Lecture 1 - Theories of Visual Perception Flashcards
What are the four theories of visual perception?
Gestalt, Gibson’s ecological theory, Marr’s info processing theory, Constructivist approach
How are receptors distributed?
Unevenly
What is perception?
How we experience outside world, aim to translate sensory information into perceptual experience
Why is perception important?
Only source of info about world, other cognitive systems rely on it
The 4 theories have diff approaches to:
Bottom up vs Top down processing, goal of perception, methods of study
What is Gestalt’s approach?
Top down, whole is greater than the sum of its parts, segregation/grouping, separating figure/ground
What are the Gestalt laws of perceptual organisation?
Similarity, good continuation, proximity, connectedness, closure, common fate, familiarity, invariance, Pragnanz “good figure”
What is similarity?
Similar things appear to be grouped together
What is good continuation?
Points when connected result in straight/smoothly curving lines are seen as belonging together
What is proximity?
Things near to one another appear to be grouped together
What is connectedness?
Closed figure preferred to open figure
What is common fate?
Things moving in same direction grouped together
What is familiarity?
Things more likely to form groups if groups appear familiar/meaningful
What is invariance?
Things perceived as same even from diff angles
What is pragnanz?
Things perceived in simplest form
What is figure-ground segregation?
How we separate objects (figures) from background (ground)
What affects figure-ground segregation?
Symmetry, convexity, area, orientation, meaning/importance
What is symmetry?
Symmetrical areas usually figure
What is convexity?
Convex shapes usually figure
What is area? (figure ground)
Stimuli with smaller area usually figure
What is orientation?
Vertical/horizontal orientations usually figure
What is meaning/importance?
Meaningful objects more likely seen as figure (implies top down)
What are problems with Gestalt?
Underplay parallel/unconscious processing, some explanation of laws wrong, description rather than explanation, ill-defined laws, stating obvious
What is Gibson’s ecological theory?
Bottom-up approach, direct, rich info received enough for interaction with environment, cognitive processes unnecessary
What is optic flow? (ambient optic array)
As observer moves, world changes and flows towards/away from them (active)
What are invariants?
Unambiguous info about environment, directly perceived (eg. Horizon ratio relation, texture gradients)
Why is motion important to Gibson’s theory?
Motion necessary to perceive invariant info (highlights)
What are the two types of motion?
- due to observer movements
- due to object movement
(Gibson focused on observer movement)
What is motion parallax?
Things far away move more slowly than those nearby (tells us distance to object)
Practical implication of optic flow?
Horizontal lines painted on road closer together as driver approaches junction to slow them down
What are affordances?
Opportunity for action of object (no need for memory/experience??)
What 4 stages are part of Marr’s info processing approach?
- Grey level
- Primal sketch (Raw + Full)
- 2 1/2D sketch
- 3D object-centred description
(emphasis on bottom up + computational nature)
How does Marr’s approach work?
Retinal image - 4 stages
What is grey-level description?
Measuring intensity of light at each point in image (done by photoreceptors)
What is primal sketch?
Representation of contrast change (blobs/edges/bars) over range of spatial frequencies (identify edges)
What is 2 1/2D sketch?
Representation of orientation/depth/colour relative to observer
What is 3D representation?
Representation of object independent of observer
What are the processes in Raw primal sketch?
Gaussian: blur images to diff degrees
Identify intensity changes: present at 2 levels of more
Assign primitives (edge/bar/termination/blob)
What are processes in Full primal sketch?
Group primitives
Place tokens grouped to form higher-order tokens
Criticisms of Marr’s approach?
Retinal image not always sufficient to allow reconstruction
Role of memory/experience?
What is constructivist approach? (Helmholtz)
Retinal image not sufficient info, perception depends on stored knowledge
What does constructivist approach generate?
Perceptual hypotheses (illusions due to inaccurate ones. eg. hollow mask illusion)
Problem: vague
How does diff theories study?
Gestalt: some experimental/lab
Gibson: experimental/outside lab
Marr: computational
Constructivist: experimental/lab
What are the diff goals of theories?
Gestalt, Marr, Constructivist: reconstruction
Gibson: action
What is unconscious inference?
Involuntary, pre-rational, reflex like mechanism part of formation of visual impressions
