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

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Chapter 1 The human 1.1 Introduction Page 12

In this chapter we will look at areas of human psychology coming under the general banner of cognitive psychology. This may seem a far cry from designing and building interactive computer systems, but it is not. In order to design something for someone, we need to understand the capabilities and limitations of that person. We need to know if there are things that person will find difficult or, even, which they will not be able to do at all. It will also help us to know what people find easy and how we can help them by encouraging these things. We will look at aspects of cognitive psychology which have a bearing on the use of computer systems: how humans perceive the world around them, how they store and process information and solve problems, and how they physically manipulate objects.

Chapter 1 The human 1.1 Introduction Page 12

We have already said that we will restrict our study to those aspects which are relevant to HCI. One way to structure our discussion of these areas is to view the user in a way which highlights the aspects in which we are most interested. In other words, to think of a simplified model of what is actually going on. Many models have been proposed and it useful to consider one of the most influential in passing, to understand the context of the discussion that is to follow. In 1983, Card, Moran and Newell [37] described the Model Human Processor, which is a simplified view of the human processing involved in interacting with computer systems. The model comprises three subsystems: the perceptual system, handling sensory stimulus from the outside world, the motor system, which controls actions, and the cognitive system, which provides the necessary processing to connect the two. Each of these subsystems has its own processor and memory, although obviously the complexity of these in each case varies depending on the complexity of the tasks the subsystem has to perform. The model also includes a number of principles of operation which dictate the behaviour of the systems under certain conditions.

Chapter 1 The human Long-term memory processes Page 35

This leads us to the third process of memory: information retrieval. Here we need to distinguish between two types of information retrieval, recall and recognition. In recall the information is reproduced from memory. In recognition, the presentation of the information provides the knowledge that the information has been seen before. Recognition is the less complex cognitive activity since the information is provided as a cue.

Chapter 1 The human 1.5 Individual differences Page 48

These differences should be taken into account in our designs. It is useful to consider, for any design decision, if there are likely to be users within the target group who will be adversely affected by our decision. At the extremes a decision may exclude a section of the user population. For example, the current emphasis on visual interfaces excludes those who are visually impaired, unless the design also makes use of the other sensory channels. However, on a more mundane level, designs should allow for users who are under pressure, feeling ill or distracted by other concerns: they should not push users to their perceptual or cognitive limits.

Chapter 1 The human 1.6 Psychology and the design of interactive systems Page 48

In this chapter we have looked briefly at the way in which humans receive, process and store information, solve problems and acquire skill. But how can we apply what we have learned to designing interactive systems? Sometimes, straightforward conclusions can be drawn. For example, we can deduce that blue should not be used for conveying important detail since it is most difficult for the user to perceive. However, in the majority of cases, application is not so obvious or simple. In fact, it may be dangerous, leading us to make generalizations which are not valid. In order to apply a psychological principle or result properly in design, we need to understand its context, both in terms of where it fits in the wider field of psychology and in terms of the details of the actual experiments, the measures used and the subjects involved, for example. This may appear daunting, particularly to the novice designer who wants to acknowledge the relevance of cognitive psychology but does not have the background to derive appropriate conclusions. Fortunately for such a designer, principles and results from research in psychology have been distilled into guidelines for design, models to support design and techniques for evaluating design. The second part of this book is concerned in part with how such guidelines, models and techniques can be used to support the design process.

Chapter 1 The human 1.6.1 Guidelines Page 49

Throughout this chapter we have discussed the strengths and weaknesses of human cognitive and perceptual processes but, for the most part, we have avoided attempting to apply these directly to design. This is because such an attempt could only be partial and simplistic, and may give the impression that this is all psychology has to offer.

Chapter 1 The human 1.6.2 Models to support design Page 49

As well as guidelines and principles, psychological theory has led to the development of analytic and predictive models of user behaviour. Some of these include a specific model of human problem solving, others of physical activity, and others attempt a more comprehensive view of cognition. Some predict how a typical computer user would behave in a given situation, others analyze why particular user behaviour occurred. All are based on cognitive theory. We discuss these models in detail in Chapter 6.

Chapter 1 The human 1.7 Summary Page 51

Human perception and cognition are complex and sophisticated but they are not without their limitations. We have considered some of these limitations in this chapter. An understanding of the capabilities and limitations of the human as information processor can help us to design interactive systems which support the former and compensate for the latter. The principles, guidelines and models which can be derived from cognitive psychology and the techniques which it provides are invaluable tools for the designer of interactive systems.

Chapter 1 The human Exercises Page 51

1.3 From what you have learned about cognitive psychology devise appropriate guidelines for use by interface designers. You may find it helpful to group these under key headings, for example visual perception, memory, problem solving, etc., although some may overlap such groupings.

Chapter 1 The human Recommended reading Page 51

M. W. Eysenck and M. T. Keane, Cognitive Psychology: A Student's Handbook, Lawrence Erlbaum Associates, 1990.

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