In dealing with people who are removed from their normal living situation, one can observe a wide range of idiosyncratic behavior, yet few individuals appear to view their own behavior patterns as anything but the norm. Spaceflight cannot be expected, for a very long time, to cater to unusual individual preferences; to a large extent the individual must adapt to the environment. However, it is necessary, in a general way, to anticipate those habitability issues of the space environment that could prove discomforting to a large number of space travelers. Among the more common disrupters are problems associated with interior space, food, hygiene, temperature, decor, lighting, odor, and noise.
Extra living area, costly even on Earth, becomes prohibitive when it must be blasted into space. Until we arrive at the point where dwellings can be constructed in space, astronauts' habitats must, of necessity, be restrictive. For the near term, the goal is to strike a reasonable balance between interior space which is unnecessary and that which is inadequate to meet the needs of the occupants. A basic habitability question concerns the minimum space individuals require, either alone or with others, to support their physical and psychological needs. Here we are concerned with the narrow question of volume requirements. The more complex questions of different perceptions of, and responses to, crowding will be considered in a later section entitled "Privacy."
Most of the estimates of volume requirements for humans to live and work in space assume that the length of confinement will be an important variable. Breeze (1961) concludes that a minimum of  50 ft3/person (1.42 m3/person) is adequate for 1 or 2 days of confinement, whereas 260 ft3 /person (7.36 m3 /person) is needed for 1 or 2 months, and 600 ft3/person (17.0 m3/person) for more than 2 months. Fraser (1968a) evaluated the results of 60 confinement studies to determine at what point physiological or psychological impairment occurred which was related to spatial restriction. He found that impairment (which he defined as the demarcation between "no impairment" and "marked impairment") occurred at between 50 ft3 (1.42 m3) for very brief confinement, and 150 ft3 (4.25 m3) for 60 day confinement. He concludes that a volume of 250 700 ft3 /person (7.08 11.82 m3) length of confinement, is adequate.1
The number of individuals sharing confinement is believed to be an important variable affecting the amount of space needed per individual. Davenport, Congdon, and Pierce (1963) employed a model which assumes that more space per individual is needed as the number of individuals increases. This assumption finds some support from the investigation of Smith and Haythorn (1972), which showed that three man crews suffered greater stress with approximately 70 ft3/man (1.98 m3/man) than did two man crews. However, it seems at least as likely that the general relationship is in the opposite direction, i.e., that less space per person is needed as crew size increases. Breeze (1961) implies this latter relationship, at least for small crews, and Fraser (1966) terms the requirements for more space per person with increasing crew size "debatable." Clearly, this relationship requires research clarification.
In addition to the variables of crew size and time in confinement, how the available space is allocated must also be considered. Fraser (1968a) suggests that habitable areas be considered in terms of four kinds of functional units: work unit (operational tasks, vehicle management), public unit (dining, recreation, exercise), personal unit (sleeping, personal privacy, personal storage), and service unit (toilet, laundry, public storage). Very little information is available on the need for functionally distinct areas, or, if such need exists, how to appropriately "mark" the area (i.e., color, style, etc.). One study which deals with this issue has recommended that working and living areas be made sharply distinct from each other by virtue of design  features such as furniture, lighting, and acoustics (Jackson, Wamsley, Bonura, and Seeman, 1972).
Another question involving interior space concerns the utilization of the available areas within the spacecraft. In theory, unrestrained in their weightless state, astronauts should be able to utilize all available space and to work from the "walls" and "ceilings" as well as the "floors" of the vehicle. It has been found that weightlessness does permit astronauts to use space more efficiently than on Earth (Berry, 1973a). However, some space travelers have experienced considerable difficulty in trying to orient themselves in the absence of the familiar cues of gravity, showing a clear preference for rooms with a defined "up" and "down."2 Research on environmental cognition indicates that mental representations help individuals to organize and manage their environment (Evans, 1980). The zero gravity in the space habitat places the individual in the totally unfamiliar environment of ungrounded three dimensional space; in this environment the normal frame of reference is fundamentally disturbed. Lynch (1960) has used the term "legibility" to describe how parts of a scene can be organized into a coherent pattern. The desire of astronauts to define direction in space can be thought of as an attempt to establish legibility in space. It needs to be determined if space travelers are able to acclimate with time (or familiarity) to a directionless world or if their need for a directional orientation persists. If the latter proves to be true, we must conclude that not all surfaces in the spacecraft can be made equally usable.
A problem in using interior space efficiently concerns mobility within the space vehicle. Each time the astronauts move to a new location they must free themselves from the restraints holding them in one area and attach themselves in the new area. Experience in Skylab indicates that of the devices used so far, the ones that keep an individual securely in place are difficult to engage and disengage,  whereas those that are easy to slip into and out of are virtually useless. Grounding shoes based on a suction principle have been tried on Shuttle, but there is little indication that this mobility problem has been solved.
Another limitation to the full use of available space comes under the heading of etiquette or acculturation. For instance, in Skylab, congestion in the dining area would have been relieved if the astronauts were willing to "float" over the table to their places. Apparently passing over an eating area was perceived as inappropriate behavior and the astronauts chose rather to squeeze past each other or to take turns in the eating area (Johnson, 1974). Issues to be addressed for future spaceflight include determining how long it takes for space travelers to adopt an etiquette appropriate to a weightless environment, and identifying visual cues or other aids that might be furnished to make the transition easier.
The Workshop on Controlled Ecological Life Support Systems (Mason and Carden, 1979) enumerated many of the food related research needs associated with advanced spaceflight. These include questions of the storage stability of food, analysis and development of feeding systems, nutritional requirements in space, and the development of criteria for evaluating health status in response to diet. From the behavioral perspective, this workshop also emphasized the question of diet acceptability, including the possible altering of acceptability by such methods as behavior modification.
Experiences in space have not provided much information on how food will be used routinely in extended spaceflight because food intake in space generally has been restricted for medical monitoring purposes. Also, because of the problems involved in preparing and consuming food in a weightless environment, attention has focused on the physical arrangements associated with food consumption, such as packaging, dispensing, scheduling, etc. On the early shortduration flights, food had to be extracted from its container and astronauts gave little attention to mealtime; food and its preparation were viewed as an inconvenience and an intrusion on a very busy schedule (Berry, 1973a). The Skylab flights were the first to demonstrate that food could be eaten from open dishes; Skylab also provided the first opportunity for astronauts to "share a meal." However, even here, astronauts did not always eat together, since there was difficulty in accessing the pantry area when all three astronauts  occupied the dining area simultaneously. One somewhat puzzling aspect involving food is an apparent change in taste between ground and space. On Skylab, food which had been judged to be adequately seasoned prior to flight tasted bland. On the Soyuz 26 mission, Cosmonaut Grechko reported that canned ham which had been judged correctly seasoned on the ground was "too salty" in space, and cosmonauts on later flights were reported to have developed insatiable cravings, for instance for apricot juice and honey (Oberg, 1981). These latter findings are particularly notable since the Russians have given considerable attention to tailoring meals to the preferences and tastes of individual cosmonauts. The reported changes may reflect taste preference shifts related to the general diet in space as compared with Earth, or they may suggest that there are taste or odor threshold changes in weightlessness.
It seems obvious that the view of mealtime as a necessary but annoying interruption in a busy day is bound to change as space travelers become more acclimated to their environment, and as menus offer greater variety and personal choice. On the 15 day Sealab II experiments, food neither offered much gratification nor occasioned much notice (Radloff and Helmreich, 1968). By contrast, on the 60 day Tektite experiments, food took on considerable importance (Berry, 1973a).
In space simulation studies, responses have ranged from food as a primary source of irritation (McDonnell Douglas Astronautics Company, 1968) to food as no problem at all (Coburn,1967). Even the effect of time in confinement on the acceptability of the food supplied has not been consistent. Experience on the Ben Franklin submersible showed that complaints about food increased during the 30 days of confinement (Grumman Aerospace Corp.,1970), whereas in a spaceflight simulation of the same duration, it was reported that the men seemed to enjoy their meals more toward the end of the mission than they had at the beginning (General Electric Corp., 1964).
Probably the most significant food related question for future spaceflight is how food will be used to fulfill psychological and social needs. Clearly, there are advantages to be gained from the social aspects of mealtime. Bluth (1982) suggests that space travelers should plan to share at least one meal a day together in order to help dissipate any tendencies towards divisiveness that might develop. However, there may be special dangers in the social or recreational aspects of food use in space. When confined in an environment which  has grown boring, subjects paradoxically tend to underutilize the recreational facilities provided. Yet these same subjects tend to place great emphasis on mealtime (Mullin, 1960). Eberhard (1967), reviewing experiences in the Arctic and Antarctic, at sea, and on missile bases, concludes that men in confinement take almost twice as long to eat as men in the general population. In a confinement experiment (Rogers, 1978) subjects spent a sizeable portion of their incomes on the embellishment of meals. Overall, expenditures for meals were about 30% higher than that required to maintain an adequate diet (Sullies and Rogers, 1975). The challenge for future spaceflight may be not only to make the food sufficiently appetizing and satisfying to meet the needs and desires of the individual, but also to provide sufficiently engaging activity options, so that the individual's psychological and social needs can be met without a harmful overreliance on food or mealtime.
Americans are accustomed to very high standards of personal hygiene. Probably related is the finding that limitations on bathing facilities and waste management problems have been high on the list of discomforts reported by participants in various confinement experiments (Hammes, 1964, 1965; Hammes and Ahearn, 1966, 1967; Hammes, Ahearn, and Foughner, 1968; Rasmussen, 1963; Strope, Etter, Goldbeck, Heiskell, and Sheard, 1960; Strope, Schultz, and Pond, 1961; Coburn, 1967). In at least two experiments, lack of water for washing was listed as the number one annoyance of subjects confined for a period of 2 weeks (Rasmussen, 1963; Rasmussen and Wagner, 1962).
The hygienic and waste management facilities of early spaceflight must be considered, at best, primitive. Following Apollo, considerable attention was given to this problem and a newly designed hygienic facility was evaluated during a 56 day simulation of Skylab (Van Huss and Heusner, 1979). Although vastly improved over earlier systems, bathing and waste management facilities on Skylab still did not allow the kind of ease and comfort that long duration space travelers would require. For instance, mechanical difficulties were encountered with the integrated fecal/urine collector.3 The  Russians have also reported difficulties in addressing hygienic problems in space. These issues and measures to deal with them were assigned high priority in the flight program of Salyut 7 (Chernyshov, 1982). Problems in the hygiene and waste management areas are well known to space planners, and it can be expected that these concerns will receive continued attention.
Temperature and Humidity
Variations in temperature affect human performance in diverse ways. In general, performance begins to deteriorate in any circumstance where heat reaches about 75% of the physiological tolerance limit (Roth, 1968), with high levels of humidity exacerbating temperature effects. Several studies (Pepler, 1958, 1959; Mackie, O'Hanlon, and McCauley, 1974) have demonstrated decrements in cognition and in psychomotor performance at temperatures at or above an effective temperature of approximately 85°F, with accuracy continuing to decrease as temperature rises. Working at a high constant temperature, performance also has been found to decrease with length of exposure (Roth, 1968). Cognitive tasks are more adversely affected than motor performance tasks (Poulton, 1970). The ability to withstand heat is limited by the amount of physical effort required. The length of time that can be tolerated at different temperature levels decreases dramatically as the amount of energy expended increases (Poulton, 1970). There is evidence that women are less able to withstand the effects of heat than men (Mackie et al., 1974), possibly due to less active sweating mechanisms. Uncomfortably high temperatures have also been related to temper outbursts and negative reactions to others (Griffitt, 1970; Griffitt and Veitch, 1971).
Decreases in temperature also can produce efficiency decrements. Most notable is the decline in skilled motor performance with continued exposure to the cold (Dusek, 1957); declines have also been found in visual reaction time (Teichner, 1957). Although skin temperature of the hands would seem to be an obvious factor in decreased motor performance, other factors also appear to be involved. Lockhart (1968) investigated the effects of a cold body, with and without cold hands, on three manipulative tasks. All three tasks were performed inefficiently when both body and hands were cold. Warming the hands improved performance on all three tasks, but did not raise performance to the level of the controls for two of the tasks.
 Temperature/humidity problems did develop on Apollo 13 and on Skylab 2 when malfunctions occurred, and apparently the Russians experienced difficulty with humidity control of Salyut 4 (Oberg, 1981). However, with the exception of the Apollo Command Module, which was reported to be too cold for sleeping, the temperature/humidity question has not been a major problem in space operations. Temperature has been reported as a source of annoyance in several confinement studies (Smith and Haythorn, 1972; Rasmussen and Wagner, 1962; Rasmussen, 1963). By itself, this finding is not particularly noteworthy, since it is possible that environmental temperature and/or humidity drifted outside an acceptable range. Of more significance are the findings of Coburn (1967) that temperature/humidity ratio was the most common source of annoyance in a 32 day space simulation study, while at the same time no single set of conditions could be identified that would satisfy all six subjects of the experiment. It may be that as space travel expands, and travelers come to expect more amenities, temperature and humidity preferences will need to be taken into account, along with other compatibility considerations. It would also be important to determine if individual differences in temperature/ humidity preference have corollaries in performance alterations.
Decor and Lighting
Space vehicles have now evolved to the point where they have something approximating decor to discuss. Rogers and his colleagues have investigated the importance of decor in confinement (Rogers, 1978). These investigators found that, in 10 day confinement, "plush" decor had very little value to all male crews who were occupied in meaningful work. Attractive surroundings were found to be more important when crews were composed of both men and women, and when all male crews had no meaningful work to perform. Decor was found to be most important when crews were both mixed and without meaningful work. In terms of extended spaceflight, it is reasonable to assume that it will become increasingly important as spaceflights lengthen.
It is generally accepted that the interior design of a spacecraft should have built in flexibility. Such flexibility could include the use of movable partitions, removable wall covers, projectible designs, etc. It can be assumed that, in space as elsewhere, there is a general aversion to sameness. Visual variety can be introduced through the judicious use of texture or color. Skylab astronauts reported that the  sameness of colors within their vehicle was disturbing (Berry, 1973a). Russian investigators have looked at the visual environment of a spacecraft and have proposed ways that changes in decor could be employed not only to relieve visual monotony but to maintain the space traveler's link to the home planet (Petrov, 1975).
In addition to a general aversion to sameness, there is also a recognized aversion to clashing designs. Terrestrial designs feature variety, but a variety which flows from a theme. Individuals experiencing this theme also have the opportunity of experiencing other themes in the course of a day. In space the number of designs must be limited. We need to ascertain what constitutes acceptable versus unacceptable variety in this closed environment. There is evidence that people prefer greater environmental complexity with time (Dember and Earl, 1957). If so, we should plan for increasingly complex arrangements as spaceflight lengthens.
Since there is no atmospheric absorption in space, the visual environment is marked by higher brightness levels than experienced on Earth and, more importantly, by abrupt contrast effects. Disruptive contrast effects could occur if, for instance, an astronaut suddenly encountered a bright object through a window, or if he or she were exposed to a glare from a reflecting surface. For these and other reasons, there has been concern that spaceflight could cause injury to eyesight, or otherwise alter the visual experience.4 In this environment lighting becomes an especially important habitability consideration. Proper lighting is important to safeguard vision, to minimize annoyance, and to enhance the visual environment. Petrov (1975) has pointed out the desirability of individual light controls on all principal instruments so that adequate visual acuity can be maintained in the presence of sudden light flashes or extreme vibration. On Skylab, crews found light levels inadequate for the performance of some tasks and offered recommendations that levels be increased up to sixfold. While modifications, at least those affecting work areas, may be required, it should be remembered that many adult Americans today grew up before energy conservation was a widespread concern and are accustomed to higher levels of illumination than are required for good vision. For extended spaceflight, it will be necessary to maintain levels of illumination adequate to the tasks required, while readapting to lower levels of illumination generally.
 In addition to its direct effect on vision, light levels can have an indirect effect on other behaviors. Changes in illumination levels have been found to influence the motor activity of animals (Alexander and Isaac, 1965) and, for humans, raising the level of illumination has been found to occasion an increase in the sound or noise level (Sanders, Gustanski, and Lawton, 1974). A related concern is how to simulate day/night cycles. it will be important to determine how the use of lighting might impact this area.
A frequently neglected aspect of habitability is the odor environment. Because particulate matter does not settle out in a weightless environment, odor problems in a space habitat may be more severe than under similar Earth conditions. Although some odors may, on occasion, be considered pleasant, "no odor" is the preferred condition. Odors have been associated with a number of medical symptoms including nausea, sinus congestion, headaches, and coughing (Goldsmith, 1973). They also contribute to general annoyance.
At the simplest perceptual level, an increase in the intensity of an odor stimulus is accompanied by an increase in response. However, adaptation effects are particularly pronounced for the olfactory sense, making the relationship between stimulus and response especially complicated. When odor stimuli are mixed, the perceptual response is further complicated. Jones and Woskow (1964) found that when two odors are mixed, the perceived intensity of the mixture is less than the sum of the subjective intensities of the component mixtures, but more than a simple average of the two. Berglund, Berglund, and Lindvall (1976) have developed a vector sum model to describe the findings that the perceived odor intensities of mixtures containing two to five odor stimuli only slightly exceeds the odor intensity of a single odor. From the standpoint of managing the odor environment, the significance of this model lies in the inverse of this relationship - i.e., that removal of some odors from a multi odor mixture does not necessarily reduce the intensity of the odor perception.
Responses to odors can be accentuated by the presence of visual cues, and can also be influenced by prior biases, such as favorable or unfavorable attitudes towards the source of the odor (Kendall and Lindvall, 1971).
 Materials used in spaceflight are subjected to testing for odor as well as for flammability and toxicity. Odor evaluations are made by a panel of test subjects who rate materials on a scale from 0 (undetectable) to 4 (irritating) with a score of 2.5 (falling between "easily detectable" and "offensive") considered passing (NASA, Office of Manned Spaceflight, 1974). It appears that, so far, the combination of material selection and adaptation effects have kept ahead of odor buildup in spaceflight. This does not mean that odor problems will not arise in the future. During the Spacelab Mission Development Test III (see Helmreich, Wilhelm, Tanner, Sieber, and Burgenbauch, 1979a, for a description of this simulation), participants complained of disturbing odors which they attributed to the primates and test rats which shared their facilities. A significant aspect of this test was that animal cages were in view during the simulation. We need to determine what odor related problems are likely to occur in space and what steps, such as physical or visual separation of areas, could help address such problems.
Many of the initial concerns about space reflected the view that the environment would be understimulating to the space traveler, possibly leading to the disorganizing effects associated with sensory deprivation (see review by Suedfeld, 1980). Although the environment of space may prove to be understimulating in some respects, it may prove to be overstimulating in others. Among the latter concerns is the question of noise or unwanted sound. Berry (1973a) has commented that in space (p.1142):
Noise has proven to be a problem in several confinement studies (Farrell and Smith, 1964; Page, Dagley, and Smith, 1964; Grumman Aerospace Corporation, 1970).
In the extreme, noise can cause pain and even damage to the inner ear, resulting in a hearing loss. Even low levels of noise can interfere with communication. Noise can also be a physiological stressor, exerting adverse effects on the cardiovascular system (Cantrell, 1975a), on the autonomic nervous system (Cantrell, 1975b), and on the vestibular system, resulting in disorientation, nausea, and dizziness (Harris, 1972). The clinical symptoms that have  been associated with noise are so extensive and nonspecific that these symptoms have been aggregated under the general heading "noise sickness" (Andreyeva Galanina, Alekeseyev, Kadyskin, and Suvorov, 1973).
The effects of noise on various performance tasks are not fully consistent However, it is generally found that noise results in a narrowing of attention. Narrowed attention allows simple tasks to be performed, but negatively affects the more demanding tasks. Grether (1971b) reports that noise generally results in decrements in performance when the task involves complex reaction time, two handed coordination, vigilance, or time estimation Cohen, Conrad, O'Brien, and Pearson (1974) found decrements in information processing related to noise, with the effects becoming more adverse as the work pace quickens. Broadbent (1979) provides evidence of higher error rates and greater variability of performance in a noisy environment. In addition to its direct effect on performance, noise is also thought to impact performance negatively by lowering motivation and morale. (For a review of the direct and indirect effects of noise on human health and welfare, see National Academy of Sciences, 1977.)
Noise data show some adaptation effects to steady source stimuli. However, intermittent noise shows reduced adaptation effects. Teichner, Arees, and Reilly (1963) found that a change in noise level, either up or down (from 81 dB), resulted in a decrement in information processing. Decisionmaking (Woodhead, 1959), monitoring of visual displays (Woodhead, 1964a), success on arithmetic tasks (Woodhead, 1964b), and information processing (Cohen et al., 1974) all have shown continuing decreased performance in the presence of intermittent noise.
In addition to its specific effects on performance, noise is generally conceded to be both fatiguing and distracting, disturbing sleep and interfering with waking activities. It constitutes a major source of irritation and has been linked to aggressive behavior. Donnerstein and Wilson (1976) and Geen and O'Neal (1969) have shown that subjects are willing to deliver a higher level of shock in a noisy environment than in a quiet one, and Mathews and Canon (1975) have found that experimental subjects are less altruistic when ambient noise levels are relatively high than when they are relatively low.
Although methods of arriving at acceptable noise standards have been quite diverse, recommendations that have evolved have been remarkably similar. The usual conclusion is that a sound level  equivalent to approximately 45 dB indoors is a desirable and safe maximum. This value reflects primarily the requirement that speech not be interfered with. However, it has proven to be an appropriate level generally (Environmental Protection Agency, 1974). It is clear that many people in large and bustling cities or those living close to airports manage to survive at higher noise levels than those recommended. However, it is also clear that even the recommended levels can disturb the sleep of a sizable portion of the population, with women more easily disturbed than men and the elderly aroused more readily from sleep than younger persons (Central Institute for the Deaf,1971).
One of the consistent problems with noise is that it is plainly annoying. Fidell, Jones, and Pearsons (1973) adopted the methodology of equipping subjects with signalling devices so that they could register annoyance levels in real time. This approach offers an alternative to survey techniques and could aid in the difficult task of quantifying annoyance data. Annoyance in response to noise has been found to be related to various factors tangential to sound. Numerous studies show noise associated with fear to be more disturbing than simple noise. Annoyance with noise stimuli has also been related to the individual's beliefs about the noise source. If the person believes that the noise causing activity is related to his or her overall well being, or that the person regulating the noise is concerned with the exposed person's well being, the individual will be less annoyed than if the reverse is true (Central Institute for the Deaf, 1971). Unpredictable noise (Glass and Singer, 1972) and noise over which the individual has no control (Cohen et al.,1979; Averill, 1973; Lefcourt,1973) result in particularly high levels of stress.
Although excessive noise is disturbing to everyone to some degree, there is considerable evidence that individuals vary dramatically in their sensitivity to noise (Borsky, 1977; Pearson, Hart, and O'Brien, 1975; Becker, Poza, and Kryter,1971). Those who are most sensitive to noise become increasingly disturbed over time, whereas the annoyance level of less sensitive individuals remains relatively constant over time (Weinstein, 1978). Several studies have shown these individual differences to be related to personality characteristics (Central Institute for the Deaf, 1971; Becker et al., 1971; Pearson et al., 1975) and to remain relatively stable over time (Becker et al.,1971). Among the traits that have been ascribed to the noise sensitive individual are reduced intellectual abilities and social skills and increased desire for privacy (Weinstein, 1978).
 In spaceflight, potential noise problems are of two general types. One type occurs during the launch and reentry phases, the other during the cruise phase of flight. During the launch and reentry phases, propulsion and aerodynamic noise levels can reach 120-130 dB in the cabin. If unabated (for instance by the helmetspacesuit system), this kind of auditory assault could be borne for only brief periods of time, and then, only at considerable cost.5 But of more importance to extended spaceflight are cruise noise levels. Cruise levels of 65-70 dB have been reported for the Apollo flights (Von Gierke, Nixon, and Guignard, 1975). Although this level did not create any serious problems for the crews, it is unlikely that an equally noisy environment would be acceptable on longer flights. Noise levels only slightly higher were found unacceptable in a 90 day simulation test (Langdon, Gabriel, and Abell, 1971). Measurements taken aboard Skylab revealed ambient noise levels lower than those of the Apollo flights, ranging from approximately 43 dB in the sleeping cubicles to 60+ dB in the working area. Although these levels are probably still too high for extended spaceflight, the reported noise problems on Skylab were concerned less with the level of noise than with the medium of transmission. At the reduced pressure of Skylab, sound was considerably dampened, and astronauts separated by only a few meters had to shout at each other to be heard (Johnson, 1974).6
Spaceflight raises the spectrum of noise questions: its effect on perception and performance, adaptation effects, the fatiguing and annoying aspects of noise, and individual sensitivity differences. A compounding problem of the space environment is the unrelieved character of the noise environment. In most terrestrial situations, the individual can retreat from a noisy environment for at least a portion of the day. This is true only to a limited extent in space. Although some noise sources can be turned off when relief is needed, others cannot. Jonsson and Hansson (1977) provide evidence that prolonged exposure to a stressful noise stimulus results in a high incidence of hypertension. Similarly, heightened blood pressure has  been found among children living close to a large metropolitan airport (Cohen, Evans, Krantz, and Stokols, 1980). An attempt to reverse aversive effects through noise abatement of classrooms had no significant effect on the hypertension of exposed children, even after one year (Cohen, Evans, Krantz, Stokols, and Kelly, 1981). To the extent that certain minimum noise levels are always present, spaceflight potentially constitutes a more stressful noise environment than a simple consideration of decibel levels would imply.
Although we have been considering noise (i.e., unwanted sound) as a potentially disruptive stimulus, it should be mentioned that the presence of sound is necessary and beneficial. Sound serves as a source of arousal and its absence can be as detrimental to the health of the individual as a noisy environment.7 Even annoying sounds, when kept within some limits, are not only accepted, but expected (Borsky, 1977). Russian experiments on the use of music in confinement conclude that unfamiliar and unusual music had a positive effect on all confined subjects "causing ecstasy in some, and in others, although even unpleasant, at least activity" (Zarakovskiy and Rysakova, as reported in Leonov and Lebedev, 1975, p.162).
Music has been found to have a special relationship to behavior. It can aid efficiency when one is required to perform a repetitious task (Fox, 1971) and particular kinds of music can influence mood and behavior (Yingling, 1962). For instance, soothing music has been found to lead to helping behavior (Fried and Berkowitz, 1979).
An issue which will ultimately assume importance in a closed environment is sound preference. Stereos or television, symphonies, country music, and rock are considered necessary background to some individuals. To others, these same sounds are an intolerable cacophony. Even in the dampened acoustical environment of Skylab, the violin selections which enlivened one astronaut's day proved a source of irritation to his two crewmates (Cunningham, 1977). Over the years, various researchers have attempted to understand the correlates of musical taste ( Farnsworth, 1950,1969; Conyers, 1963; Edmonston, 1969). Such understanding could prove helpful in planning for long duration spaceflight since some accommodation will have to be reached, either through attention to sound  compatibility of crewmembers, through training, or through the use of earplugs or other sound dampening mechanisms.
The task, then, is not to eliminate sound, or even to reduce it to a minimum, but rather to control unwanted sound (noise) while using wanted sound as a means of enhancing the total habitability of the space environment.
1 Cabin volumes were: on Mercury, 55 ft3 (1.53 m3); on Gemini, 44 ft3 (1.25 m3); and on Apollo, 107 ft3 (3.03 m3) per person (as reported in Human Factors in Long Duration Spaceflight, National Academy of Sciences, Washington, D.C. (1972).
2 Astronauts of Skylab preferred those areas where there was a local vertical, i.e., a defined "floor" and "ceiling." Astronauts felt least comfortable in the large upper deck of Skylab where, because of size and the lack of architectural cues, orientation was difficult (Life in a Space Station, New Yorker Magazine 8/30/76 and 9/6/76). Story Musgrave, Mission Specialist who participated in an Extravehicular Activity on STS 6 has reported that he felt no need to identify a particular direction as "up" or "down" (personal communication, June, 1983). He further raised the interesting possibility that the presence of a defined vertical within the vehicle might cause conflict with outside perceptions, possibly contributing to space sickness. (For a discussion of the role of sensory conflict in space sickness, see chapter 11.)
3 For a graphic description of problems of human waste in space, see: There Ain't No Graceful Way: Urination and Defecation in Zero G, Astronaut Russell Schweickart talking to Peter Warshall, Space World , Vol. P 1 181, pp. 16 19 (Jan. 1979).
4 0ther visual concerns include the effects of radiation and general effects of weightlessness.
5 Yuganov, Krylov, and Kuznetsov report that after exposures of 125 130 dB for 20 min, subjects suffered from head pain, and ringing and feelings of stuffiness in the ears for 20 40 min after exposure, and did not recover for 1 2 hr (Yuganov, Ye. M., Yu. V. Krylov, and V. S. Kuznetsov, Study of Features of High Intensity Noise Effects During Spaceflight, in Problems of Space Biology. V. N. Chernigovskiy (ed.), Nauka Press: Moscow (1971); NASA TT F 719, Washington, D.C., 29 33, (1973)).
6 Similar information has also been provided by members of the Skylab habitability team at NASA's Johnson Spaceflight Center.
7 Improvements in some aspects of mental arithmetic and in clerical tasks have been reported in the presence of sound (see review by Grether, 1971 b, op. cit.).