Device-Based
Controls
Device-based
controls, often called input devices, are the mechanisms through which people communicate
their desires to the system.
Characteristics
of Device-Based Controls
Several
specific tasks are performed using graphical systems.
·
To point at an object on the screen.
·
To select the object or identify it as the focus of
attention.
·
To drag an object across the screen.
·
To draw something free form on the screen.
·
To track or follow a moving object.
·
To orient or position an object.
·
To enter or manipulate data or information.
Direct
and Indirect Devices
Direct devices
are operated on the screen itself. Examples include the light pen, the finger, and voice.
Indirect devices
are operated in a location other than the screen, most often on the desktop.
Trackball
Description:
A
spherical object (ball) that rotates freely in all directions in its socket.
Direction
and speed is tracked and translated into cursor movement.
Advantages:
Direct
relationship between hand and pointer movement in terms of direction and speed.
Does not
obscure vision of screen.
Does not
require additional desk space (if mounted on keyboard).
Disadvantages:
Movement
is indirect, in a plane different from the screen.
No direct
relationship exists between hand and pointer movement in terms of distance.
Requires
a degree of eye-hand coordination.
Requires
hand to be removed from keyboard keys.
Requires
different hand movements.
Requires
hand to be removed from keyboard (if not mounted on keyboard).
Requires
additional desk space (if not mounted on keyboard).
May be
difficult to control.
May be
fatiguing to use over extended time.
Joystick
Description:
A stick
or bat-shaped device anchored at the bottom.
Variable
in size, smaller ones being operated by fingers, larger ones requiring the
whole hand.
Variable
in cursor direction movement method, force joysticks respond to pressure,
movable ones respond to movement.
Variable
in degree of movement allowed, from horizontal-vertical only to continuous.
Advantages:
Direct
relationship between hand and pointer movement in terms of direction.
Does not
obscure vision of screen.
Does not
require additional desk space (if mounted on keyboard).
Disadvantages:
Movement
indirect, in plane different from screen.
Indirect
relationship between hand and pointer in terms of speed and distance.
Requires
a degree of eye-hand coordination.
Requires
hand to be removed from keyboard keys.
Requires
different hand movements to use.
Requires
hand to be removed from keyboard (if not mounted on keyboard).
Requires
additional desk space (if not mounted on keyboard).
May be
fatiguing to use over extended time.
May be
slow and inaccurate.
Graphic
Tablet
Description:
Pressure-,
heat-, light-, or light-blockage-sensitive horizontal surfaces that lie on the
desktop or keyboard.
May be
operated with fingers, light pen, or objects like a stylus or pencil.
Pointer
imitates movements on tablet.
Advantages:
Direct
relationship between touch movements and pointer movements in terms of
direction, distance, and speed.
More
comfortable horizontal operating plane.
Does not
obscure vision of screen.
Disadvantages:
Movement
is indirect, in a plane different from screen.
Requires
hand to be removed from keyboard.
Requires
hand to be removed from keyboard keys.
Requires
different hand movements to use.
Requires
additional desk space.
Finger
may be too large for accuracy with small objects
Touch
Screen
Description:
A special
surface on the screen sensitive to finger or stylus touch.
Advantages:
Direct
relationship between hand and pointer location in terms of direction, distance,
and speed.
Movement
is direct, in the same plane as screen.
Requires
no additional desk space.
Stands up
well in high-use environments.
Disadvantages:
Finger
may obscure part of screen.
Finger
may be too large for accuracy with small objects.
Requires
moving the hand far from the keyboard to use.
Very
fatiguing to use for extended period of time.
May soil
or damage the screen.
Design Guidelines:
Screen
objects should be at least 3/4
Object
separation should be at least 1/8″.
Provide
visual feedback in response to activation. Auditory feedback may also be
appropriate.
When the
consequences are destructive, require confirmation after selection to eliminate
inadvertent selection.
Provide
an instructional invitation to begin using.
Light Pen
Description:
A special
surface on a screen sensitive to the touch of a special stylus or pen.
Advantages:
Direct
relationship between hand and pointer movement in terms of direction, distance,
and speed.
Movement
is direct, in the same plane as screen.
Requires
minimal additional desk space.
Stands up
well in high-use environments.
More
accurate than finger touching.
Disadvantages:
Hand may
obscure part of screen.
Requires
picking it up to use.
Requires
moving the hand far from the keyboard to use.
Very
fatiguing to use for extended period of time.
Voice
Description:
Automatic
speech recognition by the computer.
Advantages:
Simple
and direct.
Useful
for people who cannot use a keyboard.
Useful
when the user’s hands are occupied.
Disadvantages:
High
error rates due to difficulties in:
Recognizing boundaries between spoken words.
Blurred word boundaries due to normal speech
patterns.
Slower
throughput than with typing.
Difficult
to use in noisy environments.
Impractical
to use in quiet environments.
Mouse
Description:
A
rectangular or dome-shaped, movable, desktop control containing from one to
three buttons used to manipulate objects and information on the screen.
Movement
of screen pointer mimics the mouse movement.
Advantages:
Direct
relationship between hand and pointer movement in terms of direction, distance,
and speed.
Permits a
comfortable hand resting position
Selection
mechanisms are included on mouse.
Does not
obscure vision of the screen.
Disadvantages:
Movement
is indirect, in a plane different from screen.
Requires
hand to be removed from keyboard.
Requires
additional desk space.
May
require long movement distances.
Requires
a degree of eye-hand coordination.
Mouse Usage Guidelines
Provide a
“hot zone” around small or thin objects that mouse positioning. o Never use double-clicks or
double-drags as the only means operations.
Do not use mouse plus keystroke combinations.
Do not require a person to point at a moving
target.
Keyboard
Description:
Standard
typewriter keyboard and cursor movement keys.
Advantages:
Familiar.
Accurate.
Does not
take up additional desk space.
Very
useful for:
Entering text and alphanumeric data.
Inserting in text and alphanumeric data.
Keyed shortcuts—accelerators.
Keyboard mnemonics—equivalents.
Advantageous for:
Performing actions when less than three mouse
buttons exist.
Use with very large screens.
Touch typists.
Disadvantages:
Slow for
non-touch-typists.
Slower
than other devices in pointing.
Requires
discrete actions to operate.
No direct
relationship between finger or hand movement on the keys and cursor movement on
screen in terms of speed and distance.
Keyboard Guidelines
Provide keyboard accelerators.
Assign
single keys for frequently performed, small-scale tasks.
Use
standard platform accelerators.
Assign
Shift-key combinations for actions
that extend or are complementary to the actions of the key or key combination
used without the Shift-key.
Assign Ctrl-key
combinations for:
·
Infrequent actions.
·
Tasks that represent larger-scale versions of the
task assigned to the unmodified key.
Provide keyboard equivalents.
Use standard platform equivalents.
Use the first letter of the item description.
If first letter conflicts exist, use:
·
Another distinctive consonant in the item
description.
·
A vowel in the item description.
Provide window navigation through use of keyboard
keys.
Selecting the Proper Device-Based
Controls
Consider the characteristics of the task.
·
Provide keyboards for tasks involving:
o
Heavy text entry and manipulation.
o
Movement through structured arrays consisting of a
few discrete objects.
·
Provide an alternative pointing device for
graphical or drawing tasks.
·
The following are some suggested best uses:
o
Mouse—pointing, selecting, drawing, and dragging.
o
Joystick—selecting and tracking.
o
Trackball—pointing, selecting and tracking.
o
Touch screen—pointing and selecting.
o
Graphic tablet—pointing, selecting, drawing, and
dragging.
·
Provide touch screens under the following
conditions:
o
The opportunity for training is minimal.
o
Targets are large, discrete, and spread out.
o
Frequency of use is low.
o
Desk space is at a premium.
o
Little or no text input requirement exists.
Consider user characteristics and preferences.
·
Provide keyboards for touch typists.
Consider the characteristics of the environment.
Consider the characteristics of the hardware.
Consider the characteristics of the device in relation to the
application.
Provide flexibility.
Minimize eye and hand movements between devices.
Keyboard
versus Mouse
Speed is
obviously one reason. An experienced typist, through kinesthetic memory, has
memorized the location of keyboard keys. The keying process becomes
exceptionally fast and well learned. The mouse is slower,
Control
Research
A survey of the research literature comparing and evaluating different
devices yields the following summarization concerning tasks involving pointing
and dragging:
The
fastest tools for pointing at stationary targets on screens are the devices that permit direct
pointing: the touch screen and light pen. This is most likely due to their high
level of eye-hand coordination and because they use an action familiar to
people.
In terms
of positioning speed and accuracy for stationary targets, the indirect pointing devices—the
mouse, trackball, and graphic tablet, do not
differ
greatly from one another. The joystick is the slowest, although it is
as
accurate as the others. Of most importance in selecting one of these devices
will be its fit to the user’s task and working environment.
A separate confirmation action that must follow
pointer positioning increases pointing accuracy but reduces speed. The mouse
offers a very effective design configuration for tasks requiring this
confirmation.
For tracking small, slowly moving targets, the
mouse, trackball, and graphic tablet are preferred to the touch screen and light
pen because the latter may obscure the user’s view of the target.
Another common manipulation task is dragging an object across the
screen. Using a mouse, graphic tablet, and trackball for this task, as well as
pointing, was studied by MacKenzie, Sellen, and Buxton (1991). They report the
following:
The graphic tablet yielded best performance during
pointing.
The mouse yielded best performance during dragging.
The trackball was a poor performer for both
pointing and dragging, and it had a very high error rate in dragging.
Pointer Guidelines
The
pointer:
-
Should be visible at all times.
-
Should contrast well with its background.
-
Should maintain its size across all screen
locations and during movement.
-
The hotspot should be easy to locate and see.
-
Location should not warp (change position).
The user
should always position the pointer.
The shape
of a pointer:
-
Should clearly indicate its purpose and meaning.
-
Should be constructed of already defined shapes.
-
Should not be used for any other purpose other than
its already defined meaning.
-
Do not create new shapes for already defined
standard functions.
Use only
as many shapes as necessary to inform the user about current location and
status. Too many shapes can confuse a person.
Be
conservative in making changes as the pointer moves across the screen.
-
Provide a short “time-out” before making
noncritical changes on the screen.
Animation
should not:
-
Distract.
-
Restrict one’s ability to interact.
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