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

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Chapter 3 The interaction 3.2.3 The interaction framework Page 108

Conversely, an example of a good mapping is in virtual reality systems, where novel input devices such as datagloves are specifically geared towards easing articulation by making the user's psychological notion of gesturing an act that can be directly realized at the interface. Direct manipulation interfaces, such as those found on common desktop operating systems like the Macintosh, make the articulation of some file handling commands easier. On the other hand, some tasks, such as repetitive file renaming or launching a program whose icon is not visible, are not at all easy to articulate with such an interface.

Chapter 3 The interaction 3.2.3 The interaction framework Page 108

Ultimately, the user must interpret the output to evaluate what has happened. The response from the Output is translated to stimuli for the User which trigger assessment. The observation translation will address the ease and coverage of this final translation. For example, it is difficult to tell the time accurately on an unmarked analog clock, especially if it is not oriented properly. It is difficult in a command line interface to determine the result of copying and moving files in a hierarchical file system. Typesetting a report using one of the popular typesetting programs available today is made virtually impossible without some previewing facility which allows rapid (and tree-saving) feedback to assess progress.

Chapter 3 The interaction 3.3 Frameworks and HCI Page 109

In particular, the field of ergonomics addresses issues on the user side of the interface, covering both input and output, as well as the user's immediate context. Dialog design and interface styles can be placed particularly along the input branch of the framework, addressing both articulation and performance. However, it is most usually associated with the computer and so is biased to that side of the framework. The entire framework can in turn be placed within a social and organizational context that also affects the interaction. Each of these areas has important implications for the design of interactive systems and the performance of the user. We will introduce them briefly in the following sections. In Figure 3.3 these aspects are shown as they relate to the interaction framework. This clearly shows that we must also consider the presentation arrow at the upper left. We will thus discuss issues of screen design and layout in Section 3.7.

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 3.4.1 Arrangement of controls and displays Page 111

In addition to the organization of the controls and displays in relation to each other, the entire system interface must be arranged appropriately in relation to the user's position. So, for example, the user should be able to reach all controls necessary and view all displays without excessive body movement. Critical displays should be at eye level. Lighting should be arranged to avoid glare and reflection distorting displays. Controls should be spaced to provide adequate room for the user to manoeuvre.

Chapter 3 The interaction 3.4.2 The physical environment of the interaction Page 112

As well as addressing physical issues in the layout and arrangement of the machine interface, ergonomics is concerned with the design of the work environment itself. Where will the system be used? By whom will it be used? Will users be sitting, standing or moving about? Again, this will depend largely on the domain and will be more critical in specific control and operational settings than in general computer use. However, the physical environment in which the system is used may influence how well it is accepted and even the health and safety of its users. It should therefore be considered in all design.

Chapter 3 The interaction 3.5 Interaction styles Page 115

Interaction can be seen as a dialog between the computer and the user. The choice of interface style can have a profound effect on the nature of this dialog. Dialog design is discussed in detail in Chapter 8. Here we introduce the most common interface styles and note the different effects these have on the interaction. There are a number of common interface styles including

Chapter 3 The interaction 3.5 Interaction styles Page 115

command line interface

Chapter 3 The interaction 3.5 Interaction styles Page 116

three-dimensional interfaces

Chapter 3 The interaction 3.5 Interaction styles Page 116

As the WIMP interface is the most common and complex, we will discuss each of its elements in greater detail in Section 3.6.

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