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Models of Interaction
What are They?
I. Scott MacKenzie

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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)

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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

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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)

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

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

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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)

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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

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

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Microsoft Office Keyboard

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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.
Model
Name of
the model
OR

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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? Let’s see (Next slide)

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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

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

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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)

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Microsoft Office Keyboard

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Thank You
References
1. 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.
2. 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.