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Year 1: Sensation & Perception > The Eye & Sight > Flashcards

The Eye & Sight Flashcards

1
Q

Wavelength change in visual light =

A

colour change

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2
Q

Amplitude change in visual light =

A

brightness change

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3
Q

Role: Iris/Pupil

A

Control the amount of light passing through to the retina via an adjustable aperture

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4
Q

Role: Cornea/Lens

A

To focus light on the lens

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5
Q

myopia

A

nearsighteness

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6
Q

hyperopia

A

farsightedness

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7
Q

Daylight vs night-time rods and cones

A

DAY- rods: not so good, cones: work well
NIGHT- cones: useless, rods: work well

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8
Q

Stages of light levels and which cells are active

A
  • Scotopic – only rods active
  • Photopic – only cones active
  • Mesopic – both rods and cones active
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9
Q

3 Types of cones for colour perception

A

– Red (long wavelengths)
– Green (medium wavelengths)
– Blue (short wavelengths)

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10
Q

Cones vs rods function

A

cones: colour
rods: light

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11
Q

Purkinje shift

A

at night red looks darker than green as the rods are more sensitive to green light

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12
Q

fovea

A

small central area of the retina that contains only cones

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13
Q

Convergence

A

when one neuron receives signals from many other neurons

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14
Q

which has higher convergence, rods or cones?

A

rods

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15
Q

what type of cell do rods and cones converge at

A

ganglion

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16
Q

Acuity

A

the ability to detect fine details of a stimulus

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17
Q

does high convergence lead to high or low acuity

A

low acuity

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18
Q

do rods or cones have higher acuity?

A

cones

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19
Q

Do ganglion cells have a baseline action potential activity?

A

yes

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20
Q

Does low convergence increase or decrease light sensitivity?

A

Low convergence decreases light sensistivity

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21
Q

Does low convergence increase or decrease visual acuity?

A

Low convergence increases visual acuity

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22
Q

Which cells transmit lateral inhibition?

A

Horizontal and Amacrine Cells

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23
Q

Lateral Inhibition

A

It is the capacity of an excited neuron to reduce the activity of its neighbours.

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24
Q

What is lateral inhibition good for?

A

It creates a contrast in stimulation that allows increased sensory perception.

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25
Q

Function of ganglion cells

A

They respond to changes in patterns of light

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26
Q

The Herman grid illusion gives an example of what element of ganglion cells?

A

Lateral inhibition creating centre-surround antagonism depending on excitation or inhibition of ganglion cells.

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27
Q

In ganglion cells, less firing is perceived as lighter or darker?

A

darker

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28
Q

How does the simultaneous contrast illusion work in regards to central centre surround antagonism and lateral inhibition?

A

Light shining on the light surroundings of a square (an on-centre receptive field) will cause the central cell tracts to produce an OFF response to the centre. Less firing interpreted as less bright so we perceive a darker square

Whereas light shining on the dark lateral surroundings of a square (of an off-centre receptive field) will cause the central cell tracts to produce an ON response. More firing interpreted as more bright so we perceive a lighter square.

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29
Q

Optic chiasm

A

crossover point of the 2 optic nerves.

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30
Q

When does the optic nerve become the optic tract?

A

After the optic chiasm

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31
Q

What part of the brain does the optic tract lead to?

A

Lateral Geniculate Nucleus (LGN)

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32
Q

Is the LGN bilateral or unilateral?

A

bilateral

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33
Q

Does the LGN have centre-surround antagonism or orientation selectivity?

A

centre-surround antagonism

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34
Q

What does V1 signify?

A

The primary visual cortex

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35
Q

Does the primary visual cortex have centre-surround antagonism or orientation selectivity?

A

orientation selectivity

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36
Q

Retinotopic mapping in V1

A

Objects close together in the visual scene are analysed by neighbouring parts of V1.

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37
Q

Cortical magnification in V1

A

Amount of cortex devoted to representing each part of the retinal field is distorted (not even).

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38
Q

What proportion of V1 does the fovea take up?

A

8-10%

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39
Q

Orientation columns in V1

A

Orientation preferences of V1 cells arranged in ordered way.

40
Q

Are cells in LGN monocular or binocular?

A

monocular

41
Q

Are cells in V1 predominantly binocular or monocular?

A

binocular

42
Q

Ocular dominance

A

V1 cells respond better to one eye than the other

43
Q

Put these in chronological order in visual processing:
LGN cells, complex cells, ganglion cells, hypercomplex cells, simple cells, photoreceptors

A

photoreceptors, ganglion cells, LGN cells, simple cells, complex cells, hypercomplex cells

44
Q

Simple cells in V1 response depends on…

A

position of the bar within the receptive field

45
Q

Complex cells in the V1 response depends on…

A

moving oriented bars and edges, responding best to a particular direction of movement

46
Q

hypercomplex cells in V1 response depends on…

A

particular orientation of a bar AND movement in a particular direction AND a particular length

47
Q

What does V3 specialise in?

A

form

48
Q

What does V4 specialise in?

A

colour

49
Q

What does V5 specialise in?

A

motion

50
Q

What part of the brain is important in determining what an object is (object discrimination)?

A

inferotemporal cortex

51
Q

What part of the brain is important in determining where an object is (landmark discrimination)?

A

posterior parietal cortex

52
Q

What is the predominant symptom of visual form agnosia

A

Inability to identify objects

53
Q

Who would be better at posting a block through a letterbox, someone with visual form agnosia or someone with optic ataxia?

A

someone with visual form agnosia because they’re better at acting on stuff, optic ataxia mean’s people have damage to the where/how stream

54
Q

What is the main symptom of optic ataxia?

A

Problems with landmark distinction

55
Q

Marr’s approach to form perception

A

Concerned with the representation of edges, contours and other areas of contrast change

56
Q

Gestalt approach to form perception

A

concerned with rules of perceptual organisation

57
Q

Is Marr’s approach top-down or bottom-up

A

bottom-up

58
Q

Does Marr’s approach start with the input into the receptor fields or the brain’s preconceptions?

A

The receptor field, it is a bottom up approach so it starts with input to perceptual system. After this, each stage takes as its input from the information from the previous stage and transforms it into a more complex description or representation.

59
Q

What does the computational model of form perception focus on?

A

The goal of the model, the algorithm it needs and the mechanisms to achieve this.

60
Q

Order these levels of image analysis:
grey level description, 3D representation, primal sketch, retinal image, 21/2D sketch

A
  1. Retinal Image
  2. Grey level description – measuring intensity of light at each point in the image.
  3. Primal sketch -representation of contrast change (blobs, edges, bars etc) over range of spatial frequencies)
  4. 21/2D sketch - representation of orientation, depth, colour relative to the observer. It’s not 3D because it is observer-orientated. (unseen parts of scene and objects)
  5. 3D representation - representation of objects independent of observer. 2 1/2 sketch analysed for 3D volume primitives (cylinders, cones, cubes etc).
    Produces 3D representation that is independent of observer. Conscious experience of vision.
61
Q

Is Gestalt’s approach to form perception top-down or bottom up?

A

top-down

62
Q

what is multistability?

A

when a single physical stimulus produces alternations between different subjective perceptions, eg the necker cube

63
Q

What is Gestalt’s law or perceptual organisation in reference to similarity?

A

similar things appear to be grouped together

64
Q

What is Gestalt’s law or perceptual organisation in reference to conjugation?

A

Points that, when connected, result in straight or smoothly curving lines, are seen as belonging together, and the lines tend to be seen in such a way as to follow the smoothest path.

65
Q

What is Gestalt’s law or perceptual organisation in reference to proximity?

A

Things that are near to one another appear to be grouped together

66
Q

What is Gestalt’s law or perceptual organisation in reference to connectedness?

A

Things that are physically connected are perceived as a unit

67
Q

What is Gestalt’s law or perceptual organisation in reference to closure?

A

Of several geometrically possible perceptual organisations, a closed figure will be preferred to an open figure.

68
Q

what is reification?

A

the act of changing something abstract into something real -eg the kanza triangle

69
Q

What is Gestalt’s law or perceptual organisation in reference to common fate?

A

things moving in the same direction are grouped together

70
Q

What is Gestalt’s law or perceptual organisation in reference to familiarity?

A

Things are more likely to form groups if the groups appear familiar or meaningful.

71
Q

What is Gestalt’s law or perceptual organisation in reference to invariance?

A

Recognising that many different images are the same object just distorted

72
Q

What are the oculomotor cues we receive to tell us about or eye’s position to help with depth perception?

A

convergence: as your eye muscles cause you eyes to look inward (the closer the object the greater the convergence)
accommodation: as the lens bulges to focus on a near object

73
Q

What is interposition/occlusion in relation to monocular depth cues?

A

One object obscures part of another, or overlaps with it

74
Q

What is texture gradient in relation to monocular depth cues?

A

Texture becomes smaller/finer as distance increases

75
Q

What is deletion & accretion in relation to motion-produced depth cues?

A

As one object moves in front of another, deletion occurs whereby the front object covers more of the back object. As one object moves away from another, accretion occurs whereby the front object covers less of the back object.

76
Q

What is motion parallax in relation to motion-produced depth cues?

A

Motion parallax refers to the fact that objects moving at a constant speed across the frame will appear to move a greater amount if they are closer to an observer (or camera) than they would if they were at a greater distance

77
Q

What is binocular disparity/ binocular stereopsis?

A

A cue that depends on the fact that slightly different images of a scene are formed on each eye.

78
Q

Does red light have a long or short wavelength?

A

Long

79
Q

Does violet light have a long or short wavelength?

A

Short

80
Q

DEFINE: hue

A

the attribute of a colour which is dependent on its dominant wavelength and independent of intensity or lightness.

81
Q

Which colour photoreceptors are on the retina and which wavelengths do they respond best to?

A

Blue-sensitive cones maximally responsive to short wavelengths. (S-Cones)
Green-sensitive cones maximally responsive to medium wavelengths. (M-Cones)
Red-sensitive cones maximally responsive to long wavelengths. (L-Cones)

82
Q

What is the significant belief from Opponent Process Theory of colour perception?

A

There are 3 battles going on depending on which type of light there was more of there was more of: yellow v blue, green v red & black v white. Eg: a Red-Green Receptor will signal either Red or Green but not both.

83
Q

Trichromacy vs opponent process model - which one takes place in the photoreceptors and which on takes place in the LGN?

A

trichromacy at the level of the cones, opponent processes at the level of LGN

84
Q

What are anopias in relation to colour blindness?

A

An insensitivity to L, M or S wavelengths of light.
(missing a type of cone)

85
Q

What are anomalies in relation to colour blindness?

A

Misalignment of L or M in trichromats. (distribution or deficiency)

86
Q

Which cone pigment is missing in protanopia?

A

L-cone

87
Q

Which cone pigment is missing in deutanopia?

A

M-cone

88
Q

Which cone pigment is missing in tritanopia?

A

S-cone

89
Q

Which cone has an anomaly is missing in protanomaly?

A

L-cone

90
Q

Which cone has an anomaly is missing in deuteranomaly?

A

m-cone

91
Q

What us the correspondence problem in relation to motion perception?

A

How the visual system knows if an object seen at Time 1 is the same object at Time 2.

92
Q

DEFINE: Velocity transposition

A

when two images moving across the visual field at different speeds can be perceived to be moving at the same speed

93
Q

DEFINE: Induced movement

A

an object appears to move or to move differently because of other moving objects nearby in the visual field.

94
Q

DEFINE: autokinetic movement

A
  • apparent motion in stationary images (eg visual illusions)
95
Q

define: movement aftereffects

A
  • illusion of motion in the visual image caused by prior exposure to motion in the opposite direction

Year 1: Sensation & Perception (6 decks)

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