User Interface Design and Ergonomics - National Open University of ...

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Table 4:- Table: Average times for computer interface actions [Based on detailed information in Judith Reitman Olson and Gary M. Olson, "The growth of cognitive modeling in human- computer interaction since GOMS," Human-Computer Interaction, 5 (1990), pp. 221-265. Many values given in this table are averaged and rounded.] PHYSICAL MOVEMENTS Enter one keystroke on a standard keyboard: Use mouse to point at object on screen Move hand to pointing device or function key .28 second 1.5 second .3 second VISUAL PERCEPTION Respond to a brief light Recognize a 6letter word Move eyes to new location on screen (saccade) MENTAL ACTIONS Retrieve a simple item from longterm memory Learn a single "step" in a procedure Execute a mental "step" Choose among methods .1 second .34 second .23 second 1.2 second 25 seconds .075 second 1.2 second Ranges from .07 second for highly skilled typists doing transcription, to .2 second for an average 60-wpm typist, to over 1 second for a bad typist. Random sequences, formulas, and commands take longer than plain text. May be slightly lower -- but still at least 1 second -- for a small screen and a menu. Increases with larger screens, smaller objects. Ranges from .21 second for cursor keys to .36 second for a mouse. Varies with intensity, from .05 second for a bright light to .2 second for a dim one. A typical item might be a command abbreviation ("dir"). Time is roughly halved if the same item needs to be retrieved again immediately. May be less under some circumstances, but most research shows 10 to 15 seconds as a minimum. None of these figures include the time needed to get started in a training situation. Ranges from .05 to .1 second, depending on what kind of mental step is being performed. Ranges from .06 to at least 1.8 seconds, depending on complexity of factors influencing the decision. 170
A full-blown formal analysis of a complex interface is a daunting task. The example and the size of the time values in the table should give some idea of why this is so. Imagine you want to analyze two designs for a spreadsheet to see which is faster on a given task. The task is to enter some formulas and values, and you expect it to take the skilled user on the order of 10 minutes. To apply the formal action analysis approach you'll have to break the task down into individual actions, most of which take less than a second. That comes out to around 1000 individual actions, just to analyze a single 10-minute task! (There will probably be clusters of actions that get repeated; but the effort is still nontrivial.) A further problem with formal analysis is that different analysts may come up with different results, depending on how they see the task hierarchy and what actions they predict a user will take in a given situation. (Will the user scan left, then down the spreadsheet? Down then left? Diagonally? The difference might be seconds, swamping other details.) Questions like this may require user testing to settle. Because it is so difficult, we think that formal action analysis is useful only in special circumstances -- basically, when its high cost can be justified by a very large payoff. One instance where this was the case was the evaluation of a proposed workstation for telephone operators (see the article by Gray et al listed in Credits and Pointers, below). The phone company contracting the action analysis calculated that a savings of a few seconds in a procedure performed by thousands of operators over hundreds of thousands of calls would more than repay the months of effort that went into the evaluation. Another place formal action analysis can be effective is for segments of the interface that users will access repeatedly as part of many tasks. Some examples of this are choosing from menus, selecting or moving objects in a graphics package, and moving from cell to cell within a spreadsheet. In each of these examples, a savings of a few tenths of a second in an interaction might add up to several minutes during an hour's work. This could justify a detailed analysis of competing designs. In most cases, however, a few tenths of a second saved in performing an action sequence, and even a few minutes saved in learning it, are trivial compared to the other aspects of the interface that we emphasize in this book. Does the interface (and the system) do what the user needs, fitting smoothly into the rest of the user's work? Can the user figure out how the interface works? Does the interface's combination of controls, prompts, warning messages, and other feedback allow the user to maintain a comfortable "flow" through a task? If the user makes an error, does the system allow graceful recovery? All of these factors are central, not only to productivity but also to the user's perception of the system's quality. A serious failure on any of these points is not going to be countered by shaving a few seconds off the edges of the interface. b. Back-of-the-Envelope Action Analysis The back-of-the-envelope approach to action analysis foregoes detailed predictions in an effort to get a quick look at the big picture. We think this technique can be very valuable, and it's easy to do. Like the formal analysis, the back-of- the-envelope version has two 171
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] NATIONAL OPEN UNIVERSITY OF NIGER
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National Open University of Nigeria
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Summary ...........................
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UNIT 3 - GRAPHICAL USER INTERFACE (
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Assignments File Tutor-Marked Assig
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2 DESIGN and DESIGNING GOOD USER IN
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need both the study unit you are wo
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CIT 711: USER INTERFACE DESIGN AND
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UNIT 1 FUNDAMENTALS OF USER INTERFA
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3.3 TYPES OF USER INTERFACES Curren
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3.5 USER INTERFACE MODALITIES AND M
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Table of Contents 1.0 Introduction
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3.1.1 DESIGNING A GOOD USER INTERFA
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widgets properly is to read and und
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Figure 1:- Showing that alignment o
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6.0 TUTOR MARKED ASSIGNMENT a. How
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A graphical user interface is a typ
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Operating System. It is easy for a
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A list of items from which to selec
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collaborative work. For example, sc
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MODULE 1 UNIT 4 HUMAN COMPUTER INTE
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3.3 DIFFERNCES WITH RELATED FIELDS
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window blinds to automobile braking
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Wickens, Christopher D., John D. Le
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The International Ergonomics Associ
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approach, the Gilbreths reduced the
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3.6 BENEFITS OF ERGONOMICS The thre
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Another key to reducing lumbar disc
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MODULE 2 - USER INTERFACE DESIGN TE
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methods include inspection methods,
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Determine time of each operation (b
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unable to understand new informatio
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M cones, or, misleadingly, green co
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Motor skill which is a learned seri
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MODULE 2 UNIT 2 UNDERSTANDING USERS
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The users of a system must be ident
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This example brings up an important
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whether you want to have a palette
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Task analysis which includes identi
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MODULE 2 UNIT 3 USER CENTERED DESIG
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or small body text is also hard to
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Introduction to User-centered desig
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organizations themselves. Interacti
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After thorough analysis using vario
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Interaction design which is the dis
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In human-computer interaction and c
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The preferred method for ensuring u
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3.4 ISO STANDARDS FOR USABILITY ISO
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In this unit, you have been introdu
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affect the way the command is execu
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• Guides the user via the predefi
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The term direct manipulation was in
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There are two important reasons for
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UNIT 1 PROTOTYPING Table of Content
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Figure 12: The iterative steps of p
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select print Figure 13: An interfac
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Ambler, S.W. & Constantine, L.L. (2
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3.2 LOW-FIDELITY PROTOTYPES Low-fid
Page 120 and 121: Figure 14:- Example of Sketching II
Page 122 and 123: Much more important for features th
Page 124 and 125: DENIM, an extension of SILK, is a t
Page 126 and 127: • Encourage menu & forms style, r
Page 128 and 129: Another problem is that native widg
Page 130 and 131: interfaces, so that a realistic sim
Page 132 and 133: UNIT 3 INPUT AND OUTPUT MODELS Tabl
Page 134 and 135: Recall that perceptual fusion means
Page 136 and 137: 3.2 OUTPUT MODEL There are basicall
Page 138 and 139: directly-mapped pixel image will no
Page 140 and 141: Most stroke models also include som
Page 142 and 143: UNIT 4 MODEL VIEW-CONTROLLER (MVC)
Page 144 and 145: 3.3.2 AS A DESIGN PATTERN MVC enco
Page 146 and 147: The Views are XForms controls for s
Page 148 and 149: UNIT 5 LAYOUTS AND CONSTRAINTS Tabl
Page 150 and 151: 3.5 CONSTRAINTS Constraints are rel
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Page 154 and 155: MODULE 4 UNIT 1 TECHNIQUES FOR EVAL
Page 156 and 157: a. Card Sorting Card sorting is a w
Page 158 and 159: Rapid prototyping is a method used
Page 160 and 161: 3.2.1 THE USE OF PROTOTYPES It is o
Page 162 and 163: Dumas, J.S. and Redish, J.C. (1999)
Page 164 and 165: the users' respect for you as a pro
Page 166 and 167: the users will be and what kind of
Page 168 and 169: speed whenever the average load was
Page 172 and 173: phases: list the actions, and then
Page 174 and 175: Nielsen and Molich used their own e
Page 176 and 177: 7.0 REFERENCES AND FURTHER READING
Page 178 and 179: users. If you do not, you can be ba
Page 180 and 181: If you are led to develop more and
Page 182 and 183: It's very easy to shape the comment
Page 184 and 185: a. Analyzing the Bottom-Line Number
Page 186 and 187: you use. But then you need some way
Page 188 and 189: ecruit test users with more similar
Page 190 and 191: MODULE 4 UNIT 4 OTHER EVALUATION IS
Page 192 and 193: 3.2 CURRENT ISSUES CONCERNING EVALU
Page 194 and 195: 2.0 OBJECTIVES By the end this unit
Page 196 and 197: It provides a real focal point for
Page 198 and 199: 3.3.4 CONDUCTING THE TEST Having co
Page 200: The stages involved in usability te
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