ug4: hci lecture 4 1 · ug4: hci lecture 4 1 1 lecture 4: the user iv: are people really ‘in the...
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UG4: HCI Lecture 4 1
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Lecture 4:The User IV: Are People Really ‘in the Know’?
Jon Oberlander
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Introduction
Where does the knowledge necessary for acting in the worldcome from?
Is this knowledge ‘in the head’? If so, how (in a general sense) might this knowledge be
organised? If this knowledge is not all in the head, where is it?
– How do users get by if they are not experts in the domain?
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Mental Models: ‘Knowledge in the Head’?
Different kinds of knowledge may be distinguished:– Declarative, how-it-works, device knowledge– Procedural, how-to-do-it knowledge– Episodic knowledge
Declarative knowledge – a ‘mental model’ – provides means forreasoning about:– Effects of actions– Tuning procedural knowledge
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Primary Knowledge
Domain – goals relevant to application domain and the tasksrequired to accomplish them
Semantics – conceptual knowledge of ‘entities’ and ‘operations’ Syntax – dialogue rules: input/output ‘language’ Lexical – physical actions We might think of these different knowledges as an associatively
linked, layered structure
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Example: Document Formatting
Domain – document presentation; aesthetics; format Semantics – words, sentences, paragraphs, pages, typefaces;
justification, indexing; Syntax –form of command specification; sequencing rules Lexical – key, button presses; mouse movements Domain and semantic knowledge may vary according to
document type Syntactic, lexical (and often semantic) knowledge may vary
according to the system– Compare LaTex with Word
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Domainknowledge
Knowledgeof systemoperationsand entities
Knowledgeof dialogue
rules
Lexicalknowledge
Knowledge ofnatural language
How-it-worksknowledge
Knowledgeof othersystems
What ‘Knowledge in the Head’ Looks Like
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Mental Models and Interaction
If we have complete knowledge of an interface then perhapsinteraction too is ‘in the head’
But, observations suggest that knowledge in the head is:– Seldom either complete or accurate– Unstable, changing and decaying over time– Lacks firm boundaries– Not strictly ‘scientific’ or even ‘rational’
• E.g., the problem of false causality
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Secondary Knowledge
Knowledge of natural language Knowledge of using other systems/technologies
– Email• Telephone?• Post?• Elements of both?• Neither?
Secondary knowledge may encourage analogical mapping– Metaphor in interface design
Otherwise, it’s time for situated action– Affordances in interface design
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Metaphor
Linguistically: “X is like Y” Speech and thought are littered with metaphor
– Computer ‘memory’– ‘Windows’– ‘A text editor is like a typewriter’– ‘A computer is like a desktop’
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What Makes a Good Metaphor?
In the source and target domains, there should be:– Entity resemblances– Relational resemblances
People should be familiar with the source domain:– Significant entity/relational features should be ‘obvious’
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Metaphor Example
Solar system and atomic structure– Sun and planets -> nucleus and electrons– Planets revolve around sun -> electrons revolve around the nucleus– Sun much heavier than planets -> nucleus much heavier than
electrons
On delving more deeply, the metaphor is left behind andbecomes redundant
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Metaphor Scope
A good metaphor will have a wide scope The desk-top metaphor:
Domain: “Can I change the arrangement of my documents?”Semantic: “What is the wastebasket for?”Syntax: “What is the procedure for throwing a document away?”Lexical: “How do I perform the action of throwing a document
away?”; “How do I open a folder?”
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Learning and Metaphor
Exploiting existing knowledge for learning Users prefer ‘learning by doing’ or (‘learning by observing’) Metaphor provides clues for abductive reasoning ‘Text editors are like typewriters’:
– Alphanumeric keys– Space, backspace, carriage return
Mismatches prompt investigation and learning– Correspondences, non-correspondence and indeterminate
correspondence
Metaphor encourages systematic investigation
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Affordances: ‘Knowledge in the World’?
Affordances: perceived and actual properties of artefacts– Presenting the ‘potential for action’
Affordances illustrate the importance of:– Visibility– Feedback– Clues for action, supporting improvisation
“If a door handle needs a sign, then its design is faulty”D. Norman, The Psychology of Everyday Things
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Norman on doors
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Norman on doors
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Norman on doors
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Norman on doors
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Norman on doors
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Norman on doors
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Guidelines for Design
Where users are domain experts, focus on users’ knowledge ofthe application domain– Reduce learning
Where users are not domain experts, base the system image ona suitable metaphor– But don’t follow slavishly
Always make the system image explicit– Make system behaviour clear and accountable
Encourage learning by exploration– Provide safeguards; make errors easy to reverse
Reduce memorisation and support improvisation by exploitingaffordances– Put knowledge into the interface, not just interface mechanisms but
how to use them
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Further Reading and Suggested Exercise
Dix et al., 2nd ed: chapter 1, p. 36-47;3rd ed: chapter 1, p. 39-50.
Newman and Lamming, chapter 13, p. 325-43.
Consider your knowledge of the www, identifying the differentkinds you routinely employ when using it.