models of interaction what are they
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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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what is a model
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
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
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
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…
predictive model examples
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
descriptive models
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
descriptive model examples
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)
detailed discussion
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)
guiard s model of bimanual skill
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)
guiard s model of bimanual skill 2
Guiard’s Model of Bimanual Skill (2)

A pretty picture might help (next slide)

guiard s model of bimanual skill 3
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)
  • 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)
scrolling deconstructed
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
scrolling using the non preferred hand
Scrolling Using the Non-Preferred Hand

Thank you Microsoft (next slide)

key action model kam
Name of the model



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.
kam critique
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?
kam implementation
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)




the left handed gui
The Left-Handed GUI

The desktop interface is biased for left-handed users!

redesigning the right handed gui
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)
thank you
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.