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Bio Psych > Lecture 4 - Vision > Flashcards

Lecture 4 - Vision Flashcards

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1
Q

Give progress of light entering eye

A

Cornea -> Pupil (iris) -> cornea+lens -> Vitreous humour -> retina

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2
Q

Define Cornea

A

clear dome at front of eye, expands and contracts to control amount of light

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3
Q

Define Pupil

A

circular opening in centre of iris

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4
Q

Define what the cornea + lens do

A

Bends light - reversing and inverting the image

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5
Q

Define Vitreous gel

A

Clear gel that light goes through to back of eye

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6
Q

Define retina and what is does

A

Circular disc at back of eye, changes light into an electrical signal

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7
Q

How does light signals get to brain

A

Optic nerve -> visual pathway -> occipital cortex (where electrical signals are converted to an image)

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8
Q

What is the function of rods and cones

A

The photopgiment they contain converts light into a chemical/ neural signal

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9
Q

What are the 2 photoreceptor cells?

A

Rods and cones

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10
Q

What is the process of light in the retina?

A

Photoreceptors -> Bipolar cells -> Ganglian cells

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11
Q

Whats the function of bipolar cells?

A

Intergrate informatino and relay info between photorecptors and brain, via ganglion cells

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12
Q

How many rods and cones are there?

A

120 million Rods

6 million cones

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13
Q

What do rods code for?

A

Night vision, sensitive to light intensity, monochromatic information.
Poor acuity, more of a broad brush
Found mainly in peripheral retina, not fovea

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14
Q

What do cones code for?

A

Day vision, sensitive to colour, provide info about hue
Excellent acuity
Found mainly in fovea

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15
Q

At rest, what are photoreceptors like?

A

Depolarised (voltage gated ion channels open at rest) and releasing glutamate
Glutamate inhibits bipolar cells,

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16
Q

How does light reach the brain? Chemical wise

A

Light -> hyperpolarises photoreceptors ->less glutamate is released onto bipolar cell, so it is no longer inhibited -> bipolar produces more glutamate -> excitates ganglian cell -> AP

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17
Q

When axons leave the eye, what do they form?

A

Optic tract, optic chiasm and optic nerve

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18
Q

Where do axons from the eye terminate?

A

Lateral Geniculate nucleus (in thalamus) and superior calliculus

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19
Q

Defing receptive field

A

The area of visual space which changes the activity (firing rate) of a neuron. Tiny spots in your visual field that corresponds to that photoreceptors precise location on retina.
There are millions

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20
Q

What does size of ganglian cell receptive field effect?

A

Acuity - the smaller the receptive field, the better acuity

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21
Q

Define Fovea

A

Central part of retina - a small receptive field as less photoreceptors converge on ganglian cell
PARVOCELLULAR

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22
Q

Define periphery

A

surrounding area of retina - Large receptive field as many receptors converge on ganglian cells
MAGNOCELLULAR

23
Q

What is areas with worse acuity used for?

A

Less important information - e.g. movement

24
Q

How do on and off areas work?

A

In opposite - striking centre has complete opposite effect as hitting surround

25
Q

In an on-centre, off-surround cell, how does light inhibit/ excite it?

A

Light hitting centre excites cell, increases firing
Light hitting surround inhibits cell, depolarising it, reduces firing

And vice versa with an off-centre, on-surround cell

26
Q

How do ganglion cells respond to light and dark?

A

Using centre-surround receptive fields, which cause an Action potential. Need contrast, very light and very dark patches.
Cos if light hits centre and surround, it cancels out so no change in firing - why starting at sun makes you blind

27
Q

Explain the hermann grid illusion

A

Due to summation, as there is more darkness hitting photoreceptor at intersections, we see a dark spot..
Also because of lateral inhibintion - contrast between light and dark

28
Q

What process do photoreceptors work by?

A

Summation - overall interpretation of light and dark

29
Q

What are they 2 systems used to code for colour in the visual system?

A

TRICHROMATIC CODING - At level of photoreceptors (Cones)

OPPONENT PROCESS CODING - at level of ganglion cells

30
Q

explain trichromatic coding

A

Photorecptors contain different opsin (pigment), there are 3 ttypes of cones for colour vision, each absoring specific wavelengths of light:
• Red (long waves)
• Green (medium)
• Blue (short)

31
Q

What is the most common form of colour blindness

A

red-green confusion, due to red cones being filled with green opsin and vice versa

32
Q

How does the LGN fit in to lights journey to brain?

A

Optic nerve synapses at: -> LGN -> Visual cortex

33
Q

Which hemisphere percevies which visual field?

A

Right VF processed by left hem - and vice versa

Visual fields overlap - depth perception

34
Q

How do the visual fields cross?

A

Nasal half of axons cross to opposite hemisphere

Lateral half stay on same hemisphere

35
Q

What is optic nerve made of

A

Ganglion cells, each eye has an optic nerve and they converge at optic chiasm at base of brain

36
Q

Explain the negative after image optical illusion

A

Colours are reversed relating to their opposite colour, influenced by ganglion cell firing rates and colour pairs

After a contiuned exposure, cones become desensitised, allowing other colours to dominate, so after seeing green for ages, youre more sensitive to red as its opposite, so seeing white as red.

E.g. green colour inhibits red on cell ganglions, so after being excited/inhibited for ages, they show rebound - either firing faster or slower than usual - when see white, they are no longer inhibited so fire much faster and we see red

37
Q

How does opponent process coding work?

A

A specific colour in receptive field increases firing of that colour, and reduces firing of the opposite colour.

E.g. red on cell increases firing when red hits centre ,and decreases when light hits green surround. The green surround is stimulate/ inhibited and sends signals about colour to the brain

38
Q

What are the two opponent colour pairs?

A

Yellow-Blue

Red-green

39
Q

What colour cones dont we have?

A

Yellow - we see yellow when red and green cones are equally stimulated

40
Q

Outline the 6 layers of the LGN

A

Layers 1-2 = MAGNOCELLULAR

  • just about contrast, movement
  • less detailed, just about contrast

Layers 3-6 = PARVOCELLULAR
- About red ang green, much more detailed

Konicocellural sublayers (in between)
- code the colour blue
41
Q

What sort of mapping does LGN retain/

A

Retinotopic mapping - laid out like your visual field is

- i.e. fovea represented by disproprotionately large area of cortex - as its more detailed

42
Q

Where does the LGN send info to?

A

Primary visual cortex (V1)

43
Q

Describe the function of V1 (primary visual cortex)

A
  • also has 6 layers
  • found in occipital lobe
  • reconstructs image from retina that was broken down by ganglion
  • different neurons respond to different features (orientation, movement, spatial frequencey (scale), depth (retinal display), colour
44
Q

Describe V1 orientation

A

Most v1 neurouns are sensitive to orientation - respond morst strongly to light in a particular orientation, for each neuron, a certain orientation will be best and increase firing the most

45
Q

Describe V1 Perception of scale

A

If we seen an object thought to be large, but takes up little space on retina - we see it as far away, not minature.

Due to spatial frequency - cannot perceive high frequency info from greater distances (Cant see detail fair away)

46
Q

Explain monocular cues on depth perception

A
  • Can be detected by one eye
  • how much space an object takes up on retina
  • Linear perspective (parrallel lines get closer the further away)
  • Texture gradients (further away = less detailed)
  • shading
  • movement - optic flow + motion parralax = close objects seem to move quicker
47
Q

What are the 2 types of cues about depth perception in v1

A

Monocular cues, binocular cues

48
Q

Explain binocular cues on depth perception

A
  • provides vivid depth perception

* Stereoscopic vision - important for visual guideance of fine movments - e.g. threading of needle

49
Q

Explain V1: depth

A

Your eyes see slightly different images: retinal display

  • THE MORE DIFFERENT THE 2 IMAGES THE CLOSER THE OBJECT
  • if they are too different you see 2 objects (double vision)
50
Q

Most neurons in v1 are what?

A

Binocular - need two eyes to detect

51
Q

How is v1 organised?

A
  • retintopic mapping - replicates visual field
  • Divided into 2 identical colums (each with 6 layers of various functions - e.g. contrast, colour, orientation, movement etc)
  • Each colum has different portion of visual field assigned to it - analyse various info this section
  • Columns collectively receive info from whole visual field
52
Q

What can bilateral lesions to v1 cause?

A

Cortical blindess - total/ aprtial blindness even though eye is functional - could just be a tiny spot of damage so you have a blind spot

53
Q

How is the visual association cortex structured?

A

V1 is surrounded by visual association cortex - V2, V3, V4, V5, etc

  • arranged hierachically, info travels up for further analysis - can travel backwards to change what we perceive
  • e.g. Ponzo train track illusion - see the two shapes as the same according to linear perspective - but when given cues we see the boxes at the same
54
Q

What are the 2 cortical streams in the visual association cortex/

A
  1. ventral stream - extends to temporal lobe
    - what pathway, gets info from mango, parvo and koniocellular
  2. Dorsal streams - projects to parietal lobe
    - Where pathway, determines objects in space, movement and spatial location

Bio Psych (11 decks)

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