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Action & Perception > 1. Theories Of Visual Perception > Flashcards

1. Theories Of Visual Perception Flashcards

1
Q

How are receptors distributed in the retina?

A

unevenly

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2
Q

how is the cortex devoted to the visual field?

A
  • Uneven amount of cortex devoted to different parts of the visual field.
  • Different areas of the visual cortex are dedicated to certain areas of the fovea.
  • largest area of the visual cortex is designated to the fovea.
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3
Q

why is the homunculus wrong?

A

It is infinite so creates an infinite regression = obviously incorrect

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4
Q

what is perception?

A

The means by which information acquired from the environment via the sense organs is transformed into experiences of objects, events, sounds, tastes

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5
Q

what is the aim of perception?

A

To translate sensory information into perceptual experience

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6
Q

what is the difference between sensation and perception?

A

Sensation is the information coming in and perception is the processing of that information.

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7
Q

Why is perception important?

A
  • Our only source of information about world
    ○ : we have no knowledge, or experience except through perception
  • All other cognitive systems rely on perception
    ○ rely on information being received and processed by the perceptual systems
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8
Q

Difference between top-down and bottom-up processing?

A
  • Bottom up = information from the senses
  • Top-down = information from stored knowledge, knowledge we hold about the world which might help us to process or interpret visual information
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9
Q

What are the 4 theories of visual processing?

A
  1. Gestalt approach
  2. Gibson’s ecological theory
  3. Marr’s information processing theory
  4. The Constructivist approach
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10
Q

what are the 9 Gestalt laws of perceptual organisation ?

A
  1. Similarity
  2. Good continuation
  3. Proximity
  4. Connectedness
  5. Closure
  6. Common Fate
  7. Familiarity
  8. Invariance
  9. Prägnanz – “good figure”
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11
Q

What did the Gestalt School argue?

A
  • something wrong with bottom-up approach.
  • the whole is greater (different) than the sum of its parts (Max Wertheimer, 1912).
  • Gestalt psychologists interested in how we group parts of a stimulus together and the way we separate figure from ground
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12
Q

How did the Gestalt School argue/demonstrate the bottom-up approach was wrong?

A

NECKER CUBE

  • Perception flicks between alternate interpretations
  • Sensation remains the same.
  • If it was true that perception was bottom up then you would always perceive the same this as the same information going into the brain.
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13
Q

problem with the Necker Cube?

A

Since it’s a flat representation of 3D object it may be an unfair situation

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14
Q

what is the structuralism belief?

A

Perception is a combination of individual sensations that can be reduced to simple individual elements
- pure bottom-up approach

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15
Q

Gestalt argument against structuralism.

A
  • It ignores the relationship between stimuli.

- We don’t see lines and figures but forms and shapes (Gestalt means form/shape in German)

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16
Q

What is Qualia?

A

Perception

- we interpret electrical signals into senses.

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17
Q

What is the Law of Similarity?

A
  • Similar things appear to be grouped together

- Grouping can occur due to shape, lightness, hue, orientation, size

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18
Q

What is the Law of Good Continuation?

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.
  • Reification - More spatial info than is present
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19
Q

What is the Law of Proximity?

A

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

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20
Q

What is the Law of Connectedness?

A

Things that are physically connected are perceived as a unit (Rock & Palmer, 1990, December, Scientific American).

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21
Q

What is the Law of Closure?

A
  • Of several geometrically possible perceptual organisations, a closed figure will be preferred to an open figure.
  • We tend to ‘complete’ a broken figure because of the Strong closure cue for organizing what we see
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22
Q

What is the Law of Common Fate?

A
  • Things that are moving in the same direction are grouped together
  • Objects with same orientation are grouped together
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23
Q

What is the Law of Familiarity?

A

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

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24
Q

What is the Law of Invariance?

A
  • simple geometrical objects are recognized independent of rotation, translation, and scale;
  • Major problem in computer vision
  • Figure-Ground Segregation
  • Gestalt psychologists also interested in how we separate figure from ground..
  • Usually no doubt – but some reversible figure-ground patterns.
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25
Q

What does Figure-Ground describe?

A

Normally in a visual scene some objects (figures) seem prominent, and other aspects of field recede into the background (ground).

26
Q

Why is Gestalt interested in Figure Ground?

A
  • Gestalt interested in this because it infers top- down process
    ○ Input isn’t changing but perception is
27
Q

What affects if an area is seen as figure or ground?

A

○ Symmetry: symmetrical areas usually figure.
○ Convexity: convex shapes usually figure.
○ Area: stimuli with comparatively smaller area usually figure.
○ Orientation: vertical and horizontal orientations usually figure.
○ Meaning/Importance: meaningful objects more likely to be seen as figure. Implies attention - top-down

28
Q

What are the problems with the Gestalt Approach?

A
  • Underplay the parallel processing and unconscious processing that the brain does
  • Explanation of how some of their laws worked was wrong.
    ○ There is a visual representation of objects in the brain
  • Their laws provide a description of how things work rather than an explanation.
  • Their laws are ill defined – Prägnanz – what is the simplest and most stable shape?
  • Stating the obvious?
29
Q

Describe Gibson’s Ecological Theory of Perception.

A
  • Bottom-up approach
  • Sufficient information in the retinal array
  • Perception is ‘direct’ – not different from sensation
  • Retinal image provides rich information sufficient for interaction
  • Complex cognitive processes unnecessary
    Ecological – study in natural environments not labs – and allow movement
30
Q

Define the Horizon Ratio.

A

The proportion of the object above and below the horizon line is constant for objects of the same size standing on the same ground.

31
Q

What does the Horizon Ratio tell you about an object?

A

how much of object is above/below horizon in optic array will be constant (or invariant) with distance. If there is a change in proportion of object about/ below horizon, must indicate change in size

32
Q

What does texture gradients tell you about an object?

A
  • Changes in texture in the optic array tell us about distance, orientation and curvature of surfaces
  • Texture becomes smaller/finer as distance increases
33
Q

What evidence is there for the Gibson’s Ecological Theory of Perception?

A
  • Gibson & Bridgeman (1987). Participants could correctly identify objects, state their colour, identify the lighting conditions and the objects spatial orientations just from black and white photos of object surfaces.
  • The average subject identified about two- thirds of the photographs correctly
34
Q

What are the 2 types of motion?

A
  1. due to observer movements

2. due to object movements

35
Q

What is the Ambient Optic Array?

A
  • Structure of light reflected by textured surfaces
  • Changes due to observer movement when you move
  • This gives us information about objects in the environment how the objects are changing in relation to each other.
36
Q

What is Motion Parallax?

A
  • Observer Movement generates large changes in the ambient optic array.
  • things far away move more slowly than things nearby.
37
Q

How do animals use motion parallax?

A

Animals with little binocular overlap use motion parallax to determine distance.
- seen in a head bob or orthogonal running

38
Q

What does optic flow tell us?

A
  • patterns of optic flow show how the world changes for different patterns of movements – if travelling forward get a pattern of expansion, if travelling backwards get pattern of reduction.
  • can tell us how fast we are moving
39
Q

What did Gibson argue about Affordances?

A

argued that we know what objects are and what their purpose is without experience or knowledge of that object.
- know what the object affords us to do

40
Q

Describe Marr’s Approach to perception

A
  • computational approach
  • bottom up approach
  • looked at what we need to be able to perceive.
41
Q

What are the 4 stages of Marr’s Image Analysis?

A
  1. Grey level description
  2. Primal sketch (a. Raw and b. Full)
  3. 21⁄2D sketch
  4. 3D object-centred description
42
Q

What is the Grey Level description?

A
  • The intensity of light is measured at each point on the retina
  • Produced by activation of retina
43
Q

What is the Goal of the Raw Primal Sketch?

A

Identify object edges.

44
Q

What is the Process of the Raw Primal Sketch?

A
  1. Gaussian blurring: Blur images to different degrees
    § Using Gaussian filter – you blur the images, but by different degrees. This means at different levels of blur get rid of some of the details
    § Can show large changes in contrast that show what is important in that visual scene
  2. Identify intensity changes: Those present at more than 2 levels of blurring
  3. Assign primitives: 4 types of intensity change:
    § (1)Edge-segment (2)Bar (3)Termination (4)Blob.
45
Q

What is the goal of the Full. Primal Sketch?

A

Identify object outline

46
Q

What is the Process of the Full Primal Sketch?

A
  1. Group primitives together and assign place token
  2. Place tokens can be grouped to form higher-order place tokens
    Grouping based on clustering (like Gestalt proximity) and curvilinear aggregation (like Gestalt good continuation)
47
Q

What is the goal of the Primal 2 1⁄2D sketch?

A

viewer-centred description of position and depth of surfaces

48
Q

What is the Primal 2 1⁄2D sketch?

A
  • Primal Sketch combined with depth cues, colour, motion.
  • Its not 3D because it is observer-orientated. (unseen parts of scene and objects)
  • Describes how surfaces relate to one another
  • Primitives are vectors showing orientation of surface.
49
Q

What is the process of the Primal 2 1⁄2D sketch?

A

use depth cues e.g. binocular disparity, motion, texture

50
Q

What is the Goal of 3D representation?

A

Object-centred description of 3D object that allows recognition from any angle

51
Q

What is the Process of 3D representation?

A

Locate central axis of each component of object, represent as a generalised cone

52
Q

Define 3D representation.

A
  • 2 1⁄2D sketch analyzed for 3D volume primitives (cylinders, cones, cubes etc).
  • Produces 3D representation that is independent of observer
  • Conscious experience of vision.
53
Q

Why is Marr’s Computational Approach to perception important?

A
  • An algorithm/rule/system is more likely to be understood by understanding the problem that has to be solved, rather than the examining the mechanism (and hardware) in which it is embodied (AI arguments)
  • neuroscience wont tell the full story!
54
Q

Describe the constructivist Approach to Perception?

A
  • Retinal image does not provide sufficient information
  • Perception depends upon stored knowledge (memory) and experience
  • Comprised position between top-down and bottom-up approaches
55
Q

What was Helmholtz theory of perception?

A
  • Constructivist Approach to Perception
    ○ Unconscious inference
    ○ Likelihood principle
    § Interpret surrounding from sensation for survival
56
Q

What is Unconscious Inference?

A
  • Involuntary, pre-rational and reflex-like mechanism which is part of the formation of visual impressions
    ○ There are ways that are brain process information
    ○ These are hard wired ways that allow us to perceive differnces
  • Fixed unconscious neural processing.
    ○ Illusions: impervious to experience
    ○ Naïve optics (e.g. movement of sun in the sky)
57
Q

What happens in the Titchner Illusion?

A
  • Brain over emphasises size differences in grouping and separating objects.
58
Q

Explain the hollow face illusion.

A

explained by stored knowledge leading to inaccurate perceptual hypotheses
• Hollow mask illusion explained by our stored
knowledge that faces are convex

59
Q

Criticisms of the Constructivist illusion.

A

its vague.

60
Q

Criticism of Gestalt’s Reconstructivist approach?

A

it is descriptive rather than explanatory

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