HCI Paradigms and underlying Principles Lecture 5

Usability paradigms and principles z Designing for maximum usability is the goal of design z History of interactive system design provides paradigms/examples for usable designs z Principles of usability are more general means of understanding usability Effective strategies for building interactive systems

Usability Concerns How can an interactive system be developed to ensure its usability? How can the usability of an interactive system be demonstrated or measured? Approaches 1. Paradigms for usability -examples of successful interactive techniques 2. Principles for usability-theoretically driven from psychological, computational and sociological knowledge

Paradigms for Usability Historical Perspective on Interactive System Design Time-sharing (single computer supporting multiple users ) 40s and 50s – explosive technological growth 60s – need to channel the power J.C.R. Licklider -one of the leading advocates of research into human centered application of computing technology at ARPA single computer supporting multiple users instead of batch processing

more suitable medium than paper for presenting computer outputs 1962 – Sutherland's Sketchpad: computers for visualizing and manipulating data Allowed a computer operator to use a computer to create very rapidly sophiscated visual models on a display screen like TV Visual patterns could be stored in computer memory & could be manipulated by a comp’s processor Sketch pad demonstrated that: Computers could be used for more than data processing-visualising and manipulating, since it could be made to speak a more human language one person's contribution could drastically change the history of computing Paradigms (cont’d) Video Display Units

Paradigms (cont'd) Programming toolkits Engelbart at Stanford Research Institute 1963 – use computing technology to complement man's problem solving activity /computers teaching humans/human learning from computer Secret to achieving the above was in providing the right toolkit the right programming toolkit provides building blocks to producing complex interactive systems, just like carpenters produce beautiful wood work with right tools His team of programmers developed a set of programming tools they would require in order to build more complex interactive systems Their power is that small well understood components can be composed in fixed ways in order to create larger tools

Personal computing 70s – Papert's LOGO language for simple graphics programming by children -By typing in phrases like go, turn left, child programmer could teach the turtle to draw circles, squares, et.c By adapating the prog. Language to a level children could understand and use, Papert demonstrated a valuable maxim for interactive system develop’t No matter how powerful a system may be, it’ll be more powerful the easier it is to use Future of computing in small, powerful machines dedicated to the individual Kay at Xerox PARC – the Dynabook as the ultimate personal computer Paradigms (cont’d)

Paradigms (cont’d) Window systems and the WIMP interface humans can pursue more than one task at a time windows used for dialogue partitioning, to "change the topic“ 1981 – Xerox Star first commercial windowing system windows, icons, menus and pointers now familiar interaction mechanisms The beauty of WIMPs Increase usability of computer

Metaphor zrelating computing to other real-world activity is an effective technique yLOGO's turtle dragging its tail (built for children) yfile management on an office desktop yword processing as typing yfinancial analysis on spreadsheets yvirtual reality – user inside the metaphor zProblems ysome tasks do not fit into a given metaphor ycultural bias e.g. meaning of a tick and an x Used to teach new concepts relating them to the ones already understood

Paradigms (cont’d) Direct manipulation 1982 – Shneiderman describes appeal of graphically-based interaction & highlighted following features: visibility of objects incremental action at the interface with rapid feedback on all actions reversibility of actions so that users can explore without fearing severe penalties syntactic correctness of all actions so that every action is a legal operation replacement of complex command languages with actions to manipulate directly the visible objects hence DM

actions do not always speak louder than words in some cases e.g. information retrieval tasks DM – interface replaces underlying system language paradigm interface as mediator / intelligent agent User issues instructions in natural language Interface presents instructions for processing & returns results e.g. Paradigms (cont’d) Language versus Action

Paradigms (cont'd) Hypertext 1945 – Vannevar Bush and the memex key to success in managing explosion of information mid 60s – Nelson describes hypertext as non-linear (interlinked nodes) browsing structure hypermedia and multimedia for non text data Ability to store and retrieve connected pieces of data by use of links Memex had ability to produce many copies

Principles to support usability General principles which can be applied to the design of interactive systems to promote their usability Learnability the ease with which new users can begin effective interaction and achieve maximal performance Flexibility the multiplicity of ways the user and system exchange information Robustness the level of support provided to the user in determining successful achievement and assessment of goal-directed

Principles of learnability Predictability determining effect of future actions based on past interaction history operation visibility-how the availability of operations which can next be performed are shown to the user e.g. 1,2,4,16,256,...,...(what are the next two numbers Synthesizability (synthesizing from previous exp. & knowledge to come to right conclusion/decision) Ability of the user to assess the effect of past operations on the current state Assessing the effect of past actions and linking them to present tasks immediate vs. eventual honesty-ability of UI to provide an observable and informative account of such change e.g. when a file is moved from one folder to another, the process and result is observable.

Familiarity how prior knowledge applies to new system. guessability; affordance e.g. desktop metaphor from the physical office desk work area, computer keyboard from type writer keyboard, what else? Generalizability extending specific interaction knowledge to new situations which are similar but previously unencountered e.g. multi windowing systems attempt to provide cut/copy/paste operations to all applications in the same way e.g. MS Office suite, MS Visio, web browsers, search engines, etc Consistency likeness in input/output behavior arising from similar situations or task objectives e.g. warning to aircraft crew which are consistently color coded i.e. red for immediate attn, amber for warning & and green for advisory, phone keyboard & functions are consistent across brands. Very important for web /e-access for non visual users like the blind & other PWDs Principles of learnability (cont’d)

Principles of flexibility Dialogue initiative freedom from system imposed constraints on input dialogue Maximise the user’s ability to initiate action towards the system and minimize the reverse for greater flexibility Multithreading ability of system to support user interaction for more than one task at a time e.g. web browsing and word processing or Skype conference call concurrent vs. interleaving; multimodality Task migratability Shd be possible of system or user to pass control of a task to the other or shared e.g. spell checking passing responsibility for task execution between user and system

Substitutivity allowing equivalent values of input and output to be substituted for each other e.g. allowing input values in both metres or inches representation multiplicity; equal opportunity-may not be clear difference btn in put & output e.g. in a drawing program, user may draw a line & request system for its length or specify coordinates and instruct system to draw line Customizability modifiability of the user interface by user (adaptability) or system (adaptivity) e.g. Personal facebook page, chat profiles, etc. Principles of flexibility (cont’d)

Principles of robustness Observability ability of user to evaluate the internal state of the system from its perceivable representation browsability; defaults (set defaults where applicable); reachability (ability to move from one state to another); persistence (duration of efect of communication-voice does n’t last long); operation visibility Recoverability ability of user to take corrective action once an error has been recognized reachability; forward/backward recovery; commensurate effort (if difficult to undo an action, then it sh’d have been difficult to do in first place)

Responsiveness how the user perceives the rate of communication with the system Response time (duration to get state changes from system to user).instant/short durations desired e.g. web browsing Info to user on status if duration is long is necc. Stability-invariance of duration for identical or similar resources Task conformance degree to which system services support all of the user's tasks task completeness; task adequacy Principles of robustness (cont’d)

References Alan Dix, Janet Finlay, Gregory Abowd & Russell Beale (2004). Human- Computer Interaction. Hillsdale, NJ: Prentice Hall, ISBN (hardback); (paperback) only outside USA (Second Edition) ISBN Chap. 4 Revision question: (a) Explain the general Principles applied to the design of interactive systems to promote their usability (b) Using an example of an interactive system of your choice, explain how each principle given in (a) can be met to make the system usable. Use Dix etal. HCI 2 nd edition pg for reference