Chapter 2

Chapter-2

HCI Prof. Manisha Maddel(SIOM)
Prof.Manisha Maddel(SIOM) 1

Topics in syllabus:
 Usability paradigms
 object action interface
 principles and rules
 guidelines for data entry and display

HCI Prof.Manisha Maddel(SIOM) 2

Usability
Usability is a quality attribute that assesses how easy user
interfaces are to use.

Usability is defined by five quality components:
 Learnability: How easy is it for users to accomplish basic tasks
the first time they encounter the design?
 Efficiency: Once users have learned the design, how quickly can
they perform tasks?
 Memorability: When users return to the design after a period of
not using it, how easily can they reestablish proficiency?
 Errors: How many errors do users make, how severe are these
errors, and how easily can they recover from the errors?
 Satisfaction: How pleasant is it to use the design?


why study paradigms
Concerns
 how can an interactive system be developed to ensure its
usability?
 how can the usability of an interactive system be
demonstrated or measured?

History of interactive system design provides paradigms
for usable designs


What are Paradigms
 Predominant theoretical frameworks or scientific world
views
 e.g., Aristotelian, Newtonian, Einsteinian paradigms in physics

 Understanding HCI history is largely about understanding
a series of paradigm shifts


Paradigm Shifts
 Time-sharing - single computer supporting multiple users.
 Video Display Units-computers for visualizing and manipulating
data.
 Programming toolkits-the right programming toolkit provides
building blocks to producing complex interactive systems
 Personal computing- computing in small, powerful machines
dedicated to the individual.
 Window systems and the WIMP interface -windows, icons, menus
and pointers now familiar interaction mechanisms. Humans can
pursue more than one task at a time. Windows used for dialogue
partitioning, to “change the topic.
 Metaphor - relating computing to other real-world activity is
effective teaching technique.


Paradigm Shifts
 Direct manipulation - Shneiderman describes appeal of
graphically-based interaction
 visibility of objects
 incremental action and rapid feedback
 reversibility encourages exploration
 syntactic correctness of all actions
 replace language with action
 What You See Is What You Get (WYSIWYG)
 Language versus Action-
 DM – interface replaces underlying system
 language paradigm
 interface as mediator
 interface acts as intelligent agent
 programming by example is both action and language


Paradigm Shifts(Cont.)
 Hypertext-
 key to success in managing explosion of information
 mid 1960s – Nelson describes hypertext as non-linear
 browsing structure
 hypermedia and multimedia
 Multimodality-
 a mode is a human communication channel
 emphasis on simultaneous use of multiple channels for input
and output


 Computer Supported Cooperative Work (CSCW) –
 CSCW removes bias of single user / single computer system
 Can no longer neglect the social aspects
 Electronic mail is most prominent success
 The World Wide Web –
 Simple, universal protocols (e.g. HTTP) and mark-up languages (e.g.
HTML) made publishing and accessing easy
 Critical mass of users lead to a complete transformation of our
information economy.


 Agent-based Interfaces -
 Original interfaces
 Commands given to computer
 Language-based
 Direct Manipulation/WIMP
 Commands performed on “world” representation
 Action based
 Agents - return to language by instilling proactivity and
“intelligence” in command processor
 Avatars, natural language processing

 Ubiquitous Computing -


 Sensor-based and Context-aware Interaction -
 Humans are good at recognizing the “context” of a
situation and reacting appropriately
 Automatically sensing physical phenomena (e.g., light,
temp, location, identity) becoming easier
 How can we go from sensed physical measures to
interactions that behave as if made “aware” of the
surroundings?


Interaction Model
 Syntactic-semantic model was used to describe programming
and was applied to database-manipulation facilities as well as direct
manipulation .

 Distinction was made between meaningfully-acquired
semantic concepts and rote-memorized syntactic details

 Semantic concepts of user's tasks were well-organized and
stable in memory .

 Syntactic details of command languages were arbitrary and
required frequent rehearsal

 With introduction of GUIs, emphasis shifted to simple direct
manipulations applied to visual representations of objects and
actions. Syntactic aspects not eliminated, but minimized.


Interaction Model(cont.)
 There exists two basic interaction models for any given
system:
Object-Action Interface Model -The user first
selects an object and then selects the action to be
performed on the selected object .
Action Object Interface Model - The user first
selects an action to be performed and then selects
the objects on which this action will be performed.


Object-Action Interface Model
 Object-Action Interface Model
 Task hierarchies of objects and actions
 Interface hierarchies of objects and actions
 Disappearance of syntax.


Object-Action Interface Model
 The emphasis is on visual display of user task objects and
actions .
 The OAI model is an explanatory model that focuses on
task objects and actions and on interface objects and
actions
 Object action design starts with understanding of the task.
That task includes the universe of real world objects with
which user’s works to accomplish their intentions and the
actions that they apply to those objects.
 After the agreement on the task objects and actions and
their decomposition, the designer can create the
metaphoric representations of the interface objects and
actions.


Object-action design
1. understand the task.
 real-world objects
 actions applied to those object
2. create metaphoric representations of interface
objects and actions

3. designer makes interface actions visible to users


Object-Action Interface Model (cont)
 Object-Action model maps to real life environment

 The figure above shows the designer mapping from the
real world universe of objects and intentions to the
interface world universe of metaphors and plans.


Task hierarchies of objects and actions
 Tasks include hierarchies of objects and actions at different high and low
levels.
 Decomposition of real-world complex systems natural
 human body
 buildings
 cities
 Computer system designers must generate a hierarchy of objects and
actions to model users' tasks.
 The following steps are recommended (Shneiderman) in order to build
correct tasks hierarchies by designers for a system:
1. Know about the users and their tasks (Interviewing users, reading workbooks and
taking training sessions)
2. Generate hierarchies of tasks and objects to model the users' tasks
3. Design interface objects and actions that metaphorically map to the real world
universe


Interface hierarchies of objects and actions:
 Similar to the task domain, the interface domain contains
hierarchies of objects and tasks at different levels.

 Interface Objects: Users interacting with a computer get
to understand some high level concepts relevant to that
system. As an example, they learn that computer stores
information, that these information are stored in files
contained within a hierarchy of directories, and that each
file has its own attributes like name, size, date, etc ...


Interface hierarchies of objects and
actions(cont.)
 Interface Actions: These are also hierarchies of lower
levels actions.
 Example - A high level plan is to create a text file might
involve mid-level actions such as creating a file, inserting
text and saving that file. The mid-level action of saving a
file the file can be decomposed into lower level actions
such as storing the file with a backup copy and may be
applying the access control rights. Further lower level
actions might involve choosing the name of the file, the
location folder to be saved in, dealing with errors such as
space shortage, and so on


Interface hierarchies of objects and
actions(cont.)
 For the user:
There are several ways users learn interface objects and actions
such as demonstrations, sessions, or trial and error sessions. When
these objects and actions have logical structure that can be related to
other familiar task objects and actions, this knowledge becomes stable
in the user's memory.
 For the designer:
The OAI model helps a designer to understand the complex
processes that a user has to perform in order to successfully use an
interface to perform a certain task. Designers model the interface
actions and objects based on familiar example and then fine tune these
models to fit the task and the user.


Limitations and challenges:

1. It's hard to apply a series of actions, that is already
performed on an object, to another set of objects (what
command line users call "batching") .
2. It's also hard in the object-action model to perform
pipelining
3. One last challenge appears when users start to become
proficient using a certain system, and their performance
curve start to raise.


The disappearance of syntax
 In early days Users must maintain a profusion of device-dependent details in
their human memory.
 Which action erases a character
 Which action inserts a new line after the third line of a text file
 Which abbreviations are permissible
 Which of the numbered function keys produces the previous screen.

 Learning, use, and retention of this knowledge is hampered by two problems
1. Details vary across systems in an unpredictable manner .
2. acquiring syntactic knowledge is often a struggle.

 Syntactic knowledge is usually conveyed by example and repeated usage .

 Minimizing these burdens is the goal of most interface designers
 Modern direct-manipulation systems
 Familiar objects and actions representing their task objects and actions.
 Modern user interface building tools
 Standard widgets


Interface hierarchies of objects and actions
E.g. A computer system:
 Interface Objects
 directory
 name
 length
 date of creation
 owner
 access control
 files of information
 lines
 fields
 characters
 fonts
 pointers
 binary numbers
 Interface Actions
 load a text data file
 insert into the data file
 save the data file
 save the file
 save a backup of the file
 apply access-control rights
 overwrite previous version

HCI  assign a name

Theories ,principles and Guidelines

Guidance for designers of interactive
systems can be given in the form of
1. Theories &Models
2. Middle level principles
3. Specific and practical guidelines


Theories ,principles and Guidelines

 The theories and models offer framework or
language to discuss issue that are application
independent.

 Middle level principles are useful in creating
and comparing design alternatives .

 The practical guidelines provide helpful
reminders of rules uncovered by designers.


High level Theories
1. Explanatory theories
 Predictive theories
 Perceptual or Cognitive subtasks
theories
 Motor-task performance times
theories


Explanatory Theories
 Explanatory theories seek to explain the behavior of our world, they
tend to provide a more conceptual model of the world.

 Explanatory theories are help full in
 Observing behavior
 Describing activity
 Conceiving of designs
 Comparing high-level concepts of two designs
 Training

 Taxonomy is a part of Explanatory theory.
 Order on a complex set of phenomena
 Facilitate useful comparisons
 Organize a topic for newcomers
 Guide designers
 Indicate opportunities for novel products.


Other Theories
 Predictive theories:
 Enable designer s to compar e
proposed designs for execution time
or er ror r ates.

 Per ceptual or Cognitive subtasks
theories
 Pr edicting r eading times for fr ee text,
lists, or for matted displays

 Motor-task perfor mance times
theories:
 Pr edicting key str oking or pointing
times

Conceptual, semantic, syntactic, and lexical model
 Foley and van Dam four-level approach
 Conceptual level: User's mental model of the interactive system
 Semantic level: Describes the meanings conveyed by the user's
command input and by the computer's output display
 Syntactic level: Defines how the units (words) that convey
semantics are assembled into a complete sentence that instructs the
computer to perform a certain task
 Lexical level: Deals with device dependencies and with the precise
mechanisms by which a user specifies the syntax

 Approach is convenient for designers
 Top-down nature is easy to explain
 Matches the software architecture
 Allows for useful modularity during design


GOMS and the keystroke-level model By Card Moran
 Goals, Operators, Methods, and Selection rules (GOMS) model

Example –
4. Formulate Goal- edit document
 Formulate sub goal – insert word
a The operators are – perceptual or cognitive acts.
c Use methods and procedures-(move cursor to desired location
by a sequence of arrow keys).
f Selection rules- choosing among several methods available for
accomplishing the goal( delete by repeated backspace versus
delete by placing markers at the beginning and end of region and
pressing delete button).

 Keystroke-level model: Predict performance times for error-free
expert performance of tasks by summing up the time for key
stroking ,pointing ,homing, drawing, thinking and waiting for
the system to respond. This model concentrate on expert users
and error free performance and places less emphasis on
learning ,problem solving ,error handling ,subjective satisfaction
and retention.


GOMS and the keystroke-level model (cont.)
Example

Several alternative methods to delete fields, e.g.

Method 1
To accomplish the goal of deleting the field:
e Decide: If necessary, then accomplish the
goal of selecting the field
g Accomplish the goal of using a specific
field delete method
h Report goal accomplished


GOMS and the keystroke-level model
(cont.)
Method 2
To accomplish the goal of deleting the field:
3. Decide: If necessary, then use the Browse tool to go to
the card with the field
4. Choose the field tool in the Tools menu
5. Note that the fields on the card background are
displayed
6. Click on the field to be selected
7. Report goal accomplished


GOMS and the keystroke-level
model (cont.)
Selection rule set for goal of using a specific field-
delete method:
 If you want to past the field somewhere else,
then choose "Cut Field" from the Edit menu.
 If you want to delete the field permanently,
then choose "Clear Field" from the Edit
menu.
 Report goal accomplished.


Stages of action models
Norman's seven stages of action
t Forming the goal "make a nice meal".
l Forming the intention
"Make a chicken casserole using a can of prepared
sauce."
c Specifying the action
"Defrost frozen chicken, open can, ..."
c Executing the action
actually opening the can.
Perceiving the system state
the experience of smell, taste and look of the
prepared meal.
f Interpreting the system state
Putting those perceptions together to present the
sensory experience of a chicken casserole
c Evaluating the outcome
did the chicken casserole match up to the
requirement of 'a nice meal'?

Norman’s 7-stage cycle of HCI


Norman’s 7-stage cycle of HCI(cont.)
 Gulf of execution: Mismatch between the users'
intentions and the allowable actions
 Gulf of evaluation: Mismatch between the system's
representation and the users' expectations

 The designer must bridge the gulf of execution
 Design the system to ease the process of getting from the
intention to the execution
 The designer must bridge the gulf of evaluation
 Design the system so that the response after the user has
performed an action can be easily interpreted and then
evaluated


Norman's contributions
 Four principles of good design
 State and the action alternatives should be
visible
 Should be a good conceptual model with a
consistent system image
 Interface should include good mappings
that reveal the relationships between stages
 User should receive continuous feedback


Four critical points where user failures can occur
(Norman’s 7-stage cycle of HCI(cont.) )

 Users can form an inadequate goal

 Might not find the correct interface object
because of an incomprehensible label or icon

 May not know how to specify or execute a desired
action

 May receive inappropriate or misleading
feedback


Consistency through grammars
 An important goal for designers is a consistent
user interface.

 Inconsistent action verbs
 Take longer to learn
 Cause more errors
 Slow down users
 Harder for users to remember


Consistency through grammars
(cont.)
 Payne and Green addressed the multiple
levels of consistency (lexical , syntactic and
semantic) through a notational structure
called task-action grammars(TAGS)

 Task-action grammars (TAGs) try to
characterize a complete set of tasks.


Consistency through grammars (cont.)
Example: TAG definition of cursor control

 Dictionary of tasks:
 move-cursor-one-character-forward[ Direction=forward, Unit=char]
 move-cursor-one-character-backward [Direction=backward, Unit=char]
 move-cursor-one-word-forward [Direction=forward ,Unit=word]
 move-cursor-one-word-backward[ Direction=backward ,Unit=word]

 High-level rule schemas describing command syntax:
 task [Direction, Unit ]-> symbol [Direction] + letter [Unit]
 symbol [Direction=forward] -> "CTRL"
 symbol [Direction=backward] -> "ESC"
 letter [Unit=word] -> "W"
 letter [Unit=char] -> "C"

 Generates a consistent grammar:
 move cursor one character forward CTRL-C
 move cursor one character backward ESC-C
 move cursor one word forward CTRL-W
 move cursor one word backward ESC-W

Widget-level theories
 Potential benefits:
 Possible automatic generation of performance
prediction
 A measure of layout appropriateness available as
development guide
 Estimates generated automatically over many designers
and projects
 perceptual complexity
 cognitive complexity
Higher-level patterns of usage appear


Principles of Good Design
 Principle 1: Recognize the Diversity
 Principle 2: Use Golden Rules of HCI Design
 Principle 3: Prevent Errors
 Principle 4: Follow the Guidelines for Data Display
 Principle 5: Follow the Guidelines for Data Entry
 Principle 6: Balance the Automated and Human
Control


Principle 1: Recognize the Diversity
 Usage profiles
 Novice or first-time users •Task profiles
 Knowledgeable intermittent users •Decomposition into multiple middle-
 Expert frequent users level task actions, which are refined into
atomic actions
 User characteristics •task frequencies of use
 Age •matrix of users and tasks helpful
 Gender
 Physical abilities
Interaction styles
 Education
•Direct manipulation
 Cultural or ethnic background
•Menu selection
 Training •Form fillin
 Motivation •Command language
 Goals •Natural language
 Personality


Principle 2: Use the Eight Golden Rules
of Interface Design
1. Strive for consistency. Offer informative feedback
 Terminology
 Prompts e Design dialogs to yield closure
 Menus 1. Sequences of actions should be
 Help screens organized into groups
 Color 2. Beginning, middle, and an end

 Layout
e Offer error prevention and simple
error handling
 Capitalization
 Fonts
e Permit easy reversal of actions
 Most frequently violated
2. Enable frequent users to use shortcuts r Support internal locus of control
1. Abbreviations
2. Special keys Reduce short-term memory load.
3. Hidden commands
4. Macro facilities


Principle - 3 Prevent Errors

To reduce errors by ensuring complete and correct
actions:
 Correct matching pairs
 Complete sequences
 Correct commands.


Guidelines for Data Display
 Organizing the display
1. Consistency of data display
2. Efficient information assimilation by the user
3. Minimal memory load on user
4. Compatibility of data display with data entry
5. Flexibility for user control of data display


Guidelines for Data Display(Cont.)
 Getting the user's attention
 Intensity
 Marking
 Size
 Choice of fonts
 Inverse video
 Blinking
 Color
 Color blinking
 Audio


Guidelines for Data Entry
Five high-level objectives for data entry:
 Consistency of data-entry transactions
 Minimal input actions by user
 Minimal memory load on user
 Compatibility of data entry with data display
 flexibility for user control of data entry


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