Prologue
This chapter concludes the thesis, summarising and assessing the work done.
Contents
1. Introduction 2. Summary
2.1. The Job Attributes
2.2. The Behavioural Phenomena 2.3. The Model
3. The Achievement of the Original Goals 3.1. The Model 3.1.1. As a Scientific Device 3.1.2. As an Engineering Device 3.2. The Method 4. General Assessment 5. In Conclusion
1. Introduction
This is the final chapter in the thesis and is therefore concerned with both
summarising and assessing the work reported in earlier chapters. In addition, there will be a commentary in the form of some related points from the literature.
The first section presents a summary of the complete set of Job Attributes, the
complete set of Behavioural Phenomena, and the Model itself. Later sections are then concerned with assessment in two different ways. Firstly, there is an assessment of the model, as a product, with respect to the goals originally set out at the beginning of the thesis. This is followed by an assessment of the method both as it relates to the achievement of these goals and otherwise. Secondly, there is a more general assessment of the model and the contributions made by the thesis to Cognitive Ergonomics.
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2 . Summary
This section summarizes the Job Attributes, the Behavioural Phenomena and the Model. It is necessary to summarize the Job Attributes because they represent the scope of the model and the definition of the conceptual variable of multitasking. It was stated in the discussion of models in Chapter 2 that a model ought to be accompanied by such a statement of its intended scope.
The Model is summarised here since its most recent full description was in Chapter 5. The Behavioural Phenomena are restated here for completeness.
2 . 1 . The Job Attributes
The expression of the JAs which has developed in the course of the thesis is really one of six classes of properties, each of which represents a number of states. This scheme will be maintained here also.
The first, and most important, JA concerns the role of the person. This replaced the requirement for there to be interleaving. The additional JAs could be thought of as secondary to this one, providing for the differences in the various instances of multitasking. To understand this JA, it is necessary to understand the conception of tasks upon which it is based. This conception is also crucial to understanding the model, which follows in a section below, and is therefore presented here, once. In the conception, the world is taken to consist of objects. Objects have attributes, which in turn may be in a number of different states. An example of an object might be a floppy disk for a computer, which could have attributes specifying whether it had been formatted and whether it was locked, amongst others. Attributes of objects can exhibit affordances for change of state. Changes in the state of an attribute are accomplished by a task. In the example, the task of formatting a disk would change the state of the formatted attribute from unformatted to formatted. Probably the most important part of the conception concerns that which is thought to accomplish this state change. Resources are objects which are required in a transformation, but are not themselves transformed. In the example, a disk drive would be a resource required for formatting a disk (amongst other things). The person in such a world is conceived of as having two roles. Firstly they are an effector - that is to say they are modelled as a resource. Secondly, they have a control role, responsible for managing the allocation of all the other resources to all the necessary tasks.
The first JA takes, as its starting point, a need for attribute state transformations of more than one object to be going on in parallel. This is then further qualified in terms of the role of the person under consideration, such that they may have differing
degrees of control and/or effect roles in these transformations. It is proposed that for a job to be considered as multitasking for the purposes of the model, there should be at least a high control role.
The other JAs specifying the scope of the model are then as follows (in no particular order):
• Cooperation requirement. The presence of other people with whom it is necessary to coordinate one’s activities has implications for multitasking behaviour. This could range from being the only person present, through coordination concerned with different people being responsible for successive stages o f tasks, to the extreme of sharing the pool of pending tasks with a number of others in a non demarcated way.
• Reliability of the world. Efficient multitasking requires some advance planning. This JA concerns the degree to which such planning is possible. The behaviours of objects in the world could vary in their reliability.
• Familiarity of the person with the individual tasks. It was proposed early on that, because of the requirement to plan ahead, the person should be familiar with the tasks to be interleaved. This is arbitrary, but the model at present does not address behaviour arising from inexperience. This obviously has similarities with the previous JA, since experience is often required to be able to predict the behaviour of objects.
• Familiarity of the person with the particular task set. Although it may be the case that the person has experience with the individual tasks, they may not have experienced the particular combination before. This could have implications for their anticipation behaviour.
• Cost associated with error. In a world which is predictable to differing degrees by a particular individual, the cost associated with erroneous decisions is thought to have important consequences for multitasking behaviour.
The JAs constitute the terms of the definition of the scope of the model and so provide a framework by which different instances of multitasking behaviour can be identified, compared, and related to the model.
2 . 2 . The Behavioural Phenomena
The following is the complete set of Behavioural Phenomena associated with
multitasking, as proposed in the thesis. Each is accompanied by a short explanation, and they are in no particular order. It should be noted that it is envisaged that only a
subset of these phenomena will be apparent in any given instance of multitasking (see Chapter 2).
• Interleaving. It is observed that people are capable of controlling several tasks in parallel.
• Planning ahead. There is evidence to suggest that people are able to plan and coordinate the interleaving of tasks.
• Limited capacity of the Mental Workspace. The person is modelled as two
resources (see next section). It is inferred from behaviour that the person is limited to being able to think about one task at once.
• Limited capacity of the Performance System. As above, it is similarly maintained that, mainly, the person can only be physically concerned with a single task at a time.
• Parallel Mental and Physical Activity. It is observed that a person can be physically concerned with one task and at the same time mentally concerned with another. • Two stage interruption. Interruption is sometimes handled in two stages. The first
of these is concerned with finding out more about the new task, and is thought to be minimally disruptive. This information enables the person to potentially delay the second stage of the interruption - i.e. actually doing what is required - until some more suitable time.
• Partial, incomplete, plans. Although it is observed that people do plan their activities, they do not construct elaborate, complete plans, or at least they do not voice them. Instead, the plans tend to be at a higher level and varying in detail. • Some tasks done in passing. This phenomenon is thought to be closely related to
that of only forming partial plans (above). It refers to the observation that while there is some planning in advance of what to do, other behaviour is not anticipated and arises opportunistically according to the circumstances in which a person finds him or herself.
• Some information bound to plans. It is thought that it is necessary to mentally simulate the performance of some tasks in order to remember important details. Mentally executing a task in advance and thus making these points explicit has implications for planning the coordination of tasks.
• Free time. It is observed that people can be (correctly) aware of when there is nothing for them to do. This is important since it implies an awareness of all the tasks for which they are required and when they will be done.