L5: Object And Face Pereception Flashcards
Outline ‘a model of object recognition’
1) early visual processing (colour, motion, edges etc.)
2) perceptual segregation: grouping of visual elements (gestalt principles, figure-ground segmentation)
3) matching grouped visual description onto a representation of the object stored in the brain (called structural descriptions)
4) attacking meaning to the object (based on prior semantic knowledge)
Outline perceptual segregation
Separating visual input into individual objects, thought to occur before object recognition
Outline gestalt psychology
- first attempt to systematically study segregation
- Law of Prägnanz: the notion that the simplest possible organisation of the visua, environment is perceived
4 gestalt laws of perceptual organisation
Law of proximity: visual elements close in space tend to be grouped together
Law of similarity: items are grouped together due to similarity
Law of good continuation: items will be grouped together if they require the fewest interruptions of straight or curved lines
Law of closure: missing parts of a figure are filled in to complete the figure
Outline the law of Prägnanz
The notion that the simplest possible organisation of the visual environment is perceived
Name and outline the 4 gestalt laws of perceptual organisation
Law of proximity: visual elements close in space tend to be grouped together
Law of similarity: items are grouped together due to similarity
Law of good continuation: items will be grouped together if they require the fewest interruptions of straight or curved lines
Law of closure: missing parts of a figure are filled in to complete the figure
Outline figure ground segregation
- when looking at an object (the figure, which appears to be more distinct), you never see it on its own, on,y against an unimportant background ( which appears to have less form and is represents the ‘ground’ in the name of theory)
- objects likely to be perceived as figures have some of the following characteristics : convex, small, surrounded and symmetrical
- these laws assume bottom-up processing. However there is evidence that our ability to recognise and perceive objects is not just bottom-up (Vecera and Farah, 1997)
Outline the criticisms of gestalt psychology
- relied heavily on introspection and evidence from 2D drawings
- provided descriptions not explanations
- some claims could not be corroborated (supported). Also segmentation processes are also affected by top-down prior knowledge
- however most laws are still valid today
Outline recognition by components theory
-any object can be broken down in to components. Objects are made up of a set of combination of geons (shapes basically, there are 36 in total)
A few processes need to take place before the configuration of geons can be identified
- a line drawing description of the object is extracted (edges are extracted)
- the line drawing is then segmented into components (concavities appear to be very important in object recognition)
- the edges of the line drawing are then investigated to determine which edges remain invariant
According to Biederman there are 5 invariant properties:
1) curvature: various points on a curve
2) parallel: sets of points in parallel
3) co-termination: point at which 2 edges terminate
4) symmetry and asymmetry
5) Colinearity: points sharing a common line
Evaluate recognition by components theory
Positives
-good evidence for geons being very important in object recognition
- evidence that identification of concavities and edges is also of major importance
- many principles have stood the test of time
Negatives
- much recognition is viewpoint dependent
- some classes do not have invariant geons yet are still recognisable as members of a category (e.g clouds)
- de-emphasises importance of top-down influences
What is agnosia?
Impairment in object recognition (without primary visual deficits)
different impairments arise depending on the sage at which object recognition is damaged
What is apperceptive agnosia? Outline a clinical example of this condition
-damage to the lateral occipital lobe. They see parts but not the whole
E.g patient HJA
- could tell you what an object was by touching it, but not by looking at it
- ventral pathway (‘what’) is damages, whereas the ‘where’ is intact. (Processing geons, just not together?)
What is associate agnosia? Outline a clinical example of this condition
- left occipital-temporal damage
- can’t tell you what an object is for/its purpose
- see the whole but not its meaning
E.g patient LH
-could copy drawings but couldn’t name them or know what they are for
How are faces special/different to objects
Face recognition is a within-category discrimination as opposed to object recognition is across categories. Face recognition is not about being able to identify something is a face and not a laptop, it is about identifying a particular face
Faces are also very important from an evolutionary standpoint
Outline prosopagnosia
-condition in which face recognition is impaired without difficulties in early visual analysis
E.g. Man could not recognise his wife or family by facial features, but instead by clothes and voices. Note: no issues in Lower level operations with faces (matching faces from different views). Also no impairment in naming objects in general.
Note: often occurs without object agnosia (and vice versa). Suggesting they rely on different neural mechanisms.
Name the main ways in which faces may be special
- task difficulty
- holistic/configural processing
- visual expertise
- domain specificity
