Direct Manipulation: Principles, Benefits, and Applications
Introduction
Direct manipulation extends the concept of direct manipulation in personal computers to complex environments. It involves the physical operation of a system or machine at a distance, such as in surgery, power plants, and military operations.
Principles of Direct Manipulation
- Continuous representations of objects and actions with meaningful visual metaphors.
- Physical actions or presses of labeled buttons, instead of complex syntax.
- Rapid, incremental, reversible actions whose effects on the objects are visible immediately.
Features for Effective 3D Direct Manipulation
- Use occlusion, shadows, perspective, etc. carefully.
- Minimize navigation steps for users.
- Keep text readable.
- Avoid visual clutter, distraction, and contrast shifts.
- Simplify user movement.
- Prevent errors.
- Simplify object movement.
Teleoperation
Teleoperation derives from direct manipulation and process control. It involves the remote control of physical operations, such as surgery, power plants, and military operations.
Teleoperation Applications
- Telemedicine: Medical care delivered over communication links, allowing physicians to examine patients remotely and surgeons to perform operations across continents.
- Telepathology: A pathologist examines tissue samples or body fluids under a remotely located microscope.
- Virtual Colonoscopy: Allows patients to undergo a CT scan instead of a more invasive procedure, with physicians interactively navigating through a 3D model.
- Robotic Surgery: An alternative to conventional surgery that enables smaller incisions and more accurate surgical movements.
Direct Manipulation – Benefits and Drawbacks
Benefits
- Control/display compatibility
- Less syntax reduces error rates
- Errors are more preventable
- Faster Learning and higher retention
- Encourages exploration
Drawbacks
- Increased system resources
- Some action may be cumbersome
- Macro techniques are often weak
- History and other tracing may be difficult
- Visually impaired users may have more difficulty
Direct-Manipulation Systems: Video Games
Video games are a well-engineered and commercially successful example of direct-manipulation systems. They feature physical actions whose results are immediately shown on screen, no syntax to remember, and continuous feedback that encourages mastery.
Consistency
Consistency in user interfaces is important for objects, actions, color, layout, icons, fonts, and button sizes. Orderly and describable terminology helps users learn and retain information.
Design-by-Levels
This approach separates concepts into levels:
- Conceptual level: User’s mental model of the system.
- Semantic level: Meanings conveyed by user input and computer output.
- Syntactic level: Assembly of user actions into instructions for the computer.
- Lexical level: Device dependencies and mechanisms for specifying syntax.
Getting the User’s Attention
- Intensity: Use two levels, with limited use of high intensity.
- Marking: Underline, enclose in a box, point with an arrow, or use indicators.
- Size: Use up to four sizes, with larger sizes attracting more attention.
- Choice of fonts: Use up to three fonts.
- Inverse video: Use inverse coloring.
- Blinking: Use blinking displays or color changes with great care.
- Color: Use up to four standard colors, with additional colors reserved for occasional use.
- Audio: Use soft tones for regular positive feedback.
Determine User’s Skill Levels
Design goals should be based on skill level:
- Novice or first-time users: Assumed to know little of the task or interface concepts.
- Knowledgeable intermittent users: Know the task concepts but have shallow knowledge of the interface concepts.
- Expert frequent users: Thoroughly familiar with the task and interface concepts and seek to get their work done quickly.