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Human Factors and User Interface Design


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Title: Human Factors and User Interface Design

Human Factors and User Interface Design
  • Southern Methodist University
  • CSE 8316
  • Spring 2004

What is a User Interface?
(No Transcript)
  • The user is never wrong and the user is never
    stupid. In information design, only designs are
    wrong and stupid
  • Edward Tufte

  • Amer Good afternoon, Hal. How's everything
  • Hal Good afternoon, Mr Amer. Everything is going
    extremely well.
  • Amer Hal, you have an enormous responsibility on
    this mission, in many ways perhaps the greatest
    responsibility of any single mission element. You
    are the brain and central nervous system of the
    ship, and your responsibilities include watching
    over the men in hibernation. Does this ever cause
    you any - lack of confidence?

Advantages and disadvantages of graphical systems
  • Symbols recognized faster than text
  • Faster learning
  • Faster use and problem solving
  • Visual or spatial representation of information
    easier to retain
  • Exploits visual/spatial cues
  • Spatial relationships found to be understood more
    quickly (visual thinking better than logical

  • Feeling of control
  • Replaces national languages
  • Low typing requirements
  • Provides context
  • More natural

  • Greater design complexity
  • Learning still necessary
  • Lack of guidelines
  • Not always familiar
  • Human comprehension limitations
  • Production limitations
  • Some things hard to represent

Obstacles in the development path
Obstacles in the development path
  • Many of these are human in nature
  • Nobody ever gets it right the first time
  • Development is full of surprises
  • Good design requires living in a sea of changes
  • Making contracts to ignore change will never
    eliminate the need for change
  • People will still make mistakes using it!
  • User mistakes, while they will always occur, can
    be reduced

Designing for people
  • Gain complete understanding of users and their
  • Solicit early and ongoing user involvement
  • Direct conduit to knowledge
  • Confront a persons resistance to change, a common
    human trait
  • Perform rapid prototyping and testing
  • Human behavior still not well understood
  • All problems cannot possibly be predicted
  • People adapt to inefficient designs!!!

Designing for people
  • Modify and iterate the design as much as
  • Integrate the design of ALL the system components
  • A system is being constructed, not simply
  • Software
  • Documentation
  • Help functions
  • Training needs

  • the capability to be used by humans easily and
  • Easily to a specified level of subjective
  • Effectively to a specified level of human

Is this a usable system?
Is this a usable error message?
Practical Measures of Usability
  • Some measures lack scientific rigor
  • People are asking questions or often reaching for
    a manual
  • Frequent exasperation responses heard
  • Irrelevant actions being performed
  • Excessive mouse clicks, etc
  • Many things to ignore
  • Consume portion of user visual or information
    processing capabilities
  • A number of people want to use the product
  • CCS thrown out !

Objective measures of usability
  • Effective
  • Better than some required level of performance
    (speed and errors)
  • Some required percentage of the specified target
    range of users
  • Within some required proportion of the range of
    usage environments
  • Learnable
  • Within some specified time from commissioning and
    start of user training
  • Based on some specified amount of training or
    user support

Objective measures of usability
  • Flexible
  • Allow some specified percentage variation in
    tasks and/or environments beyond those first
  • Attitudes
  • Acceptable levels of human cost in terms or
    tiredness, discomfort, frustration
  • Satisfaction that causes continued and enhanced
    usage of the system

Users experiences and expectations
Users experiences and expectations
  • Everything you physically do is a series of
    interactions with objects that surround you
  • How you interact with these objects is based on
  • past experiences with these objects (and other
    objects like them)
  • expectations of how things should work when you
    see them

Users experiences and expectations
  • People try to simplify the world around them
  • Relate new/unknown things to what they know and
    are comfortable with (what they do understand)
  • To scare/confuse/humor somebody we give them a
    familiar object and change the behavior that
    normally accompanies that object (suspense and
    comedy do this!)

Users experiences and expectations
  • We tend to blame ourselves rather than the
    computer when we cant figure out how to use
  • usability professionals must constantly inform
    people that the product is being tested not the
  • Everyone carries around his or her past
    experiences like a set of permanently attached

What is a Software User Interface?
  • Interface Dictionary The place at which
    independent systems meet and act on or
    communicate with each other
  • Noun The doors to the restroom are an interface
    to deal with in a bar
  • Verb People interface with each other, which
    means they communicate in some way
  • in person
  • telephone
  • electronically using computers

What is a Software User Interface?
  • Narrowly defined Comprises the input and output
    devices and the software that services them.
  • Broadly defined Everything that shapes the
    users experiences with computers, including
    documentation, training, and human support.

Hardware components of User Interfaces
  • Keyboard
  • Pointing device
  • mouse
  • joystick
  • trackball
  • Processing unit
  • Display screen

Software components of User Interfaces
  • Items users see
  • Items users hear
  • Items users point to
  • Items users touch on the screen
  • Information with which users work
  • Other hardcopy and online information (manuals,
    references, help, tutorials, etc)

Trying to put lipstick on the bulldog
  • Only so much a pretty interface can do to dress
    up a poorly designed product
  • Building a front-end user interface can be
    effective as long as it does not force users to
    do things in a certain way because the computer
    needs the information in a certain order
  • should be designed based on the users beliefs,
    wants , needs, experiences, expectations.

The Disney experience
  • Disney follows a process similar to user
    interface design
  • first they define the experience they want users
    to have
  • then develop scripts
  • design the experience
  • test it to see if they need to make adjustments

Designing Quality Software User Interfaces
  • Communication is as important as computation.

Quality interfaces
  • Interface developers recognize importance of
  • Traditionally, software engineers have treated it
    as just another box
  • Ensuring usability is critical as user
    productivity becomes the critical bottleneck

Quality interfaces
  • User Interfaces Are Products of Interdisciplinary
    Work - Who is Involved?
  • Psychologists
  • Graphic Designers
  • Technical Writers
  • Human Ergonomical Engineers
  • Anthropologists and Sociologists

Quality interfaces
  • Individual User Level
  • Children can learn more efficiently
  • Pilots can learn to fly airplanes more

Quality interfaces
  • International Influences
  • Association for Computing Machinery - Computer
    Human Interaction special interest group has
    6000 members as of 1996
  • ESPRIT Project in Europe devotes 150 person-years
    per year to research of user interfaces
  • Japan - Ministry of International Trade and
    Industry promotes commercial efforts among

What is Quality Design?
  • How do you quantify usability goals?
  • Easy to learn
  • Easy to use
  • Fun to use
  • Quality of experience
  • way it feels in their hands
  • how well they understand how it works
  • the way they feel when theyre using it
  • how well it serves their purposes
  • how it fits into the entire context

Quality of Software Products
  • Software developers/users accustomed to using
    beta (pre-production) software
  • Buggy software has lowered our standards
  • Quality software (Wright)
  • intuitive
  • complete
  • not broken!

Interaction design criteria
Interaction Design Criteria
Understanding of users
Learnable Usable
Quality of experience
Aesthetic experience
Effective design process
Interaction Design Criteria
  • Quality of experience
  • How does effective interaction design provide
    people with a successful and satisfying
  • Understanding of Users
  • How well was the design team grounded in
    understanding the needs, tasks, and environment
    of the people for whom the product was designed?

Interaction Design Criteria
  • Effective design process
  • Is the product a result of a well thought out
    and well executed design process?
  • What were the major design issues that arose
    during the design process and what was the
    rationale and method for resolving them?

Interaction Design Criteria
  • Needed
  • What need does the product satisfy?
  • Does it make a significant social, economic, or
    environmental contribution?
  • Learnable and Usable
  • Is the product easy to learn and use?
  • Does the product communicate a sense of its
    purpose, how to begin, how to proceed?
  • Is this learning easy to retain over time?

Interaction Design Criteria
  • Appropriate
  • Does the design of the product solve the right
    problem at the right level?
  • Does the product serve users in efficient and
    practical ways?
  • How did considering social, economic, and
    technical aspects of the problem contribute to an
    appropriate solution?

Interaction Design Criteria
  • Aesthetic experience
  • Is using the product an aesthetically pleasing
    and sensually satisfying one?
  • Is the product cohesively designed, exhibiting
    continuity and excellence across graphic,
    interaction, information, and industrial design?
  • Is there a consistency of spirit and style?
  • Does the design perform well within technological

Interaction Design Criteria
  • Mutable
  • Have the designers considered whether mutability
    is appropriate or not?
  • How well can the product be adapted to suit the
    particular needs and preferences of individuals
    or groups?
  • Does the design allow the product to change and
    evolve for new and perhaps unforseen uses?

Interaction Design Criteria
  • Manageable
  • Does the design of the product move beyond
    understanding use merely as functionality and
    support the entire context of use?
  • Installation
  • training
  • maintenance
  • costs
  • supplies

Like a fine wine.
  • It must be able to age..
  • It is made with a combination of intelligence,
    determination, and skill
  • it could be appreciated by a knowledgeable
    (wine drinker) anywhere, without much
  • It must have a definable superiority
  • it must be interesting, have intensity, depth,
    richness, and be distinctive
  • ..evolves over time

  • Must seek to understand users experiences and
  • Communication is an important as computation
  • Design criteria for user interfaces is complex
    and varied

User interface models
User Interface Models
  • Whether a person likes technology or not, his or
    her economic survival depends on a basic
    knowledge (or at least an absence of fear) of
    computers. (Jamie Ray Wright)

User Goals
  • Computer is an aid in reaching our goals and
    performing our tasks
  • what are your goals?
  • Increased productivity
  • greater accuracy
  • higher satisfaction
  • more enjoyment
  • software products should be flexible
  • developers of business software should learn from
    software for the entertainment industry

People and the obstacles that are put in the way
  • How long will a driver wait before becoming
    impatient for a train to come?
  • 20 to 30 seconds
  • longer and drivers drive around the gates
  • earlier and not enough time to react

People and the obstacles that are put in the way
  • Key point understand who your users are and
    figure out how much misdirection and frustration
    they can stand before they give up and do
    something else

Users need multiple user interface styles
  • There will never be only one perfect tool,
    program, or interface
  • users are constantly changing their goals
  • Users should not be asked to choose only one user
    interface style to use
  • users have the right to change their mind at any
  • different interface techniques are more
    appropriate for different tasks

House Building Analogy
  • Three viewpoints when designing and building a
  • architect
  • studies lifestyle of homeowners, family,
    functional and aesthetic desires
  • builder
  • works within confines of design and
    specifications, using appropriate building
    materials, codes, etc
  • owner
  • paying for it and have to live in it!

Mental Models
  • Conceptual model
  • Internal representation of how users understand
    and interact with a system
  • A representation (in the head) of a physical
    system or software being run on a computer
  • contains plausible cascades of causal
    associations connecting the input to the output

User Interface Model (IBM)
Mental Models
  • People often not aware of their mental models
  • helps people predict what will happen next in a
    given situation
  • framework for analysis, understanding, and

Mental Models
  • Reasons people form mental models
  • enable users to predict future (or infer
    invisible) events
  • allow users to find causes for observed events
  • allow users to determine appropriate actions to
    cause desired changes
  • serve as mnemonic devices for remembering
    relations and events
  • means for understanding an analogous device

Mental Models
  • allow people to use strategies to overcome
    information processing limitations

Mental Models
  • Mental models are the basis for UI principles and
  • Users will always have mental models
  • Must effectively transform knowledge of the world
    around us to the world of computers
  • metaphors is a mechanism for doing this

  • Metaphor a figure of speech in which a work or
    phrase denoting one kind of object or action is
    used in place of another to suggest likeness or
    analogy between them.
  • Computer metaphor aid users in understanding a
    new target domain (e.g. a word processor) by
    allowing them to comprehend it (up to the point
    of mismatch) in terms of a source domain they
    already understand (e.g. a typewriter)

  • Adoption of a metaphor allows users to structure
    aspects of the target system or interface in
    terms of familiar and commonly understood aspects
    of the source domain
  • desktop metaphor
  • users know their way around an office
  • users know how to user objects in that
    environment (folders, cabinets, telephone, etc)
  • comfortable with office environment

Users Mental Model
  • S/W products must be designed to fit in with the
    way users view the computer system they are
    working with
  • Important differences in children and adult
  • children interface object not always obvious to
    encourage exploring
  • adults are not as likely to explore an interface
    without preconceived expectations

Users Mental Model
  • How do you find out about the users model
  • analysis of user tasks
  • surveys and interviews of actual or potential
  • visits to user work sites
  • feedback from users
  • usability testing
  • Gather feedback from users, not managers or

Users Mental Model in the Playroom (Broderbund)
Getting Reliable Feedback
  • Users often tell you what they do rather then
    what they would like to do
  • Often not knowledgeable about what is possible
    with technology
  • rely on how they think they do their work rather
    than actually how they do it
  • must watch as well as listen
  • Must have a large enough sample

The Programmers Model
  • Easiest to visualize
  • explicit
  • can be formally defined (functional
  • Interest is in the objects and data
  • Data as fields or records in a DB as opposed to
    entries in a checkbook
  • Knowledge and expertise includes development
    platform, OS, tools, etc

The Designers Model
  • The designer is the architect
  • Merges wishes, desires, needs of user with skills
    and materials of programmer to develop the
  • The designers model describes
  • objects the user works with
  • the presentation to the user
  • interaction techniques used to manipulate the

The Role of the Designers Model (IBM)
Designers model
Users conceptual model
Programmers model
The Look-and-Feel Iceberg (IBM)
The Look-and-Feel Iceberg (IBM)
  • Presentation makes up only 10 of the substance
    of the designers model
  • Las Vegas effect (overuse of color)
  • Interaction layer is the feel layer
  • keyboards, function keys, joysticks
  • Objects and object properties is the most
    important part
  • appropriate metaphors matched to user mental
    models done at this level

Summary of Interface Models
  • The house has been transformed from a shelter to
    a machine for living
  • Many products with good technological ideas have
    failed because of a lack of good user interface
  • Designing a user interface as simply the look and
    feel is not enough
  • user and consumer first impressions!!

Summary of Interface Models
  • Determining if the product works with the users
    model requires a lot of work
  • usability testing
  • Designers model best formed from the bottom of
    the iceberg up
  • the rest evolves more naturally

Know your user or client
Why people have trouble with computers
Trouble with computers
  • specialized knowledge lulls one into a false
    sense of security. It enables one to interpret
    and deal with complex or ambiguous situations on
    the basis of context cues not visible to users,
    as well as a knowledge of the computer system
    that users do not possess..the result is a
    system that appears perfectly useful to its
    designer but one that the user is unable or
    unwilling to face up to and master..

Contributing factors
  • Use of jargon
  • Non-obvious design
  • Fine distinctions
  • Disparity in problem solving strategies
  • Design inconsistency
  • Unfortunately, people remember the one thing that
    went wrong, not the many that go right errors
    are a symptom of problems! (up to 46)

Responses to poor design
  • Psychological
  • Confusion
  • Annoyance
  • Frustration
  • Physical
  • Abandonment of system
  • Partial use of system
  • Indirect use of system (FAA)
  • Modification of the task
  • Compensatory activity
  • Misuse of the system
  • Direct programming

Important human characteristics in design
The Psychology of Humans and Computers
  • People and computers have quite different, often
    diametrically opposite, capabilities
  • Ronald Becker

The Psychology of Users
  • Cognitive psychology
  • study of how our minds work
  • how we think
  • how we remember
  • how we learn
  • Information processing model
  • human cognition s similar enough to a computer
    that a single theory of computation can be used
    to guide research

Information Processing Model
  • Learning is a developmental process
  • prior experience
  • knowledge
  • expectations

  • Awareness and understanding of elements and
    objects of environment through physical sensation
    of various senses
  • Sight
  • Sound
  • Smell
  • Classify stimuli based on models stored in memory
    (things we already know)

Human Perception and Attention
  • Basic human perceptual and psychological
    limitations and capabilities must be understood
    to determine how long to display a message to a
  • Perception is not just seeing
  • hearing
  • tasting
  • smelling
  • touching

Perceptual characteristics
  • Proximity belong together if near each other
  • Similarity belong together if same color, etc
  • Matching patterns respond similarly to same
    shape in different size (alphabet)
  • Succinctness objects have perfect shape or size
    because easier to remember

Perceptual characteristics
  • Closure perception is synthetic, we will close a
    circle if not completely closed
  • Unity objects that form closed shapes are
    perceived as a group
  • Continuity shortened lines may be automatically
  • Expectancies perceive not what is there but what
    we expect to be there
  • Signals versus noise need to separate the two

Human Perception and Attention
  • Human perceptual system will attach meaning to
    information it receives, whether or not the
    meaning is intended or accurate
  • Senses are constantly processing information (we
    are unaware of this most of the time)
  • what attracts our attention is changes in the
  • cocktail party phenomenon

Human Perception Example (Mayhew 1992)
Human Perception and Attention
  • We automatically process information to the point
    where we can attach meaning to it
  • Significant changes draw attention
  • light
  • sound
  • movement
  • color
  • novelty or complexity of information being
    processed (this is why too many bells and
    whistles are distracting!)

Human Information Processing
  • Components of the human information processing
    and memory system
  • sensory storage
  • short-term memory
  • long-term memory

  • Memory is not the most stable of human attributes
    (did you ever forget a birthday?)
  • 1950s researchers thought there was only one
    memory system
  • 1970s this was expanded to short term or
    working memory
  • Information stored within lasts 10-30 seconds
  • Lowered from Miller 7 /- 2 to 3-4 today
  • Knowledge, experience, familiarity govern the
    size and complexity of info that can be remembered

  • Working memory can be increased through applying
    two senses, vision and audition, rather than one
  • Performance can be degraded when a person must
    attend to multiple information sources, and then
    must integrate the information

Sensory storage
  • This is the buffer where the automatic processing
    of information collected from our senses takes
  • Unconscious process
  • Large
  • Attentive to environment
  • Quick to detect changes
  • Constantly being replaced by newly gathered
  • Acts like a radar (cocktail party effect)

Human Information Processing and Memory System
Motor Processor
Cognitive Processor
Perceptual Processor
Sensory storage
  • Repeated and excessive stimulation can fatigue
    the sensory storage system (habituation)
  • This can be avoided in user interfaces by
    designing them such that all aspects and elements
    serve a definite purpose
  • Eliminating interface noise will ensure that
    important things are less likely to be missed

An example of noise
Sensory Storage
  • These sensory processors are not very smart but
    are very attentive
  • Must be quick to spot changes
  • Information cannot be stored very long because
    there is always new information coming in
  • when something happens that cause you to pay
    attention, information is passed on to higher
    memory functions

Sensory Storage
  • Watching a movie
  • steady flow of static frames being processed
  • higher level processes smooth out information
  • allows you to view movie as a continuous image
  • Constant or repeated stimulation tires the
    sensory mechanisms (habituation)
  • applies to information on computer screens as
    well as all other information

Sensory Storage
  • Messages on a computer screen
  • must remain there long enough
  • we must realize it is there
  • must have time to pass information on to higher
    memory functions
  • read the message
  • respond to the message
  • An animated screen background is fun but it
    causes the sensory system to process a lot of
    unwanted information
  • eye strain and fatigue

Short-Term Memory
  • Second stage of information processing
  • information processed here has been recognized
    and perceived
  • STM also gets information from long-term memory
    through the process of cognition
  • STM is weakest link in the whole information
    processing system
  • memory buffer limited (7 plus/minus 2)

Short-Term Memory
  • FIFO effect (new information coming in bumps out
    older information)
  • Information can only be maintained in STM for
    about 30 seconds (without practice)
  • Also called working memory
  • where your thinking occurs
  • multiply 8 times 46

Short Term Memory
  • Short term memory limitations
  • Trying to remember a phone number long enough to
    make the call
  • Techniques to remember
  • rehearsing
  • repeating the number over and over
  • phone companies will repeat number to help you
  • new information may cause you to lose information

Short Term Memory
  • chunking
  • taking many pieces of information and grouping
    them together by associations, order, meaning
  • 1-800-IBM-SERV
  • Annoying to remember information from screen to
  • good user interface design prevents the user from
    having to do this

Long Term Memory
  • Memory warehouse with limitless capacity and
  • Main problem is how to access the information
  • Strategies
  • Mnemonics (attaching meaning to information you
    are trying to remember)
  • Chunking (SSN, ATM password)

Strength Weaknesses
Humans Pattern recognition Low capacity STM
Selective retention Fast decaying STM
Capacity to learn Slow processing
Infinite capacity LTM Error prone
Rich multi-keyed LTM Unreliable access to LTM
Computers High capacity memory Simple template matching
Permanent memory Limited learning capacity
Fast processing Limited capacity LTM
Error free processing Limited data integration
Reliable memory access
Long Term Memory
  • Computer interfaces should be sensitive to the
    LTM retrieval problem and provide help
  • recognition trying to retrieve information with
    some cues present
  • menus and lists for recognition of items
  • recall trying to retrieve information without
    any clues
  • key combo for pasting text in word processor

Long term Memory
  • LTM contains the knowledge we possess
  • Information is encoded in LTM (process called
  • Learning improved through repetition
  • Learning improved if information is structured
    and familiar
  • Human active vocabulary (words that can be
    recalled) is about 2-3K
  • Passive vocabulary (words that can be recognized)
    is about 100K
  • Recognition better than recall

Minimize the need for a mighty memory
  • Present information is an organized, structured,
    familiar way
  • Place all information for task performance in
    close proximity
  • Give the user control over the place of
    information presentation

Summary of memory
  • Must understand human capabilities and
    limitations to know
  • when to lead
  • when to follow
  • when to support
  • A good interface will
  • reduce users reliance on their own memory
  • use computer strengths to support user weaknesses

Other human factors
Visual acuity
  • The capacity of the eye to resolve details is
    called visual acuity
  • Objects become more distinct as we turn our eyes
    towards it and vice versa
  • Relative visual acuity is approximately halved at
    a distance of 2.5 degrees from the point of eye
  • Average viewing distance from screen is 19
  • Optimal visual acuity on screen is 1.67
  • Average character size implies about 88
    characters in this area

Visual acuity
  • Eye is not perfectly steady it trembles
  • Tremor improves the detection of edges of objects
    being looked at
  • Can sometimes create problems
  • Things close together can shimmer
  • Patterns for fill-in areas (bars, circles, etc)
    must be carefully chosen

Visual acuity
50/50 chance of getting these right
3213123 54321212345 6543211123456 765432101234567
6543211123456 54321212345 3213123
Its the physical size, not the number
of characters
This will have implications when we start talking
about screen grouping guidelines
Foveal and peripheral vision
  • Foveal vision is used to focus on something
  • Peripheral vision senses anything in the area
    surrounding the area being looked at
  • These two form a cooperative and competitive

Peripheral vision
  • Peripheral vision can provide clues as to where
    to go next in a visual search
  • Patterns, etc can guide eye in a systematic way
    through a screen
  • Can also compete for attention, acting as visual

Movement control
  • Once data has been perceived and an appropriate
    action decided upon, a response must be made
  • Usually in the form of a movement
  • Keyboard keys
  • Mouse (moving and clicking)
  • Fitts Law time required to acquire a target is a
    function of distance to and size of the target

Movement control
  • The bigger the target is, or the closer it is,
    the faster it will be reached
  • Provide large objects for important functions
  • Take advantage of pinning actions on screens
  • Big buttons are better than small buttons (larger
  • Create toolbars that bleed into the edges of a
    display rather than a one pixel boundary to click

  • Process of encoding information in short term
  • Requires some effort on our part
  • Differentiates us from machines
  • Over time can get better at any task
  • Designers too often use learning ability as an
    excuse to justify complex design
  • We can all learn to use a tightrope but a bridge
    is better !

  • A design that minimizes learning can accelerate
  • Like learning many other things, we like to be
    active, to explore, and to use a trial and error
  • Enhance learning by
  • Allowing skills acquired in one situation to be
    used in others like it
  • Provide complete and prompt feedback
  • Using a phased approach

  • The essence of skill is performance of actions or
    movements in the correct time sequence with
    adequate precision
  • Skills are hierarchical in nature and many basic
    skills may be integrated to form complex ones
  • System and screen design must permit development
    of increasingly skillful performance

Individual differences
  • In reality, there is no average user
  • We all differ
  • Looks
  • Motor abilities
  • Intellectual abilities
  • Learning abilities and speed, etc
  • Used to be that systems had to be designed to the
    lowest common denominator
  • Now systems can be tailored

End of lecture