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perception and action > theories of visual perception > Flashcards

theories of visual perception Flashcards

1
Q

what are gestalt’s laws of perceptual organisation

A
  1. similarity
  2. good continuation
  3. proximity
  4. connectedness
  5. closure
  6. common fate
  7. familiarity
  8. invariance
  9. Pragnanz - good figure
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2
Q

similarity

A

similar things appear to be grouped together

grouping can occur due to shape, lightness, hue, orientation, size…

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3
Q

good continuation

A

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

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4
Q

reification

A

the experienced percept contains more explicit spatial information than the sensory stimulus on which it is based

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5
Q

proximity

A

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

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6
Q

connectedness

A

things that are physically connected are perceived as a unit

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7
Q

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 organising what we see

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8
Q

for which rules does reification occur

A

closure
good continuation

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9
Q

common fate

A

things that are moving in the same direction are grouped together

objects with the same orientation are grouped together

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10
Q

familiarity

A

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

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11
Q

invariance

A

simple geometrical objects are recognized independent of rotation, translation, and scale; as well as several other variations

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12
Q

which rule of gestalt is a serious problem in computer vision

A

invariance

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13
Q

figure-ground segregation basics

A

normally in a visual scene some objects (figures) seem prominent, and other objects recede into the background

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14
Q

what does figure-ground segregation infer

A

top down processing

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15
Q

properties that affect whether an area is seen as figure or ground

A

symmetry
convexity
area
orientation
meaning/ importance

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16
Q

symmetry figure ground segregation

A

symmetrical areas usually figure

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17
Q

convexity figure ground segregation

A

convex shapes are usually figure

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18
Q

area figure ground segregation

A

stimuli with comparatively smaller area are usually figure

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19
Q

orientation figure ground segregation

A

vertical and horizontal orientations usually figure

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20
Q

meaning/ importance figure ground segregation

A

meaningful objects more likely to be seen as figure
implies attention: top-down process

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21
Q

problems with the gestalt approach

A

underplay the parallel processing and unconscious processing the brain does

explanation of how some of their laws worked was wrong

their laws provide a description of how things work rather than an explanation

some of the laws are ill defined
-e.g. pragnanz: what is the simplest and most stable shape?

stating the obvious?

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22
Q

pragnanz

A

when people are presented with complex shapes or a set of ambiguous elements, their brains choose to interpret them in the easiest manner possible

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23
Q

distal stimulus

A

object in the real world

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24
Q

proximal stimulus

A

representation of the stimulus on the retina

25
Q

gestalt psychology

A

the whole is greater than the sum of its parts - max wertheimer

26
Q

segregation

A

how we separate figure from ground

27
Q

grouping

A

how we group parts of a stimulus together

28
Q

structuralism

A

perception is a combination of individual sensations that can be reduced to simple, individual elements

29
Q

optic flow

A

the way the world flows and expands toward us, and contracts and flows behind us

30
Q

what did Gibson notice about optic flow?

A

that it was active - movement of the observer provided an additional stream of information

31
Q

ambient optic array

A

the structured arrangement of light reflected by textured surfaces with respect to a point of observation
-changes due to movement

32
Q

invariants

A

unambiguous information about the environment
can be directly percieved

33
Q

horizon ratio relation

A

proportion of object above the horizon is constant with changes in distance (of the same size standing on the same ground), but not with changes in size

34
Q

texture gradient

A

changes in texture in the optic array tell us about distance, orientation and curvature of surfaces

texture becomes smaller as distance increases

35
Q

empirical support for Gibson’s theory

A

Gibson and Bridgeman (1987)

participants could correctly identify objects, state their colour and identify the lighting conditions and spatial orientations just from black and white photos of objects surfaces

the average subject identified ~2/3 of the photographs correctly

36
Q

motion parallax

A

things far away move more slowly than things nearby

speed of movement tells us about the distance to the object

monocular cue to depth

37
Q

motion parallax in animals

A

used much more by animals that dont have much binocular overlap

head bobbing and orthogonal running

38
Q

expansion (optic flow) is a combination of

A

motion parallax and retinal size

39
Q

practical application of Gibson’s optic flow ideas

A

horizontal lines on the road painted closer together as the driver approaches junctions. Creates the illusion of increasing speed which causes the driver to slow down

40
Q

what is an affordance?

A

an action possibility formed by the relationship between an agent and its environment

memory and experience not necessary?

41
Q

criticisms of Gibson’s theory of perception

A

vague? how is this information picked up?
ignores top down processing (experience and memory)
ignores neuroscience

42
Q

grey level description

A

measuring intensity of light at each point in an image (each point on the retina)

produced by activation of retinal photoreceptors

43
Q

primal sketch

A

representation of contrast change (blobs, edges, bars etc.) over a range of spatial frequencies

44
Q

2 1/2 D sketch

A

representation of orientation, depth and colour relative to the observer

45
Q

3D representation

A

representation of of objects independent of the observer

46
Q

raw primal sketch goal

A

identify the objects edges

47
Q

primal sketch to 2 1/2 D sketch

A

primal sketch combined with depth cues, colour, motion

it is not 3D because it is observer oriented (unseen parts of scene and objects)

48
Q

2 1/2 D sketch to 3D sketch

A

2 1/2 D sketch analysed for 3D volume primitives (cylinders, cones, cubes etc.)

produces 3D representation that is independent of observer

conscious experience of vision

49
Q

importance of the computational approach

A

an algorithm is more likely to be understood by understanding the problem that has to be solved, rather than examining the mechanism in which it is embodies

to understand perception by studying neurons is like trying to understand a bird in flight by only studying feathers

50
Q

criticism of Marr’s information processing approach to perception

A

retinal image is not always sufficient to allow reconstruction

role of memory and experience?

51
Q

the constructivist approach to perception

A

retinal information does not provide sufficient information

perception depends upon knowledge (memory) and experience

generation of perceptual hypotheses

52
Q

unconscious inference

A

involuntary, pre-rational and reflex-like mechanism which is part of the formation of visual impressions

fixed unconscious neural processing

53
Q

examples of fixed unconscious neural processing

A

illusions: impervious to experience

naive optics

54
Q

titchner illusion

A

brain over emphasises size differences in grouping and separating objects

55
Q

helmholtz

A

unconscious inference
likelihood principle

56
Q

what explains many illusions

A

explained by stored knowledge leading to inaccurate perceptual hypotheses

57
Q

what is the hollow mask illusion explained by?

A

our stores knowledge that faces are convex

58
Q

positives and negatives of the constructivist approach to perception

A

pro: highlighted the importance of both bottom-up and top down processing

con: criticised for being vague

perception and action (2 decks)

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