COMP 3715 Spring 05

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

Interface design principles Naturalness Consistency Relevance Supportiveness Flexibility

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

Consistency Input format Output format Menu layout Messages No surprises!

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

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

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

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

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

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

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

Interaction style -- GUI Question and answer

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

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?

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

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

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

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

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

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

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

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

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

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

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