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PSY3051 > Topic 3 - Visual Perception > Flashcards

Topic 3 - Visual Perception Flashcards

1
Q

Challenges of object perception

A
  • Stimulus on the receptors is ambiguous
  • objects can be hidden or blurred
  • Objects look different from different viewpoints
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2
Q

Inverse projection problem

A

an image on the retina can be caused by an infinite number of objects - the task of determining the object responsible for a particular image on the retina

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3
Q

Viewpoint invariance

A

the ability to recognise an object seen from different viewpoints, regardless of the viewpoint

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4
Q

Structuralism (Wundt)

A

perceptions are created by combining elements called sensations
- can no explain apparent movement or illusory contours

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5
Q

Illusory contours

A

illusion of physical edges where there are none

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6
Q

Gestalt Approach

A

The whole is different from the sum of its parts - perception is a result of perceptual organisation

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7
Q

(Principles of perceptual organisation)

Good continuation

A

connected points resulting in straight or smooth curves belong together

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8
Q

(Principles of perceptual organisation)

Pragnanz (principle of simplicity)

A

every stimulus is seen as simply as possible

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9
Q

(Principles of perceptual organisation)

Similarity

A

similar things appear to be grouped together

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10
Q

(Principles of perceptual organisation)

Proximity

A

things that are near each other are grouped together

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11
Q

(Principles of perceptual organisation)

Common fate

A

things that are moving in the same direction appear to be grouped together

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12
Q

(Principles of perceptual organisation)

Common region

A

elements that are within the same region of space appear to be grouped together

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13
Q

(Principles of perceptual organisation)

Uniform connectedness

A

a connected region of the same visual properties is perceived as a single unit

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14
Q

(Principles of perceptual organisation)

Synchrony

A

elements occurring at the same time are seen as belonging together

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15
Q

Perceptual segretation

A

the perceptual segregation of one object from another

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16
Q

Figure-ground segregation

A

determining which part of the environment is the figure so that it stands out from the background

  • Figure is more “thing-like”, more memorable, closer
  • Ground is more unformed, extends behind figure
  • border separating the two belongs to the figure
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17
Q

Reversible figure-ground

A

Figure and ground that can be perceived either way

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18
Q

Image based factors for figure

A
  • Elements are located in lower part of displays
  • On the convex side of borders
  • Units are symmetrical
  • Elements are small
  • Oriented vertically
  • Have meaning
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19
Q

Global image features

A

perceived rapidly and are associated with specific types of scenes

  • Degree of naturalness
  • Degree of openness
  • Degree of roughness
  • Degree of expansion
  • Colour
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20
Q

Physical regularities in the environment

A
  • Light from above assumption
  • Oblique effect - people perceive horizontals and verticals more easily than other orientations
  • Uniform connectedness - elements are defined by areas of the same texture and colour
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21
Q

Semantic regularities in the environment

A

Characteristics associated with the functions of scenes
- Scene schema - knowledge of what scene typically contains

Hollingworth - observers were presented with a scene and then an object, and asked where the object would be placed in the scene
Palmer - Observers saw a context scene, followed by a target picture, flashed briefly, and are asked to identify the target picture

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22
Q

Theory of unconscious inference (Helmholtz)

A

made to explain why stimuli can be interpreted in more than one way, but we prefer one

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23
Q

Likelihood principle

A

We perceive the object that is most likely to have caused the pattern of stimuli we have received

24
Q

Bayesian inference

A

our estimate of the probability is determined by

  • the prior probability (initial estimate)
  • the likelihood (extent to which available evidence is consistent with outcome)
25
Q

Contextual modulation

A

stimuli outside of neuron’s receptive field can affect neural firing
- when they follow good continuation and are perceived as part of a figure

26
Q

Binding

Binding Problem

A

the process by which features are combined to create perception of coherent objects
- only occurs when we pay attention

Binding problem - features of objects are processed separately in different areas of the brain

Treisman and Gelade

  • Preattentive stage - features of objects are separated
  • Focused attention stage - features are bound into a coherent perception
27
Q

Illusory Conjunctions

A

features that should be associated with an object become incorrectly associated with another

Triesman and Schmidt

  • Stimulus was four shapes flanked by two numbers, flashed briefly, followed by a mask
  • Task was to report numbers first followed by shapes at four locations
  • Incorrect associations of features occurred 18% of the time
28
Q

Balint’s syndrome

A

patients with parietal lobe damage show lack of focused attention results in incorrect combinations of features

29
Q

Conjunction search

A

finding target with two or more features

- patients with parietal lobe damage cannot perform conjunction searches well

30
Q

Functions of colour perception

A
  • helps classify and identify objects
  • Facilitates perceptual organisation of elements into objects
  • May provide an evolutionary advantage when foraging for food
31
Q

Colours can be changed by:

A
  • Intensity which changes perceived brightness
  • Saturation
  • Wavelength
32
Q

Reflectance curves

A

plots of percentage of light reflected for specific wavelengths

33
Q

Chromatic colours

A

eg. blue, green, red - occur when some wavelengths are reflected more than others (called selective reflection)

34
Q

Achromatic colours

A

eg. white, grey, black

35
Q

Selective transmission

A

only some wavelengths pass through the object or substance

36
Q

Transmission curves

A

plots of the percentage of light transmitted at each wavelength

37
Q

Making green

A
  • Blue absorbs long-wavelength light and reflects some short and medium wavelength light
  • Yellow absorbs some short-wavelength light and reflects some medium and long wavelength light
  • The only wavelengths reflected when mixed are those that are reflected by both paints in common - aka some medium-wavelength light
38
Q

Mixing paint and light

A

Mixing paints is called a subtractive colour mixture

Mixing lights is called an additive colour mixture
- All light reflected from two colours is reflected

39
Q

Hues, Saturation, Value

A

Hues - another word for chromatic colours - differ because of saturation and value

Saturation - how much white is added

Value - the light-dark dimension

40
Q

Trichromatic Theory of colour vision

A
  • Proposed by Young and Helmholtz

Three different receptor mechanisms are responsible for colour vision

41
Q

Colour matching (experiment)

A
  • Observers adjusted three wavelengths in a comparison field to match a test field to one wavelength
  • Needed three wavelengths to match colour
  • Those with colour deficiencies could do it with less wavelengths, but only matched in their eyes
42
Q

Physiological evidence for trichromatic theory

A
  • Researchers measured absorption spectra of visual pigment in receptors, found pigments that responded maximally to short, medium and long wavelengths
  • Genetic differences for coding proteins of three pigments
  • Colour perception is based on the response of the three different types of cones
  • Colour matching experiments show that colours that are perceptually similar (metamers) can be caused by different physical wavelengths
43
Q

Are three receptors necessary?

A

Vision with one receptor (monochromats) - absorption of a photon causes the same effect, no matter what the wavelength is - any two wavelengths can cause the same response by changing the intensity

Two receptors (dichromats), three receptor types (trichromats)

44
Q

Principle of univariance

A

once a photon is absorbed by a visual pigment molecule, the identity of the light’s wavelength is lost

45
Q

Opponent-Process theory of colour vision

A

Colour vision is caused by opposing responses generated by blue and yellow, and by green and red

Behavioural evidence - types of colour blindness are red/green, blue/yellow - colour afterimages (complementary afterimages) and simultaneous colour contrast show opposite pairings

46
Q

Opponent-process mechanisms

A

Three mechanisms: red/green, blue/yellow, white/black

  • The pairs respond in an opposing fashion to the absorbance of light, such as positively to red and negatively to green
  • Believed to be the result of chemical reactions in the retina
  • Researchers found opponent neurons located in the retina and LGN
  • Respond in an excitatory manner to one end of the spectrum and an inhibitory manner to the other
47
Q

Trichromatic and Opponent-process theories combined (“zone” theories)

A

Each theory describes physiological mechanisms in the visual system

  • Trichromatic theory explains the responses of the cones in the retina (long, medium and short)
  • Opponent-process theory explains neural response for cells connected to the cones further in the brain, colour blindness and afterimages
48
Q

Opponent neurons

A

single-opponent (centre surround)

double-opponent (side by side) neurons

49
Q

Monochromatism

A
  • usually hereditary, occurs in 10 out 1 million
  • No functioning cones, only need one primary to match colour
  • Can be called colour blind
  • Only see in white, grey and black
  • Poor visual activity and very sensitive to bright light
50
Q

Dichromatism

A

Missing one of the three cone pigments, experience some colours, need two primary colours to match

Unilateral dichromat - trichromatic vision in one eye and dichromatic in the other

51
Q

Forms of Dichromatism

A

Protanopia - 1 percent of males, 0.02 percent of females, missing long wavelength

Deuteranopia - 1 percent of males, 0.01 percent of females, missing medium wavelength

Tritanopia - very rare, missing short wavelength

52
Q

Anomalous trichromatism

A

needs three primaries in different proportions to normal trichromat

53
Q

Colour constancy

A

perception of colours as relatively constant in spite of changing light sources

  • Sunlight has approximately equal amounts of energy at all wavelengths
  • Tungsten lighting has more energy in long-wavelengths
  • LED bulbs emit light at substantially shorter wavelengths
54
Q

Chromatic adaptation

A

prolonged exposure to chromatic colours

  • Receptors “adapt” when the stimulus colour selectively bleaches a specific cone pigment
  • Receptors decrease in sensitivity to colour
  • Occurs to light sources, leading to colour constancy
  • The eye reduces sensitivity to the light shining on the eye, therefore making colours seem constant
55
Q

Chromatic adaptation Uchikawa experiment

A
  • Observers shown sheets of coloured paper in three conditions:
  • Baseline - paper and observer in white light
  • Observer not adapted - paper illuminated by red light; observer by white
  • Observer adapted - paper and observer in red light - partial colour constancy is shown
56
Q

Possible causes of colour constancy

A

Effect of surroundings

Memory and Colour - past knowledge of an object’s colour can impact perception

57
Q

Colour constancy Hansen experiment

A
  • presented observers with pictures of fruits with characteristic colours against a grey background
  • Adjusted the colour of fruit and spot of light to match the background
  • Spot of light was perceived as grey but fruit still perceived as coloured

PSY3051 (6 decks)

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