This is the sixth of nine parts.
1. Introduction.
2. The cognitive processing element.
3. Ways of meeting the cognitive needs.
4. 'Sequencers' and the contextual overview in working storage.
5. Working storage : updating and capacity.

Lisanne Bainbridge

Another important aspect of behavioural flexibility is the way in which different working methods can be used to meet a given goal or need, depending on the circumstances. For example, the steelworks operator sometimes obtained a numerical value by calculation, sometimes by judgement. So there must be some mechanism which can choose whatever working method is most appropriate at a particular moment. So far, the stepped arrow part of the cognitive element has just been used as a symbol for : to meet this need use this method ('routine'). The stepped arrow actually represents a decision mechanism which deals with flexibility in how a given need is met, and has other interesting powers. The notion is that the cognitive need and the working method for meeting it are independent, and that the link between them is the point of choice between working methods, by comparing meta-knowledge about the methods with the context at the particular moment. The place of this link in the control of mental workload is discussed in below, part 6.3. The way in which it might be expanded to account for multitasking is noted below, part 6.4. Its possible role in learning is discussed in Section 7.

6.1. Choice based on meta-knowledge

The mechanism suggested here is that each working method has associated with it meta-knowledge about its properties, for example how long it takes, how accurate its result is, how much mental effort it takes, etc. This meta-knowledge about the method is then compared with the context (which is in working storage) : how much time and mental effort are available, what level of accuracy is required, etc., as a basis for choosing the method which has the best fit to the present situation. For a working method to be usable for many purposes, especially in contexts in which it has not been used before, its meta-knowledge would also need to include data about the general nature of the outcomes that can be obtained by using it. Which dimensions of meta-knowledge are needed will depend on what is important at this point, see Section 7, part 7.2.1.

The stepped arrow in the processing element diagrams represents the point at which the choice between alternative working methods is made. Figure 6.1.1 gives a simple example. In his verbal protocol the furnace operator, when predicting the power usage after a change in the steel-making stage a furnace was in, sometimes made this prediction by judgement and sometimes by calculation. Figure 6.1.1 suggests some of the dimensions the operator might consider in choosing between these two methods. Note that in the operator's verbal protocols there was explicit evidence that an operator used different methods for doing the same task, but there was no direct evidence about how the choice between them was made. Figure 6.1.1 is based on analyst's inference. When there is no direct mention of this decision in the verbal protocols, this could suggest that the decision is made unconsciously.

Figure 6.1.1 : Obtaining a quantitative answer, the choice between calculation and judgement (Bainbridge, 1975, Figure 2).


Two important additions are needed to Figure 6.6.1. Firstly it is useful (see below, part 6.3) to distinguish between task related dimensions of the meta-knowledge about a working method (e.g. what accuracy of result it gives) and personal dimensions of the meta-knowledge (e.g. how difficult the person finds it to do, or their expectation of success). Secondly, it is suggested that a working method is chosen by comparing this meta-knowledge about the alternatives with dimensions of the context in working storage : for example, how much mental effort the person is willing to make, how much time is available, what accuracy is required. Table 6 describes the same example as in Figure 6.1.1, but expanded to include these two aspects.

Dimensions of meta- knowledge	Potential utilities and costs		Actual values in present context (in working storage) which must be matched
	CALCULATION	JUDGEMENT
	TASK : referring to task demands
time needed	3 operations	1 operation (consciously experienced)	amount of time available
accuracy provided	high accuracy	low accuracy	level of accuracy required
	SELF : referring to effort for operator
mental ability required	arithmetic required	easy after practice	nature of mental operations person can do
working storage capcity required	2 items in working storage	no need for working storage (assumption)	amount of working storage capacity currently available

Table 6 : A tabular representation of the knowledge in Figure 6.1.1 (adapted from Bainbridge, 1978, Table 1).

Figure 6.1.2 gives a fuller instance. Rasmussen and Jensen (1974) found that electronic maintenance technicians used three alternative strategies for doing their fault diagnosis, and Rasmussen and Jensen suggest reasons why the technicians might choose between these strategies. Figure 6.1.2 represents the choice between two of the strategies, using the mechanism proposed here. It shows two strategies, each with three properties which are compared with dimensions of the context at the time of choice. This mechanism was suggested in Bainbridge, 1975.

Figure 6.1.2 : The choice between topographic and functional strategies for fault diagnosis (Bainbridge, 1992, Figure 5) (based on evidence in Rasmussen and Jensen, 1974).


These points suggest several additional theoretical considerations. If the choice between methods is made by comparing meta-knowledge with the task context, this expands the notion of context used in previous Sections, to include not only aspects related to task needs, such as how urgent it is to make an action or what accuracy is needed, but also aspects describing personal needs, such as how much effort the person feels like making, or how much they want to succeed.

The choice mechanism, with its parameters, could then be the locus of operation for several personal effects. For instance, the 'self' aspects considered by someone when choosing a way of doing things could include whether it is amusing or interesting, as well as aspects of self-image such as expectation of success, learned helplessness, fear of failure or success, and other emotions.

A decision mechanism is needed, for comparing the meta-knowledge about methods with the context, and making a choice between methods. The use of context suggests that the two sorts of choice involved in adaptive behaviour which have been discussed (i.e. the choice of which part of the task to do next and the choice of how to do it) are made by interrelated mechanisms. Both choices involve comparison with the context, and similar dimensions (such as how urgent an action is) are involved in both choices. The contextual choice between cognitive needs, the choice about what part of the task to do next, has been described as being made by conditional elements in the 'sequencers' (Section 4). The contextual choice between working methods for meeting a given cognitive need has been described by conditional elements in a 'routine' (Section 4, part 4.6) or by multidimensional comparison of meta-knowledge (above). These are not necessarily two distinct types of decision mechanism. The conditional elements in a 'sequencer' actually carry out multidimensional comparisons, but in a way which has several advantages which are described in Section 4, part 4.3. It is possible that the meta-knowledge decisions could also use this double mechanism, of referring to the available data in parallel, or using a working method to find missing meta-knowledge if necessary.

6.2. Goal-means independence

If there can be several methods for meeting any one cognitive need, this means that the cognitive need and the means for meeting it are independent (except as discussed in Section 7, part 7.3). The stepped arrow represents a point at which there is a choice about how to meet the cognitive need named in an element. The need and the means for meeting it (the 'routine' or, more generally, the working method) are independent. This independence leads to the mechanism having at least four useful and important properties.

1. It allows the potential for adapting the working method used to the circumstances. Any one need can be met by several working methods, and any one method can be used to meet several needs or purposes. For example, if one wants to hammer a nail in, and a hammer is not available, then anything heavy and solid can be used instead. And a hammer is not only useful for hammering nails in, it can also be used for pulling nails out or as a paperweight.

2. If the working method and the need for which it is used are independent, then it is important to store the result of using a method with the need, rather than with the method. Then the method can be used for other purposes. This occurs in the cognitive element mechanism, as the results of the main 'routines' are stored in the overview structured by the 'sequencers'.

3. A given need is only expanded into a method for meeting it at the time it is considered, to allow for the specific circumstances at that time. This expansion into 'lower' levels of greater detail is not permanently fixed in a hierarchy (though see Section 7, part 7.3). The items are stored as a heterarchy or network of potential links. The hierarchical nature of behaviour organisation, into different levels of detail, is an emergent property of this network, one which appears when the behaviour is carried out rather than being fixed in advance, as suggested in Figure 6.2.

Figure 6.2 : Items stored independently appear as a hierarchy when used.

4. Behaviour may therefore be actively controlled at multiple levels simultaneously.

This paper will now discuss how this link point, at which working methods are chosen, can be a powerful mechanism in the control of mental workload and multitasking (below) and in the control of learning and the choice of mode of processing (Section 7).

6.3. Control of mental workload

It is possible to suggest that this choice between alternative working methods, using meta-knowledge about alternative working methods, accounts for two aspects of mental workload :
how mental workload is maintained at an acceptable level when task workload changes.
the way in which mental effort decreases with increased skill. This will be mentioned in Section 7, part 7.3.

Sperandio (1972) discovered that people change their working methods to keep their mental workload within limits. He found that air-traffic controllers could use two strategies to bring aircraft into the airport. The strategies differed in the amount of mental effort required to handle one aircraft. When there were more aircraft to bring in, the controllers changed to the strategy which required less mental work per aircraft, thus maintaining their overall mental workload at a steady level while the task workload increased. Sperandio summarised this finding as in Figure 6.3.1. So there is not necessarily a monotonic relation, or direct mapping, between task demands, mental workload and task performance, as there is in physical work. This means it is important to distinguish between these three when discussing mental workload.

Figure 6.3.1 : Effect of changing working method on relation between task demands and mental workload (Bainbridge, 1974b, Figure 1, adapted from Sperandio, 1972).

The (unconscious) mechanism of meta-knowledge plus choice could produce this adaptive behaviour. Suppose that the controller uses meta-knowledge about task aspects to choose a working method which meets the performance demands imposed by the task. This adjustment is summarised in Figure 6.3.2. Suppose also that the controller uses meta-knowledge about self-related aspects to choose a strategy which keeps the amount of mental work done to within unstressful limits. This adjustment is summarised in Figure 6.3.3. The process of coming to a balance between the two demands, of meeting the task performance requirements while keeping mental workload within acceptable limits, is then summarised in Figure 6.3.4. The basis for the actual mechanism is illustrated in Table 6. The overall result of the operation of this mechanism can be described in several ways. The overall outcome which emerges from this mechanism, described as the interaction between the factors involved, is represented in Figure 6.3.4 The overall outcome which emerges from this mechanism, described as the relation between task demands and mental workload, is represented in Figure 6.3.1.

Figure 6.3.2 : The adaptation of performance to task demands, via choice of working method (Bainbridge, 1974b, Figure 2).

Figure 6.3.3 : The adaptation of mental work done to available mental capacity, via choice of working method (Bainbridge, 1974b, Figure 3).

Figure 6.3.4 : The balancing of working method to meet both task demands and mental capacity (Bainbridge, 1974b, Figure 4).

The choice of how to do something could interact with the choice of what to do next. For example, someone might choose to do something only if a method for doing it was available which could be done in the time available. This interaction of what and how might account for some errors human errors in behaviour organisation, such as when people under stress do what they find easiest rather than what has the highest priority.

This sort of account could presumably be expanded to include multiple resources. There is also the possibility that this choice point could be the locus of operation for various aspects of behaviour which are studied in other areas of applied psychology, such as the effect of motivation and satisfaction on performance, in industrial psychology, or the effect of fear of failure and fear of success, in clinical psychology.

6.4. Multitasking

Multitasking involves interleaving several different tasks at the same time. Doing this requires a mechanism which can choose which part of which task to do next, on the basis of their urgency, importance, pertinence, etc.

Two areas of choice have been described in this paper :
the choice between different parts of the same task, between different main cognitive needs,
the choice between different ways of doing the same task, of meeting the same need.
These are both decisions which involve comparing the values of several dimensions against the prevailing context in working storage.

I have not yet worked out an explicit example of how the mechanisms proposed in this paper could be expanded to deal with multitasking. However, I would take these choice mechanisms as the starting point. I assume that the choice of what to do next within one main task, and the choice of which part of which task to do next when multi-tasking, are done by very similar mechanisms.

Amalberti (1992) has developed a meta-knowledge based mechanism for doing multitasking, in relation to planning, which I hope is compatible with the ideas presented in the present paper.

Summary of main points in Section 6

* The cognitive need and the working method for meeting it are independent. This independence means that several working methods might be used to meet one cognitive goal, or one working method might be used to meet several goals.
* Working methods ('routines') have stored with them meta-knowledge about their properties. Some of these properties are task-related, such as how long they take and their outcome, some are self-related, such as how difficult the person finds them to do..
* The best working method to use, for meeting a given cognitive need at a particular moment, is chosen by comparing the meta-knowledge with the context of the choice : how much time there is, how much effort the person is willing to put in, etc.
* The choice between working methods allows people to choose their working method so that their mental workload is maintained within acceptable limits.
* Working methods are not stored in a fixed hierarchy, but a hierarchy emerges in practice, as choices about how to meet cognitive needs are made at the time of use.
* The result of using a working method is stored with the cognitive need which called on it, rather than with the working method itself.

©1998 Lisanne Bainbridge