Visual Explanations Barbara Tversky Stanford University

1. Visual ExplanationsBarbara TverskyStanford University

2. External representations: Cognitive tools • Augment memory/processing by offloading, alleviating limited working memory • Use space to represent literal & metaphoric space • Allow creation, revision, inference by community • Uniquely human

3. Two kinds of graphics • Visualizations of inherently visual • Maps • Ancient • Visualizations of metaphorically visual • Graphs, charts, diagrams • Modern

4. Ancient Babylonian clay map

5. Eskimo coastal map

6. South Sea Islanders’ map

7. 18th c. graph

8. Some ways graphics augment cognition • Record information • Convey information • Promote inferences • Enable new ideas • Facilitate collaboration

9. Good graphics schematize • Not “realistic;” omit irrelevant • Emphasize, simplify, distort relevant

11. Graphics consist of: • Elements • Spatial relations among them • These can convey meaning directly

12. Spatial relations Map information at varying levels of specificity: • Categorical: spacesbetweenwords, ( ) • Ordinal: lists, outlines, trees • Interval/ratio: graphs

13. Meaningful use of space • Proximity in space signifies proximity on abstract dimension • Directionality • Verticalloaded: up is more, better, stronger • Horizontal neutral • Parallels in language & gesture

15. Mixing spatial metaphors

16. Elements • Iconic • Metaphoric • Schematic

17. Elements • Iconic: perceptual similarity to what they represent • Metaphoric: conceptual similarity to what they represent • Schematic: meaningful abstract forms

19. Meaningful abstract forms • Lines, crosses, arrows, blobs • Meanings related to mathematical/Gestalt properties • Meanings context-specific

20. Meanings:simple, efficient, neutral, abstract • Line: 1-D, path, link • Cross: intersection of 2 paths • Arrow: asymmetric path • Blobs: enclosure, area

21. Meaningful abstract forms • Bars and lines in graphs • Arrows in mechanical diagrams • Curves, lines, crosses, & blobs in route maps

22. Producing descriptions from graphs Please describe in a sentence what is shown in the graph above:

23. Bars Contain, separate Yield discrete comparisons Lines Connect Yield trends Bar vs. Line graphs

24. Discrete higher—lower greater—less more—fewer stronger—weaker Trend rising—falling increasing—decreasing function relationship trend Two categories of description

25. Proportion of trend responses Bar Graph Line Graph 0% 12% Discrete Domain 7% 61% Continuous Domain

26. Producing graphs from descriptions Discrete Description Trend Description Height for males is greater than for females. Height increases from females to males. Discrete Domain Height for 12-yr-olds is greater than for 10-yr-olds. Height increases from 10-yr-olds to 12-yr-olds. Continuous Domain

27. Proportion of Line Graphs Discrete Description Trend Description Height for males is greater than for females. Height increases from females to males. Discrete Domain 30% 65% Height for 12-year-olds is greater than for 10-year-olds. Height increases from 10-year-olds to 12-year-olds. 100% 56% Continuous Domain

28. Bars and Lines: Summary • Interpretations: bars as discrete comparisons, lines as trends • Productions: discrete comparisons yield bars; trends yield lines • Despite conflicting real-world domain

29. Arrows • Natural interpretation of directionality • Arrow heads • River beds • Many uses, interpretations: • Pointing, labeling • Direction in space, time, motion, etc.

30. Arrows for mechanical systems

31. Describe diagrams with or without arrows • Without arrows: structural descriptions • A is attached to B • A is above B • With arrows: functional descriptions • A pushes down on B • When A does B, C happens

32. Arrows have many meanings • Asymmetric--> symmetric <--> extent <--> • Connecting, pointing, labeling • Temporal: sequence • Causal • Movement: direction, manner • Movement; change over time, increases/decreases • Forces

42. Route maps & route directions • Are the schematizations similar? • Ask hungry students how to get to fast food restaurant

43. Depictions: landmarks & paths

44. Depictions: landmarks & paths

45. Directions: landmarks & paths • From Roble parking lot • R onto Santa Theresa • L onto Lagunita (the first stop sign) • L onto Mayfield • R onto Bowdoin • L onto Stanford Ave • R onto El Camino • go down a few miles. It’s on the right.

46. Directions: landmarks & paths Go down street toward main campus (where most of the buildings are as opposed to where the fields are) make a right on the first real street (not an entrance to a dorm or anything else). Then make a left on the 2nd street you come to. There should be some buildings on your right (Flo Mo) and a parking lot on your left. The street will make a sharp right. Stay on it. That puts you on Mayfield Rd. The first intersection after the turn will be at Campus Dr. Turn left and stay until you get to El Camino. Turn right (south) and Taco Bell is a few miles down on the right.

47. Segmentation according to Denis • Start point: “you leave the building” • Reorientation: “you turn left” • Path/progression: “you follow Main St.” • End point: “until you get to the restaurant”

48. Elements Turn, take a Go down Follow around Landmarks Arrows

49. Depictive & descriptive elements • Parallel, suggesting same underlying representation • Both tool kits sufficient to create directions • Automatic translation? • Why do they work, despite schematization?

50. Depictive & descriptive elements • Parallel, suggesting same underlying representation • Both tool kits sufficient to create directions • Automatic translation? • Why do they work, despite schematization? • Context disambiguates