Design Models 2 – GOMS and State Transition
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7 Interaction Design Models
•
•
•
•
•
•
Model Human Processor (MHP)
Keyboard Level Model (KLM)
GOMS
Modeling Structure
Modeling Dynamics
Physical Models
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GOMS
Goal/task models can be used to explore the methods people use to
accomplish their goals
• Card et al. suggested that user interaction could be described by
defining the sequential actions a person undertakes to
accomplish a task.
• The GOMS model has four components:
–
–
–
–
goals
operators
methods
selection rules
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GOMS
• Goals - Tasks are deconstructed as a set of goals and subgoals.
• Operators - Tasks can only be carried out by undertaking
specific actions.
• Methods - Represent ways of achieving a goal
– Comprised of operators that facilitate method completion
• Selection Rules - The method that the user chooses is
determined by selection rules
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GOMS – CMN-GOMS
CMN-GOMS can predict behavior and assess memory requirements
• CMN-GOMS (named after Card, Moran, and Newell) -a detailed
expansion of the general GOMS model
– Includes specific analysis procedures and notation descriptions
• Can judge memory requirements (the depth of the nested goal
structures)
• Provides insight into user performance measures
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CNM-GOMS example
GOAL: CLOSE-WINDOW
.
[select GOAL: USE-MENU-METHOD
.
.
MOVE-MOUSE-TO-FILE-MENU
.
.
PULL-DOWN-FILE-MENU
.
.
CLICK-OVER-CLOSE-OPTION
GOAL: USE-CTRL-W-METHOD
.
.
PRESS-CONTROL-W-KEYS]
For a particular user, U1:
Rule 1: Select USE-MENU-METHOD unless another
rule applies
Rule 2: If the application is GAME,
select CTRL-W-METHOD
So here we have one Goal with either of two Methods, one of which requires a sequence of
three Operators, the other requires just one Operator; for U1 we have 2 Selection rules
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GOMS – Other GOMS Models
• NGOMSL (Natural GOMS Language), developed by Kieras,
provides a structured natural-language notation for GOMS
analysis and describes the procedures for accomplishing that
analysis
– NGOMSL Provides:
• A method for measuring the time it will take to learn specific method
of operation
• A way to determine the consistency of a design’s methods of
operation
• Bonus learning – see
ftp://www.eecs.umich.edu/people/kieras/GOMS/NGOMSL_Guide.pdf
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GOMS – Other GOMS Models
• CPM-GOMS represents
– Cognitive
– Perceptual
– Motor operators
• CPM-GOMS uses Program Evaluation Review Technique
(PERT) charts
– Maps task durations using the critical path method (CPM).
• CPM-GOMS is based directly on the Model Human Processor
– Assumes that perceptual, cognitive, and motor processors function in
parallel
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GOMS – Other GOMS Models
• Program Evaluation Review Technique (PERT)
chart Resource Flows
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Modeling Dynamics
Understanding the temporal aspects of interaction design is
essential to the design of usable and useful systems
• Interaction designs involve dynamic feedback loops
between the user and the system
– User actions alter the state of the system, which in turn
influences the user’s subsequent actions
• Interaction designers need tools to explore how a
system undergoes transitions from one state to the next
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Modeling Dynamics – State Transition Networks
• State Transition Networks can be used to
explore:
– Menus
– Icons
– Tools
• State Transition Networks can show the
operation of peripheral devices
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Modeling Dynamics – State Transition Networks
• State Transition Network
• STNs are appropriate for showing sequential
operations that may involve choice on the part of the
user, as well as for expressing iteration.
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State transition networks (STN) – example
• circles - states
• arcs - actions/events
click on
circumference
click on centre
Circle 1
select 'circle'
Start
rubber band
Circle 2
draw circle
Finish
Menu
select 'line'
Line 1
click on
first point
rubber band
double click
Line 2
draw last
line
Finish
click on point
draw a line
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• Each circle denotes a ‘state’ the system can be
in.
• For example, Menu is the state where the
system is waiting for the user to select either
‘circle’ or ‘line’ from the menu, and
• For instance, state Circle 1 is where the system
is waiting for the user to select the circle’s
center.
• If the user clicks on a point, the system moves
into state Circle 2 and responds by drawing the
rubber band between the point and the current
mouse position.
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• Circle 2 is the state after the user has entered the
circle center and is waiting for the point on the
circumference
• From this state, the user can click on another
point, upon which the system draws the circle and
then moves into the special Finish state.
• STN is able to represent a sequence of user
actions and system responses.
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State transition networks - events
• arc labels a bit cramped because:
– notation is `state heavy‘
– the events require most detail
click on
circumference
click on centre
Circle 1
select 'circle'
Start
rubber band
Circle 2
draw circle
Finish
Menu
select 'line'
Line 1
click on
first point
rubber band
double click
Line 2
draw last
line
Finish
click on point
draw a line
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State transition networks - states
• labels in circles a bit uninformative:
– states are hard to name
– but easier to visualise
click on
circumference
click on centre
Circle 1
select 'circle'
Star t
rubber band
Circle 2
draw circle
Finish
Men u
select 'line'
... ... ...
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• additional composite states represented as rectangles
• Each of these rectangles denotes the whole STN for the relevant submenu.
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Modeling Dynamics – Three-State Model
The Three-State Model can help designers to determine
appropriate I/O devices for specific interaction designs
• The TSM can reveal intrinsic device states and their subsequent
transitions
– The interaction designer can use these to make determinations
about the correlation between task and device
– Certain devices can be ruled out early in the design process if
they do not possess the appropriate states for the specified
task
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Modeling Dynamics – Three-State Model
• The Three-State Model (TSM) is capable of
describing three different types of pointer movements
– Tracked: A mouse device is tracked by the system and
represented by the cursor position
– Dragged: A mouse also can be used to manipulate screen
elements using drag-and-drop operations
– Disengaged movement: Some pointing devices can be
moved without being tracked by the system, such as light
pens or fingers on a touchscreen, and then reengage the
system at random screen locations
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state 0 is clearly different from states 1 and 2.
However, if we look at the state 1–2 transaction, we
see that it is symmetric with respect to the two
states.
State 2 requires a button to be pressed, whereas
state 1 is one of relative relaxation (whilst still
requiring hand–eye coordination for mouse
movement). There is a similar difference in tension
between state 0 and state 1.
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Modeling Dynamics – Three-State Model
Mouse Three-State Model.
Trackpad Three-State Model.
Alternate mouse Three-State Model.
Multibutton pointing device Three-State Model.
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Fitts’ Law
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Hearing
• Provides information about environment:
distances, directions, objects etc.
• Physical apparatus:
– outer ear
– protects inner and amplifies sound
– middle ear
– transmits sound waves as
vibrations to inner ear
– inner ear
– chemical transmitters are released
and cause impulses in auditory nerve
• Sound
– pitch
– sound frequency
– loudness
– amplitude
– timbre
– type or quality
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Touch
• Provides important feedback about environment.
• May be key sense for someone who is visually impaired.
• Stimulus received via receptors in the skin:
– thermoreceptors
– heat and cold
– nociceptors
– intense pressure, heat, pain
– mechanoreceptors – pressure(some instant, some
continuous)
• Some areas more sensitive than others e.g. fingers.
• Kinethesis - awareness of position of body and limbs
-affects comfort and performance.
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Movement
• Time taken to respond to stimulus:
reaction time + movement time
• Movement time dependent on age, fitness etc.
• Reaction time - dependent on stimulus type:
– visual
~ 200ms
– auditory ~ 150 ms
– pain
~ 700ms
• Increasing reaction time decreases accuracy in the
unskilled operator but not in the skilled operator.
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• Fitts' Law describes the time taken to hit a screen
target:
Mt = a + b log2(D/S + 1)
where: a and b are empirically determined
constants
Mt is movement time
D is Distance
S is Size of target
targets as large as possible and the distances as
small as possible
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The constants a and b depend on the particular pointing
device used and the skill of the user with that device.
However, the insight given by the three-state model is that
these constants also depend on the device state.
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Fitts’ law coefficients
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Modeling Dynamics – Glimpse Model
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Modeling Dynamics – Glimpse Model
• Forlines et al. (2005):
– Because the pen and finger give clear feedback
about their location when they touch the screen and
enter state 2, it is redundant for the cursor to track
this movement
– Pressure-sensitive devices can take advantage of the
s1 redundancy and map pressure to other features
– Undo commands coupled with a preview
function (Glimpse) can be mapped to a
pressure-sensitive direct input device
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Modeling Dynamics – Glimpse Model
Previewing potentially useful to scroll momentarily to another part
of a document (but then return to where you were), or to look
around in a virtual environment
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Modeling Dynamics – Glimpse Model
• Some applications
– Pan and zoom interfaces—Preview different magnification
levels
– Navigation in a 3D world—Quick inspection of an object
from different perspectives
– Color selection in a paint program—Preview the effects of
color manipulation
– Volume control—Preview different volume levels
– Window control—Moving or resizing windows to view
occluded objects
– Scrollbar manipulation—Preview other sections of a
document
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Uses of State-Transition Networks
• Not well-suited to complete models of modern GUIs
– Too many options (transitions) from any given state – combinatorial
explosion (in fact, that’s just the flexibility a good GUI is supposed to
give)
• Better for limited/embedded user interfaces
– Automated teller machine
– Digital watch
– Car key/alarm device
• Excellent for checking completeness of design
– Be sure that all transitions are represented (and hence will get coded and
tested in implementation)
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PHYSICAL MODEL
• The physical model maps the physical work
environment and how it impacts upon work
practice, for example, an office plan showing
where different work activities happen.
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Digital Assignment 1 b
You are designing a new system to help people
manage their ‘to do’ lists. Use the contextual
inquiry approach to interview a colleague to see
how they make use of such lists. Make sure you
interview them in context – in their study or
workplace for example. Produce sequence, flow,
artifact, cultural and physical models of the
activity.
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