User-centered interface design

In this subsection, I pay attention to what is generally known as user-centered human-computer interface design. Next to a positive attitude toward interfaces, and the acceptance of the notion that a user has some goal he tries to accomplish, I show how the growth of the user population has led to the more balanced perspective of human-computer interface instead of user interface. Especially significant for user-centered interface design is the upcoming of the field of Human-computer interaction (or HCI for short). Finally, I make clear how user-centered design is achieved by involving users and taking their needs into account throughout the design process.

A positive attitude toward interfaces

As a first step on the way to user-centered human-computer interface design, I like to take the opportunity to preach a positive attitude toward interfaces. From a rather negative point of view, the interface defines the boundary between the human being and the computer application he uses. Or, as Norman [1990] explains, the real problem with the interface is that it is an interface, and interfaces get in the way. A boundary can be set up easily. A more positive point of view is the notion of common ground. Or, as Laurel [1993] puts it, an interface is not simply the means whereby a person and an application represent themselves to one another; rather it is a shared context for action. The interface must at all time reflect the progress that is made. Therefore it is essential that the common ground, the shared information, remains up to date. Accumulation of the common ground should be an interactive process between human and interface.

Not only is this attitude more positive, it is also more difficult to accomplish. It means that the designer has to understand the user of its product thoroughly. That is, he has to be aware of the user's task and how the final result is normally achieved. The designer should put himself in the position of the envisioned user or communicate with his audience in order to thoroughly test his designs. Because this is difficult, it may turn out to be a costly affair. Although Nielsen [1993] claims that with engineering for usability cost savings may be gained.

From application to task

Laurel distinguishes three dimensions that describe a person's activity space. A person is task- oriented or goal-oriented: he pursues goals. In order to reach these goals, he has to fulfil numerous activities. In turn, activities are often accomplished by using computer applications like word processors, spreadsheets, drawing programs or database management systems.

Where the translation from goals into activities seems almost natural, the interpretation of activities into computer applications causes problems. First of all, not (yet) all activities are supported by computer applications. Think about activities, like cooperative work, that involve the exchange of rich information through high touch communication rather than impersonal, quantitative data. Possible solutions for these types of problems may be found in using multi media data types and corresponding human-computer interface techniques. According to Buxton [1991], multi media is simply design that makes better and broader use of the human's capabilities to receive and transmit information. The use of multi media may be accompanied by the improvement of the infrastructure for computer-mediated communication (networks). Second, although an application claims to support a certain task, it is likely that all sorts of particular mismatches cannot be alleviated by it.

According to Nielsen, the application model is constraining to users who must carry out complicated, integrated tasks: they require multiple applications. Hence they stumble across different human-computer interfaces. To meet this match, integrated programs were build. However, no single program is likely to satisfy all users. A different approach has proven more succesful: standardisation. By using overlapping subsets of identical tools, functions, and widgets in related applications, it is possible to gradually break down the application barrier and create a larger, more goal-oriented context. Well known examples are available on most popular hardware platforms: graphical interface widgets that formally specify the visual presentation of data and functions, cut-and-paste mechanisms, standard on-line help facilities, and dynamic linking capabilities. However, the basic application model that requires each document to belong to a specific application at any given time, still rules. The application model and a person's activities as the basic assumption for it, will eventually be left behind. The overall goal a person pursues will become the new starting point for building better suited, more usable computer systems.

From user to human

As yet another step on the way to user-centered design, I prefer to use the term human-computer interface in stead of user interface. As Grudin [1993] rightfully explains, it is time to drop 'user interface' and pick up this 'more balanced perspective' for three reasons:

• computer users do not consider themselves 'users'. Often, the word 'user' is seen as a negative characteristic, for example, as in 'drug user';
• the term 'user' retains and reinforces an engineering perspective. Yet, engineers are not the only ones using computers anymore;
• the term 'user' suggests that there exists a typical user or range of users. However, the user population is changing rapidly.

That other areas for computing arise, besides offices and factories, is clear. More computers find their way into the homes of families each year. Thus more different categories of 'users' must be taken into account (e.g., consider the kitchen interface which applies a kitchen as metaphor).

HCI stresses user-centered design

The largest step toward user-centered human-computer interface design is the upcoming of the field of Human-computer interaction or HCI, a true science of interface design, which was probably founded somewhere around the early eighties, when user interface practitioners and scientists (which they were before they became human-computer interface practitioners and scientists) first met to form themselves into a field in Gaithersburg, Maryland (in the USA) in March of 1982 at the first of what has become the annual CHI conference (Curtis and Hefley [1994]).

Norman [1986] refers to a 'science of interface design' as cognitive engineering. This requires, he states, some formal models of people and of interaction, models that need only be approximations, but that are precise enough to lead to design rules. He speaks of creating an entirely new discipline, one that combines two already complex fields: psychology and computer science. Further on, I point out that the number of fields contributing to HCI has grown already; it has become a true multidisciplinary field of research.

Prescriptions for design principles

Also, Norman mentions a number of prescriptions for design principles which I find particularly useful:

• Create a science of user-centered design. As I already mentioned, for this, principles are needed that can serve as guidelines at the time of the design (that is: these should be applied before implementation).
• Take interface design seriously as an independent and important problem. In terms of Rudd and Isensee [1994] this means: become multidisciplinary! It takes at least three kinds of special knowledge to design an interface: first, knowledge of design, of programming, and of the technology; second, knowledge of people, of the principles of mental computation, of communication, and of interaction; and third, expert knowledge of the task that is to be accomplished. Not many people are likely to be specialists regarding all this knowledge. Thus, human-computer interface design is in essence a cooperative task (Kyng [1991]), more specific, an intellective group task in terms of McGrath [1984].
• Separate the design of the interface from the design of the system. This is the principle of modularisation in design. It allows the previous point to work. It is only the interface module, which incorporates the whole team's knowledge regarding interaction, that should be in communication with the user. Besides, modularisation allows the entire system to change without affecting the interface and vice versa. Thus, iterative design becomes possible without ever affecting the functional core subsystem. Also in The COOPerator, we have separated the interface from its functional core subsystem.
• Do user-centered system design: Start with the needs of the user. The important thing to keep in mind, is that from the point of view of the user of the system,

  the interface is the system!

  Norman suggests to let the requirements for the interaction drive the design of the interface whereas the ideas about the interface should, in turn, dominate the design of the rest of the system.

Though so far the importance of computer science and (cognitive) psychology are emphasized, HCI incorporates a number of other disciplines.

Contributors to HCI

HCI is a multidisciplinary field. The main contributions come from computer science, cognitive psychology, and ergonomics and human factors. However, other areas of interest include artificial intelligence, (graphic) design, engineering, and even psychology, sociology, and anthropology:

Moreover, Laurel shows the similarities between theatre and human-computer interaction and Staples [1993] shows that visual arts and art history can contribute significantly to the insights within the field.

Principles for user-centered design

Norman's principles were conceptual in nature; they reside on a fairly high level. In this section, I want to pay attention to lower-level, practical principles for involving users in human-computer interface design. Preece [1993] mentions the following:

• Early design is dominated by collecting and synthesizing information about users' needs and capabilities. The main techniques for obtaining this information are:
  • Requirements analysis; in this stage, information is typically acquired by using interviews and questionnaires or by observing and analysing current practice.
  • Task analysis; in this analysis, details of the user's task and information about the task environment is collected, so that the user's needs are well understood. Preece distinguishes macro methods, in which the whole system is analysed in terms of organisational, social, and environmental aspects, from micro methods in which discrete tasks are decomposed into hierarchical structures and finally into small cognitive units. Examples of the latter include the well-known GOMS family of models (Goals, Operators, Methods, and selection Rules) and TAG (Task-Action Grammar).
  • Usability tests; when usability testing is integrated into the design cycle by being quantitatively specified in advance, it is known as usability engineering (Nielsen). Otherwise, this technique is often applied for evaluation purposes to provide information for upgrading and maintenance of existing systems.
• The conceptual design of an interface generally involves creating sketches of screens which demonstrate surface features of the system. Again, these can be tested with users to establish their appropriateness, for example, to check that the right metaphor was used.
• As the design process develops, the design will be transformed through various forms of specification (e.g., a natural language description or all sorts of diagrams, or even some form of non-executable prototype that is presented with video equipment) and prototypes.

Nowadays, these principles are incorporated into many design methodologies or user-centered design cycles, like Lee's [1994] life-cycle approach for object oriented graphical user interface development, Nielsen's usability engineering lifecycle, Barfield's [1993] design framework, and the iterative model shown here which was adapted from Preece.