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 is
this?
Figure 2-1
Distal Stimuli,
Proximal Stimuli, and
Percepts.
Perceptual Constancies
Shape Constancy
Tendency to see an object as keeping its form
despite changes in orientation.
Perceptual Constancies
Size Constancy
Tendency to view an object as constant in
size despite changes in the size of the retinal
image.
http://www.psychologie.tu-dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/assets/images/constancy.jpg
Perceptual Constancies
Illusions
Gestalt
Approach
Figure
Ground
Figure 2-2
Gestalt
Approach
Subjective
Contours
Figure 2-3
Gestalt principles of
Perceptual Organization
Proximity
http://www.sapdesignguild.org/resources/optical_illusions/images/proximity.gif
Gestalt principles of
Perceptual Organization
Similarity
http://www.aber.ac.uk
http://chd.gse.gmu.edu/immersion/knowledgebase/strategies/cognitivism/gestalt/Image6.gif
Gestalt principles of
Perceptual Organization
Good continuation
what most people not this
would see
http://www.aber.ac.uk
Gestalt principles of
Perceptual Organization
Closure
http://daphne.palomar.edu
http://www.aber.ac.uk/media/Modules/MC10220/Images/seal.gif
http://graphicdesign.spokanefalls.edu/tutorials/process/gestaltprinciples/closure/closure_a.gif
Gestalt principles of
Perceptual Organization
Common fate
Gestalt
principles of
Perceptual
Organization
Figure 2-5
Two Interacting Aspects of Perception
Bottom-up processing
Processing based on
incoming stimuli from the
environment
Also called data-based
processing
Top-down processing
Processing based on the
perceiver’s previous
knowledge
Also called knowledge-
based processing
http://jurmo.us/log/wp-content/uploads/2007/04/topdownbottomup.jpg
Bottom-Up Processes
Template
matching
The number “4” from the check is compared to a list of
stored templates.
Bottom-Up Processes
Problems with Template Matching
Large number of stored templates needed
How are new templates made?
An object can be “more or less” like the
template
Wecan 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…)
Featural Analysis
Geons
Featural
Analysis
Letter
detection
Figure 2-14
A depiction of Selfridge’s
(1959) Pandemonium
model.
Bottom-Up Processes
Featural Analysis
Feature Properties
Detectors can respond at different
intensities
Connections between detectors can
have different strengths
It is possible to change what a
detector will respond to
Bottom-Up Processes
Prototype Matching
Bottom-Up Processes
Prototype Matching
http://www.palm.com