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University Year 1 > Intro 1-Visual Perception > Flashcards

Intro 1-Visual Perception Flashcards

1
Q

What is the anatomy of the human eye?

A

2.5cm diameter. Lens. Fovea . Retinal landmarks. Retina. Sclera. Macula. Optic disc. Optic nerve. Optical system

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2
Q

What is the fovea?

A

Central vision, highest acuity. Most detailed vision

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3
Q

What is the retina?

A

Light sensitive surface on 75% of inner eye

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4
Q

What is the sclera?

A

Outer layer of eye. Tough fibrous coat

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5
Q

What is the disease of the macula?

A

Macular degeneration-deterioration of retina in macula (fovea). Irreversible blindness/loss of central vision

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6
Q

What is the optic disc?

A

Blind, usually unaware as corresponds with ‘seeing’ retina in other

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7
Q

What is the optic system?

A

Iris, pupil, cornea, ciliary muscle

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8
Q

What is light?

A

Electromagnetic energy, measured in wavelengths (visible light is 400-700nm)

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9
Q

What is the 1st transformation in the visual process?

A

Transform light into retinal image. Inverted object representation on retina. Focus-ciliary muscles tighten and relax to change thickness of lens to bend light to fill the fovea. The problem is there is a fixed distance between lens and retina

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10
Q

What is accommodation in the visual process?

A

Process where the eye changes optical power to focus on an object as distance varies. There is an accommodation limit which increases with age

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11
Q

What is accommodation to a far target?

A

Relaxed ciliary muscles-slim lens (slight curvature so light is only bent a little). Focus point on fovea-image is sharp. Near target-focus point behind retina-image is blurred

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12
Q

What is accommodation to a near target?

A

Tightened ciliary muscles-thick lens (much curvature so light is bend a lot). Focus point on fovea-image is sharp. Far target-focus point before retina-image is blurred

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13
Q

What are two common visual problems?

A

Myopia and hyperopia

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14
Q

What is myopia?

A

Nearsightedness. Lens is too thick so bends light too much, or the eyeball is too long. Requires concave corrected lenses

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15
Q

What is hyperopia?

A

Farsightedness. Eyeball is too short. Requires convex correction lenses

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16
Q

What is the second transformation in the visual process?

A

Transduction-image on retina transformed into electrical energy. Light eaves move down from ganglion cell to the photo receptors (rods and cones). Optic disc=blind spot (no photo receptors at that retinal location

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17
Q

How do rods and cones differ?

A

120 million rods compared to 6 million cones. Cones adapt to dark quicker but rods are more through. Higher sensitivity in rods (dark adapted eye). Better visual acuity in cones (light adapted eye). More convergence of rods, increasing sensitivity. Less convergence in cones increases acuity. Rods more sensitive to shorter wavelengths, and cones to long. Purkinje shift. Rods operate at low luminance (no colour sensation). Cones operate at high luminance (s cones blue, m cones green, l cones red)

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18
Q

What are two types of vision?

A

Photopic vision (cone dominated) and scotopic vision (rod dominated). Furthermore, mesopic vision is rod and cone vision together

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19
Q

What is ganglion cell input?

A

Neural convergence-receives input from 126 photo receptors which excites or inhibits ganglion cell depending on where in ganglion’s receptive field the stimulus is

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20
Q

What is the receptive field of a neuron?

A

Part in visual field which stimulus is able to modify firing rate of this neuron

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21
Q

What are the excitatory and inhibitory areas?

A

Excitatory area (‘on’ area) increases firing rate. Inhibitory area (‘off’ area) decreases firing rate

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22
Q

What are the three main types of ganglion cells?

A

Magnocellular (M) cells (most input from rods, not colour specific). Parvocellular (P) cells (input from single M or L cones-colour specific to green/red on/off). Koniocellular (K) cells (excitatory input from S cones and inhibitory inout from M and L cones-blue on)

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23
Q

What are the parts of the retinogeniculostriate pathway?

A

Retina, lateral geniculate nucleus and striate visual cortex

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24
Q

What is lateralisation of vision?

A

Optic chiasm-nasal axons cross over to other side of brain-temporal axons stay on the same side. Visual fields now represented in contralateral hemisphere

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25
What are the layers of the geniculate nucleus?
6 layers with axons from P neurons (top four layers), M neurons (bottom two layers), and K neurons
26
What is the visual cortex?
Primary visual cortex-v1-striate visual cortex. Extrastriate visual areas-v2/v3/v4/v5 (midle temproal area) and IT (inferotemporal cortex)
27
What happens when visual information travels through cortex?
Ongoing neural convergence. Neurons' receptive fields increase. Visual information gets more and more complex-ongoing integration
28
What is v1?
Striate cortex. Magno/parvo areas from LGN/retina preserved in v1 input layers but merge subsequently. Some v1 neurons are orientation selective (elongates receptive fields to capture edges in particular orientation). Receptive field not stimulated or with non-preferred orientation will not cause a response. v1 Single cell recording (Hubel and Wiesel). Other neurons are motion direction selective or selective for colour/brightness
29
What is v2?
Receptive fields twice as large as v1. Respond to basic stimulus features and more complex ones?
30
What did Ungerleider and Mishkin's monkey study look at?
Dorsal (parietal-where?) and ventral (temporal-what?) streams
31
What is V3 and MT?
In parietal/dorsal stream. V3 receptive field 5x larger than v1. MT 8x larger than v1. Integrated information over large area of retina
32
What is v4?
In temporal/ventral stream. Receptive field 5x larger than v1. Responds to object-defining features
33
What is sensation?
Un-interpreted sensory impressions created by detection of a stimulus
34
What is perception?
Psychological processes of making sense of the sensations
35
What is structuralism?
Study of elements of consciousness. Conscious experience broken down into basic elements, then combined to describe all human experiences
36
What psychologist is part of structuralism?
Wundt who had the first psychological lab, in Leipzig, Germany, and used the technique of introspection
37
What is a strength of structuralism?
First psychology 'school of thought'
38
What are the weaknesses of structuralism?
Validity (descriptive but has no measures), reliability (not consistent or constant), objectivity (biased-observations depend on observer)
39
What is psychophysics?
Fechner-basic idea is measuring the absolute (perception) threshold: 1) method of adjustment, 2) method of limits, 3) method of constant stimuli
40
What is method of adjustment?
Participants adjust intensity of test light, until they are jut able to perceive the light
41
What is method of limits?
Participants presented with trials of increasing/decreasing light intensity
42
What is method of constant stimuli?
Similar to method of limits but many more trials per light intensity, and randomised light intensity across trials
43
What does Weber look at?
Measuring the different threshold. Weber's law-the change in a stimulus, to discriminate it from another stimulus, is a content ratio of that original stimulus
44
What does Stevens look at?
Subjective magnitude estimation. Measuring relation between stimulus intensity and perceived intensity. Steven's power function is P=KSn where P=perceived intensity, K=constant (scales values to size), S=stimulus intensity and n=exponent
45
What are strengths of psychophysics?
Valid, reliable and objective
46
What is a weakness of psychophysics?
No theoretical account of perception
47
What is Gibson's theoretical account of perception?
Ecological theory of perception. Rational-perception is direct (=sensation). Perception must be investigated in natural environment
48
What is Gibson's basic idea?
Perception takes place in optic array directly based on invariant information in the visual field, which is extracted by observer's movement
49
What are examples of Gibson's view of perception?
Optic flow pattern (landing point of pilot remains motionless while rest of visual field moves away from this point), texture gradient (elements of textured ground are denser in distance), horizon ration
50
What are the strengths of Gibsons theoretical account of perception?
It is a theoretical account, and assumes perception is fast and always accurate
51
What is erroneous perception?
Visual illusions-what we perceive is not always what is represented on our retina
52
What is equivocal perception?
Ambiguous figures-we perceive different objects from some retinal image
53
What are examples of visual illusions?
Fraser spiral illusion, vertical-horizontal illusion, Jastrow illusion, irradiation illusion, figure/ground ambiguity, feature ambiguity, depth ambiguity-Necker cube
54
What are examples of real world visual illusions?
Moon illusion, waterfall illusion (motion aftereffect), and the wagon wheel effect (stroboscopic effect)
55
What are examples of real world visual ambiguity?
Ambiguous retinal images: inverse projection problem/superimposed objects/untypical angles
56
What do perceptual illusions and ambiguity show?
Perception is more than sensation. Theories that account for this are top-down accounts
57
What is Gregory's theory?
Constructive theory of perception that suggests perception is indirect and constructive process of hypothesis testing, based on individual factors. Incorrect hypotheses can form, leading to perceptual errors
58
What are the strengths of Gregory's theory?
Theoretical account and explains perceptual failure and ambiguity
59
What are the weaknesses of Gregory's theory?
Cannot explain why illusions persist, suggests perception is not effortless which doesn't often match our subject experience
60
What is Gestalt psychology?
Talked about by Wertheimer, Köhler and Koffka. State that the whole is more than the sum of it's parts. The whole is achieved by perceptual organisation (grouping and segmentation)
61
What are Gestalt psychology laws/principles?
Proximity, similarity, common fait, good continuation, closure, relative size, surroundedness, orientation, symmetry
62
What is a strength of gestalt psychology?
Provides set of useful perceptual heuristics
63
What is a weakness of gestalt psychology?
Mainly descriptive rather than theoretical account
64
What is good about colour vision?
It enhances perceptual organisation, top down control, and automatic bottom up processing
65
What is the visible light spectrum?
Different wavelengths of light spectrum are perceived as different colours. Light does not contain colour, colour is non veridical
66
How do the wavelengths correspond with perceived colour?
Short and medium is blue, medium is green, medium and long is yellow, long is red
67
What are reflected wavelengths?
Chromatic colours are result of selective reflection. Achromatic colours are result of equal reflection
68
What are transmitted wavelengths?
Chromatic colours are result of selective transmission. Achromatic colours are result of equal transmission
69
What are three colour dimensions?
Hue (colour value) represented on colour wheel, saturation(amount of white added to the colour), and brightness (amount of light reflected)
70
How many colours are there?
Along the three dimensions, around 7 million colours can be made. The Bureau of Standards identified 7500 colour names
71
How are colours mixed?
By mixing light or mixing pigments
72
What is mixing light?
Additive colour mixture. All wavelengths present along are also present when other wavelengths are superimposed
73
What is mixing pigments?
Subtractive colour mixture. Pigments still absorb the same wavelengths they absorb alone-only the wavelengths reflected by both pigments in common remain
74
What is trichromatic theory of colour?
Young-Helmholtz. Colour matching experiments (full colour vision based on ability to combine three different wavelengths). Physiological evidence (S/M/L cones). Colour vision based on three different receptor mechanisms. Impaired colour vision due to monochromatism (colour blind) or dichromatism (colour deficiency)
75
What is opponent process theory of colour?
Hering. Complementary afterimages (3 opponent channels: Blue and yellow, green and red, black and white). Physiological evidence: opponent neurons in v1, v4 and inferotemporal cortex, with single opponent or double opponent receptive fields
76
What are depth cues?
Body related, and stimulus related
77
What are body related depth cues?
Oculomotor cue (state of the eyes)-accommodation and convergence
78
What are stimulus related depth cues?
Monocellular cues and binonocular cues
79
What are monocellular cues?
Pictorial cues (occlusion, relative height, relative size, familiar size, perspective convergence, atmospheric perspective, texture gradient), and motion based cues (motion parallax and deletion/accretion)
80
What are binocular cues?
Binocular vision=stereoscopic vision. Retinal disparity (retinal images in left and right eye are slightly shifted)
81
What is retinal disparity?
Image falls into fovea in both eyes. Two fovea are corresponding points. All objects same distance as fixation point fall on corresponding retinal points. Horopter-imaginary plan through fixation point connecting all objects of which retinal images fall on corresponding retinal points
82
What is stereopsis?
Ability to use retinal disparity as a cue to perceive depth. Neuronal evidence-disparity-selective neurons in v1 and along both ventral and dorsal streams
83
What is size perception?
Size of retinal object representations measured in degree of visual angle. Depends on object size and physical distance from observer. Larger visual angle when closer to observer. Two objects at different sizes/distances can have same visual angle
84
What is size constancy?
Perception of size-relatively consistent when viewed from different distances. Size distance scaling equation is S=K(RxD) where S=perceived size, R=size of retinal image and D=perceived distance. Explains relative size illusions, Ponzo illusion and moon illusion
85
What is real motion?
A stimulus that really moves
86
What is illusory motion?
Apparent motion. Perceived motion in a static stimulus. Illusion of motion for successively presented stimulus eg film and 19th century TV. Induced motion-moving frame of reference can produce illusion that stationary object moves in opposite direction (clouds and moon). Motion aftereffects and visual illusions
87
What is retinal motion?
Successive receptor stimulation by moving stimulus in visual field. Only real motion produces retinal motion. Motion illusions do not = retinal motion
88
What is the physiobiological basis of perception of real motion?
Motion direction selective neurons in v1. Middle temporal area (v5) where almost all neurons are direction selective. Single neuron's receptive field only covers part of visual field. None respond to whole visual field (a problem for motion perception).
89
What was Newsome et al's study?
Monkey experiment with moving dot displays. Single-cell recording. Increasing motion direction coherence, monkeys judged motion direction more accurately. MT neurons fired more rapidly (highly specialised)
90
What is the aperature problem?
Direction of moving stimulus through aperture is ambiguous. Individual direction-selective neuron not sufficient to indicate movement direction. Solutions are pooling responses of multiple neurons or end-stopped cells signal end of a stimulus
91
What is the superior temporal sulcus?
Receives projections from MT and IT. It combines input about object form and motion direction
92
What is biological motion?
Self produced motion of biological being-real motion that produces retinal motion
93
What is corollary discharge theory?
Motion perception depends on retinal motion and eye movements.
94
Where are the eye muscles?
Four at the bottom, top, left and right of each eye, and two wrapped around it
95
What are the three relevant signals in corollary discharge theory?
Image displacement signal, motor signal and corollary discharge signal. These signal whether or not real motion has occurred
96
What is behavioural evidence of corollary discharge theory?
Motion perception matches the model predictions
97
What is neuronal evidence of corollary discharge theory?
Galletti/Fattori-real motion neurons
98
What are the three main approaches to object perception and recognition?
Template matching (though a large number of templates is required), feature analysis (though this ignores spatial arrangement of features), and structural analysis
99
What is structural analysis?
Marr: 1) Raw primal sketch (process intensity changes across retina), 2) Full primal sketch (geometric organisation), 3) 2 1/2D sketch (spatial locations/depth from observer's viewpoint), 4) 3D model (representation independent of of observer's position)
100
What is good about structural analysis?
It inspired a cognitive model, and explains a mechanism plus predicts the functioning of it. This can be tested, verified, falsified
101
What is the cognitive model inspired by structural analysis?
Ellis and Young's 1988 model: Object, initial representation, viewer-centred representation to object-centred recognition (recognition shortcut removes this stage), to object recognition units, to semantic system, to name retrieval
102
Who tested the models predictions?
Benson and Greenberg with Mr S

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