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Human Visual System Lecture 3 Human Visual System – Recap

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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 l
d 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


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