TECHNICAL REPORT STANDARD TITLE PAGE 

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 

FAA-AM-71- 29 

4. Title and Subtitle 5. Report Dote 

June 1971 

THE EFFECTS OF SIMULATED SONIC BOOMS ON TRACKING 6. Performing Orgoni zoti on Code 

PERFORMANCE AND AUTONOMIC RESPONSE. 

7. Authorl s) 8. Performing Organization Report No. 

Richard I. Thackray, Ph.D., R. Mark Touchstone, B.S., 

and Karen N. Jones _1. B.s. 

9. Performing Organi zotion Name and Address 10. Work Unit No. 

FAA Civil Aeromedical Institute 

P. 0. Box 25082 11. Contract or Grant No. 

Oklahoma City, Oklahoma 73125 

13. Type of Report and Period Covered 

12. Sponsoring Agency Nome and Address 

Office of Aviation Medicine OAM Report Federal Aviation Administration 

800 Independence Avenue, s.w. 14. Sponsoring Agency Code 

Washington. D. c. 20590 

15. Supplementary Notes 

This research was performed under Task AM-A-7l..PSY -21. 

16. Abstract 

Subjects were exposed to four simulated "indoor" sonic booms over an approximate thirty-minute period. The overpressure levels were 1.0, 2.0 and 4.0 psf (as 

measured ''outdoors") with durations of 295 milliseconds. Subjects performed 

a two-dimensional compensatory tracking task during the exposure period and 

continuous recordings were obtained of heart rate and skin conductance. No 

evidence of performance impairment was found for any of the overpressure levels. 

Rather, performance improved significantly following boom stimulation along with 

heart-rate deceleration and skin conductance increase. The obtained pattern 

suggests that the simulated booms may have elicited more of an orienting or 

alerting response than a startle reflex. The results are discussed in terms 

of the possible importance of rise time as a determinant of the physiological and performance effects which may be produced by sonic booms. Since faster 

rise times of the simulated booms might have increased loudness sufficiently 

to change these results considerably, care should be taken to avoid drawing unwarranted conclusions, relative to general sonic boom effects, on the basis 

of these findings alone. 

17. Key Words 18. Distribution Statement 

Attention, Heart Rate, Noise Availability is unlimited. Document may Orienting Reflex, Performance, Skin be released to the National Technical 

Conductance, Sonic Booms, Startle, Information Service, Springfield, Tracking Virginia 22151, for sale to the public. 

19. Security Classif. (of this report) 20. Security Classil. (of this page) 21. No. of Pages 22. Price 

Unclassified Unclassified 15 $3.00 

Form DOT F 1700.7 (s-s9l 

THE EFFECTS OF SIMULATED SONIC BOOMS ON TRACKING 

PERFORMANCE AND AUTONOMIC RESPONSE 

I. Introduction. 

There is evidence that the startle resulting 

from a sudden, high-intensity sound may produce 

a transitory, but significant impairment in performance.18 19 21 22 Since sonic booms are often 

reported to be "startling''/ 6 13 20 one might ~xpect these stimuli as well to produce a temporary impairment in performance. As yet, however, very 

few relevant studies have been conducted. Part 

of this is due to the difficulty involved in conducting controlled field studies using actual booms 

and part with the problems inherent in construct~ ing adequate simulators to study sonic boom effects in the laboratory. 

Of the laboratory studies which have been reported, the results suggest that some impairment 

in performance may be produced by sonic booms 

on certain tasks and/or with booms of sufficient 

overpressure level. However, impairment is not 

invariably found and in some cases performance 

improves with exposure to sonic booms. Woodhead,23 for example, studied the indoor effects of 

simulated sonic booms having outdoor peak overpressures of 0.80, 1.42, and 2.53 pounds per square 

foot (psf). The 2.53 psf level produced a significant increase in omissions, but not errors, on 

a symbol-matching task during the 30-sec. poststimulus period. (The task was one which required the matching of a series of continuously 

moving symbols against a row of stationary 

ones). Neither of the other two levels had a 

significant effect on performance. There were 

wide individual differences, with 33 subjects out 

of the 108 improving their performance following stimulation and 21 showing no change whatsoever. 

Other studies have examined the effects of 

sonic booms as heard indoors on motor coordination.10 11 Both studies were conducted with the 

same indoor boom simulator and both employed 

the same task (a stylus tracing task involving 

1 

fine eye-hand coordination). Simulated booms 

having overpressures of 1.2 psf (as measured 

"outdoors"), durations of 100 msecs., and rise 

ti~es of 10 msecs. were used in the first study, 

while booms having overpressures, durations, and 

effective rise times of 2.5 psf, 270 msecs., and 10 

msecs. respectively were employed in the second. 

The results of the first study suggested a slight 

impairment in performance upon initial exposure 

to the booms, but an improvement in performance 

with repeated presentations of the stimuli. These 

effects were not statistically significant, however. 

The second study examined performance immediately following boom presentations and found 

some evidence for a slight decrement followed 

by a period of performance improvement. The 

decrement was confined to the initial 2.5-sec. 

period subsequent to the booms. In contrast to 

the findings of the earlier study, repeated exposure to the booms was found to result in progressively poorer performance. Because of the small 

number of subjects, however, the authors consider their findings quite tentative. 

The present study was conducted in order to 

provide further information on the effects of 

sonic booms on psychomotor performance and 

autonomic activity, including recovery patterns 

following stimulation and the effects of boom 

repetition. Stimuli were produced by an indoo!' 

sonic boom simulator with overpressure levels 

chosen to include both the expected and extreme 

values which Kryter7 has indicated would likely 

be produced by an SST-type aircraft flying at 

cruising altitude. According to Kryter, within 

an area 12.5 miles on either side of the flight 

track, approximately 98 per cent of the sonic 

booms would have overpressures falling between 

1.5-2.0 ps£, with the remaining 2 per cent reaching 4 psf or higher or 1 psf or lower. Values 

for the duration of the "N-waves" of the simulated booms were also selected to be representative of the durations of the booms which might 
be produced by an SST -type aircraft and were 

based upon data collected during the XB-70 

flights conducted at Edwards Air Force BaseY 

Durations of the booms produced by this aircraft 

(which approximates the proposed SST in size) 

ranged from 260 to 320 msecs. 

Because of design characteristics of the simulator, rise times of the simulated sonic booms 

increased in a manner which was almost proportional to increases in overpressure. Thus, rise 

times of the simulated booms employed ranged 

from approximately 7 msecs. for a 1 psf boom 

to 21 msecs. for a 4 psf boom. Although these 

values are considerably higher than the median 

rise time of 6 msecs. for the Edwards XB-70 

tests,8 they nevertheless fall within the range of 

values which were reported for this particular 

aircraft during those testsY 

The task and general design employed in the 

present study were the same as that used in an 

earlier one concerned with the recovery of motor 

performance and autonomic activity following 

an unexpected burst of 115 dB sound pressure 

level random noise.18 This was done to enable 

direct comparison of the known effects of a startling stimulus on performance and autonomic 

response with the effects produced by the simulated booms. The only major differences between the two studies were in the nature of the 

auditory stimuli employed and in the number of 

stimuli presented. (Each subject received four 

stimuli in the present study while only two were 

used in the previous one.) 

II. Method. 

Subjects. Forty paid male college students between the ages of 18 and 25 served as subjects 

( Ss ). All were right-handed, had no reported 

hearing loss, and had not participated in the 

earlier startle study. 

Apparatus. The sonic boom simulator was constructed by Stanford Research Institute and has 

~een described in detail elsewhere.10 Essentially, 

1t was a simulator designed primarily to study 

the effects of sonic booms, as experienced indoors, 

on sleep. Consequently, the test room was built 

to approximate the dimensions (13%' X 12' X 8') 

of a bedroom in a "typical" frame house. Standard housing construction was employed with drywall interior surfaces. There were two windows 

in the room, with one being a one-way mirror 

2 

used for S observation. A two-foot diameter 

piston was coupled to a hermetically-sealed pressure chamber, one side of which formed one of 

the walls of the test room. Activating a "oneshot" clutch resulted in the rotation of a cam 

through 360° causing a forward and backward 

motion of the piston. This generated anN-wave 

of pressure in the sealed chamber to create the 

boom. Changing the cam offset varied the peak 

overpressure level of the boom, and levels ranging from 1.0 to 9.0 psf could be achieved in this 

manner. (It should be noted that, unless otherwise specified, the values stated for all boom 

parameters refer to values as measured "outdoors" (in the pressure chamber) and not to 

levels occurring in the room.) Duration of the 

boom could be varied from 100 to 300 msecs. by 

changing the rpm of the DC motor. As noteQ_ 

earlier, because of the manner in which over~ 

pressure levels were varied in the simulator, it 

was not possible to manipulate rise time of the 

booms independently of overpressure levels. 

Thus, increases in cam offset, resulting in longer 

piston travel, yielded an increase in rise time of 

the boom which was approximately proportional 

to the overpressure level. 

The pressure chamber was calibrated with a 

Bruel and Kjaer type 4146 condenser microphone, 

a Bruel and Kjaer type 2631 carrier amplifier, 

and a Consolidated Electrodynamics Corporation, Model 5-124 recording oscillograph. In addition to the oscillograph, the booms were also recorded during the experimental sessions on a Consolidated Electrodynamics Corporation, Model 

VR3700 tape system. 

A console containing the oscilloscope display 

for a two-dimensional compensatory tracking 

task was located in the center of the test room. 

The spot on the oscilloscope was driven in a 

random manner by means of a cam function 

generator which constantly varied the voltages 

to the horizontal and vertical deflection plates of 

the oscilloscope. S's task was to attempt to keep 

the spot continuously at the center of the oscilloscope by means of a small control stick located 

at his right hand. Minimal muscular effort was 

required to move the stick, and an excursion of 

approximately 1 in. in any direction from center 

was sufficient to move the spot to the edge of the 

scope. Voltages defining the position of the 

target on the oscilloscope (i.e., the algebraic sum 

of the function generator and control stick volt-
ages) were fed to a PACE TR-20 analog 

computer and the output voltages (absolute 

horizontal and vertical error) were separately 

integrated by Beckman Type 9873B resetting 

integrator couplers. The entire tracking task 

was essentially a slightly modified version of 

one previously described by Pearson.12 

Onset of the booms, as well as the intervals 

between booms, was automatically controlled by 

a series of electric timers. These timers were 

also used to program and control the duration of 

the training trials, the inter-trial rest periods, 

and the onset of a warning light which occurred 

prior to each training trial. 

A Beckman Type R Dynograph recorded the 

physiological variables as well as the integrated 

tracking error. Beckman biopotential electrodes 

were attached to the lateral walls of S's chest 

and the leads connected to a Beckman Type 9857 

cardiotachometer coupler. Skin resistance was 

obtained from two Fels zinc-zinc sulphate electrodes leading to a Fels Model 22A Dermohmmeter. One electrode was attached to the palmar 

surface of the left hand and the other to the 

ventral surface of the left wrist. Current density 

was 22.3 microamps/cm.2 The output of the 

Dermohmmeter led to another channel of the 

recorder. 

All equipment, with the exception of that used 

by the S in performing the task, was located outside the test room. Figures 1 and 2 show details 

of the boom generating apparatus and the interior 

of the test room respectively. 

FIGuRE 1. Exterior view of the pressure chamber of the sonic boom simulator showing details of the boom generating apparatus. 

3 
FIGURE 2. Interior view of the test room. The displays to the right on the console were not used in the experiment. The left wall forms one of the walls of the pressure chamber. 

Procedure. Subjects were assigned to one of 

the three experimental groups or the control 

group on a simple rotational basis. The experimental groups will be subsequently referred to as 

the 1, 2, and 4 psf groups, although the actual 

obtained overpressures departed slightly from 

these values. Table 1 shows the obtained mean 

overpressures as well as the corresponding durations and rise times of the booms as measured 

in the pressure chamber. Also shown are the 

mean "indoor" values obtained for each of the 

three groups. These latter values were obtained 

with the microphone suspended in the test room 

at S's head level. As would be expected, there 

was considerable attenuation of the booms as recorded in the test room. It is interesting to note 

that there was also a relative increase in the rise 

4 

TABLE 1.-Mean overpressure, rise time, and duration 

of the booms administered to the 1, 2, and 4 psf groups 

as measured in the pressure chamber and in the test 

room. 

Actual 

Peak Rise Duration 

Location Group Over- Time (in msecs.) 

pressure (in msecs.) 

(in psf) 

Pressure 1 psf 1.0 6.8 299.5 

Chamber 2 psf 2.1 13.1 286.9 

4 psf 3.9 20.9 302.2 

1 psf 0.13 12.1 283.6 

Test Room 2 psf 0.23 18.0 295.6 

4 psf 0.40 23.7 301.3 
times of the booms in the test room. Boom duration was relatively unchanged by the test room. 

After being seated in the test room, S was 

played a tape which explained that the purpose 

of the experiment was to investigate physiological 

changes associated with prolonged performance 

on a perceptual-motor task. Electrodes were then 

attached and the task explained in detail. Briefly, 

the instructions informed S that the first or training phase would consist of a series of 2-min. trials 

with 35-sec. rest periods between them. His task 

was to try to keep the moving spot on the oscilloscope as close to center as possible during the 

trials. He w~c; informed that a small red warning light would be illuminated 5 sec. prior to the 

beginning of each trial. Fifteen training trials 

were then administered. 

Following completion of training, S was allowed a 10-min. rest period. He was then informed 

that the next phase of the experiment would be 

similar to the training phase just completed except that he would have to perform the task 

without any rest periods for 35 to 40 min. (The 

actual length of this period was 26 min.) In 

addition, Ss in each of the experimental groups 

were told that during this period they might hear 

certain sounds which were not present during 

the training period. However, it was emphasized 

that their task was to try to maintain consistent 

tracking performance regardless of any sounds 

or noises they heard. (No indication was given 

regarding the nature of the sounds and no S was 

aware that the experiment had anything to do 

with sonic booms.) Two minutes after the test 

phase began, the first boom was presented. This 

was followed by three more booms each separated 

by a 6-min. period. Upon completion of this 

phase, electrodes were removed and S completed 

a post-experimental questionnaire. 

Scoring of Test- and Training-Phase Data. 

Scoring of the physiological and performance 

data was essentially the same as employed in the 

earlier study/8 i.e., the 1-min. periods following 

each boom were divided into 12 5-sec. intervals. 

Total tracking error (sum of the horizontal and 

vertical integrator resets) in each interval was 

then determined for each S. Skin resistance was 

measured at the end of each interval and the 

values converted to conductance. To determine 

the magnitude and course of heart-rate change 

following stimulation, the maximum heart rate 

5 

(single fastest beat as measured from the cardiotachometer recording) was obtained for each 

interval. 

Response to the booms was evaluated in terms 

of change from pre-stimulus levels. In order to 

make the pre- and post-stimulus units comparable, the 1-min. period preceding each boom was 

also divided into 12 5-sec. intervals. The number 

of integrator resets and the maximum heart rate 

in each of the 12 intervals were obtained and 

means computed for each S. Levels of skin conductance prior to each boom were found by taking the mean of the conductance level measured 

1-min. before stimulus presentation and the level 

at the moment of stimulation. Change scores 

for each variable were obtained by taking the 

difference between the pre-stimulus values for a 

given boom and the values in each of the 12 5-sec. 

intervals folowing that particular boom. 

All of the physiological and performance data 

for the control group were scored in the same 

way as the data for the experimental groups. 

While the control group received no boom or 

other auditory stimulus, the "pre- and post-stimulus" periods analyzed were those corresponding 

in time of occurrence to comparable periods 

analyzed for the experimental groups. 

III. Results. 

Tables 2, 3, and 4 show the mean values for 

tracking error, maximum heart rate, and conductance level during the 1-min. period prior to 

each boom. Repeated-measures analyses of variance conducted on these data revealed no significant differences between groups on any of the 

variables (p>.05). There were, however, significant pre-stimulus differences between the 

TABLE 2.-Mean tracking error during the one-minute 

period prior to each boom. Values are expressed in 

terms of number of integrator resets per five-second 

interval. 

Booms 

Groups 

1 2 3 4 

1 psL _____ 8.36 9.73 11.12 11.61 

2psf_ _____ 8.70 10.71 10.61 10.61 

4 psf_ _____ 8.24 9.41 9.54 9.77 

ControL ___ 6.22 8.32 8.29 7.89 

Means _____ 7.88 9.54 9.89 9.97 
TABLE 3.-Mean maximum heart rate in beats per minute TABLE 4.-Mean conductance level in micromhos during 

during the one-minute period prior to each boom. the one-minute period prior to each boom. 

Booms Booms 

Groups Groups 

1 2 3 4 1 2 3 4 

1 psL _____ 74.9 77.4 76.5 75.3 1 psL _____ 11.88 10.81 10.84 11.43 

2 psL _____ 74.3 75.6 75.8 77.1 2 psf_ _____ 11.54 10.69 10.77 10.69 

4 psf_ _____ 72.0 74.0 73.6 75.6 4 psf_ _____ 9.41 9.39 9.30 9.32 

ControL ___ 70.6 73.1 71. 1 74.3 ControL ___ 11.75 10.81 10.84 10.75 

Means _____ 73.0 75.0 74.3 75.6 Means _____ 11. 14 10.43 10.44 10.55 

4 BOOM 4 BOOM 2 

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2 3 4 5 6 7 8 9 10 II 12 2 3 4 5 6 7 8 9 10 I I 12 

FIVE- SECOND INTERVALS 

FIGURE 3. Relative change in tracking error for each group during the one-minute period following each boom. 

6 
booms. The F-values for tracking error, maximum heart rate, and conductance level were 15.73 

(df=3/36, p<.01), 6.59 (df=3/36, p<.01), and 

10.18 (df=3/36, p<.01) respectively. There 

were no significant boom x group interactions. 

The significant differences between the pre-stimulus levels of the four booms appear to reflect 

progressive changes which are not unlike those 

reported in the previous startle study and which 

suggest fatigue effects resulting from the rather 

demanding visual task. 

Change scores for tracking error during the 

4 BOOM 

..: 

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12 5-sec. intervals in the minute following each 

boom are shown in Figure 3. (In this figure, as 

well as in the subsequent figures, positive values 

always represent increases in the variable relative 

to the pre-stimulus value.) Examination of 

Figure 3 suggests that the initial effect of the 

booms was to produce an apparent improvement in 

tracking performance followed by a gradual return to pre-stimulus levels. A p x q x r repeatedmeasure analysis of variance24 performed on these 

data revealed significant differences between 

groups (F=7.37, df=3/36, p<.01) and periods 

4 BOOM 2 

3 

• 2 II 

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I 

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2 3 4 5 6 7 8 9 10 I I 12 

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Groups -3 

-4 I, 2, 8 4 psf l 0-0 Combined 

-5 Control ·---· -6 

-7 

2 3 4 5 6 7 8 9 10 II 12 

FIVE- SECOND INTERVALS 

FIGURE 4. Comparison of the combined overpressure groups with the control group with respect to relative change 

in tracking error following boom stimulation. 
(F=2.27, df=ll/396, p<.05). There were no 

significant differences between booms ( p > .05) 

and no significant interactions (p>.05). Newman-Keuls tests24 revealed the control group to 

differ significantly from the 1, 2, and 4 psf 

groups (p<.05), but interestingly enough, the 

experimental groups did not differ significantly 

among themselves. Comparisons were also made 

of the differences between periods. Only the difference betweeen period 3 and period 12 was sig4 

3 

2 

IJ 

BOOM 

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nificant at the .05 level using the Newman-Keuls 

test. Since there were no significant differences 

between the experimental groups, the data were 

combined and plotted along with the control 

group. These data, as shown in Figure 4, rather 

clearly reveal the general improvement in performance immediately following boom stimulation which tends to diminish toward the end of 

the 1-min. period. 

4 

3 

2 

0 

-I 

-2 

-3 

-4 

-5 

-6 

-7 

4 

3 

2 

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BOOM 2 

2 3 4 5 6 

BOOM 4 

Groups 

I psf o-o 

2 psf t:.-t:. 

4 psf D-D 

Control •---• 

7 8 9 10 II 12 

2 3 4 5 6 7 8 9 10 I I 12 

FIVE- SECOND INTERVALS 

FIGURE 5. Relative change in heart rate for each group during the one-minute period following each boom. 

8 
The pattern of heart-rate charge following 

boom stimulation is shown in Figure 5. The 

general effect displayed by the experimental 

groups in this figure is one of heart-rate deceleration which reaches its peak about 10 sec. following stimulation. This is followed by oscillations 

which are generally below the pre-stimulus level 

for the remainder of the minute. However, 

while the analysis of variance revealed significant 

differences between groups (F=3.04, df=3/36, 

p < .05) , there was no evidence of significant 

BOOM 

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differences between the post-stimulus periods 

( F = 1.44, df = 11/396, p > .05). There were also no 

significant differences between booms ( F < 1.00) 

and none of the interactions were significant. 

Multiple comparisons using Newman-Keuls tests 

revealed that, while each of the three experimental groups differed from the control at the 

10 per cent level, only the difference between the 

4 psf group and the control was significant at 

the 5 per cent level. There were no significant 

differences among the experimental groups them4 

3 

2 

0 

-I 

-2 

-3 

-4 

-5 

-6 

-7 

BOOM 2 

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\ 

2 3 4 5 6 7 8 9 I 0 I I 12 

BOOM 4 

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It 

• Groups 

I, 2, S 4 psf } 

Combined 0-0 

Control ·---· 

2. 3 4 5 6 7 8 9 10 II 12 

FIVE- SECOND INTERVALS 

FIGURE 6. Comparison of the combined overpressure groups with the control group with respect to relative change 

in heart rate following boom stimulation. 

9 
selves. Because of the similarity between the 

patterns displayed by the three experimental 

groups and because the experimental groups were 

shown not to differ among themselves, it would 

appear reasonable to assume that the overall 

effect o£ the boom stimulations was a general 

heart-rate deceleration £or all three groups, but 

that subject variability within the 1 and 2 ps£ 

groups may have been sufficiently great to mask 

the boom effect. Consequently, it seemed appropriate to test the combined experimental groups 

against the control. A Scheffe test for multiple 

comparisons2 yielded a significant difference 

(p<.10) between the average of the 1, 2, and 

4 ps£ groups and the control. (Since this is a 

conservative test, Scheffe2 suggests employing the 

10 per cent rather than the 5 per cent level.) 

As was done with the tracking data, the heartrate data for the experimental groups were combined and, along with the control data, are 

shown in Figure 6. 

Figure 7 displays the change in skin conductance following boom stimulation. The expected effect o£ such stimuli would be an initial 

increase in conductance with a gradual return 

to pre-stimulus levels. It is readily apparent 

that this is the nature o£ the patterns shown in 

the figure. Interestingly enough, the greatest 

change appears to occur in the 2 ps£ group. In 

the analysis o£ variance, significant differences 

were found between groups (F=9.25, d£=3/36, 

p<.01), booms (F=2.92, df=3/108, p<.05), 

periods ( F = 28.35, d£ = 11/396, p < .01) , and the 

period x group interaction (F=6.71, d£=33/396, 

p<.01). None o£ the other interactions approached significance at the .05 level. Multiple 

comparisons o£ the experimental and control 

group means were again made to clarify the 

nature o£ the between-groups effect. NewmanKeuls tests revealed each o£ the three experimental groups to differ significantly £rom the control (p<.05) and the 2 ps£ group to differ significantly (p<.05) £rom both the 1 and the 4 

ps£ groups. The latter two groups did not differ 

significantly £rom each other. 

The significantly greater conductance change 

obtained £or the 2 ps£ group is interesting in view 

o£ the £act that this group gave no evidence o£ 

differing £rom the other two groups in terms o£ 

either heart-rate response or change in tracking 

error. This suggests that the increased conductance change might have been due to a difference 

10 

in sudomotor responsiveness of this group rather 

than to any peculiar characteristic of the 2 psf 

stimulus. To test this hypothesis, the three experimental groups were compared with regard to 

their conductance change to the red warning light 

which occurred at the beginning o£ the test 

phase and prior to any boom presentations. Mean 

change in conductance £or the three groups was 

0.41, 0.74, and 0.24 micromhos (p.mhos) £or the 

1, 2, and 4 ps£ groups respectively. A singleclassification analysis o£ variance conducted on 

these data yielded an F-value of 3.00 (df=2/25) 

which exceeded the 10 per cent level, but was not 

significant at the 5 per cent. Consequently, although the mean £or the 2 ps£ group was in the 

predicted direction, the data provide only suggestive support £or the hypothesis that the 2 ps£ 

group was a more autonomically reactive group 

per se. 

Since a significant F-value was obtained for 

the differences between booms, Newman-Keuls 

tests were conducted on the mean conductance 

values £or each boom. These values were 0.40, 

0.66, 0.44, and 0.47 p.mhos £or the first, second, 

third, and fourth booms respectively. The second 

boom was found to differ significantly £rom the 

first (p<.05), but there were no other significant 

differences among the means. 

Because of the significant period x group interaction, tests were conducted on the simple effects 

o£ periods £or each o£ the four groups. 24 Significant decreases in conductance over the 12 

periods were obtained £or the 1 ps£ (F=16.07, 

d£=11/396, p<.01), the 2 ps£ (F=28.59, d£=11/ 

396, p<.01) and the 4 ps£ (F=2.91, d£=11/396, 

p<.01) groups. As would be expected, the obtained F-value £or the control group was nonsignificant (F<l.O). 

Since the 2 ps£ group differed significantly 

£rom the 1 and 4 ps£ groups, the data were not 

combined as was done with the heart rate and 

tracking data. It should also be pointed out 

that the abrupt increase in conductance shown in 

Figure 7 in the control group data was the result 

o£ one S. This S's conductance changed £rom 

12.41 to 16.93 p.mhos during the eighth 5-sec. 

interval o£ the 4th boom. The reason £or this 

shift is unknown, but may have been caused by 

a gross shift in body position. 

The results of the subjective rating scale administered to the experimental Ss at the close 

of the test session are shown in Table 5. It can 
2.0 

1.8 

1.6 

1.4 

1.2 

1.0 

en 0.8 

0 

..c. 0.6 

E 0.4 0 

.... 

0 0.2 

E 0.0 

- -0.2 

w -0.4 (!) 

z -0.6 

<{ 

I 

u 

w 2.0 u 

z 1.8 

<{ 

1- 1.6 

u 1.4 ::> 

0 1.2 

z 

0 1.0 

u 0.8 

1>< 0.6 

0.4 

0.2 

0.0 

-0.2 

-0.4 

-0.6 

BOOM 

.. , •-...... ,' .......... _ .... 'e, 

,.,,._,·~----·--· 

2 3 4 5 6 7 8 9 10 I I 12 

BOOM 3 

., ____ .,,., .-- ,.,,.--·--· ,._ -·--

2 3 4 5 6 7 8 9 10 II 12 

2.0 

1.8 

1.6 

1.4 

1.2 

1.0 

0.8 

0.6 

0.4 

0.2 -• ,,. 0.0 ~-~ ·-...... __..~-...,...,.., ..... .-"------=----=:..._=.=.::..! -- '-•--•--·--· 

-0.2 

-0.4 

- 0. 6 L-..~--'---L--IL....-..L..--L...---L..---.J-.L--'-.....J...--I 

2.0 

1.8 

1.6 

1.4 

1.2 

2 3 4 5 6 7 8 9 10 I I 12 

BOOM 4 Groups 

I psf 

2 psf 

4 psf 

Control 

0-0 

t:.-t:. 

D-D 

·---· 

1.0 0 

0.8 \ 

06 o........_o........_ · o....._o, o-g~c-n-o-o-o-o....._ o.4 'o-o....._ - _., o-o o-· 'e,, 0.2 p....._ • ,' o-a...... 

0.0 1------------T----------ll 

-0.2 ·--e I 

--·--·--·--·--·--· 

-0.4 

-0.6~-'-.....J...~~~-L~-L-4--L~--~~ 

2 3 4 5 6 7 8 9 10 I I 12 

FIVE- SECOND INTERVALS 

FIGURE 7. Relative change in palmar skin conductance for each group during the one-minute period following each 

boom. 

be seen that there is a tendency for each successive boom to be rated somewhat less "startling" 

than its predecessor. (The values were derived 

from a five-point scale with end points consisting 

of "not startled at all" (scale value of 1) to "extremely startled" (scale value of 5).) Friedman 

two-way analyses of variance16 conducted on each 

11 

overpressure group revealed the differences between booms to be significant for the 1 and 2 psf 

groups (p<.05), but not £or the 4 ps£ group 

(p>.03). The data in Table 5 suggest that the 

2 and 4 psf groups might have been more startled 

by the booms than was the 1 psf group. However, Kruskal-Wallis analyses of variance16 re-
TABLE 5.-Mean ratings of "startle" to the four booms. 

A rating of 1.0 signifies "not startled at all," while a 

rating of 5.0 would signify "extremely startled." 

Booms 

Groups Means 

1 2 3 4 

1 psL _____ 2.8 1.9 1.8 1.7 2.0 

2 psf_ _____ 3.5 2.7 2.6 2.3 2.8 

4 psf_ _____ 3.0 2.7 2.6 2.4 2.7 

Means ___ 3.1 2.4 2.3 2.1 

vealed no significant differences (p>.05) between 

the ratings of the three groups for each boom. 

Because the nature of the task required that ratings be obtained at the completion of the experiment rather than after each boom, the rating data 

should be viewed as suggestive rather than conclusive. 

IV. Discussion. 

The results of the present study clearly indicate an improvement in performance following 

exposure to the simulated sonic booms. This improvement reached its maximum approximately 

15 sec. after the booms occurred, with a gradual 

return to pre-stimulus performance levels during 

the 1-min. period following boom presentations. 

While no evidence of impairment, especially 

with the 4 psf boom, was a somewhat surprising 

finding, it should be recalled that neither Lukas 

and Kryter10 nor Lukas, Peeler, and Kryter11 

found much evidence of impairment in psychomotor performance following simulated booms, 

with both studies reporting some evidence of 

performance improvement. The Lukas, Peeler, 

and Kryter study, which was the more comprehensive of the two, found the impairment to be 

confined to the 2.5-sec. period immediately after 

boom presentation. Following this, there was a 

period of performance facilitation. It is interesting to note that the authors of the above study 

feel that the impairment, although appearing 

to be the result of a muscular (startle) reflex, 

may well have been caused by the mechanical 

vibration of the room (and the subject as well) 

resulting from the boom stimulus and causing 

the stylus used in the tracing task to move momentarily off target. Since the boom simulation 

:facility used in the present study was patterned 

after the one used by Lukas, Peeler, and Kryter, 

12 

it is probable that similar levels of room vibration were present in both studies. However, the 

tracking task used in the present study would 

seemingly be much less susceptible to the influence 

of mechanical vibration, and it would appear 

quite unlikely that a slight vibration of the room 

would result in any detectable increase in performance error. 

If the explanation offered by Lukas, Peeler, 

and Kryter to account for their impairment is 

correct, then their finding of subsequent performance facilitation would agree with the findings of the present study, and would suggest that 

differences between the studies with reard to initial impairment may simply be a reflection of 

differences between the tasks in their sensitivity 

to vibration. 

In considering the nature of the "startle" response, if any, which was elicited by the simulated 

sonic booms, it is of interest to compare the response patterns obtained in this study with those 

obtained in the previous study by Thackray and 

Touchstone.18 In the earlier one, the initial unexpected burst of 115 dB random noise resulted 

in a significant increase in tracking error lasting 

from 10-15 seconds. During the remainder of 

the 1-min. post-stimulus period, performance 

fluctuated about the pre-stimulus level. The 

heart-rate response was rather clearly diphasic 

and consisted of an initial significant acceleration 

during the first 5-sec. interval after stimulation 

followed by a rather abrupt deceleration. The 

pattern of heart-rate change during the first 15-

20 sec. appeared to mirror the recovery pattern 

obtained for tracking performance. A second 

presentation of the noise stimulus 15 min. after 

the first produced similar patterns of heart-rate 

and performance change. As would be expected, 

palmar skin conductance increased significantly 

to both presentations of the stimuli. 

In the present study, heart rate showed both 

initial and sustained deceleration and, as already 

noted, performance improved. Surprisingly, 

there were no differences between the three overpressure groups in magnitude of heart-rate and 

performance change, although there was a difference between the 2 ps:f group and the other 

two groups in magnitude of conductance change. 

However, since the finding of a significantly 

greater conductance change in the 2 psf group 

clearly departs from the results obtained for 

heart rate and tracking, it would appear that the 
most I?arsimonious explanation for this discrepancy is that the 2 psf group probably differed 

by chance from the 1 and 4 psf groups in sudomotor reactivity. 

It is evident that the "startle" evoked by the 

stimuli employed in the two studies resulted in 

quite different response patterns. The initial pattern of heart-rate acceleration and performance 

impairment found in the Thackray and Touchstone study suggests that at least part of the 

classic startle pattern9 was elicited by the stimuli. 

However, the pattern produced by the simulated 

sonic booms reveals little or no evidence of a 

true startle response, but rather suggests an orienting or alerting response :followed by a period 

of heightened attention to the task. Initial heartrate deceleration is known to be a principle component of the orienting reflex,4 and there is evidence that sustained reduction in heart rate reflects a state of heightened attention.5 

Since orienting responses are more likely to 

occur to acoustic stimuli of low intensity, with 

defensive (or startle) responses occurring to 

higher intensities/4 the differences in obtained 

patterns may have been the result of differences 

in "intensity levels" o:f the stimuli employed in 

the two studies. There is evidence that such 

differences did exist. Thus, although Ss in both 

the present study and the previous one rated the 

stimuli employed as "startling," the range of 

mean ratings given to the booms ("mildly startled" to "moderately startled") was less than the 

range of mean ratings to the random noise 

("quite startled" to "extremely startled"). Also, 

Ss were observed through a one-way window 

during the boom presentations and, except :for 

an occasional slight orientation of the head toward 

the source of the sound, there were no observable 

body responses. This was in contrast to the 

earlier study in which body jerks were the rule 

rather than the exception. Lastly, there is evidence of greater change in skin conductance to 

the noise stimuli presented in the previous study 

than to the simulated sonic booms. Mean change 

(2.49 p.mhos) to the random noise stimulus was 

significantly greater than the mean change (1.00 

p.mhos) of the combined 1, 2, and 4 psf groups 

(t=4.93, df=58, p<.001). A comparison of 

conductance levels immediately prior to the above 

stimuli in both studies yielded no significant 

differences (t=0.4'7, p>.05). 

13 

The results obtained in this study would suggest that the response to sonic booms might be 

more appropriately characterized as an alerting 

or orienting response than as a classical startle 

response. However, in terms of generalizing 

from these results, the question must be asked 

"Is the type of response obtained to the simulated 

booms employed in this study representative of 

the typical response which would be generallly 

expected to occur to sonic booms produced by 

aircraft under field conditions?" 

In answering this question several factors need 

to be considered. One :factor is the judged 

realism of the simulated booms. Ss who had 

previously heard sonic booms under indoor conditions were asked to evaluate the booms at the 

completion of the experiment. A majority of 

these Ss felt that the simulated booms sounded 

similar to real ones they had heard. Because 

many o:f these Ss had been exposed to the Oklahoma City sonic boom tests conducted in 1964, 

reasonable reliance can probably be placed on 

these judgments. Ss did: comment, .however, on 

the booms originating from one wall o:f the room 

whereas there was less directionality associated 

with real sonic booms they had experienced indoors. Also, the duration o:f the simulated booms 

(N-waves) appeared longer than ones with which 

they were familiar. This, of ·course, was the 

result of atte:tnpting to simulate the longer duration of the booms produced by an SST-type aircraft. Interestingly enough, only three Ss reported the simulated booms to be less startling 

than ones they had heard, although this evaluation must be viewed with considerable caution 

because of the time factor involved in the comparisons. 

The other factor relates to spectral energy 

characteristics of the simulated booms. As 

Kryter6 has noted, the maximal energy o:f sonic 

booms is largely concentrated in the frequency 

regions usually considered subaudible, with a 

rapid decline in energy at the higher frequencies. 

Power spectral density function analyses o:f the 

simulated booms as measured in the test room 

revealed that the simulated booms also displayed 

maximal energy in the subaudible range with a 

peak at approximately 3 Hz. There was a decline 

in energy at frequencies above this value with 

energy down 45 dB at 1000 Hz. However, as was 

indicated earlier, the rise times of both the 2 and 

4 ps:f booms employed in the present study were 
considerably longer than the median rise time 

obtained :for the XB-70 aircraft during the Edwards tests. 8 Faster rise times of the simulated 

booms would have increased the spectral energy 

in the :frequencies above 200 Hz and presumably 

increased their loudness.15 25 Whether reduction 

in rise times o:f the 2 and 4 ps:f booms to this 

level (6 msecs.) would have increased loudness 

sufficiently to have produced startle reflexes and/ 

or impairment in tracking performance is not 

known. Evidence :from animal research would 

suggest that rise times of acoustic stimuli are 

significant determinants o:f the resulting behavioral response, with startle responses occurring only i:f the rise times are sufficiently short.3 

The simulator employed is capable of modifications to achieve greater control over the effective 

rise time. Research incorporating such modifications is currently being planned in order to obtain needed information relative to the importance of this variable in influencing the type of 

response produced by sonic booms. Until such 

information is available, some degree of caution 

should be exercised in generalizing :from the results of this study, especially with regard to the 

2 and 4 ps:f booms, to booms of comparable levels 

occurring under field conditions. 

Finally, no evidence of adaptation to the :four 

booms was :found :for either the physiological 

responst3S or performance change. Skin conductance response did show a significant change with 

the second boom, but this was in the nature of 

an increase rather than a decrease. There is no 

ready explanation :for this discrepant result. 

14 

With regard to the subjective responses, all three 

overpressure groups rated each successive boom 

as less startling than its predecessor. These differences were significant :for the 1 and 2 ps:f 

groups, but not :for the 4 ps:f group. Ho~ever, 

as noted earlier, Ss were continuously tracking 

during the test period and ratings had to be obtained at the completion of the experiment 

rather than after each boom. Because of this, 

greater reliance should probably be placed in the 

physiological and performance data than in the 

subjective responses in terms of evaluating possible adaptation effects. 

V. Conclusions. 

While the results of the present study revealed 

a :facilitative effect of the simulated indoor sonic 

booms on psychomotor performance, it should be 

emphasized that care must be taken to avoid 

drawing unwarranted conclusions, relative to 

general sonic boom effects, on the basis of these 

findings alone. As previously mentioned, the 

use of :faster rise times might have changed the 

results considerably. Also, the present study 

was only concerned with one aspect of behavior 

(visual-motor coordination) and did not consider 

the possible effects of booms on other behaviors 

or on sleep disturbance. Lastly, the study was 

in no way concerned with annoyance levels of 

sonic booms, and there is ample evidence that 

booms having overpressures within the range of 

values employed in this study are considered 

by sizable segments of the population to be unacceptable.7 8 17 
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of the special study group on noise and sonic boom 

in relation to man. Washington, Department of the 

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2. Edwards, A. L. : Experimental design in psychological 

research, New York, Holt, 1960. 

3. Fleshier, M. : Adequate acoustic stimulus for startle 

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AND PHYSIOLOGICAL PSYCHOLOGY, 60:200--207, 

1965. 

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15 

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