Research is described which evaluates manipulating environmental light intensity as a means to attenuate fatigue. A counter balanced, within-subjects design was used to compare nine male subjects exposed to dim (100 lux) and bright (3000 lux) light conditions. Oral temperature values were greater for the bright light group over the dim light condition. Melatonin levels were suppressed by bright light treatment. Also, the frequency of eye blink rate was less for subjects during bright over dim light exposure. Light exposure was without effect on subjective fatigue. However, irrespective of light condition, significant effects on confusion, fatigue, and vigor mood dimensions were found as a result of 30 hour sleep deprivation. The findings suggest that bright lights may be used to help sustain nocturnal activity otherwise susceptible to fatigue. Such findings may have implications for the lighting arrangements on space flights during the subjective night for astronauts

Brainard, G.

French, J.

Hannon, P. J.

Schiflett, S.

Whitmore, J.

English

NASA Technical Reports Server

N92-22333
PHOTIC EFFECTS ON SUSTAINED PERFORMANCE
Frenchl,J., Whitmore1,J., Hannon2,p.J., Brainard3,G., and Schiflettl,S.
1 Armstrong Labs/CFTO Brooks AFB, TX USA 78235-5300
2 Health Sciences, Northern Arizona Univ. Flagstaff, AZ
3 Neurology, Jefferson Medical College, Philadelphia, PA
ABSTRACT
The advent of space exploration requires attention to
the adaptability of human circadian rhythms in the
unique environment of space. Circadian disruption,
related to altered sleep work cycles and accelerated
solar clues, can lead to fatigue that may impede
mission success particularly as the duration of space
flights increase. Research is described which evalu-
ates manipulating environmental light intensity as a
means to attenuate nocturnal fatigue.
A counter-balanced, within subjects design was used
to compare 9 male subjects exposed to dim (100 lux)
and bright (3000 lux) light conditions. Oral temperature
values were greater for the bright light group over the
dim light condition. Melatonin levels were suppressed
by bright light treatment. Also, the frequency of eye
blink rate was less for subjects during bright over dim
light exposure. Light exposure was without effect on
subjective fatigue. However, irrespective of light condi-
tion, significant effects on confusion, fatigue and vigor
mood dimensions were found as a result of 30 hr sleep
deprivation. The findings suggest that bright lights, may
be used to help sustain nocturnal activity otherwise
susceptible to fatigue. Such findings may have implica-
tions for the lighting arrangements on space flights
during the subjective night for astronauts.
Key Words: Light, Temperature, Melatonin, Perfor-
mance, Eyeblink, Mood
INTRODUCTION
Acclimatization to extraterrestrial environments repre-
sents a challenge to human productivity during future
space missions. As extended flights become more
frequent, a greater demand on the sustained vigilance
This research supported by NASA Grant NAGU1196 and USAFSAH (-
F3361S-ST-D-o6o1) to GB, OoO Grant (OoO Suso-13u end USAF Grant
(AFOSR ss-o164) to PH.
of the crew increases the likelihood of performance
problems associated with cumulative fatigue. Disrupt-
ed sleep is reported to be a common difficulty on
shuttle flights particularly when dual shifts are required
(Santy, et al., 1988). Fatigue problems related to
alterations in circadian sleep work cycles and from
unfamiliar light and dark solar cues have been known
for some time and have been termed desynchronosis
(Winget, et al., 1984). Although most astronauts
quickly adjust to the demands of new work shifts in
space, some never do and become chronically fatigued
(Graeber, 1987 ). It may be that this fatigue results
from an inability to resynchronize to the new circadian
work rest cycles required in orbit. Light may serve as
an adaptive counter measure for pre-shifting astro-
nauts.
The adaptive characteristics of the circadian cycle to
the unique environment of space is relatively unknown.
Phase shifting of the sleep cycle as a result of travel
across time zones on the earth can produce changes
in the topography of the normal sleep EEG (Endo, et
al., 1985) that may account for the inadequacy of the
rest experienced during orbit. The fatigue produced by
circadian disruption can be studied on earth albeit in
the absence of microgravity. Effective treatment for
fatigue related to circadian disruption may improve the
potential for a successful mission. The present study
evaluated the effects of ambient light as a counter
measure to human fatigue degraded performance and
may serve as a model of inducing circadian dysrhyth-
mia.
Recent evidence supports a relationship between
environmental light and improved nocturnal alertness
(Campbell, et al., 1990, French, et al., 1990). The effec-
tiveness of light exposure on performance enhance-
ment is hypothesized to be related to the ability of light
to attenuate the normal nocturnal surge of the pineal
hormone melatonin. In support of this hypothesis,
many studies suggest that melatonin acts as an
endogenous sleep enhancing substance. For example,
human subjects given relatively low doses (2 mg) of
melatonin for three weeks experienced increased
fatigue (Arendt, et al., 1984). Similarly,
Lieberman, et al., (1985) using an acute oral dose of
482
https://ntrs.nasa.gov/search.jsp?R=19920013090 2020-03-17T11:53:39+00:00Z
240mgof melatoninfoundreducedvigor,elevated
fatigue,increasedconfusionandslowedreactiontime.
Additionally,plasmalevelsof melatoninaregreatest
duringthesleepphaseofthehumancircadiancycle.
Orallyadministeredmelatoninhasalsobeenfoundto
alleviatetranscontinentaldisruptionofcircadiansleep
wakecycles (Petrie, et al., 1989). Further, melatonin
has a high affinity for receptor sites in the suprachi-
asmatic nucleus (SCN) of the hypothalamus where it is
purported to trigger hormonal entrainment and regulate
circadian and circannual rhythms (Reppert, et al., 1988;
Brainard, et al., 1988).
Bright, light acutely suppresses plasma melatonin
levels in animals (Benshoff, et a1.,1987; Brainard, et
a1.,1982) including humans (Lewy, et al., 1980). The
current study addressed the consequences of mela-
tonin suppression via elevated ambient light intensity
on temperature, melatonin levels, cognitive abilities, eye
blink rate as measured by the electroogulogram and
subjective mood.
METHODS
A counter-balanced, within subjects analysis of
variance design was used to compare 9 male subjects
exposed to dim (100 lux) and bright (3000 lux) condi-
tions. Subjects were recruited from non-smoking
civilian and military personnel who indicated a normal
nocturnal sleep pattern. During both conditions,
scores on cognitive performance tests developed for
military human performance labs (Hegge, et al., 1985)
were obtained every 2 hours throughout the 30 hour
testing session. Beginning at 0600, subjects were
stabiliized on the performance measures under dim
light training conditions. Then at 1800, the light treat-
ment (either dim or bright) began and continued until
0600 the next day. Finally, dim illumination was used
until the completion of the experiment at 1200.
Immediately after each performance trial, oral tem-
perature was measured and plasma samples were
obtained for later melatonin assays (Brainard, et al.,
1991). Monopolar electrodes attached to the bony
orbit of the left eye and referenced to the pinna of the
left ear were used to determine the blink rate for each
subject during a 2 minute recording session, which
also followed the performance trial. Blink rate per
minute was then visually appraised from 1 minute of ar-
tifact free record in a blinded manner. Subjects
completed profile of mood surveys (POMS) every 4
hours. They were then allowed 2 weeks before expo-
sure to the second light condition. Subjects were
prevented from drinking any caffeinated beverages and
were fed the same foods (crackers, chips, sandwiches,
fruit, pizza, milk, water, juices) at the same times during
each light session.
Five subjects were evaluated at a time during each
light session Each subject was assigned to a testing
booth that contained a wide spectrum Vita-Light
fluorescent lamp (Duro-test Corp., Fairfield, N.J., 07007
Part # 1157030) as the adjustable illumination source
and a PC workstation. Each booth was separated
from adjacent booths by sound attenuating, frame
partitions that restricted the subject's view to their
individual workstation. A comfortable chair allowed the
subject to sit close to a work table that contained the
workstation. The light source was mounted on a wood-
en frame over the workstation and suspended from an
adjustable height to provide directed illuminance within
either the dim or the bright treatment ranges. The
subjects required to stay in the booth throughout the
study with the exception of short (< 10 minute restroom
breaks). Social interaction was kept to a minimum
between subjects by the experimenter and by the
demands of the testing schedule. Dependent measures
on the cognitive tasks consisted of response time and
accuracy variables. The order that the tests were
presented did not vary throughout the study. The 10
performance tests used consisted of the choice reac-
tion time (CRT), column addition and subtraction
(CAS), the manikin test (MT), serial addition and
subtraction (SAS) and Wilkinson reaction time (WRT).
A subjective mood survey was also taken. As well, a
tower puzzle (TP), following directions (FD), the num-
bers (N) and words (W) dual process task and route
planning (RP) tests were used.
RESULTS
Oral temperature levels were significantly elevated in
the bright light condition compared to the dim light
condition at the 2130, 0130 and the 0330 sample
points (p <.05) as shown in Fig. 1. Subjects in con-
stant dim light had typically low levels of melatonin
during daytime and higher levels at night. In contrast,
this melatonin rhythm was suppressed by the bright
light condition (Figure 2).
i
_E
_., 2 D
_r7 -
- LICH? ©_ +
, ' +/i
r
Figure 1. The effect of bright light on oral temperature.
The onset of the bright light is indicated and differenc-
es from the dim light condition are marked with an *
483
rlOl]M^t MAt E VOLIItlTFEFIS (rl-7)
5_JgTAIHI D PERrO;IMAHCE
t
......
I co _r_co 2_00 0600 _ 0
] I_IE {tlOtJrS)
Figure 2. The suppression of normal nocturnal plasma
melatonin levels was accomplished by bright light
exposure. The open bar beneath the abscissa indi-
cates the light exposure period.
Analyses of performance data indicate that bright
light treatment improved response time while reducing
the number of errors, particularly at the 2400 through
the 0400 sample points. Table 1 shows the number of
cognitive tests which were increased or decreased
during bright light treatment. As shown in Table 1 the
most effective time for bright light exposure to affect
the cognitive tests occurred at midnight, 0200 and
0400 hrs. The effectiveness of the bright light expo-
sure on cognitive ability did not extend beyond 0400
and may be detrimental when dim illumination is
reinstated after 0600 as indicated in Table 1.
Table 1. The number of cognitive test results
either increased or decreased by the application of
bright lights at sequential times. A total of 10 per-
formance tests were given at each time. The individual
tests are identified (parentheses) at each time point. If
response time or accuracy or if both were affected are
indicated by a - or + or __+,respectively.
# OF TESTS # OF TESTS
TIME INCREASED DECREASED
Liqht on
1800 1 (CRT+) 0
2000 1 (RP+) 0
2200 1 (SAS-) 0
2400 4 (SAS- N+ W+ FD±) 0
0200 2 (SAS- N+) 0
0400 2 (SAS- N+) 0
0600 0 1 (FD±)
Light off
08OO
i000
0
1 (SAS-)
3 (FD± N+ W+)
1 (FD±)
Seven of the tests (CRT, RP, SAS, N, W, FD and
MT) were sensitive to the effects of the illuminanca
conditions. Light exposure seemed to have beneficial
effects on SAS, RP and N tasks as shown in Table 1,
whereas the FD task seemed to be the most suscepti-
ble to disruption following extended exposure to bright
light. Only response time performance variables were
improved for the SAS test throughout the test session
while the FD and W tasks demonstrated alterations in
response time and accuracy variables at the times
indicated. Only accuracy variables were susceptible on
the N, CRT and the RP tasks. All of these results
represent light x time awake interaction effects (9 <
.05). The bright light condition improved an accuracy
variable (number of errors) on the MT as a main effect
across all time points.
EYEBLINK FREOUENCY
_ J
- ,---_-- , _._, .,-- ,-- --,--,.--
IsOO 2000 _20o 2400 o_oo 0400 06O00SO0 Ioo0
IIML
Figure 3. The increase in blink frequency per minute is
shown during dim light (1800 - 0600 hrs) compared to
the bright light exposure.
The results shown in Figure 3 demonstrates that light
treatment was associated with significant differences in
eyeblink rate as determined by the EOG. An overall
main effect of light on eyeblink frequency was found
(9<.05) but no interaction of light condition by time
was found. However, the EOG differences did not par-
allel the time course of the melatonin or performance
variables sensitive to bright light exposure.
There was no effect on subjective mood as a result
of bright light exposure. However, as the duration of
the sustained performance task increased 3 mood
dimensions were affected as shown in Fig. 4. Subjec-
tive impressions of confusion, fatigue and vigor as
shown in Fig 4a, 4b and 4c, respectively were affected
during the later trials (time) when compared to the
earlier trials, independant of light condition. According-
ly, the bright and dim light groups were averaged
together in Fig. 4 for each mood state and graphed
across hours awake. There was no effect on subjec-
484
tive anger, tension or depression as a result of extend-
ed hours awake, as shown in Fig. 4d, 4e and 4f,
respectively.
4a CONFUSION
., ,o . ,, ,, ,, . ,, ,.
vlgc .,i,p
4d ANG[R
m,
4b fATIGUE
./
- , , i -- ? - , .-, T--r-- F-
.=u ,l_b.i
4o DEPRESSION
N ii . m..._ . M !
4¢ YIGOR
bl no . i_ IB i* ii tq _o
41 TENSION
°I
QI
o_
_ ,* ,i iq ii ol oq _ _
Figure 4. The effect of sustained performance on
mood. No effects were found between light exposure
conditions. Early trials were significantly different from
later trials (p < .05) as indicated by an *. Bright and
dim light groups were combined due to an absence of
a light effect.
DISCUSSION
Exposure to bright light produced effects on oral
temperature, melatonin levels and eye blink frequency.
Although not sensitive to light condition, specific
subjective mood states were responsive to the sus-
tained performance test battery and to sleep depriva-
tion. The times during which bright light exposure
improved cognitive performance was similar to the time
in which oral temperature was elevated and melatonin
was suppressed. The levels of illumination used (3000
lux) were completely effective in suppressing melatonin
to daytime levels. Although not excessive, 3000 lux
seems to be more than adequate to control the normal
nocturnal surge of melatonin.
Bright light exposure may improve performance
otherwise susceptible to fatigue. However, it appears
that there is no duration of the light effect beyond the
exposure period. In fact, since performance begins to
degrade somewhat after 10 hours of bright light ex-
posure, the effectiveness of the lights in reducing
fatigue degraded performance may have been exceed-
ed. The absence of an interaction between light expo-
sure and mood suggests that bright light did not
improve mood state or make the the subjects feel less
tired or more vigorous. Although effects on physiologi-
cal state and cognitive performance were found,
subjective mood was more sensitive to the duration of
the sleep deprivation inherent in the 30 hour sustained
performance test.
CONCLUSIONS
The protocol used may present the opportunity to
evaluate adaptation problems, such as determining the
optimal conditions for pre-shifting astronauts in earth
bound labs. These and other problems associated
with cumulative fatigue and shiftwork in the unique
habitats and working conditions required in space
could be studied with much greater facility in the
absence of microgravity and the best solutions could
then be applied to space operations. Also, the results
may have implications for lighting conditions on board
space flights, particularly for shift workers required to
work during their subjective nights. Accuracy and
response time might be improved by increased light
intensity.
REFERENCES
Arendt, J., Borbely, A., Franey, C; & Wright, J. (1984)
The effects of chronic, small doses of melatonin given
in the late afternoon on fatigue in man: a preliminary
study. Neuroscience Letters. 45:317-321.
Benshoff, H.M., G.C. Brainard, M.D. Rollag and G.R.
Lynch, 1987, suppression of pineal melatonin in Perom-
yscus leucopus by different monochromatic wave-
lengths of visible and near-ultraviolet light (W -A). Brain
Research. 420:397-402.
Brainard, G., Richardson, B.A., Petterborg, LJ. and
Reiter, R.J., The effect of different light intensities on
pineal melatonin content, Brain Res., 233, 75-81, 1982.
Brainard, G., Lewy, A.J., Menaker, M., Fredrickson,
R.H., Miller, LS., Weleber, R.G., Cassone, V., and
Hudson, D. Dose response relationship between light
irradiance and the suppression of plasma melatonin in
human volunteers, Brain Research, 454, 212-218, 1988
Brainard, G.C, Rollag, M.D., Hannon, P., French, J.
and Storm, W.F., Effects of bright illumination on
plasma melatonin in normal volunteers during sus-
tained performance, Sleep Research, 20, 444, 1991.
485
Campbell, S.S. and Dawson, D. Enhancement of
nightime alertness and performance with bright ambient
light. Phys. and Beh., 48, 317-320, 1990.
Endo, S. and Sasaki, M. The possible mechanisms of
the disturbed circadian sleep wake rhythm after time
zone changes. Sangyo Ika Daigaku Zasshi, 7,
Suppl. p 151-61, 1985.
French, J., Hannon P. and Brainard, G. Effects of
bright illuminance on human performance and body
temperature. Ann. Rev. of Chronopharm., 7, 45-49,
1990.
Graeber, R.C. Sleep in space. Proceedings of the 27th
DRG seminar sleep and its implications for the military.
p 59-69, 1987.
Hegge, F.W. Unified tri-service cognitive performance
assessment battery (UTC-PAB). Design and specifica-
tion of the battery. JWD3 MILPERF Report No. 85-1,
U.S. Army Medical Research and Development Com-
mand, Ft. Detrick, Maryland, 1985
Lewy, A.J., Wehr, T.A., Goodwin, F.K., Newsome,
D.A.,& Markey,S.P. (1980). Light suppresses melato-
nin secretion in humans. Science 210: 1267-1269.
Lieberman, H.R., Garfield, G., Waldhauser, F., Lynch,
H.J., & Wurtman, W. (1985). Possible behavioral
consequences of light-induced changes in melatonin
availability. In The Medical and Biological Effects of
Ught. R. Wurtman, M. Baum, & J. Potts Jr., Eds. The
New York Academy of Sciences. New York, 453:242-
251.
Petrie, K., Conaglen, J.V., Thompson, L. and Chamber-
lain, K. (1989) Effect of melatonin on jet lag after long
haul flights. British Medical Journal, 298, 705-707.
Reppert, S.M., Weaver, D.R., Rivkees, S.A. and Stopa,
E.G. (1988) Putative melatonin receptors in a human
biological clock,Science, 24, 78-79.
Santy, P.A., Kapanka, H., Davis, J.R. and Stewart, D.F.
Analysis of sleep on shuttle missions. Aviat. Space
Environ. Med., p 1094-7, 1988.
Winget, C.M., DeRoshia, C.W., Markley, C.L. and
Holley, D.C. A review of human physiological and
performance changes associated with desynchronosis
of biological rhythms., Aviat. Space Environ. Med., 55
(12), p 1085-98, 1984
486


Photic effects on sustained performance

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server