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pa ge ~ The literature concerning stress is extensive and complex, extending through fields as varied as clinical applied psychology, anthropology, sociology, psychosomatic medicine, industrial relations, and epidemiology. Not included in this list are' of course, the extensive studies dealing with the biochemical and physiological of the responses to stress. These responses have been involved in mechanisms as basic as immunological function, metabolic function, and fundamental psychological processes, such as memory and learning. Since one of the primary problems in stress research is conceptual, and this problem takes many forms, there is a great deal of confusion in the field. Because stress researchers lack a common vocabulary, each writer must define his/her own terms, and the reader must scrutinize each article carefully in order to understand the writer's vocabulary The lack of a uniform and consistent vocabulary is a substantial impediment to progress and adds materially to the confusion in the field. Although the term rstressn is used throughout the literature, it is apparent that this term has multiple meanings, depending upon the particular field in which the concept is being investigated. Within the context of this report, we shall attempt to use one set of operational definitions to define stress, and at least to be consistent with our own definitions of the primary psychological variables that induce many of the profound long-term effects commonly attributed to stress. Stress can be approached from a purely behavioral perspective, and it effects studies on primarily behavioral outcomes. However, stress has also been viewed predominantly as a physiological and psychosomatic process, and the outcomes arestudies on either pathophysiological processes or basic biological processes. This report, however, will focus on an integration of these two perspectives and present a psychobiological view of stress.

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Page 3 It is important to note that, historically, the concept of stress has been predominantly implicated with changes in the endocrine systems. Initially, the changes were specifically related either to increased secretion of catecholamines or to activation of the pituitary-adrenal system. The problems are best illustrated by examining the concept of stress beginning with Selye's (1936) early work in which he defined a general adaptation syndrome (GAS) in rodents. This nonspecific response occurred after diverse noxious agents, such as exposure to cold, surgical injury, spinal shock, and muscular exercise. The essential argument was that the response did not depend upon the type of agent that produced it; rather, like inflammation, it was deemed as nonspecific. GAS was divided into three stages: an alarm reaction, a stage of resistance, and a stage of exhaustion. The initial stage included activation of the pituitary-adrenal system and eventually resulted in adrenal hypertrophy, thymicolymphatic involution, and gastric ulceration if the noxious stimuli persisted. If the response to the aversive situation was sustained, physiological resistance ultimately developed, and it was hypothesized that stressed subjects would enter a third stage--exhaustion--which occurred 1-3 months after the initial exposure. Problems with this view have occurred at several levels. First, there was an early emphasis on the physical and chemical aspects of the stressful stimuli, and we now know that psychosocial stimuli are also potent elicitors of the stress response. Second, Selye has received much criticism for the "nonspecificity" view because, with modern hormone assays, it is now possible to detect differential endocrine responses to certain stimuli. Further, the importance of the final stage of exhaustion has been questioned. Diseases due to exhaustion of this syndrome are rare, and, with the exception of a few animal models (e.g.,

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Page 4 intruders in wild rat colonies), have not been demonstrated as a response to psychosocial stimuli (Allen, 1972). Moreover, a number of physicians have studied moribund patients and have found that adrenal exhaustion did not occur even at death. Rather, there is usually increased adrenal output immediately before and after death (Sandberg et al., 1956~. The dramatic picture described by Selye is emphatically different from the present day concept of stress in the lay literature, which includes the daily troubles and anxieties of commuters and executives. The broader use of the term has resulted in an urgency to reduce or eliminate stress in both personal and professional arenas, even though Selye (1974) himself has minimized the significance of this type of stress and stated that its absence occurs only after death. This paradoxical situation reveals that we do not have a clear and generally accepted definition. As a consequence, there is a serious communication problem and increasing talk about a crisis in stress research (Wolf et al., 1979). At the very least, there is a growing impatience with the present state of vagueness in an area so vitally important for issues of health and quality of life. We believe that much of the controversy over stress theory can be eliminated through clarification of the Different limb,. that is, by focusing on the nature of the stimuli that provoke physiological responses rather than on the physiological responses themselves. This type of investigation requires an unusual integration of physiology and psychology--disciplines which have traditionally been separated--and puts the major emphasis on psychological variables.

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Page 5 One of the purposes of this report is to examine the importance of psychological variables that have been determined to have profound endocrinological consequences both in animals and humans. In fact, the major conceptual framework pervading this report is that one of the primary aspects of stressful stimuli eliciting an endocrine response is psychological in nature. This perspective is derived from Mason's (1968, 1975a,b) review of psychoendocrine research, particularly involving the pituitary-adrenal cortical system. As mentioned above, much of the early stress research had emphasized the nonspecificity of the organism's response to a wide variety of physical stressors (Selye, 1950). However, even in the 1950s, it was becoming increasingly apparent that psychological factors were importantly involved. For example, in one study, Renold et al. (1951) examined the physiological response of participants in the Harvard Boat Race. Utilizing a traditional measure of that period, the decline in eosinophils following stress, they found that eosinophils in the crew members were markedly lower 4 hours after the race. This decline could have been attributed solely to the exercise and physical strain, but the investigators also discovered that the coxswains and coaches had similar eosinophil drops, even though their stress was purely psychological. In Mason's major review of the stress literature in 1968, he pointed out that much of the prior work, including the experiments on physical stimuli, shared one important characteristic, namely, that a typical aspect of the stressful experience was exposure to novel, strange, or unfamiliar environments. Therefore, the common threat that may have explained the animals' response was the psychological dimension of the stimuli, rather than the particular physical trauma to which they had been exposed. In subsequent research, Mason (1975a,b) was able to show that when animals are exposed to the

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Page 6 stimuli in such a way that they do not experience distress or novelty, then typical stressors such as heat or fasting do not necessarily result in activation of the pituitary-adrenal system. The concept that psychological variables can activate, and inhibit, the endocrine system has subsequently received much support in experimental studies on both animals and humans. PITUITARY-ADRENAL SYSTEM Although the response to stress can best be defined as a syndrome, which includes many changes in neurochemical and metabolic processes, for the purposes of this report we will focus on the response of the pituitary-a/renal system. It is important to remember, however, that we are utilizing this as a model system. There is abundant evidence indicating that the hormone function of ocher endocrine systems--including insulin, growth hormone, and prolactin--can also be influenced by psychological variables. In addition, it has been demonstrated recently that the endorphins are also extremely responsive to stress. In fact, it appears that almost all of the stimuli capable of eliciting an ACTH response from the pituitary are also capable of releasing beta endorphins (Guillemin et al., 1977). There are two reasons for focusing on the pituitary-adrenal system in illness. First, there is an extensive data base showing the effects of psychological variables on the pituitary-adrenal system. Second, and perhaps more important, is the profound influence that adrenal hormones have on many basic functions related to health. There have been many attempts in recent years to resolve the issue of the primary stimuli that elicit the endocrine response, in particular pituitary-adrenal responses, which occur under conditions of stress. As Mason

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Page 7 (1975a) pointed cut, when the psychologically threatening or arousing aspects of the situation were altered, classical stresses such as fasting and heat no longer activated the pituitary-adrenal system. In the case of heat, there was, in fact, a reduction in the corticoids when the mode of presentation was gradual. The importance of the rate of presentation of a particular stimulus was also demonstrated in another experiment that used a potent physiological insult to induce adrenocortical activity. Hemorrhage in the magnitude of 10 ml/kg at the rate of 6.6 ml/kg/min actively stimulates the adrenal cortex of the dog. In contrast, if the same ultimate volume of blood loss is achieved at a much slower rate of hemorrhage (i.e., 0.3 ml/kg/min), the pituitary-adrenal system does not activate (Gann, 1969). That rapid hemorrhaging induces adrenocortical activity, while slow rates of hemorrhaging do not, once again indicates that the rate of stimulus change is one important parameter for the induction of pituitary-adrenal activity. The fact that dexamethasone blocks the pituitary-adrenal response at a high rate of hemorrhaging clearly indicates that neuroendocrine systems are involved and that the effect was not mediated peripherally. Regardless of the specific explanation that accounts for these results, their general significance cannot be underestimated. Hare recent studies on psychoendocrine responses have indicated further that it may be possible to use adrenal activity as a measure of specific emotional responses, rather than simply as a reflection of undifferentiated arousal (Hennessy and Levine, 1979; Mason, 1975a,b). In addition, studies on psychological stress bring out one point quite clearly; the great individual differences typically observed in response to a given stressor can best be explained in terms of cognitive mechanisms. For example, a subject's perception

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Page 8 of a stressor as z th.ea_, or the coping responses that are available to the subject, may well determine the physiological response. It may be insufficient, therefore, to merely describe the stimulus operations involved in producing a stressor. A psychobiological approach to understanding endocrine function cannot escape making reference to cognitive processes. In his new description of arousal theory, Berlyne (1960, 1967) provides a framework for the description of the processes by which stimulators of arousal (and thus, activators of the pituitary-adrenal response) operate. Novelty, uncertainty, and conflict are considered primary determinants of arousal. These have been labeled by Berlyne as collative factors, because in order to evaluate them, it is necessary to compare similarities and differences between stimulus elements (novelty), or between stimulus-evoked expectations (uncertainty). The basic cognitive process involved in stimulation of the pituitary-adrenal system, then, is one of comparison. To a large extent, the cognitive processes of comparison can be best understood by adding the concept of uncertainty, although there are some differences between uncertainty and novelty. Uncertainty seems to be a major factor underlying many psychological responses. The processes involving neuroendocrine activation under conditions of uncertainty are best explained by a model elaborated by Sokolov (1960) to account for the general process of habituation. The pattern of habituation is familiar to most people. A subject is presented with an unexpected stimulus and shows an alerting reaction. Physiological components of this orienting reaction are well known--general activation of the brain, decreased blood flow into the extremities, changes in electrical resistance of the skin; and increases in both adrenomedullary and cortical hormones. If the stimulus is frequently repeated,

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Page 9 all of these reactions gradually dim~nisn and eventually disappear, and the subject is said to be habituated. It does appear, however, that physiological responses may habituate more slowly than the observed behavioral reactions. Sokolov's model, in essence, is based on a matching system in which new stimuli or situations are compared with a representation in the central nervous system of prior events. This matching process results in the development of expectancies whereby the organism is either habituated or gives an alerting arousal reaction (Pribram and Melges, 1969). Thus, the habituated organism has an internal representation of prior events with which to deal with the environment--expectancies--and if the environment does not contain any new contingencies, the habituated organism no longer responds with the physiological responses related to the alerting reaction. Activation of the pituitary-adrenal system by any change in expectancy can also be accounted for by invoking the powerful explanatory capacity of the Sokolov model. NOVELTY AND UNCERTAINTY Exposure of an animal to novelty is one of the most potent experimental conditions leading to an increase in pituitary-adrenal activity. Novelty can be classified as a collative variable, since the recognition of any stimulus situation as being novel requires a comparison between present stimulus events and those experienced in the past. Increases in pituitary-adrenal activity in response to novelty have been demonstrated in humans as well as animals. For example, increased adrenocortical activity, as evidenced by elevated levels of circulating cortisol, are observed in individuals during their first exposure to procedures involved in drawing blood at a blood bank. However, if they have had

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Page 10 prior blood bank experience, there are no such increases (Mendoza and Barchas, 1982). Further, in an experiment to be discussed in detail later, young adults experiencing their first jump off a tower during parachute training also show a dramatic elevation of adrenocortical activity, which is not observed on subsequent jumps from the tower (Levine, 1978). Studies on animals also indicate another important characteristic of the cognitive process which results in pituitary-adrenal activation, that is, the ability of the animal to discriminate similar vs. unfamiliar stimulus elements. In a series of experiments on rats and mice it was demonstrated that if novelty was varied along a continuum with increasing changes in the stimulus elements, there was a graded adrenocortical response according to the degree.to which the environment represented a discrepancy from the normal cage living environment of the organism (Hennessy and Levine, 1977 ; Hennessy et al., 1979~ . Thus, minor changes, such as placing the animal in a different cage, but one identical with its home cage, resulted in an elevation of plasma corticosterone, but one that was significantly less than when the animal was placed in a totally novel cage containing none of the elements of its familiar living conditions. This capacity to make fine discriminations resulting in graded elevations of pituitary-adrenal activity are clearly demonstrative of the remarkable capacity of the central nervous system to regulate the output of pituitary-adrenal response. Novelty, according to the theory presented by Sokolov, should indeed be one of the most potent variables that elicits increases in pituitary-adrenal activity. Insofar as an organism has no expectations about an unfamiliar environment, that environment should represent a degree of uncertainty that should lead to increases in neuroendocrine activity.

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Page 11 Although novelty can be subsumed under the general concept of uncertainty, not all conditions which create uncertainty are novel. Uncertainty can also be evoked by insufficient information concerning the nature of upcoming events. Uncertainty can be seen to vary along the continuum from highly certain, predictable events to highly uncertain, unpredictable events. The presentation of a novel stimulus is likely to lead to an increase in uncertainty because, by definition, there is little information the organism can use to predict forthcoming events. However, uncertainty can also be defined in terms of contingencies between environmental events. Experimentally, the dimension of uncertainty can be controlled by limiting the amount of information available to the organism to predict the occurrence of a specific event. Thus, one would hypothesize that if an organism is given information about the occurrence of either an appetitive or an aversive stimulus, such predictability should lead to a reduction in the pituitary-adrenal response. Further, situations in which there is an absence of predictability should lead to a dramatic increase. There are many experiments that illustrate the value of predictability in modifying the pituitary-adrenal response to a variety of stimuli (Weinberg and Levine, 1980). One illustration of the effects of reducing uncertainty by" providing predictability can be seen in a study by Dess et al. (1983). Dogs were subjected to a series of electric shock which were either controllable or predictable. The predictable condition involved presenting the animal with a tone prior to the onset of shock. In the unpredictable condition, no such tone was presented. The adrenocortical response observed on subsequent testing of these animals clearly indicated the importance of reducing uncertainty by predictability. Animals that did not have the signal preceding the shock showed

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. Page ;2 an adrenocortical response which was two to three times that observed in animals with previous predictable shock experiences. It should be noted that the procedures used in this experiment are typical of those utilized in experiments examining learned helplessness (Selig~an, 1975). Learned helplessness refers to the protracted effects resulting from prolonged exposure to unpredictable and uncontrollable stimuli of an aversive nature. It has been observed that organisms exposed to this type of an experimental regimen show long-term deficits in terms of their inability to perform appropriately under subsequent testing conditions. Further, these animals show ~ much greater increase in adrenocortical response when exposed to novelty (Levine et al., 1973) than do control animals. Thus, an organism exposed to an uncontrollable and unpredictable set of aversive stimuli not only shows a dramatic increase in adrenocortical activity while exposed to these conditions, but there is also a long-term effect in other unrelated test conditions. The concept of control is particularly important in understanding these long-term effects, and it will be dealt with later when the issue of coping is discussed. There is yet another series of experiments related to the issue of uncertainty. These do not utilize aversive stimuli typical of stress research, but are more directly related to a psychological response commonly described as frustration. Frustration can be evoked when the organism fails to achieve a desired goal following a history of successful fulfillment of these goals. Experimentally, the operations utilized to produce frustration involve either preventing an animal from making the appropriate response to achieve a desired object, or not reinforcing the animal for a response that has had a prior history of reinforcement. In a broader sense, frustration involves the failure of an

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Page 36 not prove to be tenable, Glass and Singer did conclude on the basis o. their work that exposure to unpredictable uncontrollable stress produces post-st.muiation deficits in performance on a number of tasks, and that the ability to predict and control stressors ameliorates these deficits. It is not the purpose of this report to comprehensively review all of the studies that have shown deficits in some aspect of performance as a consequence of prior exposure to uncontrollable and unpredictable stress. However, some examples of the type of research conducted in this area and a review of the findings would suffice. Using noise as a stressful stimulus, Glass and Singer (1972) reported a number of studies that examined post-stimulation effects after exposure to unpredictable uncontrollable noise (pp. 47, 50, 52, 55, 80). These studies typically involve approximately 25 minutes exposure to 108-110 dB random in~cermit~cent bursts of broad band conglomerate noise made up of a nuder of typical urban sounds. During noise exposure, the subjects worked on simple cognitive tasks. Autonomic response was monitored during stressor exposure. Immediately after noise exposure, one or more of three measures were administered to the subject: tolerance for frustration tasks (Feather, 1961), a proof-reading task (Glass and Singer, 1972), and the Stroop (1935) Color-Word task. The Feather test requires a subject to work on two soluble and two insoluble line puzzles for 15 minutes. The subject can only work on one puzzle at a time and cannot return to a puzzle after moving on to the next. The puzzles are presented so that the first and third are insoluble and the second and fourth are soluble. The criterion measure for amount of tolerance of frustration is the number of trials, puzzle cards, or amount of time spent on insoluble puzzles. The proof-reading task involves correcting misspellings, grammatical mistakes,

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Page ~7 incorrect punctuations, transpositions, and typographical errors. Each subject is usually given 8-15 minutes, and the quality of performance is measured as the percentage of errors not found out of the total number of errors that could have been detected at the point the subject was told to stop. In the Stroop task, the stimuli are names of four colors--green, red, orange, and blue--each of which is printed in one of the other three colors. For example, the word preen may be printed in red, orange, or blue. The four color words are randomly presented over a series of trials, and the subject is asked to name the color and the word which is printed. The control version of the task, in which the subject is required to name the colors of a set of asterisks or zeros, is also administered to each subject. Stroop interference scores on accuracy and speed are obtained by subtracting the subject's score on the control stimuli from the subjects's Stroop scores. Post-stimulation deficits in performance occurred in all of the studies in all three of the tasks. The data presented by Glass and Singer appear to be highly reliable and have been replicated by several other authors (Gardner, 1978; Rotton et al., 1978; Wohlwill et al., 1976). Although the Glass and Singer research suggests that post-stimulation effects occur only following unpredictable noise, at least two studies reported similar deficits following exposure to high intensity steady-state continuous noise. Such steady-state continuous noise presumably does not have unpredictable components (Broadbent, 1979; Hartley, 1973). Thus, the data on post-stimulation effects of noise producing deficits on performance appear to be consistent for variable continuous and steady-state continuous noise, as well as for unpredictable noise. .

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Page ;8 Although noise has received a considerable amount of attention in the experimental literature (due to the ability to control this particular variable more closely than others), there is evidence that other stressful conditions do produce post-exposure effects. Studies have indicated that subjects who have experienced high taskload perform more poorly following task completion than those who have been exposed to low taskload. Cohen and Spacapan (1978) found in a forced reaction time experiment that those required to respond to 100 lights/minute had less tolerance for frustration following task completion than those responding to 50 lights/minute. Hartley (1973) reports that those required to perform a serial reaction time task for the first 20 minutes of an experiment perform more poorly on the same task in the last 20 minutes than those who simply read during the initial phase of the study. Rotton et al. (1978) found that the subjects who expected to be required to recall a speech, even though never actually required to do so, showed lower tolerance for frustration following task completion than those subjects not expecting a recall test. Crowding also appears to effect subsequent performance and to produce post-exposure deficits. Studies on the effects of crowding on human behavior have found it necessary to distinguish two kinds of crowding conditions: spatial density and social density. Spatial density is manipulated by varying available space but keeping the number of people constant; social density is manipulated by varying the number of people occupying a fixed quantity of space. As an example of the aftereffects of spatial density, She rood (1974) had groups of female high-school students perform a number of tasks in either ~ large or a small room. After 1 hour of exposure the subjects were moved into a larger area. Each student was then tested at her own desk on tolerance for frustration at a

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Page 39 proof-reading task. Those subjects who had been working in a high-density small room showed less tolerance for frustration than did their low-density large room counterparts. However, there were no differences on the proof-reading task. Some of the post-crowding deficits varying spatial density have been reported by Evans (1979) and Aiello et al., (1977). The existing studies in which spatial density was varied indicate that exposure to high-density conditions produced post-exposure deficits on the limited number of tasks investigated. However, the few studies which have varied social density provide evidence indicating that, although social density may produce post-stimulation deficits on performance, these effects interact with a number of other variables. Saegert et al. (1975) required male and female subjects to do a number of tasks in a railway station during crowded and uncrowded times of the day. Whereas females who had been exposed to high levels of density performed more poorly on the S troop test than did their low-density counterparts, males performed better after high than after low density. Glass and Singer also have reported that there are post-exposure deficits in performance following a variety of other stressful conditions, which include electric shock, a frustrating experience with a bureaucracy, and an experience of arbitrary or sex discrimination. The previously cited studies provide evidence for both the reliability and generality of the post-exposure effects of stress on performance. These effects have appeared in the vast majority of studies and these studies have used a wide range of stressors. The data suggest that the effect is most likely to occur when the stressor is clearly unpredictable and when a sensitive aftereffects measure is used. Moreover, the factors that might mediate the stressfulness of the situation, i.e., subject gender, perception of

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Page 40 control, individual need for personal space, all appear to be important determinants of whether a particular manipulation will produce a significant deficit in subsequent performance. Within the context of coping theory, control, predictability, and feedback are considered to be important psychological dimensions which lead to a reduction in the psychological and biological responses to stress. The data in the stress and performance field are almost unanimous in supporting the role of both perceived and implemented control in ameliorating the post-exposure effects of the stressful experience. In some cases, groups with control performed as if they were not exposed to a stressor (Gardner, 1978; Glass et al., 1973); whereas in others, Sherrod et al. (1977) control provided some improvement in the post-stress task performance but did not completely ameliorate the effect. What does appear to be particularly cogent is the control, or perceived control, over the termination of the stress. There is a single study that indicates that initiation control, that is, the ability to control the onset of the stress, similarly produces an amelioration of the post-stress performance deficits. Providing someone with more than one kind of control does appear to be more effective than only having control over termination of the stressors. The role of predictability in reducing the aftereffects of stress has not received much attention, although the existing evidence does indicate (Glass and Singer, 1972) that the post-exposure deficits in performance are more likely to occur following exposure to an unpredictable, rather than to a predictable stress. In view of the abundance of data produced experimentally indicating post-exposure effects on subsequent performance, it is not surprising that investigators have also studied the effects of these stressful experiences in

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Page 41 more naturalistic settings. Several investigators have studied the effects of long exposure to community noise on the performance of elementary school students. In one exemplar study, Cohen et al. (1973) tested children living in an apartment building built on bridges spanning a busy expressway. When tested in a quiet setting, children who lived in noisier apartments showed greater impairment of auditory discrimination and reading ability than those who lived in quieter apartments. The length of time in residence increased the magnitude of the correlation between noise and auditory discrimination. A subsequent study of children attending school in the air corridor of a busy metropolitan airport (Cohen et al., 1980) indicated that children living and attending school in the air corridor were poorer on both a simple and a difficult problem-solving task and were more likely to give up the task than their quiet-neighborhood controls. There are several studies which have also investigated the naturalistic effects of crowding. Rodin (1976) reported that 6- to 9-year-old children from high-density apartments of a low-income housing project were less likely than children from less dense homes in the same project to control (choose) their own outcomes on a reward task. In a subsequent study, 8th grade children from high-density apartments were more adversely affected by a learned helplessness pretreatment (insoluble puzzles) than were their low-density counterparts. These effects persisted even after statistical control for social class and race were used. Although these naturalistic studies on crowding do not specifically address the issue of stress on performance, they do indicate chronic effects of crowding on certain aspects of human behavior.

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Page 42 1!} summary, the following conclusions can be generated from the material whoosh we have just reviewed on the post-exposure effects of stress on performance. (1) The post-exposure effects of unpredictable uncontrollable stress on performance have been replicated in many different laboratories and with a variety of subject populations. They occur as a result of a wide range of stressors, such as noise, electric shock, social density, etc. Interventions that increase control and predictability are effective in reducing these effects. However, it is important to note that the laboratory research has used a limited number of tasks with which to measure the post-exposure effects on performance. (2) Post-exposure effects of environmental stresses occur following prolonged exposure in naturalistic settings. These studies have suggested that the effects are mediated by helplessness. However, the studies in naturalistic settings--particularly those related to crowding--are not specifically directed toward performance deficits. (3) There is evidence that various forms of control have ameliorative effects similar to those of perceived control over the termination of the stressor. These include termination control, in which one actually performs a coping response, as well as initiation, choice, and information control. There is some evidence to suggest that combining more than one form of control will further improve post-exposure performance. This improvement, of course, cannot exceed the performance level reached by the no-stress conditions. Thus far, most of the data we have presented in this report on the relationship between stress and performance indicates that stress has a negative effect and results in performance decrements. However, it would be erroneous to conclude that there is always a negative relationship between stress and

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Page 43 performance. Hennessy and Levine (1979) presented a comparison between the concepts of stress and arousal and concluded that the concept of stress might be subsumed under the umbrella of arousal theory. Both stress and arousal can be considered as representing a "state phenomenon" referring to the tonic nature of the effects. A distinction has been drawn between stimulus response (SR) or motor systems with direct pathways through the brain, and estates or arousal systems with diffuse central nervous system connections (Groves and Thompson, 1970; Thompson and Spencer, 1966). This proposition was derived from the results of studies of response plasticity within SR systems; when a motor response is evoked, SR and arousal systems are activated. The two types of systems appear to be independent, yet interaction is possible. One of the most pervasive findings in the literature with relationship to arousal and performance is that these relationships are curvilinear--that the relationship between arousal and performance is characterized by a U-6haped function, rather than being monotonic. One of the earliest studies to show an inverted U-shaped curve between stress and performance was that of Yerkes and Dodson (1908) who found that when animals are exposed to electric shock of medium intensity, they made fewer errors in learning than they did when exposed to weaker or stronger shocks. Finan (1940) also found that equated groups of rats deprived of food for 1, 12, 24 and 48 hours showed differences in conditioning strength in a Skinner apparatus when conditioning strength was measured in terms of extinction. The optimal deprivation interval was 12 hours. Conditioning strength was less for intervals shorter and longer than the optimal. Levine (1966) also reported a study in which, as electric shock increased in an avoidance learning paradigm, the ability of the animals to learn declined beyond

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Page 44 optimal levels of the unconditioned stimulus electric shock. Within the human literature, Freeman (1940) studied reaction time in palmer conductance, an index of autonomic activity. Over a period of many days, 100 measures of palmer conductance and reaction time were taken. When the pairs of values were plotted, an orderly function appeared. Low palmer conductance (thus, less autonomic activity) was associated with slow reaction times, and high conductance was associated with fast reaction times. However, beyond the optimal range of palmer conductance, reaction time once again became slower. Thus, we have the classic demonstration of the relationship between arousal and performance, in this instance reaction time, resulting in the U- or inverted U-shape function. Reviewing all of the literature on U- or inverted U-shaped functions would represent another volume. The inverted U-function has been one of the most robust in the psychological literature. Classical activation theorists, such as Duffy, Lindsley, and Hebb have all stressed the importance of this curvilinear function. It is of interest that Pavlov in his writings contained reference to this phenomenon: for every one of our animals [dogs] there is a maximum stimulus, a limit of harmless functional strain' beyond which begins the intervention of inhibition [the rule of the limit of intensity of excitation]. A stimulus, the intensity of which is beyond that maximum, instantly elicits inhibition, thus distorting the usual rule of the relationship between the magnitude of the effect and the intensity of excitation; a strong stimulus may produce an equal and even smaller effect, than a weak one.... (Pavlov, 1930, p. 213, quoted by Malmo, 1958). Given the robust relationship between arousal (stress) and performance, it would certainly be erroneous to assume that stress invariably leads to a decrement in performance. There is clearly some optimal

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Page 45 level of arousal which is required for organisms to perform. What is also apparent, however, is that beyond this optimal level of arousal, performance decrements are indeed the rule. However, perhaps the most difficult issue concerning the relationship between stress and performance emerges from the U-shaped relationship between arousal and performance. Individual differences in response to stress, both physiological and behavioral, emerge throughout all of the studies on stress and performance. It would appear, therefore, that what would be an optimal arousal level for one individual may indeed be detrimental to another. The number of variables which contribute to the marked individual differences in optimal arousal levels are perhaps the most difficult to specify. As mentioned previously, there are gender differences. In addition, prior experiences with either controllable or uncontrollable stressful events certainly appear to affect the relationship between stress and performance. There is a large literature which indicates that experiences occurring early in development can also markedly affect the relationship between stress and performance. Further, there is recent evidence that indicates that there may be strong genetic factors determining the response characteristics of individual organisms to stressful stimuli. Perhaps the only generalization that one can make is that individual differences pervade every step in the process of stress arousal/reduction. Lazarus (1974) has repeatedly stated that at the level of a specific individual, the problem is to determine what kind of stress evokes what kind of stress response in what kind of person. What does emerge from the theoretical considerations presented here and from the experimental data on the biological and behavioral consequences of stress, is that control is a major mechanism by which organisms can effectively deal with

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Page 46 stressful conditions; and that the absence of control or loss of control can indeed have profound and permanent effects on individual performance on a wide variety of tasks.