As noted earlier, because of design character-
istics of the simulator, rise times (as defined by
time to peak overpressure) increased in a manner
which was almost proportional to increases in
overpressure. In order to hold rise time approx-
mately constant over varying overpressures, a
photocell was employed whose light source was
nomentarily interrupted at the points of maxi-
num forward and backward excursion of the
viston. The electrical transient which resulted
‘rom each light interruption was amplified and
?ed to an Altec Lansing 419A Biflex speaker lo-
vated in the pressure chamber. By properly
ynchronizing the speaker output with the wave
‘ront. produced by the piston, it was possible to
chieve simulated sonic booms which differed in
werpressure but which had approximately equal
‘ise times. The resulting impulsive stimuli were
udged by persons familiar with the sound of
onic booms heard indoors to be quite similar to
he booms produced by actual aireraft.

The pressure chamber was calibrated with a
3ruel and Kjaer Type 4146 condenser micro-
thone, a Bruel and Kjaer Type 2631 carrier am-
lifier, and a Honeywell Visicorder. A Hughes
torage oscilloscope was used to monitor the
coms during the experimental session. Onset
f the booms, as well as intervals between booms,
vas automatically controlled by timers.

The S’s task apparatus consisted of a sensitive
lectro-mechanical device for measuring small-
mplitude arm-hand movements. The top of a
nall rod was aimed at the center of a 5 mm
rele, and it was the 8’s task to try to keep it
1 that position during each test run. The base
f the rod was attached to several potentiometers
y means of a gimbal and this, in turn, was
counted on an 18 x 12 x 7 cm plastic instrument
ise. Outputs from the instrument allowed re-
wrdings of both left-right and up-down move-
ents. The steadiness apparatus was placed on
small table and the S performed the task while
ated. The S faced the observation window with
s head located 40 inches from the wall of the
cessure chamber. A photograph of the steadi-
»ss tester is shown in Figure 1.

A Beckman Type R Dynograph recorded the
itputs from the steadiness tester. The recorder
as calibrated to yield 1 mm of pen deflection
r 1 mm of hand movement in either plane.
t addition to the performance measures, the
ynograph also recorded the physiological meas-

ures. Heart rate was obtained from Beckman
biopotential electrodes attached to the lateral
walls of the S’s chest and the leads were con-
nected to a cardiotachometer coupler. Palmar
skin resistance was obtained from zinc-zine sul-
phate electrodes attached to the palmar and
ventral surfaces of the left hand. Leads were
connected to a Fels Model 22A Dermohmmeter,
the output of which led to the Dynograph. Beck-
man miniature biopotential electrodes placed
above and below the right eye recorded blinks.
In addition to the physiological and performance
measures, one channel of the Dynograph also re-
corded the onset of the booms from a microphone
located in the test room. All equipment was lo-
cated outside the S's test room.

C. Procedure. Each S was arbitrarily assigned
to either the 50 N/m? or 150 N/m? boom condition
with ten Ss in each group. Following initial
instructions, the S was instrumented for phys-
iological recording and the task explained in
detail. He was told that whenever a set of small
yellow indicator lights on the table was illumi-
nated, he was to grasp the top of the stylus of
the steadiness tester with the thumb and index
finger of his right hand and to try to keep it
pointed at the small circle. He was instructed
to continue doing this until the yellow lights
went off. He was further told not to rest his
arm or elbow on the table while holding the
stylus, and told that he might hear certain sounds
during the period that the yellow lights were
on. However, he was to attempt to ignore the
sounds and continue trying to keep the pointer
aimed at the circle. The S was given no other
information concerning the nature of the sounds,
and no S was aware that the experiment had
anything to do with sonic booms.

The one-hour test session was divided into
12 five-minute periods. During the first four
minutes of each five-minute period, the S per-
formed an auditory 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 combina-
tion of odd-even-odd digits occurred. This task
was incorporated simply to maintain a reason-
able level of alertness over the one-hour period
and, since the results are not relevant to the
present study, the data will not be reported here.



Table 4

Pre-Stimulus and Change Values for Conductance and Heart Rate During Boom Exposure.

Physiological Measure

Boom Exposure Number

Pre-Stimulus Conductance
Level (u mhos)

Conductance Change (u mhos)
Pre-Stimulus Heart Rate

(bpm)

Heart-Rate Change (bpm)

Physiological Measure

Pre-Stimuls Conductance
Level (p mhos)

Conductance Change (p mhos)

Pre-Stimulus Heart Rate
(bpm)

Heart-Rate Change (bpm)

Exposure
Group (N/m) L 2 3 4 5 6 Me.
50 W115 1115 11.05 1.250 11,40 11.57 1
150 12,53 12,63 12.39 12.01, 11.79 11,91 2
50 0.43 0.45 0.46 0.47 0.44 0.42 0
150 1.58 1.44 1,22 1.31 1.23 1.03 1
50 75 76 76 5 7 76 75
150 89 85 86 86 84 84 85
50 -2.2 -2.5 2.2 1.6 5.4 -0.7 2
150 5.2 4.8 2.9 1.2 4.0 2.3 3
Table 5
Pre-Stimulus and Change Values for Conductance and Heart Rate
Obtained to the Pistol Shot.
Exposure Mean of
Group (N/m?) Mean Combined Gre
50 12,23
12,23
150 12.24
50 1.22
1.46
150 1.70
50 71.1
74.4
150 78.4
50 10.9
11.25
150 11.6


Table 1

Means of the Physical Measurements Obtained Outside the Test Room (Within the

Pressure Chamber of the Simulator) and at the $'s Location Within the

Test Room for the Two Exposure Groups.

Inside
Outside Measurements Measurements
verpressure (N/m?) Rise Time (msecs) Duration (msecs) Blin’ dBlin' © g BA”
51 5.5 240 128 105 74
151 5.6 240 137.5 111 83

As measured with a Bruel and Kjaer Type 2204 Impulse Sound Level Meter set on Impulse Hold

position.

As measured with the same meter, but set to non-impulse mode, fast scale.

Table 2

Mean Values Obtained for the Eye-Blink and Arm-Hand Response to the Pistol Shot.

Eye-Blink Data

Arm-Hand Data
(Combined Left-Right and Up-Down)

Eye-Blink Response Amplitude
as Expressed as a Percentage

Overpressure Group Latency (msecs) of Voluntary Blink Amplitude Latency (msecs) Amplitude Increase (mm)
50 N/m 66 131 159 8,00
150 N/m 60 81 143 11.61
Combined Groups
Mean 64 106 152 9.80
Range 20 - 80 20 - 241 90 - 210 3.25 = 22,75

tined to the pistol shot. A median test? con-
ucted on the blink amplitude data, and ¢ tests
f eye-blink latency, arm-hand latency, and arm-
and amplitude increase revealed no differences
p>.05) between the two groups on any measure
ad the data were combined. Both the mean
rm-hand latency of 152 msecs and the range of
ctencies (90 to 210 msecs) were virtually iden-
cal to the mean value (150 msecs) and range
100 to 230 msecs) obtained to a pistol shot for
omparably aged female Ss in a previous study.”
‘he obtained latency range was also comparable
» the range of arm-hand startle latencies (125
» 195 msecs) reported by Landis and Hunt.?
{ean latency of the eye-blink response was 64
secs with a range of 20 to 80 msecs, This mean
uue is somewhat higher than the mean (40

msecs) reported by Landis and Hunt, but
differences in technique (high-speed motion pho-
tography used by Landis and Hunt vs. electro-
myography used in the present study) may
account for this slight difference.

The latency ranges actually used in scoring
eye-blink and arm-hand responses to the simu-
lated booms extended from 20 to100 and 90 to
230 msees respectively. Note that for each meas-
ure 20 msecs were added to the longest latencies
obtained to the pistol shot. This was done to
minimize measurement error, since accuracy of
measurement was only +20 msees (0.5 mm on the
chart recording). Since the mean response time
(230 msecs) to the 1000 Hz tone fell within the
range of the arm-hand startle latencies to the
pistol shot, there was no way to be absolutely



At the end of the four minutes, the yellow signal
lights were illuminated and the S grasped the
pointer of the steadiness tester. Fourteen to 28
seconds after the signal lights were illuminated
(these time intervals were randomly determined
for each period), a boom either occurred or it
did not. Booms were presented during three of
the six five-minute periods in each half-hour with
the remaining periods serving as controls for
expectancy effects, Determination of the periods
in each half-hour in which booms occurred was
random. Each § was given practice on each task
prior to the beginning of the one-hour session.

At the completion of the session, reaction times
to a series of ten 1000 Hz, 60 dBA tones were
obtained. JInterstimulus intervals were ten sec-
onds. The required response was a movement of
the pointer of the steadiness tester away from the
center position as rapidly as possible as soon as
each tone was heard. In addition to the reaction-
time tests, response to a .22 caliber pistol shot was
also obtained at the completion of the session.
Noise level of the pistol shot at the S’s location
was 122 dBlin (as measured by a Bruel and
Kjaer Type 2204 Impulse Sound Level Meter).
This latter test was conducted in such a way that
the S had no prior knowledge that it would be
any thing other than another boom or control
run. The purpose of the reaction-time and pistol
shot tests was to provide a measure of voluntary
response and response to a known startling
stimulus in order to evaluate the reaction pattern
to the simulated booms.

D. Criteria for Defining Startle Responses.
Primary criteria for deciding whether an arm-
hand response to a sonic boom was an involun-
tary, reflexive startle response or whether it
might be a form of voluntary or reaction-time
response were obtained from the latencies of the
arm-hand response to the pistol shot. In addi-
tion, reflex eye-blink responses were also included
in evaluating the total startle response.

Two levels of startle response to the booms
were designated. A minimal startle response was
said to occur if a given boom evoked an eye-
blink refléx whose latency (time from noise onset
to the beginning of eye closure) fell within the
range of latencies obtained to the pistol shot. In
order for an arm-hand response to be considered
as a component of a more pronounced startle re-
action, it had to meet three criteria:

‘stimulus intervals.

1. It had to be associated with a blink refle
which met the latency requirement mentione:
above.

2. The arm-hand response had to occur in bot:
the left-right and up-down planes with a mea
latency which fell within the range of arm-han-
latencies obtained to the pistol shot.

38. The amplitude of the arm-hand response i
both planes had to exceed the maximum peak-tc
peak amplitude of hand tremor occurring in th
five-second period preceding the boom.

E. Measurement of the Physiological Respons.
Galvanic skin responses to each boom and to th
pistol shot were obtained by measuring the min
mum resistance following stimulation and the re
sistance level immediately prior to each stimulu
These measures were converted to conductanc
values and difference scores obtained. Magn
tude of heart-rate change was determined b
taking the difference between the maximum hea
rate in the five-second pre-stimulus and pos
In addition to these aut
nomic measures, one other measure was obtaine
for each eye blink falling within the require
latency range. The measured amplitude of tl
blink response was expressed as a percentage ¢
the amplitude of the first voluntary blink to pr:
cede it.

F. Physical Measures of the Simulated Boom
Table 1 shows the actual mean values of ove
pressure, dBlin, dBA, rise time and duration fc
the simulated booms to which the 50 N/m? ar
150 N/m? groups were exposed. As is evider
from this table, actual measured overpressur
and rise times differed only slightly from the ii
tended values. Overpressures and rise times «
the booms inside the test room are not given
the table. Although indoor measures of ove
pressure and rise time were reported in the pr
vious study, it was subsequently decided th
complexities in the waveform resulting fro
acoustic and vibratory responses of the test roo
made it virtually impossible to arrive at mea
ingful, consistent measures of rise time and, to
lesser extent, overpressure. Consequently, indo:
measures of dBA (fast scale) and dBlin using :
impulse sound level meter were employed.

Il. Results.
Behavioral Response
A. Establishment of Startle Latency Valu
Table 2 shows the behavioral response data o


Table 3

Eye-Blink and Arm-Hand Data for Responses Which Met the Startle Criteria.

Eye-Blink Data

Arm-Hand Data
(Combined Left-Right and Up-Down)

Mean Eye-Blink Response

Mean Amplitude as Expressed Mean Mean
Boom Per Cent Showing Latency as _a Percentage of Per Cent Showing Latency Amplitude
2 Number Startle Response (msecs) Voluntary Blink Amplitude Startle Response (msecs) Increase (nm)
1 30 73 18 0 - —
2 40 70 8 30 173 4.98
ima 3 60 75 4 30 160 5.42
4 50 80 18 10 160 1,25
5 20 60 1% 0 —
6 30 3 18 0 -- a=
Mean 38 72 15 12 164 3.88
1 90 73 33 80 172 7.21
> 2 90 60 86 60 133 8.25
ee) 90 62 85 70 141 5.96
4 90 62 78 70 151 7.21
5 90 7 37 50 158 4.25
6 90 67 46 40 7 6.37
Mean 90 66 64 62 150 6.54

s significant (p>.05), with the exception of
-blink amplitude change. The obtained U
this measure was 1.0 (p<.01).

1, Habituation Effects. The data presented in
rle 8 suggest little or no habituation effects
yss the six exposures for either of the two
m levels. The only possible exceptions would
ear to be in the percentage of Ss showing
-blink and arm-hand responses to the 50 N/m*
arm-hand responses to the 150 N/m? booms.
wever, sign tests of the number of responses
le by each S to the first and last three booms
which each was exposed revealed the differ-
3s to be nonsignificant (p>.05).

', Magnitude of Boom Response Relative to
Pistol Shot. The group exposed to the 150
a? boom was used tg compare response to the
ulated booms with response to the pistol shot.
50 N/m? group was excluded because of the
measurements available on these Ss. In
sr to enable comparisons of response to these
stimuli, means of each measure averaged
ss booms for each S were compared with
esponding values obtained to the pistol shot.
iificant differences were found for arm- hand
‘litude increase (¢=3.57; p<.05) and for per
change in eye-blink response (sign test,
05). As an inspection of Tables 2 and 3
reveal, the greater amplitude changes oc-
ed to the pistol shot. No differences were

found for either eye-blink latency (¢=1.97;
p>.05) or arm-hand latency (t=1.69; p>.05).

Autonomic Response

A. Differences Between Overpressure Groups.
Table 4 shows pre-stimulus and change values
for skin conductance and heart rate across the
six boom exposures. Analyses of variance re-
vealed no evidence of habituation for either pre-
stimulus or change values for heart rate and
conductance (p>.05). Likewise none of the in-
teraction effects between boom exposures and
overpressure groups was significant (p>.05).
There were significant differences, however, be-
tween the overpressure groups on pre-stimulus
heart rate (F=5.17; p<.05), heart-range change
(F=12.86; p<.005), and conductance change
(F=4.74; p<.05). It is interesting to note that
the heart-rate response for the 150 N/m? group
was an increase in rate, while that for the 50
N/m? group was a decrease. The higher pre-
stimulus heart rate for the 150 N/m? group was
present even prior to the first boom exposure.
This suggests that the difference between the
two groups on this measure was the result of a
sampling bias and not the result of the experi-
mental conditions.

B. Comparison With Response to the Pistol
Shot. Except for pre-stimulus heart-rate level
which approached significance (¢=1.80; p<.10),



TECHNICAL REPORT STANDARD TITLE PAGE

1. Report No. °2. Government Accession No. 3. Recipient's Catalog No.
FAA-AM-73" 16

4. Title and Subtitle 5. Report Date

A COMPARISON OF THE STARTLE EFFECTS RESULTING FROM Decenber 1973
EXPOSURE ,TO TWO LEVELS OF SIMULATED SONIC BOOMS & Performing Organization Code

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

Richard I. Thackray, Ph.D., Robert M. Touchstone, M.S.
and Joe P. Bailey, B.S.

9. Performing Organization Name and Address 10. Work Unit No.
FAA Civil Aeromedical Institute
P. O. Box 25082 TT. Contract or Grant Ne.

Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Name and Address
Office of Aviation Medicine

Federal Aviation Administration OAM Report
800 Independence Avenue, S.W. 14. Sponsoring Agency Code
Washington, D. C. 20591

15. Supplementary Notes

This research was conducted under Tasks No. AM-B-72-PSY-31 and AM-B-73-PSY-31.

16. Abstract

Subjects were exposed indoors to simulated sonic booms having outside overpressures
of 50 and 150 N/m“. Rise times were held constant at 5.5 msecs. In addition to the
outside measurements, inside measures of dBlin and dBA were also obtained. Subjects
attempted to hold a hand-steadiness device on target during boom exposure and
amplitude of the arm-hand startle response was determined. Recordings were also
obtained of the skin conductance and heart-rate responses as well as the eye-blink
reflex. Although the 50 N/m2 boom produced slight arm-hand startle responses in a
small percentage of subjects, the frequency of these responses was significantly
greater to thé higher boom level. There was no difference between the levels in
amplitude of the response. The predominant autonomic response pattern to the lower
exposure level was similar to that obtained for orienting responses, while a startle
pattern was obtained for the higher level. The results are compared with the find-
ings of other studies, and the tentative conclusions advanced that sonic booms
experienced indoors may cause slight arm-hand startle responses which could have
adverse effects on occupational tasks in which arm-hand steadiness is the principal
skill required, but that it seems unlikely these responses would significantly
impair performance on less sensitive psychomotor tasks.

7. Key Words 18. Distribution Statement

Attention Performance Availability is unlimited. Document may
Zye-Blink Reflex Skin Conductance be released to the National Technical
Jeart Rate Sonic Booms Information Service, Springfield, Virginia
Noise Startle 22151, for sale to the public.

drienting Reflex

7. Security Classif. (of this report) 20. Security Classif. (of this page) i No. of Pages | 22. Price
Inclassi fied Unclassified 11 $3.00

um DOT F 1700.7 (8-69) -



performance on less sensitive psychomotor tasks,
a practical example of which would be auto-
mobile driving. Indeed, there is little evidence
that real or simulated sonic booms experienced
indoors significantly impair such behavior. Lukas
and Kryter,? for example, found no significant
impairment in tracking performance when sub-
jects were exposed to simulated booms having
outdoor overpressures of approximately 58 N/m?.
In a later study by Lukas, Peeler, and Kryter,*
a slight impairment in tracking performance was
found to simulated booms of approximately 120
N/m®*, but the authors felt that this may have
been caused by vibratory responses of the test
room acting upon the tracking stylus rather than
as the result of a direct startle effect. Rylander,
Sorensen, Berglund, and Brodin® found that Ss
performing on an automobile-driving simulator
indoors and exposed to outdoor sonic boom levels
of 40 to 650 N/m? exhibited very little adverse
effects. The authors state that “.. . sonic boom
exposures of the levels studied here to not sig-
nificantly influence the muscular performance of
persons driving a car when they know that boom
exposures might occur, provided that boom levels
do not exceed the values studied in this experi-
ment.” Indoor overpressures in this study ranged
from 20 to 260 N/m*. Thus, while the rather
long rise times of the 100 and 200 N/m? booms
employed in the previous study by Thackray,
Touchstone, and Jones‘ may have contributed to
the apparent lack of startle effect noted, it is in-
teresting that of the above studies, one of which
exposed Ss to a wide range of overpressure,’ none
found any appreciable evidence of performance
impairment on complex psychomotor tasks when
Ss were exposed to sonic booms while indoors.
In conclusion, it is important to emphasize that
in virtually all of the studies reviewed here out-
door overpressure has been the primary measure
employed to evaluate indoor exposure effects.
This is admittedly not the best measure to em-
ploy, but it is the only one common to all the
above studies. While some of the studies, in-
cluding the present one, report some measure of
indoor exposure level, it is not known which of
many possible measures is the most adequate one
to use. A comprehensive parametric study to
determine the indoor acoustical measure yielding
the highest relationship with startle effects has

10

not as yet been conducted and would requi
complex simulation facility capable of faitht
producing booms covering a wide range of o
pressures and rise times. In spite of the lin
tion in using only outside overpressure, ther
a rather remarkable agreement among the ax
able studies concerning the indoor exposure efi
of real and simulated booms, and it is felt
the present evidence can serve as a useful gu
line for making initial, practical decisions. ]
of the apparent agreement may be due to the
that in all the studies the test rooms in whicl
experienced the real or simulated booms wer
similar frame or wood-metal construction, 1
at least one wall of the room directly exp:
to the booms. This would also suggest that
observed indoor effects would likely be near
maximal expected.

V. Summary.

Subjects were exposed indoors to simul
sonic booms having outside overpressures o:
and 150 N/m*, Rise times were held constar
5.5 msecs. In addition to the outside meas
ments, inside measures of dBlin and dBA \
also obtained. Subjects attempted to hold a hi
steadiness device on target during boom expo
and amplitude of the arm-hand startle resp
was determined. Recordings were also obta
of the skin conductance and heart-rate resp
as well as the eye-blink reflex. Although
50 N/m* boom produced slight arm-hand sté
responses in a small percentage of the Ss,
frequency of these responses was significa
greater to the higher boom level. There wa
difference between the levels in amplitude of
response. The predominant autonomic resp
pattern to the lower exposure level was sin
to that obtained for orienting responses, wh
startle pattern was obtained for the higher
The results are compared with the finding
other studies, and the tentative conclusions
vanced that sonic booms experienced indoors
cause slight arm-hand startle responses w
could have adverse effects on occupational t
in which arm-hand steadiness is the principal
required, but that it seems unlikely that t
responses would significantly impair perform
on less sensitive psychomotor tasks.


asts revealed no significant differences between
two exposure groups for the pistol-shot data
conductance or heart-rate levels prior to the
tol shot or in magnitude of change to this
nulus (p>.05). Mean values for these meas-
s are shown in Table 5. Since no significant
ferences were obtained, combined means are
> shown in the table. Statistical comparisons
mean heart rate and conductance change to the
‘N/m? booms with change in these two meas-
s to the pistol shot revealed a significant dif-
ance for heart-rate change (t=4.59; p<.01),
not for conductance change (#=1.80; p>.05).

Discussion.

“he present study revealed that low-level simu-
xd sonic booms experienced indoors can pro-
e slight arm-hand startle reactions in a small
centage of Ss. Although these brief startle
ations presumably also occurred to the com-
able exposure level (50 N/m? overpressure; 6
‘es vise time) employed in the previous
ly they did not produce any apparent per-
nance impairment on the tracking task used.
seems likely that the relative insensitivity of
tracking task to slight startle responses, the
vequency with which they were found to occur
the present study, and the pronounced per-
nance facilitation following boom exposure
ch was found in the earlier study all tended
bscure the momentary impairment which prob-
7 occurred,

imulated booms having three times the out-
: overpressure, but with the same rise times,
e found to produce arm-hand startle responses
ch differed from the lower boom level in fre-
acy of occurrence but not in response ampli-
>» For the eye-blink reflex, the higher boom
nsity produced both a greater number of re-
ases and a greater amplitude of response.

; is interesting that similar results for the
-hand response were also obtained to actual
¢ booms experienced indoors during a recent
{ study of startle effects.2 Flyovers of super-
c aircraft generated booms having outside
‘pressures ranging from 60 to 640 N/m? with
ean rise time of 2.5 msecs, Mean arm-hand
onse amplitude (using the same task used
he present study) was virtually the same in
1 studies, Although there was evidence in
field study which suggested a slightly greater
litude of response to the more intense booms,

the primary effect of increases in overpressure
was an increase in the percentage of Ss showing
startle reactions. Percentages of Ss exhibiting
startle reactions to the 50 and 150 N/m? booms
in the present study were almost identical to the
percentages obtained for comparable overpres-
sures in the field study.

Taken together, the results of both studies sug-
gest that the indoor stimulus intensities, for the
range of boom exposure levels employed, were
at or only slightly above the threshold level for
evoking startle reactions strong enough to involve
arm-hand responses. Higher overpressures levels
simply evoked these marginal startle reactions in
a greater number of Ss than did lower levels,
with little or no evidence of a corresponding in-
crease in response amplitude. The startle reac-
tions are considered marginal since, in both the
present study and in the field study, arm-hand
response to a “standard” startle stimulus (.22
caliber pistol shot) was approximately twice the
mean amplitude obtained to the booms.

Autonomic changes noted in the present study
would appear to be entirely consistent with the
skeletal-muscular responses obtained to the two
boom levels. Thus, the heart-rate deceleration
associated with the 50 N/m? level suggests that
the predominant response was an orienting re-
action”? and this is supported by the relatively
few startle reactions involving either eye-blink
or arm-hand movements which occurred. On the
other hand, heart-rate acceleration, which is asso-
ciated with the startle reflex,° was the typical
pattern associated with the 150 N/m? level, and
the majority of Ss responded with eye-blink re-
flexes and with total startle reactions extensive
enough to involve measurable arm-hand responses.
Heart-rate acceleration to the pistol shot was
significantly greater than to the 150 N/m? boom
level and, as has previously been mentioned, this
was accompanied by a larger arm-hand response.

Both the present study and the previous field
study are in agreement that startle reactions
can occur to sonic booms experienced indoors and
that these reactions tend to occur with increas-
ing frequency as overpressure increases. While
startle reactions involving arm-hand movements
of only half a centimeter (the approximate mean
amplitude in both studies) could be quite dis-
ruptive in skills or occupations requiring precise
arm-hand control, it is doubtful that reflex re-
sponses of this magnitude would seriously disrupt



nw ft a wo

PISTOL SHOT
x =150 msec

” L
=
S)
i L
Ww
a
DS Ir
Ma OW 1 4 1 1 1 L
O 6b
a 1000 Hz TONE
W 5 -
a x= 230 msec
= abl
D
2

3b

2b

i

On 1 1 J 1

80- |100- I20- I40- I60- 180- 200- 220- 240- 260- 280- 300-
99 II9 139 159 179 199 219 239 259 279 299 319

MILLISECONDS

Fioure 2. Latency distributions of arm-hand response to the pistol shot and to the 1000 Hz tone.

certain that an arm-hand response to the simu-
lated booms was a startle reaction rather than a
form of voluntary response. However, the dif-
ference between mean response time to the tone
and pistol shot was significant (t=7.34; p<.01)
and, as shown in Figure 2, there was relatively
little overlap between the distributions. Also.
it should be recalled that the criteria for desig-
nating an arm-hand response as a startle reaction
included not only latency criteria but required
that the arm-hand response amplitude exceed
the pre-stimulus amplitude, that the response
occur in both planes of movement, and that a
reflex eye-blink response occur in conjunction
with the arm-hand response. With these addi-
tional requirements, it was felt that the likeli-
hood of scoring a voluntary response as a startle
reaction was minimal.

B. Behavioral Response to the 50 and 150
N/m* Booms. Table 3 provides a summary of

the eye-blink and arm-hand data for response
which met the startle criteria. The most prc
nounced differences between the two exposur
groups were in the percentages of Ss showin
eye-blink and arm-hand responses to the boom
In order to make statistical comparisons of the:
differences, Ss were classified according t
they showed a startle response to either 0 to

or 3 to 6 of the booms presented. The obtaine
chi squares were 5.49 and 7.50 for the eye-blin
and arm-hand responses respectively. Bot
values were significant (p.<.05), indicating

greater frequency of response to the more ii
tense boom level.

To evaluate differences between the groups :
eye-blink latency, eye-blink amplitude chang
arm-hand latency, and arm-hand amplitude iv
crease, each S’s mean response to the six boon
was obtained for each measure and Mann-Whi
ney J tests’ conducted. None of the compariso)


In addition to studying performance effects,
physiological recordings of heart rate, palmar
skin conductance, and eye-blink response were
obtained. It was hoped that the inclusion of
these measures would help to clarify the nature
of the total response pattern resulting from ex-
posure to these two boom levels.

II. Method.

A. Subjects. Twenty paid, male university
students ranging in age from 18 to 29 served as
subjects (Ss). All were right-handed, had no re-
ported hearing loss, and had not participated in
previous startle or sonic boom experiments.

B. Apparatus. The sonie boom simulator was
constructed by Stanford Research Institute and
the features of this type of simulator have been
fully described by Lukas and Kryter.* Essen-

Fieurs 1.

2

tially, however, it consisted of a 1314 x 12 x {
foot test room. <A two-foot diameter piston wa:
coupled to a hermetically sealed pressure chamber
one side of which formed one of the walls of thi
test room. Activating a one-shot clutch resultec
in the rotation of a cam through 360° causing :
forward and backward motion of the piston
This generated an N-wave of pressure in th
chamber to create the boom. Overpressure wa
changed by varying piston travel and duration
by changing motor speed. Walls of the test roon
were of dry-wall construction, the floor was car
peted, and there was acoustical tile on the ceiling
‘Two 47 x 35 inch windows were located in th
test room. One was a conventional glass pan
located in the wall forming the pressure chamber
The second window was a one-way mirror locate
on the opposite wall.

The arm-hand steadiness apparatus with pointer held in readiness position.




A COMPARISON OF THE STARTLE EFFECTS RESULTING FROM
EXPOSURE TO TWO LEVELS OF SIMULATED SONIC BOOMS

Introduction.

In a previous study it was found that simulated
nic booms as experienced indoors and having
itside overpressures of. approximately 50, 100,
id 200 N/m? had no adverse effects on tracking
wformance. ‘On the contrary, the booms ap-
vared to increase task attention and facilitate
arformance.

Several possible explanations suggest them-
lves as reasons for the apparent lack of per-
rmance disruption produced by the simulated
oms. The tracking task employed may have
en too insensitive to reveal any slight, momen-
ty startle effect following onset of the booms.
aximum performance disruption following
urtle is known to occur within the first one or
‘o seconds following stimulation,’ ° * and it has
en shown that this impairment may be followed

a period of performance facilitation? By in-
yrating tracking error over successive five-
sond periods, as was done in the previous study,
y weak startle reaction which may have oc-
rrecd could have been masked by the stronger
silitory effect.

A second possibility is that the simulated
oms elicited responses more appropriately char-
cerized as alerting or orienting-type responses
in as startle reflexes. Thackray’ has recently
Yerentiated between startle and orienting re-
mses to impulsive stimuli, e.g., sonic booms,
d discussed the increasing evidence which sug-
sts the importance of rise time as a significant
‘erminant of the resulting response. Although
acise relationships have not as yet been estab-
hed, in general the faster the rise time the
sater the likelihood that a startle reflex (as-
siated with initial performance disruption)
her than an orienting response (associated
th heightened attention and performance im-
ovement) will occur. Unfortunately, because
design characteristics of the simulator em-
vyed in the previous study, rise times of the

booms increased in a manner which was almost
proportional to increases in overpressure. For
the three levels of overpressure studied (50, 100,
and 200 N/m:), the rise times were 6.8, 13.1, and
20.9 msecs. Since the latter two rise times are
relatively slow, the increased overpressure levels
may have contributed little to the startle qualities
of the stimuli and may have, in fact, resulted in
approximately equivalent orienting-type responses
to all three levels.

The present study was designed to correct the
primary deficiencies of the previous study, and
thus allow a more adequate assessment of the
extent of startle responses occurring to different
overpressure levels with rise time controlled. The
changes involved a modification of the simulator
and the substitution of a different task. With
respect to the simulator, the wave front of the
simulated booms was modifled by sychronizing
an acoustic transient from a loudspeaker with the
wave front of the primary pressure wave pro-
duced by the simulator. Although this technique
allowed only limited control over rise time, it
was determined that outside overpressures rang-
ing from 50 to 150 N/m? could be produced with
a minimum rise time of approximately 5 msecs.

The task employed consisted of a specially con-
structed device for measuring small-amplitude
arm-hand movements. This was the same task
used in a recent field study of sonic boom startle
effects. and was considered to be far more sensi-
tive in recording slight, short-duration startle re-
sponses than the tracking task employed in the
Thackray, Touchstone, and Jones study.TM

Two levels of outside overpressure were studied
(50 and 150 N/m?) with rise time held at approx-
imately 5 msecs for each level. These overpres-
sure levels approximate the range of overpressures
(75 to 175 N/m*) expected along the centerline
of the sonic boom carpet for the Concorde SST“
and the rise time was virtually the same as the
median rise time (6 msecs_ reported for the XB-
70 during the Edwards Air Force Base tests.*





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