2. chapter 3 the interaction

3. We are interested in how the human user uses the computer as a tool to perform, simplify or support a task. In order to do this, the user must communicate his requirements to the computer.

4. ways in which the user can communicate with the system batch input interactive

5. Interaction we consider the communication between user and system: the interaction. We will look at some models of interaction that enable us to identify and evaluate components of the interaction, and at the physical, social and organizational issues that provide the context for it. We will also survey some of the different styles of interaction that are used and consider how well they support the user.

6. The interface must therefore effectively translate between user and system to allow the interaction to be successful. The use of models of interaction can help us to understand exactly what is going on in the interaction and identify the likely root of difficulties. They also provide us with a framework to compare different interaction styles and to consider interaction problems.

7. OVERVIEW  Interaction models help us to understand what is going on in the interaction between user and system. They address the translations between what the user wants and what the system does.  Ergonomics looks at the physical characteristics of the interaction and how these influence its effectiveness.  The dialog between user and system is influenced by the style of the interface.  The interaction takes place within a social and organizational context that affects both user and system.

8. What is interaction? communication user  system Interaction involves at least two participants: the user and the system but is that all … ? –see “language and action” in chapter 4 …

9. User and System Both are complex and very different from each other in the way that they communicate and view the domain and the task. The interface must therefore effectively translate between them to allow the interaction to be successful.

10. The Interaction interaction models –translations between user and system ergonomics –physical characteristics of interaction interaction styles –the nature of user/system dialog context –social, organizational, motivational

11. Interaction models Interaction models help us to understand what is going on in the interaction between user and system. They address the translations between what the user wants and what the system does.

12. models of interaction terms of interaction Norman model interaction framework Models describe the interaction in terms of the goals and actions of the user.

13. Some terms of interaction domain – the area of work under study A domain defines an area of expertise and knowledge in some real-world activity. e.g. graphic design goal – what you want to achieve e.g. create a solid red triangle task – how you go about doing it – ultimately in terms of operations or actions e.g. … select fill tool, click over triangle context - The interaction takes place within a social and organizational context that affects both user and system. Note … –traditional interaction … –use of terms differs a lot especially task/goal !!!

14. Domain A domain defines an area of expertise and knowledge in some real-world activity. Some examples of domains are graphic design, authoring and process control in a factory. A domain consists of concepts that highlight its important aspects. In a graphic design domain, some of the important concepts are geometric shapes, a drawing surface and a drawing utensil.

15. Task Tasks are operations to manipulate the concepts of a domain. For example, one task within the graphic design domain is the construction of a specific geometric shape with particular attributes on the drawing surface. Task analysis involves the identification of the problem space for the user of an interactive system in terms of the domain, goals, intentions and tasks.

16. Goal A goal is the desired output from a performed task. For example, one task within the graphic design domain is the construction of a specific geometric shape with particular attributes on the drawing surface. A related goal would be to produce a solid red triangle centered on the canvas.

17. Intention An intention is a specific action required to meet the goal.

18. traditional interaction Traditionally, the purpose of an interactive system is to aid a user in accomplishing goals from some application domain.

19. System and User The System and User are each described by means of a language that can express concepts relevant in the domain of the application. The System’s language we will refer to as the core language and the User’s language we will refer to as the task language. The core language describes computational attributes of the domain relevant to the System state, whereas the task language describes psychological attributes of the domain relevant to the User state.

20. Norman uses this model of interaction to demonstrate why some interfaces cause problems to their users. He describes these in terms of the gulfs of execution and the gulfs of evaluation. The user and the system do not use the same terms to describe the domain and goals. The gulf of execution is the difference between the user’s formulation of the actions to reach the goal and the actions allowed by the system. If the actions allowed by the system correspond to those intended by the user, the interaction will be effective. The interface should therefore aim to reduce this gulf. Donald Norman’s model

21. Seven stages –user establishes the goal –formulates intention –specifies actions at interface –executes action –perceives system state –interprets system state –evaluates system state with respect to goal Norman’s model concentrates on user’s view of the interface

22. چرخه ی اجرا و ارزیابی کاربر یک طرح از عملیاتی که توسط واسط اجرا می شود را فرموله می کند. سپس کاربر نتیجه اجرای هر عمل را در واسط مشاهده کرده و ارزیابی می کند، آنگاه تصمیم می گیرد که در ادامه چه عملی انجام دهد. چرخه ی تعامل به دو بخش تقسیم می شود : – اجرا – ارزیابی

23. execution/evaluation loop user establishes the goal formulates intention specifies actions at interface executes action perceives system state interprets system state evaluates system state with respect to goal هر مرحله یک عمل را که توسط کاربر انجام می شود را نشان می دهد. system evaluationexecution goal

24. execution/evaluation loop user establishes the goal formulates intention specifies actions at interface executes action perceives system state interprets system state evaluates system state with respect to goal system evaluationexecution goal

25. execution/evaluation loop user establishes the goal formulates intention specifies actions at interface executes action perceives system state interprets system state evaluates system state with respect to goal system evaluationexecution goal

26. execution/evaluation loop user establishes the goal formulates intention specifies actions at interface executes action perceives system state interprets system state evaluates system state with respect to goal system evaluationexecution goal

27. Using Norman’s model Some systems are harder to use than others Gulf of Execution user’s formulation of actions ≠ actions allowed by the system تفاوت بین فرمول های عملیات کاربر و عملیات مجاز توسط سیستم Gulf of Evaluation user’s expectation of changed system state ≠ actual presentation of this state تفاوت بین انتظار کاربر از تغییر حالت سیستم و نمایش واقعی از این حالت

28. Human error - slips and mistakes slip understand system and goal correct formulation of action incorrect action mistake may not even have right goal! Fixing things? slip – better interface design mistake – better understanding of system

29. Human error – slips and mistakes Human errors are often classified into slips and mistakes. We can distinguish these using Norman’s gulf of execution. If you understand a system well you may know exactly what to do to satisfy your goals – you have formulated the correct action.

30. Slips perhaps you mistype or you accidentally press the mouse button at the wrong time. These are called slips; you have formulated the right action, but fail to execute that action correctly.

31. mistake If you don’t know the system well you may not even formulate the right goal. For example, you may think that the magnifying glass icon is the ‘find’ function, but in fact it is to magnify the text. This is called a mistake.

32. Norman’s model It only considers the system as far as the interface. It concentrates wholly on the user’s view of the interaction. It does not attempt to deal with the system’s communication through the interface. An extension of Norman’s model, proposed by Abowd and Beale

33. Abowd and Beale framework extension of Norman… their interaction framework has 4 parts –user –input –system –output each has its own unique language interaction  translation between languages problems in interaction = problems in translation S core U task O output I input

34. The interaction framework attempts a more realistic description of interaction by including the system explicitly, and breaks it into four main components, the System, the User, the Input and the Output. Each component has its own language. In addition to the User’s task language and the System’s core language, there are languages for both the Input and Output components. Input and Output together form the Interface. Abowd and Beale framework

35. Using Abowd & Beale’s model user intentions  translated into actions at the interface  translated into alterations of system state  reflected in the output display  interpreted by the user general framework for understanding interaction –not restricted to electronic computer systems –identifies all major components involved in interaction –allows comparative assessment of systems –an abstraction

36. Abowd and Beale framework As the interface sits between the User and the System, there are four steps in the interactive cycle, each corresponding to a translation from one component to another. The User begins the interactive cycle with the formulation of a goal and a task to achieve that goal. The only way the user can manipulate the machine is through the Input, and so the task must be articulated within the input language. The input language is translated into the core language as operations to be performed by the System.

37. Abowd and Beale framework The System then transforms itself as described by the operations; the execution phase of the cycle is complete and the evaluation phase now begins. The System is in a new state, which must now be communicated to the User. The current values of system attributes are rendered as concepts or features of the Output. It is then up to the User to observe the Output and assess the results of the interaction relative to the original goal, ending the evaluation phase and, hence, the interactive cycle.

38. Four main translations Articulation, performance, presentation and observation.

39. Assessing overall interaction The interaction framework is presented as a means to judge the overall usability of an entire interactive system.

41. ergonomics physical aspects of interfaces industrial interfaces

42. Ergonomics Ergonomics looks at the physical characteristics of the interaction and how these influence its effectiveness.

43. Ergonomics Study of the physical characteristics of interaction Also known as human factors – but this can also be used to mean much of HCI! Ergonomics good at defining standards and guidelines for constraining the way we design certain aspects of systems ارگونومی برای تعریف استاندارها و دستورالعمل برای محدود کردن روشی که ما جنبه های اصلی سیستم را طراحی می کنیم، مفید است

44. Ergonomics - examples arrangement of controls and displays e.g.controls grouped according to function or frequency of use, or sequentially surrounding environment e.g.seating arrangements adaptable to cope with all sizes of user health issues e.g.physical position, environmental conditions (temperature, humidity), lighting, noise, use of colour e.g.use of red for warning, green for okay, awareness of colour-blindness etc.

45. Arrangement of controls and displays Safety-critical applications such as plant control, aviation and air traffic control: In each of these contexts, users are under pressure and are faced with a huge range of displays and controls. Here it is crucial that the physical layout of these be appropriate.

46. Arrangement of controls and displays functional controls and displays are organized so that those that are functionally related are placed together; sequential controls and displays are organized to reflect the order of their use in a typical interaction (this may be especially appropriate in domains where a particular task sequence is enforced, such as aviation); frequency controls and displays are organized according to how frequently they are used, with the most commonly used controls being the most easily accessible.

47. Industrial interfaces Office interface vs. industrial interface? Context matters! office industrial type of datatextualnumeric rate of changeslowfast environmentcleandirty … the oil soaked mouse!

48. Glass interfaces ? industrial interface: –traditional … dials and knobs –now … screens and keypads glass interface +cheaper, more flexible, multiple representations, precise values –not physically located, loss of context, complex interfaces may need both Vessel B Temp 0 100200 113 multiple representations of same information

49. Indirect manipulation office– direct manipulation –user interacts with artificial world industrial – indirect manipulation –user interacts with real world through interface issues.. –feedback –delays system interface plant immediate feedback instruments

50. interaction styles dialogue … computer and user distinct styles of interaction

51. style The dialog between user and system is influenced by the style of the interface.

52. Common interaction styles command line interface menus natural language question/answer and query dialogue form-fills and spreadsheets WIMP(windows, icons, menus and pointers) point and click three–dimensional interfaces

53. Command line interface Way of expressing instructions to the computer directly –function keys, single characters, short abbreviations, whole words, or a combination suitable for repetitive tasks better for expert users than novices offers direct access to system functionality command names/abbreviations should be meaningful! Typical example: the Unix system

54. Menus Set of options displayed on the screen Options visible –less recall - easier to use –rely on recognition so names should be meaningful Selection by: –numbers, letters, arrow keys, mouse –combination (e.g. mouse plus accelerators) Often options hierarchically grouped –sensible grouping is needed Restricted form of full WIMP system

55. Natural language Familiar to user speech recognition or typed natural language Problems –Vague (Language is by nature vague and imprecise) –ambiguous –hard to do well! Solutions –try to understand a subset –pick on key words

56. Natural language The ambiguity of natural language makes it very difficult for a machine to understand. Language is ambiguous at a number of levels. First, the syntax, or structure, of a phrase may not be clear. If we are given the sentence The boy hit the dog with the stick we cannot be sure whether the boy is using the stick to hit the dog or whether the dog is holding the stick when it is hit.

57. Query interfaces Question/answer interfaces –user led through interaction via series of questions –suitable for novice users but restricted functionality –often used in information systems Query languages (e.g. SQL) –used to retrieve information from database –requires understanding of database structure and language syntax, hence requires some expertise

58. Form-fills Primarily for data entry or data retrieval Screen like paper form. Data put in relevant place Requires –good design –obvious correction facilities

59. Spreadsheets first spreadsheet VISICALC, followed by Lotus 1-2-3 MS Excel most common today sophisticated variation of form-filling. –grid of cells contain a value or a formula –formula can involve values of other cells e.g. sum of all cells in this column –user can enter and alter data spreadsheet maintains consistency

60. WIMP Interface W indows I cons M enus P ointers … or windows, icons, mice, and pull-down menus! default style for majority of interactive computer systems, especially PCs and desktop machines

61. Point and click interfaces used in.. –multimedia –web browsers –hypertext just click something! –icons, text links or location on map minimal typing

62. Three dimensional interfaces virtual reality ‘ordinary’ window systems –highlighting –visual affordance –indiscriminate use just confusing! 3D workspaces –use for extra virtual space –light and occlusion give depth –distance effects flat buttons … … or sculptured click me!

63. elements of the wimp interface windows, icons, menus, pointers +++ buttons, toolbars, palettes, dialog boxes also see supplementary material on choosing wimp elements

64. Windows Areas of the screen that behave as if they were independent –can contain text or graphics –can be moved or resized –can overlap and obscure each other, or can be laid out next to one another (tiled) scrollbars –allow the user to move the contents of the window up and down or from side to side title bars –describe the name of the window

65. Icons small picture or image represents some object in the interface –often a window or action windows can be closed down (iconised) –small representation fi many accessible windows icons can be many and various –highly stylized –realistic representations.

67. Pointers important component –WIMP style relies on pointing and selecting things uses mouse, trackpad, joystick, trackball, cursor keys or keyboard shortcuts wide variety of graphical images

68. Menus Choice of operations or services offered on the screen Required option selected with pointer problem – take a lot of screen space solution – pop-up: menu appears when needed

69. Kinds of Menus Menu Bar at top of screen (normally), menu drags down –pull-down menu - mouse hold and drag down menu –drop-down menu - mouse click reveals menu –fall-down menus - mouse just moves over bar! Contextual menu appears where you are –pop-up menus - actions for selected object –pie menus - arranged in a circle easier to select item (larger target area) quicker (same distance to any option) … but not widely used!

70. Menus extras Cascading menus –hierarchical menu structure –menu selection opens new menu –and so in ad infinitum Keyboard accelerators –key combinations - same effect as menu item –two kinds active when menu open – usually first letter active when menu closed – usually Ctrl + letter usually different !!!

71. Menus design issues which kind to use what to include in menus at all words to use (action or description) how to group items choice of keyboard accelerators

72. Buttons individual and isolated regions within a display that can be selected to invoke an action Special kinds –radio buttons – set of mutually exclusive choices –check boxes – set of non-exclusive choices

73. Toolbars long lines of icons … … but what do they do? fast access to common actions often customizable: –choose which toolbars to see –choose what options are on it

74. Palettes and tear-off menus Problem menu not there when you want it Solution palettes – little windows of actions –shown/hidden via menu option e.g. available shapes in drawing package tear-off and pin-up menus –menu ‘tears off’ to become palette

75. Dialogue boxes information windows that pop up to inform of an important event or request information. e.g: when saving a file, a dialogue box is displayed to allow the user to specify the filename and location. Once the file is saved, the box disappears.

76. interactivity easy to focus on look what about feel?

77. INTERACTIVITY When looking at an interface, it is easy to focus on the visually distinct parts (the buttons, menus, text areas) but the dynamics, the way they react to a user’s actions, are less obvious.

78. Speech–driven interfaces تعاملات بوسیله گفتار rapidly improving … … but still inaccurate how to have robust dialogue? … interaction of course! e.g. airline reservation: reliable “yes” and “no” + system reflects back its understanding “you want a ticket from New York to Boston?”

79. Speech–driven interfaces In an airline reservation system, so long as the system can reliably recognize yes and no it can reflect back its understanding of what you said and seek confirmation. Speech-based input is difficult, speech- based interaction easier.

80. Look and … feel Interactivity is also crucial in determining the ‘feel’ of a WIMP environment. All WIMP systems appear to have virtually the same elements: windows, icons, menus, pointers, dialog boxes, buttons, etc. However, the precise behavior of these elements differs both within a single environment and between environments.

81. Look and … feel WIMP systems have the same elements: windows, icons., menus, pointers, buttons, etc. but different window systems … behave differently e.g. MacOS vs Windows menus appearance + behaviour = look and feel

82. Look and … feel In MacOS you have to keep the mouse depressed throughout menu selection; In Windows you can click on the menu bar and a pull-down menu appears and remains there until an item is selected or it is cancelled. Similarly the detailed behavior of buttons is quite complex.

83. Initiative In older computer systems, the order of interaction was largely determined by the machine. You did things when the computer was ready. In WIMP environments, the user takes the initiative, with many options and often many applications simultaneously available. The exceptions to this are pre-emptive parts of the interface, where the system for various reasons wrests the initiative away from the user, perhaps because of a problem or because it needs information in order to continue.

84. Initiative who has the initiative? old question–answer– computer WIMP interface– user WIMP exceptions … pre-emptive parts of the interface modal dialog boxes –come and won’t go away! –good for errors, essential steps –but use with care

85. modal dialog boxes When a dialog box appears the application will not allow you to do anything else until the dialog box has been completed or cancelled.

86. Error and repair Interactivity is also critical in dealing with errors. If users can detect errors then they can correct them. So, even if errors occur, the interaction as a whole succeeds.

87. Error and repair can’t always avoid errors … … but we can put them right make it easy to detect errors … then the user can repair them hello, this is the Go Faster booking system what would you like? (user) I want to fly from New York to London you want a ticket from New York to Boston (user) no sorry, please confirm one at a time do you want to fly from New York (user) yes … … …

88. Context تا بحال ما تعامل بین یک نفر و کامپیوتر را بررسی کردیم اما در عمل کاربر دریک شرایط اجتماعی و سازمانی گسترده تری کار می کند. In reality, users work within a wider social and organizational context. This provides the wider context for the interaction, and may influence the activity and motivation of the user. The presence of other people in a work environment affects the performance of the worker in any task.

89. Context In the case of peers, competition increases performance, at least for known tasks. Similarly the desire to impress management and superiors improves performance on these tasks. However, when it comes to acquisition of new skills, the presence of these groups can inhibit performance, owing to the fear of failure. Consequently, privacy is important to allow users the opportunity to experiment.

90. Context In order to perform well, users must be motivated. There are a number of possible sources of motivation, including fear, allegiance, ambition and self- satisfaction. The last of these is influenced by the user’s perception of the quality of the work done, which leads to job satisfaction. If a system makes it difficult for the user to perform necessary tasks, or is frustrating to use, the user’s job satisfaction, and consequently performance, will be reduced.

91. Involving actual users in the design process The user may also lose motivation if a system is introduced that does not match the actual requirements of the job to be done. Often systems are chosen and introduced by managers rather than the users themselves. In some cases the manager’s perception of the job may be based upon observation of results and not on actual activity. The system introduced may therefore impose a way of working that is unsatisfactory to the users. If this happens there may be three results: the system will be rejected, the users will be resentful and unmotivated, or the user will adapt the intended interaction to his own requirements. یا کاربر به تعامل تعیین شده با نیازش خو می گیرد. This indicates the importance of involving actual users in the design process.

92. Context Interaction affected by social and organizational context other people –desire to impress, competition, fear of failure motivation –fear, allegiance, ambition, self-satisfaction inadequate systems –cause frustration and lack of motivation

93. Feedback Providing adequate feedback is an important source of motivation for users. In general, an action should have an obvious effect to prevent this confusion and to allow early recovery in the case of error. Similarly, if system delays occur, feedback can be used to prevent frustration on the part of the user – the user is then aware of what is happening and is not left wondering if the system is still working.

94. Experience, engagement and fun designing experience physical engagement managing value

95. Satisfaction Ask many in HCI about usability and they may use the words ‘effective’ and ‘efficient’. Some may add ‘satisfaction’ as well. It is not sufficient that people can use a system, they must want to use it.

96. Understanding Experience Shopping is an interesting example to consider. Shopping is as much about going to the shops, feeling the clothes, being with friends. You can go shopping and never intend to spend money. Shopping is not about an efficient financial transaction, it is an experience. But experience is a difficult thing to pin down; we understand the idea of a good experience, but how do we define it and even more difficult how do we design it?

97. Engagement and Flow Csikszentimihalyi looked at extreme experiences such as climbing a rock face in order to understand that feeling of total engagement that can sometimes happen. He calls this flow and it is perhaps related to what some sportspeople refer to as being ‘in the zone’. This sense of flow occurs when there is a balance between anxiety and boredom. If you do something that you know you can do it is not engaging; you may do it automatically while thinking of something else, or you may simply become bored.

98. Flow Alternatively, if you do something completely outside your abilities you may become anxious and, if you are half way up a rock face, afraid. Flow comes when you are teetering at the edge of your abilities, stretching yourself to or a little beyond your limits.

99. Education In education there is a similar phenomenon. The zone of proximal development is those things that you cannot quite do yourself, but you can do with some support, whether from teachers, fellow pupils, or electronic or physical materials. Of course, this does not fully capture the sense of experience, and there is an active subfield of HCI researchers striving to make sense of this, building on the work of psychologists and philosophers on the one hand and literary analysis, film making and drama on the other.

100. Experience? home, entertainment, shopping –not enough that people can use a system –they must want to use it! psychology of experience –flow (Csikszentimihalyi) –balance between anxiety and boredom education –zone of proximal development –things you can just do with help wider... –literary analysis, film studies, drama

101. Designing experience real crackers –cheap and cheerful! –bad joke, plastic toy, paper hat –pull and bang

102. Designing experience virtual crackers –cheap and cheerful –bad joke, web toy, cut-out mask –click and bang

103. Designing experience virtual crackers –cheap and cheerful –bad joke, web toy, cut-out mask –click and bang

104. how crackers work sender fill in web form To: wxv From:.. receive email recipient closed cracker page open message recipient clicks cracker opens... very slowly joke links open cracker page web toy mask sender watches progress

105. The crackers experience real crackervirtual cracker Surface elements designcheap and cheerfulsimple page/graphics playplastic toy and jokeweb toy and joke dressing uppaper hatmask to cut out Experienced effects sharedoffered to anothersent by email message co-experiencepulled togethersender can't see content until opened by recipient excitementcultural connotationsrecruited expectation hiddennesscontents insidefirst page - no contents suspensepulling crackerslow... page change surprisebang (when it works)WAV file (when it works)

106. Physical design Ergonomic You cannot physically push buttons if they are too small or too close. Physical The size or nature of the device may force certain positions or styles of control. For example, a dial like the one on the washing machine would not fit on the MiniDisc controller; high-voltage switches cannot be as small as low- voltage ones.

107. Physical design Legal and safety Cooker controls must be far enough from the pans that you do not burn yourself, but also high enough to prevent small children turning them on. Context and environment The microwave’s controls are smooth to make them easy to clean in the kitchen. Aesthetic The controls must look good. Economic It must not cost too much!

108. Physical design many constraints: –ergonomic – minimum button size –physical – high-voltage switches are big –legal and safety – high cooker controls –context and environment – easy to clean –aesthetic – must look good –economic – … and not cost too much!

109. Design trade-offs constraints are contradictory … need trade-offs within categories: e.g. safety – cooker controls front panel – safer for adult rear panel – safer for child between categories e.g. ergonomics vs. physical – MiniDisc remote ergonomics – controls need to be bigger physical – no room! solution – multifunction controls & reduced functionality

110. Fluidity do external physical aspects reflect logical effect? –related to affordance (chap 5) logical state revealed in physical state? e.g. on/off buttons inverse actions inverse effects? e.g. arrow buttons, twist controls

111. inverse actions yes/no buttons –well sort of ‘joystick’ also left side control

112. spring back controls one-shot buttons joystick some sliders good – large selection sets bad – hidden state

113. a minidisk controller series of spring-back controls each cycle through some options –natural inverse back/forward twist for track movement pull and twist for volume – spring back – natural inverse for twist

114. physical layout controls: logical relationship ~spatial grouping

115. compliant interaction state evident in mechanical buttons rotary knobs reveal internal state and can be controlled by both user and machine

116. Managing value people use something ONLY IF it has perceived value AND value exceeds cost BUT NOTE exceptions (e.g. habit) value NOT necessarily personal gain or money

117. Weighing up value value helps me get my work done fun good for others cost download time money £, $, € learning effort if we ask someone to do something or use something they are only likely to do it if the value to them exceeds the cost.

118. in economics Net Present Value: –discount by (1+rate) years to wait in life people heavily discount –future value and future cost –hence resistance to learning –need low barriers and high perceived present value Discounted future

119. example – HCI book search value for people who have the book helps you to look up things –chapter and page number value for those who don’t … sort of online mini-encyclopaedia –full paragraph of context … but also says “buy me”!!

120. Value and organisational design coercion tell people what to do! value = keep your job enculturation explain corporate values establish support (e.g share options) emergence design process so that individuals value  organisational value

121. General lesson … if you want someone to do something … make it easy for them! understand their values

122. SUMMARY In this chapter, we have looked at the interaction between human and computer, and, in particular, how we can ensure that the interaction is effective to allow the user to get the required job done. We have seen how we can use Norman’s execution– evaluation model, and the interaction framework that extends it, to analyze the interaction in terms of how easy or difficult it is for the user to express what he wants and determine whether it has been done.

123. SUMMARY We have also looked at the role of ergonomics in interface design, in analyzing the physical characteristics of the interaction, and we have discussed a number of interface styles. We have considered how each of these factors can influence the effectiveness of the interaction.

124. SUMMARY Interactivity is at the heart of all modern interfaces and is important at many levels. Interaction between user and computer does not take place in a vacuum, but is affected by numerous social and organizational factors. These may be beyond the designer’s control, but awareness of them can help to limit any negative effects on the interaction.