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|Year : 2003 | Volume
| Issue : 21 | Page : 3--16
The effects of background noise on cognitive performance during a 70 hour simulation of conditions aboard the International Space Station
DG Smith, JV Baranski, MM Thompson, SM Abel
Defence Research and Development Canada - Toronto, Ontario, Canada
D G Smith
Defence Research and Development Canada - Toronto, 1133 Sheppard Avenue West, P.O. Box 2000, Toronto, Ontario M3M 3B9
A total of twenty-five subjects were cloistered for a period of 70 hours, five at a time, in a hyperbaric chamber modified to simulate the conditions aboard the International Space Station (ISS). A recording of 72 dBA background noise from the ISS service module was used to simulate noise conditions on the ISS. Two groups experienced the background noise throughout the experiment, two other groups experienced the noise only during the day, and one control group was cloistered in a quiet environment. All subjects completed a battery of cognitive tests nine times throughout the experiment. The data showed little or no effect of noise on reasoning, perceptual decision-making, memory, vigilance, mood, or subjective indices of fatigue. Our results suggest that the level of noise on the space station should not affect cognitive performance, at least over a period of several days.
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Smith D G, Baranski J V, Thompson M M, Abel S M. The effects of background noise on cognitive performance during a 70 hour simulation of conditions aboard the International Space Station.Noise Health 2003;6:3-16
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Smith D G, Baranski J V, Thompson M M, Abel S M. The effects of background noise on cognitive performance during a 70 hour simulation of conditions aboard the International Space Station. Noise Health [serial online] 2003 [cited 2020 Feb 27 ];6:3-16
Available from: http://www.noiseandhealth.org/text.asp?2003/6/21/3/31685
The International Space Station (ISS) is a unique environment with multiple potential stressors. Some of the stressors are exotic, such as the lack of gravity or the possibility of a decompression event; other stressors are mundane, but are just as likely to have an impact, such as the lack of living space or noise from machinery. The crew of the ISS is constantly subjected to moderate intensity (about 72 dBA) ambient noise generated from machinery. In order to maximize performance it is important to determine which stressors are likely to affect performance negatively. In this paper we focus on the effects of background noise on cognitive performance.
Noise and performance
Noise is unwanted or meaningless sound that may distract attention from cues that are important for task performance. Significant background noise may negatively affect performance in a number of ways (see e.g. Smith, 1989). In some cases the noise may directly affect one's ability to perform a task but there are also many ways in which noise can disturb task performance indirectly. For instance noise may disrupt sleep patterns, disturb normal social behavior or increase subjective feelings of stress all of which could ultimately lead to poor performance in cognitive tasks.
Loud background noise (above 90 dBA) typically reduces the quality of performance. A number of studies have demonstrated that noise hinders performance on cognitive tasks involving vigilance, decision-making, and memory (see Broadbent, 1971, Smith, 1989; Salas et al, 1996; Banbury, et al, 2001 for reviews of the literature). However, most of these studies involved artificially generated noises in artificial settings and exposure was usually short-term (i.e., hours not days). In an experiment more relevant to the ISS setting it has been shown that reducing noise levels in a factory setting improves work performance by reducing the number of work errors (e.g. Broadbent and Little, 1960). According to Broadbent's, now classic, theoretical treatment of the effects of noise on performance, loud noise leads to over-arousal, which narrows attention, restricting ones focus to a limited range of cues. This inability to attend to less salient cues ultimately leads to deterioration of performance.
The negative effects of noise are not limited to cognitive performance. Recent work has demonstrated that noise disrupts both social behavior and indices of subjective stress (see Salas, Driskelle and Hughes, 1996 for a review). These effects may have important consequences for group situations like that aboard the ISS. The subjective impression of stress, especially in combination with poor social functioning may lead to situations where the subject is emotionally upset and thus may affect performance. Even if the effects on cognitive performance are small, they may compound in the long term, leading to a slow degradation in performance over time.
Unlike a factory or typical laboratory situations, the ISS crew must experience the background noise 24 hours a day. Hence, the possibility that the noise will disrupt sleep is also an important issue. Both home and controlled laboratory studies indicate that noise results in greater difficulty in falling asleep, more frequent awakenings during the night and reports of poorer sleep quality (e.g., Jurriens et al., 1983; Thiessen, 1978; Ohrstrom, 2000, 2002). Since sleep deprivation has well-known negative consequences on performance it is possible that poor quality sleep in a noisy environment could disrupt performance.
However, in the majority of the classic studies on noise subjects were exposed to high intensity (90 dBA and higher), and sometimes, variable noise. Hence it is uncertain whether these effects would generalize to the noise experienced by the ISS crew.
Some past research has suggested that certain individual differences can affect sensitivity to noise stressors, and, in turn, performance in noisy environments (Smith, 1989). For example, locus of control, or beliefs about the degree to which an individual's actions will affect outcomes, have been shown to be related to performance under noise conditions. Related work has demonstrated that individuals scoring high on anxiety measures such as neuroticism perform more poorly under noise stress, relative to individuals who are less anxious (e.g. Nurmi and von Wright 1983; von Wright and Vauras, 1980). Finally, some research in the psychological resiliency area has demonstrated a relationship between other individual differences and the tendency to perform well under a variety of stressful conditions, although this relation has not been yet demonstrated for noise stress specifically. Although not a central focus of this study, personality measures assessing individual differences in control, anxiety, and general psychological resiliency were also included in this research.
Noise on the ISS
It is clear from the previous discussion that high intensity background noise can distract, irritate, and hinder performance. Although the level of noise on the ISS is only of moderate intensity (~72 dB), other attributes of the noise lead to the possibility that it could be detrimental to cognitive performance. There are three major factors that determine the effect of noise on cognitive performance: Intensity (loudness), type of noise, and duration. Moderate levels of noise can affect performance, depending on it's type and duration. For example, moderate intensity white noise (55 dB), has little or no effect on performance while moderate intensity irrelevant speech can seriously disrupt performance (LeCompte, 1994; Smith, 1999). The effect of duration has received little attention to date, however, Smith and Miles (1985) have demonstrated that the longer the exposure the greater the decrement in performance. These characteristics of the noise in addition to the fact that the crew is on board for long periods of time suggest that performance might be improved if the noise were reduced.
The effect of noise on performance is complex and depends on the specific characteristics of the noise as well as characteristics of the task. Characteristics of the sound like frequency (Broadbent, 1957), intermittency (Poulton, 1978), and periodicity (Glass and Singer, 1972) all determine whether noise will affect performance. Psychological variables like sleep deprivation (Hartely and Shirley, 1977) and the perception of control over the noise (Glass and Singer, 1972) also have effects. Hence, unless noise is particularly loud and unpredictable, it is difficult to determine whether the precise level and type of noise in a particular environment will likely cause a disruption in performance. The noise level on the ISS is moderate yet variable, hence it is difficult to predict, based on the literature, whether it will likely hinder performance. Therefore we put the question to an empirical test.
The goal of this study was to determine whether noise recorded from the service module of the space station is sufficient to disrupt cognitive performance as well as hearing, communications and cardiac function. However, in this paper, we will focus on cognitive performance and subjective indices of mood. We attempted to simulate ISS conditions as closely as possible by cloistering groups of five subjects in a (dry) experimental diving chamber. Subjects remained in the diving chamber for 70 hours and their cognitive performance was tested a total of nine times per subject. A recording of the noise from the service module of the ISS was obtained from NASA. ISS noise was simulated by playing the tape continuously over a system of loudspeakers placed strategically throughout the chamber.
Twenty-five male and female, military and civilian personnel, volunteered to participate in the study. Age ranged from 21 to 47 years. Before participation, subjects were medically screened to ensure they had no conditions that would preclude them from participating in this experiment. Subject selection and assignment to conditions was random but constrained by their availability, the availability of the diving facility as well as the number of subjects which could be tested simultaneously. Subjects were paid for their participation according to DRDC - Toronto guidelines.
Test Chamber. The investigation was carried out in a hyperbaric chamber housed in the Experimental Diving Unit at DRDC Toronto. The chamber was comprised of three physically separate but connecting pods. The first or "living" pod comfortably provided living quarters for five subjects, and was used primarily for leisure activities and eating. Lounges converted to bunks for sleeping. The second (transfer) pod housed sink and toilet facilities. The third pod, comprising two areas (one normally "dry" and the other normally "wet" for diving experiments) separated by a divider was set up to carry out the majority of the tests. These two areas accommodated workspaces for two and three subjects, respectively. The hatches at the ends of the living and test pods, which allowed access from the outside, were covered with opaque curtains during the test sessions.
An auxiliary ventilation system was used to provide an adequate fresh air supply to the subjects at all times. Since the system was intrinsically quiet, noise from the blower could not be detected inside the chamber. The participants were continuously monitored by video to permit appropriate intervention if and when required. A designated physician was on pager throughout the study in case any medical concerns or emergencies arose.
Tests. The cognitive test battery and the questionnaires were completed on IBMcompatible laptop computers, each with an 8" x 11" screen and an IBM mouse. The mouse was used as the input device for all tests with the exception of the recognition memory test, which required keyboard input. During the experimental phase, all cognitive testing was performed in the "normally wet" pod of the diving chamber. Subjects were tested all at once, with two on one side of the pod and three on the other (the pod was naturally divided in half by a partition). Each subject was tested behind partitions placed on a common table.
Subjects were tested in groups of five. One group acted as the control and did not experience the recorded noise. Two groups experienced the noise throughout their stay in the diving chamber. The remaining two groups experienced the noise only during the daytime (we will refer to these groups as the day noise condition), the noise was turned off during their sleep period (between 2200 hrs and 0600 hrs) to determine if any performance detriment resulted from disrupted sleep.
Subjects participated over the course of four days from 0900 hrs on Monday through 2000 hrs on Thursday. Baseline tests and familiarization with the test chamber were scheduled for Monday morning and afternoon. Cloistering began on Monday evening at 1700 hrs and terminated on Thursday afternoon at 1500 hrs. During this period, subjects remained in the chamber. Over the course of the 70-hr period of cloistering, subjects were tested repeatedly in morning, afternoon and evening sessions during a 14-hr work day. They arose at 0600 hrs and retired at 2200 hrs. Test sessions were interspersed with meals, snacks, and entertainment breaks. During entertainment breaks subjects played cards, read books which they brought with them, and watched movies (with the sound turned off so as not to interfere with the background noise manipulations). Daytime napping was strictly forbidden, so that the effect of circadian rhythm on performance would not be compromised.
At regular periods over the 70 hr experimental session subjects' heart rate, blood pressure, hearing, and sleep quality were monitored and they were given tests of cognitive performance, fatigue, mood, and speech communication. In this paper we report only on the measures of cognitive abilities, fatigue, and mood as well as pre-experimental personality tests. Details of these tests are presented below. The results from the remaining tests and measures will be reported in a subsequent publication.
Five individual differences questionnaires were administered to participants. Two questionnaires assessed perceptions of control. The Locus of Control scale (Rotter, 1966) contains 22 items (e.g., "If I were to fail at some task, it would cause me to question my ability"), with a 7-point response scale (1 - disagree, 2 - moderately disagree, 3 - slightly disagree, 4 - neither agree nor disagree, 5 - slightly agree, 6 - moderately agree, 7 - agree). The Desirability of Control Scale (Burger and Cooper, 1979) contains 20 items (e.g., "I prefer a job where I have a lot of control over what I do and when I do it") with 7point response scale (1 - doesn't apply to me, 2 - usually doesn't apply to me, 3 - most often does not apply to me, 4 - unsure whether it applies to me or not, 5 applies more often than not, 6 - usually applies to me, 7 - always applies to me. The Anxiety Sensitivity Questionnaire (Reiss et al., 1986), is related to neuroticism and is a 16 item scale (e.g. "It scares me when my heart beats rapidly" with an accompanying 5point response scale (0 - very little, 1 - a little, 2 - some, 3 - much, 4 - very much). Two final questionnaires assessed general psychological resiliency. Specifically, psychological hardiness (Bartone, 1995) was measured by a 15-item scale (e.g., "By working hard, you can always achieve your goals") with a 4 point response scale (0 - not at all true, 1 - a little true, 2 - quite true, 3 - completely true). The final questionnaire in the package was the 7 item Mastery Scale (Pearlin et al., 1981) (e.g., "I can do just about anything I set my mind to") that included 5 response options (1 - strongly disagree, 2 - disagree, 3 - neither agree nor disagree, 4 - agree, 5 - strongly disagree).
The individual difference questionnaires were administered to each of the participants prior to cloistering. All were administered independently to subjects via computer. Subjects were allowed up to one hour to complete the personality measures.
Cognitive Test Battery
The cognitive test battery included a subset of tasks which have been used extensively in previous sleep loss and performance studies conducted at DRDC Toronto (e.g., Baranski et al., 2002; Angus and Heslegrave, 1985; Baranski et al., 1994; Pigeau et al., 1995). The tasks were selected for the study to investigate a diverse range of fundamental cognitive processes and to allow comparison with findings obtained in previous studies. They were presented to the subjects on individual lap top computers. The tasks that comprised the battery were always performed in the same order and included:
Subjective Questionnaires (approx. 2 min): The questionnaires included a number of items that probed the subjects' current level of mental and physical fatigue, motivation, and mood. Eight of the items comprised the GVA index (Monk, 1991), which will be elaborated below. All questions involved a visual analogue scale (VAS) from 1 to 10, which was anchored at both ends by a short verbal description (e.g., "Not at all tired" vs. "Very tired"). The subject "hooked" a visual pointer on a sliding scale with the computer mouse and dragged the pointer on the monitor to the appropriate location on the scale.
Short Term Memory(4 min): In this task subjects were presented with strings of numerical digits to learn. Each digit was presented for 1 sec, and then 0.5 sec later the next digit was presented. The subject's task was to memorize the complete string of digits and recall the string immediately after the last digit is presented. Recall is requested in the same order that digits were presented. If the subjects answered correctly, the string length is increased by 1. If the answer was incorrect, the length of the string was decreased by 1. The initial string length was four digits. A sensitive dependent measure for this task is the maximum string length attained by the participant.
Four-Choice Serial Reaction Time (3 min): On each trial, four response buttons (P, G, L, and S) were presented on the computer monitor in a square configuration (i.e., two above and two below). Directly above the displayed letters, a probe letter (P, G, L, or S) was presented. The subject's task was to work as quickly and accurately as possible and use the mouse to move a visual pointer over the response button corresponding to the probe letter, and to depress the mouse button. The probe letter varied on each trial and was randomly generated by the program. Response times were recorded from the appearance of the probe letter to the depression of the response button on the mouse.
Mental Addition (6 min): The addition task required subjects to add a random sequence of eight numbers (between 1 and 16) which were presented on the computer monitor at a rate of 1 number per 1.25 s. The sequence was terminated by the presentation of a visual prompt (=>) at which time subjects typed in their response using the mouse and a visual keypad presented on the monitor. Response times and response accuracy was measured on each trial.
Detection of Repeated Numbers (DRN) Vigilance Task (6 min): The DRN is a vigilance task that required subjects to detect by pressing a key with the mouse, when two three-digit numbers occurred in succession. Three-digit numbers were presented at a rate of 1 per second. In total, eight repeated numbers occurred randomly distributed within each minute of the task. Correct detections occur when the subject pressed a key with the mouse within 2 s of a repeated number; misses occurred when repeated numbers are presented but the mouse button was not pressed; false alarms occurred when the mouse button was pressed but successive numbers were not presented.
Logical Reasoning Task (3 min): On each trial of the Logical Reasoning Task (LRT), a pair of letters was presented at the top of the screen: A B or B A. Directly below the pair of letters was a statement concerning the spatial arrangement of the letters: e.g., A precedes B; B does not follow A, etc…. The subject's task was to determine if the statement was true or false, by pressing with the mouse the appropriate response button (T or F) on the screen. Response time and response accuracy were measured on each trial.
Visual Perceptual Comparison (3 min): The comparison task required the relative judgment of line length. Each trial began with the presentation of an instruction ("LONGER" or "SHORTER") which was displayed near the top of the computer monitor. One second later, the visual display appeared which consisted of two horizontal lines, divided by one short vertical line. The display remained on the screen until the subject responded. The subject's task was to determine which of the two lines was longer or shorter, depending on the instruction. Subjects responded by depressing either the left or the right button on the mouse to indicate that the left or right line was the longer or the shorter. Four levels of judgment difficulty were randomly presented to the subjects; the difficulty was defined a priori on the basis of the ratio of the longer to the shorter line: 1.01, 1.03, 1.05, and 1.07. All lines appeared black on a white background. Subjects were encouraged to respond as quickly and as accurately as possible. Response time and response accuracy were recorded on each trial.
Recognition Memory Task (approx. 10 min): The recognition memory test consisted of a study phase and a test phase. For the study phase, subjects were told that they would be asked to remember a word list consisting of 80 words presented one at a time on a computer screen at a rate of 3 sec. an item. Subjects initiated presentation of the word list with a key-press. Each word was presented in the middle of the screen in a black Times Roman font on a white background. The height of each word as it appeared on the screen was approximately 1cm. Once presentation of all 80 words was complete, test instructions were presented on the screen.
Half the 160 test trials were tests of old items and half were tests of new items. Subjects were told that each trial would consist of the presentation of a single word in the centre of the screen. The word could be old (from the study list) or new (not shown before) with equal probability. Below the word the following scale appeared "(sure new) 3 2 1 1 2 3 (sure old)". The scale shown on the screen corresponded to numbers pasted on the keyboard. Subjects were instructed to press the right hand "3" key for words that they were sure were on the study list, the right-hand "2" key if they were less sure, and the right-hand "1" key if they were unsure or guessing. If they were sure the word was not on the list they were asked to press the left-hand "3" key, "2" if they were less sure, and "1" if they were unsure or guessing. Subjects were instructed to try and use each response key an equal number of times during the course of testing.
Stimulus items consisted of a list of 1675 twosyllable words chosen using the MRC Psycholinguistic Database (Coltheart, 1981). The mean written frequency (from the Kucera and Francis (1967) word count) of the words was 30.73 occurrences per million, the minimum and maximum frequencies were 4 and 626 occurrences per million respectively. For each session 160 words were randomly selected from the pool. 80 of the words were studied while the remaining 80 items were used as lures during the test phase. Words were selected in such a way that for each subject no word was used in more than a single session. Responses were made on a computer keyboard where the digits " 3", "2", "1", "1", "2, ", "3" were pasted to the "Z", "X", "C", "", "?" keys respectively.
We first conducted analyses to ensure that the any group differences that emerged were not affected by any pre-existing individual differences among the participants. Results of one-way ANOVAS, indicated that the groups did not differ on any of the individual difference measures (all F's Cognitive Task Battery
Mean performance across conditions is presented in [Table 1]. Overall performance for these tasks are generally consistent with previous studies using the cognitive task battery (See Pigeau et al, 1995, Baranski et al, 1998, and Baranski, et al, 2002). All of the results pertaining to the cognitive task battery are based upon separate repeated measures Analyses of Variance (ANOVAs) with the three experimental conditions as the between-groups factor and the nine testing sessions as a within-subjects factor. A summary of all ANOVA results is provided in [Table 2].
GVA. Following Monk (1991), the eight items that comprise the Global Vigor and Affect (GVA) scale were combined to form the two subscales of Vigor and Affect. The only effect to attain statistical significance was a main effect of Session for the Vigor index. As is evident in [Figure 1], participants showed generally reduced vigor in sessions 2, 5, and 8, which were in each case the early morning sessions performed at 0800. The error bars for [Figure 1] and all the plots to follow denote the standard error of the mean across participants.
Fatigue, Mood, and Motivation. Of all the scales related to fatigue, mood, and motivation, the only effects to achieve reliability involved the mood scale; a main effect of session and a group x session interaction. However, a post-hoc comparison failed to reveal any systematic differences between the various conditions across sessions.
ANOVAs revealed neither a main effect of Group nor any interactions involving Group and Session for the serial reaction task (RT), mental addition task (% correct), detection of repeated numbers task (# correct / minute), logical reasoning task (% correct), perceptual comparison task (RT and % correct), and shortterm memory test (% correct).
Of all of these analyses, reliable main effects of Session were obtained for serial reaction time, addition, DRN vigilance, logical reasoning RT, and comparison. In each case, the effect of Session confirmed the anticipated improvements of performance with increasing practice. [Figure 2],[Figure 3] show the results for the serial reaction time and additions tasks respectively, as examples of the effects of practice on reaction time and accuracy.
The findings for the recognition memory task were a bit more complex and are presented in [Figure 4]. First, two subjects (one from the control group and one from the day noise condition) had data missing from one session. Accordingly, we replaced the missing cells (2 / 225 cells or 0.8%) with the subject's average proportion correct from adjacent sessions. [Figure 4] shows mean proportion correct as a function of group and session. The control group and the day noise group show a decline in performance over sessions while the continuous noise group shows relatively steady performance. The ANOVA revealed a reliable effect of session, and a reliable interaction between session and group but there was no main effect for group. According to a planned comparison, the decrease in proportion correct between the first three and the last three sessions was greater for the silent control group than for the noise group, F(1,22) = 9.873, p <0.005. To check this result we performed the ANOVA a second time but with the subjects that had missing files removed completely from the analysis. Like the previous analysis, proportion correct did not differ between groups, but decreased across sessions, F(2,20) = 2.015, p <0.05. There was, however, no interaction between group and session.
Response time on the logical reasoning task differed reliably between groups. However, like the recognition task (and contrary to our hypothesis), performance was superior (fastest) for the experimental (day and night noise) group.
The purpose of this study was to determine if the background noise aboard the ISS is sufficient to aversely affect cognitive performance. We measured cognitive performance using tests of memory, reasoning, perceptual decisions, and vigilance. None of these tasks were performed more poorly in the noise conditions than in the quiet condition. There were also no differences in reported vigor, fatigue, mood, or motivation between noise and quiet conditions. Importantly, previous studies have shown that the tests within the cognitive test battery are sensitive to stressors at least in the context of sleep loss and performance (See Pigeau et al, 1995, Baranski et al, 1998, and Baranski, et al., 2002). Furthermore, previous studies, which have found negative effects of noise on performance, have used dependent measures similar to those in the battery (i, e., vigilance, decision making, and memory). Hence, one would expect, that if the noise aboard the ISS disrupts performance, we would have detected the effects with our dependent measures. Our results suggest that the level and type of noise aboard the ISS is not likely to deleteriously affect cognitive performance at least for a short exposure duration. We cannot be certain what the effect of the background noise would be over durations longer than the 70 hours of exposure to each experimental condition.
There are three potential problems with our study. Firstly, our noise conditions may not realistically represent those of the ISS. Even though the noise was re-produced from a recording of noise within the ISS and the noise conditions were carefully controlled, it is possible that the tape was somehow atypical of the noise experienced by the ISS crew; for instance, the crew could be exposed to other, more infrequent noises that disrupt performance. Intermittent noises are known to disrupt performance more than continuous noise (Poulton, 1978). Secondly, the subjects may simply not have been exposed to the noise for long enough to be affected. It is possible that noise disrupts sleep patterns or affects social behavior (which may, in turn, affect work performance) in subtle ways that compound over long periods of time. Thirdly, due to constraints related to the availability of subjects and the availability of the diving facility sample size was restricted. With the current design we estimate that if the true effect size were large (one standard deviation) we had about a 35% chance of detecting an effect. However, because we used a variety of dependent variables one would expect that, if there were truly a large negative impact of background noise in this study, we would have found at least one effect in the expected direction.
Although we found no evidence that noise aboard the ISS has detrimental effects on cognitive function we hesitate to suggest that the noise level is acceptable. Very long term exposure to noise may aversely affect mental and physical health (see Pelmear, 1985 for a review). Henehan (1985) found that exposure to loud noise (95-105 dB) caused an increase in diastolic blood pressure. Cantrell (1974) demonstrated that long-term (30 day) exposure to fairly loud noise (85 dB SPL) caused elevated cortisol and cholesterol levels for several days after the exposure. These physiological signs of stress suggest that noise, aside from acting as a psychological stressor, may also have negative physiological effects. Hence it is likely that very long-term exposure to loud noise may have negative health consequences.
This study was funded by the Canadian Space Agency. Sharon M. Abel's contribution was funded in part by an Isabel Silverman CISPO Senior Scientist Award. We thank Andrea Hawton, Tonya Stokes-Hendriks, Wendy Sullivan, and Sarah Young for collecting and analyzing the data for the cognitive task battery and Garry Dunn for installing the sound system. We also thank Cdr Bob Gwalchmai and Lt(N) Jay Frew and their colleagues of the Experimental Diving Unit, DRDC Toronto for allowing the investigators to use their Diving Research Chamber for the study, and for graciously assisting in the use of this facility and organizing 24-hr subject monitoring. Finally, we thank Dianne Moroz and Krista Howarth of Moroz Biomeasurement Systems, Inc who oversaw subject recruitment, scheduled medical screening, created the subject groups, and organized and delivered meals. Portions of this manuscript appeared as part of DRDC Toronto External Client Report ECR 2003-004.
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