LECTURE 02:

MENTAL AND VISUALIZATION MODELSJanuary 21, 2015

COMP 150-04Topics in Visual Analytics

Note: slide deck adapted from R. Chang, Fall 2010

Announcements (1 / 2 )

• Course website has moved:http://www.cs.tufts.edu/comp/150VAN/

• Piazza Q&A is now live:https://piazza.com/tufts/spring2015/15004/home

• Piazza > Resources:• Posted 5 (potentially) interesting datasets (many with nice APIs)• I’ll continue to add more as I find them, feel free to post your own!

Announcements (2 / 2 )

• Drag-and-drop visualization tool suite• Tableau for Teaching has donated license keys (good for one year) for this course

• Want one? Instructions posted on Piazza

Outline

• Mental Models• Illustration: the 9-dot problem• Properties of mental models

• Visualization Models• Reference model (Card, Mackinlay, & Shneiderman)• Data state reference model (Chi)• Model of visualization (van Wijk)• Visual analytics model (Keim)• Sensemaking Loop (Pirolli & Card)

The 9-dot ProblemTask 1: Connect all 9 dots using only straight lines

The 9-dot ProblemTask 2: Connect all 9 dots using 4 straight lines

The 9-dot ProblemTask 3: Connect all 9 dots using 3 straight lines

The 9-dot ProblemTask 4: Connect all 9 dots using 1 straight line

Mental Models: a Sketch

Mental Models: Formalization

A person’s decision-making process is bounded1 by:1. the (incomplete) information they have available2. the (finite) processing power of their brain3. the (limited) amount of time they have to decide / act

To cope with this, we construct mental models: abstracted, simplified versions of the world that are more tractable

So how do mental models work?

1 Simon, Herbert (1957). "A Behavioral Model of Rational Choice", in Models of Man, Social and Rational: Mathematical Essays on Rational Human Behavior in a Social Setting. New York: Wiley.

1. We tend to see what we expect to see

• Mental models are constructed from prior experience• We expect new input to “fit” the existing model• Recalibration is costly: given input that almost fits, we

are willing to distort information in order to avoid re-fitting the model

• Expectation is at least as strong as perception

2. Mental models form quickly, and update slowly:

• “First impressions matter”• The first pieces of information can have the highest

impact• The order in which we present pieces of information can

shape how a person comes to understand the whole• Once a mental model is formed, it takes effort to alter it

3. New information gets incorporated into the existing model

• Integrating competing perspectives into a single model can be challenging

• Switching between two or more perspectives (visually or mentally) is also difficult

• Real-world analysis (e.g. good guys vs. bad guys) often requires such perspective switching

4. Initial exposure interferes with accurate perception

Blur

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4. Initial exposure interferes with accurate perception

• Note: the images in the blurry pictures may not have directly contradicted your initial mental model

• The longer someone is exposed to ambiguous data, the more confident they become in their initial model (even if new data presents strong evidence it is wrong)

• Incremental information can be misleading• Important to be aware of this when designing overviews

The good, the bad, and the ugly…

The good:• Well-tuned mental models make experts capable of processing

huge amounts of information quickly• This frees up more processing power, compares with having to

build a new mental model from scratch

The bad:• People (esp. experts) tend not to notice information that

contradicts their mental model• A “fresh pair of eyes” can be beneficial

The ugly:• Mental models are unavoidable: everyone has them, and no

two are exactly alike• The key is to be aware of how mental models form, how they

shape perception, and how to support (or challenge) them

Questions?

Models in Visualization and Visual Analytics

Mental models = abstractions of how the world works

Visualization / VA models = abstractions of how vis works:• Provide a way of picturing/talking about how humans interact with

visualizations• Common language for describing different parts of the visual

analytic process• Every model is an (over) simplification: reader beware!

1999: A reference model for visualization

Image source: Card, Stuart K., Jock D. Mackinlay, and Ben Shneiderman, eds. Readings in information visualization: using vision to think. Morgan Kaufmann, 1999. pp 17.

Raw Data: Idiosyncratic formatsData Tables: Relations (cases by variables) + metadataVisual Structures: Spatial substrates + marks + graphical propertiesView: graphical parameters (position, scaling, clipping, …)

Discussion

What’s missing in this model?

2000: Chi’s Data State Reference Model

Value: The raw dataAnalytical Abstraction: Data about data, or information (aka, metadata)Visualization Abstraction: Information that is visualizable on the screen using a visualization techniqueView: The end-product of a visualization mapping, where the user sees and interprets the picture presented

Data Transformation: Generates some form of analytical abstraction from the value (usually by extraction)Visualization Transformation: Takes an analytical abstraction and further reduces it into some form of visualization abstraction, which is visualizable content.Visual Mapping Transformation: Takes information that is in a visualizable format and presents a graphical view.

2000: Chi’s Data State Reference Model

Model applied to visualizing web sites

Image source: Chi, Ed H. "A taxonomy of visualization techniques using the data state reference model." Information Visualization, 2000. InfoVis 2000. IEEE Symposium on. IEEE, 2000.

Discussion

What’s missing in this model?

2005: Van Wijk’s Model of Visualization

Image source: Van Wijk, Jarke J. "The value of visualization." Visualization, 2005. VIS 05. IEEE. IEEE, 2005.

2005: Van Wijk’s model of visualization

• D = Data• V = visualization• S = specification (params)• I = image• P = perception• K = knowledge• E = exploration

(1)

(2)

(3)

(4)

(5)

Discussion

What’s missing in this model?

2008: Keim’s Visual Analytics Model

input

Pre-process

interactions

interactions

Image source: Keim, Daniel, et al. Visual analytics: Definition, process, and challenges. Springer Berlin Heidelberg, 2008.

Discussion

What’s missing in this model?

Pirolli-Card Sensemaking Loop

Model: Pirolli, Peter, and Stuart Card. "The sensemaking process and leverage points for analyst technology as identified through cognitive task analysis." Proceedings of International Conference on Intelligence Analysis. Vol. 5. McLean, VA: Mitre, 2005.

Image source: Thomas, James J. and Kristin A. Cook "Illuminating The Path" (2005): pp. 44

Pirolli-Card Sensemaking Loop

• Bottom up:• Search and filter• Read and extract• Schematize• Build case• Tell story

• Top down:• Re-evaluate• Search for support• Search for evidence• Search for relations• Search for information

Discussion

What’s missing in this model?

Questions / Comments?

For next class

• Please read the Executive Summary and Ch.1 of [R1] (available on the course website)

• Next week, we’ll be doing two crash courses• Monday: data wrangling with Python• Wednesday: statistical analysis with R

• If you have a laptop and want to follow along, please install python and Rstudio before you come to lecture