HUMAN-COMPUTER INTERACTION SECOND EDITION
Dix, Finlay, Abowd and Beale

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Chapter 1 The human Problem space theory Page 42

An important feature of Newell and Simon's model is that it operates within the constraints of the human processing system, and so searching the problem space is limited by the capacity of short-term memory, and the speed at which information can be retrieved. Within the problem space framework, experience allows us to solve problems more easily since we can structure the problem space appropriately and choose operators efficiently.

Chapter 2 The computer The QWERTY keyboard Page 57

The electric typewriter and now the computer keyboard are not subject to the original mechanical constraints, but the QWERTY keyboard remains the dominant layout. The reason for this is social -- the vast base of trained typists would be reluctant to relearn their craft, whilst the management is not prepared to accept an initial lowering of performance whilst the new skills are gained. There is also a large investment in current keyboards, which would all have to be either replaced at great cost, or phased out, with the subsequent requirement for people to be proficient on both keyboards.

Chapter 2 The computer 2.3.3 Keyboard-based positioning devices Page 68

Thumb-wheels are different in that they have two orthogonal dials to control the cursor position. Such a device is very cheap, but slow, and it is difficult to manipulate the cursor in any way other than horizontally or vertically. This limitation can sometimes be a useful constraint in the right application. For instance, in CAD the designer is almost always concerned with exact verticals and horizontals, and a device that provides such constraints is very useful, which accounts for the appearance of thumb-wheels in CAD systems. Another successful application for such a device has been in a drawing game such as Etch-a-Sketch in which straight lines can be created on a simple screen, since the predominance of straight lines in simple drawings means that the motion restrictions are an advantage rather than a handicap. However, if you were to try to write your signature using it, the limitations are all too apparent. The appropriateness of the device depends on the task to be performed.

Chapter 2 The computer 2.5.1 Printing Page 79

If anything, computer systems have made it easier to produce paper documents. It is so easy to run off many copies of a letter (or book), in order to get it looking 'just right'. Older printers had a fixed set of characters available on a printhead. These varied from the traditional line printer to golf-ball and daisy-wheel printers. To change a typeface or the size of type meant changing the printhead, and was an awkward, and frequently messy, job, but for many years the daisy-wheel printer was the only means of producing high-quality output at an affordable price. However, the drop in the price of laser printers coupled with other cheap high-quality printers means that daisy-wheels are fast becoming a rarity. All of the popular printing technologies, like screens, build the image on the paper as a series of dots. This enables, in theory, any character set or graphic to be printed, limited only by the resolution of the dots. This resolution is measured in dots per inch (dpi). Imagine a sheet of graph paper, and building up an image by putting dots at the intersection of each line. The number of lines per inch in each direction is the resolution in dpi. For some mechanical printers this is slightly confused: the dots printed may be bigger than the gaps, neighbouring printheads may not be able to print simultaneously and may be offset relative to one another (a diamond-shaped rather than rectangular grid). These differences do not make too much difference to the user, but mean that, given two printers at the same nominal resolution, the output of one looks better than that of the other, because it has managed the physical constraints better.

Chapter 2 The computer 2.6 Memory Page 89

The details of computer memory are not in themselves of direct interest to the user interface designer. However, the limitations in capacity and access methods are important constraints on the sort of interface which can be designed. After some fairly basic information, we will put the raw memory capacity into perspective with the sort of information which can be stored, as well as again seeing how advances in technology offer more scope for the designer to produce more effective interfaces. In particular, we will see how the capacity of typical memory copes with video images as these are becoming important as part of multimedia applications (see Chapter 15).

Chapter 3 The interaction 3.4 Ergonomics Page 110

Ergonomics (or human factors) is traditionally the study of the physical characteristics of the interaction: how the controls are designed, the physical environment in which the interaction takes place, and the layout and physical qualities of the screen. A primary focus is on user performance and how the interface enhances or detracts from this. In seeking to evaluate these aspects of the interaction, ergonomics will certainly also touch upon human psychology and system constraints. It is a large and established field, which is closely related to but distinct from HCI, and full coverage would demand a book in its own right. Here we consider a few of the issues addressed by ergonomics as an introduction to the field. We will briefly look at the arrangement of controls and displays, the physical environment, health issues and the use of colour. These are by no means exhaustive and are intended only to give an indication of the types of issues and problems addressed by ergonomics. For more information on ergonomic issues the reader is referred to the recommended reading list at the end of the chapter.

Chapter 3 The interaction 3.4.5 Ergonomics and HCI Page 115

Ergonomics is a huge area, which is distinct from HCI but sits alongside it. Its contribution to HCI is in determining constraints on the way we design systems and suggesting detailed and specific guidelines and standards. Ergonomic factors are in general more established and better understood than cognition and are therefore used as the basis for standardizing hardware designs. This issue is discussed further in Chapter 5.

Chapter 3 The interaction Exercises Page 139

3.2 Look at some or all of the following objects: a book, a pair of scissors, a cup, a corkscrew. Discuss the affordances of the objects and the constraints that these place on their use.

Chapter 5 The design process Detailed design Page 182

Typically, there will be more than one possible refinement of the architectural component which will satisfy the behavioural constraints. Choosing the best refinement is often a matter of trying to satisfy as many of the non-functional requirements of the system as possible. Thus the language used for the detailed design must allow some analysis of the design in order to assess its properties. It is also important to keep track of the design options considered, the eventual decisions that were made and the reasons why, as we will discuss in Section 5.6 on design rationale.

Chapter 5 The design process 5.2.2 Validation and verification Page 184

Proofs which are for verification of a design can frequently occur within one language or between two languages which both have a precise mathematical semantics. Time constraints for a design project and the perceived economic implications of the separate components usually dictate which proofs are carried out in full formality and which are done only rigorously (if at all). As research in this area matures and automated tools provide assistance for the mechanical aspects of proof, the cost of proof should decrease.

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