Lecture 3 Human Visual System Recap Human Visual

Lecture 3 Human Visual System – Recap Human Visual System – Gestalt Principles – Motion Perception – – – Space Perception Lighting Model Depth Cues – Relative Importance © Anselm Spoerri

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 © Anselm Spoerri

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

Spatial Frequency Acuity Contrast Sufficient Contrast for Fine Details Need Spatial Freq. © Anselm Spoerri

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 © Anselm Spoerri

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 © Anselm Spoerri

Pre-Attentive - Summary © Anselm Spoerri

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 © Anselm Spoerri

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 © Anselm Spoerri

What do you see? © Anselm Spoerri

What do you see? © Anselm Spoerri

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

Gestalt Laws – Proximity © Anselm Spoerri

Gestalt Laws – Proximity © Anselm Spoerri

Gestalt Laws – Similarity © Anselm Spoerri

Gestalt Laws – Similarity Separable dimensions Integral dimensions © Anselm Spoerri

Gestalt Laws – Continuity Visual objects tend to be smooth and continuous © Anselm Spoerri

Gestalt Laws – Continuity Connections using smooth lines © Anselm Spoerri

Gestalt Laws – Continuity & Connectness © Anselm Spoerri

Gestalt Laws – Symmetry © Anselm Spoerri

Gestalt Laws – Symmetry © Anselm Spoerri

Gestalt Laws – Closure © Anselm Spoerri

Gestalt Laws – Closure © Anselm Spoerri

Gestalt Laws – Relative Size Smaller components tend to be perceived as objects Prefer horizontal and vertical orientations © Anselm Spoerri

Gestalt Laws – Figure and Ground Rubin’s Vase – Competing recognition processes © Anselm Spoerri

Contour Finding © Anselm Spoerri

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 © Anselm Spoerri

Motion Patterns Limitation due to Frame Rate Increase Correspondence by using additional symbols © Anselm Spoerri

Michotte’s Causality Perception © Anselm Spoerri

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 © Anselm Spoerri

What do you see? © Anselm Spoerri

What do you see? © Anselm Spoerri

Space Perception Depth Cues Shape-from-Shading Shape-from-Texture Shape-from-Contour Shape-from-Motion © Anselm Spoerri

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

Standard Lighting Model Ambient Illumination Specular Refection Diffuse Reflection = Lambertian © Anselm Spoerri

Standard Lighting Model Diffuse Lambertian (cont. ) Specular Ambient Shadows © Anselm Spoerri

Examples © Anselm Spoerri

Examples © Anselm Spoerri

Shape-from-Shading Specular reveals fine detail © Anselm Spoerri

Textures for Surface Orientation © Anselm Spoerri

Depth Cues – Occlusion strongest depth cue © Anselm Spoerri

Perspective © Anselm Spoerri

Depth Cues – Perspective © Anselm Spoerri

Perspective (Cockburn and Mc. Kenzie) Position Occlusion Perspective © Anselm Spoerri

Depth Cues – Shadows © Anselm Spoerri

Depth Cues – Shape-from-Motion Optical Flow Fields and Their Structure © Anselm Spoerri

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 © Anselm Spoerri

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) © Anselm Spoerri

Depth Cues – 3 D Options Vergence Motion Parallax Shape-from Shading or Texture Focus Stereo Perspective Occlusion © Anselm Spoerri