Editing Workload (section)

==Theory and modelling==
There is no one agreed definition of mental workload and consequently not one agreed method of assessing or modelling it.<ref name="Longo 2022"/> One example definition by Hart and Staveland (1988) describes workload as "the perceived relationship between the amount of mental processing capability or resources and the amount required by the task". A more generally applicable operational definition of workload is that "Mental workload (MWL) represents the degree of activation of a finite pool of resources, limited in capacity, while cognitively processing a primary task over time, mediated by external stochastic environmental and situational factors, as well as affected by definite internal characteristics of a human operator, for coping with static task demands, by devoted effort and attention".<ref name="Longo 2022"/>

Workload modelling is the analytical technique used to measure and predict workload. The main objective of assessing and predicting cognitive workload is to achieve an evenly distributed, manageable workload and to avoid overload or underload. Another aspect of workload is the mathematical predictive models used in human factors analysis to support the design and assessment of safety-critical systems.
===Theories===
[[File:KTS1workload.jpg|thumb|Figure 1: Wickens' Multiple Resource Theory (MRT) Model]]
Wickens' (1984) multiple resource theory (MRT) model <ref>Wickens, C.D. (1984). "Processing resources in attention", in R. Parasuraman & D.R. Davies (Eds.), ''Varieties of attention'', (pp. 63–102). New York: Academic Press.</ref> is illustrated in figure 1:

Wickens' MRT proposes that the human operator does not have one single information processing source that can be tapped but several different pools of resources that can be tapped simultaneously. Each box in figure 1 indicates one cognitive resource. Depending on the nature of the task, these resources may have to process information sequentially if the different tasks require the same pool of resources or can be processed in parallel if the task requires different resources.

Wickens' theory views performance decrement as a shortage of these different resources and describes humans as having limited capability for processing information. Cognitive resources are limited, and a supply and demand problem occurs when the individual performs two or more tasks that require a single resource (as indicated by one box on the diagram). Excess workload caused by a task using the same resource can cause problems, errors, or slower performance. For example, if the task is to dial the phone, then no excess demands are placed on any component. However, if another task is being performed simultaneously that demands the same component(s), the result may be an excess workload.

The relationship between workload and performance is complex. It is not always the case that as workload increases, performance decreases. Performance can be affected by workload being too high or too low (Nachreiner, 1995). A sustained low workload (underload) can lead to boredom, loss of situation awareness and reduced alertness. Also, as workload increases, performance may not decrease as the operator may have a strategy for handling task demands.

Wickens' theory allows system designers to predict when:
* Tasks can be performed concurrently.
* Tasks will interfere with each other.
* Increases in the difficulty of one task will result in a loss of performance of another task.

Like Wickens, McCracken and Aldrich (1984) describe the processing, not as one central resource but as several processing resources: visual, cognitive, auditory, and psychomotor (VCAP). All tasks can be decomposed into these components.
* The visual and auditory components are external stimuli that are attended to.
* The cognitive component describes the level of information processing required.
* The psychomotor component describes the physical actions required.

They developed rating scales for each VCAP component, which provide a relative rating of the degree to which each resource component is used.

Joseph Hopkins (unpublished) developed a training methodology. The background to his training theory is that complex skills are, in essence, resource conflicts where training has removed or reduced the conflicting workload demands, either by higher-level processing or by predictive time sequencing. His work is based on Gallwey (1974) and Morehouse (1977). The theory postulates that the training allows the different task functions to be integrated into one new skill. An example of this is learning to drive a car. Changing gear and steering are two conflicting tasks (i.e. both require the same resources) before they are integrated into the new skill of "driving". An experienced driver will not need to think about what to do when turning a corner (higher level processing) or may change gear earlier than required to give sufficient resources for steering around the corner (predictive time sequencing).

=== Creating a model ===
With any attempt at creating a workload model, the process begins with understanding the tasks to be modelled. This is done by creating a task analysis that defines:
* The sequence of tasks performed by individuals and team members.
* The timing and workload information associated with each task.
* Background scenario information.

Each task must be defined to a sufficient level to allow realistic physical and mental workload values to be estimated and to determine which resources (or combination of resources) are required for each task – visual, auditory, cognitive and psychomotor. A numerical value can be assigned to each based on the scales developed by McCracken and Aldrich.

These numerical values against each resource type are then entered into the workload model. The model sums the workload ratings within each resource and across concurrent tasks. The critical points within the task are therefore identified. When proposals are made for introducing new devices onto the current baseline activities, this impact can then be compared to the baseline.
One of the most advanced workload models was possibly developed by K Tara Smith (2007). This model integrated the theories of Wickens, McCracken and Aldrich and Hopkins to produce a model that not only predicts the workload for an individual task but also indicates how that workload may change given the experience and training level of the individuals carrying out that task.
Workload assessment techniques are typically used to answer the following types of questions: Eisen, P.S and Hendy, K.C. (1987):
* Does the operator have the capability to perform the required tasks?
* Does the operator have enough spare capacity to take on additional tasks?
* Does the operator have enough spare capacity to cope with emergencies?
* Can the task or equipment be altered to increase spare capacity?
* Can the task or equipment be altered to increase/decrease the amount of mental workload?
* How does the workload of a new system compare to the old system?

===Cognitive workload in time-critical decision-making processes===
It is well accepted that there is a relationship between the media by which information is transferred and presented to a [[decision maker]] and their cognitive workload. During times of concentrated activity, single-mode information exchange is a limiting factor. Therefore, the balance between the different information channels (most commonly considered visual processing and auditory, but could also include haptic, etc.) directly affects cognitive workload (Wickens 1984). In a [[time-critical]] decision situation, this workload can lead to [[human error]] or delayed decisions to accommodate the processing of the relevant information. (Smith, K.T. & Mistry, B. 2009).<ref>Smith, K.T., Mistry, B (2009) Predictive Operational Performance (PrOPer) Model. Contemporary Ergonomics 2009 Proceedings of the International Conference on Contemporary Ergonomics 2009 http://www.crcnetbase.com/doi/abs/10.1201/9780203872512.ch28</ref> 
Work conducted by K Tara Smith has defined some terms relating to the workload in this area. The two main concepts relating to workload are:
* '''workload debt''' - which is when an individual's cognitive workload is too high to complete all relevant tasks in the time available, and they decide (either consciously or subconsciously) to postpone one or more tasks (usually low priority tasks) to enable them to decide on the required timeframe.
* '''workload debt cascade''' - when, because of the high workload, the postponed tasks mount up so that the individual cannot catch up with the tasks they are required to do, causing failure in subsequent activities.