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  “Interazione uomo-macchina” - Alan Dix, Janet Finlay, Gregory D. Abowd, Russell Beale Answers for tutors and extra exercises 1. The human EXERCISE 1.4  What are mental models , and why are they important in interface design? answer available for tutors only   Mental models are the theories people build to understand the causal behaviour of systems. These are often partial, unstable and subject to change. They may be internally inconsistent. They may be superstitious and based on incorrect interpretation of evidence. They are important, as errors can occur if the user's model is incorrect or if the designer has a different model than the user. One way of minimising problems is supporting conventions - another is to make the correct model explicit. EXERCISE 1.5  What can a system designer do to minimise the memory load of the user? answer available for tutors only   Discuss two ways of remembering - recognition  is the knowledge that you have seen something  presented to you; recall   is the reproduction of something from memory. Recognition is simpler - the information required is provided as the cue. Recall is more complex as the information has to  be retrieved from memory but cues can help this - e.g. using categories or images. The interface designer can where possible allow recognition by providing information up front (e.g. labelled  buttons). Where this is not possible support recall by using cues such as iconic images, categories of menu item. The answer may also discuss short term memory where chunking and restricting number of items are important. EXERCISE 1.8  [extra - not in book] What is the difference between recognition  and recall   in relation to human memory? Discuss the implications of this for interface designers. answer available for tutors only   Recognition is the knowledge that you have seen something presented to you. Recall is the reproduction of something from memory. Recognition is simpler - the information required is  provided as the cue. Recall is more complex as the information has to be retrieved from memory  but cues can help this - e.g. using categories or images. Implications for interface designers include the need, where possible, to allow recognition by providing information up front (e.g. labelled buttons). Where this is not possible support recall by using cues such as iconic images, categories of menu item. Copyright ©  2004 – The McGraw-Hill Companies srl  “Interazione uomo-macchina” - Alan Dix, Janet Finlay, Gregory D. Abowd, Russell Beale EXERCISE 1.9  [extra - not in book] A little psychology is worse than none at all . Do you agree with this statement? Justify your stand in the context of designing usable interactive systems. answer available for tutors only   There are different ways of answering this question depending on the stand you take. One  problem with knowing a little psychology is the danger of applying psychological principles out of context and making simplistic judgements. Principles and guidelines that derive from  psychology are context dependent. For example, predictability is a principle that might not apply to a computer game. So it is important that the underlying theory is interpreted appropriately and that the context in which the rule is applied is comparable to that of the theory. An example of misuse of psychology is in the application of the 7+/- 2 short term memory limit to menu design. Menus support recognition by presenting the options to the user - this is not a task that relies on short term memory. Therefore the oft-heard recommendation to limit menu items to 7+/- 2 is a misapplication of psychology. Try to find more examples of well and badly applied psychology for yourself. EXERCISE 1.10  [extra - not in book] What is the difference between a  slip  and a conceptual error? How might a designer minimise the occurrence of both among users of a system? answer available for tutors only   A slip is an error that occurs when the context of skilled behaviour is changed. A conceptual error occurs due to lack of understanding on the part of the user. This may be a result of an inadequate or incorrect mental model. Answer should discuss ways of supporting mental models - e.g. transferring user's knowledge from other domains, using familiar objects, maintaining consistency between platforms, providing feedback, etc. Slips can be avoided by ensuring consistency, taking account of stress in skilled operation, etc. EXERCISE 1.11  [extra - not in book] How might you use the notion of reward in interface design to increase the positive emotional response of users? Can you find any examples of this? answer available for tutors only   Reward is essentially positive reinforcement of desired or good behaviour. This could be through  providing explicit praise (used frequently in educational systems when a correct answer is given) or through more implicit elements that engage or entertain the user. Novelty, social interaction, feedback and surprise are all potentially rewarding to the user. For example, seeing a direct relationship between action and effect (feedback) can be rewarding. However care needs to be taken because each of these things can backfire and become irritating if not used properly. An Copyright ©  2004 – The McGraw-Hill Companies srl  “Interazione uomo-macchina” - Alan Dix, Janet Finlay, Gregory D. Abowd, Russell Beale example of this is the Microsoft Office paperclip (see Chapter 11), which attempts to motivate users by making getting help a novel social interaction, was actually irritating to users and was eventually dropped. 2. The computer EXERCISE 2.2  Exercises 2.2 and 2.3 involve you examining a range of input and output devices in order to understand how they influence interaction. A typical computer system is comprised of a QWERTY keyboard, a mouse, and a colour screen. There is usually some form of loudspeaker as well. You should know how the keyboard, mouse and screen work - if not, read up on it. What sort of input does the keyboard support? What sort of input does the mouse support? Are these adequate for all possible applications? If not, to which areas are they most suited? Do these areas map well onto the typical requirements for users of computer systems? If you were designing a keyboard for a modern computer, and you wanted to produce a faster, easier to use layout, what information would you need to know and how would that influence the design? answer available for tutors only   The keyboard supports a single type of event, a keypress, which includes data that signals the value of the key pressed. This data is represented as an ASCII key value or some other international standard representation, such as UNICODE. Some keys on a keyboard introduce new modes, or interpretations of keystrokes, so you can use the same key to send uppercase and lowercase letters, or introduce special commands or modifiers (such as Control-A). Many keyboards also include special function keys, which produce non-ASCII keyboard events that must be handled in special ways. A mouse provides two main pieces of information. One piece of information is the location, in screen coordinates, of the mouse pointer. The other piece of information is any event information from the pressing and releasing of buttons of the mouse. Certain mouse designs include additional inputs, such as a wheel that sends discrete directional scroll events. The information needed to redesign keyboard layout would include the frequency of letters or commands to be issued by the keyboard as well as empirical data on motor actions of the hands and fingers in performing typing actions. Various modified keyboard layouts do exist, such as the DVORAK keyboard, but none has been successful in supplanting the QWERTY standard. EXERCISE 2.4  What is the myth of the infinitely fast machine? Copyright ©  2004 – The McGraw-Hill Companies srl  “Interazione uomo-macchina” - Alan Dix, Janet Finlay, Gregory D. Abowd, Russell Beale answer available for tutors only   The adverse effects of slow processing are made worse because the designers labour under the myth of the infinitely fast machine. That is, they design and document their systems as if response will be immediate. Designers should plan explicitly for slow responses where these are  possible. A good example, where buffering is clear and audible (if not visible) to the user, is telephones. Even if the user gets ahead of the telephone when entering a number, the tones can  be heard as they are sent over the line. This type of serendipitous feedback should be emulated in other areas. EXERCISE 2.5  Pick one of the following scenarios, and choose a suitable combination of input and output devices to best support the intended interaction. It may help to identify typical users or classes of user, and identify how the devices chosen support these people in their tasks. Explain the major  problems that the input and output devices solve. Environmental database A computer database is under development that will hold environmental information. This ranges from meteorological measurements through fish catches to descriptions of pollution, and will include topographical details and sketches and photographs. The data has to be accessed only by experts, but they want to be able to describe and retrieve any piece of data within a few seconds. Word processor for blind people A word processor for blind users is needed, which can also be operated by sighted people. It has to support the standard set of word-processing tasks. answer available for tutors only   The environmental database will be operated by skilled experts. It is likely that they will want geographic displays of information, so leveraging off of operations on a map seem likely to be intuitive. Various parameters would likely be overlaid on the map, so some intuitive way to select among parameters, possibly with a purpose-built keyboard with function keys representing the parameters to be revealed. There should be an analysis of current practices by these experts in which the way they like to view information is revealed and the way they like to manipulate information. It seems that an interface to encourage exploration to reveal trends in data would be useful, so how this exploration can be made natural would impact design recommendations for input devices. Copyright ©  2004 – The McGraw-Hill Companies srl
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