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PV182
Human-Computer Interaction
Lecture 3
Mental Models
Fotis Liarokapis
liarokap@fi.muni.cz
23rd September 2019
High level models of humancomputer
behaviour
Are there theories that describe how people interact
with computers?
What is Shneiderman’s syntactic/semantic model?
What is Norman’s stages of human interaction?
Publish or perish …
• Dilbert blog comment meltdown (thanks to
AskTog):
• The blog allowed writing “draft”. Drafts were only
available to select readers. You could “publish”
the draft. After Scott Adams “published” the
draft, he didn’t need the draft, so he deleted it.
However, there was no difference between the
draft and the published version in the software.
Scott Adams deleted his own work…and 500
comments from users on it.
Human errors – Sliperies and Mistakes
• Slippery
– Understand system and goals
– Well formulated (chosen) action
– Incorrect (improper) action
• Mistake
– Not even the right goal !
• Repair ?
– Slippery – better UI design
– Mistake – better system´s understanding
Low-level models of human-computer
behaviour
• Some low-level theories can be used to
predict human performance
– Fitt’s law
• Time to select an item with a pointing device
– Keystroke level model
• Sums up times for keystroking, pointing, homing,
drawing, thinking and waiting
Not in this lecture, later …
High-level models of human-computer
behaviour
• Developing Theories in HCI
– Must explain and predict human behavior in the humancomputer
system
– Must work in a wide variety of task situations
– Must work within broad spectrum of system designs and
implementations
• General models that explain human behavior with
machines
– Syntactic/semantic model (Shneiderman)
– Stages of interaction (Norman)
– All of psychology!
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Syntactic/semantic model of user
knowledge
• A high level model of interaction, developed
by Ben Shneiderman
Action ObjectAction Object
Task Computer
Semantic Syntactic
Syntactic Knowledge
• The rules or combinations of commands and
signals
– Seen as device-dependent details of how to use
system
– Examples:
• backspace key delete previous character
• right mouse button raise menu
• grep < word> <file> finding a word in a file
• tab moves to next field in a form
• <cntl> X! enlarges window by one line (gmacs)
Syntactic Knowledge .
• User problems with syntactic knowledge
– syntactic details differ between (and
within!) systems
• little consistency–> arbitrary
• e.g. leaving mail reading in gmacs
– “q” to quite mail system
– “<cntl> x <cntl>c” to quit gmacs
– “<cntl> d or logout” to quit Unix
– hard to learn
• acquired by rote memorization
• repeated rehearsals to reach competency
• must be frequently applied for retention over
time
– easily forgotten
• expert/frequent users ok
• novice/casual users troubled by syntactic
irregularities
Syntactic
Semantic knowledge: Computer
concepts
• The meaning behind computer concepts
• Usually follows a hierarchical structure
– high level concepts decomposed to many low level
concepts
– objects
• stored informationas directoriesand files as name, length,
creationdate, owner,...
– actions
• saving a file, creating backups, verify access control, etc.
• How it works
– people learn computer concepts by
• meaningfullearning
• demonstrations
• explanationsof features
• trial by error
• model of concepts (abstract, concrete, analogical)
– e.g. file hierarchies are like file/folder systems
Action Object
Computer
Semantic knowledge: Computer
concepts .
• Properties of semantic knowledge (computer concepts)
– Relatively stable in memory
• High level concepts
• Logical structure
• Cognitive model produced
– Usually transferable across computer systems
• But not always!
• Problems
– Many people now using computers are not computer
scientists!
– Must be trained in “computer literacy”
– People prefer to concentrate on task, not on computer
knowledge
Semantic knowledge: Task concepts
• The meaning behind the task concepts
– Is independent of the computer
• Similar in mechanism to computer concepts
• Examples
– How to write a business letter
• Format concerns
• Stylistic concerns
• Paragraph structure, etc.
– creating lecture notes Action Object
Task
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What Syntactic/Semantic Model
reveals
• Mapping between three items is extremely important
– Task semantics to computer semantics to computer syntax
• task semantics: write letter
• computer semantics: open a file, use editor, save it to disk
• computer syntax: select menu items, key strokes for
formatting,...
– Bad mapping: using latex to write letter
• aside from task semantics, must also know semantics/syntax of:
– text editor
– latex
– Unix compilingand printing sequence (to typeset and print)
– Relatively good mapping: trashcan to throw away files
• must know mouse syntax of selecting and dragging
• computer semantics almost analogous to task semantics
Guideline suggested by
syntactic/semantic model
• Reduce the burden to the task-oriented user of
learning a separate computer semantics and
syntax
• Methods
– computer semantics
• metaphors allow computer artifacts to be represented as
task artifacts
– e.g. office workers: files/folders represent hierarchical
directory/file systems
• information hiding
– don’t force people to know computer concepts that are not
relevant to their work
Guideline suggested by
syntactic/semantic model .
• Reduce the burden to the task-oriented user of
learning a separate computer semantics and syntax
• Methods
– computer syntax
• A little learning should go a long way...
• Should be as understandable as possible (tied to semantics)
– e.g. meaningful command names, icons, keyboard shortcuts
• Should be as simple as possible and uniformly applicable
– e.g., object selection with mouse: single click selects, double click
activates
• Generic commands
– same command can be applied across different objects
• Syntax should be consistent between systems!
The Four Stages of an Interaction
• Intention, Selection, Execution, Evaluation
– a simplified versionof Norman’s 7 stages
• 1. Forming an intention
– “What we want to happen”
– internal mental characterization of a goal
– may comprise goals and sub-goals (but rarely are they
well planned)
– similar to task semantics
• e.g. “begin a letter to Aunt Harriet”
• 2. Selecting an action
– review possible actions and select most appropriate
– similar to mapping between task and compute semantics
• e.g. “use the emacs editor to create a file harriet.letter”
The stages of user activities when
performing a task
Physical activity
Execution
Action
Specification
Intention
Goals
Evaluation
Interpretation
PerceptionMental activity
expectation
The Four Stages of an Interaction .
• 3. Executing the action:
– carry out the action using the computer
– similar to mapping between semantics and computer
syntax
• e.g. type “emacs –nw harriet.letter”
• 4. Evaluate the outcome
– check the results of executing the action and compare it
with the expectations
• e.g. see if emacs editor is on the display and verify that buffer
name is “harriet.letter”
– requires perception, interpretation, and incremental
evaluation
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A typical task: making a business letter
look better
intention-1
intention-2
intention-3
action
specification
evaluate-1
evaluate-2
evaluate-3
interpretation
intention-4 evaluate-4
look better
block para
.pp->.sp
execution perception
get
formatted
output
action
specification
execution
interpretation
printer
perception
What the four stages model reveals
• The “Gulf of Execution”
– do actions provided by system correspond to the intentions of the
user?
– Gulf: amount of effort exerted to transform intentions into selected
and executed actions
– A good system:
• direct mappings between Intention and selections
• e.g. printing a letter:
– put document on printer icon
– vs select print from menu
– vs “latex letter.tex; lpr -Palw3 latex.dvi”
– drawing a line: move mouse on graphical display vs “draw (x1, y1, x2, y2)”
Goals
Physical
System
gulf of
execution
What the four stages model reveals .
• The “Gulf of Evaluation”
– can feedback be interpreted in terms of intentions and
expectations?
– Gulf: amount of effort exerted to interpret feedback
– a good system: feedback easily interpreted as task
expectations
• e.g. graphical simulation of text page being printed
– a bad system: no feedback or difficult to interpret feedback
• e.g. Unix: “$”, “bus error”, “command not found”
Goals
Physical
System
gulf of
evaluation
Is it a good feedback ?
Bridging the Gulf of Execution and
Evaluation
GoalsPhysical
System
execution bridge
intentions
action
specificationsinterface
mechanism
evaluation bridge
interpretations
interface
display
evaluations
Design rules for HCI
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Errors Errors
Errors HCI Ergonomy – adapted evaluation
Design rules - Schneiderman Design rules - Norman
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Design rules - Nielsen
Source of rules and recommendations
?
Usability principles categories - Dix
Using four stages to ask design
questions
• How easily can a user
– Determine the function of the system?
– Tell what actions are possible?
– Determine mapping from intention to selection?
– Perform the action?
– Tell what state the system is in?
– Determining mapping from system state to
interpretation?
– Tell if system is in the desired state?
Using four stages to ask design
questions
• Questions similar to principles of good design:
– visibility
• can see state of application and alternatives for actions
– good conceptual model
• consistency in presentations of operations and results
• coherent system image
– good mappings
• relations between
– actions and results
– controls and their effects
– system state and what is visible
– feedback
• full and continuous feedback about results of actions
• Principle of transparency
– “the user is able to apply intellect directly to the task;
– the tool itself seems to disappear”
You Know Now
• Several high level theories exist that describe how
people interact with computers
• Shneiderman’s syntactic/semantic model
– A user’s mapping between computer syntax,
computer semantics, and task semantics
– Problems identified when the user’s mapping is poor
• Norman’s stages of human interaction
– Intention, selection, execution, evaluation
– Problems identified as gulfs of execution and
evaluation
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Meaning of these buttons? Old vs. new concept
Scott Jenson: Default thinking
A bit of wisdom …
• Bertrand Russell
– “The trouble with the world is that the stupid are
cocksure and the intelligent are full of doubt.”
• Daniel Boorstin
– “The greatest obstacle to discovery is not ignorance
— it is the illusion of knowledge.”
Once upon a time …
• Analog Microwave:
– Turn the timer to 30 seconds
– Turn the power to low
– Put in the food
– Close the door
– Press Start
Current Way of Living
• Digital Timer Microwave:
– Tap the 10-second button three times to get 30
seconds
– Tap the Power/Level button four times
(to cycle down from 100 percent power
to 70 percent power
to 50 percent power
to 30 percent power)
– Put in the food
– Close the door
– Press Start
Mental Model and Interface
https://developer.apple.com/
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Questions Acknowledgements
• Special Thanks to Prof. Jiri Sochor