1. COMP 3715 Spring 05

2. Computer Interface Interaction between human and computer Has to deal with two things  User’s mental model Different user has different models  The state of the computer Need to adapt to different user’s need

3. Interface design principles Naturalness Consistency Relevance Supportiveness Flexibility

4. Naturalness Intuitive to user Natural language  Minimize IT jargon  But jargon related to the task ok Instructional, not personal Self-explanatory  Minimize human pre/post-process Need to adopt to user

5. Consistency Input format Output format Menu layout Messages No surprises!

6. Relevance No redundancy Minimize required input  Key strokes  Minimize required information Minimize output messages  Unnecessary information  Irrelevant information scare users

7. Supportiveness Need adequate information to user  Enough feedback to user Need to determine the user’s need  Novice vs. Expert

8. Flexibility Need to accommodate differences  User preference  User requirement  User expertise Personalization  But, more personalization = less help among users  Need a way to restore and remember

9. Interaction style – command language E.g. DOS prompt, UNIX prompt Typically restricted language set (list of commands) Commands with modifiers/parameters Advantages:  Flexibility  Speed for expert users  Feeling of control Disadvantages  Non-supportive  Not necessarily natural

10. Interaction style – command language Design questions  What should be the legal command?  Long form vs. abbreviation  Error messages need to be supportive  Hierarchy of commands?  Learning curve

11. Interaction style Graphical user interface  Question and answer  Menu  Form

12. Interaction style -- GUI Question and answer  System ask question, user answers, system decide what to do next  Answer can be in different formats Choices: radio buttons, acceptable characters Free form  Advantages: Moderately supportive Flexible: short-cuts, various input types  Disadvantages Can be tedious if not careful Problem of irrelevancy magnified

13. Interaction style -- GUI Question and answer

14. Interaction style -- GUI Question and answer  Design issues Need careful planning of dialog Avoid getting stuck in loops Don’t ask the same thing twice unless necessary Default is useful  Nicely designed, good for novices

15. Interaction style -- GUI Menus  Various types Bars Block Button Full screen Pop-up, tear-off Cascade menus  System dictates what can be input next  Advantage Supportive: clear signal of what to input next  Disadvantage Less flexible: amount of input limited Multiple selection can be cumbersome What if user want to select nothing?

17. Interaction style -- GUI Menus  Design decisions 7  2 rules: avoid too many items on menus  Also make novice hard to choose Naming menus Unify menus if possible Board vs. Deep menus Ordering of menu items Frequency vs. Alphabetical vs. Categorical vs. Conventional

18. Interaction style -- GUI Forms  A predefined sequence  User cannot move-on until all parts of form filled  Auto-skip feature to move to the next input  Advantage Supportive: very clear directives  Disadvantage Non-flexible

19. Interaction style -- GUI Forms  Design issues Ordering/Division of requests “Next step” When to check for errors

20. Issues in GUIs Use of metaphors  Process: drag and drop mimics moving  Symbols: icons represent objects/tasks E.g. of iconic interfaces  Desktop  Paintbox  Spreadsheet

21. Why icons  Metaphor mimic reality – comfort for users  Easy to learn  Easy to retain knowledge  Good feedback available

22. Limitations  Possibility of confusion Meaning of icons Meaning of action  Selection vs Dragging  Single-click vs. double-click  Lack of flexibility

23. Guideline in designing GUI for human need Need to concern about human responses  Reaction time  Movement time  Attention  Selective attention  Focused attention  Divided attention  Sustained attention

24. Reaction time  Typically 200ms  Longer if unexpected  Longer for young and old  Longer if periphery vision Movement time  Movement speed varies for different directions/part of body

25. Selective attention  Monitoring multiple channels watch two windows Listen and watch  Memory limitation 7  2 principle Stressful = less attention  Design notes Need to be clear about importance of each channel Should avoid surprises (let user know what will likely to happen next) Channels should be close together

26. Focused attention  Attention to a single channel without distraction Typing on the WordPad while other things are happening  Design guidelines Channel of interests should demand attention Competing channels should be far apart & distinct

27. Divided attentions  Attempting to do multiple things at once  Design guidelines Tasks should be easy Allow prioritization