Models of Interaction What are They?

1. Models of InteractionWhat are They? I. Scott MacKenzie

2. What is a Model? • A model is… • a simplification of reality • A model is… • useful only if it helps in designing, evaluating, or otherwise providing a basis for understanding the behaviour of a complex artifact such as a computer system • To be useful, a model must be… • simpler than the behaviour it models (I.e., extremely complex models are of questionable value)

3. Descriptive Models Predictive Models Summary statistics Descriptions Prediction equations Performance measurements Taxonomies User categories Interaction categories Relationships between variables A Model of Models 1 Model Continuum Analogy / Metaphor Mathematical Equations 1 First attempt. Can you think of a way to improve this model?

4. Predictive Models • Aka engineering models or performance models • Useful because they… • allow metrics of human performance to be determined analytically without undertaking time-consuming and resource-intensive experiments • Useful because they… • allow a design scenario to be explored hypothetically without implementing a real system and gathering the same performance metrics through direct observation on real users • Predictions so generated are a priori

5. While these empirical results are of direct use in selecting an Interaction technique,1 it would obviously be of greater benefit if a theoretical account of the results could be made. For one thing, the need for some experiments might be obviated; for another, ways of improving interaction1 might be suggested. Card, English, and Burr (1978, p. 608) 1 Edited to recast in general terms Card, Moran, and Newell (1978) • Recall the quote cited earlier…

6. Predictive Model Examples • Hick-Hyman model for choice reaction time • KLM (keystroke-level model) • GOMS model (goals, operators, methods, selection techniques) • Fitts’ law • Fitts-digraph model

7. Descriptive Models • Descriptive models… • provide a framework or context for thinking about or describing a problem or situation • Descriptive models may be… • little more than a verbal or graphic articulation of categories or identifiable features in an interface • The simple possession of a descriptive model… • arms the designer with a tool for studying and thinking about the user interaction experience

8. Descriptive Model Examples • KAM (key-action model) • Three-state model of graphical input • Model for mapping degrees of freedom to dimensions • Guiard’s model for bimanual control • Fitts’ throughput (a descriptive measure) • Language model • KSPC (Keystrokes per character)

9. Detailed Discussion • We just identified 5 examples of predictive models and 7 examples of descriptive models • A detailed discussion of these requires a full course of study • In this presentation, we’ll have a look at just two… • Guiard’s model of bimanual skill • Key-action model (KAM)

10. Guiard’s Model of Bimanual Skill • Rationale • Humans are not only two-handed, they use their hands differently • Studying the between-hand division of labour in everyday tasks reveals that most tasks are asymmetric (I.e., our hands have different roles and perform distinctly different tasks) • Guiard’s model… • identifies the roles and actions of the non-preferred (non-dominant) and preferred (dominant) hands (next slide)

11. Guiard’s Model of Bimanual Skill (2) A pretty picture might help (next slide)

12. Preferred hand • follows the non-preferred hand • works within established frame of reference set by the non-preferred hand • performs fine movements • Non-preferred hand • leads the preferred hand • sets the spatial frame of reference for the preferred hand • performs coarse movements Guiard’s Model of Bimanual Skill (3)

13. Insights • Is Guiard’s model of bimanual skill useful? • Yes. For one, it suggests that one of the most common interaction tasks in graphical user interfaces is poorly implemented • The task is scrolling (next slide)

14. Scrolling Deconstructed • Insight: • Scrolling should be performed by the non-preferred hand • But typically, scrolling is by the preferred hand, namely… • By keys (Page Up, Page Down, Home, End, arrows) • By the mouse • By the wheel in a mouse

15. Scrolling Using the Non-Preferred Hand Thank you Microsoft (next slide)

16. Microsoft Office Keyboard

17. Name of the model Model OR Key-Action Model (KAM) • Keyboard keys can be categorized as… • Symbol keys • Deliver graphic symbols — typically, letters, numbers, or punctuation symbols — to an application such as an editor • Executive keys • Invoke actions in the application or at the system-level or meta-level. Examples include ENTER, F1, or ESC • Modifier keys • Do not generate symbols or invoke actions. Rather, they set up a condition necessary to modify the effect of a subsequently pressed key. Examples include SHIFT or ALT.

18. Let’s see (Next slide) KAM Critique • Simple. Has a name. Identifies three categories of keys, providing for each a name, a definition, and examples. • What do you think of this model? • Is it correct? • Is it flawed? • Do all keyboard keys fit the model? • Can you think of additional categories or sub-categories to improve the model or to make it more accurate or more comprehensive? • Do some keys have features of more than one category? • Can you think of a graphical illustration of the model to improve its expressive power? • Is the model useful?

19. KAM Implementation • Here it is… • Is this useful? • Hmm… there appears to be a right-side bias of executive and modifier keys, or “power keys” • In fact, this is great for left-handed users (next slide) Unique power keys

20. The Left-Handed GUI The desktop interface is biased for left-handed users!

21. Redesigning the Right-Handed GUI • Right-handed users manipulate the mouse with their right (preferred) hand • There is a need to empower the left hand; e.g., scrolling and access to power keys • The solution? (next slide)

22. Microsoft Office Keyboard

23. Thank You • References • MacKenzie, I. S. (in press). Motor behaviour models for human-computer interaction. In J. M. Carroll (Ed.) Toward a multidisciplinary science of human-computer interaction. San Francisco: Morgan Kaufmann. • MacKenzie, I. S., & Guiard, Y. (2001). The two-handed desktop interface: Are we there yet? Extended Abstracts of the ACM Conference on Human Factors in Computing Systems – CHI 2001, pp. 351-352. New York: ACM.