Attention resources, or, in simpler terms, attention, refers to the amount of cognitive capacity that is dedicated to a particular task or stage of processing. This amount can vary considerably from routine and well-practiced assembly tasks with reduced demands for attention to tasks related to air traffic control that require a high level of attention. In addition, this cognitive capacity can be applied in a very direct way, as in a specific point of a particular part of the information processing system of the human being called focused attention, or, in a much more diffused way to several or all of the information processing system of the human being, which is called divided attention. An example of attention focused on working memory could occur while an operator tries to remember a query processing code while entering it into a computer-controlled machine tool. The focus of attention can be improved by reducing the number of competing sources of information or the demands of the human information processing system or by separating those sources as different as possible.
On the other hand, when an inspector classifies apples on a conveyor belt, he divides his attention between the visual perception of the defects and sizes of the apples, the decision making about the nature of the defect and the size of the apple, with reference to the memory and the images stored from the training he received, and the movements of the hands to remove the damaged apples and classify by size those that are in good condition in the appropriate containers. The latter case consisting in performing several tasks simultaneously is also known as multitasking or time sharing. Because the cognitive resources of attention are relatively limited, the sharing of time between several tasks will likely result in a deterioration of the performance of one or more tasks compared to a single one of them. Again, it may be difficult to improve the performance of the task in these situations, but similar strategies are also used, such as those studied in the case of focused attention. The number and degree of difficulty of the tasks must be minimized. It is necessary that the tasks are carried out in the most dissimilar way possible in terms of the demands demanded at the processing stage of Figure 7.1. While a manual assembly task with only auditory instructions can be carried out smoothly, a musician who is tuning an instrument will have trouble hearing verbal comments.
An extension of the modes of attention to multiple resources is related to the measurement of the mental workload or the demands that are imposed on the information processor of the human being. A definition uses the list of resources that are required and the resources available, where time is one of the most important among the large amount of resources that are needed.
In the examples mentioned above, simple assembly can be a time consuming task, but does not demand cognitive resources in particular. On the other hand, the control of air traffic during peak hours can be a very demanding task. In fact, it can be very difficult to quantify the demands imposed on the operator. Some of the methods that are used to quantify them are the following:
■ The measures of the main task can be the time that is required to carry out the task divided by the total time available, or the number of items completed per unit of time. The problem with this method is that the timeshare of some of these tasks is better than that of others.
■ The measurement of the secondary task uses the concept of reserve capacity that, if not directly related to the performance of the main task, will be used by the secondary task (reaction time to the choice), which can be controlled and more easily measured. The problem with this method is that, in general, the secondary task seems artificial and intrusive and that it is difficult to identify the way in which the operator assigns priorities to the performance of both tasks.
■ Physiological measures (for example, heart rate variability, eye movement, pupil diameter, electroencephalograms) are thought to respond to the stress imposed by the mental workload; Although they usually do not interfere with the performance of the main task, the equipment needed to measure them can do so.
■ Subjective measures are thought to aggregate all aspects of the mental workload into a simple general value (or a weighted average at several scales). Unfortunately, subjective reports do not always accurately reflect actual performance; Motivation can also signifi cantly affect values.