Environmental pressure, in space as elsewhere, can result in complex patterns of responses. Multiple stressors can yield responses which are different in kind from those associated with the component stressors; furthermore, effects may first appear, or become pronounced, after the offending stimulus has been withdrawn.
 Multiple Stressors
In assessing how the conditions of spaceflight may affect behavior, it is important to note that stressors are rarely isolated or independent, and that interactional effects may vary in complicated ways. Murray and McCally (1973) provide a review of laboratory studies involving multiple or combined environmental stressors. The measures of interest in these studies were either physiological or perceptual shifts, or changes in one or more performance tasks. These authors note that environmental stressors may, hypothetically, interact in three general ways: by addition, when the physiological effects of multiple stressors are equal to the linear sum of the single effects; by synergism, when the combined effects are greater than the simple sum of effects; or by antagonism, when the total effect is less than the linear sum of the single effects. Complex patterns of response to multiple stressors have also been reported when psychological adjustment and social interactions are observed. The more interesting effects here result from stressors that combine to reduce the response of a single stressor alone. In one study, subjects experiencing the stress of confinement exhibited more hostility when they had sufficient space than when they had the added stress of being crowded (Smith and Haythorn, 1972). Palamarek and Rule (1979) found that men who had been insulted in a comfortable room showed more aggression than men who had been insulted in a very hot room; Baron and Bell (1976) report that high temperatures facilitated aggression among subjects who had received a positive evaluation from their experimental partners, but that high temperatures actually inhibited aggression among subjects who had been negatively evaluated. In a study of groups at the French Antarctic station, it was found that problems of psychological adjustment "paradoxically appear to increase with greater physical comforts" (Crocz, Rivolier, and Cazes, 1973, p. 362).
One explanation of why hostile behavior should decrease with added stress comes from the study of Baron and Bell (1976). These authors hypothesize that, for instance, a reasonably comfortable person, on experiencing a high ambient temperature, reacts with aggression; however, for a person made to feel uncomfortable by a negative evaluation, and then exposed to a high ambient temperature, the drive to escape or to minimize the discomfort may overshadow aggressive inclinations. An alternate explanation for the lessening of aggression following multiple stressors is that a certain energy level is required either to complain or to act out. Below that energy level the person must spend his efforts coping rather than  objecting. Whatever the dynamics, multiple stressors are likely to extract a high cost, both physiologically and in terms of reduced performance, even though they may serve to limit the expression of aggression.
Stressors present in an environment can influence behavior even after the triggering stimuli have been withdrawn. Cohen et al. (1980) found decreased performance on a cognitive task among children tested in a quiet environment but who were chronically exposed to a noisy environment. Examining the literature related to aftereffects, Cohen (1980) concludes that negative effects are not restricted to particular stimuli, but occur as a result of a wide range of both physical and psychological stressors. Although most studies of aftereffects have examined performance decrements, social behavior can also be affected. For extended spaceflight, a particularly worrisome form of poststressor behavior involves the finding of decreased sensitivity to, and increased hostility toward, others following exposure to stress (Cohen, 1980). Glass and Singer (1972) report that the onset of negative responses may not occur until sometime after the passing of the stressful situation (p. 10):
Interventions that increase personal control over the situation or that render the stress more predictable have been found to mitigate poststressor as well as stressor effects (Glass and Singer, 1972; Cohen, 1980). Various hypotheses have been offered as to why environmental stressors should result in later performance decrements. A widely accepted explanation, based on the findings of Selye (1976), is that after a time of coping with stress, exhaustion sets in, with this exhaustion showing itself in various behavioral changes. Another explanation, similar to that offered for multiple stressors above, is that negative behavior requires an expenditure of energy that may be unavailable during stress. If this latter explanation is correct, negative reactions may signal the beginning of recovery.