Lecture 1 - Theories of Visual Perception

Question 1

What are the four theories of visual perception?

Answer 1

Gestalt, Gibson’s ecological theory, Marr’s info processing theory, Constructivist approach

Question 2

How are receptors distributed?

Answer 2

Unevenly

Question 3

What is perception?

Answer 3

How we experience outside world, aim to translate sensory information into perceptual experience

Question 4

Why is perception important?

Answer 4

Only source of info about world, other cognitive systems rely on it

Question 5

The 4 theories have diff approaches to:

Answer 5

Bottom up vs Top down processing, goal of perception, methods of study

Question 6

What is Gestalt’s approach?

Answer 6

Top down, whole is greater than the sum of its parts, segregation/grouping, separating figure/ground

Question 7

What are the Gestalt laws of perceptual organisation?

Answer 7

Similarity, good continuation, proximity, connectedness, closure, common fate, familiarity, invariance, Pragnanz “good figure”

Question 8

What is similarity?

Answer 8

Similar things appear to be grouped together

Question 9

What is good continuation?

Answer 9

Points when connected result in straight/smoothly curving lines are seen as belonging together

Question 10

What is proximity?

Answer 10

Things near to one another appear to be grouped together

Question 11

What is connectedness?

Answer 11

Closed figure preferred to open figure

Question 12

What is common fate?

Answer 12

Things moving in same direction grouped together

Question 13

What is familiarity?

Answer 13

Things more likely to form groups if groups appear familiar/meaningful

Question 14

What is invariance?

Answer 14

Things perceived as same even from diff angles

Question 15

What is pragnanz?

Answer 15

Things perceived in simplest form

Question 16

What is figure-ground segregation?

Answer 16

How we separate objects (figures) from background (ground)

Question 17

What affects figure-ground segregation?

Answer 17

Symmetry, convexity, area, orientation, meaning/importance

Question 18

What is symmetry?

Answer 18

Symmetrical areas usually figure

Question 19

What is convexity?

Answer 19

Convex shapes usually figure

Question 20

What is area? (figure ground)

Answer 20

Stimuli with smaller area usually figure

Question 21

What is orientation?

Answer 21

Vertical/horizontal orientations usually figure

Question 22

What is meaning/importance?

Answer 22

Meaningful objects more likely seen as figure (implies top down)

Question 23

What are problems with Gestalt?

Answer 23

Underplay parallel/unconscious processing, some explanation of laws wrong, description rather than explanation, ill-defined laws, stating obvious

Question 24

What is Gibson’s ecological theory?

Answer 24

Bottom-up approach, direct, rich info received enough for interaction with environment, cognitive processes unnecessary

Question 25

What is optic flow? (ambient optic array)

Answer 25

As observer moves, world changes and flows towards/away from them (active)

Question 26

What are invariants?

Answer 26

Unambiguous info about environment, directly perceived (eg. Horizon ratio relation, texture gradients)

Question 27

Why is motion important to Gibson's theory?

Answer 27

Motion necessary to perceive invariant info (highlights)

Question 28

What are the two types of motion?

Answer 28

1. due to observer movements 2. due to object movement (Gibson focused on observer movement)

Question 29

What is motion parallax?

Answer 29

Things far away move more slowly than those nearby (tells us distance to object)

Question 30

Practical implication of optic flow?

Answer 30

Horizontal lines painted on road closer together as driver approaches junction to slow them down

Question 31

What are affordances?

Answer 31

Opportunity for action of object (no need for memory/experience??)

Question 32

What 4 stages are part of Marr's info processing approach?

Answer 32

1. Grey level 2. Primal sketch (Raw + Full) 3. 2 1/2D sketch 4. 3D object-centred description (emphasis on bottom up + computational nature)

Question 33

How does Marr's approach work?

Answer 33

Retinal image - 4 stages

Question 34

What is grey-level description?

Answer 34

Measuring intensity of light at each point in image (done by photoreceptors)

Question 35

What is primal sketch?

Answer 35

Representation of contrast change (blobs/edges/bars) over range of spatial frequencies (identify edges)

Question 36

What is 2 1/2D sketch?

Answer 36

Representation of orientation/depth/colour relative to observer

Question 37

What is 3D representation?

Answer 37

Representation of object independent of observer

Question 38

What are the processes in Raw primal sketch?

Answer 38

Gaussian: blur images to diff degrees Identify intensity changes: present at 2 levels of more Assign primitives (edge/bar/termination/blob)

Question 39

What are processes in Full primal sketch?

Answer 39

Group primitives Place tokens grouped to form higher-order tokens

Question 40

Criticisms of Marr's approach?

Answer 40

Retinal image not always sufficient to allow reconstruction Role of memory/experience?

Question 41

What is constructivist approach? (Helmholtz)

Answer 41

Retinal image not sufficient info, perception depends on stored knowledge

Question 42

What does constructivist approach generate?

Answer 42

Perceptual hypotheses (illusions due to inaccurate ones. eg. hollow mask illusion) Problem: vague

Question 43

How does diff theories study?

Answer 43

Gestalt: some experimental/lab Gibson: experimental/outside lab Marr: computational Constructivist: experimental/lab

Question 44

What are the diff goals of theories?

Answer 44

Gestalt, Marr, Constructivist: reconstruction Gibson: action

Question 45

What is unconscious inference?

Answer 45

Involuntary, pre-rational, reflex like mechanism part of formation of visual impressions