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Lec2: Perception (What is Perception (Perceptions can change based on…
Lec2: Perception
What is Perception
Perceptions can change based on added info
Involves process similar to reasoning or problem solving
experience resulting from stimulation of the senses
occur in conjunction with actions
Why is it so difficult to design a perceiving machine
Objects can be hidden or blurred
Objects look diff from diff viewpoints
viewpoint invariance
Inverse Projection Problem
task of determining object responsible for a particular image on retina
involves starting with retinal image & then extending outward to source of that image
What & Where pathways
Approaches to understanding perception
Top-down processing
Features
Person's knowledge, experience, expectations
Perception may start with brain
constructive perception theories
ppl actively construct perceptions using info based on expectations
Helmholtz' Theory of Unconscious Inference
we use our knowledge to inform our perceptions->infer much of what we know abt the world
Likelihood principle
we perceive world in way that is most likely based on past exp
some of our perceptions->result of unconscious assumptions we make abt environment
Bayesian Inference
Prior probability (initial belief abt prob of an outcome)
Likelihood of given outcome
one's estimate of prob of a given outcome is influenced by 2 factors
Physical regularities
Oblique effect
horizontal & vertical orientations perceived more often than oblique orientations
Light-from-above assumption
concave or convex problem
Semantic regularities
Scene schema
eg. when shown a bread in kitchen easier than recognising mailbox in a kitchen
Bottom-up processing
features
incoming raw data
Energy registering on receptors
Perception may start with senses
Direct perception theories
Parts are identified & put tgt, & then recognition occurs
perception comes from stimuli in the envrt
Gestalt
mind groups patterns according to built-in laws of perceptual org
Gestalt laws of Perceptual org
Law of Pragnanz
Every stimulus pattern is seen such that resulting structure is as simple as possible
Law of similarity
Similar things appear grouped tgt
Law of good continuation
Lines tend to be seen as following smoothest path
Law of closure
Tendency to see visual items as part of larger object
Figure-ground segregation
Bottom-up process
Heuristics & Algorithms
Algorithm
procedure guaranteed to solve problem, slow but definite
Gestalt laws are heuristics
Heuristic
rule of thumb->fast & often correct
Recognition-by-components theory (RBC)
Geons
What is it
36 diff geons proposed
objects are recognised when enough info is available to identify object's geons
3D volumes
Local viewpoints
can identify objects from many diff orientations
problems with geons
only 36 geons->may not represent all shapes
Dk how r/s among geons are coded
Tarr's experiment
geon cannot be identified equally quickly at different angles
we perceive objects by perceiving elementary features
Movement facilitating perception