Illusion

1
Perception

• Illusion
• A false representation of the environment
• Perception
• Selection
• Organization
• Interpretation

2
Illusory Contours

• Perceived edges that do not physically exist
• Visual system fills in the gaps
• Inspired Gestalt School
• Max Wertheimer (1880-1943)
• Wolfgang Kohler (1887-1967)
• Kurt Koffka (1886-1941)
• Gestalt Grouping Rules

3
Perception Selection
Selective attention Cocktail party effect The
process whereby the brain sorts out, and only
attends to, the important messages from the
senses. Feature detectors Specialized cells in
the brain that respond only to certain sensory
information. Based on experience. Habituation The
tendency of the brain to ignore environmental
factors that remain constant.
4
Perception Organization

• Form
• Constancy
• Color
• Depth

5
Organization Form
Gestalt ability to perceive the whole stimulus
rather than perceiving its discrete part as
separate entities good continuation
6
Organization Form
Figure and Ground see a main object relative to
ground
7
Organization Form
Proximity items near each other are grouped
together
8
Organization Form
Continuity perceive smooth as continuous patterns
9
Organization Form
Closure fill in the gaps
10
Organization Form
Similarity image chunks that are similar to each
other will be grouped together
11
Violations of Perceptual Organization by Form
Ambiguous Figure
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Violations of Perceptual Organization by Form
Ambiguous Figure
13
Violations of Perceptual Organization by Form
Impossible Figure
14
Violations of Perceptual Organization by Form
Impossible Figure
15
Violations of Perceptual Organization by Form
Impossible Figure
16
Organization by Constancy
Perceptual Constancy the tendency for the
environment to be perceived as remaining the
same even with changes in sensory
input Size Shape Color Brightness
17
Organization by Color
Trichromatic Theory color perception results
from mixing three distinct color systems - red,
green, and blue Opponent-Process Theory color
perception is based on three systems of color
opposites - blue-yellow, red-green, and
black-white
18
Organization by Depth
Depth Perception the ability to see three
dimensions although the images that strike the
retina are in two dimensions Binocular
Cues Monocular Cues
19
Depth Perception
20
Binocular Cues Retinal Disparity
21
Binocular Cues Retinal Disparity
22
Monocular Cue
Relative Size assuming same size can
discriminate distance
23
Monocular Cue
Interposition blocked objects will appear closer
24
Monocular Cue
Relative Clarity hazy objects are perceived to
be further away
25
Monocular Cue
Texture Gradient coarse objects are perceived as
being closer
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Monocular Cue
Relative Height higher objects are perceived to
be farther away
27
Monocular Cue
Relative Motion nearer things are perceived to
move faster
28
Monocular Cue
Linear Perspectives more line convergence gives
the perception of greater distance
29
Monocular Cue
Relative Brightness dimmer is perceived to be
farther away
30
Perception Interpretation
Perceptual Adaptation we adapt to changes in
perceptions Perceptual Set previous experiences
affect our perceptions Individual
Motivation personal interests affect our
perceptions Frame of Reference perceptions
change as context changes
31
Object Recognition

• Naïve Template Theory
• Visual object would have to match existing
  template to be perceived
• Structural Description Theories
• Visual object is recognized by its specific parts
  and the relationships between its parts.
• Multiple Recognition Committees
• Visual objects are recognized by multiple means
  simultaneously
• Grandmother Cell Theory
• Single cells are responsible for recognizing
  specific objects

32
Naïve Template Theory
33
Structural Description Theories
34
Multiple Recognition Committees
35
Grandmother Cell Theory