Assignment 2 review

• What is the user centered design process?
• Why write personas?
• Why write scenarios?

Requirements

• Identify a dataset
• Write a persona description
• Write a scenario

World Food Programme

“Pranab is a 35-year-old food aid worker who works with an advocacy organization that solicits donations for food contributions for emergency relief.”

Refugee Dataset

Role of graphical perception

Visualization process

Graphical perception

“The visual decoding of information encoded in graphs” - Cleveland/McGill

• Our task: encode data with graphical properties that are most easily/accurately decoded
• Semiotics of graphics

“The study of symbols and how they convey meaning” - Ware 2004

Is this possible?

• Can there be a science of visualization?
• Arbitrariness (Saussure)
• Cultural relativism
• Ware 2004

Sensory versus arbitrary symbols

Definitions

• Sensory: meaning derived without learning
• Arbitrary: understanding depends on learned information

Sensory symbols

• Understanding without training
• Resistance to instructional bias
• Sensory immediacy
• Cross-cultural validity

Understanding without training

Resistance to instructional bias

Arbitrary symbols

• Hard to learn
• Easy to forget
• Embedded in culture and applications
• Formally powerful
• Capable of change

Sensory versus arbitrary

Model of perceptual processing

Three stages

• Stage 1: Parallel processing of low level information
• Stage 2: Pattern perception
• Stage 3: Goal directed processing

Stage 1

• Neurons process information in parallel
• Extract features (color, texture, movement, orientation)

Stage 2

• Slower serial processing
• More detailed processes such as segmentation

Stage 3

• Executing advanced visual queries
• Requires active attention

Aim to communicate your primary message through stage 1 or stage 2 processing

Preattentive cognition

Preattentive cognition

• Processing prior to conscious attention
• Stage 1 processing of sensory symbols
• Resistant to distractors
• Rooted in sensory symbols

Resistant to distractors

Importance

• Dictates ease of use
• Determines hierarchy of interpretation
• Distinguishing categories from one another
• Drawing attention to a single element

Preattentive attributes

Are all preattetive attribues equally effective?

Rapid processing time

Using color

Drawing attention

Semantic depth of field

Gestalt grouping

Overview

• Tendency to visually group elements
• Distinguishing sets from one another
• Pattern perception
• Eight laws (Ware 2004)

Gestalt laws

• Proximity
• Similarity
• Connectedness
• Continuity
• Symmetry
• Closure
• Relative size
• Common fate

Acknowledgement: Jeffery Heer

Proximity

Proximity

Similarity

Connectedness

Closure