Human-Computer Interface

                       

 

Possible reference:

  • Shneiderman, Designing the User Interface (Addison Wesley)

 

Topic objective:The student should understand the factors that are considered for human-computer interface and be aware of several methods that are used, especially in graphic user interfaces. 


 

  Human-computer interface facilitates communication between human and computer 

 

Good human-computer interface        easier, more efficient computer usage

                                                              easier, faster computer usage is enabled

                                                                        (user-friendly)

 

            software – how information is effectively organized

                                    [–  graphically (GUI: graphic user interface)]

            hardware – how design of data-entry instruments (keyboard, pointing devices, …)

and data display can be enhanced in their effectiveness

 

 

The design of the human interface needs to consider proper functionality (tasks and subtasks required to run), standards (similar characteristics in various applications), integration (usable by different applications and tools), consistency (same sequence of actions, same way of presentation, …) and portability (can be used in various software and hardware environments).

 

Measures for evaluating the quality of a user interface:

  • time to learn to use it
  • speed of execution of a benchmark task
  • user error rate
  • retention period – how long user knowledge can be retained
  • user satisfaction

 

Human factors required to be taken into account in the design of user interfaces: physical ability and physical workplace, cognitive and perceptual abilities, personality differences, cultural and national variations, users with disabilities, elderly users

 

Several models for human interfaces:

      conceptual, semantic, syntactic and lexical model: 4 levels – conceptual (user's model of the system), semantic (meaning carried by user input and computer output display), syntactic (how semantic units are combined to yield instructions), lexical (dependabilty of devices and exact mechanism)

      GOMS model: goal, operator, method and selection rule – user formulates goal and subgoals, each using methods or procedures; operator is an elementary action on the state of mind of the user or task environment, selection rule is the control structure for method selection; and key strike level model: measure time for key strike, pointing, direction guide, drawing, thinking and waiting for system response, to determine performance

      action level model: 7 levels of user action – form goal, form intention, specify action, execute action, perceive system condition, interpret system condition, evaluate result

      action grammar, task-action grammar – syntax for actions, to give an interface which is consistent

      widget (GUI primitves: windows, menus, buttons and switches, scroll bar, data-entry fields, boxes and dividing lines, sliders, gauges and meters, …) level theory

      object-action interface model: GUI with visual representation of objects (e.g. files by corresponding icons) and actions (e.g. garbage can icon for deletion; command bar) – direct manipulation, syntax dissapearance

 

 

Primary interaction styles:

        direct manipulation: pointing to visual representation of object and action, etc

advantages: easy to be learnt, easy to be remembered, avoid errors, encourages exploration, high satisfaction

disadvantages: may be difficult to program, requires graphic display and pointing device

        menu choice: user chooses an item from a given list

advantages: easy to be learnt, reduces key hits, structures decision-making, facilitates error handling

disadvantages: danger of too many menus, slows down frequent users, takes up screen space, requires fast display

        form filling: data for certain field is entered

advantages: simplifies data entry, little training needed

disadvantages: takes up screen space

        command language: text with certain syntax

advantages: flexible, liked by expert users, supports user initiative, allows the creation of user-defined macros

disadvantages: poor error handling, requires a lot of training and memorizing

        natural language: natural language sentences/phrases

advantages: no need to learn syntax

disadvantages: requires expalination dialogue, probably requires more keystrokes, probably does not show context, unpredictable

dialogue box: combination of menu, form

 

Interaction devices:

        keyboard and function keys, cursor

        pointing devices – for choosing, placing at certain positions, choosing directions, determining path, giving numerical values, manipulating text – light pen, touch screen, mouse, trackball, joystick,graphic pad, touch pad, nipple

        speech recogniser, digitiser and generator

        image and video displayer

        printer

 

 

 

 

 

 

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