m

Kx

REFERENCES

. Bakan, P.: Extraversion-Introversion and Improve-

ment in an Auditory Vigilance Task, BRITISH
JOURNAL OF PSYCHOLOGY, 50 :325-332, 1959.
Landis, C., and W. A. Hunt: The Startle Pattern,
New York, Farrar and Rinehart, 1939.

. Lukas, J. S, and K. D. Kryter: A Preliminary

Study of the Awakening and Startle, Effects of
Simulated Sonic Booms. Stanford Research Insti-
tute Report No, NASA-CR-1193, 1968.

. Thackray, R. I.: Sonic Boom Exposure Effects IL3:

Startle Responses, JOURNAL OF SOUND AND
VIBRATION, 20 :519-526, 1972.

. Thackray, R. I., R. M. Touchstone, and K. N. Jones:

Effects of Simulated Sonic Booms on Tracking Per-
formance and Autonomic Response, AEROSPACE
MEDICINE, 43 :13-21, 1972.

12

6, Thackray, R. I., R. Rylander, and R. M. Touchstone:
Sonic Boom Startle Effects—Report of a Field
Study. FAA Office of Aviation Medicine Report
No, AM-73-11, 1973,

Thackray, R. I, R. M. Touchstone, and J. P. Bailey:

A Comparison of the Startle Effects Resulting From

Exposure to Two Levels of Simulated Sonic Booms,

JOURNAL OF SOUND AND VIBRATION, 33 :379-

389, 1974,

Thackray, R. I, R. M. Touchstone, and J. P. Bailey:

A Photographic Analysis of Human Startle Reac-

tions to Sonic Booms, AEROSPACE MEDICINE,

45 :803-806, 1974.

9. Warren, C, H. E.: Sonic Boom Exposure Effects:
The Sonic Boom—Generation and Propagation,
JOURNAL OF SOUND AND VIBRATION, 20:485-
497, 1972.

a

bd


booms, and the test was conducted in such a way
that the S had no knowledge that it would be
anything other than another boom or control
run. Following the pistol shot, subjective rat-
ings of startle and annoyance were obtained.
(The subjective scale used is given in Appendix
1)

D. Criteria for Defining Startle Responses.
Two levels of startle response to the booms were
designated. A minimal response consisted of
only an eyeblink reflex, while a more pronounced
response involved an arm-hand movement. In
order for either of these responses to be consid-
ered as a reflex response, its latency had to fall
within 20 to 100 msec for the blink response or
90 to 230 msec for the arm-hand response. These
ranges were empirically determined from re-
sponses to a pistol shot in a comparable previous
study.” Although Ss in the present experiment
were also exposed to pistol shots of the same
sound pressure level, there were slight differences
between the two studies in the range of latencies
obtained. In order to enable direct comparisons
between the results of the two studies, it was
decided to use the pistol shot data from the
earlier study in establishing latency ranges. It
should be noted that differences between the
mean latencies obtained in both studies were not
significant for either the eyeblink response
(¢=127; p>.05) or the arm-hand response
(¢=0.11; p>.05).

To be considered a startle reaction, an arm-
hand response had to (1) occur in conjunction
with an eyeblink reflex, (2) have latencies in
both the left-right and up-down planes that fell
within the latency ranges obtained from re-
sponses to the pistol shot, and (3) have response
amplitudes in both planes that exceeded the
maximum peak-to-peak amplitude of hand
tremor occurring in the 5-second period preced-
ing the boom.

E. Measurement of the Physiological Response.
Galvanic skin responses to each boom were ob-
tained by measuring the minimum resistance
following stimulation and the resistance level
immediately prior to each stimulus. These
measures were converted to conductance values,
and difference scores were obtained. The mag-
nitude of heart-rate change was determined by
obtaining the difference between the maximum
heart rates in the 5-second prestimulus and post-
stimulus intervals.

II. Results.

A. Behavioral Response. Table 1 provides a
summary of the eyeblink and arm-hand responses
that met the startle criteria. As is evident from
the data presented, the only evidence of any
startle reactions to the lowest exposure level was
in the small percentage of Ss showing eyeblink
responses. There were no arm-hand responses
to this level. Although the 30-N/m? level ap-
peared to evoke a greater percentage of startle
reactions than the 50-N/m? level, chi-square tests
revealed the differences between these two levels
to be nonsignificant for percent eyeblink re-
sponse, percent arm-hand response, and arm-
hand response amplitude (p>.05).

B. Autonomic Response. Skin conductance
and heart-rate measures are shown in Table 2.
The general decline in autonomic level across
boom presentations was found to be significant
for both prestimulus conductance level (F=8.99;
p<.01) and prestimulus heart rate (F=3.64;
p<.01). There were no significant differences
between the exposure groups themselves on any
of the physiological measures, and none of the
interactions were significant (p>.05). It is in-
teresting that heart rate decelerated following
the booms and, although the differences between
groups were not statistically significant, the
magnitude of cardiac deceleration appeared to
increase with decreasing exposure levels.

C. Subjective Data, Chi-square tests revealed
no differences between the groups in their rated
annoyance with the booms (p>.05). All groups
felt that regular exposure to booms of the levels
used would be mildly to moderately annoying.
Sixty to seventy percent of all Ss felt that they
would eventually adapt to or become virtually
unaware of booms of this level, and the groups
did not differ in this respect. Percentages of Ss
who indicated that the booms startled them were
50, 70, and 90 percent for the 16-, 30-, and 50-
N/m? overpressure levels, respectively. The dif-
ferences between the groups, however, were not
significant (p>.05). Median values assigned to
the subjective startle experience evoked by the
booms were 15, 33, and 25 for the 16-, 30-, and
50-N/m? levels, respectively. These values are
with reference to the pistol shot, which was as-
signed an arbitrary value of 100. The differ-
ences between groups were not significant

(p>.05).



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Taste 1, Eyeblink and Arm-Hand Data for Responses That Met the Startle Criteria

Eyeblink Data

Percentage of Ss Show=-
ing Startle Response ing Startle Response. Amplitude (mm)

Overpressuye Boom
Group (N/m") Number

10
20
10
00
20

16

AUPWNE

90
Mean 10

30

Aurwon-e
I8S38sses

Mean 78

50
80

50 80

OuFwnre

70
60
0
Mean 68

Experiment IT
I. Method.

A. Subjects. Twenty paid male university
students, ranging in age from 18 to 29, served as
Ss. All were right handed, had no reported
hearing loss, and had not previously participated
in startle or sonic boom experiments.

B. Apparatus. This study employed the pis-
ton of the simulator but modified the N-wave
for overpressures greater than 50 N/m? in order
to hold rise time approximately constant. To
accomplish this, a photocell, whose light source
was momentarily interrupted at the points of
maximum forward and backward excursion of
the piston, was employed. This provided a trig-
ger for the same transient circuit and speaker
used in Experiment I. By properly synchroniz-
ing the speaker output with the wavefront pro-
duced by the piston, it was possible to achieve
simulated booms greater than 50 N/m? with
nearly equal rise times. Booms were calibrated
in the same manner as described in Experiment I.

Arm-Hand Data

(Combined Left-Right and Up-Down)

Percentage of Ss Show- Mean Response

00 oo
00 oon

siss3s

10

r)

30
40
00
10
22

00
20
30 2.42
10 3.25
20 3.75
30 0,75
19 3.61

The task employed and the physiological meas-
ures obtained were the same as those in Experi-
ment I.

C. Procedure. Ten Ss were arbitrarily as-
signed to each of two exposure levels: 50 and
130 N/m*. (As in Experiment I, these values
refer to peak overpressures as measured in the
pressure chamber and not in the testroom itself.)
Sound pressure levels in the testroom were 72
and 81 dBA (fast scale) for the 50- and 180-
N/m? levels, respectively. Mean rise time of the
50-N/m? boom was approximately 6 msec; for
the 130-N/m? level, rise time was 4 msec. Dura-
tion was 210 msec for both levels.

Ss performed both the steadiness task and the
vigilance task as in Experiment I. The basic
procedure was the same; the major differences
were the number of booms presented and the
duration of the experiment. Twelve booms were
presented during two 40-minute sessions sepa-
rated by a 5-minute rest pause. Booms were
presented in six of the eight 5-minute periods


Since there was evidence of significant ha-
bituation effects, evaluations of possible differ-
ences between the 50- and 130-N/m? groups in
frequency or amplitude of startle reactions were
made by using only responses to the first six
booms. Chi-square tests revealed no differences
between the exposure groups in either percent
eyeblink or percent arm-hand response (p>.05).
Likewise, 1 Mann-Whitney U-test revealed no
difference between groups in amplitude of the
arm-hand responses (p>.05).

B. Autonomic Response. Prestimulus and
change values for conductance and heart rate
are shown in Table 4. Analyses of variances
revealed a significant decline across boom ex-
posures for conductance change (F=5.62; p<
.01) and prestimulus heart rate (F=3.25; p<.01)
and a significant difference between the two
overpressure levels for heart-rate change (F=
10.56; p<.01). None of the other effects were
significant. As in Experiment I, the heart-rate
response to the 50-N/m? exposure level was one
of cardiac deceleration. Cardiac acceleration oc-
curred to the 130-N/m? level.

C. Subjective Data. Although Ss exposed to
the higher overpressure level tended to rate the
booms as more annoying than did those exposed
to the lower lever, a chi-square test revealed the
difference between groups to be nonsignificant
(p>.05). Combining the ratings of both groups
gave a mean rating to both exposure levels of
“moderately annoying.” Seventy percent of the
Ss exposed to the lower level and 60 percent of
those exposed to the higher level felt that they
would eventually adapt to or become virtually
unaware of the booms. One hundred percent of
the Ss in each group stated that they were
startled by some or all of the booms. With ref-
erence to the pistol shot, which had an arbitrary
value of 100, the median startle value assigned
to the booms by the 50-N/m? group was 37.5
while the 130-N/m? group assigned a value of
143.5, A chi-square test revealed this difference
to be significant (p<.01).

Discussion

Experiment I demonstrated that groups ex-
posed indoors to simulated sonic booms having
outside overpressures of 30 and 50 N/m? (inside
dBA levels of 71 and 74) did not differ in the
frequency of evoked startle responses. Percent
response for the two levels combined was ap-

proximately 20 percent for arm-hand responses
and 73 percent for eyeblink responses. Reduc-
ing the outside overpressure level to 16 N/m?
(65 dBA inside) resulted in an exposure level
that was not sufficient to evoke arm-hand startle
responses in any of the Ss and that evoked eye-
blink responses in only about 10 percent of the
Ss. The results thus suggest that outside over-
pressures must be below 30 N/m? (71 dBA in-
side), and possibly as low as 16 N/m? (65 dBA
inside), in order to insure that measurable startle
responses involving arm-hand movements will
not occur.

Of more theoretical interest than practical
importance was the finding that heart-rate re-
sponse to the three overpressure levels was that
of cardiac deceleration rather than acceleration,
with the magnitude of deceleration appearing to
increase with decreases in exposure level. Since
heart-rate acceleration is the typical cardiac re-
sponse to startle,‘ this deceleration in heart rate
coupled with the relatively small percentage of
reactions involving muscular movements suggests
that the predominant response to these low ex-
posure levels was more of an orienting, or alert-
ing, response than a startle reaction.‘

Subjectively, it was judged that repeated ex-
posure to booms of the levels employed would be
mildly to moderately annoying, and the groups
did not differ in this respect. Sixty to seventy
percent of the Ss felt that they would eventually
adapt to or become virtually unaware of booms
of these intensities. Those Ss who felt that the
booms were subjectively startling evaluated the
startle experience as being approximately one-
sixth to one-third as startling as the pistol shot
to which they were exposed.

Experiment II revealed that exposure to a
series of 12 simulated booms resulted in a sig-
nificant reduction in the frequency of arm-hand
startle responses. This was found for both the
130-N/m? (81 dBA inside) and 50-N/m? (72
dBA inside) overpressure levels. Interestingly
enough, the series of 12 boom exposures occur-
ring over a relatively short period of time failed
to result in complete habituation of these skeletal-
muscular responses. On the basis of the habitua-
tion that did occur, it could be hypothesized that
prolonged exposure to sonic booms of these levels
would undoubtedly result in a further reduction
in the number of persons responding with arm-
hand movements. It is uncertain whether com-



Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Recipient’s Catalog No.
FAA-AM-74-9

4, Title and Subtitle 5. Report Date
BEHAVIORAL, AUTONOMIC, AND SUBJECTIVE REACTIONS TO September 1974
LOW- AND MODERATE-LEVEL SIMULATED SONIC BOOMS: A 6. Performing Organization Code

REPORT OF TWO EXPERIMENTS AND A GENERAL EVALUATION

OF SONIC BOOM STARTLE EFFECTS

7. Author's) Richard I. Thackray, Ph. D., R. Mark
Touchstone, M.S., and Joe P. Bailey, B.S.

[8. Performing Organization Report No.

9. Performing Organization Name ond Address 10. Work Unit No. (TRAIS)
FAA Civil Aeromedical Institute
P.O. Box 25082 TT, Contract or Grant No.

Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

12, Sponsoring Agency Name and Address
Office of Aviation Medicine

Federal Aviation Administration
800 Independence Avenue, SW. 14. Sponsoring Agency Code
Washington, D.C. 20591

15. Supplementary Notes

OAM Report

This research was conducted under Tasks AM-E-74-PSY-47 and AM-E-75-PSY-47,

16. Abstract

Two separate studies are reported. The first attempted to determine a sonic boom
exposure level below which startle reactions would not occur. Subjects were
exposed indoors to six simulated sonic booms having outside overpressures of 50,
30, and 16 N/m? (inside sound pressure levels of 74, 71, and 65 dBA). Approxi-
mately 20 percent of the subjects gave small-amplitude arm-hand startle responses
to the two higher exposure levels, while none responded to the lowest level. In
the second study, subjects were exposed indoors to a series of 12 simulated booms
in grder to assess habituation effects. Outside overpressures were 130 and 50
N/m* (indoor sound pressure levels of 81 and 72 dBA). Significant, but not
complete, habituation occurred to booms of both levels. Autonomic and eyeblink
responses, as well as ratings of subjective annoyance, were obtained in both
studies. The final section of the report summarizes the expected behavioral,
autonomic, and subjective effects of exposure to various levels of sonic booms,

17. Key Words 18. Distribution Statement

Annoyance Availability is unlimited. Document may
Noise be released to the National Technical
Performance Information Service, Springfield, Virginia
Sonic Booms 22151, for sale to the public.

Startle

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No, of Pages | 22, Price
Unclassified Unclassified 14 $3.00

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized



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10


plete habituation of this response would ever
occur in all individuals even to the lower level
employed in this study.

There was no evidence of habituation of minor
(eyeblink) startle reactions to either level. This
finding is in accordance with the studies reported
by Landis and Hunt, in which the eyeblink
component of the total startle pattern rarely, if
ever, disappeared, even among police marksmen
during target practice.

The 1830-N/m? level used in this experiment
evoked more frequent eyeblink and arm-hand
responses than did the 50-N/m? level. However,
the differences in frequency of responses failed
to reach significance at the 5-percent level.

Conductance change to the booms and pre-
stimulus heart rate showed some evidence of
habituation, but there was no change in pre-
stimulus conductance levels or heart-rate re-
sponses across booms, Heart-rate response was
that of cardiac acceleration to the higher expo-
sure level and that of deceleration to the lower
level.

The exposure groups did not differ in their
rated annoyance of the booms and generally felt
that frequent exposure to booms of the levels
employed would be moderately annoying. As in
Experiment I, 60 to 70 percent of the Ss felt that
they would eventually adapt to and become vir-
tually unaware of booms having levels compar-
able to those to which they were exposed.
Subjects exposed to the 50-N/m? booms rated
their subjective startle to this level to be about
one-third as startling as the pistol shot. Rather
surprisingly, the 130-N/m? level was rated to be
somewhat more startling than the pistol shot.
This latter finding must be viewed with some
degree of caution, however, since Ss were rating
their subjective startle experiences. In several
previous studies, Ss were exposed both to a pistol
shot that was comparable in intensity to that
employed here and to sonic booms with over-
pressures approximately equal to the 130-N/m?
level used in Experiment II. It was found that
the actual magnitude of the reflex arm-hand re-
sponse to the pistol shot was about twice that
evoked by the booms.*?

The results of the two experiments reported
here, along with the results of several previous
studies that used both real and simulated sonic
booms,*?* allow an evaluation of startle effects

over a reasonably wide range of exposure levels.
A summary of the behavioral, physiological, and
subjective data obtained are presented in Table
5. Several general comments concerning these
data are in order before the results are discussed.
The data on males were obtained by using simu-
lated sonic booms (the same simulator was used
in all cases), while the data on females were ob-
tained during a field study in which actual sonic
booms were used. All Ss were exposed to the
sonic booms (simulated or real) while indoors,
and the same arm-hand steadiness device was
used in all studies. The testrooms used in both
the field study and the simulation studies had
similar dimensions, and both were of wooden
frame construction. Recordings of indoor dBA
were taken in all of the studies, but instrumenta-
tion problems during the field study resulted in
many missed readings of the low- and moderate-
level booms. Consequently, indoor overpressures
are given in the table for these levels, with dBA
values given only for the highest levels. With
the exception of data shown for booms in the
highest exposure category, all data in the table
were obtained on Ss exposed to either five or six
booms, and the response percentages represent.
mean values to booms of the intensities shown.
Subjects exposed to the boom levels shown for
category IV had been exposed to at least five
booms on preceding days. Consequently, the re-
sponse percentages may be somewhat depressed
as a result of possible habituation effects. Fin-
ally, although the field study employed two age
groups, the response percentages shown in the
table pertain only to the younger group. This
was done in order to make the data of the field
study as comparable as possible to the data of
the simulator studies, in which only 18- to 29-
year-old males were used.

The data in Table 5 have been divided into
four exposure categories, These categories are
based upon the hypothesis, outlined in a previous
study of a hierarchical pattern of behavioral
response to increasing stimulus intensity; that
is, there appear to be ranges of exposure levels
within which the effects are approximately com-
parable, Data obtained thus far suggest that
with increases in exposure level, there exist cer-
tain critical, or “threshold,” stimulus levels in
which the transition from one level to the next
is accompanied by a rather definite change in
the extent of skeletal-muscular response. The



in each session with the nonboom (control)
periods inserted randomly for each S. As in
Experiment I, Ss were exposed to a .22-caliber
pistol shot of 103 dBA at the end of the experi-
ment and the subjective questionnaire was ad-
ministered.

D. Criteria for Defining Startle Responses.
The same latency ranges employed in Experi-
ment I were used in Experiment II. Likewise,
all other criteria for evaluating startle response
to the booms were the same.

E. Measurement of the Physiological Response.
The physiological variables and methods of scor-
ing were the same as described for Experiment
I.

Il. Results.

A. Behavioral Response. A summary of the
eyeblink and arm-hand responses that met the
startle criteria are shown in Table 3. In com-
paring responses to the first six booms with
responses to the last six booms, sign tests revealed
no evidence of habituation of the eyeblink re-
sponses in either the 50- or 130-N/m? groups
(p>.05). For arm-hand responses, sign tests
revealed a significant decrease in percent re-
sponse for both exposure groups (p<.05). The
effect, of repeated boom exposure on response
amplitude could not be determined because the
number of Ss responding to the last six booms
was too small to allow adequate statistical com-
parison.

Taste 3, Eyeblink and Arm-Hand Data for Responses That Met the Startle Criteria

Eyeblink Data Arm-Hand Data
Overpressure Boom Percentage of Ss Show- Percentage of Ss Show- Mean Response
Number ing Startle Response ing Startle Response Amplitude (mm)

1 40 30 5.17

2 60 10 4.75

3 80 30 1.25

4 70 20 4.25

5 50 10 1.75

6 50 30 4.50
Mean 58 22 3.61

50

7 60 10 9.50

8 50 10 1.25

9 40 10 9.75
10 60 QO coor
11 50 O cone
12 zo Jo 2.75
Mean 55 7 7.06

1 80 70 8.68

2 90 50 6.45

3 90 40 7.56

4 100 60 4.12

5 100 40 2.31

6 _80 60 2.29
Mean 90 53 5.23

130

7 80 20 4.00

8 80 30 3.08

9 80 30 4.75
10 70 20 2.25
1 70 10 5.50
12 80 20 1.87
77 22 3.57


amplifier, and a Honeywell Visicorder. A
Hughes storage oscilloscope was used to monitor
the booms during the experimental session.

The task apparatus used by the subject (S)
was a sensitive electromechanical device for
measuring small-amplitude arm-hand movements.
The tip of a small rod was aimed at the center
of a 5-mm circle, and it was the S’s task to try
to keep the rod in that position during each test
run. The base of the rod was attached to several
potentiometers by means of a gimbal and this,
in turn, was mounted on an 18-x12-x7-cm
plastic instrument case. Outputs from the in-
strument allowed recordings of both left-right
and up-down movements. The steadiness ap-
paratus was placed on a small table, and the S
performed the task while seated at the table.
Photographs of this device are shown in several
previous reports.*?

A Beckman type R Dynograph recorded the
outputs from the steadiness tester. The recorder
was calibrated to yield 1 mm of pen deflection
for 1 mm of hand movement in either plane. In
addition to the performance measures, the Dyno-
graph also recorded the physiological measures.
Heart rate was obtained from Beckman bipo-
tential electrodes attached to the lateral walls of
the S’s chest with the leads connected to a cardio-
tachometer coupler. Palmar skin resistance was
obtained from zinc-zinc sulphate electrodes at-
tached to the. palmar and ventral surfaces of the
left hand with the leads connected to a Fels
model 22A Dermohmmeter, the output of which
led to the Dynograph. Beckman miniature bio-
potential electrodes placed above and below the
right eye recorded blinks. In addition to the
physiological and performance measures, the on-
set. of the booms was recorded on one channel of
the Dynograph by means of a microphone lo-
cated in the testroom. All recording equipment
was located outside the S’s testroom.

C. Procedure. Ten Ss were arbitrarily as-
signed to each of three exposure levels: 50, 30,
and 16 N/m*. (These values refer to peak over-
pressures of the booms as measured outside; ie.,
in the pressure chamber.) Mean sound pressure
levels inside the testroom were 74, 71, and 65
dBA (fast scale) for the 50-, 30-, and 16-N/m?
overpressures, respectively. Mean rise time of
the booms was 4 msec and duration was 210 msec.

Following initial instructions, the S was in-
strumented for physiological recording and the
task was explained in detail. He was told that
whenever a set of small yellow indicator lights
on the table was illuminated, he was to grasp
the top of the stylus of the steadiness tester with
the thumb and index finger of his right hand
and try to keep the stylus pointed at the small
circle. He was instructed to continue doing this
until the yellow lights went out. Further, he
was not to rest his arm or elbow on the table
while holding the stylus. He was told that he
might hear certain sounds during the period in
which the yellow lights were illuminated. He
was, however, to attempt to ignore the sounds
and continue trying to keep the pointer aimed
at the circle. The S was given no other infor-
mation concerning the nature of the sounds, and
no S was aware that the experiment had any-
thing to do with sonic booms.

The 1-hour test session was divided into twelve
5-minute periods. During the first 4 minutes of
each 5-minute period, the S performed an andi-
tery vigilance task similar to that described by
Bakan.t Essentially, it consisted of the numbers
0 through 9 presented in random order over a
ceiling loudspeaker at the rate of one number
per second. The S responded by pressing a
button each time a successive combination of
odd-even-odd digits occurred. (This task was
incorporated simply to maintain a reasonable
level of alertness over the 1-hour period and the
results will not be reported here.) At the end
of the 4 minutes, the yellow signal lights were
illuminated and the S grasped the pointer of the
steadiness tester. Fourteen to twenty-eight sec-
onds after the signal lights were illuminated
(these time intervals were randomly determined
for each period), either a boom occurred or it
did not. Booms were presented in three of the
six 5-minute periods in each half-hour; the re-
maining periods served as controls for expect-
ancy effects. Determination of the periods in
which booms occurred was random. Each S was
given practice on both the steadiness and vigi-
lance tasks prior to the beginning of the experi-
mental session. At the completion of the session,
the § was exposed to the sound of a .22-caliber
pistol shot. The noise level of the shot at the
S’s location was 103 dBA (fast scale). The
purpose of the pistol shot was to provide a ref-
erence for evaluating subjective startle to the


Appendix 1

Subject No. Name

Study.

Condition

Post-Experimental Questionnaire

Except for the pistol shot, the sounds you heard in the test room were
designed to simulate the sounds of sonic booms produced by aircraft flying
at supersonic speeds. The following information is needed in order to
assess the degree of possible annoyance which could result from exposure
to sonic booms of this level,

1, Have you ever heard actual sonic booms? Yes No.
2, Did you associate the sounds you heard with sonic booms?
Yes. No.
3. If you have heard actual sonic booms, were there any major differ-

ences between these simulated booms and real ones as heard indoors?
(more or less startling, louder, sharper, etc.)

4. Suppose that you were regularly exposed 10 to 20 times a day to actual
sonic booms of the level of these simulated booms while indoors at home,
work, or school. Would you estimate this to be

Not annoying Mildly Moderately Quite Extremely
at all Annoying Annoying Annoying Annoying

(Place a check on the line nearest the words which best describe your
estimated annoyance.)

5. Do you think that you would eventually adapt or become virtually unaware
of sounds of this level?

Yes. No.

6. (a) Were you startled at all by any of the simulated sonic booms you
heard?

Yes__—ts«CN,

18



BEHAVIORAL, AUTONOMIC, AND SUBJECTIVE REACTIONS TO LOW-—
AND MODERATE-LEVEL SIMULATED SONIC BOOMS: A REPORT
OF TWO EXPERIMENTS AND A GENERAL EVALUATION OF
SONIC BOOM STARTLE EFFECTS

Measurable startle reactions of sufficient in-
tensity to evoke arm-hand movements have been
found to occur in subjects (Ss) exposed indoors
to real or simulated sonic booms having outside
overpressures as low as 50 to 70 N/m? (indoor
sound pressure levels of approximately 72 to 74
adBA).°’ These startle reactions tend to occur
in 20 to 30 percent of Ss who have had little or
no previous exposure to sonic booms, with the
percentage appearing to diminish with repeated
exposure.*’ Although total body flexion is sel-
dom, if ever, evident to booms of this level, the
startle response does involve arm-hand move-
ments of sufficient magnitude to potentially dis-
rupt performance on tasks requiring precise
arm-hand control. These findings are of sig-
nificance because they suggest that startle reac-
tions can occur to sonic booms having overpres-
sures below the range of overpressures (75 to
175 N/m?) expected along the centerline of the
sonic boom carpet of the Concorde SST.®

This report presents the results of two separate
experiments. The first was conducted to deter-
mine an exposure level below which arm-hand
startle responses would not occur. The second
study was designed to provide further informa-
tion on habituation of these startle responses to
both low- and moderate-level ‘sonic booms. In
addition to arm-hand response data, subjective
ratings of startle and annoyance and physiologi-
cal recordings of heart rate, palmar skin con-
ductance, and eyeblink response were obtained
in both studies.

Eaperiment I
I, Method.

A. Subjects. Thirty paid male university
students, ranging in age from 18 to 29, served as
Ss. All were right handed, had no reported
hearing loss, and had not previously participated
in startle or sonic boom experiments.

B. Apparatus. The basic simulator consisted
of a 4.1-x3,7-x24-meter testroom, one wall of
which formed one of the sides of a hermetically
sealed pressure chamber. Complete details of
the simulator are given in several previous re-
ports.3** In typical usage, the simulated booms
are produced by a motor-actuated piston, which
generates an N-wave of pressure in the chamber.
In the present two studies, it was necessary to
introduce certain modifications in order to either
hold rise time constant or achieve exceedingly
low overpressure levels,

In Experiment I, the simulator’s motor-
actuated piston was not employed because this
mechanism was not capable of faithfully produe-
ing the extremely low overpressures with con-
stant rise time that was required. Instead,
simulated booms of constant rise time and dura-
tion were produced by brief electrical transients,
which, after amplification, were led to an Altec
Lansing 419A Biflex speaker located in the
pressure chamber. Electronic timers were used
to control the interval between the two pulses of
each N-wave. It should be noted that the piston
could have been used to produce the highest
overpressure (50 N/m?) used in this experiment.
However, although the impulsive stimuli pro-
duced by the speaker were quite similar to those
produced by the piston, it was decided that
slight differences in sound quality warranted
using only the speaker for all of the overpressure
levels employed. Persons familiar with the
sound of sonic booms heard indoors judged the
resulting impulsive stimuli to be quite similar
to the booms produced by actual aircraft.

The pressure chamber was calibrated with a
Bruel and Kjaer type 4146 condenser micro-
phone, a Bruel and Kjaer type 2631 carrier





categories in Table 5 represent an attempt to
identify those exposure levels associated with a
pattern of similar effects.

Category I describes a level in which reflex
eyeblink responses occasionally occur, but there
is no evidence that the degree of startle elicited
is of sufficient magnitude to involve arm-hand
movements. The heart rate decelerates to stimuli
of this Jevel, and repeated exposure is likely to
be only mildly annoying. The indoor sound
pressure level associated with this category is at
least 65 dBA and less than 71 dBA.

Category II exposure levels evoke a higher
percentage of eyeblink responses, and arm-hand
movements begin to appear in 10 to 25 percent
of the Ss. Heart-rate response is still that of
deceleration, which suggests that this exposure
range generally tends to evoke reactions more
appropriately considered alerting, attending, or
orienting reactions rather than startle reactions.
Continual exposure would probably be mildly to
moderately annoying. Indoor sound pressure
levels producing these effects apparently range
from approximately 71 dBA to less than 81
dBA.

The exposure levels included in category III
produce a rather marked increase in the number
of Ss (53 to 70 percent) showing arm-hand
movements. Also, it is to these levels that gross
body responses corresponding to the traditional
startle pattern? begin to appear and heart-rate
acceleration occurs. The booms are judged to be
moderately annoying. Indoor sound pressure
levels are likely to be at least 81 to 84 dBA and
probably less than 92 dBA.

Category IV exposure levels represent boom
intensities in which the percentage of Ss showing
arm-hand responses approaches 100 percent.
Unfortunately, the high-speed-motion photog-
raphy used during the field study was not em-
ployed on the day these exposure levels occurred,
and therefore there are no data on the extent of
gross body reactions. However, the frequency
of arm-hand movements is approximately the

ll

same as that obtained on earlier test days to a
reference startle stimulus (.22-caliber pistol shot,
100 dBA).’ Since most Ss who displayed arm-
hand movements to the pistol shot also displayed
the full startle pattern, it seems reasonable to
assume that the frequency of gross body reac-
tions to category IV levels considerably exceeds
the frequency shown for category III levels.
There are no subjective data available for cate-
gory IV boom levels, but it is likely that re-
peated exposure to booms of these levels would
be considered quite annoying. Indoor sound
pressure levels associated with this category
ranged from 92 dBA to 96 dBA.

It is emphasized that Table 5 should be viewed
primarily as a guide in predicting the general
effects of indoor sonic boom exposure. With the
exception of the data presented for category IV,
the behavioral, physiological, and subjective data
presented in the table represent the typical or
mean responses of Ss exposed to five or six sonic
booms. Percent response to the first boom to
which Ss are exposed is generally greater than
the values shown in the table. Likewise, re-
peated exposure to booms would be expected to
reduce the response percentages shown in Table
5. Both the Experiment II results reported in
this paper and the results of the earlier field
study® suggest that some habituation of the arm-
hand startle response occurs to all overpressure
levels except perhaps the highest levels. In the
field study, there was no convincing evidence of
any habituation to booms having outside over-
pressures of 300 N/m? and above among Ss with
prior exposure to 10 or more booms.

In the studies (including the, present experi-
ments) conducted to date,** the mean magnitude
of hand responses to category II, III, and IV
boom levels has been found to range from ap-
proximately 4.0 to 6.0 mm. This amount of hand
movement could disrupt performance on tasks
requiring precise arm-hand coordination. It is
unlikely that the magnitude of these responses
would. seriously impair performance on less sen-
sitive psychomotor tasks.’



Appendix 1

(b) If your answer is yes, assume that the pistol shot startled
you by an arbitrary value which we will consider to be 100.
Try to recall the startle you experienced to the simulated booms
and attempt to assign a number to this startle experience which
would be in proportion to the amount the pistol shot startled
you (e.g., if the booms were twice as startling as the shot,
the numerical value would be 200; if they were half as startling,
the value would be 50; if one-tenth as startling, the value
would be 10; etc.).

Place your number here:

14