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Models of Interaction What are They? . I. Scott MacKenzie. 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

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Models of interaction what are they l.jpg

Models of InteractionWhat are They?

I. Scott MacKenzie

What is a model l.jpg
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)

A model of models 1 l.jpg

Descriptive Models

Predictive Models














between variables

A Model of Models 1

Model Continuum

Analogy /




1 First attempt. Can you think of a way to improve this model?

Predictive models l.jpg
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

Card moran and newell 1978 l.jpg

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…

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Predictive Model Examples an

  • Hick-Hyman model for choice reaction time

  • KLM (keystroke-level model)

  • GOMS model (goals, operators, methods, selection techniques)

  • Fitts’ law

  • Fitts-digraph model

Descriptive models l.jpg
Descriptive Models an

  • 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

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Descriptive Model Examples an

  • 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)

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Detailed Discussion an

  • 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)

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Guiard’s Model of Bimanual Skill an

  • 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)

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Guiard’s Model of Bimanual Skill (2) an

A pretty picture might help (next slide)

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  • Preferred hand an

  • 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)

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Insights an

  • 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)

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Scrolling Deconstructed an

  • 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

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Scrolling Using the Non-Preferred Hand an

Thank you Microsoft (next slide)

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Name of the model an



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.

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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?

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KAM Implementation an

  • 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)




The left handed gui l.jpg
The Left-Handed GUI an

The desktop interface is biased for left-handed users!

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Redesigning the Right-Handed GUI an

  • 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)

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Thank You an

  • 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.