Object Recognition Flashcards
(46 cards)
What ist he main challenge the visual system is faced with?
Quick identification of any object at any size, orientation, location etc
What are Gestalt’s laws of - like what are tehy for?
Perceptual organisation
What are Gestalt’s 5 main rules
Similarity Common fate - same direction Proximity Good continuation - same path Pragnanz - 'good form
What is the basis of the Pragnanz rule?
Koffka (1935) – of several possible geometrical organisations the one that willl actually occur posseses the best, simplest and most stable shape
Who came up with the new gestalt laws?
Palmer and Rock
What were the new gestalt laws?
Common region - same region of space
Connectedness
Synchrony - occur at same time
TWo limitations of Gestalt approach?
Doesn’t relaly explain how we perceive objects, more just a description of perceptual process and perceptual phonemona
Difficult to say sometimes what constitutes ‘simplest’/’best’ or what ‘good continutation’ is
What is the next advancement from Gestalt’s approach?
Triesman’s Feature Integration Theory
what is the order of events in Triesman’s view?
Object – identify primitives – combine primitives – perceive object – compare to memory – identify object if match
Where does attention come in or not come in in Triesman’s theory?
Identify primitives = pre-attnetive
Combining primitives = focused attention
What is Triesmans’ theory based on?
Feature ‘primitives’ – combine to make defined object
What are teh two main ways of determining primitives?
Image segmentation – 2 regions contianing different primitives - boundary will appear
Pop- out – if efficiecy of visual search = independetn of no of items presented = pop out
What are some examples of identified primtiives?
Curvature, tilt, colour, line crossings, line ends, movement
What can explain illusory conjuctions with regard to visual primitives?
Primtiveis = procesed independently
If stimulus possesses 2 primtivie features = sometimes combined inappropriately
Disadvantage of Triesman approach?
Largely tell us how we might combine features as opposed to how we recognise objects
Advantages of Triesman approach?
Basis of feature combining and role of attention in object recognittion
What are the two main models of object recognition
Bannerman Recognition by Component model
Marr’s computation approach
What does BAnnerman’s model involve>
It uses 36 simple geometric primitives to recognise complex objects
WHat are three poroperties of geons?
View invariance - can be recognised from almost all angles
Discriminability - can tell one from another from almost all angles
Resistant to visual noise
What are geons defined by/
Properties that dont change from view to view e.g. brick = 3 parallel edges, inner y vertex and 3 outer arrow vertices
How does Biederman’s model work? STeps?
Edge extraction – detection of non-accidental properties – parsing of regsions of concavitiy — determination of components – matching of components to object representation
What happens once an image has been parsed up?
You can detect the accidental propetires in each of the volumetric shapes to idetnify each geon. When geons can be extracted - subject can be recognised
What evdience is htere with regard to the importance of regions of concavities?
Biederman (1987) – removal of controus defining concavitities affects object recogntion.
No RoC = 50% recognition accuracy. Just RoC = 70%
Full pic = 100%
What can priming tell us about this model and who’s experiment showed us this?
Biederman & Cooper, 1991 – Pic for 500ms, 7 minutes, pic for 200ms. If pic 1 and pic 2 have same geons, then raction time will be faster when looking at 2nd pic. If they are sam object but with different geons, no priming takes place (semantic priminng does but no visual priming)
