The document discusses human-computer interaction (HCI) and the importance of usability in user interface design. It covers topics like the definition of a user interface and its components, principles of good interface design, the history and evolution of screen designs, factors that influence usability like learnability, efficiency and satisfaction, and how to improve a system's usability through techniques such as default values, accelerators, and accommodating individual user differences.

2. Human-computer interaction HCI is the study, planning, and design of how people and computers work together so that a person’s needs are satisfied in the most effective way. HCI designers must consider a variety of factors. HCI disciplines includes many topics (e.g., theoretical foundations of HCI; cognitive, physiological, and psychological models of human behavior; paradigms of interaction, user interfaces, design process, Web interfaces, usability engineering). In this course, we concentrate on Web interfaces and GUIs.

3. What is a user interface? The user interface is the part of a computer and its software that people can see, hear, touch, talk to, or otherwise understand or direct. The user interface has essential two components: input and output. Input is how a person communicates his or her needs or desires to the computer (e.g., keyboard, mouse, trackball) Output is how the computer conveys the results of its computations and requirements to the user (e.g., display screen)

4. Well designed user interface Proper interface design is a mixture of well-designed input and output mechanisms. The best interface is like the best waiter/waitress – “not noticeable”. It allows the user to focus on the information and task at hand, but not on the mechanisms used to present the information and perform the task.

5. History of screen design Ambiguous messages often required referral to a manual to interpret. Effectively using this kind of screen required a great deal of practice and patience. A 1970s design often consisted of many fields with very cryptic and often unintelligible captions. It was visually cluttered, often possessed a command field that challenged the user to remember what had to be keyed into it.

6. History of screen design (continued) In the 1980s screens began to use grouping and alignment of elements. Instructions and reminders to the user had to be inscribed on the screen in the form of prompts. User memory was supported by providing clear and meaningful field captions and by listing commands on the screen, and enabling them to be applied through function keys.

7. History of screen design (continued) The new controls were much more effective in supporting a person’s memory, now simply allowing for selection from a list of instead of requiring a remembered key entry. The advent of graphics allowed using more sophisticated control elements (visually enhanced groupings, buttons, menus for implementing commands, the use of different font sizes and styles, and colors.

8. “ User-Friendly” “ User friendly” term is sometimes used regarding well designed user interface. Although, it is not liked much by HCI professionals for two reasons: Users don’t need machines to be friendly to them. In reality, different users have different needs. Instead, HCI specialists talk about “usable interface” referring to the concept of usability.

9. System acceptability Social acceptability Practical acceptability System acceptability Usefulness Utility Usability Easy to learn Efficient to use Easy to remember Few errors Subjective pleasing Cost Compatibility Reliability Etc. J. Nielsen, “Usability Engineering”, p. 25

10. Definition of usability Usability means that people who use the product can do so quickly and easily to accomplish their own tasks. Usability is not a single, one-dimensional property of a user interface, but it has multiple components and is traditionally associated with five usability attributes: Learnability Efficiency Memorability Errors Satisfaction

11. Learnability It is the most fundamental usability attribute and probably the easiest usability attribute to measure. Focus on novice users Focus on expert users Usage proficiency and efficiency Time

12. Learning curve for typical products 100 80 60 40 20 0 Average % of product used

13. Efficiency of use Efficiency refers to the expert user’s steady-state level of performance at the time when the learning curve flattens out. To measure efficiency of use for experienced users, one obviously needs access to experienced users. Usability tests are used to measure efficiency, also during the design stage. They are brought in and asked to use the system for a certain number of hours, after which their efficiency is measured.

14. Memorability Casual users are the third major category of users besides novice and expert users. Casual users are people who are using a system from time to time rather that having the fairly frequent use assumed for expert users. Casual use is typically seen for utility programs (e.g., antivirus), for supplementary applications, as well as for programs that are inherently only used at long intervals.

15. Few and noncatastrophic errors Users should make as few errors as possible when using a computer system. An error is defined as any action that does not accomplish the desired goal. The system’s error rate is measured by counting the number of such actions made by users while performing some specific task. Some errors are corrected immediately by the user and have no significant effect. These errors need not to be counted separately. Other errors are more catastrophic (not discovered by the user, leading to faulty product work, or destroying user’s work).

16. Subjective satisfaction Subjective satisfaction refers to how pleasant it is to use the system. It is especially important usability attribute for systems that are used in a nonworking environment (home computing, games, interactive fiction, or creative painting). Subjective satisfaction is normally measured during usability tests by a short questionnaire that is given to users.

17. How to improve usability? Provide user interface with multiple interaction styles. E.g., any operation that is activated by double-clicking should also be made available as a menu choice or in some other visible fashion. Default values. All users would benefit from appropriate choice of default values. E.g., an installation of some software, where there is a list of installation options: “Full”, “Default”, and “Custom”. “ Accelerators” in the interface are the elements that allow the user to perform frequent tasks quickly.

18. Usability trade-offs Trade-offs are inherent in any design process. E.g., the desire to avoid catastrophic errors may lead to extra questions are asked to assure that the user is certain about wanting a particular action. Also, security consideration may lead to designs violating some usability principles.

19. Individual user differences Two important issues for usability are: The users’ task. The users’ individual characteristics and differences.

20. Experience of users Minimal computer experience Extensive computer experience Novice user of system Expert user of system Knowledgeable about domain Ignorant about domain

21. Users and system usage Sometimes, a system has an explicit “user orientation”. Examples? Most interfaces, however, are intended for both novice and expert users and thus needs to accommodate both usage styles. Accelerators in the interface allow expert users to use faster, but less obvious, interaction techniques. Most people do not acquire comprehensive expertise in all parts of a system, no matter how much they use it. Any given user makes extensive use of a small subset of features.

22. Users and system usage (continued) Users also differ in other ways than experience. Some differentiating factors are: age, gender, differences in spatial memory and reasoning abilities, preferred learning style. Some people simply love using computers. These are called super-users (also “power users”).

23. Usability slogans Your best guess is not good enough The user is always right The user is not always right Users are not designers Designers are not users Vice-presidents are not users Less is more Details matter Help doesn’t help Usability engineering is process