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

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

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

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

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

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

Pre-Attentive - Summary

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

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

What do you see?

What do you see?

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

Gestalt Laws – Proximity

Gestalt Laws – Proximity

Gestalt Laws – Similarity

Gestalt Laws – Similarity Separable dimensions Integral dimensions

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

Gestalt Laws – Continuity Connections using smooth lines

Gestalt Laws – Continuity & Connectness

Gestalt Laws – Symmetry

Gestalt Laws – Symmetry

Gestalt Laws – Closure

Gestalt Laws – Closure

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

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

Contour Finding

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

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

Michotte’s Causality Perception

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

What do you see?

What do you see?

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

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

Standard Lighting Model Ambient Illumination Specular Refection Diffuse Reflection = Lambertian

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

Examples

Examples

Shape-from-Shading Specular reveals fine detail

Textures for Surface Orientation

Depth Cues – Occlusion  strongest depth cue

Perspective

Depth Cues – Perspective

Perspective (Cockburn and McKenzie) Position Occlusion Position Occlusion Perspective

Depth Cues – Shadows

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

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

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

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