Metaphors and Styles of
Human-Computer Interaction
The psychology of metaphors
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Like affordances, having a metaphor can tell you
how you might use something.
Unlike affordances (which are direct), metaphors
are indirect (require more inferences)
The psychology of metaphors
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a metaphor provides a lot of information
it enables the transfer of skills
good metaphors provide natural mappings
metaphors are not taken literally
they can highlight underlying assumptions
metaphors are not symmetrical
they can be violated
The psychology of metaphors
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metaphors can be mixed (e.g., windows and
desktops)
metaphors can be misleading (putting a disk
in the trash)
some things don’t seem to have any obvious
metaphor (ex: UNDO)
one metaphor is better than another if it leads
to more correct predictions about a system’s
behavior.
Popular metaphors for computers
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computer as vast library
(Memex, 1945)
computer as giant calculator
(ENIAC, 40s-50s)
computer as intelligent assistant (Licklider, 1957)
computer as sketchpad
(Sutherland, 1962)
computer as tool or typewriter (Engelbart, 1963)
computer as human pretender (Weizenbaum, ‘60s)
computer as network
(Taylor, 1968)
computer as book (portable)
(Kay, Xerox PARC)
computer as desktop/windows (Xerox PARC, ‘70s)
with objects
computers for the rest of us
(Apple, 1984)
More or less successful metaphors
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text editing as using a typewriter
voice mail as answering machine or
mailbox
data as files (in folders or directories),
represented as icons on desktop/in windows
deleting a file as throwing it in the trash
applications as tools (sometimes w/ icons)
programming as building objects
programming as directing actors on a stage
applications as agents
Metaphors often suggest
styles of interaction
Some styles of interaction:
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Commands (& queries, keyboard shortcuts)
Menus (and W.I.M.P. interfaces)
Direct manipulation
Conversation (often w/ speech or natural language)
Browsing
Forms and spreadsheets
Immersive environments
Metaphors often suggest
styles of interaction
Some styles of interaction:
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Commands (& queries, keyboard shortcuts)
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Typing in choices to a vending machine
Telling a dog to go fetch
Interacting with VMS, DOS, Unix, or protocols such as
Telnet, ftp, etc.
Programming your VCR to record a TV show
Command interface advantages
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Domain-specific language
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The user tells the system what to do
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Similar to scripting language
e.g. tell the time, copy a file, save a file
The user is in control (takes the initiative)
Very common conceptual model for operating a
device (little or no intelligence in the device)
Main benefits:
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Powerful (especially for experts and frequent users)
Supports fast and efficient interaction
Good for repetitive kinds of actions
Example: Copy command (DOS)
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Copies files from one location to another. The destination
defaults to the current directory.
> copy file1 [destination]
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If multiple files are to be copied, the destination must be a
directory, or an error will result.
> copy file1 file2 file3 [destination]
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Files may be copied to devices. To send file to printer:
> copy file lpt1
To display file on screen ("console"): (alternatively: type file)
> copy file con
>
No feedback given after one of these commands; just a prompt >
Equivalent Unix command: cp
Command interface drawbacks
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The user needs to know exactly where the
information is and how it’s organized
The user needs to know command syntax
No tolerance whatsoever for errors
Can be cryptic, especially if little feedback is given
Another example: SQL queries
Which companies sell everything FabCo sells?
(List companies such that there does not exist
an item sold by FabCo that they do not sell.)
“Which companies sell everything FabCo sells?”
select distinct X.name
from suppliers X
where 0 = (select count (*)
from suppliers Y
where Y.name = “FabCo”
and 0 = (select count (*)
from suppliers Z
where Z.name=X.name
and Z.item=Y.item))
“Which companies sell everything FabCo sells?”
There must be an easier way!!
(Schneiderman, 1986)
“Since computers can display information 1000
times faster than people can enter
commands, it seems advantageous to use
the computer to display large amounts of
information and allow novice and intermittent
users simply to choose among the items.”
Styles of interaction
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Commands (& queries, keyboard shortcuts)
Menus (and W.I.M.P. interfaces)
Direct manipulation
Conversation (often w/ speech or natural language)
Browsing
Forms and spreadsheets
Immersive environments
Menus
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Users are given predetermined choices
Are often part of a
WIMP interface (point & click)
 Windows and window managers
 Icons
 Menus
 Pointing devices
Menus
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enforce a hierarchy on the user’s goals
represent well-trodden paths - you can do
only what the designer envisioned
You cannot filter and combine the world in
novel ways
Decisions in menu design
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What is the task hierarchy?
How to order or group items?
How to trade off depth vs. breadth?
What labels to choose?
Whether to include shortcuts?
Menu types (not mutually exclusive)
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Permanent
Pull-down
Fall-down
Pop-up
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Binary
Extended
Multiple selection
Radio buttons
Embedded
Styles of interaction
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Commands (& queries, keyboard shortcuts)
Menus (and W.I.M.P. interfaces)
Direct manipulation
Conversation (often w/ speech or natural language)
Browsing
Forms and spreadsheets
Immersive environments
Direct Manipulation Interfaces
Representations behave as if they were the
objects they represent.
This reduces the distance between users and
their goals.
What You See Is What You Get
(WYSIWYG)
(Hutchins, Hollan, & Norman, 1986)
Direct manipulation
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Invented by Ivan Sutherland (Sketchpad, 60’s)
Term was coined by Ben Shneiderman (1983)
Theory developed by Hutchins, Hollan, & Norman
Involves dragging, selecting, opening, closing
and zooming actions on virtual objects
Exploit’s users’ knowledge of how objects behave
in the physical world (various metaphors)
Consistent with “what you see is what you get”
(WYSIWYG)
Features of direct manipulation
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continuous representation of the objects of
interest
Features of direct manipulation
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continuous representation of the objects of
interest
physical actions, not complex syntax
Example: copying a file to a diskette:
> copy file.txt to b:\file.txt
versus
dragging a file icon to a diskette icon
(move vs. copy confusion)
Features of direct manipulation
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continuous representation of the objects of
interest
physical actions, not complex syntax
rapid, incremental, reversible operations with
immediate visual feedback
Features of direct manipulation
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continuous representation of the objects of
interest
physical actions, not complex syntax
rapid, incremental, reversible operations with
immediate visual feedback
easy to learn, easy to remember
can operate upon output representation and
use it as input back to the system
Direct Manipulation
(semantic distance)
Gulf of Execution
What do I
do now?
User’s
Goals
System
Gulf of Evaluation
(articulatory distance)
What does
that mean?
Hutchins, Hollan, & Norman
Why are DM interfaces enjoyable?
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Novices can learn the basic functionality quickly
Experienced users can work extremely rapidly to carry
out a wide range of tasks, even defining new functions
Intermittent users can retain operational concepts over
time
Error messages are rarely encountered
Users can immediately see if their actions are furthering
their goals and if not, do something else
Users experience less anxiety
Users gain confidence and mastery and feel in control
Some problems with D.M.
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Sometimes: information overload or screen clutter
Not all tasks can be represented by objects
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With DM, user is responsible for doing everything; but
some tasks are better achieved by delegating!
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it’s hard to represent abstract things
DM must function in the “here” and “now”
icons can be just as cryptic as words (the Vocabulary Problem:
stay tuned)
e.g. spell checking
repetitive actions are tedious!
Moving a mouse around the screen can be slower than pressing
function keys to do same actions
Some DM metaphors are taken too literally
Debate about styles of interaction
Direct Manipulation
v.
Conversation
(tool metaphors)
(agent metaphors)
(Schneiderman, 1986)
“People are different from computers, and humanhuman interaction is not necessarily an
appropriate model for human operation of
computers. Since computers can display
information 1000 times faster than people can
enter commands, it seems advantageous to use
the computer to display large amounts of
information and allow novice and intermittent
users simply to choose among the items.”
(Schneiderman, 1986)
“People are different from computers, and humanhuman interaction is not necessarily an
appropriate model for human operation of
computers. Since computers can display
information 1000 times faster than people can
enter commands, it seems advantageous to use
the computer to display large amounts of
information and allow novice and intermittent
users simply to choose among the items.”
But what about:
“Which companies sell everything FabCo sells?”
Styles of interaction
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Commands (& queries, keyboard shortcuts)
Menus (and W.I.M.P. interfaces)
Direct manipulation
Conversation (often w/ speech or natural language)
Browsing
Forms and spreadsheets
Immersive environments
Dialogue systems
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May take initiative
Underlying metaphor is having a conversation
with another person
Ranges from simple voice recognition systems
to more complex ‘natural language’ dialogues
Examples include dialogs about timetables,
search engines, advice-giving systems, help
systems
May (or may not) consist of anthropomorphic
agents who converse with you or are part of an
interface, e.g. Microsoft’s Bob and Clippy
Agents
A metaphor for an “intelligent” process that takes
some initiative and perform tasks on the user’s
behalf
The user delegates responsibility to the agent.
This feels very different from direct manipulation!
Agents can be amplifiers or alternatively,
prosthetics (2 distinct metaphors for agents)
Tasks for Agents (Laurel; Maes)
Delegation
 Information retrieval - Web “bots”
 Sorting, organizing, filtering
 Coaching, tutoring, providing help
 Reminding
 Programming, doing repetitive things
 Advising
 Entertaining
 Navigation
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Agents (anthropomorphic or not)
The most obvious metaphor for an interactive
system that seems intelligent or takes
initiative may be a human-like character.
(But note: agents can be non-anthropomorphic
as well… a form can take initiative and act
“intelligent” by filling in the right values
automatically.)
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What agent interfaces have you used?
Food for thought:
To what extent is dialog with a person
similar to interacting with a computer?
(Shneiderman: not at all!)
(Others: If the system can take the
initiative and act “intelligently”, then
conversation is a good metaphor for
interacting with an agent.)
Should representations ever
be anthopomorphic?
CON:
Ben Shneiderman
Sherry Turkel
Joseph Weizenbaum (Eliza)
PRO:
Brenda Laurel
I say: It depends on the situation!!
Drawbacks of delegation
“Intelligent” interfaces can be
unpredictable.
 How do you come to “trust” your agent?
 Are anthropomorphic interfaces honest?
 There may be problems with
anthropomorphizing an interface
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 (Shneiderman’s
arguments)
Theater and stage metaphors
(Brenda Laurel; Laura Gould)
Interfaces are like theater we suspend disbelief.
Claim: Anthropomorphizing an interface is
not a problem: People aren’t so easily
fooled.
(This contrasts w/ Shneiderman’s claims.)
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(What do you think?)
Initiative
Some kinds of human conversations
are scripted - who takes the initiative is
relatively fixed.
 In other kinds of conversation,
neither person takes all the initiative.
 Ideally, initiative should be flexible.
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Human-Computer Dialog
What can go wrong?
 A dialog can be under-determined.
when the user is mystified about
what to do next and is
forced to take the initiative.
(a blank screen, cryptic commands)
(Harold Thimbleby)
Human-Computer Dialog (cont.)
A dialog can be over-determined
when a system is authoritarian
and takes too much initiative.
(unnatural constraints)
Advantages:
 reduces the consequences of errors
 what the user does is predictable
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Dialog Design
Avoid under-determined dialogs by
providing help and by reducing options.
 Avoid over-determined dialogs by
letting users undertake tasks in flexible
orders.
Don’t force them to do unnecessary
things.
 Support alternative styles of interaction
whenever possible
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Different users are different!
Interfaces that take the initiative are
better for novices.
 Interfaces that let the user take the
initiative are better for experts.
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An interface is over- or under-determined
with respect to a particular user.
Direct manipulation and menu
interfaces are sometimes (not always)
over-determined.
 Command languages and natural
language are sometimes (not always)
under-determined.
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Pros & cons of conversational style of
interaction
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Dialogue allows users, especially novices and
technophobes, to interact with the system in a
way that is familiar.
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makes them feel comfortable, at ease, not scared
Misunderstandings arise when the system fails
to parse what the user says.
Sometimes interfaces pretend to use natural
language, which can lead to problems.
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e.g. child types into a search engine, that uses
natural language the question: “How many legs
does a centipede have?” and the system responds:
Styles of interaction
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Commands (& queries, keyboard shortcuts)
Menus (and W.I.M.P. interfaces)
Direct manipulation
Conversation (often w/ speech or natural language)
Browsing
Forms and spreadsheets
Immersive environments
Exploring and browsing
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Similar to how people browse information
with existing media (e.g. newspapers,
magazines, libraries, pamphlets)
Information is structured to allow flexibility in
way user is able to search for information
 e.g. multimedia, web
Browsers, hypertext, links
Forms and spreadsheets
Forms can vary from over-determined
(enforcing a fixed order) to quite flexible
(allowing user initiative)
 Spreadsheets are extremely flexible,
allowing “user programming”. They can
sometimes be underdetermined
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Immersive environments
Virtual reality (stay tuned)
 Often mimic real life (representations
are highly literal; go well beyond
metaphors)
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Different styles of interacting lend
themselves to very different metaphors
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Commands
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Menus
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acting on objects and interacting with virtual objects
Conversational dialogue systems
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selecting from pre-determined choices
Direct manipulation
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typing commands via keyboard; function key shortcuts
interacting with the system as if having a conversation
Exploring, browsing, & foraging for information
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finding out and learning things
browsers (different from menus)
Choose the right interaction style and
the right metaphor
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Understand how the system works.
(use the system yourself)
(ask engineers)
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Figure out what problems users have.
(watch them use similar systems)
(create prototypes and watch users)
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Generate metaphors and examine their
properties.
Ask these Qs:
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Does the metaphor have enough structure?
Is the structure relevant to the application or
problem? (or is it superficial?)
Is the metaphor easy to represent? Concrete
enough?
Will the users “get it”?
Can it be extended?
Is the metaphor misleading? Annoying?
Does the metaphor fit with the style of interaction?
Problems with interface metaphors
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Sometimes they break conventional and cultural
rules
 e.g. recycle bin placed on desktop
Can overly constrain designers in the way they
conceptualize a problem space
May conflict with principles of good design
Forces users to understand the system in terms of
the metaphor
Designers can inadvertently use bad existing designs
and transfer the bad parts into the new designs
Limits designers’ imagination in coming up with new
conceptual models
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Metaphors for Human-Computer Interaction