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4 Stress The battlefield environment is a stressful place and, as graphically de- scribed by Keegan (1976), those stresses are amplified within the armored vehicle. Indeed, the post-transition phase of any team situation will impose a substantial degree of stress, incorporating time pressure at a minimum, often augmented by danger, noise, and a host of other environmental stres- sors. The concept of stress as it influences human performance may be understood in the context of Figure 4.1. At the top of the figure are identi- fied a set of stressors; these are influences on information processing and cognition that are not inherent in the content of the information itself. Stressors may include features of the work environment like noise, vibration, heat, dim lighting, and high acceleration, as well as such psychological factors as anxiety, fatigue, and danger. Such stressors may have different manifesta- tions: subjective experience, physiological changes, and performance dec remeets. Stressors may affect a subjective experience. For example, individuals are usually (but not always) able to report a feeling of frustration, or arousal, as a consequence of a stressor. Closely linked, a change in physiology is often observable. This might be a short-term change- such as the influence on heart rate associated with the demands of flying as pilot-in-command (Hart and Hauser, 1987) or the stress of controlling air traffic in high-load situations (Romhert, 19799. Or it might be a more sustained effect, such as the change in the output of catecholamines, measured in the urine, after periods of simulated combat maneuvers flying in an F16 (Burton et al., 1977), inflight emergencies, or actual battlefield events (Bourne, 1971~. 94
STRESS 95 The subjective and physiological characteristics are often, but not invar~antly, linked. The subjective experience of stress may also mediate performance. For example, one who does not realize the risk or danger of a particular situation will experience less stress than one who does a subjective ap- praisal of the situation, thereby mediating stress effects on performance (Coyne and Lazarus, 1980J. As Figure 4.1 shows, the effects may be either direct or indirect. Direct effects are stressors that influence the quality of information perceived by the human operator or the precision of the motor response. For example, vibration will reduce the quality of visual input (as well as the quality of motor output), and noise will do the same for auditory input. Time stress may simply curtail the amount of information that can be perceived, in a way that will quite naturally degrade performance. Direct effects also in- clude the effects of noise on working memory (Poulton, 1976~; rehearsal of a set of instructions or coordinates, for example, will be more difficult in noise. Direct effects can also include the distraction experienced by an operator who is concerned about personal problems or danger, who may therefore redirect attention to thinking about those problems, rather than to the job at hand. Some direct-effect stressors (e.g., noise or vibration) as well as others for which no direct effect can be observed (e.g., anxiety or fear) also influ- ence the efficiency of information processing. In this chapter we first con- sider stressors that are characteristic of the physical work environment in which the tank crew operates, described in Chapter 1. We then address what is known about the effects of psychological stress on performance Direct. . . E.g., lighting, noise, heat, vibration INPUT STRESSORS ' Indirect... `` E.g., anxiety, ~ fear, fatigue 1, INFORMATION PROCESSING FIGURE 4.1 Influence of stress on human performance. Direct... E.g., heat, vibration ~ , ~ BEHAVIOR
96 WORKLOAD TRANSITION under conditions of high anxiety and arousal. Finally, we consider stress in the context of team performance, examining the characteristics of teams that make them more stress resistant. The discussion emphasizes to a greater extent the stress effects present in the post-transition period. In Chapter 5 we consider the most potent stressors of the pretransition period: sleep loss and fatigue and their influence on both pre- and post-transition performance. STRESS IN THE WORK ENVIRONMENT The term work environment encompasses all the variables that deter- mine the physical comfort level of users. These include ambient tempera- ture, relative humidity, atmospheric pressure, airflow, the presence or ab- sence of noxious fumes or toxic substances, motion, acceleration (normally expressed as G-loading), and ambient sound and light levels. For most of these parameters there exist absolute limits within which humans can func- tion and beyond which they cannot function or, for some variables, even survive. There are, in general, much narrower limits within which humans feel comfortable. An example of such a comfort zone is contained in the American Society of Heating, Refrigerating, and Air-Conditioning Engi- neers (ASHRAE) comfort standard (American Society of Heating, Refriger- ating, and Air-Conditioning Engineers, 1985~. The definitive military hu- man factors standard, MIL-STD-1472C (U.S. Department of Defense, 1981), specifies such zones for several environmental variables. The degree to which comfort enhances performance is a function of the nature of the tasks that must be completed. The differential effects of many environmental factors have been demonstrated on the performance and physical workload of various types of tasks. There are well-known relationships between certain environmental variables, such as ambient temperature and relative humidity and the ability to do physical work (Occupational Safety and Health Administration, 1974~. Among the factors known to increase workload or, more accurately, to decrease performance are high levels of ambient noise (Davies and Jones, 1982), high temperature and humidity (Hancock, 1981), low temperature (Enander, 1984), and motion and vibra- tion (International Organization for Standardization, 1978~. Obviously, high levels of toxic materials in the environment can have a substantial impact on the user's ability to perform tasks. The tank environment combines some of the most potent factors that have been shown to adversely affect performance. Even in a nonchemical/ biological-warfare (non-CBW) battlefield scenario, tank crew members are subjected to elevated temperature and humidity due to the fact that tanks are not air conditioned. Heat casualties are quite common during training in field exercises. It is also common for the interior of the tank to be filled with noxious fumes from leaking hydraulic fluid and spent propellant from
STRESS 97 ordnance. When buttoned up, the interior of the tank is pressurized by an air movement system that brings outside air in through filters that remove particulate and some chemical components. This air is not conditioned for temperature or humidity. In the COW battlefield environment, these condi- tions are exacerbated by the requirements of wearing environmentally pro- tective clothing or "MOPP gear" and remaining buttoned up inside the tank for long periods of time. Even in non-CBW environments, all crew members must wear helmets with integral earphones and a movable microphone. The purpose of these helmets is not so much to protect crew members from external ordnance as it is to protect them from head injuries caused by hitting the interior surface of the tank while it is moving over terrain. The large, fully enclosing earphones insulate the crew members from noise generated by the tank running gear. The helmet allows crew members to communicate with each other and with other tanks in their platoon. Unfortunately, the helmets are heavy and tend to trap heat. The earpieces press against the sides of the head causing discomfort after even short periods of time. It is reasonable to infer that environmentally extreme conditions will affect some tasks more than others. Some tank crew positions are primarily physically oriented, i.e., those of loader and driver, whereas others are con- cerned mainly with cognitive tasks, i.e., those of gunner and tank com- mander. However, even those crew positions that are physically oriented have task responsibilities that require mental sharpness. Specifically, all crew members are expected to search for threats and targets. During opera- tions of long duration, the crew is put on a sleep-wake cycle that requires all crew members to assume the responsibility of searching for enemy threats. The result of this division of responsibilities is that adverse environmental factors are likely to increase the workload of all tank crew members and, consequently, decrease the performance of the tank crew as a whole. Long-duration operations also bring into play another environmental factor that should be noted. Tanks contain no toilet facilities. When but- toned-up, crew members are not allowed to leave the confines of the tank. The unpleasant, but inevitable result of these restrictions is that all bodily functions must be accommodated within the tank. It is probably an under- statement to observe that such a situation can lead to an environment that is not conducive to superior task performance. STRESS AND HUMAN PERFORMANCE Many aspects of the relation between stress and performance are related to the construct of arousal. The relation between stress-induced arousal and performance has sometimes been described in terms of an inverted U-shaped function, as shown in Figure 4.2. With increasing arousal, performance
98 Optimum Level of Arousal o a) // // WORKLOAD TRANSITION Simple Task \ \~<plex Task Level of Arousal FIGURE 4.2 The Yerkes-Dodson law. The solid portion of the curve represents the arousal effects. The dashed portion represents the effects caused by attentional narrowing. first improves, up to an optimal level, and then deteriorates when arousal is too high. Based on data originally collected in 1908, the relation is some- times called the Yerkes-Dodson law (Yerkes and Dodson, 1908) and has served as a framework for understanding human performance under stress by more recent investigators (Broadbent, 1971; Easterbrook, 1959; Kahneman, 1973~. An example of the role of stress in the inverted-U relation is pro- vided by an experiment carried out by Simonov et al. (1977~. Simonov et al. measured performance of parachute jumpers on a visual detection task, as the time of their first jump approached. As time passed and their level of stress (assessed by physiological measures) continuously increased, perfor mance first improved and then degraded until just prior to the jump. Elaborating on the Yerkes-Dodson law, analysis and synthesis of ex- perimental data carried out by Easterbrook (1959) and Kahneman (1973) suggested that the upward and downward "limbs" of the inverted-U shown in the figure are the results of different factors. The upward limb appears to result from an energizing process, which simply expands the amount of
STRESS 99 cognitive effort or resources mobilized for task performance. In contrast, the downward limb is the consequence of a more specific effect of high arousal on the selectivity of attention, which causes the operator to focus on a more restricted set of environmental or internal sources of information. An appropriate metaphor is to say that high levels of stress narrow the spotlight of attention. Extending this argument logically leads to the conclusion that high arousal should be more detrimental to tasks that require the processing of several information sources (i.e., complex tasks) than to tasks which depend on only a few cues (i.e., executing a well-practiced skill). This difference in arousal effects resulting from task complexity is depicted by the differ- ences between the two curves in Figure 4.2. The optimum level of arousal for the simple (or the more highly practiced) task is higher than for the complex task. A relevant example of the different effects of stress on performance as a function of complexity is an experiment carried out by Berkun (1964~. Using Army soldiers engaged in simulated (but highly realistic) tasks, Berkun employed three different experimental manipulations to induce a very real- istic experience of stress. In one manipulation, subjects were led to believe that the aircraft in which they were flying was in danger of crashing as they attempted to fill out an insurance form. In a second manipulation imposed during combat exercises, subjects were led to believe that artillery shells were exploding around them as a result of a confusion about their location, as they tried to follow procedures to initiate a radio call to redirect the fire. In the third manipulation, subjects believed that a demolition that they had initiated had accidentally caused a serious injury to one of their fellow soldiers, and they were now required to call for medical assistance. Thus, in all cases, subjects were deceived to believe that they, or someone for whom they felt responsible, were at serious mortal risk. Berkun found that in all three cases, the high level of stress and arousal induced by the anxiety or perceived danger led to degraded performance on following the necessary procedures. However, this degradation was less for soldiers with greater experience. This last finding may be placed nicely into the context of Figure 4.2, if it is assumed that the more skilled soldier faces a less complex task in problem solving. Much of the perceptual and short-term memory requirements of task solution are replaced by direct recall from long-term memory. The increased arousal caused by stress then exerts a less degrading effect. While Berkun's study clearly illustrates the loss of performance under stress, it is less illuminating regarding the qualitative manner in which per- formance is affected. This issue of qualitative stress effects will now be addressed in more detail.
100 WORKLOAD TRANSITION QUALITATIVE PATTERN OF STRESS EFFECTS Hockey (1984, 1986) expanded on the two factors (arousal and tunnel- ing) that underlie the Yerkes-Dodson law and has attempted to identify more subtle patterns of stress effects on performance. Reviewing a large number of studies that examined the effects of stress on human perfor- mance, Hockey distilled the pattern of stress effects into the form shown in Table 4.1. Each stressor appears to be identified by a profile or signature of effects across a set of five critical information processing components: general arousal, selectivity of attention, speed and accuracy of performance, and capacity of short-term memory (working memory). The focus in this section is on a stressor that is an important character- istic of many operational environments in the team transition situation: the anxiety, fear, or arousal associated with failures of task performance or dangerous' threatening environments (Idzikowski and Baddeley, 1983a, 1983b). This fear is often coupled with a shortage of time to deal with the crisis. (The direct effects of time pressure on performance were discussed in some detail in Chapter 3.) This stressor may characterize the experiences of the flight crew, following an engine stall in midair in which both danger and time stress are imposed; the nuclear control room personnel, following ini- tial alerting of a failure; or the tank crew moving into combat. Idzikowski and Baddeley (1983a, 1983b) present a review of research and case study findings related to this form of stress; the reader can refer to treatments by Hamilton and Warburton (1984), Broadbent (1971), and Hockey (1986) for broader discussions of stress. In the following review of research, we also capitalize on the psychological equivalence of signature patterns between noise and anxiety as shown in the table, allowing us to extrapolate from the effects of noise to those of danger-producing anxiety. It is reasonable, also, to assume that in the noisy and dangerous environment of the tank, these two effects would be additive. In the following discussion, we use the term stress to refer to the combined effects of danger, anxiety, and noise. Within the framework of teams in transition addressed in this report, the transition effects involve a rapid jump from the left to the right side of the Yerkes- Dodson curve. Our focus in Chapter 5 is on the left side of the curve. Here we address performance effects on the right or high end. Attentional Tunneling Weltman et al. (1971) compared the performance of two groups of divers on a central and peripheral signal detection task. One group was led to believe it was under conditions of a 60 foot dive in a pressure chamber; the other was not. In fact, there was no change in pressure for either group. Both groups showed similar performance on the central task, but perfor
STRESS TABLE 4.1 The Patterning of Stress Effects Across Different Performance Indicators. 101 Performance Indicators Speeded Responding GA SEL S A STM Sources/Reviews Noise Anxiety Incentive Stimulant drugs + Later time of day Heat Alcohol Depressant drugs Fatigue Sleep loss Earlier time of day + + O. - + + O - + + + + + + + O - + _ _ + O + O - O _ O o + + 2,3,4,5,7,8 4,12 2,4,5 2,4,13 1,2,4,5,6,8 2,4,11 2,4,7,8,13 2,4,10,13 2,4,9 2,4,5,7,8 1,2,4,5,6,8 The table summarizes the typical outcome in various studies using these stress variables in terms of their effect on the five behavioral indicators show: GA general alertness/activation (subjective or physiological arousal); SEL - selectivity of attention; S and A refer to overall speed and accuracy measures in speeded responding tasks; STM short-term memory. A plus (+) indicates a general increase in this measure, a zero either no change or no consistent trend across studies, and a minus (-) a general tendency for a reduction in the level of the indicator. A question mark is used to indicate cells where there is insufficient data. Sources of data: (1) Blake (1967a, 1971); (2) Broadbent (1971); (3) Broadbent (1978); (4) Davies & Parasuraman (1982); (5) M.W. Eysenck (1982); (6) Folkard (1983); (7) Hamilton, Hockey, & Rejman (1977); (8) Hockey (1979); (9) Holding (1983); (10) Johnson and Chernik (1982); (11) Ramsey (1983); (12) Wachtel (1967, 1968); (13) Wesnes and Warburton (1983). SOURCE: G.R.J. Hockey, "Changes in Operator Efficiency as a Function of Stress, Fatigue, and Circadian Rhythms." P. 44-39 in K.R. Boff, L. Kaufman, and J.P. Thomas (eds.), Hand- book of Perception and Human Performance. Chichester, England: John Wiley and Sons, 1986. Reprinted by permission. mance on the peripheral task was significantly degraded for the pressure group. This group also showed greater anxiety-related increases in heart rate, substantiating the increased level of stress. Stress may also cause a focusing of attention on one particular task or cognitive activity, as well as on a particular perceptual channel. In the analysis of cockpit voice record- ings at times of high stress prior to accidents, Helmreich has found evi- dence of severe breakdowns in the pilots' ability to handle multiple tasks or multiple concerns. Although perceptual or cognitive tunneling produced by stress usually degrades performance, it is also possible to envision circumstances in which this tunneling may actually facilitate performance, in which focused atten
102 WORKLOAD TRANSITION lion on critical task aspects is desired. Indeed, this positive effect was observed in a study by Houston (1969), who found that noise stress im- proved the focus of attention on the relevant aspect of a stimulus and re- duced the distracting effect of irrelevant aspects. Data provided by Houston's experiment and others suggest that the attentional or cognitive tunneling resulting from stress is defined in terms of subjective importance or priority. That is, performance of those tasks or processing of that information thought to be most important remains unaf- fected or perhaps is enhanced (through arousal), while processing informa- tion with lower perceived priority is filtered (Bacon, 1974; Broadbent, 1971~. In one sense, this kind of tunneling is optimal, but it will produce undesir- able effects if the subjective importance that defines the attended channel proves to be unwarranted. Such was the case, for example, in the incident of the Three Mile Island nuclear power plant (Rubinstein and Mason, 1979~. Immediately after the crisis in the plant developed and under the high stress caused by the initial failure, the operators appeared to be fixated on a single faulty indicator, supporting an incorrect belief that the water level in the reactor was too high, thereby preventing their attention from focusing on more reliable indicators that supported the opposite (and correct) hypoth- esis. As suggested by this example and elaborated below, this narrowing effect can be directly related to biases in decision making. But for the operator who has a well-structured and accurate model of task demands and a well-developed skill in discriminating sources of useful (versus trivial) information, it can be expected that stress should lead to little degradation of performance, as reflected by the behavior of the United Airlines flight 232 crew (Predmore, 1991~. Working Memory Loss Mandler (1979) has discussed the degrading effects of anxiety on work- ing memory. Correspondingly, many of the difficulties in following proce- dures that Berkun (1964) observed when his Army subjects were placed under the stress of perceived danger can also be attributed to reduced work- ing memory capacity. Logie and Baddeley (1983) and Lewis and Baddeley (1981) have noted similar working memory decrements of divers perform- ing at depth. Idzikowski and Baddeley (1983a, 1983b) observed an anxiety- related working memory loss of speakers waiting in the wings to give their first public speech. Noise, as well as danger and anxiety, has also produced consistent effects on working memory (Hockey, 1986~. While it is intu- itively evident that the presence of noise would disrupt the ability to re- hearse verbal information in working memory (Poulton, 1976), it appears also that the combined stress effects of noise and anxiety may disrupt spa- tial working memory systems as well (Stokes et al., 1990; Stokes and Raby,
STRESS 103 1989~. Indeed, in a simulation study of pilot decision making, Wickens et al. (1988) observed that the effects of noise stress were greatest on decision problems that relied on spatial visualization for their successful resolution. Communications Successful communications depend heavily on working memory, to re- member what has just been said. Hence, it is not surprising that communi- cations have sometimes broken down under conditions of stress. Analyses of crew communications in accidents in which a prolonged inflight emer- gency preceded ultimate disaster provide compelling evidence of the com- munication breakdowns that occur under conditions of extreme threat. These include fragmented communications, failures to process the information com- municated, and inability to deal with multiple tasks or concerns (Predmore, 1991). Long-Term Memory While stress appears to disrupt working memory, it appears to have less of an effect on the retrieval of information from long-term memory, to the extent that information is well rehearsed and memorized. For example, in their study of pilot judgment, Wickens et al. (1988) found that those judg- ments requiring direct retrieval of facts from long-term memory were rela- tively unimpaired by stress. The differences in Berkun's findings between more and less skilled soldiers is also consistent with this view. Stokes et al. (1990) found that the decision-making performance of novice pilots deteriorated under stress, whereas performance of a group of highly trained pilots in the same circumstances was not affected. Presumably the latter group was more able to rely on direct retrieval of information from long-term memory in making their deci- sions. Similar to the narrowing effect that stress exerts on perception and selective attention, however, stress appears to restrict the information re- trieved from long-term memory more specifically to those habits that are well learned or overlearned (Eysenck, 1976~. Although there do not appear to be much experimental data supporting this claim, at least one study shows that increased stress actually eliminates some of the benefits of ex- pertise and training in decision making (Ben Zur and Breznitz, 1981~. Studies by Fitts and Seeger (1953) and Fuchs (1962) and analyses of aircraft acci- dents carried out by Allnutt (1987) have all suggested that stress will lead to a regression to earlier learned and more compatible response patterns, when these patterns may conflict with incompatible (but appropriate) ones. Col- lectively, these findings suggest the importance of extensive training in
104 WORKLOAD TRANSITION procedures and actions that may need to be taken in emergency. They further emphasize that such procedures should require only actions of high compatibility. The findings, however, emphasize the extent to which cre- ative innovative problem solving may be degraded under stress since, by definition, such problem solving will not have been accomplished in the same way in the past and hence repetitive practice of the same steps cannot be achieved. Strategic Shifts There is some evidence from behavioral studies that stress leads to consistent shifts in processing strategy. In the study of the anxiety brought on by the first parachute jump, for example, Simonov et al. (1977) observed a shift in detection performance that can be characterized by a riskier crite- rion setting. The paratroopers were simply more likely to respond "yes" and hence made more hits and more false alarms. Hockey (1986) concludes that there is a general effect of noise and/or anxiety stress on the speed- accuracy tradeoff, shifting performance to a less accurate but not slower level. In their study of pilot judgment, Wickens et al. (1988) found that judgments were less accurate but not necessarily slower under the combined stress effects of noise, time pressure, and threat of loss of income. The tendency of those under the stress of an emergency to shift perfor- mance from accurate to fast (but error prone) responding has been cited as a concern in operator response to complex failures in nuclear power control rooms. The operator often has a desire to do something rapidly, when in fact this impatience is often counterproductive until the nature of the failure is well understood. In the Three Mile Island incident the hasty action of the control room operators was to shut down an automated device that had in fact been properly doing its job. Decision Making Understanding the effects of stress on decision making has always been of great interest to the human factors profession. The importance of this knowledge has been enhanced by the analysis of the faulty decisions made in the Three Mile Island incident and, more recently, by concerns over the decisions made in the U.S.S. Vincennes incident (U.S. Navy, 1988; see also Chapter 81. Both of these incidents are particularly relevant to the focus of this report because of the involvement of teams of operators in making decisions following a fairly abrupt transition of system state, under a high level of stress. The concern that decisions degrade under stress is rein- forced by anecdotes and case studies of poor pilot judgments that have occurred under stressful conditions of bad weather, spatial disorientation, or
STRESS 105 aircraft failure (Jensen, 1982; Nagel, 1988; Simmel et al., 1987~. However, caution must be exercised in forming firm conclusions on the basis of post hoc accident analysis for, without tight experimental control, it is often difficult to know if a real-world decision that failed was in fact a poor one in foresight as well as in hindsight. Furthermore, it is often difficult to tell whether stress was itself a causal factor in the poor decision or whether the conditions that produced the stress were also those that, for example, de- graded the information available in such a way that the poorer decision became more likely. To predict the effects of stress on decision making, one approach is to adopt a componential approach (Wickens and Flach, 19881. Since different decisions may involve varying dependence on such components as working memory, attention, and long-term memory retrieval, each decision may be affected differently by stress as a function of the components on which it depends and of the differential effects of stress on those components as described in the previous pages (Wickens et al., 19881. An alternative approach is to examine the results of experiments that impose stress on decision making, diagnosis, and problem-solving tasks. While few such studies exist, their results are consistent with the picture of a stress-sensitive decision-making process. Such studies have not only shown that decisions of various sorts degrade under stress but have also concluded that this degradation takes specific forms. Thus, for example, Cowen (1952) found that subjects perseverated longer with inappropriate or rigid problem solutions under the stress produced by threat of shock, a sort of action tunneling that is consistent with the idea of attentional tunneling. Keinan et al. (1987) found that the allocation of attention to a word problem became increasingly nonoptimal and unsystematic as stress was imposed by the threat of an electrical shock. The investigators also observed that this stressor produced a premature closure: subjects terminated their decision before all alternatives had been considered. Ben Zur and Breznitz (1981) found that stress, while leading to some filtering of information, also led subjects to give more weight to negative task dimensions and, as a conse- quence, make less risky decisions. Driskell and Salas (1991) observed that stress actually increased the receptivity of members of a dyed to judgments provided by the other mem- ber in reaching a problem solution. They imposed stress on U.S. Navy personnel who believed they were one component of a cooperative deci- sion-making dyed. In fact, unknown to the subjects, the other component of the dyed was always the same source of computer-generated information for all subjects. The investigators were interested in the extent to which per- ceived stress influenced the receptivity to information received from a team member when that member was perceived to be either above or below them in the military chain of command. Not surprisingly, greater receptivity to
106 WORKLOAD TRANSITION information was shown when the member was perceived of higher rank. But whether the rank was higher or lower, both groups were more willing to accept the information under the conditions of perceived stress. As we have discussed above, Wickens et al. (1988) observed that the combined stress of noise, time pressure, risk, and task loading produced a general degradation of pilot judgments on a computer-based flight simula- tion. The stress effect, however, was selectively observed only on decision problems that were difficult in terms of their spatial memory demand. As noted before, their data indicated that decisions did not degrade under stress when long-term memory retrieval was the primary mechanism. These con- clusions are related to those drawn by Klein (1989), who argues that expert firefighters use direct long-term memory retrieval to make their decisions. Given this characteristic, experts making decisions about familiar courses of action should be less likely to suffer degrading effects of stress. The conclusion drawn by Klein, however, is partially contradicted by a study carried out by Koehler and McKinney (1991), who evaluated the decision-making performance of Air Force pilots in 195 aircraft malfunc- tion mishaps. Their analysis of decision quality revealed that experts (long- time pilots) did not necessarily perform better than relatively new pilots under the high-stress conditions of an inflight malfunction. Although this conclusion must be tempered by the fact that experts were more often flying a lead aircraft in formation, thereby adding to their attention demands, a second finding is consistent with the picture presented here. That is, expert performance was particularly disrupted when the malfunctions were novel and unique, more so than the performance of the novices. This is consistent with the view that experts had available well-learned solutions in long-term memory for the routine problems that were not available for the unique ones. The novices had fewer such solutions available for either problem type, and the loss in their performance from routine to unique would there- fore be less. Attention and Arousal As indicated by the Yerkes-Dodson law depicted in Figure 4.2, a stres- sor can sometimes have a facilitating effect on performance if that stressor moves the operator closer to the optimal level of arousal. There are, indeed, studies that have shown improved performance at higher stress levels. For example, Kennedy and Coulter (1975) found that performance on a vigi- lance monitoring task was improved by the threat of a shock. Hockey (1970) found that noise stress improved performance on a tracking task presented centrally although, consistent with perceptual tunneling effects, the same stressor disrupted peripheral monitoring performance. Lazarus and Ericksen (1952) observed that the threat of failure improved perfor
STRESS 107 mance on a cognitive test for those subjects of higher ability, although it degraded performance for those of lower ability. This interaction is inter- pretable in the framework of the Yerkes-Dodson law, if it is assumed that the task was of greater complexity for the low-ability subjects, and they were therefore presumably already operating above their optimal level of arousal in the absence of the threat, while the higher-ability subjects, for whom the task was less complex, were below their optimal level. Conclusion What emerges from this literature are a series of somewhat tentative conclusions that must be offered without an extensive empirical data base. In particular, most of the experimental studies have used fairly generic laboratory tasks, therefore avoiding the examination of skilled operators, experiencing stress in a domain in which they are experts. Hence the extent to which stress may produce failures of processes in memory and attention in such skilled operators cannot be asserted with confidence. Furthermore, given the qualitative differences in expert versus novice performance on routine tasks, it may well be that the documented stress effects on attention and working memory would not influence expert performance to the extent that those processes are not involved in the expert's performance of routine tasks (Stokes et al., 1990~. The negative effects of stress on experts per- forming nonroutine tasks within their domain still awaits empirical valida- tion, because it is clear that case studies provide contradictory information (Koehler and McKinney, 1991~. MEDIATING EFFECTS The effects of a given stressor on performance may be mediated by at least two other factors: additional stressors that may be present and indi- vidual differences in personality. With regard to the first of these mediating influences, the effects of combinations of stressors is often complex (Broadbent, 19711. Thus, it is not possible to say that the effect of two stressors in combination is the sum of their individual effects nor even necessarily that it is greater than that sum (a positive interaction). Sometimes the effects of one stressor may compensate for another's degrading effects. Fortunately, however, these interactive effects may sometimes be understood in the con- text of the inverted-U function (Broadbent, 1971~. For example, although both sleep loss and noise will typically degrade performance, their effect in combination is generally less than either effect alone (Wilkinson, 1963~. This effect makes sense when it is realized that each is pulling arousal in a different direction on the function depicted in Figure 4.2, and the net effect is to maintain arousal nearer the peak.
108 WORKLOAD TRANSITION Individual differences between operator personality types describe a second mediating effect. These are complex, not well understood, and their full treatment is beyond the scope of this chapter. Locus of control de- scribes the extent to which individuals believe that they, rather than other forces, have control over the things that influence their lives. These two beliefs describe an internal versus external locus of control, respectively. There is some evidence that those with an internal locus of control are less stressed by anxiety-provoking situations, because of their belief that they can exert some control over the situation. The distinction between intro- verted and extroverted personality types has also been found to mediate the effects of stressors. In general, extroverts are more affected by all stressors, although more specific patterns of difference between the two personality types, the time of day (am versus pm), and stimulants that increase or decrease the level of arousal have also been reported (Hockey, 1986~. A description of these effects is beyond the scope of this chapter. Closely related is the idea of cognitive appraisal (Coyne and Lazarus, 1980~. Two individuals could be placed in identical situations of danger. The one who correctly appraises the personal danger of the situation will be more likely to realize stress effects on performance. Stress effects here will also be mediated by differences in the extent to which individuals believe they can cope with the stress-inducing events. COPING WITH STRESS There are a variety of different techniques that may be adopted in the effort to minimize the degrading effects of stress on human performance. Roughly these may be categorized into design solutions that address the task and personal solutions that address the operator (either through strate- gies or training) or the characteristics of the whole team. Design Solutions Design solutions may focus on good human factors of displays. If perceptual narrowing among information sources or unsystematic scanning does take place, then reducing the amount of unnecessary information (vi- sual clutter) and increasing its organization will surely buffer the degrading effects of stress. For example, Zhang and Wickens (1990) found that inte- grating the separate displays of information into a single object display reduced the degrading effects of noise on performance in a multitask envi- ronment. Schwartz and Howell (1985) observed that graphical rather than numerical data display could reduce the derogating effects of time pressure on a command-and-control task. Whitaker and Klein (1990) have identified five principles for designing
STRESS 109 s~ess-resistant displays: metaphors (use of the familiar), streamlining (eliminating nonessential elements), functional prototypes (display information directly necessary for action), foregrounding or highlighting, and fusion or display integration. Similarly, it is clear that any design efforts that minimize the need for operators to maintain or transform information in working memory should be effective. Emergency procedures, which must be referred to on- line, must be clear and simply phrased as they will undoubtedly need to be followed under the very circumstances that make working memory for their contents extremely fragile. It is desirable also that procedural instructions of what to do are redun- dantly coded with speech as well as print, should avoid arbitrary symbolic coding (abbreviations or tones other than general alerting alarms), and should be phrased in direct statements of what action to take, not as statements of what not to do (avoid negatives) or statements that only describe the current state of the system. This is the policy inherent in voice alerts for aircraft in times of emergencies, in which commands are directed to the pilot of what to do to avoid collision (e.g., "pull up") (Chappel, 1989~. Also, whenever possible, the number of steps that need to be taken in following emergency procedures should be minimized. Adhering to fundamental principles of design compatibility in all of its forms (Wickens, 1992) is certainly one of the best techniques for minimizing the damaging effects of stress on perfor mance. Strategies There are strategies that can be adopted by the operator to minimize the degrading effects of stress. Certainly one of the most effective of these is planning, anticipating, and rehearsing actions to be taken under stress- either expected actions or those required by emergencies. While advance planning requires working memory capacity at the time it is being done, such planning can compensate for the fact that fewer resources will be available under stressful conditions. Furthermore, research has shown that, if individuals can predict, understand, and have knowledge of and a sense of control over the stressor, then they are more likely to develop successful coping strategies (Bourne, 1971~. Training A number of investigators have reported that well-learned responses appear less subject to interference from extraneous environmental condi- tions (Krueger, 1989; Kubala and Warnick, 1979; Webb and Levy, 1984; Williams and Williams, 1966~. Zajonc (1965) suggested that increased stress leads to the increased probability of selecting the dominant response with a
110 WORKLOAD TRANSITION consequent decrease in the probability of selecting other responses. Thus, under conditions in which the best learned (dominant) response is the most appropriate, stress may lead to enhanced performance. In addition to training for automaticity, there is also a family of training approaches aimed at reducing stress reactions. Relaxation training (Wolpe, 1958) and biofeedback techniques (Dewitt, 1980; Lawrence and Johnson, 1977) are both designed to reduce stress levels. Another important ap- proach is cognitive training. Cognitive training or cognitive restructuring refers to a wide variety of techniques that help individuals modify their thoughts and perceptions of stress (Dewitt, 1980; Ellis, 1974; Lazarus, 1968~. For example, in one study DeWitt (1980) combined cognitive and biofeed- back training for football and basketball players. Subjects improved sig- nificantly in pre- and post-treatment performance ratings and reported greater comfort and confidence. In a review of relaxation training, biofeedback techniques, and cogni- tive restructuring, Druckman and S wets (1988:123) concluded that "there is no evidence to indicate that biofeedback training has any effect on stress or on performance under conditions of stress." They found cognitive restruc- turing and the simple provision of realistic information to be most useful in reducing stress. These stress management procedures focus on the reduc- tion of uncertainty and the increase in control that follows from this reduc- tion. At the same time, others warn that stress reduction is not necessarily beneficial to performance. A soldier's stress may be seen as legitimate and valuable; reducing it to very low levels may reduce combat performance. Earlier in this chapter the beneficial effects of training were discussed- in particular, extensive training of key emergency procedures so that these will become the dominant and easily retrieved habits from long-term memory, when stress imposes that bias. In fact, a case can possibly be made that training for emergency procedures should be given greater priority than training for routine operations. This emphasis should be particularly real- ized whenever emergency procedures (or those to be followed in high-stress situations) are in some way inconsistent with those followed in normal operations. For example, under normal operations, Step A precedes Step B. but under an emergency the two steps are to be reversed in sequence. Clearly, as a design solution, systems should be designed so that procedures fol- lowed under an emergency are as consistent as possible with those followed under normal operations, and the perceptual cues for any changes are prominent and easily visible. It is also true that successful experience in a stressful situation can greatly reduce the anticipated anxiety of repeated performance. For ex- ample, Ursin et al. (1978) assessed physiological measures of stress prior to the first and second parachute jump made by a group of paratroop trainees. The investigators observed a large drop in those measures between the two
STRESS 111 jumps, signaling the relief, as it were, that successful performance was possible. In this regard, it is not surprising that, in a wide variety of contexts, research findings demonstrate the efficacy of prestress training, geared at providing preparatory information in order to reduce the novelty of the stressful situation. Novelty, as Rose (1987) and others have indi- cated, is a primary component of the intensity of the stress response: the greater the novelty, the greater the intensity of the stress experienced in many settings. Thus, training should be a crucial component of any pro- gram to enable tank crews to manage stressful environments. Finally, there appears to be considerable merit in training that makes crews aware of the potentially degrading effects of stress. Survey data collected from civilian and military flight crews using the Cockpit Manage- ment Attitudes Questionnaire (CMAQ) contain items aimed at determining attitudes regarding personal awareness of the effects of external stressors on human performance. In particular, a Recognition of Stressor Effects subscale of the CMAQ measures perceptions of personal capabilities when faced with stressful conditions and the ability to put aside stresses caused by personal problems when faced with the need to perform at high efficiency. One of the striking findings from the survey data is how little awareness flight crews have of the deleterious effects of stress on individual and group performance (Helmreich, 1984~. The model pilot tends to endorse a posi- tion reflecting an ability to leave behind personal problems and a perception that personal performance is unaffected by life-threatening, emergency con- ditions. Such attitudes represent the classic model of the "white scarf,' aviator. TEAM MODELS: IMPLICATIONS FOR STRESS MANAGEMENT The bulk of the research on stress addresses individual-level responses (physiological, psychological, and behavioral) often in laboratory settings removed from the more complex contexts in which multiple stressors usu- ally occur. Prevention and intervention programs are also often addressed as individual-level strategies for reducing negative stress-related consequences (e.g., therapy, exercise, training programs). Fewer studies examine the group and organizational level structures and processes that might be modified in order to diminish the problems created for individuals enduring a high level of stress in the workplace. A simple example is the case with air traffic controllers. Studies typically focus on the effects of the stress of their jobs on their own responses, physiological and psychological (as well as on their families). As Matteson (1987) suggests, stress may often be relieved, not by training particular individuals in how to cope with stress, but by altering the conditions that create the negative stress responses. Human and organi- zational resources can be used, for example, to hire more controllers to
2 WORKLOAD TRANSITION handle peak times and high volumes of traffic Kahn (1987) concludes a recent review of stress research indicating optimism about the potential for organizational-level interventions. While research findings concerning the responses of individuals in vari- ous occupations to stressful situations or encounters are important, perhaps even more useful for the investigation of teams in transitions, such as tank crew operations in stressful environments, are the studies of teams and team-building strategies. Numerof (1987) and S. alas and coworkers (Baker and Salas, 1992; Driskell and Salas, 1992; Tannenbaum et al., 1992) pro- vide models of team characteristics that may be relevant to teams in a workload transition. Teams are defined by Numerof as groups that have a high level of energy directed toward accomplishing a goal, usually in set- tings in which the tasks to be performed require multiple inputs and cannot be handled by any individual alone, which is generally true of tank crews during periods of engagement. Effective teams are referred to as groups that have a combination of high loyalty, morale, commitment, adaptability, and exchange and coordinate information. These good team qualities, which may provide a buffer against organizational stress, include: effective lead- ership, appropriate selection of members, commitment and cohesion, open climate, achievement motivation, effective work methods, clarity of proce- dures, giving and acceptance of constructive criticism, individual initiative, high creativity, positive intergroup relations, and role clarity. These characteristics are briefly described below, based on Numerof's (1987) review. Various studies support the significance of the individual components of the model, but what remains to be specified is the relative impact of each component on team performance and the optimal mix. Ef- fective leadership is viewed as one of the most important components, given the wealth of research on this factor (see Chapter 10~. What appears to be critical is the ability of the leader to change leadership style based on the requirements of the situation and to integrate the needs and individual abili- ties of the team members to meet the demands of the task situation. We will expand on our discussion of this factor subsequently, given its significance for team performance. Appropriate selection of members refers to the extent to which the individuals are well matched as a team to the task requirements. This includes the match between each individual and the job requirements, or what is referred to above as the job-person fit. This issue is discussed in greater detail in Chapter 10 in the context of airline crews, on which there has been a great deal of research involving the task and social skills re- quired to maximize crew performance ire the cockpit in particular, to opti- mize crew performance and decision-making skills under the high stress produced by emergency situations. Commitment and group cohesion are referred to frequently in the litera
STRESS 113 lure on group productivity and effective teams. The usual assumption is that high levels of cohesion and commitment enhance group productivity. While this is generally true (see review by Ridgeway, 1983), high cohesion may also result in lower group productivity if the performance noes of the group run counter to those of the overall organization (e.g., the normative pressures in some work groups that limit work output or the rate of produc- tion). Furthermore, highly cohesive groups may also be subject to the problem identified by Janis (1972) as groupthink, situations in which group members who offer information or criticisms that deviate from the more popular decision in the group are ignored. According to Ridgeway (1983), this high level of cohesiveness may cause groups to make poorer decisions than they otherwise might. And yet highly cohesive groups often have more trust in each other and coordinate their behavior more. It has been found (Kelley et al., 1965) that outside stress makes it harder for members to trust one another and coordinate their behavior together, which greatly increases the social difficulty of the group's task, although some evidence provided by Driskell and Salas (1991) suggests that this may not invariably be true. Therefore, more cohesive groups whose members have good interpersonal relationships should perform better under high stress conditions (Shils and Janowitz, 1948~. Many of the remaining team components are self-evident; thus, only those that are less so are discussed. An open climate is critical because it represents a team that has open direct communication and trust. In such groups members often feel at ease in taking what they consider appropriate risks, which in turn enhances opportunities for innovation and creativity. Achievement motivation refers to the extent to which team members are motivated toward performance goals and are willing to use feedback mechanisms to improve performance over time. Individual initiative is also an important component in effective teams since members are encouraged to emphasize their own unique contributions and to raise constructive ques- tions concerning procedures or suggestions and actions of other group members. Risk-taking is also encouraged, as is creativity. These factors may be less important during routine activity for tank crews, but they may be crucial during the transition phase and periods of high stress. The significance of cohesion, described above, arises in the context of team-building activities since teams may become isolated and more oriented to the enhancement of group performance, at the expense of other teams or units. For tank crew teams this is essential because of the interunit commu- nication and coordination required for successful maneuvers. Positive in- tergroup relations and corporate role clarity are critical for this reason. The former refers to the nature of the working relations with other teams or units, the latter to a clear picture of the way in which each team fits into a larger whole. Training could enhance both of these factors through simula
4 WORKLOAD TRANSITION lion exercises and team-building strategies that increase cohesion without increasing intergroup competition. Often intergroup competition is used to enhance group cohesion, which would be counterproductive for the situa- tion in which intergroup cooperation is required, as in the transition phase and during subsequent maneuvers. However, to the extent that team building is useful to improve perfor- mance, raise levels of trust and commitment, and reduce stress that results from external factors as well as internal factors such as poor integration, lack of goal clarity, low levels of participation, and commitment, then strong leadership is required to counteract the stress created by a more open cli- mate involving more feedback and open management of conflict. Thus, we return to the importance of leadership. Good team qualities provide a buffer against stress, organizational as well as environmental. Trust, participation in decision making relevant to the work being performed, excellent communications, and a commitment to collaboration have all been identified as conducive to effective team-build- ing processes (Numerof, 1987; Tannenbaum et al., 1992~. Organizational resistance to effective team building comes from two sources, perceived threat and resistance to change. While some of these characteristics are not particularly relevant to the tank crew environment, other features are of central importance given that tank crews fit the above definition of a team (i.e., a group that requires coordination and cooperation to produce an out- come that no individual alone can produce). Various organizational effects resulting from the failure to implement good team-building strategies for both group and organizational-level out- comes have also been identified (Numerof, 1987~. For example, suboptimization occurs when organizational objectives are not clearly communicated. Indi- viduals may perform their own functions appropriately, but coordination is lacking. Organizational objectives may not be clearly defined or may change often and thus result in greater stress and uncertainty. If there is low commitment to the group and/or the organization and low cohesion, stress in the group will be high and team performance will be impaired. In orga- nizations in which work is characterized by high levels of interdependence, frequent problem-solving efforts, and high demands for accuracy and/or timeliness, team building is very important (Numerof, 1987~. For tank crews and, similarly, air crews, this model has implications for selection, recruitment, training, and the organization of roles and work assignments. In addition to environmental buffers (e.g., alterations in the actual tank environment), team-building efforts can be employed to minimize commu- nication problems and the stress-related inefficiencies in decision-making and problem-solving tasks, described in later chapters.
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