User Modeling
CIS 376
Bruce R. Maxim
UM-Dearborn
What is HCI?
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Answer: human computer interaction
Not just human factors
No strong agreement
Main emphasis of HCI is user interface
design
User interface involves
• Hardware
• Behavior of software
• Supporting documentation
Typical Human Factors Measures
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Time to learn
Speed of performance
User error rates
Retention over time
Subjective satisfaction
Where do user interfaces come
from?
• Designed by programmers
• Functionality dominates software design
and marketing
• Designer intuition is often used rather than
user modeling (not good)
HCI Goals for Designers
• Improve user's quality of life by building
quality (not flashy) interactive systems
• Promote attention to user interface issues
which should be considered by managers
• Become successful designers of systems
that go beyond intuitive concepts like "user
friendliness" and focus on supporting the
user's real task goals
Motivation for Including Human
Factors in User Interface Design
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Life critical systems
Industrial and commercial uses
Personal applications
Exploratory, creative, and cooperative
systems
Accommodating Human
Diversity in Design
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Physical workspaces
Cognitive and perceptual ability differences
Personality differences
Cultural and international diversity
User disabilities
Elderly users
US Military Standards for Human
Engineering and Design
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Achieve required performance
Minimize personnel training requirements
Achieve required reliability
Foster design standardization
How is this done?
• Ensure functionality by basing design on user task
analysis
• System reliability requires designer attention to
details like privacy, security, and data integrity
• Standardization requires attention to issues like
system integration, consistency, and portability
• Schedule and budget must allow for human factors
work like user analysis and testing
Approaches to User Interface
Design
• Human Factors: prototype and test
• Cognitive theory: production system
• Engineering models:
– KLM (keystroke level model)
– GOMS Models (goals, operators, methods,
selection rules)
Keystroke Level Model (KLM)
• Choose representative user task scenarios
• Specify design to point that keystrokes defining actions
can be listed
• List keystrokes (operators) required to perform task
• Insert mental operators at points user needs to stop and
think
• Look up standard execution time for each operator
• Add up the execution times for the operators
• Total is estimated time to complete task
Standard Execution Times
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K - key press (0.2 sec = 55 wpm)
P - point with mouse (1.1 sec)
B - mouse button press (0.1 sec)
BB - press and release button (0.2 sec)
H - home hands to keyboard or mouse (0.4 sec)
M - mental act of thinking (1.2 sec)
Current Design: Delete a file by
dragging it to the trash icon
1. Point to file icon (P)
2. Press & hold mouse button (B)
3. Drag file to trash icon (P)
4. Release mouse button (B)
5. Point to original window (P)
3P + 2B = 3.5 sec.
New Design:
Adding a command to menu
1. Point to file icon (P)
2. Click button (BB)
3. Point to file menu (P)
4. Press and hold button (B)
5. Point to delete command (P)
6. Release mouse button (B)
7. Point to original window (P)
4P + 4B = 4.8 sec.
Assumptions
• These previous scenarios work only work if
the user is currently able to view all the
needed windows and icons.
• If the trash icon for example is buried under
other windows the first procedure is slowed
down quite a bit.
Inserting Mental Operators:
Where does the user stop and think?
1. Initiating a process.
2. Making strategic decisions.
3. Retrieving a chunk from user’s short term
memory
4. Finding something on the screen.
5. Verifying intended action is complete.
Mental Operators
New vs Experienced Users
• New users stop and check feedback after
every step
• New users have small chunks
• Experienced users have elaborate chunks
• Experienced users may overlap mental
operators with physical operators
Delete a file by dragging icon to trash
1. Initiate delete. (M)
2. Find file icon. (M)
3. Point to file icon. (P)
4. Press & hold button. (B)
5. Verify icon reverse video.
(M)
6. Find trash icon. (M)
7. Drag file to trash icon. (P)
8. Verify trash reverse video.
(M)
9. Release button. (B)
10. Verify bulging trash icon.
(M)
11. Find original window.
(M)
12. Point to window. (P)
3P + 2B + 7M = 12.6 sec.
Placement of Mental Operators
• Hard to do - requires good intuition from
designer
• Consistency in the number of Mental's
assigned is more important than exact
positioning
GOMS Model
Goals Operators Methods Selection Rules
Advantages
• GOMS models are executable
• GOMS models allow simulated execution of user task
• Provide a rigorous description of what user must learn
• Provide estimate of size or complexity of interface
(number of distinct methods and their length)
• Can estimate both learning time (about 30 sec per step and
execution time (total of KLM operators)
• Allow designer to evaluate the effect of reusing or sharing
methods among several tasks
This example is extracted from:
David Kieras, A Guide to GOMS Task Analysis,
University of Michigan Technical Report,
Spring, 1994.
User Goals
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Delete a file.
Move a file.
Delete a directory.
Move a directory.
To accomplish goal of deleting a file:
1. Accomplish goal of dragging file to trash.
2. Return with goal completed.
To accomplish goal of moving a file:
1. Accomplish goal of dragging file to
destination.
2. Return with goal completed.
To accomplish goal of deleting a directory:
1. Accomplish goal of dragging directory to
trash.
2. Return with goal completed.
To accomplish goal of moving a directory:
1. Accomplish goal of dragging directory to
destination.
2. Return with goal completed.
Generalized Methods
Method for accomplishing goal of deleting an object:
1. Accomplish goal of dragging object to trash.
2. Return with goal completed.
Method for accomplishing goal of moving an object:
1. Accomplish goal of dragging object to destination.
2. Return with goal completed.
Sub Method
Accomplish goal of dragging item to destination:
1. Locate icon on screen.
2. Move cursor to item icon location.
3. Hold mouse button.
4. Locate destination icon.
5. Move cursor to destination icon.
6. Verify destination icon reverse video.
7. Release mouse button.
8. Return with goal accomplished.
Method for GOMS Model Construction
• Make a list of top-level user goals
• Write a step-by-step method for accomplishing each goal
on list
• Continue refining each step that is not a keystroke level
operator by defining it as a subgoal and add it to the list of
user goals
• Continue processing user goals until list is empty (meaning
that all user goals are defined in terms of keystrokes)
• If there are multiple methods to accomplish a goal supply
decision rules to choose which method to invoke