EFFECTS OF BACKSCATTER OF BRIEF HIGH INTENSITY LIGHT ON
PHYSIOLOGICAL REPONSES OF INSTRUMENT-RATED
PILOTS AND NON-PILOTS

The view is fairly common that some of the
mmediate effects of intermittent photic stimula-
ion may result in altered states of consciousness,
vertigo, fear and visceral disturbances.? #37 #81
This has wide implications for people exposed
© flickering light stimulation. Of most concern
3 the effect of intermittent light stimulation on
irplane pilots since impairment of ability to
unction can have the gravest consequences in
he event of an emergency.

The nature of the evidence for the view that
atermittent photic stimulation can cause impair-
aent of ability to function comes from several
ourees. First, much of the evidence is of an
necdotal sort and as such presents problems of
valuation, The second form of evidence comes
vom clinical EEG laboratories where intermit-
mt photic stimulation is used as a tool in assess-
ig epilepsy. The third type of evidence comes
com. experimental research laboratories. Since
rere are wide variations in research methodol-
zy, the intensity of the photic stimuli used, the
tte at which the light pulses were presented,
id in the subject populations employed, there
room for contradictory claims. Discussion of
ifferent aspects of the problem as well as good
wiews of the literature are abundant.! 4 7-1 16 16 20

Most of the earlier experiments dealing with
e effects of intermittent light stimulation on
iysiological indices and performance have em-
oyed frequencies higher than the flash rates of
ost airplane anticollision lights and have used
ectroencephalograms almost exclusively as the
dex of physiological response. These studies
» not bear as directly on the problem confront-
g pilots flying through clouds or fog as would
udies which use flash frequencies in the range
countered by pilots. It was the purpose of the
st experiment to determine under controlled
nditions the effects of brief high intensity light

pulses from an actual airplane anticollision light
flashing at 1.27 Hertz on a variety of physiologi-
cal measures in a normal non-pilot population.
Post-experimental verbal reports of the experi-
ence were also obtained from the subjects.

EXPERIMENT I
Methods

Subjects, A group of 13 young adult males
(age range 17-25 years) comprised of medical
students from the University of Oklahoma Med-
ical School and introductory psychology classes
from Oklahoma City University with no history
of epilepsy participated in the experiment. Each
experiment lasted for about one hour. Subjects
were paid for participation in the experiment.

Procedure. Upon arriving at the laboratory,
subjects were told that they would be part of a
visual stimulation experiment and that a variety
of physiological responses would be monitored.
Skin surfaces where recording electrodes were
to be attached were cleaned with acetone. Grass
silver cup electrodes were used to record EEG
and eye blinks. The occipital EEG lead was
attached 1 cm above and 1 cm to the right of the
occiput. This lead was referenced to the ipsi-
lateral ear lobe. For eye blinks, leads were at-
tached above and below the left eye. Plate EKG
leads were attached on the right shoulder and on
the chest below the heart. Beckman skin potential
leads were attached to the second finger tip of the
left hand and to the volar surface of the left arm.
A common ground lead was attached to the
volar surface of the left arm above the reference
skin potential lead. A strain gauge respiration
lead was attached across the chest at the bottom
of the rib cage. Physiological responses were
recorded on a Beckman Type RM rectilinear
inkwriting dynograph running at a paper speed
of 10 mm/sec.



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= 16F
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2 10F
a
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X 4b During Stimg—= mors
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aig 1 A 1 4
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Ss 1-5 6-10 11-15 16-20

TRIAL BLOCKS

Ficure 7. Mean magnitude of skin potential responses
in millivolts for 5 trial blocks pre- and during-
light flash stimulation.

Figure 7 presents the skin potential response
data in summary form. The three-factor anal-
ysis of variance for the skin potential data indi-
cates that (1) pilot and non-pilot groups did not
differ in their overall level of skin potentail re-
sponding (F=1, df=1,22, p>.05); (2) there
was a significant groups-x-trials interaction
(F=3.48, df=3,66, p<.05). The interaction.
was due to the fact that pilots did not differ in
their pre-stimulus or during-stimulus responses
nor did they change their responding over trials.
The non-pilot group, on the other hand, had a
stable pre-stimulus response rate over trials but
their response to the flashing light stimulus was
largest initially and showed steady decrement
(habituation) over trials.

Figure 8 summarizes the heart rate data. The
analysis of variance of the heart rate data did
not disclose any significnt differences between
groups in either basal heart rate or in pre-during
stimulus heart rate changes, although there was
a non-significant decrease in rate from pre-
stimulus base to stimulus for both groups. There
was a significant trials effect (F=4.5, df=3,66,
p<.01) indicating that for both groups heart
rate decreased over trial blocks.

Figure 9 summarizes the EEG data. Figure
9, inconjunction with a three-factor analysis of
variance, indicates that neither groups, nor
stimulus, nor trials had any significant effect on
percent alpha rhythm.

2 75

a

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PILOTS

< During Stim $= non-piors

Ir

2 65,

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1-5 6-10 1-15
TRIAL BLOCKS

16-2

Froure 8. Mean heart rate in 5 trials blocks pre- an¢
during- light flash stimulation.

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1-5 6-10 11-15,
TRIAL BLOCKS

18-20

Ficure 9. Mean percent brain wave activity in tt
alpha range (8-12 Hertz) for 5 trial blocks in th
pre- and during- light flash periods.

In the control group there was suggestive ev
dence with the physiological measures that tl
degree of change or contrast determines tt
amount of physiological responding to the flasl
ing light. The control subjects who received th
flashing lights with the overhead light off r
sponded with larger responses than did subjec
who received the flashing light with the ove
head lights on. The effect was not statistical
significant because there was one reversal ar
the sample size was too small to tolerate such
reversal,


a highly significant increase in blinking to the
light flashes when compared with the pre-stimulus
blink rate (t=8.30, df=12, p<.001). Second,
the blinking rate to the flashing lights did not
habituate as indicated by a nonsignificant Fried-
man nonparametric analysis of variance for
trend across trials. Third, no significant changes
in basal blink rate occurred over trials as indi-
sated by a second Friedman analysis of variance.

8

\ During Stim oo
Pre-Stim e—e

8

25. \

15

MEAN SPR IN MV.

05 +

° n L n 1
1-10 11-20 21-30 31-40

TRIAL BLOCKS

1GURE 2. Mean magnitude of skin potential responses
in millivolts for 10 trial blocks pre- and during-
light flash stimulation.

Figure 2 summarizes the results for the skin
otential data. A Friedman nonparametric
ialysis of variance indicated that the decrement
. responding across trial blocks was significant
3=12.15, df=3, p<.01). Further testing in-
cated that a significant decrement occurred be-
veen the first and second trial blocks (t=2.51,
?=9, p<.05). None of the other comparisons
as significant. Thus, most of the decrement
curred in the first 10 trials with no consistent
‘ange occurring thereafter.

Figure 3 summarizes the results for respiration
ita in 10 trial blocks. Collapsing across trials,
significant difference in respiration rate was
und with rate increasing during photic stimu-
tion when compared to the rate just preceding
votic stimulation (t=2.83, df=9, p<.02). The
spiration changes across trial blocks were not
mificant for either the pre- or during-stimulus
te.

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itd

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z

< os -Sti

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= o r 4 1. ,
1-10 11-20 21-80 31-40

TRIAL BLOCKS

Figure 3. Mean rate of respiration in 10 trial blocks
pre- and during- light flash stimulation.

80
=
oa i
o 7
z 5
4
I
6 70 o——© During Stimulus
2 @— Pre-Stimulus
oL L

n n 1
1-10 11-20 21-30 31-40

TRIAL BLOCKS

Fievre 4. Mean heart rate over 10 trial blocks pre-
and during- light flash stimulation.

Figure 4 summarizes the results for heart rate
data over trial blocks, Collapsing across trials,
a small but highly reliable heart rate deceleration
was found when comparing pre- with during-
stimulus heart rate (t=5.65, df=12, p<.001).
The decrease in basal heart rate as measured
over trial blocks in the pre-stimulus interval was
not significant (C=4.88, df=3, p<.05). How-
ever, the heart rate decrease across trial blocks
during light stimulation was significant (C=13.3,
df=3, p<.01).



Design. The experiment was set up to provide
40 trials, each of which was 10 seconds in dura-
tion, of high intensity condenser discharge light
stimulation. The light source was a Grimes
model no. 30-360-1 high intensity condenser dis-
charge airplane anticollision light. Flash rate
was constant at 1.27 flashes per second. The
intertrial interval between each 10 seconds of
flash stimulation was 30-90 seconds, varying
randomly in 15-sec steps as determined by a table
of random numbers. A Gerbrands tape pro-
grammer turned on a Hunter 111C timer for
10-second periods at the randomly prescribed
intervals. The Hunter timer, in turn, controlled
the power source to the Grimes light. Prelimi-
nary tests indicated that the sound of the capaci-
tor charging in the Grimes light was a
confounding cue which would trigger physiologi-
cal responses not due to the light flashes. To
circumvent this problem, a Grason-Stadler 901B
white noise generator was employed in conjunc-
tion with a Koss Pro 44 headphone set. Further
testing revealed that an 80 db re: .0002 dyne/em*
white noise effectively masked the capacitor
charging sound and other equipment sounds.

Response quantification. Occipital EEG was
recorded with a 0.3-second time constant and at
a gain of 50 p» volts/em. To be scored as alpha
wave activity, two or more consecutive brain
waves of 8-12 Hertz had to be present in the
EEG. Visually, alpha stands out from the back-
ground EEG in the awake subject by being of
larger amplitude than the background activity
and by exhibiting synchrony (ie. when alpha
occurs, it is generally present in “bursts” of
several waves in a row). The percent alpha in
the 10 seconds preceding each stimulus was scored
as well as the percent alpha in the 10 seconds
during flashing light stimulation.

Eye blinks were recorded at a gain of 0.2
mv/om with a 0.1-sec time constant. Since
spontaneous blinks occur with a frequency greater
than zero and the spontaneous blink rate varies
among individuals, blinks were scored both dur-
ing the 10 sec preceding each stimulus and during
the 10 sec of each stimulus.

Skin potential responses were recorded with
a 1.0-sec time constant at a gain of 0.5 millivolts/
cm. Response amplitude was measured in milli-
volts from response onset to peak of response.
Response amplitudes were summed separately for
the 10-see pre-stimulus periods and 10 see during

light stimulation periods to yield baseline and
stimulus-elicited responding scores, respectively.

Respiration rate was recorded with a 1.0-sec
time constant. A flexible tube, which changec
its resistance when stretched, was taped to the
subject’s chest. This changing resistance wai
part of one arm of a Wheatstone bridge circuit
The distance between respiration peaks wa:
measured and converted to rate/min. Rate it
the 10 sec preceding a stimulus and the firs
complete respiration cycle during the stimulu
were recorded for each trial.

Heart rate was recorded by a cardiotachomete
coupler. It was qualified in terms of mean beat
per minute change from the mean of the 10-se
period before stimulation compared to the 10 se
during stimulation.

Results

All trials effect comparisons were based on tk
nonparametric Friedman analyses of variance
pre-during stimulus comparisons and specif
trial comparisons were based on correlated di
ference between means t-tests. The p<.05 tw:
tailed rejection region was adopted throughov

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bE “—~——»__,
<
e st
x
z 7 o—o During Stimulus
a
MO 6F e—e Pre-Stimulus
z
q -
w
2 ab
1 L .
1-10 11-20 21-30 31-41
TRIAL BLOCKS
Fieure 1. Mean number of eye blinks in 10 trial blo

pre- and during- light flash stimulation.

Figure 1 summarizes the results for the e
blink data. Both the mean pre-stimulus bli
rate and the mean rate of blinking during phc
stimulation are presented in 10 trial bloc
Several results are evident from this figt
First, collapsing the data across trials, there \


vas 100%. A flashing Grimes airplane anti-
ollision strobe light was placed below and be-
und the subject. The fog density was such that
either the experimenters nor the subject could
ee more than five feet in the fog chamber. On
wo occasions the fog generator iced up and the
ata from the subjects were not used because the
og density thinned visibly.

Design. The experiment was designed to pro-
ide 20 trials, each 40 seconds in duration, of
apetitive high intensity condenser discharge
ght stimulation. The light source was a Grimes
rodel no. 30-360-1 high intensity condenser
ischarge airplane anticollision light. Flash rate
vas constant at 1.27 flashes per second and flash
uration was & 10 psec. The intertrial interval
‘as 30-90 seconds, varying randomly in 15-sec
‘eps as determined by a table of random num-
ars. A Gerbrands tape programmer operated
Hunter 111C timer for 40-second periods at the
indomly prescribed intervals. The Hunter timer,
i turn, controlled the power source to the Grimes
ght. Sound masking was provided by a Grason-
tadler 901B white noise generator via a Koss
ro 4A headphone set. The white noise gen-
vator was set to provide 80 db re: 0,0002 dyne/
n? white noise at the earphones.

Both instrument-rated pilots and the control
roup of non-pilots received the same sequence
: 20 trials of flashing light stimulation, For
e pilot group a 100-watt overhead light was
1 in the fog chamber at all times during the
:periment.

The non-pilot matched control subjects re-
ived the flashing light under two conditions.
or one-half of the control subjects the overhead
zht was on for the first half of the experiment
id was turned off for the second half of the
‘periment. For the second half of the control
bjects, these conditions were reversed. This
‘ocedure tested the hypothesis that the physi-
ogical and subjective effects of the flashing
tht stimulus are determined, in part, by con-
ast or amount of light change.

For each response measure the data were
alyzed by 3-factor repeated measures (Case 1)
alyses of variance.*? Factor one was the in-
cument-rated pilot versus non-pilot dimension.
itor two was the pre-stimulus basal measure
mpared with the during-stimulus measure.
wtor three was repetition, i.e., response change

over 4 trial blocks. In all cases two-tailed tests
were used and the criterion for rejection of the
null hypothesis was set up at p<.05 or better.

Results

Figure 6 summarizes the results for the eye-
blink data. Both the mean pre-stimulus blink
rate and the mean rate during light flash stim-
ulation are presented for the four trial blocks.
The instrument-rated pilots did not differ sig-
nificantly in overall blink rate from the age-
matched non-pilot group (F<1, df=1, 22,
p>.05) indicating that the blink rate between
groups was nondifferential. There was a sig-
nificant groups-by-stimulus interaction (F=
11.46, df=1, 22, p<.01), with the instrument-
rated pilot group having a higher pre-stimulus
blink rate than stimulus rate, whereas the group
of non-pilot showed increased blinking during
the flashing light stimulus over their pre-
stimulus rate.

25
w
Di bad oy
4
Xiah
E4
2
a
z 10
& Pre-Stim = Ke sore
= st —_—-Ouring Stimg-~- HOR muons
° 1 A

1 1
1-5 6-10 11-15 16-20

TRIAL BLOCKS

Figure 6. Mean number of eye blinks in 5 trial blocks
pre- and during- light flash stimulation.

There was a significant trials effect (F=4.64,
df=3,66, p<.01) indicating that blink rate in-
creased over the course of the experiment. The
groups-x-trials interaction was not significant,
suggesting that both pilots and non-pilots con-
tributed about equally to the significant trials
effect.



TECHNICAL REPORT STANDARD TITLE PAGE.

T. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
FAA-AM-72-8

4. Title and Subtitle 3. Report Date
EFFECTS OF BACKSCATTER OF BRIEF HIGH INTENSITY LIGHT March 1972
ON PHYSIOLOGICAL RESPONSES OF INSTRUMENT-RATED 6. Performing Organization Code
PILOTS AND NON-PILOTS

7 Author(s) 8. Performing Organization Report No.

Arthur R, Zeiner, Ph.D.
Gerhard A. Brecher, M.D., Ph.D.

9. Performing Organization Name and Address 10. Work Unit No.
The University of Oklahoma Health Sciences Center
P. 0. Box 26901 11. Contract or Grant No.
800 N.E. 13th Street
Oklahoma City, Oklahoma 73190 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

6. Abstract

Thirty-nine human subjects were exposed to repetitive backscatter light
stimulation (off a white wall or fog) from a Grimes capacitance discharge
airplane anticollision light flashing at 1.27 Hertz. Both tonic (light
stimulus absent) and phasic (light stimulus present) stimulus-bound occipital
EEG, heart rate, respiration, skin potentials, and eyeblinks were recorded.

In the first experiment, response decrement (habituation) to the flashing light
occurred only with one out of five response measures (skin potential) over a
40-trial session indicating that the flashing light was a potent stimulus.
None of the subjects demonstrated photic driving, seizure activity, or theta
wave activity in his EEG. Most subjects reported the light as noxious, none
became nauseated, but many became drowsy over the course of the experiment and
several reported dark deadaptation from the flashing light. In Experiment IT,
eyeblink and skin potential measures differentiated between an instrument-
rated pilot group and an age-matched control group of non-pilot professional men.

The results suggest that, although the flashing anticollision light induces
changes in physiological measures which are resistant to habituation, these
changes do not extend to the induction of nausea.

7. Key Words 18, Distribution Statement
Effects of Backscatter, EEG, Heart Availability is unlimited. Document may
Rate, Respiration, Skin Potential, be released to the National Technical
Eyeblinks, Anticollision Light Service, Springfield, Virginia 22151,

for sale to the public.

5. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No, of Pages | 22, Price

Unclassified Unclassified 9 $3.00

om DOT F 1700.7 (8-69)



not significantly different although they were in
the same direction as had been the case in the
first experiment. A plausible explanation for
this discrepancy is attributable to either (1) the
fact that the intensity of backscatter from fog
in the second experiment was much less than the
backscatter from the white wall in the first ex-
periment, or (2) the fact that young college-age
subjects are more responsive than are older
subjects.

Our finding, that none of the subjects in either
experiment became nauseated, does not mean
that under actual flying conditions pilots may
not be affected. A potentially significant factor
which was not present in our experiment but
which is present under actual flying conditions
is vestibular input and its interaction with visual
phenomena.

Our finding that there was a consistent de-
crease in heart rate to the flashing light which
did not habituate cannot be accounted for as an
epi-phenomenon or by-product of respiration
change. Since the first complete respiration
cycle during light stimulation showed a consist-
ent increase over the pre-stimulus respiration
rate, then, if anything, heart rate during the
light should have increased if it were positively
related to respiration. Graham and Clifton’ in
reviewing the literature on heart rate change to
a variety of stimuli have concluded that the
orienting response to stimuli is heart rate de-
celeration, a conclusion in line with our findings.

Subjects in other experiments? as well as sub-
jects in our experiments have noted that the
experimental chamber appears appreciably
darker just after light offset. This finding sug-
gests that a marked degree of dark de-adaptation

occurs which may lead to a brief temporar;
interference with seeing the instrument pane
under conditions of backscatter from clouds 0
fog.

Conclusion

The purpose of the experiments was to deter
mine, under controlled conditions, the effects o
short, high-intensity light pulses from an actue
aircraft anticollision light flashing at 1.27 Hert
on a variety of physiological measures. Pos!
experimental verbal reports of the subjectiy
experience were also obtained from the partic
pants. Three groups of subjects composed c
instrument-rated pilots, age matched non-pilot
and medical students without flying experien:
were used for experiments in the laboratory «
the University of Oklahoma Medical School ar
in the fog chamber of the FAA Civil Aeromed
cal Institute in Oklahoma City. The light sour:
was a Grimes model No. 30-360-1 high-intensi
condenser discharge flash tube. Heart, respir
tion and blink rates, EEG, and galvanic sk
response were recorded. In general, heart ra
and skin potential were slightly elevated in t.
early part but decreased in the later part of t
experiments. The blink-rate responses were di
ferent for the three groups: the pilots showed
decrease, and the non-pilots and medical studer
showed an increase in eye blinks in the course
exposure. None of the subjects demonstrat
photic driving, seizure or theta-wave activity
his EEG, or nausea but experienced the bac
seattered light as noxious, and many becai
drowsy. The results bear directly on the prc
lem of anticollision lights used during flig
under backscatter conditions.


The post-experimental questionnaire results
ndicated that none of the subjects in either pilot
r non-pilot groups experienced any subjective
eelings of nausea. Eight out of 12 pilots and
even out of 12 non-pilots developed severe
rowsiness over the course of the experiment.
‘ome felt that had the experiment continued
onger they could not have stayed awake. There
‘as no difference in the noxiousness rating as-
igned to the flashing light by pilots or non-pilots.
‘he non-pilot controls who received the flashing
ght under overhead light-on and overhead
ght-off conditions, rated the flashing light sig-
ifieantly more noxious when the overhead light
vas off (t=5.05, df=11, p<.001).

DISCUSSION

In Experiment I, 13 young adult males rang-
g from 17-25 years of age were exposed to
ary intense reflected intermittent light flashes
‘om a Grimes condenser discharge airplane
iticollision light. Their EEG, eye blinks, skin
otential responses, heart rate, and respiration
te were monitored. Over a 40-trial session,
wbituation (response decrement) occurred only
ith the skin potential response.

In Experiment II, 26 adult males ranging
om 31 to 51 years of age were exposed to very
tense backscatter off man-made fog produced
’ a Grimes condenser discharge airplane anti-
llision light. Brain wave activity, eye blinks,
in potential responses and heart rate were
ntinuously monitored over the course of twenty
-sec trains of light pulses. Heart rate and
ain wave activity did not differentiate between
oups, but significant differentiation occurred
th eye blinks and skin potential measures.

In our sample of subjects neither photic driv-
g nor EKG seizure activity occurred. These
dings are in line with the results of previous
periments which indicate that for both photic
iving and EEG seizure activity, the adequate
mulus is a light flashing at faster than 4
artz.8

Data of the present experiment readily fit into
2 framework of the habituation literature.‘ *
w finding that the skin potential response
bituates sooner than does the occipital alpha
ycking responses to intermittent light stimula-
n supports the findings of Sokolov? * and his
workers.

The fact the eye blinks to the anticollision
light flashes showed no decrement over trial
blocks in either Experiment I or IT suggests
that the reflected light may have been intense
enough to elicit a protective reflex. None of the
commercially made photic stimulators on the
market puts out a light even approaching the
intensity of the Grimes anticollision light. Thus,
there is a scarcity of data with which to compare
our findings on this point.

In Experiment II there was actually a sig-
nificant increase in blinking in the pilot and
non-pilot groups over trials. Since the increase
occurred not only to the light stimulus but also
during the pre-stimulus base level periods, it was
probably not due to the effects of the light be-
coming more noxious over repeated presenta-
tions. A more parsimonious explanation would
ascribe the increase to the humid environment.
This interpretation is supported by statements
of subjects from the post-experimental question-
naire,

The fact that pilots blinked less to the flashing
light than during the pre-stimulus period can be
ascribed to a combination of greater familiarity
and possible adaptation to flashing light and to
greater defensiveness by the pilots than non-
pilots. Support for the latter interpretation
comes from the post-experimental questionnaire.
Several pilots volunteered the information that
they actively resisted the effects of the flashing
lights by concentrating on their great toe or on
an imaginary instrument panel. Non-pilot sub-
jects did not report engaging in such activities.

The skin potential data also offer support for
the view that instrument-rated pilots were more
defensive than non-pilot subjects. Whereas non-
pilot subjects showed habituation of responding
to the flashing light as had college students in
Experiment I, the pilots by concentrating on
something else while the light was flashing, were
able to suppress their responses so that there was
no difference in their pre-stimulus base versus
during-stimulus response measures.

In our first experiment in which a younger,
more responsive college student population was
utilized for subjects, significant physiological
changes to backscatter off a white wall from the
Grimes light occurred in all measures (occipital
EEG, skin potential, heart rate, respiration, eye
blinks). In the second experiment, responses
with occipital EEG and heart rate measures were



40°
<
I —TM
a sof
a
¢
E o—* Pre-Stimulus
2
a 20F o— During Stimulus
"4
w
a _
z 10
q
w
=

1 L al

n
1-10 11-20 21-30 31-40

TRIAL BLOCKS

Ficure 5. Mean percent brain wave activity in the
alpha range (8-12 Hertz) for 10 trial blocks in the
pre- and during- light flash periods.

Figure 5 presents the mean percent brain wave
activity in the alpha range (8-12 Hertz) in the
pre-stimulus period and in the light stimulus
period across trial blocks. As is evident from
Figure 5, there was a highly reliable reduction
in alpha activity while the light was flashing
when compared to the pre-stimulus alpha base-
line (t=3.68, df=12, p<.001). Although Figure
5 shows an increase in percent alpha over trial
blocks in response to the light stimulus, the
trend was not significant (C=2.82, df=3,
p>.05). Similarly, the changes in percent base-
line alpha over trial blocks were also nonsignifi-
cant (C=1.2, df=3, p>.05). In summary, these
tests indicate that habituation of alpha blocking
to light stimulation did not occur.

Questionnaire data indicated that none of the
subjects became nauseated during the experiment.
A majority found the light flashes irritating or
annoying. A couple of subjects claim that they
experienced “eye strain” or “eye fatigue” from
exposure to the light flashes. Several reported
that for about 1-2 seconds after photic stimulus
offset. the room background illumination seemed
to dim and the room and everything in it ap-
peared subjectively darker. Most of the subjects
reported drowsiness toward the end of the ex-
periment.

EXPERIMENT II

Since the subjects in the first experiment were
not pilots and the possibility exists that pilots
may respond differently to flashing lights than
non-pilots, the first experiment was repeated, but
jt utilized instrument-rated pilots as subjects as
well as an age-matched control group of non,
pilots. Secondly, the actual back-scatter condi
tions were simulated more closely by using back
scatter from man-made fog as the stimulus.

Methods

Subjects, A group of 12 instrument-ratec
pilots from the Oklahoma City area and a grou}
of 14 non-pilot professional men from the Uni
versity of Oklahoma Medical School served a
subjects in the experiment. The average age 0
the subjects was 40 years. Pilots and non-pilot
did not differ significantly on average age. Bac
session lasted about 80 minutes. At the end c
the experiment subjects were administered
post-experimental questionnaire. Post-exper
mental verbal reports and ratings were also ol
tained from the subjects. Subjects were paid fc
participation in the experiment.

Procedure. Upon arriving at the laborator
subjects were told that they would be a part of
visual stimulation experiment and that a variet
of physiological responses would be monitore
Electrode placements and data quantificatic
were the same as in Experiment I except th
the pulse train duration in Experiment II w
extended to 40 seconds for pre- and durin
stimulus measures. For eye blinks, skin pote
tial responses, and alpha EEG activity, da
were quantified over 40-second intervals inste:
of the 10-second intervals of Experiment I. F
heart rate the data were scored over the 10 se
onds preceding a stimulus and the first ten se
onds during the stimulus because prelimina
data indicated that that is where the chang
were taking place. Respiration was not scor
in the second experiment because of recordi
difficulties with the transducer.

Experiment II was performed in the f
chamber of the Civil Aeromedical Institute
the FAA Center in Oklahoma City. After bei
instrumented, the subject, clad in a surgi
gown, was placed in a semi-reclining position
a plastic lawn chair in the fog chamber. 1
temperature was 72° F.+:2° and the humid






ACKNOWLEDGMENTS

We wish to thank the FAA Civil Aeromedical Institute in Oklahoma
City, Oklahoma, for the use of its facilities during our data collection for
Experiment II and Drs. P. F. Iampietro and C. E. Melton for their assist-
ance and advice. We also thank Dr. E. A. Higgins, who manned the fog
generator in Experiment II, and Gerald Vardiman, who worked hard and
ably as our assistant.





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. Mundy-Castle, A. C.

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