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           Rebecca W. Boren, Ph.D.
           IEE 437/547
           Introduction to Human Factors
           Arizona State University
           October 24, 2011

Think of as many control
devices as you can and write
them down.

1950 Zenith Remote Ad
    Computer Input Devices


DataHand                Keyboard
          Automobile Controls

The one on the right is all
         hand operated.

Designing for visibility means that
just by looking, users can see the
possibilities for action. Visibility is
often violated in order to make
things "look good“.


Multi head Shower
Onscreen Computer Controls
Onscreen Computer
Control or the Real Deal?
What do these control?

   Display is the perception.
     Seeing, hearing, or other sense

   Control is the action after a decision
    is made.
   Involves the selection and execution
    of responses.
   Includes the feedback loop.
Model of Human Processing
   Principles of
Response Selection
Decision complexity

   The speed with which an action can
    be selected is strongly influenced by
    the number of possible alternative
    actions that could be selected.
Decision complexity

   Hick-Hyman Law of reaction time
    shows a logarithmic increase in
    reaction time (RT) as the number of
    possible stimulus-response
    alternatives (N) increases. Humans
    process information at a constant
    rate. RT = a + bLog2N
Hick-Hyman Law
   The most efficient way to deliver a
    given amount of information is by a
    smaller number of complex decisions
    rather than a large number of simple
    decisions. An example is typing versus
    Morse code.
    Response expectancy
  We perceive rapidly and accurately
   that information that we expect.
 We don’t expect a car

 to suddenly pull in front
 of us on the freeway. It
 takes time to perceive
 and to respond.
Response expectancy

   We use the yellow caution light to help
    us anticipate a red light.

   Good stimulus-response compatibility
    (display-control compatibility) aids in
    response selection.
   Two sub principles:
       Location compatibility (mapping)
       Movement compatibility (moving a lever
        right should move the display to the right).
Location Compatibility
Location Compatibility
Location Compatibility
Movement Compatibility
How do I turn this computer on?

                   Usability and Human Factors
                   Web Workshop series at
                   Monash University
How do I turn this computer on?

   About 4 or 5 years ago I'd just started a new job
   I had a choice of using a fairly new Macintosh or a
    rather old PC - I wanted to use the Mac
   I'd never used a Mac before
   And I couldn't figure out where the "ON" switch was
   After messing around for a long time, I accidentally
    turned it on after randomly pressing a whole bunch
    of keys on the keyboard
   I still didn't know how I'd done it, so I turned it off
    and tried the keys again until I realized it was the
    Apple key that brought the machine to life
Speed-accuracy tradeoff

   Sometimes positively correlated,
    sometimes negatively correlated.
   The first three principles result in a
    positive correlation. Whatever makes
    the response selection faster makes it
    less prone to error.
Principles of Speed-accuracy

1.   Good stimulus-response compatibility
     (display-control compatibility) aids in
     response selection.
2.   Location compatibility (mapping)
3.   Movement compatibility (moving a
     lever right should move the display to
     the right).
Speed-accuracy tradeoff

   In a few cases, control devices differ in
    the speed-accuracy tradeoff because
    one induces faster, but less precise
    behavior or more careful but slower
    behavior (2nd order).

   Instantaneous or nearly instantaneous
    feedback is helpful.
   If there is a lag of even 100 msec, an
    unskilled operator will have difficulty.
   What kinds of feedback are helpful?
    Name some.
Discrete Control Activation

   Physical feel. There should be some
    feedback as to state change: a click,
    beep, flashing light, change of color,
   Feedback lights should be redundant
    with another signal and should be
Discrete Control Activation

A toggle switch
   provides visual
   feedback, an
   auditory click, and
   a tactile snap with
   the sudden loss of
Discrete Control Activation

   Size. Smaller keys are
    difficult for humans. In
    relationship to the size of
    large hands, it is easy to
    make mistakes by
    pressing the wrong key
    or two keys at once.
Discrete Control Activation

   Confusing labeling. Key press or control
    activation errors also occur if the identity of
    a key or control is not well marked for
    novice users.
Discrete Control Activation

   Well-labeled
Positioning Control Device

   A common human-machine task is to
    position an entity in space.
   The positioning or pointing task is
    defined as “movement of a controlled
    entity, called a cursor, to a
    destination, called the target.”
Positioning Task

   Movement of a controlled entity, called
    a cursor, to a destination, called the


Positioning Control Device
   Movement time: controls typically require
    two different movements:
     movement of the hand or fingers to the
      control device
     movement of the control device in
      some direction.
Movement Time
   Predicted by Fitts’ Law
              MT = a + b log2(2A/W)
       MT is movement time
       A is amplitude (distance) of the movement
       W is width of the target (corresponds to
       log2(2A/W) is the index of difficulty (ID)
       a and b are constants
   MT is proportional to the index of difficulty
Movement Time – Fitts’ Law
       MT = a + b log2(2A/W)
Fitts’ Reciprocal Tapping Task
Movement Time Examples

   If the keys on a keyboard are made
    smaller, without the space also made
    proportionally smaller, then movement
    is more difficult.
   Foot reaching a foot pedal
   Assembly and manipulation under a
Device Characteristics

   Direct position controls: Light pen
    and touch screen
   Indirect position controls: Mouse,
    touch pad, and touch tablet.
   Indirect velocity controls: Joystick
    and cursor keys
    Direct Position Controls
   Light pen and touch
    screen using a stylus
    or finger on a tablet.
   Position of the human
    hand or finger directly
    corresponds to the
    desired location of
    the cursor.
    Direct Position Controls
   Light pen and
    touch screen
    using a stylus or
    finger on a tablet.
   Position of the
    human hand or
    finger directly
    corresponds to the
    desired location of
    the cursor.
    Indirect Position Controls

    Mouse, touch pad,
     and touch tablet.
    Changes in the
     position of the limb
     directly correspond to
     changes in the
     position of the cursor,
     but on a different
    Indirect Position Controls

    Mouse, touch pad, and
     touch tablet.
    Changes in the position
     of the limb directly
     correspond to changes
     in the position of the
     cursor, but on a
     different surface.
    Indirect Velocity Controls

    Joystick and cursor keys.
    An activation of control in
     a given direction yields a
     velocity of cursor
     movement in that
     direction. For cursor keys
     the operator may repeat
     or hold down.
Three Types of Joysticks

    Isotonic
    Isometric
    Spring-loaded
Isotonic Joystick

   Typically, cursor moves as a result of
    movement of the joystick handle.
   Handle does not move back to a neutral
Isometric Joystick

   Cursor moves as a result of the force
    applied to the joystick handle.
   Joystick does not move at all.
Spring-loaded Joystick

   Resistance is proportional to force
   Displaced, but returns to a neutral
   Offers proprioceptive and kinesthetic
   This is the
    preferred joystick

   Feedback and gain are two important
   Feedback should be salient, visible,
    and immediate.
   Gain is defined as the change of
    cursor position/change of control
Usability - Gain

   Gain is defined as
      change of cursor position
      change of control position
   If a 3 inch change in the cursor position
    results from a 1 inch change in the
    control position, then the gain is 3.
Usability - Gain

   A high gain device is one in which a
    small displacement of the control
    produces a large movement of the
   A low gain device aids in precision.
   The ideal gain is task dependent.
     Choice of Control Device

   For pointing and dragging, direct position
    devices (touch screen and light pen) may be
   Problems in accuracy may arise with a
    direct position device due to parallax errors,
    instability of the hand or fingers, or the
    imprecision of the finger area in specifying
    small targets.
Choice of Control Device

   Indirect positioning devices have
    greater precision and may be
    adjusted for gain.
Choice of Control Device

   Dependent on the work space
   Mouse takes up a lot of space.
   Vibration in a cab ride.
   Voice control difficult in a noisy
Choice of Control Device

   High gain devices are faster in moving
    to a target, but less precise (can
    overshoot the target).
   Humans work well with a gain between
    1 and 3.
   Humans can adapt to a greater range
    of gain with experience.
Numeric Input Devices

   Numerical data is usually entered by
    numeric keyboards or voice.
   There are two styles of key pads for
    data entry.
Numeric Input Devices

   The telephone style is the preferred
Voice Input

   Pros: useful in time-sharing activities in
    which the visual and manual systems
    are both occupied.
   Cons: cost, recognizer speed, acoustic
    quality, speaker dependent, noise,
    stress, loss of privacy, and
    compatibility with task.
   Voice recognition is complex and still
    under development.
Voice Input

   “How does voice input interfere with
    short-term memory?”
End of Part 1. Questions?
Continuous Control & Tracking

   In contrast to discrete cursor
    movement to a target, sometimes we
    want to track a moving target. This
    requires continuous control.
   Examples: bringing a fly swatter down
    on a moving fly, driving on a winding
    Continuous Control & Tracking
   Using a moving car
    as an example: the
    operator perceives
    a discrepancy or
    error between the
    desired state of the
    vehicle and the
    actual state.
    Continuous Control & Tracking
   The operator must
    turn the steering
    wheel to put the car
    back on track.
    Continuous Control & Tracking

   A" track” is a continuously moving
    dynamic target.
    The Tracking Loop
    The basic elements of the tracking loop: e(t) = error function
     of time; f(t) = force applied to the control device; u(t) = output
     function from the human; o(t) = system output; i(t) = position.
     Our goal is i(t) = o(t) and e(t) = 0. ic(t) are command inputs
     (changes in the target). id(t) are disturbance inputs.
Control Order

   If a control is designated as zero-
    order, it means that the cursor controls
    the position of the target.
   First-order means it controls the
    velocity of the target.
   Second-order control means a change
    in the position of the cursor changes
    the acceleration of the target.
Control Order

   Position Order: (zero-order).
   Pen across paper, marker on the white
    board, moving a computer mouse to
    reposition a cursor on the screen.
   If you hold the control still, the system
    output will also be still.
   More precise, more human effort.
Control Order

   Velocity order: first-order (rate of
    change of position).
   Some joysticks and car radio scanners
    are first-order controllers.
   As you hold the joystick in a direction,
    the velocity increases.
   Can conserve human effort, but has
    more lag.
    Control Order
   Acceleration order: second-order (rate of
    change of velocity).
   Second-order control systems are rarely used
    because they are hard to control (sluggish and
   Think of an astronaut trying to maneuver in
    space by firing thrust rockets. Can get pilot-
    induced oscillations.
   Requires a great deal of experience and effort
    on the part of the operator.
Control Order - Driving
   Driving an
    automobile is a
    combination of first-
    order and second-
    order control
   The task of
    maintaining speed
    is a first-order
Control Order - Driving

   The task of steering or lane-keeping
    is a second-order control.
Solutions to the Problems of
Second-order Control Systems
1.   Predictive displays
2.   Teach the tracker strategies of
     anticipation. Experienced drivers look
     further down the road than novices
3.   Automate to bring it to a lower-order
Predictive Displays

        Air Traffic Predictive Display
Predictive Displays
Other issues related to controls

   Instability – caused by lag somewhere
    in the total control loop
       Overcorrection due to high gain in the
       Human trying to correct too quickly
        before the lagging system has had a
        chance to stabilize.
Other issues related to controls

   Open-loop versus closed-loop systems
     Open-loop – no feedback – used by
      experienced operators
     Closed-loop – feedback is valuable
      in learning or fine-tuning a mental
Electronic Controls

   Well-designed products have
    controls that don’t require fine
    fingering to operate.
   The following controls are shown
    in descending order, from easiest
    (1) to most difficult (7).

2           3

Use larger muscles rather than smaller

    6                            5

Control and Display
Principles are closely
Standardized shape-coded knobs
for US Air Force aircraft.
For transmitting discrete
For transmitting continuous
For transmitting cursor
position information

   Tapping experiment

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