocellualr layer of LGN?

A

layers 3-6: relay information about colour (red & green) and fine detail
○ High acuity- picking up a lot of the cones
* Sublayers are koniocellular – relay information about colour
○ Relay of info about the colour blue (cones)

54
Q

what happens as we go fruther up the hierarchy of LGN?

A

more detail recieved by the right and left eyes

55
Q

what is the straite cortex also known as?

A

the primarty visual cortex

56
Q

how many layers is the cortical region of the straite cortex organised into, and what are they?

A

6 layers
○ V3a motion
○ V3 Form
○ V2 Relay signals
○ V1 catalogues input
○ VP relay signals
○ V4 colour and form

57
Q

what is the role of the straite cortex?

A
  • Takes on board the theme, form, general layout of the object
  • Info passed to the extrastriate cortex: finer detail- colour
58
Q

what is the dorsal stream?

A

where object is in space
○ Moving across our vision
○ Helps with perception of how an object is moving across our retinal image

59
Q

what is the extrastriate cortex?

A
  • Surrounds the Striate cortex / primary visual cortex (V1)
    • Combines information for perception
60
Q

how is the extrasriate cortex arranged hierarchically?

A

(V2-V8)
* Information moves up the visual association cortices, where it is analysed then passed on to higher centres for further analysis
○ In the parietal and temporal lobes- add info about what we are visualising
* Hierarchy of receptive fields in the visual system: receptive fields become larger and more complex

61
Q

what are the two cortical processing streams of the extrastriate cortex?

A

○ Dorsal – “where” pathway
§ Cant identify where the object is in our visual field
§ If object is moving or static
○ Ventral – “what” pathway
§ Cant identify what the object is

62
Q

what colour are high frequency light waves?

A

violet

63
Q

what colour are low frequency light waves?

A

red

64
Q

how many light detecting cells are in rods?

A

one- only see light or no light

65
Q

how many light detecting cells in cones?

A

3- can see red, gree, blue (form other colours through a mixture of each of the cones)

66
Q

what are the two systems of code colour?

A
  1. trichromatic coding (cones)
  2. opponent-processing coding (ganglion cells)
67
Q

what is trichromatic coding?

A
  • Retina contains three types of cones responsible for colour vision
  • Processed by different parts of the visual system
    ○ Red (long nm)
    ○ Green (medium nm)
    ○ Blue (short nm)
68
Q

what is a comon form of colour blindness?

A

the confusion between red and green colours.
* Due to a genetic defect (affecting ~10% of males) resulting in “red” cones being filled with “green-cone” photopigment or vice versa.
* 1 in 10 males are red-green colourblind

69
Q

what is opponent-processing coding?

A
  • Three colour system is converted into opponent-colour system
    • 2 types colour-sensitive ganglion cells, respond to colour pairs
      ○ Yellow - Blue
      ○ Red - Green
    • Cant see the two colours at the same time
70
Q

what happens when a red light is shown to the eye?

A

it stmulates the red cone: red-green gangliuon cell= excitatory and signals red

71
Q

what happens when a green light is shown to the eye?

A

stimulate sthe green cone: red-green ganglion cell= inhibited, signals green

72
Q

what happens when the light is shown the colour yellow?

A

stimulates the red and green cones equally: red-green= exitation and inhibition cancel each other out so no chnage in the signal is detected.
yellow-blue ganglion cells= exitatory so signals yellow

73
Q

what happens when the colour blue is shown to the eye?

A

stimulates the blue cone: yellow-blue ganglion cell is inhibited so signals blue

74
Q

what is negative afterimage caused by?

A

Due to adaptation in the rate of firing of ganglion cells

75
Q

what is a rebound effect?

A

If ganglion cells are excited/inhibited for a prolonged time, they will fire less/more relative to baseline activity

76
Q

give an example of negative afterimage?

A
  • Looking at the green apple inhibits red-ON green-OFF cells excites green-ON red-OFF cells
    ○ both interpreted by the brain as green
  • Looking at a white background (reflecting neutral coloured light containing all colours) makes red-ON green-OFF cells fire more and green-ON red-OFF cells fire less
    ○ interpreted by the brain as red

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