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Device-Based Controls

Device-based controls, often called input devices, are the mechanisms through which people communicate their desires to the system.

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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