~~ FAA-AM-83- 15

AGE, ALTITUDE, AND WORKLOAD EFFECTS

ON COMPLEX PERFORMANCE

H. W. Mertens, E. A. Higgins, and J. M. McKenzie

Civil Aeromedical Institute

Federal Aviation Administration

Oklahoma City, Oklahoma

September 1983

Document is available to the public through the

National Technical Information Service

Springfield, Virginia 22161

Prepared for

U.S. DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

Office of Aviation Medicine

Washington, D.C. 20591

-.A .- 2(A

I Li I I Ii
NOTICE

This document is disseminated under the sponsorship of the

Departmant of Transportation in the interest of information

exchange. The United States Government assumes no liability

for its contents or use thereof.

qi

II
Technical Repodt Vocumentation Page

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

FAA-AM- 83 -15

4. Title and Subtitle 5. Report Dote

Age, Altitude, and Workload Effects on SEPTEMBER 1 98

Complex Performance 6. Performing Orgonization Code

8. Performing Organization Report No,

7. Author's)

H. W. Mertens, E. A. Higgins, and J. M. McKenzie

9. Performing Organization Name and Address 10 Work Unit No. (TRAIS)

FAA Civil Aeromedical Institute

P. 0. Box 25082 I1. Controct or Gront No.

Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Name and Address

Office of Aviation Medicine OAM Report

Federal Aviation Administration

800 Independence Avenue, S.W. 14. Sponsoring Agency Code

Washington, D.C. 20591

15. Supplementary Notes

Work was done under approved tasks AM-A-82-PSY-85, AM-A-82-PHY-131, and

AM-A-83-PSY-94.

16. Abstra Fifteen healthy men in each of three age groups, 20-29 yrs, 40-49 yrs,

and 60-69 yrs. were evaluated regardingn complex performance in two altitude

conditions (ground level vs. 3,810 m) which were administered during performance

testing. Performance was measured during a 3-h test session with the Multiple

Task Performance Battery (MTPB) which involved time-shared performance of several

flight-related tasks presented in different combinations to vary workload.

MTPB tasks consisted of monitoring of warning lights and meters, mental arithmetic, problem solving, visual target identification, and tracking. Heart rate

decreased slightly at the 3,810 m altitude in the 60-69 yr group, but increased

significantly at altitude in the two younger groups. Both epinephrine and

norepinephrine excretion rates were highest in the 20-29 yr group and lowest

in the 40-4 9 yr group. epinephrine excretion rate was significantly higher at

altitude in all age groups, but thatftw- not-theecase with norepinephrine

excretion rate. Urinary 17-ketogenic steroid excretion rate and Fatigue Check

List responses yielded no significant effects of either age or altitude.

Complex (time-shared) performance of MTPB tasks decreased with age.) Age

related decrements occurred in monitoring tasks, information-processing tasks,

and a tracking task involving psychomotor-cooirdination.- Performance

differences occurring as a function of age were evident predominantly at

moderate and high workload levels. There wera no important effects of altitude

on performance. Physiological and biochemical responses had little relation to

performance. Implications of these fLndings for future research i-clating age

to pilot performance are discussed.

17. Key Words 16. O.istribution Statement

Aviation environment, Simulation, Age, Document is available to the public through

Complex performance, Workload the_ National Technical Information Service,

Springfield, Virginia 21161

19, Security Clossif. (of this raport) 20. Security Cloesif. (of this page) 21. No. of Pages 22. Price

Unclassified Unclassified 15

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Age, Altitude, and Workload Effects

on Complex Performance

Introduction

Receri. reviews of the literature on aging and pilot performance have

pointed to the paucity of research investigating the relation of age to

perceptual, cognitive, and intellectual functions of pilots (10,15).

Although many laboratory studies of the relation of age to performance have

shown age-related declines in tasks involving such functions as

perceptual-motor reaction time, speed of visual processing, memory, and

problem solving (2,4,6,10,12,14;15,23,24,25,28), most of these experiments

were not controlled for health ot Vubjects and it is difficult to generalize

their findings to pilots who, as a group, are highly selected and controlled

for health. The research of Szafr;xn (24,25), who employed actual pilots as

subjects, has shown that workload may be a critical factor in studies that

attempt to relate age to pilot )e.1-formance of flight-related tasks. He

found no performance deficits as a function of age in a serial-choice

reaction time task performed by i!self. Only when workload was increased by

requiring simultaneous performnr.ck of a short-term memory task did age effects appear. Workload-iodu,:ed performance decrements were found to

increase with age in pilots under age 60.

The importance of the in.4re-..ction of age with workload is corroborated

by single task studies involvine. nonpilots who have shown age.-related

prorii•,,ce decrewent- U11iy wri, task difficulty or workload was increased

by varying such factors as siýtual rate in vigilance tasks or complexity of a

problem solving task (5,24,25,26,27). The above findings concerning the

age/workload interaction suggest that future research on aviation stressors,

which may interact with age, should include workload as a controlled

variable. The work of Szafran (24,25) discussed above, and several studies

in which the time-sharing performance of pilots in the laboratory was shown

to be predictive of actual flight performance (7,11,22), also suggest that

measurement of time-shared performance of flight-related tasks may be

particularly appropriate for study of age-related effects of aviation

stressors.

The Civil Aeromedical Institute's Multiple Task Performance Battery

(MTPB) measurcs time-shared performance on several flight-related tasks.

The present research was conducted to evaluate the utility of the MTPB as a

tool for future age-related research. It was expected that workload-induced

performance decrements would increase with age and that performance might

not differ between age groups in low-workload conditions.

In this study, the physiological condition and intellectual ability of //

subjects in different age groups was controlled by requiring that all

subjects pass the equivalent of a Class III airman's physical examination,

exhibit pulmonary function in the normal range, and have an intelligence

quotient (IQ) in the normal range or above.

12
Method

Subjects. Forty-five subjects, fiiteen in each of three age groups,

20-29 yrs, 40-49 yrs, and 60-69 yrs, were evaluated. TT.ese subjects passed

the equivalent of a Class III airman's physical examination including simple

blood and urine tests, and had pulmonary function within the normal range;

i.e., measurements were greater than 80 percent of the predicted normal

values (21) regarding forced vital capacity, forced expiratory volume (1-s

and 3-s)m peak flow, and forced expiratory flow for the middle half of

forced expiratory volume. All subjects also had intelligence in the normal

range or above as measured by the Shipley Institute of Living Scale and four

subtests of the Wechsler Adult Intelligence Scale (vocabulary, information,

block design, and picture completion). With the exception of four subjects

in the 60-69 yrs group, subjects were free of chronic disease and not taking

medication. The exceptions were three subjects who were successfully being

treated for hypertension whose blood pressure and other physiological

measurements were within the normal range. A fourth subject exhibited a

trace of sugar in a urine test, but had no other symptoms.

Procedure. Following 15 hours of training on the MTP8, 3 hours on each

of 5 successive days, the subjects performed in two 3-h experimental

sessions, one at ground level and one at a simulated altitude of 3,810 m

(12,500 ft). The two experimental sessions were separated by 2 days and the

order of conditions was reversed in approximately half the subjects.

Altitude simulation was accomplished by gas mixtures administered through

face masks worn by the subjects. During each 3-h experimental session the

subjects performed on the MTPB for three consecutive 56-min periods. The

MTPB included time-shared performance in vigilance (monitoring of green and

red warning lights and meters), problem solving, mental arithmetic, visual

target identification, and tracking tasks. These tasks have been described

in detail elsewhere (13,16). Four workload intervals occurred in each

period, i.e., in four successive 14-mml intervals. All intervals involved

monitoring of warning lights and meters. The first interval (low workload)

included target identification in addition to monitoring. The second

interval (high-moderate workload) included target identification and problem

solving in addition to monitoring. The third interval (low-moderate

workload) included mental arithmetic, tracking, and monitoring. The fourth

interval (high workload) included mental arithmetic, tracking, problem

solving and monitoring.

Several physiological and biohemical measurements were made during tne

two test sessions. The urine formed during each 3-h experimental session

was collected and urine samples were analyzed for epinephrine,

norepinephrine, and 17-ketogenic steroids. Heart rate (HR) was r-ecorded

continuously during each 3-h session.

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. Task

compostte scores were calculated as follows: for each measure of

performance on a task, the raw scores for all subjects were converted to

3tandard 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. The sign of scores

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

better performance and lower scores, poorer performance. An overall

composite score was also calculated for each subject and each treatment by

averaging the composite scores for different tasks so that each task made an

equal contribution to the variance. Analyses of task and overall 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 conditons than the individual measurements of performance; and

(iii) have higher reliability than raw score data on individual performance

measures (16).

On experiment days, subjects reported to the laboratory at 0830. Each

subject emptied his bladder as completely as possible without collection of

urine. The time was recorded and urine was subsequently collected at the 4 end of each experiment. The volume was recorded and a portion of the sample

was frozen for later analysis of catecholamines and 17-ketogenic steroids.

The subjects were then fitted with adhesive chest electrodes which were

connected to an electromagnetic tape recorder for continuous HR recording.

At 0900 subjects donned face masks and the performance testing was begun.

Each subject filled out a Fatigue Check List (FCL) prior to and following

both test sessizns.

Results

All data were treated by analysis of variance techniques.

an l ls. PU1z03.Be The effects oi age and

altitude on heart rate, urinary excretion rates for epinephrine,

norepinephrine, 17-ketogenic steroids, and FCL responses are shown in

Table 1.

At the 3,810 m altitude, the mean heart rate over the 3-h experimental

session was higher than at ground level in the two younger groups. Heart

rate decreased slightly at altitude, as compared to ground level, in the

60-69 yr group. The interaction of age with altitude was statiitically

significant (p < .02) for heart rate data.

EptnanhrinA Pyordat~nn vz- datsa ys 1 i-n~~ n (p-4 .1 ma man

effect of age and a significant (p < .01) main effect of altitude, but the

interaction of age and altitude was not significant. 6:cretion rate was

highest in the 20-29 yr group, and lowest in the 40-49 yr group. Excretiun

rate was consistently higher for all groups at the simulated 3,810 m

altitude than at ground level.

Norepinephrine excretion rates manifested a significant main effect of

age (p < .01) and a significant interaction of age and altitude (p < .03).

At both ground level and a simulated altitude of 3,810 m, excretion rate was

lowest in the 40-49 yr age group. At ground level, excretion rate wan

highest in the 20-29 yr group, and at 3,810 m excrction rate was highest in

the 60-69 yr group.

3
Table I. Physiological and Biochemical Measurements and Fatigue

Check List Responses as a Function of Age and Altitude

Heart Rate (beats per min)

Age (yrs)

20-29 40-49 60-69

Mean S.D. Mean S.D. Mean S.D.

Ground Level 77.5 7.2 78.5 15.1 85.3 19.1

3,810 m 84.9 10.9 82.6 12.7 82.0 16.1

Epinephrine (ng/h)

Age (yrs)

20-29 40-49 60-69

Mean S.D. Mean S.D. Mean S.D.

Ground Level 2314 959 1444 684 1695 715

3,810 m 2962 1050 1577 728 2028 900

Norepinephrine (ng/h)

"Age (yrs)

20-29 40-49 60-69

Mean S.D. Mean S.D. Mean S.D.

Ground Level 5688 2323 4451 2146 4956 1827

3.8...521 1 8. 3931 ,-5, 7375 4526

17-ketogenic steroids (mg/h)

Age (yrs)

20-29 40-49 60-69

Mean S.D. Mean S.D. Mean S.D.

Ground Level .550 .165 .520 .221 .729 .710

3,810 m .553 .174 .597 .346 .542 .327

rFatigue ihek TLst+ Score

Age (yrs)

20-29 40-49 60-69

Mean S.D. Mean S.D. Mean S.D.

Ground Level 12.4 2.8 12.2 3.7 11.1 3.3

3,810 m 12.6 2.9 11.9 4.7 11.4 3.2

4
Urinary 17-ketogenic steroid excretion rates and FCL responses yielded

no significant effects of Aither age or simulated altitude.

Complex Performance. The overall and individual task composite score

data (means and standard deviations) are shown for the main effects of age,

altitude, period, and workload in Table 2 and Table 3. Since all tasks did

not occur at all workloads, overall composite scores were averaged over

workload conditions. Overall performance declined with age. Although the

performance of the 40-4 9 yr group was not significantly less than the 20-29

yr group, performance in the 60-69 yr group was significantly (p < .01) less

than in both the younger groups. Performance was also consistently lowest

in all individual tasks in the 60-69 yr group, and significantly so in the

case of monitoring of green (p < .01) and red (p < .05) lights, problem

solving (p < .01) and tracking (p < M)1). Altitude had little effect on

performance as measured by overall composite scores or individual task

composite scores, with the exception of the monitoring of red lights.

Performance in the latter case was significantly (p < .05) higher at 3,810 m

than at ground level, but that effect was small relative to the effect of

age. Overall performarce in successive 1-h periods of experimerntal sessions

tended to be highest in Period 3 and lowest in Period 2. Although that

tendency was slight, the main effect of period was statistically significant

(p < .05). In the composite score data for individual tasks, the effect of

period vas statistically significant only in the cases of problem solving,

mental arithmetic, and tracking. For problem solving and mental arithmetic,

performance was again highest in Period 3. In the tracking task,

performance consistently declined across successive periods.

The main effect of workload was statistically significant in all MTPR

tasks as shown in Table 3. The workload variable was significant at the R <

.01 level in monitoring of green lights, meters, target identification,

mental arithmetic, and tracking, and at the L < .05 level in monitoring of

red lights and problem solving. The workload vaci-able will be considered in

greater detail below in the context of the interaction of age with workload.

The three monitoring tasks tend to be given lower priority than other MTPB

tasks which require more active participation. The monitoring tasks,

therefore, generally have secondary status and provide an index of residual

attention inversely related to workload.

The pattern of main effects in monitoring performance indicates that

task demands (workload) were highest (and monitoring performance lowest) in

Workload 4 with Workloads 2, 3, and 1 following in that order. That order

is in general accord with the number of tasks presented in each interval.

Interactions. The interaction of age with workload is shown for all

tasks in Table 4. There was a significant interaction of age with workload

in four tasks including all three monitoring tasks, green lights (p < .01),

red lights (p < .01), and meters (p < .01), and in target identification (p

< .01). The decrease in performance on these tasks with increasing workload

was smallest in the 20-29 yr group and greatest in the 60-69 yr group. That

trend, although not statistically significant, is also apparent in problem

solving and mental arithmetic.

5

-- -- -- - - - - - - - -
Table 2. Main Effects of Age and Altitude for Overall Composite

Scores and Composite Scores for Individual Tasks

AGE (yrs) ALTITUDE

Ground

20-29 40-49 60-69 Level .3,810 m,

Overall Mean 522.9 512.2 465.9"0 499.9 500.8

S.D. 48.5 39.6 45.3 55.4 47.2

Green Mean 547.1 522.2 430.7"0 500.4 499.6

Lights S.D. 78.4 75.2 103.2 97.8 102.1

Red Mean 510.3 521.9 467.8* 494.6 505.4*

Lights S.D. 95.1 58.6 126.0 109.C 89.Q,

Meters Mean 518.5 504.2 477.3 497.4 502.6

S.D. 81.5 73.5 130.6 102.7 97.0

Target Mean 504.4 516.9 478.7 500.1 499.9

Identif. S.D. 91.1 64.0 104.1 93.9 84.8

Problem Mean 535.4 493.3 471.3"* 499.5 500.5

Solving S.D. 60.4 58.3 75.9 73.6 67.4

Mental Mean 525.5 497.0 477.4 502.6 497.4

Arith. S.D. 66.4 72.8 99.3 88.0 78.0

Tracking Mean 523.4 530.0 446.6"* 502.4 497.6

S.D. 78.5 107.6 72.2 99.3 91.1

* D < .05

"00 p < .01

6
Ai

Table 3. Main Effects of Period and Workload for Overall Composite

Scores and Composite Scores for Individual Tasks

PERIOD WORKLOAD

1 2 3 12 3 14

Overall Mean 00.5 497.1 503.5* . . . ..

S.D. 51.9 54.4 48.0

Green Mean 500.2 495.3 504.5 526.7 488.0 511.5 473.80#

Lights S.D. 98.0 104.7 96.8 92.2 105.1 87.3 105.5

Red Mean 501.7 497.8 500.5 519.3 490.1 515.8 474.80

Lights S.D. 95.2 110.8 92.9 82.7 112.8 77.6 114.1

Meters Mean 494.2 500.0 505.5 535.2 492.0 519.4 453.5"*

S.D. 123.8 99.7 68.0 24.5 75.4 41.8 167.6

Target Mean 507.7 492.9 499.4 530.3 469.7 - -

Identif. S.D. 82.9 99.3 84.6 69.4 96.7

Problem Mean 494.0 497.2 508.94 - 505.1 - 494.9*

Solving S.D. 70.5 75.4 64.5 66.9 73.7

Mental Mean 495.7 495.7 508.6' - - 516.9 483.1"*

Arith. S.D. 83.0 92.1 72.5 67.3 93.4

Tracking Mean 506.9 498.4 494.7* - 51.0 459.0*"

S.D. 100.8 93.3 91.1 95.5 75.4

* p < .05

" p < .01

7
Table 4. Interaction of Age with Workload for Each Task of the MTPB

WORKLOAD WORKLOAD

.01 2 3 14 1 2 3 4

Green Problem

Lights* Solving

20-29 yr Mean 555 548 545 536 20-29 yr - 538 - 533

S.D. 93 66 75 6 -6 55 - 65

40-49 yr Mean 552 514 533 492 40-49 yr - 497 - 488

S.D. 52 85 62 82 - 65 - 50

60-69 yr Mean 472 405 456 397 60-69 yr - 481 - 465

S.D. 99 99 92 100 - 66 - 81!

Red Mental

Lights* Arithmetic

20-29 yr Mean 504 514 512 504 20-29 yr - - 538 515

S.D. 123 80 100 69 - - 58 72

40-49 yr Mearn 533 518 535 500 40-49 yr - - 511 485

S.D. 56 59 33 72 - - 62 80

60-69 yr Mean 518 439 500 422 60-69 yr - - 505 455

S.D. 44 154 80 157 ,- - 76 113

Meters* Tracking

20-29 yr Mean 535 517 525 494 20-29 yr - - 560 h85

S.D. 29 37 36 113 - - 73 65

40-49 yr Mean 539 501 524 455 40-49 yr - - 576 480

S.D. 9 38 26 94 - . 103 90

60-69 yr Mean 532 456 509 412 60-69 yr - - 486 409

S.D. 15 82 36 255 - - 81 32

Target

Identification*

20-29 yr Mean 524 483 - - S.D. 91 86 - -

40-49 yr Mean 536 499 - -

S.D, 58 64 - -

60-69 yr Mean 531 429 - -

S.D. 51 118 - -

*Interaction significant at the p < .01 level

i......................... ... . ... .. .. . . . . . .
Three c-ther ~intera ctions viere Rtatistical.IN signlAicant, as nho-iýn in

Table 5. The interaction of agý, with timin period was signil'icant in the

trackirg task- (p < .01). Tracking pei-fornance declinod ove.- the three

periods of a session in the 20-29 yr and 111-49 yr groups3, but was maintainied

ait a fairly constant level. in the 60-69 yr group, clthough performance in

the istter group was greatly i-if'cri;Dr to t.oaekiiug performanlce or the younger

grourps. The interaction of' altitude with time period wao stacistic.ally

sign.'ficant (r < .05) in the case of mental arithmetic althoug.h t,,e changes

in per'formance with Lime wero small compared to those '-tfeccts discussed

abovi- involving age. With the except~ion. of Period 2, perfoir~ance at ground

level was superior to performance at 3,810 m. ND oth*-,r signit'icant

interactions cf altitude with other variables were four~d.

The intnraction of' time period wit~h workload was st~at~ietical).y

significant in the case of the monttor~lng of meters. Tfhat interac2tion

indicat~es that. perform,-.nce in Workicads I and 2 did not vary over the thiree

peri,30 of a 3esvion vhi le performance was highest in Workload 3 at the

secoftd hour of t~he expeiriment.al session and highest in Workload 4I at, the.

third. lour of tie sessiconDiscussion

Performnance cf MTFB tasks generally decrea-sed with increasing age, with

the exce-ptiori of the mronttoring of red ligh~ts and in tracking; in thosce two

tasks, performsar~ce was highest in the ~40-119 yr age group. Performjance in

the 60-.69 yr group wae consisteintly lowest in all tasks. An age-related

decline in oerforrnance is consistent with findings of the single- and

dual-task studI.es when workload stress was involved, as discussed above.

TNh, wost iwpcv,.tan,.. finding of the present stvidy was the sign~flcan!

interactibn of age with workload in the performance of several component

t~aksk of the MT.PE. Increa~sIng wo.-koad generally caused a decrease in

performance in a--, age groups, but. the hmount. of decrease was greater as age

incruased. This trend was statistnai3.y significant in all monitoring

tasks, and igost probably reflects the lower priority given the monitoring

tasks relative to the other tasLr..; including mental arithmetic, target.

identification, probl~em solving and tracking, which demanded greater

activity and cognitive resources for performance. The greater sensitivity

of the monitoring tasks to workload in older subjects may indicate a

decrease in. renqiduai ateto at Mhighcr work'Loads "'or older subjects. it

should also be noted that the trend of greater detrimental effect of

increasing workload in older subjects also occurred in several of the more

"active" tasks: problem solving, mental arithmetic, and target

identification. The interaction of age with workload was of lesser

magnitude in these active tasks, but was statistically significant in the

case of target identification. Workload mignt have had a significant

interaction in other active tasks if they had been presented in a wider

range of workload conditions.

The consistent appearance of age-related effects of w')rkload in

performance of MTPB tasks in subjects selected for health and pulmonary

function, is similar to the effec.t of increasing workload in pilots which

9
Table 5. Other Significant Interactions

MENTAL ARITHMETIC

Period

1 2 3

Ground Level 503 491 517

3,810 m 442 503 503

TRACKING

Period

1 2 3 -

20-29 yr 538 512 517

Age 40-49 yr 537 529 519

60-69 yr 44k, 453 445

METERS

Period

1 2 3

Work- 2 495 489 490

load 3 520 579 520

4 426 459 476

10
Szafran found with a dual task situation (24,25). This finding of age

sensitivity in MTPB performance suggests that the MTPB may be a useful tool

in evaluations of a variety of biomedical factors in the aviation

environment which may interact with age. Such factors may include fatigue

due to sleep deprivation, cumulative sleep deprivation, and work-shift

changes which are planned for study in this laboratory.

In the present study, complex performance measured over a 3-h

experimental session did not reveal any important time-related changes in

overall performance scores. Significant effects of time period were

observed in individual task scores only in the casis of problem solving and

mental arithmetic, in which performance improved in the third hour, and in

tracking, in which performance decreased in successive hours of the session.

The opposite trends in these tasks cancelled each other in the overall index

of performance. These findings ruggest a reciprocal change with time in the

relative priorities among the three tasks. No loss of residual attention

seems to have occurred with time since monitoring performance did not

decline over the course of the 3-h session.

A mild simulated altitude of 3,810 m had no important effects on

performance in the present experiment in any age group. This contrasts with

the finding of a detrimental effect of a 3,810 m simulated altitude as compared to ground level in a previous experiment in this laboratory which

also involved time-shared MTPB performance (13). The present lack of an

altitude effect is unexplained in light of the previous positive finding,

but it suggests that if effects of the mild 3,810 m altitude exist, they are

small and variable.

Findings concerning the relation of age to heart rate during MTPB

performance and the interaction of age with altitude in heart rate

measurements are in gen"p'al accord with findings in the literature. Mean

heart rate for a 3-h experimental session increased at simulateu altitude in

the 20-29 yr and 40-49 yr groups of the present study, but decreased

slightly in the 60-69 yr group. McFarland (19) found a similar pattern in

his studies of the age/altitude interaction. The agreement of present

findings with his, regarding heart rate, suggests that our method of

altitude simulation was effective. The failure to observe a performance

deficit at the 3,810 m simulated altitude is, therefore, not likely due to

our method of simulating altitude.

The effective altitude in pressurized air carrier aircraft is less than

the 3,810 m altitude simulated in this study, usually less than 2,438 m

(8,000 ft). The present finding of no significant effect of the higher

3,810 m altitude on performance in any of the three age groups, therefore,

provides some support for the use of aircraft simulators without simulation

of cabin altitude in future studies. It should be noted, however, that some

stressors such as sleep deprivation may interact with mild altitude as

suggested by McFarland (20). Aircraft simulators typically do not have

altitude sJmulation facilities. Should the simulation of altitude be

required in future simulator studies, the use of special gas mixtures

breathed through standard aviation face ma3ks could be considered for

simulation of mild altitude hyp~xia.

11
Epinephrine excretion rates have often been associated with arousal

and, hence, performance; arousal hypotheses have been used to explain age

effects in performance (18). Although epinephrine excretion rates were

highest in the 20-29 yr group which had highest performance, rates were not

lowest for the 60-69 yr group which had the lowest level performance among

the three age groups. Epinephrine excretion rates were also significantly

higher at the siniulated 3,810 m altitude.

The significant main effect of age on norepinephrine excretion rates,

as with epinephrine, reflected the lower rates in the 40-49 yr group.

Norepinephine excretion rates increased greatly at altitude in the 60-69 yr

group, but decreased at altitude in the younger groups. There was no

apparent association of performance with the excretion rates of epinephrine,

norepinephrine, or 17-ketogenic steroids.

The effects of workload on catecholamine excretion rates could not be

assessed in the present research design because all workload conditions

occurred in each session and excretion rates could only be measured for the

whole session. It may be useful in future research to evaluate the relation

of age and workioad to such biochemical responses in order to seek

clarification of the complex relation of biochemical and performance

measurements.

In healthy subjects, complex (time-shared) performance of

flight-related tasks decreased with age. Age related performance Cecrements

occurred in monitoring tasks, informatic'i-processing tasks, and a task

measuring psychomotor coordination. Differences occurring as a function of

age were evident predominantly at moderate and high workload levels.

Phyaioiogical and biochemical responses had little relation to performance.

Implications for future research concerning the relation of age to

actual flight performance which may be conducted are as follows: 1) These

findings suggest that age-related decrements may occur in a number of

important flight related psychological functions and have adverse effects on

flight performance, but these decrements may not be revealed unless the

pilot experiences moderate or high workload levels; 2) Secondary monitoring

tasks may be particularly useful in studies of the relation of age to

performance of pilots in operational or simulated operational situations;

3) A synthetic work situation such as the MTPB may bf useful and

C.St.effeCt.VC for pralizinairy evaluation of a variety of aviation-related

stressors which may interact with age; 4) Possible sex differences in the

relation of age to performance should 3e evaluated.

12

.* i A l 
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15