FAA-AM-85- 3 

THE EFFECTS OF AGE, SLEEP DEPRIVATION, 

AND ALTITUDE ON COMPLEX PERFORMANCE 

Henry W. Mertens and William E. Collins 

Civil Aeromedical Institute 

Federal Aviation Administration 

Cklahoma City , Cklahoma 73125 

HAY 1985 

Document is available to the public through the 

National Technical Information Service, 

Springfield, Virginia 22161. 

Prepared for 

U.S. DEPAR~T OF TRANSPORTATION 

Federal Aviation Administration 

Office of Aviation Medicine 

Washington, DC 20591 
Technical ~eport Documentation Page 

1. Re porl No. 2 . Gove rnmen t Acce ssi on No. 

FAA-AM-85-3 

4 . Ti lie ond Subti! le 

THE EFFECTS OF AGE, SLEEP DEPRIVATION, AND ALTITUDE 

ON COMPLEX PERFORMANCE 

7. Autho rls) 

Henry W. Mertens and William E. Collins 

9 . Perform ing Orgon i zation Name and Addre s s 

FAA Civil Aeromedical Institute 

P.O. Box 25082 

Oklahoma City , Oklahoma 73125 

12. Spon s oring Agency Nome and Address 

Office of Aviation Medicine 

Federal ·Aviation Administration 

800 Independence Avenue, SW. 

I Washington, DC 20591 

15. Supplementary Notes 

Work was performed under task AM-A~83/84/85-PSY-94. 

16. Abslrucl 

,3. Recipienl ' s Co l o log No. ! 

I 

I I 

' 5. Repo rl Do le I 

I MAY 1985 i 

6. Perform ing Organ· :at• on Cod e I l 

I I 

I 8. Performing Orgon i zotion Report N o . 

I 

10 . Work Un il No . (T RAI S) 

11. Contract or Gran t N o. 

13. Type o f Reporl on d Perio d Co ve re d 

14 . Sponsori n g Age ncy Cod e 

I 

Little research has been concerned with the combined effects on performance of age, 

sleep deprivation, and altitude. This study examined their potential interaction 

with laboratory tasks measuring aviation-related psychological functions. Healthy 

men in two age groups, 30-39 yr (N=16) and 60-69 yr (N=14), were evaluated for 

complex (time-shared) performance in the four possible combinations of two altitudes 

(ground level vs. 3,810 m (12,500 ft)) and two sleep conditions (sleep permitted vs. 

sleep deprived). Following training, performance was evaluated during 3-h test 

sessions in the morning and afternoon of each of 4 test days. Complex performance, 

measured by the Multiple Task Performance Battery (MTPB), included: monitoring of 

warning lights and meters, mental arithmetic, problem solving, target identification, 

and tracking. Workload was varied within each hour by varying the tasks performed 

simultaneously. Performance was significantly lower in the older subjects, but age 

did not interact significantly with sleep deprivation or altitude. There was, 

however, a significant interaction of sleep deprivation and altitude. When subjects 

were rested, altitude had no effect. When subjects were sleep deprived, performance 

was significantly lower in general, and the greatest decrement in performance 

occurred at altitude. Increasing workload enhanced the interaction of sleep 

deprivation and altitude. The performance of older subjects tended to be more 

affected by increases in workload, but decrements induced by sleep deprivation and 

altitude did not appear to interact with age. These findings provide empirical 

evidence in support of warnings in the aeromedical literature concerning greater 

effects of sleep deprivation as altitude increases within the general aviation range. ! 

17. Key Words 

Age Effect 

Altitude Effects 

Sleep Deprivation 

Performance 

19. Security Classif. (of this report) 

Unclassified 

Form DOT F 1700.7 (8-72) 

1 B. Di stri but ion Stat ement 

Document is available to the public 

through the National Technical Information 

Service, Springfield, Virginia 22161. 

20. Security Classif. (of thi s page) 21. No. of Page s 22. Pri ce 

Unclassified 18 

Reproduction of completed page authorized 
ACKNOWLEDGMENT 

The authors wish to acknowledge the contributions made by Nelda Milburn, who 

organized the screening of subjects and assisted in the training of subjects, 

data collection, and data analysis. Linda Van Buskirk also assisted in 

screening, data collection, and data analysis and, with Wayne Prim, supervised 

subjects during sleep deprivation periods. Jerry Hordinsky, M.D., selected and 

evaluated medical screening tests. The tests were performed by Elaine Moser for 

blood and urine analyses, Wilma Fairman for EKG tests, and Michael Lategola, 

Ph.D., Mary Jo Burr, and Peggy Lyne for pulmonary function tests. 
INTRODUCTION 

THE EFFECTS OF AGE, SLEEP DEPRIVATION, 

AND ALTITUDE ON COMPLEX PERFORMANCE 

Two aviation stressors, sleep deprivation and altitude, have been studied 

individually regarding their frequently adverse relation to performance, but 

little research has been concerned with their combined effects or the 

interaction of those effects with age in spite of concerns expressed by some 

writers for such potentially adverse synergistic effects (Institute of Medicine, 

1981; Johnson, 1982; Webb and Levy, 1982). 

A small study by Lottig (1938) over 45 years ago suggested a possible adverse 

interaction of sleep deprivation and altitude, but the issue appears not to have 

been addressed in research since that time. In Lottig's study, three out of six 

subjects manifested an average decrease of 250 ft (76.2 m) in the altitude at 

which symptoms of altitude sickness first appeared when sleep was reduced from 8 

to 4 hours, and there was corresponding evidence of mental impairment in a 

handwriting task and in subjective observations of speech, mood, and thought 

processes. The effects observed by Lottig appeared only at altitudes greater 

than 5,000 m (16,404 ft); however, the normal range of general aviation 

altitude is limited to 3,810 m (12,500 ft) for continuous operations without 

supplemental oxygen in unpressurized aircraft. The possibility should be 

examined that more sensitive flight-related tasks would reveal an interaction of 

altitude with sleep deprivation at lower altitudes within the range of the 

present-day general aviation environment. · 

McFarland (1941) and Mertens, Higgins, and McKenzie (1983) have studied the 

interaction of age and altitude. Both studies examined subjects within the age 

range of approximately 20 to 70 years. Although both studies found that 

performance decreased with age, the effects of altitude did not differ among age 

groups. The age-related performance decrements found by Mertens et al., which 

were not affected by a 3,810-m general aviation altitude, occurred only in 

higher workload conditions, suggesting that the workload factor should be 

systematically varied in research on the interaction of stressors with age. 

Two studies have found an interaction of age with sleep deprivation. Webb and 

Levy (1982) evaluated the performance of 10 young subjects, 20-22 yr, and 10 

older subjects, 40-49 yr, in a number of psychological tasks during the second 

night of sleep deprivation (approximately 41-45 h of sleep depriv~~ion). 

Although the rested performance of the older subjects was initially higher, the 

decrements in performance were larger in the older subjects for several tasks. 

Brezinova, Hart, and Vojtechovsky (1969) studied the effects of prolonged sleep 

deprivation on alertness as measured by electroencephalographic responses in a 

group of middle-aged alcoholics (average age = 40 yr) and a group of younger 

alcoholics (average age= 22 yr). They concluded: "In the first phases of 

sleep deprivation, after the first and second nights of the vigil, s~s of a 

relatively smaller decrease in vigilance in older subjects were found •• ~ During 

prolonged sleep deprivation, after the fourth and fifth nights without sleep, 

signs of better tolerance were seen in younger subjects ••• " There is apparent 

disagreement between the findings of Webb and Levy and the findings of Brezinova 

1 
et al. regarding the effects of sleep deprivation as a function of age during 

the first 48 h of sleep deprivation. Clearly, additional research on the 

age/sleep deprivation interaction is needed. 

It is the purpose of the present study to reexamine the effects and interactions 

of the aviation stressors age, sleep deprivation, and altitude. The second 

order interaction of age, sleep deprivation, and altitude has not been 

previously evaluated experimentally. These possible interactions were evaluated 

in the present preliminary experiment with (i) two age groups, 30-39 yr vs. 

60-69 yr, (ii) two sleep deprivation conditions, a normal night's sleep vs. 

loss of one night's sleep, and (iii) two altitude conditions, ground level vs. 

3,810 m. The Civil Aeromedical Institute's Multiple Task Performance Battery 

(MTPB) was used to measure the effects of stressors on complex (time-shared) 

performance of several flight-related tasks under varying workload conditions. 

METHOD 

Subjects. Thirty men, 16 in a 30- to 39-yr age group and 14 in a 60- to 69-yr 

age group, served as subjects. Physiological condition and intellectual ability 

of subjects in both age groups were controlled by requiring that subjects pass 

the equivalent of a Class III airman physical examination, exhibit pulmonary 

function in the normal range, and have an intelligence quotient in the normal 

range or above. 

MTPB. The MTPB is well known in the performance literature through the work of 

Alluisi, Chiles, Adams, Morgan, and others (Alluisi, 1967; Chiles, Alluisi, and 

Adams,1968; Morgan, and Alluisi, 1972; Chiles and Alluisi, 1979). The Civil 

Aeromedical Institute's version of the MTPB was developed by Chiles (Jennings, 

Chiles, and West, 1972). Five subjects can be run independently at the same 

time with this system. The MTPB tasks have high content validity and high face 

validity for aviation and are presentrd in various combinations to produce a 

synthetic work situation involving variation of workload and time sharing of 

work in assorted tasks. One of the consoles at which subjects work is shown in 

Figure 1. The MTPB tasks are described as follows: 

Monitoring of Warning Lights. Two tasks involved monitoring of red and green 

warning lights. These are choice reaction~time tasks involving monitoring of 

five green lights (normally on) and five red lights (normally off). The 

subjects were instructed to push the light/switch whenever a light changed 

state. Response times were recorded separately for red and green lights. 

Monitoring of Meters. This task involved monitoring four meters arrayed across 

the top of the console. The pointers of these meters constantly moved at random 

about the center position. The subjects were instructed to respond to a shift 

in mean position of the pointer to the left or right of center by pushing a 

button under the meter on the side of the deflection. Response times were 

scored. 

Mental Arithmetic. The subject was required to add two two-digit numbers and 

subtract a third number from the sum of the first two without using paper and 

pencil. Answers were recorded with a 10-key pad. Response time and accuracy 

were assessed. 

2 
• 

y 

••• ••••• il . 

Figure 1. Multiple Task Performance Battery console. 

Target Identification. A standard histogram pattern was displayed on a six- by 

six-cell matrix for 5 s by successive presentations of two comparison patterns 

for 3 s each. The subject then decided if one, neither, or both of the 

comparison patterns matched the standard pattern. The answer was given by 

pressing the appropriate response button. Response latency and accuracy were 

recorded. 

Tracking. The display for the two-dimensional compensatory tracking task was an 

oscilloscope screen. A varying amplitude disturbance was imparted to the green 

dot target in each dimension; the subject attempted to counteract the 

disturbance to keep the dot at screen's center by moving a control stick. 

Performance is measured in arbitrary units by analog circuity in terms of mean 

vector absolute error and mean vector root mean square error. 

Problem Solving. For the problem-solving task, each test panel was equipped 

with five response buttons, a task "active" light, and three "feedback" lights, 

all located·at the left center of the test panel. The problem for the subject 

was to discover the correct sequence in which to press the five response 

buttons. Each button appeared only once in a given sequence. The subject was 

3 
instructed to use a trial-and- error procedure with a left-to-right search 

procedure. Pressing a button in incorrect order caused a red light to turn on 

and stay on until the next correct response was made. Pushing all five buttons 

in correct order caused a blue light to turn on. When a problem was solved, a 

lapse of 15 s occurred, following which the same problem was presented a second 

time. The subject was expected to reenter the previous solution from memory on 

the second, confirmation presentation. After another 15 s, a new problem was 

presented. Performance measures were: (i) mean response latencies for the 

first solution and confirmation stage and (ii) the mean number of errors per 

problem made during the confirmation stage. 

MTPB Workloads. MTPB tasks were administered in a basic 1-hour schedule that 

was constant throughout training and experimental testing. The basic 1-hour 

schedule involved five 10-min intervals of work under various combinations of 

MTPB tasks followed by a 1 0-min rest period. All five MTPB workload intervals._ . ..,.,. 

involved monitoring of red and green warning lights and meters. The first 

10-min MTPB interval (low workload) always included tracking in addition to 

monitoring. The second interval (moderate workload) involved mental arithmetic 

and problem solving, in addition to monitoring. The third interval (moderate 

workload) involved problem solving and tracking, in addition to monitoring. The 

fourth interval (high workload) involved problem solving and target 

identification, in addition to monitoring. The fifth 10-min interval (high 

workload) included mental arithmetic, target identification, and tracking, in 

addition to monitoring. 

Performance was assessed in terms of composite scores for each task. Composite 

scores summarized all measures of performance for the particular task. An 

overall composite score (all tasks) was also obtained, as well as a composite 

score for the three monitoring tasks (red lights, green lights, meters) and a 

composite score for the four "active" tasks (mental arithmetic, target 

identification, tracking, problem solving), which involved greater demand on 

cognitive resources. Task composite scores were calculated as follows: For 

each measure of performance on a task, the raw scores for all subjects were 

converted to standard scores with a mean of 500 and a standard deviation of 100. 

The task composite score for each subject and experimental treatment was the 

mean of standard scores on each performance measurement for that task. The sign 

of scores was changed, when necessary, so that higher standard scores always 

indicated better performance, and lower scores, poorer performance. Overall, 

monitoring and active composite scores were computed by averaging the 

appropriate task composite scores for each subject and treatment so that each 

task made an equal contribution to the variance. Analyses of the composite 

scores were made because they (i) simplify the evaluation of a large amount of 

data, (ii) have been found to be more sensitive to the effects of experimental 

conditions than individual measurements of performance, and (iii) have higher 

reliability than raw-score data on individual performance measures (Jennings, 

Chiles, and West, 1972). 

Procedure. Following 21 h of training on the MTPB, subjects participated in 

four experimental test sessions spread over a 2-week period with at least 2 days 

between each two tests. Subjects were run in groups of five, with at least two 

members of each age group in each group of five. The four test conditions 

included the four possible combinations of the two altitude and two sleep 

4 
conditions. The altitude conditions, 3,810 m or ground level (approximately 396 

m), were administered during all performance measurement sessions. Altitude 

simulation was accomplished by gas mixtures administered through face masks worn 

by subjects. The mixture used to simulate the 3,810-m altitude contained 13.5 

percent oxygen and 86.5 percent nitrogen. Compressed air was used for the 

ground level condition. 

The two sleep conditions involved normal unregulated sleep at home prior to 

performance testing vs. sleep deprivation involving loss of one night's sleep 

immediately prior to performance testing. In the sleep deprivation condition, 

subjects reported to the laboratory at 2030 in the evening and remained there 

until performance testing was completed the following day. Subjects were 

closely supervised by two experimenters to prevent dozing. Caffeine and food 

intake were controlled during the sleep deprivation period and during 

performance sessions. During the sleep deprivation period, subjects were 

permitted to play cards, ·ping-pong, computer games, and video games; watch 

television; or read, but no vigorous exercise was permitted. In the normal 

sleep condition, subjects slept at home, ate a prescribed light breakfast, and 

reported to the laboratory at 0800 of the performance test day. 

In all four experimental conditions, the morning MTPB performance session began 

at 0900 and involved three repetitions of the basic 1-hour work schedule, ending 

at 1200. After a lunch break, the afternoon session began at 1300 and involved 

a schedule similar to the morning session. During every morning and afternoon 

experimental test session, subjects breathed the appropriate gas mixture for the 

entire 3-hour duration. Questionnaires concerning amount of sleep and breakfast 

intake and mood rating scales were administered before the morning performance 

session. Mood rating scales were also administered after both morning and 

afternoon sessions. Subjects rated mood, on nine-point scales, regarding levels 

of attentiveness, tiredness, tenseness, boredom, and irritation (Thackray, 

Bailey, and Touchstone, 1977). 

RESULTS 

All data were treated by analysis of variance techniques. 

Complex Performance. The main effects of age, sleep deprivation, altitude, and 

workload are shown in Table I. Data are shown for performance of individual 

tasks, an overall composite summarizing scores in all tasks, and composites 

summarizing performance separately for the monitoring tasks (green lights, red 

lights, and meters) and the active tasks (mental arithmetic, target 

identification, problem solving, and tracking). Since all active tasks did not 

occur at all workloads, overall composite scores and composite scores for active 

tasks were averaged over workload intervals. Overall performance was 

consistently lower in the 60- to 69-yr group than in the 30- to 39-yr group in 

all tasks, and significantly so in the overall composite scores (p < .01); 

monitoring composite scores (p < .05); and two individual tasks, the monitoring 

of red lights (p < .001) and the monitoring of green lights (p < .05). 

Sleep deprivation consistently decreased performance. The effect of sleep 

deprivation was highly significant in all individual tasks and all composite 

scores. 

5 
TABLE I. The Main Effects of Age, Sleep Deprivation, and Altitude in Composit

Scores and Individual Task Scores 

Sleep Altitude Workload Interval 

Score 30's 60's Yes No Gnd Alt 1 2 1 4 

OVerall Mean 513 484• 519 48o•• 502 4971 

Composite S.D. 53 39 33 55 46 52 

Monitoring Mean 519 47711 517 482 .. 501 498 528 497 504 482 4

Composite S.D. 63 71 54 80 67 73 52 65 64 80 

Active Tasks Mean 508 490 520 479** 503 496•• 

Composite S.D. 60 41 38 58 50 56 

Arithmetic Mean 509 489 512 487•• 504 4951 * - 544 - - 4

S.D. 84 76 74 87 77 85 - 55 - - 

0\ Target Mean 499 500 533 467•• 506 .4931 * - - - 495 5

!dent. S.D. 103 84 44 118 84 104 - - - 99 

Problem Mean 513 485 517 482•• 500 499 - 500 531 467 

Solving S.D. 87 69 65 89 81 80 - 75 66 86 

Tracking Mean 512 486 519 48o•• 502 497 573 - 462 - 4

S.D. 100 82 100 81 94 92 95 - 65 - 

Green Lights Mean 534 461• 519 48o•• 503 496 533 500 500 483 4

S.D. 80 106 93 102 100 99 86 102 96 102 1

Red Lights Mean 511 486•• 511 488•• 498 502 5211 487 508 486 4

S.D. 95 103 90 107 105 94 81 105 87 107 1

Meters Mean 513 484 520 480U 504 4951 527 505 506 477 4

S.D. 85 112 54 127 88 109 54 89 89 121 1

• p < .05 

•• p < .01 

··' •t. 
The effect of altitude was significant in the meters (p < .05), mental 

arithmetic (p < .01), and target identification tasks (p < .01) as well as in 

the overall (p < .05) and active tasks composite scores (p < .01). As will be 

shown below, this effect of altitude was due to an interaction of sleep deprivation and altitude. 

The main effects of sessi•on and hourly period within a session were small and, 

therefore, are not shown in Table I. Performance tended to be slightly lower in 

afternoon sessions, but the main effect of sessions was significant only in the 

scores for the meters task (p < .05) and tracking (p < .05), not in composite 

measures. 

Performance in successi ~e 1-h periods of experimental sessions tended to be 

highest in period 1 and lowest in period 3, but that effect of periods was 

significant only in the case of the meters (p < .05) and tracking tasks (p < 

.001), as in the case of the effects of sessions. 

The main effect of workload was statistically significant in all tasks except 

target identification. The effect of workload was significant at the p < .001 

level in the composite scores for monitoring as well as several individual 

tasks, including red-light and green-light monitoring, mental arithmetic, 

problem solving, and traoking. The workload effect was significant at the p < 

.01 level in the meter~ tasks. The three monitoring tasks tend to be given 

lower priority by su'bjeets than other MTPB tasks that require more active 

participation. The monitoring tasks, therefore, ~neral~y have secondary status 

and provide an index of residual attention that is inversely related to 

workload. The pattern ot main effects in monitoring performance indicates that 

task demands (workload) wer.e highest (and monitoring performance lowest) in 

workload 4 with workloads 5, 2, 3, and 1 following in that order. That order is 

in general accord with the r 1um.ber of tasks presented in each interval, with the 

exception of workload int,ervctls 4 and 5. The combination of problem solving and 

target identification w:'i,.th Dll'Oni toring apparently created higher workload than 

did the combination of ariU1metic, problem solving, and tracking with 

monitoring, even though qne less task was involved. 

Interactions. Cell mea·as and standard deviations for the interaction of age, 

sleep deprivation, and alti t~ude are shown for individual tasks and composite 

scores in Table II. 

Data are averaged' ~ver work:l.oad, session, and period in these tables. The 

second order interar~tion 0 1r age, sleep deprivation, and altitude was not 

significant in any casE';, nor· wa.B the first order interaction of age with sleep 

deprivation. There wc.s a s:ignificant interaction of age with altitude, but only 

in the case of. the pr oblem···Sol ving task ( p < • 05), not in any other task or in 

any composite score ~ 

In contrast, tb;d, in.teractio1n of sleep depri vation with altitude was significant 

in overall (~ ·< .004), monitoring (p < .004), and active-task (p < .05) 

composite '.:leo res, as well a::1 in three individual tasks including monitoring of 

red lig~~ts (p < .05) and me ers (p < .05) and in target identification (p < 

• 0 5) • This interactit.>n is Lllustrated for overall composite scores in Figure 2. 

7 
TABLE II. Composite and Individual Task Scores as a Function of Age, 

30-39 E 60-69 yr 

Score Sleep No Sleep Sleep No Sleep 

Gnd Alt Gnd Alt Gnd Alt Gnd Alt 

Overall Mean 533 535 500 483 499 502 472 463 

Composite** S.D. 30 29 58 66 30 27 39 44 

Monitoring Mean 531 541 511 494 494 494 463 455 

Composite** S.D. 33 25 55 66 39 38 52 57 

Active Tasks Mean 534 531 493 474 503 508 478 469 

Composite** S.D. 37 40 64 71 33 30 41 46 

Arithmetic Mean 529 522 500 486 495 498 ll89 474 

S.D. 36 64 73 70 45 41 44 60 

Target Mean 536 537 477 447 527 529 484 460 

Ident. * S.D. 37 31 107 139 47 33 77 104 

Problem Mean 534 533 500 482 494 502 468 475 

Solving S.D. 57 62 77 88 44 34 70 49 

Tracking Mean 539 531 494 483 498 504 472 468 

S.D. 69 76 68 61 43 53 41 40 

Green Lights Mean 559 554 520 501 476 477 444 445 

S.D. 34 37 48 61 72 64 76 71 

Red Lights* l-Ean 506 533 510 495 498 504 473 470 

S.D. 80 45 56 65 44 48 72 59 

Meters* Mean 529 535 502 487 509 502 473 452 

S.D. 35 17 83 104 39 44 90 119 

Significance of the sleep deprivat i •on by altitude 

interaction: .. ; .. _ . p < .05 .. p < .01 

8 
• 

' 

w 

0::: 

0 

u 

(/) 

0 

0::: 

<( 

0 

z 

<( 

1-

(/) 

550 

500 

450 

o-----~0 

CONDITIONS 

0 SLEEP 

~ NO SLEEP 

400~---------L----------~--------~ 

GROUND 3,810 m 

ALTITUDE LEVEL 

Figure 2. Mean overall performance as a function of sleep deprivation and altitude. 

The form of the sleep by altitude interaction indicated that, while there was no 

important effect of altitude on performance in rested subjects, detrimental 

effects of altitude appeared when subjects were sleep deprived. 

A significant second order interaction, which can be seen in Figure 3 for 

overall composite scores, involved the factors of age, sleep deprivation, and 

sessions. Performance in both the 30- to 39-yr and 60- to 69-yr groups 

maintained a fairly constant level over the 6 hours of performance during test 

days of both conditions in which subjects were not sleep deprived. When 

deprived of a night's sleep, the younger subjects maintained performance at a 

lower level that was similar in morning and afternoon sessions. In older 

subjects, however, there was a decline in performance from morning to afternoon 

when they were sleep deprived. This interaction was significant in the overall 

performance (p < .028) and in composite scores for active tasks (p < .008), but 

not in monitoring performance. Among individual tasks, the interaction of age, 

sleep deprivation, and session was significant for mental arithmetic (p < .05), 

problem solving (p < .05), and target identification (p < .006). Note in Figure 

3 that, although performance declines with time in sleep-deprived older 

subjects, the decline in performance due to the combined effects of sleep 

deprivation and time is not greater in older subjects. The interaction of age, 

sleep deprivation, and time seems, rather, to be due to less effect of sleep 

deprivation in the morning session in older subjects than in younger subjects. 

Workload had a significant main effect in almost all tasks but had interactions 

with other factors only in the case of monitoring performance. Figure 4 shows 

monitoring performance as a function of sleep deprivation, altitude, and 

workload separately for each age group. The interaction of age with workload 

was significant in monitoring composite scores (p < .001). Increasing workload 

had a greater adverse effect in older subjects. The sleep deprivation by 

9 
30-39 YR 60-6

550 r 550 ro- -o 

I 

lJ.I 

0:: 

u 0 500 500 t- o- 

(/) 6----6 

0 0:: 

45J 

A-

<( 

0 

-

-

t-' z 

0 450 

(/) D SLEEP 

A NO SLEEP 

400 400 I I 

AM PM AM 

SESSION SESSI

Figure 3. Mean overall performance as a function of age, sleep depri

• 
...... 

...... 

30-39 YR 60-69 YR 

600 r 600 I 

D--0 SLEEP

0--D SLEEP 

550 r -....... 550 I NO SLE

' ___ 

-

1:::.--t::. NO SLE

u i 500 r " ' 500 

.......... 

.......... 1:::. ........ 

<{ 

tC/) 450 t- 450 

2 3 4 5 2 3 4 

WORKLOAD INTERVAL WORKLOAD INTERV

Figure 4. Mean monitoring performance as a function of age, sleep deprivatio

and workload interval. 
altitude by workload interaction was also significant (p < .032) in monitoring 

performance. The sleep by altitude interaction tended to appear at moderate or 

high workloads. The third order interaction of sleep deprivation, altitude, 

session period, and workload also was significant in the monitoring composite 

scores, indicating that the sleep by altitude by workload interaction was 

greatest in the second and third hours of the morning session. 

Reliability of MTPB Performance. Since altitude variation as performed in this 

experiment had no effect on performance when subjects were rested, performance 

measurements for the two conditions not involving sleep deprivation provide an 

opportunity to examine the reliability of MTPB performance. The mean 

performance of subjects in those two conditions had a correlation of .93, as 

shown in Table III, which shows the intercorrelation of mean performance for the 

four experimental conditions. 

TABLE III. Intercorrelation of Performance in the Four Sleep 

Deprivation/Altitude Conditions 

Sleep/ No Sleep/ No Sleep/ 

Altitude Ground Altitude 

Sleep/Ground • 9 3 • 73 • 61 

Sleep/Altitude .68 .55 

No Sleep/Ground .go 

The correlations among the six 1-h test periods of the ground-level condition 

not involving sleep deprivation ranged from a low of .84 for the first and fifth 

hours to a high of .93 for the first and second hours. Performance of rested 

subjects at the 3,810-m altitude had correlations among the six 1-hour periods 

that ranged from a low of .82 for the first and fifth hours to a high of .91 for 

the third and fourth hours. 

The correlation of mean overall performance scores in the two sleep deprivation 

conditions was • 9 0, similar to the correlat·ion of performance in the two 

conditions involving rested performance. The correlations among means for 

1-hour periods of the two sleep deprivation conditions were also comparable, 

ranging from .73 to .92. As shown in Table III, the correlations were lower 

between performance in conditions involving rested performance and performance 

in sleep-deprivation conditions. 

Subjective Rating Responses. The main effects of age, sleep deprivation, 

altitude, and time (when responses were obtained during a session) on subjective 

rating responses are shown in Table IV for each rating scale. Compared to the 

younger group, subjects of the older group gave significantly higher ratings of 

attentiveness (p < .05) and significantly lower ratings of tiredness (p < .001) 

and boredom (p < .05). 

12 
TABLE IV. The Main Effects of Age, Sleep Deprivation, Altitude, and Time of Measureme

on Subjective Rating Responses 

Rating Scale §! Sleep Altitude Time 

30-39 60-69 Yes No Gnd Alt 0900 1200 1600 

Attentiveness Mean 4.8 5.4• 5.5 4.7*** 5.1 5.1 5.4 5.1 4.8

S.D. 1.7 1.5 1. 5 1.6 1.5 1.7 1.4 1.7 1.6 

Tiredness Mean 6.5 5.7*** 5.0 7.2*** 6.0 6.2 5.5 6.2 6.5*

S.D. 1.8 1.8 1.6 1.4 1.7 1.9 1.9 1.7 1.7 

Tenseness Mean 4.5 4.6 4.3 4.8• 4.6 4.5 4. 1 4.5 5.0*

S.D. 2.0 1.5 1.6 1.9 1.7 1.8 1.6 1.8 1.8 

Boredom Mean 4.6 3.5* 3.7 4.5*** 4.1 3.9 3.5 4.2 4.5*

,_. S.D. 1.9 1.6 1.7 1.9 1. 8 2.0 1.5 2.0 2.0 w 

Irritation Mean 2.2 2.0 1.9 2.4• 2. 1 2. 1 1.7 2.2 2.6*

S.D. 1.8 1.4 1.4 1.8 1.6 1.7 1 • 1 1.6 1.9 

• p < • 05 

•• p < .01 

••• p < • 001 
Sleep deprivation had the significant effects of decreasing attentiveness (p < 

.001) and increasing tiredness (p < .001), tenseness (p < .05), boredom (p < 

.001), and irritation (p < .05). There was no significant effect of altitude on 

responses for any rating scale. The time that ratings were performed had a 

significant effect on all types of ratings. Attentiveness declined over the 

workday (p ( .01), while tiredness, tenseness, boredom, and irritation increased 

significantly (p < .001). 

Significant interactions in subjective rating data are shown in Tables V and VI. 

The significant interaction of sleep deprivation with altitude in ratings of 

attentiveness (p < .05) and boredom (p < .05) are in agreement with performance 

data; the adverse effect of sleep deprivation was greater at altitude than at 

ground level in both cases. The significant interaction of sleep deprivation, 

altitude, and time in attentiveness (p < .05) and tiredness (p < .05) ratings 

indicates that the interaction of sleep deprivation and altitude was strongest, 

if it appeared at all, at the end of the morning session. The significant 

interaction of age, sleep deprivation, and time of measurement in ratings of 

attentiveness (p < .05), tiredness (p < .01), and tenseness (p < .05), as shown 

in Table VI, indicates that the adverse effect of sleep deprivation on those 

ratings was greater in older subjects than in younger subjects at the time of 

the first rating of the day, and that the change in ratings over the course of 

the workday was less for the older group in sleep-deprived conditions and less 

for the younger group in rested conditions. 

DISCUSSION 

The present results provide empirical support for previous suggestions in the 

literature regarding a significant interaction of sleep deprivation and 

altitude. Both information processing and monitoring performance were sensitive 

to this interaction. This finding supports warnings in the aeromedical 

literature that the effects of sleep deprivation may be more important for 

pilots than for other occupations because of the altitude factor. The data of 

this study corroborate the validity of those warnings for altitudes in the 

general aviation range. Although a mild 3,810-m altitude may have no adverse 

effect on performance of rested pilots, fatigued pilots may suffer greater 

performance decrements when reaching that altitude than they would at lower 

altitudes or on the ground. It would be highly desirable to examine the 

practical significance of the interaction of sleep deprivation with altitude 

using flight task performance measures in an aircraft simulator. 

The present findings confirm previous research findings of McFarland (1941) and 

of Mertens, Higgins, and McKenzie (1983), which indicated no interaction between 

age and altitude in rested performance, but the present findings do not indicate 

increased sensitivity to sleep deprivation in older subjects as found by Webb 

and Levy. A possible explanation of this disagreement could be the use of 

different amounts of sleep deprivation. Webb and Levy deprived subjects of 

sleep for 41 h before evaluating performance, whereas the present study involved 

an average of approximately 25.5 h of sleep deprivation before performance 

tests. It should be noted, however, that the level of sleep deprivation used in 

the present study was effective in producing a large performance decrement in 

14 
...... 

Ul 

TABLE v. Significant Interactions (p < .05) in Subjective Responses as a FUnction of Sleep 

Altitude, and Time of Measurement 

SLEEP DEPRIVATION/ALTITUDE 

ATTENTIVENESS BOREDOM 

No No 

Sleep Sleep Sleep Sleep 

Ground Mean 5.4 . 4.6 Ground Mean 3.9 4.4 

s.D 1.4 1.6 S.D 1.7 1.7 

Altitude He an 5.6 4.5 Altitude Mean 3.4 4.6 

S.D. 1.5 1. 6 S.D • 1.7 2.1 

SLEEP DEPRIVATION/ALTITUDE/TIME 

ATTENTIVENESS TIREDNESS 

Sleep No Sleep Sleep 

Time Gnd Alt Gnd Alt Time Giid Alt 

0900 Mean 6.0 5.7 5.0 5.0 0900 ' Mean 4.2 4.3 

S.D. 1.3 1.6 1.0 1.3 S.D. 1.5 1.6 

1200 Mean 5.2 5.9 5.2 4.1 1200 Mean 5.3 5.2 

S.D. 1.5 1.5 1.7 1.6 S.D. 1 • 1 1 .4 

1600 Mean 5.0 5.4 4.3 4.4 1600 Mean 5.4 5.6 

S.D. 1.2 1.5 1.7 1.7 S.D. 1.5 1.7 
...... 

(J\ 

TABLE VI. The Significant Interaction of Age, Sleep Deprivation, and Time of Measurem

Ratings of Attentiveness ( p < • 05), Tiredness ( p < • 0 1), and Tenseness ( p < 

ATTENTIVENESS TENSENESS 

30-39 1!. 60-69 E 30-39 'i!.. 6 

No No No 

Time Sleep Sleep Sleep Sleep Time Sleep Sleep Sle

0900 Mean 5.5 4.8 6.2 5.3 0900 Mean 4.3 4.2 3

S.D. 1.0 1.2 1.8 1.0 S.D. 1.3 2. 1 1

1200 Mean 5.6 4.1 5.4 5.2 1200 Mean 4 .1 4.5 4

S.D. 1.5 1.9 1.6 1.6 S.D • 1.9 2.3 1

1600 Mean 5.3 3.8 . 5.1 5.0 1600 Mean 4.8 5.2 4

S.D. 1.5 1.8 1.2 1.3 S.D. 1.8 2.4 1

TIREDNESS 

30-39 'i!.. 60-69 'i!.. 

No No 

Time Sleep Sleep Sleep Sleep 

0900 Mean 4.8 6.9 3.6 6.6 

S.D. 1.2 1.2 1.9 1.3 

1200 Mean 5.3 7.6 5.2 6.8 

S.D. 1.5 1.5 0.9 1.4 

1600 Mean 6 .o 8 .1 5.2 6.7 

S.D. 1.7 1.0 1. 4 1 .2 
all tasks. The difference between amounts of sleep deprivation in the two 

studies remains as a possible explanation of the discrepancy between f~ndings. 

Other factors that might be considered as possible causes of different findings 

on the sleep deprivation by age interaction are task differences, di~ferences in 

the amount of training on tasks, and time of day that performance was measured. 

The highly trained subjects of the present experiment may have been more 

resistant to the effects o~ stressors. The importance of task differences 

cannot be evaluated without further research. Webb and Levy measured the 

age-related effects of sleep deprivation in the early morning hours of the 

second night or sleep deprivation. In contrast, performance was measured during 

normal daytime working hours in the present research. The possible importance 

of circadian rhythm, or time of day, as a factor in age-related effects of sleep 

deprivation on performance should be considered. 

Subjective ratings had some positive relation to trends in performance data 

regarding the effects of sleep deprivation and the interaction of sleep 

deprivation and altitude. There was no indication, however, of greater 

subjective experience of fatigue among older subjects, and there was no evidence 

of greater time-related changes for older subjects over the course of the 

workday in the sleep deprivation conditions, as was the case in performance. 

Age-related biases-in the use of such rating scales may limit their usefulness 

in performance studies involving the age factor. 

CONCLUSIONS 

1. While there were age-related differences in performance, the present 

findings do not indicate significant variation in sensitivity to sleep 

deprivation, altitude, or their combined effects as a function of age. Future 

research should reexamine the age by sleep deprivation interaction with longer 

periods of sleep deprivation. That research should consider the possible 

importance of kind of task, amount of training, and circadian rhythms. 

2. Age-related differences in performance were greatest at higher workloads. 

Future studies of the relation of age to pilot performance in operational or 

simulated operational situations should include systematic variation of 

workload. 

3. The combination of age-dependent performance decrements with age-independent 

performance decrements due to altitude/sleep deprivation stressors may cause 

performance of older subjects to reach critical levels earlier under more 

stressful conditions. This possibility should be examined in future research on 

altitude/sleep deprivation/performance with performance measured in a more 

realistic aircraft simulator environment and with pilots of an age range similar 

to that of the subjects used in the present study. 

4. Warnings in the aeromedical literature concerning the greater deleterious 

effects on performance of sleep deprivation with increasing altitude were 

supported. The present study emphasizes those warnings by providing an 

empirical example of that interaction effect at a simulated altitude within the 

operational range for unpressurized aircraft. 

17 
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18