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PROPOSED AND ACTUAL ALTITUDE PROFILE
30786 PROPOSED TEMPERATURE PROFILE . 43,000
ROOM AIR TEMPERATURE eee aE
25477 GLOBE TEMPERATURE Po Age tO 1,500
poles Hors tisiiiiiiiiiiisiriiiiiisiitiiiiiint,
4 8 I2 16 20 24 28 32 36 40 44 48 S2 S56 60 64 68 72
TIME (MINUTES)
Tete tate te tatete tare cota ec!
‘A= TRACKING B= TRACKING, MONITORING * MONITORING
MONITORING ARITHMETIC ARITHMETIC
Freure 1, Protocol of the experiment. ‘The thermocouple for room air temperature was adjacent to the chamber

control sensor and the black globe was at chest level of the subject.
formed for five minutes.

Each task combination (A, B, C) was per-

During the second training session, the sub-
jects were given 15 minutes of practice, a short
break, and then 75 minutes of practice. In the
third training session, the subjects were fitted
with all of the physiological recording sensors
and were given a 75-minute training session with
no breaks. The training was always given at the
same time of day (morning or afternoon) that
the subject. was to be tested.

Subjects reported to the laboratory about 30
minutes before the test session for a given day to
be fitted with the physiological recording sensors.
They then entered the test chamber, accompanied
by the medical monitor, where attachment to the
recording apparatus was completed. Subjects
were fitted with an absorbent head band to pre-
clude the possibility that perspiration might
cause direct interference with vision.

The test profile was the same for each condi-
tion. During the first 15 minutes the chamber
was shifted from the training condition to the
environmental condition for the particular ses-

sion to be experienced. The chamber was then
maintained at that condition for 80 minutes. The
environmental condition was then returned to
normal over a 15-minute period, and performance
testing was continued for 15 minutes for a post-
exposure baseline. The order of exposure to con-
ditions was counterbalanced across subjects so
that each condition occurred first, second, and
third the same number of times (three).

III. Results,

Performance. The data for each of the per-
formance measures were evaluated using a re-
peated measures analysis of variance model. The
variables entered in each analysis were: subjects;
environmental condition (Alt, Temp and Temp-
Alt); 15- minute interval of the 75-minute ses-
sion; and 5-minute interval of the 15-minute
session (there were two 5-minute intervals per
15-minute interval for arithmetic and tracking
measures while the other measures were taken in
all three 5-minute intervals).



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TIME (MINUTES)

Ficure 10. Rectal temperature (A) and mean skin temperature (B) during exposure to combinations of tempera-
ture (23.9° and 60° C.) and altitude (ground level and 14,000 ft.). Values are means with standard error
shown at ten minute intervals.

cant (P<.01) for mean skin temperature; the ambient temperature of 60° C. in the production

effects of altitude were not significant. of decrements in the performance of tasks of
velevance to aircrew activities. Adding the
IV. Discussion. elevated temperature to the altitude condition did

little more than “solidify” the apparent effects of
The results rather clearly suggest that, for a altitude alone. For only one measure and one

30-minute exposure duration, a pressure altitude time period was theré any evidence of a signifi-
of 14,000 feet is a more powerful factor than an cant effect. of temperature alone on tracking per-


dimension, .10<P<.20.) There were significant
differences between 5-minute intervals for all six
measures of tracking performance; this cor-
responds to the effect of the simultaneous per-
formance of arithmetic and tracking as compared
to tracking by itself.

The effect of environmental conditions on
tracking performance is shown graphically in
Figures 2 through 7. In each case, the Alt and
Temp-Alt conditions are quite similar and both
reflect: substantially poorer performance than the
Temp condition. This apparent effect was
evaluated by the application of non-parametric
tests (Wilcoxon T) to the Temp versus the Alt
data and the Temp versus Temp-Alt data.
(Since this is a non-parametric test, the error
squared and the RMS measures would be expected
to reveal the same results; hence, only the error
squared data were subjected to the Wilcoxon T
analysis.) The results of this analysis showed
the Temp condition to differ significantly from
the Temp-Alt condition for all four measures
analyzed—horizontal absolute (P<.05), hori-

VERTICAL
ABSOLUTE ERROR
70- oo TemperaTuRE
. ALTITUDE
4 A TEMPERATURE + ALTITUDE
60
a
2
5
2
2
«
3
«
&
o
50F
40 L L L jl

15 30 45 60
TIME (MINUTES)

Ficure 5, Vertical absolute error in volts (arbitrary
scale) on the tracking task. Subperiods of the
experimental sessions are plotted for each experi-
mental condition and for the mean of all conditions.
Time of initiation of the subperiod is shown on the
abscissa.

zontal error squared (P<.01), vertical absolute
(P<.01), and vertical error squared (P<.01).
For the comparison of the Temp and the Alt
conditions, neither measure of horizontal error
was significant but both measures of vertical error
were significant (P<.01 in each case).

VERTICAL
ERROR SQUARED
esr O——0 TEMPERATURE
. ALTITUDE
Q———A TEMPERATURE + ALTITUDE
20+
ao
5
3
2
« cAS~~._N,
7] a NT ta
4 . ~~,
& Oe N 4
ise Aa as
ay
6 Ag
“Mean
oe
° O——__,
10 n \ 1 1
18 30 45 60

TIME (MINUTES)

Fioure 6. Vertical error squared in volts (arbitrary
scale) on the tracking task. Subperiods of the
experimental sessions are plotted for each experi-
mental condition and for the mean of all conditions.
Time of initiation of the subperiod is shown on the
abscissa.

As noted in the two preceding paragraphs, the
environmental condition was significant for
several tracking measures, the 15-minute period
was significant for all but one tracking measure,
and the two variables did not interact. The ef-
fects of the 15-minute period, averaged over the
three environmental conditions are also shown
(as the squares connected by dashed lines) in
Figures 2 through 7. Although there are differ-
ences in the shapes of the curves for the in-
dividual conditions (especially in the Temp curve
as compared to the other two conditions), as was
just noted, the interaction of 15-minute period
and condition was not significant. This means
that, within the limits of the statistical power of
the experiment, time has about the same effect
irrespective of the environment being considered.



HORIZONTAL
ABSOLUTE ERROR
O TEMPERATURE
© ALTITUDE
—4 TEMPERATURE + ALTITUDE

°.

ERROR (VOLTS)
©
°
T

70
15 30 45 60
TIME (MINUTES)
Fieure 2. Horizontal absolute error in volts (arbitrary

scale) on the tracking task. Subperiods of the ex-
perimental sessions are plotted for each experimental
condition and for the mean of all conditions. Time
of initiation of the subperiod is shown on the

abscissa.
HORIZONTAL,
ERROR SQUARED
40r °. © TEMPERATURE
°. © ALTITUDE
O———A TEMPERATURE + ALTITUDE
35
o
re
5
fo
2
«
3
i
=
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25

TIME (MINUTES)

Fieune 3, Horizontal error squared in volts (arbitrary
scale) on the tracking task. Subperiods of the
experimental sessions are plotted for each experi-
mental condition and for the mean of all conditions.
Time of initiation of the subperiod is shown on the
abscissa.

HORIZONTAL
RMS ERROR
O——-0 TEMPERATURE
8.0r . ALTITUDE
A—— =A TEMPERATURE + ALTITUDE
75b
o
2
5
3
2
«
2 poh
= 70
&
oN
oe
ON
eer NN
‘0
1 1 1 jl
15 30 45 60

TIME (MINUTES)

Fiaure 4. Horizontal RMS error in volts (arbitrary
scale) on the tracking task. Subperiods of the
experimental sessions are plotted for each experi-
mental condition and for the mean of all conditions.
Time of initiation of the subperiod is shown on the
abscissa.

Significant effects of the environmental condi-
tions were found for four of the six measures of
tracking performance, but not for any of the
other measures. The effect of environment was
significant for the measure of integrated absolute
tracking error in the horizontal dimension
(F=4.617, P<.05) ; integrated absolute error in
the vertical dimension (F=7.917, P<.01); in-
tegrated error squared in the vertical dimension
(F=5.808, P<.01) ; and Root Mean Square error
in the vertical dimension (F=6.465, P<.01). In
each case the degrees of freedom for the F-test
were 2 and 16. For none of these measures was
the interactions of the environmental condition
with any of the other variables significant. For
all but one of the tracking measures (RMS error,
vertical dimension) the effect of 15-minute
period (time) was significant; ie. there was
significant variation in tracking. performance
during the course of the 75-minute test period.
(For Root Mean Square error in the vertical


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TIME (MINUTES)

Ficure 9. Heart rate during exposure to combinations of temperature (23.9° and 60° C.) and altitude (ground

level and 14,000 ft.).

final training session were used as a baseline
condition (i.e., normal temperature, ground level
atmospheric pressure). The data are plotted
graphically in Figures 9, 10A and 10B using the
means of the various measures.

Heart rate was significantly increased by the
exposure to a temperature of 60° C. (P<.01).
As seen in Figure 9, for both the Temp and the
Temp-Alt conditions, heart rate changed with
time (P<.01), reaching a maximum rate of ap-
proximately 110 beats per minute during the
final measurement interval of the period of ex-
posure to the environmental extreme. Heart rate
then gradually decreased as the temperature was
returned to normal but remained approximately
10 beats per minute above the baseline condition
xt the end of testing. The Alt condition had a
slight but not significant incremental effect on
heart rate with an almost immediate return to
the baseline rate when the chamber began to
descend to ground level.

Values are means with standard error shown at ten minute intervals.

Rectal temperature was significantly increased
by the exposure to 60° C. (P<.01) (Figure 10A).
For both the Temp and the Temp-Alt conditions,
rectal temperature reached a peak 10 to 15
minutes after the beginning of the return of the
environment to normal. The peak value in both
cases was approximately 0.5° C, higher than at
the beginning of the experimental session in
question. For the Temp condition, rectal tem-
perature was still at its pealc value at the end of
the experiment; for the Temp-Alt condition, it
showed a slight drop during the final 15 minutes
under normal conditions. Altitude did not affect
rectal temperature. However, as seen in Figure
10A, there is a suggestion (though not statisti-
cally significant) that altitude may have exercised
a moderating influence on the effect of ambient
temperature on rectal temperature.

Mean skin temperature reflected rather closely
the changes in Globe temperature (Figure 10B).
‘The effects of ambient temperature were signifi-



TECHNICAL REPORT STANDARD TITLE PAGE

1. Report No. 2. Government Accession No. 3. Recipient's Catclog No.
FAA-AM-71-17

4, Title and Subtitle 5. Report Date
COMBINED EFFECTS OF ALTITUDE AND HIGH TEMPERATURE April 1971
ON COMPLEX PERFORMANCE 6. Performing Organization Code

7. Author's) W, D, Chiles, Ph.D., P. F. Iampietro, Ph.D. 8. Performing Organization Report No.

E, A, Higgins, Ph.D., J. A. Vaughan, B.S.,
Georgetta West, B.S., G. E. Funkhouser, B.S.

9, Performing Organization Name ond Address 10. Work Unit No.

FAA Civil Aeromedical Institute

Contract or Grant No.

P. 0. Box 25082 Mu
Oklahoma City, Oklahoma 73125

13. Type of Report ond Period Covered

12. Sponsoring Agency, Name ond Address
Office of Aviation Medicine

Federal Aviation Administration

OAM Report

800 Independence Avenue, S.W. 14,
Washington, D.C. 20590

‘Sponsoring Agency Code

15. Supplementary Notes

This study was conducted under AM-B-70-PHY-48 and AM-A-71-PSY-13.

16. Abstract

Nine well-trained subjects were tested on a complex performance device designed
functions of relevance to aircrew activities. The tests, which involved
tracking, monitoring, and mental arithmetic, were performed during exposure to
altitude (14,000 feet) and heat (60° C.) both singly and in combination. Several
physiological measures were taken. Exposure durations were 30 minutes for each
condition with both pre- and post-testing.

The only clear-cut effects of the conditions were significant differences across
the environmental conditions on a perceptual-motor tracking task related to
manual aircraft control. Altitude was clearly a more powerful variable than
temperature in this study. This was evidenced by the fact that performance
under the temperature-plus-altitude and the altitude-only conditions were
approximately the same; performance under the temperature-only condition was
significantly better than performance for either of the other two conditions.
there was some evidence that the two environments in combination produced a
persistent effect on performance that did not dissipate with return to normal
conditions. Measured physiological functions of the subjects were within the
tolerable range.

17. Key Words 18, Distribution Statement

Heat, High Temperatures, Physiological | Availability is unlimited. Document may

Responses, Psychological Performance,
Aircrew, Pilots, Supersonic Aircraft,
Altitude, Hypoxia

be released to the National Technical
Information Service, Springfield,
Virginia 22151, for sale to the public.

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified 10

21 No. of Pages | 22. Price

$3.00

Form DOT F 1700.7 (2-69)



tasks, which involved tracking, monitoring, and
arithmetic, were performed during exposures to
14,000 feet altitude and 60° C. (140° F.) ambient
air temperature, both singly and in combination.
Several physiological measures were made. Ex-
posure durations were 30 minutes for each con-
dition, preceded by a 15-minute period required
to reach the environmental extreme and followed
by both (a) a 15-minute period during which the
environment was returned to normal, and (b) a
15-minute period under normal conditions. Per-
formance testing was carried on throughout the
75-minute test session. Recordings were made of
heart rate, rectal temperature, mean skin tem-
perature, and finger temperature.

The only clear-cut effects of the conditions were
the significant differences across environmental
conditions on tracking performance. Altitude
was clearly a more powerful variable than tem-
perature in this study. This was evidenced by
the fact that performance under the temperature-
plus-altitude and the altitude-only condition was
approximately the same; performance under the
temperature-only condition was significantly
better than for either of the other two conditions.

Evidence for an effect of temperature acting by
itself was only suggestive. There was some evi-
dence that the two environments combined pro-
duced a persistent effect on performance that did
not dissipate with return to normal conditions.
The measured physiological responses were well
within expectations from previous research with
no evidence of any joint effect of the two environ-
mental conditions.

The following conclusions are drawn from this
study :

1. Exposure to an altitude of 14,000 feet for
30 minutes produces decrements in a perceptual
motor task related to the manual control of an
aircraft. Specifically, two-dimensional compensa-
tory tracking suffers when that task is time
shared with monitoring and with arithmetic tasks.

2. Decrements will be no larger but may be
more consistent across subjects if the exposure
conditions involve both 14,000 feet and 60° C. in
combination. Decrements may also be more per-
sistent under this condition.

3. Exposure to 60° C. for 30 minutes is prob-
ably at or near the threshold for the production
of performance decrements.

REFERENCES

1. Allnutt, M. F.: Human performance under heat and
hypoxia, Royal Air Force Institute of Aviation
Medicine Report No. 466, 1969a.

2. Allnutt, M. F.: Human performance under heat and
hypoxia. Royal Air Force Institute of Aviation
Medicine Report No, 482, 1969b.

10

3. Iampietro, P. F., W. D. Chiles, E. A. Higgins and
H, L, Gibbons: Complex performance during expo-
sure to high temperatures, AEROSPACE MED.,
40 1331-1335, 1969,


formance, and this finding must be treated as
suggestive in that the order of magnitude of the
decrement under the Temp condition was much
less than that for the Alt condition. Only two
pieces of evidence were found for a combined
effect of altitude and temperature. One was the
observed lack of a significant difference for the
Temp-Alt condition when the periods at the en-
vironmental extreme were compared with the
post-exposure baseline period; the correspond-
ing difference for the Alt condition was signifi-
cant. The other evidence of a combined effect of
the two conditions was the fact that the Temp-
Alt condition differed significantly from the
Temp condition during this final measurement
period, whereas the Alt condition did not.
These two findings together are interpreted to
suggest that when subjects are exposed to the two
environmental extremes in combination, there is
a persistent deficit built wp that does not dis-
sipate within the 15-minute interval it took to
return the environment to normal plus the 10
minutes during which testing on the tracking
task was carried out. The statistical mechanism
at work would appear to be that there are rather
large individual differences in the reaction to ex-
posure to altitude and the dissipation of those
effects. Adding temperature to altitude results in
a more uniform response to the condition across
subjects.

Several possible factors may have been operat-
ing to cause the persistent decrement in perform-
ance during the post-exposure period in the case
of the Alt-Temp condition, but one is prominent
among these. During exposure to this condition,
the subject’s oxygen requirement is increased (be-
cause of increased tissue oxygen requirements
related to increased body temperature); at the
same time, his blood oxygen saturation has de-
creased because of the reduced partial pressure
of oxygen at 14,000 feet. The increased body
temperature persists during the post-exposure
period, and, therefore, the tissue requirement for
oxygen remains high during this period. Un-
fortunately, blood oxygen saturation was not
measured in this study. Therefore, we can only
speculate that the pre-exposure oxygen saturation
level was not re-established after returning to
ground level and, thus, left the subjects relatively
hypoxic during the post-exposure period. This
relative hypoxia could have been the cause of the
persistent decrement in performance observed.
under the Alt-Temp condition.

The only measured behavior that suffered from
exposure to the two environmental conditions
(acting either jointly or for altitude alone) was
tracking performance. This task, much more so
than the others, requires sustained attention but
with a high degree of flexibility if the time-
shared performance of tracking and the other
tasks is to be maintained without decrements.
The amount of training given the subjects was
adequate to assure that they had acquired the
necessary arithmetical and scanning skills to
maintain their performance on the monitoring
and arithmetic tasks. However, any decrease in
their ability to shift back and forth between
arithmetic and monitoring on the one hand, and
tracking on the other, would most likely be re-
flected in decrements in tracking performance.
Our rationale for this assertion is as follows:
First, the stimulus to which the subject responded
in the case of the tracking task was much less
compelling than the stimuli to which the subject
responded on the other tasks. Second, since
tracking involves a continuous succession of dis-
play changes (whereas the other tasks involve
discrete display elements), tracking would be
more likely to suffer from momentary lapses of
attention or slowness in the shift of attention;
this involves a simple probability inference. And
third, tracking is the only task in which the
subject himself can exert a direct influence on
the momentary difficulty of the task; he may in-
advertently introduce error which he then must
cancel out. The absence of decrements on the
monitoring and arithmetic tasks suggests that the
decrements in tracking performance were not the
direct result of interference with the neuro-
muscular system. A more likely explanation is
that the two environmental conditions, either
directly or through the production of interfering
responses, alter a central, attentional process and
that the tracking task, for the reasons noted
above, is more sensitive to such an alteration.

The measured physiological responses of the
subjects were very close to those that would be
expected from previous research on the two
variables.

Vv. Summary and Conclusions.

Nine well-trained subjects were tested on a
complex performance device designed to assess
functions of importance to aircrew activities; the



VERTICAL
RMS ERROR
O———O TEMPERATURE
. © ALTITUDE
45~  O———0 TEMPERATURE + ALTITUDE
_ 40b
a
2
5
3
2
«
S
<
=
6
35b
—
"O° eo
‘o
30 nl nl 3

15 30 45 60
TIME (MINUTES)

Fiaure 7. Vertical RMS in volts (arbitrary scale) on
the tracking task. Subperiods of the experimental
sessions are plotted for each experimental condition
and for the mean of all conditions. Time of initia-
tion of the subperiod is shown on the abscissa.

Again, Wilcoxon T tests were applied to clarify
this question. The performance of the subjects
during the two 15-minute periods at the environ-
mental “extreme” was compared with their per-
formance during the 15 minutes of post-exposure
baseline performance. A separate analysis was
carried out for each environmental condition for
each of the two 15-minute periods at the environ-
mental extreme for each of four measures of
tracking performance. In the case of the Temp
condition, the final 15 minutes (baseline) differed
significantly (P<.05) from the periods at tem-
perature for only one measure—vertical absolute
error; performance was poorer during the first
15 minutes of exposure to the high temperature.
In the case of the Alt condition, a significant
difference was found for both the horizontal ab-
solute error (P<.05) and horizontal error
squared (P<.01); in each case performance dur-
ing the second 15-minute period at altitude was
poorer than performance during the post-ex-
posure period. In no case was performance dur-
ing exposure to the Temp-Alt condition signifi-
cantly poorer than that during the post-exposure
period; generally, performance was numerically

poorer during the post-exposure period for the
Temp-Alt condition than for the Alt condition.
Both of these conditions were compared with the
Temp condition during this final 15 minutes of
the experiment using Wilcoxon T tests (again,
the RMS error was not analyzed for either track-
ing dimension). For no measure did the Alt
condition differ significantly from the Temp con-
dition. For three of the four measures (all but
horizontal absolute error), the Temp-Alt con-
dition differed significantly from the Temp con-
dition (P=.05 or better).

O——O TEMPERATURE
3.6 ° © ALTITUDE

A———A TEMPERATURE + ALTITUDE

3.5-

3.3-

32r

RESPONSE TIME (SECONDS)

3.0! tl L
15 30 45 60

TIME (MINUTES)

Fiaure 8. Mean response time on the arithmetic task
as a function of the experimental subperiod for
each experimental session. Abscissa values desig-
nate time for the initiation of the subperiod.

The only other finding relevant to performance
was a significant interaction (P<.05) between
environmental condition and 15-minute period in
the case of the arithmetic response time measure
(F=2.153; d.f.=8.64). This effect is shown
graphically in Figure 8. The apparent effect is
that the combination of altitude and temperature
has a cumulative influence that does not dissipate
upon return to normal room environment condi-
tions; another possible contributor to this inter-
action is the difference between the Temp condi-
tion and the other two conditions during the first
15 minutes at the environmental extreme.

Physiological Responses. The data for heart
rate, rectal temperature, and mean skin tem-
perature were analyzed using a repeated meas-
ures analysis of variance model; the data of the



Physiological Measures. The following pa-
rameters were measured at five-minute intervals
during each experimental session using the indi-
cated method: rectal temperature—thermistor
probe and Yellow Springs Instrument Co. tele-
thermometer; heart rate—chest electrodes
(Telemedic) and a Grass Model 5C polygraph;
and weighted average skin temperature—a four-
point distribution using copper-constantan ther-
mocouples on the forehead (a weight of 0.10),
chest (weight of 0.40), right forearm (weight of
0.14), and right calf (weight of 0.36). All skin
temperatures were recorded on a Honeywell
Electronik 16 recorder.

Performance Measures. The apparatus used in
this investigation was the same as that used in the
previously reported study.+ Since the apparatus
was described in detail in the earlier report, it
will be mentioned ony briefly here. The subjects
performed two primary, active tasks—two-
dimensional compensatory tracking and mental
arithmetic. They also performed three monitor-
ing tasks—choice reaction to the onset of a red
and a green light, simple reaction to the onset of
an amber light, and response to the drift of the
pointer of either of two meters (drift either up
or down from a normally horizontal position).
The same combinations of tasks were used as in
the previous study—tracking plus the three
monitoring tasks; tracking, mental arithmetic,
and monitoring; and mental arithmetic and
monitoring. These task combinations were per-
formed in 15-minute cycles with five minutes of
performance of each of the three combinations in
the order listed.

The measures of performance were: tracking—
integrated absolute error, integrated error squared
and Root Mean Square (RMS) error in each
dimension; arithmetic—percentage correct and
solution time; red and green lights—reaction
time and total time (movement time was derived
by subtraction) ; amber light—response time; and
meter monitoring—response time.

Environmental Conditions. -All training and
testing sessions were conducted in the Civil Aero-
medical Institute altitude chamber which is
cylindrical in shape: it is 18 feet long, 7 feet 2
inches wide at floor level, and 8 feet 6 inches high.
The interior of the chamber was illuminated at
a comortable level by fluorescent fixtures. The
subject sat on a padded wooden chair with his

back toward the door; he was dressed in a short-
sleeved, loose shirt, trousers, shoes and socks.

Altitude was controlled in the conventional
manner. The temperature was controlled by two
methods. The primary system provided a con-
vective input that controlled air temperature di-
rectly. However, this system by itself was not
capable of achieving the desired rates of tempera-
ture increase. Therefore, an auxiliary system of
six, 5-kw. radiant heaters was used to bring the
temperature up to the specified value in the de-
sired 15-minute period. Once the desired tem-
perature had been reached, the auxiliary heaters
were turned on and off as required to maintain
the chamber at 60° C. Control of relative
humidity was automatic. The convective system
maintained a continuous flow of turbulent air at
a rate of 50 to 100 feet per minute at the subject
position at all temperatures.

The chamber conditions used were as follows:

Training (Train)—23.9° C. (75° F.); water
vapor pressure, 3.1 mm Hg; relative hu-
midity, 14%; altitude, 1284 ft. (MSL)
(725.9 mm Hg).

Temperature (Temp)—60° C. (140° F.);
vapor pressure, 17.9 mm Hg; relative hu-
midity, 12%.

Altitude (Alt)—Temperature and humidity
same as for training; altitude, 14,000 ft.
MSL (446.6 mm Hg).

Temperature plus altitude (Temp-Alt)—
Temperature and humidity as for the
temperature condition; pressure altitude as
for the altitude condition.

The environmental profiles are shown in
Figure 1. Dry bulb temperature was monitored
by means of an air probe located just above and
to the right of the subject’s head. Subsequent
checks showed the black Globe temperature to
average about 5° ©. below the air temperature.

Procedure. The subjects were given three
sessions of training, one on each of three differ-
ent days. The first session was preceded by a
brief physical exam, after which the subject re-
ported to the chamber. During that first session,
approximately 15 minutes were devoted to ex-
plaining the nature of the experiment, the safety
precautions being taken and the nature of each
task. Subjects then performed for 15 minutes—
five minutes on each of the task combinations:
after a short break, the subjects were given a 80-
minute training session.


COMBINED EFFECTS OF ALTITUDE AND HIGH TEMPERATURE ON
COMPLEX PERFORMANCE

I. Introduction.

A number of the conditions associated with
the operation of advanced aircraft have the
potential for introducing heat loads on the air-
crew (and, in the case of commercial aircraft, on
passengers) with possibly deleterious effects on
the man’s performance capabilities. Thus, an
emergency condition involving the loss of both
the cooling and cabin pressurization systems
would expose the operator to a combined stress
situation about which very little is known.

In a previous study conducted at the Civil
Aeromedical Institute, we found significant decre-
ments in the performance of aircrew-related tasks
during a 30-minute exposure to a temperature
of 71.1° C. (an effective temperature of 38.4° C.) ;
both two-dimensional tracking performance and
mental arithmetic were adversely affected.*
Another part of that experiment involved a 30-
minute exposure to a temperature of 60° C. (an
effective temperature of 35° C.). When the data
for the first ten subjects tested at 60° C. were
analyzed separately, significant decrements were
observed; decrements were not found for the
second ten subjects nor for the two samples com-
bined. This finding was interpreted to suggest
that the (effective) temperature for performance
decrements on a complex task during a 30-minute
exposure was at or near 35° C. For the purposes
of those experiments and the present experiment,
complex performance is intended to mean the
time-shared performance of several tasks simul-
taneously.

In each of these previous experiments, testing
was carried out at local ground level (1284 ft.
MSL). In actuality, a number of the conditions
which might result in subjecting aircrew to high
temperatures might also be accompanied by an
increase in the altitude of the cabin environment.
Subsequent to the completion of this study, two
reports came to our attention which are relevant

to these combined conditions. Allnutt + examined
the performance of subjects during the final 40
minutes of a 90-minute exposure to 34.4° C. effec-
tive temperature combined with a simulated
altitude of 10,000 ft. Performance differed
significantly (about 10% lower) from a control
condition on only one measure, the Cattel IPAT
Culture Fair Test of intelligence. In a second
experiment? the first three subjects exposed to
an effective temperature of 344° C. combined
with a simulated altitude of 15,000 ft. “had to be
removed from the environment on medical ad-
vice.” The criterion of removal, a heart rate of
180 beats per minute, was substantially more
conservative than that used in our laboratory.
In fact in our previous temperature study, sub-
jects exposed to 71.1° C. (884° C. effective
temperature) exhibited a mean heart rate of
about 135 beats per minute at the end of the 30-
minute exposure.

The present study examined the effects of alti-
tude as a variable when added to temperature.
A pressure altitude of 14,000 feet was selected to
yield a partial pressure of oxygen that would be
at or slightly above the threshold for the produc-
tion of performance decrements as an individ-
ually imposed environmental condition, A
temperature of 60° C. was selected as a value that
was at or just below the threshold for the produc-
tion of temperature- induced decrements.

II. Methodology.

Subjects. The subjects used in the study were
FAA Aeronautical Center male employees who
volunteered to participate in response to an item
in the Center information bulletin. The selec-
tion criteria exercised in recruiting subjects were
that they were required to have at least a private
pilot’s license and a current medical certificate.
Nine subjects were used: their ages ranged from
30 to 46.



ACKNOWLEDGMENTS

The authors thank the subjects who experienced some discomfort during
the course of the experiment. They also acknowledge the valuable assistance
of Mr. J. L. Black, Mr, C. D. Valdez, and J. S. Mann in controlling the
chamber altitude. We also wish to thank the following physicians for their
assistance in monitoring subjects and/or giving physical exams: Dr. P. L.
Brattain, Dr. D. F. Campbell, Dr. A. W. Davis, Jr., Dr. R. H. Delafield,
Dr. M. Flux, Dr. H. L. Gibbons, Dr. B. J. F, Kramer, and Dr. C, A. Lynn.