Lecture 3
Human Visual System – Recap
Human Visual System
– Gestalt Principles
– Motion Perception
–
–
–

Space Perception
Lighting Model
Depth Cues
Depth Cues – Relative Importance
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Human Visual System – Recap
Sensory vs. Cultural
Sensory Representations Effective
because well matched to early stages of neural processing
–
–
Understanding without training
Perceptual Illusions Persist
Physical World Structured
–
–
–
Smooth Surfaces and Motion
Temporal Persistence
Structured Light + Law of Gravity
Stages of Visual Processing
1 Rapid Parallel Processing
–
–
–
–
Feature Extraction: Orientation, Color, Texture, Motion
Bottom-up processing
Popout Effects
Segmentation Effects: Edges & Regions
2 Slow Serial Goal-Directed Processing
–
–
Object Recognition: Visual attention & Memory important.
Top-down processing
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Parallel Processes  Serial Processes
Parallel Processing
•
•
•
•
Orientation
Texture
Color
Motion
Detection
• Edges
• Regions
• 2D Patterns
A
Serial Processing
• Object Identification
• Short Term Memory
5 ± 2 = 3 to 7 Objects
B
C
D
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Spatial Frequency Acuity
Contrast
Sufficient Contrast
for Fine Details
Need
Spatial Freq.
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Human Visual System – Recap
(cont.)
Eye is NOT a light meter
– Designed to detect CHANGES
Not good for detecting Absolute Values
– Designed to extracts Surface Information
– Discounts Illumination Level & Color of Illumination
– Sensitive over 9 orders of magnitude
Mechanisms
1 Adaptation
– Receptors bleach and become less sensitive with more light
– Takes up to ½ hour to recover sensitivity
2 Simultaneous Contrast
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Human Visual System – Recap
Luminance Channel
Detail
Form
Shading
Motion
Stereo
(cont.)
Color Channels
Surfaces of Things
Sensitive to Small Differences
Rapid Segmentation
Categories
(about 6-10)
Not Sensitive to Absolute Values
Unique Hues:
Red, Green, Yellow, Blue
Small areas = high saturation
Large areas = low saturation
 Luminance More Important than Color
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Pre-Attentive - Summary
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Human Visual System – Recap
(cont.)
900
Pre-Attentive Processing
700
Important for Design of Visualizations
500
Pre-Attentive Properties can be perceived immediately
3
6
12
Number of distractors
Pre-Attentive Demo by Christopher Healey
Laws of Pre-Attentive Display
Must Stand Out in Simple Dimension
Position
Color
Simple Shape = orientation, size
Motion
Depth
Pre-Attentive Conjunctions
Position + Color
Position + Shape
Position + Form
Color + Stereo
Color + Motion
Design of Symbols
Simple Visual Attributes
Distinct
–
(or combination thereof)
Use different visual channels for different types of information
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Human Visual System – Recap
(cont.)
Mapping Data to Display Variables
–
–
–
–
–
–
Position (2)
Orientation (1)
Size (spatial frequency)
Motion (2)++
Blinking?
Color (3)
Accuracy Ranking for
Quantitative Perceptual Tasks
Position
More
Accurate
Length
Angle
Slope
Area
Volume
Less
Accurate
Color
Density
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What do you see?
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What do you see?
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Gestalt Laws
Max Westheimer, Kurt Koffka and Wolfgang Kohler (1912)
Proximity
Similarity
Continuity
Symmetry
Closure
Relative Size
Figure and Ground
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Gestalt Laws – Proximity
a
x
b
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Gestalt Laws – Proximity
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Gestalt Laws – Similarity
a
b
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Gestalt Laws – Similarity
Separable dimensions
Integral dimensions
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Gestalt Laws – Continuity
Visual objects tend to be smooth and continuous
a
b
c
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Gestalt Laws – Continuity
Connections using smooth lines
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Gestalt Laws – Continuity & Connectness
a
c
b
d
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Gestalt Laws – Symmetry
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Gestalt Laws – Symmetry
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Gestalt Laws – Closure
a
b
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Gestalt Laws – Closure
A
B
C
D
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Gestalt Laws – Relative Size
Smaller components tend to be perceived as objects
Prefer horizontal and vertical orientations
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Gestalt Laws – Figure and Ground
Rubin’s Vase
– Competing recognition processes
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Contour Finding
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Motion
Motion Phenomena
– Motion Capture demo
– Kinetic Depth demo
– Anthropomorphic Form from Motion
demo
Demo Source: George Mather
Motion is Highly Contextual
– Moving objects are grouped in hierarchical fashion
Use Simple Motion Coding
–
–
–
–
–
Phase, Frequency, or Amplitude
Causality
Urgency
Communication
Emotion
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Motion Patterns

a
Limitation due to Frame Rate
Increase Correspondence by
using additional symbols
b
c
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Michotte’s Causality Perception
100%
Direct Launching
Delayed launching
No causality
50%
100
Time (msec.)
200
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Recommendations
Gestalt Laws useful as Design Guidelines
Luminance Contrast
– Patterns should be present in luminance
Size + Scale Contrast
– Patterns should be the appropriate size
Motion under-researched
but evidence suggest its power
Use Simple Motion Coding
–
–
–
–
Causality
Urgency
Communication
Emotion
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What do you see?
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What do you see?
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Space Perception
Depth Cues
Shape-from-Shading
Shape-from-Texture
Shape-from-Contour
Shape-from-Motion
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Perception of Surface Shape
Simple Lighting Model
Light from above and at infinity
Diffuse, Specular and Ambient Reflection
Oriented Texture enhances Shape Perception
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Standard Lighting Model
Ambient Illumination
Specular Refection
Diffuse Reflection =
Lambertian
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Standard Lighting Model
Diffuse
Lambertian
(cont.)
Specular
Ambient
Shadows
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Examples
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Examples
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Shape-from-Shading
Specular reveals fine detail
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Textures for Surface Orientation
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Depth Cues – Occlusion
 strongest depth cue
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Perspective
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Depth Cues – Perspective
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Perspective
(Cockburn and McKenzie)
Position
Position
Occlusion
Occlusion
Perspective
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Depth Cues – Shadows
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Depth Cues – Shape-from-Motion
b
a
c
Optical Flow Fields and Their Structure
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Stereo Vision Basics
P a n u m 's F u s i o n a l A r e a
S c reen
R i g h t ey e
d i sp a rity
a
=
a
- b
b
L ef t ey e
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Depth Cues – Relative Importance
Depth Contrast
0.001
Motion
parallax
Occlusion
0.01
Relative size
0.1
Binocular
disparity
Convergence
accommodation
1.0
1
Aerial
10
100
Depth (meters)
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Depth Cues – 3D Options
Vergence
Motion
Parallax
Shape-from
Shading or
Texture
Focus
Stereo
Perspective
Occlusion
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