Tactical Display for Soldiers Human Factors Considerations (1997) / Chapter Skim
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6 STRESS AND COGNITIVE WORKLOAD
6 STRESS AND COGNITIVE WORKLOAD
Pages 130-163
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From page 130... ...
Coupled with this stress comes the new burden of cognitive workload associated with the operation and management of new technological systems. The Land Warrior System, as currently conceived, is but one version of a potential family of advanced systems each of which may generate its own combination of stresses.
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From page 131... ...
This reduces the resources available for explicit task performance, and so efficiency is reduced accordingly. It must be emphasized that the demands of the primary task itself may well act in this depleting fashion.
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Since the functions stay the same, the way in which task performance falls off mirrors the way in which physiological capacity is impaired. The Army is accustomed to providing physiological support for its personnel, in terms of energy, resources, and specific equipment to avoid threat.
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From page 133... ...
For the infantry soldier, mission requirements themselves have to be considered the proximal source of stress, and other outside influences, such as heat, noise, fatigue, etc., are seen as forms of stress that interact with the primary demands of the task. This new perspective is particularly important when we consider the cognitive demands associated with advanced technologies.
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From page 134... ...
In depriving the enemy of their sources of information, our forces must avoid doing the same to themselves by producing an incomprehensible avalanche of information. This is especially true for the dismounted infantry soldier, who needs only a few sources of vital information during engagement.
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From page 135... ...
group of occupations impose physical demands. The job of the infantry soldier requires considerable physical work at the same time as critical decision making.
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From page 136... ...
Not only is heat stress a consequence of the geographical location of operations, but also, in any encounter in which the use of chemical or biological weapons is suspected, heat stress can affect military personnel wearing exclusion garments for protection. The heat load on the operator, generated by these exclusion garments is considerable, and on occasion has been sufficient to cause missions to be canceled or mission goals to be changed.
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From page 137... ...
Predicting the breakdown in behavioral decision making from heat stress can be derived from Figure 6-3; this figure also includes information about body temperature, so it can evaluate the combined effects of physical and mental demand. Cold Whereas heat presents a number of unique problems, cold also provides considerable contextual challenge for advanced systems.
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From page 138... ...
Noise is an intermittent stress. In World War I, noise was one of the major forms of annoyance for the infantry soldier; partial deafness from shelling was not uncommon.
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From page 139... ...
Using the axes of exposure time and stress intensity, three major zones of worker performance efficiency are distinguished. The heat stress axis is expressed in terms of effective temperature (ET)
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An important factor that remains uncertain is the length of an individual engagement and consequently the duration of mission that the infantry soldier is expected to sustain. In ground-based warfare of the immediate past decades, emphasis has been given to the first 72 hours of engagement.
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using the Land Warrior System are needed to establish the tolerance and reaction of soldiers wearing such equipment under operational conditions. The Problem of Interaction In approaches to understanding stress effects, one great limitation is the failure to investigate and capture the effects of multiple interactive sources of stress.
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From page 142... ...
Independent of original specifications, it is absolutely vital that user acceptance is evaluated at all stages of development of the Land Warrior System. EFFECTS OF STRESS ON PERFORMANCE Fatigue Fatigue, a subset of general stress effects, is a concatenation of a variety of physiological and psychological factors.
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From page 143... ...
Both subjective and physiological measures of cognitive workload (discussed in a later section) can be used to measure the onset of failure.
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From page 144... ...
A career in the military, ascending through the chain of command, has been traditionally accompanied by progressively greater responsibility and the burden of increasingly important decision making. Contemporary and proposed technologies are making changes in the challenge to the dismounted infantry soldier, in which significant cognitive demands are added to physical demands.
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From page 145... ...
Cognitive workload is best seen as a continuum on which both too much and too little are liable to result in problems. The number and kinds of mental processes that can be carried out in a given amount of time are limited.
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From page 146... ...
A given task receives the resources necessary for performance; spare capacity can be measured by giving subjects a secondary task, providing an index of the capacity required to perform the primary task. In this way, the capacity demands of a variety of tasks can be measured and used to predict dual-task performance.
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From page 147... ...
and indeed whether resources are a useful concept at all (Navon, 1984; Allport, 1993) , the multiple resource model still offers a useful perspective on cognitive workload.
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Thus there appears to be a mechanism involved with some aspects of memory retrieval and possibly memory transformation (as in mental rotation) , which is strictly serial and constitutes a significant bottleneck in dual-task performance.
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Table 6-1 lists four classes of workload measurement with their pros and cons. Primary task performance and subjective measures can be used for the initial screening of designs.
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Subjective measures are an attempt to systematically query subjects about their own awareness of task difficulty. The Cooper-Harper scale is one of the earliest efforts to assess workload.
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The NASA task load index or TLX (Hart and Staveland, 1988) asks operators to make ratings on six dimensions: mental demands, physical demands, temporal demands, performance, effort, and frustration.
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Primary and Secondary Task Measures Primary task measures simply try to infer workload from performance on the task of interest. Primary task performance is obviously the critical variable.
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. Finally, the secondary task can be intrusive and therefore disruptive of primary task performance.
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P300 therefore offers an increase in diagnosticity over behavioral measures. As we have pointed out, the secondary task method can be modified by using an embedded task.
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A thorough understanding of task interference and competition for limited capacity mechanisms will probably require a detailed simulation of how humans perform a given task. Such a simulation should provide a detailed account of the order, duration, and capacity limits of the elementary cognitive processes assembled for a given task.
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Unresolved Problems As noted throughout this chapter, there are many unresolved problems concerning the assessment and interpretation of cognitive workload and its demands. Already mentioned are the unknown effects of combining physical and mental demands.
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Confusion has often lost battles, and certainly it is a source of extreme stress to the infantry soldier. Therefore, any technology that serves to reduce confusion is at one and the same time helping mission performance and reducing the incidence of stress.
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From page 158... ...
By complexity, we specifically mean the number of degrees of freedom in the system, which translates to the number of potential states of the system that can be communicated to the operator. With pull-down menus, window systems, and direct database accessing, it will be technically feasible in the near future to give the infantry soldier almost unlimited on-line access to all aspects of human knowledge.
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From page 159... ...
In essence, the problem of individual differences in response to cognitive workload one of the most underresearched areas in all human factors is critical to performance success. More knowledge is needed in this area to ensure the success of the new technologies.
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From page 160... ...
In our consideration of the Land Warrior System's helmet-mounted display, which will be used to display maps, symbology, sensor images, and other information, we have reviewed recent work in psychology directed toward reducing the cognitive workload associated with visual displays of information. Based on visual and cognitive limitations that can make information hard to see and interpret, Wickens (1992)
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From page 161... ...
Close processing proximity can be enhanced by close display proximity and similarly for distant processing and display proximity. Wickens and Carswell describe several display techniques that are designed to manipulate display proximity and achieve the desired goals in terms of the operator's task.
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From page 162... ...
Although there is extensive information about physical effort and physical workload, as well as some insight into cognitive workload, we do not yet know enough about their combined effects to make definitive pronouncements relevant to future infantry operations. One reason is that current models of stress and performance are insufficient to determine how combined physical and mental effort may affect performance.
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From page 163... ...
3. Present salient information in the center of the visual display.
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