1. Human Visual System Lecture 3 Human Visual System – Recap
Gestalt Principles
Motion Perception
Space Perception
Lighting Model
Depth Cues
 Depth Cues – Relative Importance

2. 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

3. Parallel Processes  Serial Processes
Parallel Processing
Orientation
Texture
Color
Motion
Detection
Edges
Regions
2D Patterns
Serial Processing
Object Identification
Short Term Memory 5 ± 2 = 3 to 7 Objects

4. Spatial Frequency Acuity
Need Sufficient Contrast
for Fine Details
Contrast
Spatial Freq.

5. 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
Adaptation
Receptors bleach and become less sensitive with more light
Takes up to ½ hour to recover sensitivity
2 Simultaneous Contrast

6. Human Visual System – Recap (cont.)
Luminance Channel
Detail
Form
Shading
Motion
Stereo
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

7. Pre-Attentive - Summary

8. Human Visual System – Recap (cont.)3 6 1 2 N u m b e r o f d i s t a c 5 7 9
Pre-Attentive Processing
Important for Design of Visualizations
Pre-Attentive Properties can be perceived immediately
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 (or combination thereof)
Distinct – Use different visual channels for different types of information

9. Human Visual System – Recap (cont.)
Mapping Data to Display Variables
Position (2)
Orientation (1)
Size (spatial frequency)
Motion (2)++
Blinking?
Color (3)
Angle
Slope
Length
Position
Area
Volume
Color
Density
More
Accurate
Less
Accuracy Ranking for Quantitative Perceptual Tasks

10. What do you see?

11. What do you see?

12. Proximity Similarity Continuity Symmetry Closure Relative Size
Gestalt Laws
Max Westheimer, Kurt Koffka and Wolfgang Kohler (1912)
Proximity
Similarity
Continuity
Symmetry
Closure
Relative Size
Figure and Ground

13. Gestalt Laws – Proximity

14. Gestalt Laws – Proximity

15. Gestalt Laws – Similarity

16. Gestalt Laws – Similarity
Separable dimensions
Integral dimensions

17. Gestalt Laws – Continuity
Visual objects tend to be smooth and continuous

18. Gestalt Laws – Continuity
Connections using smooth lines

19. Gestalt Laws – Continuity & Connectness

20. Gestalt Laws – Symmetry

21. Gestalt Laws – Symmetry

22. Gestalt Laws – Closure

23. Gestalt Laws – Closure

24. Gestalt Laws – Relative Size
Smaller components tend to be perceived as objects
Prefer horizontal and vertical orientations

25. Gestalt Laws – Figure and Ground
Rubin’s Vase
Competing recognition processes

26. Contour Finding

27. Motion is Highly Contextual
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

28. Motion Patterns Limitation due to Frame Rate
Increase Correspondence by using additional symbols

29. Michotte’s Causality Perception

30. Gestalt Laws useful as Design Guidelines Luminance Contrast
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

31. What do you see?

32. What do you see?

33. Depth Cues Shape-from-Shading Shape-from-Texture Shape-from-Contour
Space Perception
Depth Cues
Shape-from-Shading
Shape-from-Texture
Shape-from-Contour
Shape-from-Motion

34. Perception of Surface Shape
Simple Lighting Model
Light from above and at infinity
Diffuse, Specular and Ambient Reflection
Oriented Texture enhances Shape Perception

35. Standard Lighting Model
Ambient Illumination
Specular Refection
Diffuse Reflection =
Lambertian

36. Standard Lighting Model (cont.)
Diffuse Lambertian
Specular
Ambient Shadows

37. Examples

38. Examples

39. Shape-from-Shading
Specular reveals fine detail

40. Textures for Surface Orientation

41. Depth Cues – Occlusion  strongest depth cue

42. Perspective

43. Depth Cues – Perspective

44. Perspective (Cockburn and McKenzie)
Position
Occlusion
Position
Occlusion
Perspective

45. Depth Cues – Shadows

46. Depth Cues – Shape-from-Motion
Optical Flow Fields and Their Structure

47. a a Stereo Vision Basics R i g h t e y S c r e n a b P u m ' s F i o ld p t y = - L e f t y

48. Depth Cues – Relative Importance
Depth Contrast
Depth (meters)
0.001
0.01
0.1
1.0 1 10
100
Motion
parallax
Occlusion
Binocular
disparity
Relative size
Convergence
accommodation
Aerial

49. Depth Cues – 3D Options Vergence Focus Motion Parallax Stereo
Shape-from
Shading or
Texture
Perspective
Occlusion