perception. question of the day why is recognizing an object so easy for humans, but so difficult...
TRANSCRIPT
Perception
Question of the Day
Why is recognizing an object so easy for humans, but so difficult for computers?
Points of Confusion
http://i.ivillage.com/E/325/Celebrities/FaceReader/FaceReaderIntro_325.jpg
http://www.apogeephoto.com/mag1-6/mag2-5mf1.jpg
Perception:attaching meaning to incoming sensory information
What isthis?
The number “4” from the check is compared to a list of
stored templates.
Bottom-Up Processes
Template matching
Problems with Template Matching Large number of stored templates
needed How are new templates made? An object can be “more or less” like the
templateWe can recognize many variations of a
template
Bottom-Up Processes
Figure 2-8
Bottom-Up Processes
Featural Analysis
features (“parts”) of a stimulus are recognized by feature detectors and added together to help us perceive an object
Lines or edges Geons Phonemes Parts of a face (eyes, nose…)
Bottom-Up Processes
Featural Analysis
Geons
Figure 2-14 A depiction of Selfridge’s (1959) Pandemonium model.
Featural
Analysis Letter
detection
Bottom-Up Processes
Featural Analysis
Feature PropertiesDetectors can respond at different
intensitiesConnections between detectors can
have different strengthsIt is possible to change what a
detector will respond to
Bottom-Up Processes
Prototype Matching
http://www.palm.com
Bottom-Up Processes
Prototype Matching
Figure 2-19
An example of context effects in perception.
Top-Down Processes
Top-Down Processes
Perceptual Learning
Top-Down Processes
Change Blindness
http://viscog.beckman.uiuc.edu/grafs/demos/10.html
Word Superiority Effect
Top-Down Processes
K
OWRK
WORK
K D
Bottom-Up and Top-Down Processing working togetherWord Perception Connectionist Model
Features(lines)
Letters
Words
I
B
Bat
_at
Flying Animal
Gestalt Psychology (Wertheimer, Koffka, and Kohler – 1920s)“The whole differs from the sum of its
parts”Perception is not built up from
sensations but is a result of perceptual organization
We use heuristics to make “best guesses” about the identity of stimuli
Theories of Perception
The Gestalt Approach Principles of perceptual organization
Pragnanz - every stimulus is seen as simply as possible
Figure 2-5
Gestalt principles of Perceptual Organization
Gestalt principles of Perceptual Organization
Similarity
http://www.aber.ac.uk
Gestalt principles of Perceptual Organization Good continuation
what most people would see
not this
http://www.aber.ac.uk
The Gestalt Approach Principles of perceptual organization
Good continuation Connected points resulting in straight or smooth
curves belong together Lines are seen as following the smoothest path
http://www.owlnet.rice.edu/~psyc351/Images/Wolfe-Fig-04-07-0.jpg
http://graphicdesign.spokanefalls.edu/tutorials/process/gestaltprinciples/continuation/continuation_a.gif
Gestalt principles of Perceptual Organization
http://www.aber.ac.uk
Proximity
The Gestalt Approach
Principles of perceptual organization Proximity - things that are near to each other are grouped
together
Gestalt principles of Perceptual Organization
Common fate
http://www.tutkie.tut.ac.jp/~mich/humanmotion.gif
Principles of perceptual organization Meaningfulness or familiarity - things form groups if they
appear familiar or meaningful
The Gestalt Approach
http://www.customflamepainting.com/noncgi_parts/upload/samples.901.11.jpg
Principles of perceptual organization Common region - elements in the
same region tend to be grouped together
Uniform connectedness - connected region of visual properties are perceived as single unit
Synchrony - elements occurring at the same time are seen as belonging together
The Gestalt Approach
Properties of figure and ground The figure is more “thinglike” and more memorable
than ground The figure is seen in front of the ground The ground is more uniform and extends behind
figure The contour separating figure from ground belongs
to the figure
Perceptual Segregation
Perceptual Segregation
Figure-ground segregation - determining what part of environment is the figure so that it “stands out” from the background
Reversible figure-ground
http://www.apogeephoto.com/mag1-6/mag2-5mf1.jpg
Perceptual Segregation
Gestalt principles of Perceptual Organization
Closure
http://daphne.palomar.edu
Figure 3-26 (p. 91)Example of stimuli used in the PET scan study of processing words.
Word Perception Neuropsychological Perspective
Direct Perception vs. Constructivist Approach
Biological motion http://www.psico.univ.trieste.it/labs/acn-lab
/eng_p/e051c1m1_curr.html
Optic flow
Affordances: Information from the stimulus that specifies
how it can be used
Direct Perception
Visual Agnosia
http://scien.stanford.edu/class/psych221/projects/06/cukur/intro_files/image021.jpg
Visual Agnosia
Associative Visual Agnosia Can copy, but unaware what it
is; cannot assign meaning to object
Difficulty in transferring visual info into words
Apperceptive Visual Agnosia Cannot recognize by shape Cannot copy drawings Often involves ‘prosopagnosia’
http://scien.stanford.edu/class/psych221/projects/06/cukur/intro_files/image021.jpg
Agnosia
Identification of Faces and Members of Categories
Prosopagnosia
The Fusiform Face Area:
http://www.psy.vanderbilt.edu/faculty/gauthier/picts/mona_lisa.jpg
Perceptual Intelligence
light-from-above heuristic