LECTURE SIX Flashcards
HIERARCHICAL OBJECTS
- Hierarchical structure
- Objects can be made of objects
- My car is an object, but so are the wheels, and so are the bolts on the hubcaps
- Global superiority effect
- Largest grouping (global) preferred over smaller groupings (local) – to a point
OBJECT
- Stable grouping of visual information
- Figure as opposed to ground
- One level of hierarchical structure
- Region of interest, depending on task
GESTALT GROUPING
- Gestalt grouping principles
- Heuristics for grouping perceptual information into
larger objects - System for organizing a messy world into discrete
groups of objects
SUBJECTIVE EDGES
Subjective edge – edge that exists for an observer, but not actually an edge
- Exists when Gestalt principles imply it should exist
* Continuation – straight edges continue while occluded
* Closure – Edges are assumed to be “closed” and solid
FIGURE AND GROUND
Major part of grouping is determining figure and
ground
* Figure – object of interest
* More enclosed by other, smaller
* Greater familiarity
* Ground – background, not an object
ACCIDENTAL VIEWPOINT
At a given angle, things may look different
SHADING
- Objects with a three-dimensional structure shade
themselves - If light is coming from one source – or at least one
direction – this shading will be predictable and uniform - Biased to assume light is coming from above
- Note this bias is involved with many other illusions
OBJECT RECOGNITION
Determining what constitutes an object is a good
start
* Once an object is defined, how do we recognize
what it is?
* Object constancy and viewpoint
- Two possibilities for object representation:
* Distributed – recognition by components
* Local – recognition by views
RECOGNITION BY COMPONENTS
- Segment an object into geometrical components AKA geons
- Sometimes called “geon theory”
- Determine position and relation between parts
- Match information with mental representation
GEONS
- Geons are viewpoint invariant
- Relation between geons holds true for all viewpoints, as long as geons are visible
- Helps resolve problem of object invariance
- Can be modeled computationally
- Faster object naming times when geons can be
identified properly
RECOGNITION BY VIEWS
- Different views of same object are stored in LTM
- Exemplars
- Objects are then matched with exemplars
- Best match is the object
CANONICAL OBJECT VIEWS
- Most “obvious” viewpoint
- Reflected in reaction time when naming picture
- What you would likely draw
- Mental image
- Recognition by Views
- Canonical viewpoints are easily matched (you’ve seen
the object in that view the most) - Stronger (or more) exemplar(s)
- Recognition by Components
- Canonical viewpoints have easily identifiable geons and clearly show relation between them
RBC and RBV - ARE THEY MUTUALLY EXCLUSIVE
- Some things might be better recognized using RBC
- Basic level objects (“a dog”)
- Entry-level categories (first word that comes to mind)
- Some things might be better recognized using RBV
- Specific instances of category (“my dog, Flapjack”)
- RBC can’t really recognize specific members
- Discriminating between two faces – geons are the same
OBJECT AGNOSIA
Difficulty or inability to engage in object recognition
* Two forms - Apperceptive Agnosia & Associative Agnosia
APPERCEPTIVE AGNOSIA
- Cannot identify objects based on vision
- Problem with scale (only pays attention to fragments)
ASSOCIATIVE AGNOSIA
- Can see and even reproduce objects
- But can’t recognize them as what they are
- No access to name, usage, or meaning
VISUAL INDETERMINANCY
Before object recognition occurs, object is
“indeterminant”
OPTIC ATAXIA
Inability to recognize where the object is, but able to identify what it is
DIFF BTW ASSOCIATIVE AGNOSIA AND OPTIC ATAXIA
- People with associative agnosia can locate objects
(and properly act on them!) but do not explicitly know the identity of the object - Damage to the inferior temporal lobe (where occipital
lobe meets temporal) - People with optic ataxia can identify objects but
have difficulty locating and acting on them - Damage to the posterior parietal lobe (where occipital
lobe meets parietal) - Double dissociation
- Can see this anatomically as well
DUAL VISUAL SYSTEM THEORY
STUDY THE DAMN DIFFERENCES AND THE MEANING OF DOUBLE DISSOCIATION
AFFORDANCES
- Every object in the world can be acted on in some way
- Object affordances – potential actions you can take on an object (Gibson). EG: A mug affords holding and
drinking (moving arm to mouth), A pencil affords grasping and writing or A big red button affords pushing - Dorsal stream, vision for action
HOW WE DIFFERENTIATE FACES FROM OTHER OBJECTS
- Innate face representations
- Holistic processing
- Face special neural representations
FACE PERCEPTION
We appear to be highly specialized to detect and process faces
* Even newborn infants show a preference for “face-like” stimuli
PAREIDOLIA
Seeing patterns (objects / faces) in other things
WHY ARE FACES SO IMPORTANCE
- Social identification: Friends and enemies & Familiar and unfamiliar
- Emotional identification: Approach vs. avoid & Threat detection
PROSOPAGNOSIA
Sensation without Perception.
HOLISTIC PROCESSING
- We process faces “holistically”
- Which means we process it as a whole object, NOT
its parts alone - Only for upright and aligned faces
INVERTED FACES
- In fact, we are so specialized to deal with faces holistically that weird things can happen with interrupted processing
- Inverted faces are less subject to holistic (global) processing
- Face illusions are really strange
HOLLOW MASK ILLUSION
- Objects are generally convex
- Faces are ALWAYS convex
- Faces processed holistically
- One step further – combine structure from motion with hollow mask illusion
FACE ADAPTATION
- Adapting to a face can lead to a face aftereffect
- Most likely same process (basically) as motion and color aftereffects
Face adaptation and flicker face illusion (next up)
work because we compensate in an opposite
direction based on facial features - Adapt to one feature – next face looks “opposite” on
those features
FUSIFORM FACE AREA
Located in the right temporal lobe
* Selective for faces
* However, also active when car experts identify particular cars
* Left FFA (VWFA) highly active during reading
* Visual expertise in very similar stimuli?
GREEBLES
- Highly homogeneous artificial stimuli used to study
object classification similar to facial recognition - When people become “expert” Greeble
recognizers…. - The FFA is active during Greeble recognition!
