Ficure 1.

Subject instrumented for physiological recording and performing tasks. The displays to the right on the

console were not used in this experiment.

termined, all Ss received them in the same
positions.

Following completion of training, S was al-
lowed a 10-minute rest period. He was then
informed that the next or test phase of the ex-
periment would be similar to the training phase
just completed, except that he would have to
perform both tasks without rest periods for 35
to 40 minutes. He was also told to respond to all
auditory stimuli presented through the head-
phones and that not all stimuli would be the
same. (No indication was given that any of the
stimuli would be loud or startling.) It was
emphasized that § should try to maintain track-
ing at all times even when making the button
response to auditory stimuli. The test phase
actually lasted only 30 minutes. Two minutes

after the phase began, the first 115 db startle
stimulus was presented. The same stimulus was
again presented 15 minutes later. (These two
high-intensity, “startle” stimuli will be subse-
quently referred to as S, and S,, respectively.)
Fifteen of the 1,000 Hz, 75 db stimuli were again
presented at random intervals during this phase,
although as with the training phase, all Ss re-
ceived them in the same temporal position. None
of the 75 db stimuli was presented during the
90-second periods immediately prior to or fol-
lowing S,; or S.. Upon completion of this phase
Ss were administered a post-experiment ques-
tionnaire. Audiograms were also taken at this
time to insure that no hearing loss had occurred.

Scoring of the test and training phase data.
Although the tracking task was essentially con-



their immediate startle effect. For example, a
comparison of the absolute level of tracking error
(integrator resets) during the initial 5-second
interval following S, with absolute level of error
during the same interval following. S, yielded
no evidence of a difference (¢=0.77; p>.05), nor,
as indicated earlier, was there any apparent dif-
ference between reaction times to S, and S,. Also,
neither the maximum heart rates during the first
5-second interval nor the maximum conductance
levels following startle were different for S, and
S.. The obtained é-values were 149 (p>.05)
and 0.76 (p>.05) for heart rate and conductance
level respectively. It should be noted, though,
that while there was little evidence from the
physiological or performance data to suggest any
substantial difference between the startle stimuli,
there did appear to be a subjective difference
between them. A five-point rating scale with
endpoints consisting of “not startled at all”
(scale value of 5) to “extremely startled” (scale
value of 1) was administered following the ex-
periment. The mean rating for S, was 4.5 and
for S, 3.6. A sign test’ indicated this difference
to be significant (p<.001).

Individual differences. To enable comparison
of the characteristics of those Ss whose tracking
performance was poorest following startle with
those whose performance was best, the distribu-
tions of absolute error scores (integrator resets)
were obtained for the first 5-second interval fol-
lowing S, and S,. A correlation of 0.60 (p<.01)
between these two distributions revealed a mod-
erate degree of consistency among Ss in their
performance following startle. Since primary
concern was only with examination of the char-
acteristics of extreme reactors, two groups were
formed. Those Ss whose scores were in the top
third of both distributions were designated as
high error (HE) Ss and those in the bottom
third of both distributions as low error (LE)
Ss. Eight HE and six LE Ss were obtained in
this manner. For S, the obtained mean error
scores were 12.87 for the HE group and 4.08 for
the LE group. For S, the comparable values
were 13.56 and 4.00 for the HE and LE groups
respectively.

In comparing the two groups with respect to
possible differencés prior to startle, neither the
pre-startle values for conductance level nor for
maximum heart rate approached significance.
There were, however, significant differences be-

tween the groups with regard to tracking error
prior to startle. The pre-startle means for S,
were 6.56 and 3.67 for the HE and LE groups
respectively. For S, mean values for the two
groups were 8.09 and 4.90. These differences
between the groups were significant for both pre-
startle periods (S, (¢=2.96; p<.05) ; S, (¢=2.51;
p<.05)).

In terms of: response to the startle stimuli,
there were no significant differences between the
HE and LE groups in mean conductance change
to either S, or S,. This was not the case with
heart rate response, however. For S, the heart
rate response (maximum heart rate during the
5-second interval following stimulation minus
maximum heart rate in the 5-second interval
preceding stimulation) was 20.4 b.p.m. for the
HE group and 8.3 b.p.m. for the LE group.
This difference was significant (¢=2.54; p<.05).
A similar trend was found for S., but the differ-
ence between the mean HE change of 17.2 b.p.m.
and mean LE change of 9.7 b.p.m. was not sig-
nificant (t=1.95; p>.05).

With regard to the subjective ratings obtained
from the post-experiment questionnaire, the HE
group rated S, more startling than did the LE
group (U=3; p=.004). Although the trends
were the same, the two groups did not differ
significantly with respect to their ratings of S;
(U=18; p=.18).

IV. Discussion.

The results of the present study revealed the
recovery of tracking performance following
startle to be quite rapid. Upon initial presenta-
tion of the startle stimulus, maximum disruption
was found to occur during the first 5 seconds
after stimulation, with significant, but consider-
ably less disruption during the second 5-second
interval. Interpretation of the effects of the
second startle on tracking was difficult because
of the elevated level of tracking error prior to
the stimulus. Neither presentation of the startle,
however, yielded any indication of adverse effects
after the initial 5- to 10-second post-stimulus
interval. Beyond this, startle appeared to have
an alerting effect in which performance was gen-
erally improved relative to pre-stimulus levels.

Recently, Vlasak*? has reported a study which
also dealt with recovery of motor performance
following startle. He employed a simple task in


7.4 (-
T.2F

a
°o
T

6.8
6.6

oP PD
on tf
TT OT

5.8
5.6 f-

deeds
wm +
TT

TRACKING ERROR (x no. integrator resets/5-sec. int.)

5.04

"T

3 4 5

THREE- TRIAL BLOCKS

Ficure 2. Mean tracking error during the 15-trial training period.

12, only the eighth (¢=3.43; p<.01) was sig-
nificantly different from the pre-stimulus level.

Maximum heart rate in beats per minute
(b.p.m.) increased significantly from a pre-
stimulus value of 80.2 to 95.7 (¢=7.57; p<.01)
during the first interval, declined below the pre-
stimulus value during the third and fourth in-
tervals, rose to about the pre-stimulus level during
the fifth, sixth, and seventh intervals, and then
steadily declined during the remainder of the
minute. With the exception of the first interval,
only intervals 11 and 12 differed significantly
(p<.05) from the pre-stimulus value, although
the ¢-values for intervals three (1.68) and four
(1.81) approached significance (p<.10).

Conductance level increased to a maximum
during the first interval and then began a gen-
erally consistent decline throughout the remainder
of the minute. Comparisons of each interval
with the value at the time of stimulation yielded
t-values which were significant (p<.05) for all
intervals.

Of the two physiological measures, heart rate
was the only one which revealed any possible
covariation with the curve of performance re-
covery. This appeared to extend up to at least
the sixth interval. Beyond this the fluctuations
in tracking performance were not. generally
paralleled by any corresponding heart rate
changes. Because of the apparent relationship



tinuous in terms of the stimulus and response,
the measure of performance (integrator resets)
was a discrete measure. In order to plot the
recovery of tracking proficiency following startle,
the number of integrator resets had to be ob-
tained for successive periods of time. From
some initial pilot data, it appeared that a 1-
minute period following startle would be ade-
quate in terms of encompassing the duration of
performance disruption. The same pilot data
also suggested that 5-second scoring intervals
would be reasonable for plotting the recovery of
tracking as well as the physiological data. Con-
sequently, the 1-minute periods following S, and
S. were each divided into twelve 5-second in-
tervals, The number of resets in each interval
of the horizontal and vertical integrators was
then determined for each S. Skin resistance was
measured at the end of each interval and the
values converted to conductance. In addition,
the minimum resistance occurring within the 10-
second period following startle was also obtained
for each S and converted to conductance. This
latter measure constituted a more precise deter-
mination of the magnitude of conductance change
to startle and was used for purposes of inter-
individual comparison. To determine the course
of heart rate recovery following stimulation, the
maximum heart rate (single fastest beat as meas-
ured from the cardiotachometer recording) was
obtained within each interval.

The mean number of horizontal and vertical
integrator resets per 5-second interval was ob-
tained for the 2-minute period immediately pre-
ceding each startle stimulus. This was done for
the purpose of obtaining a stable estimate of
pre-startle tracking performance against which
to compare the change following stimulation.
For heart rate, the maximum rate was obtained
for the 5-second interval immediately preceding
S, and S,. Skin resistance was measured at the
moment of stimulation and converted to con-
ductance.

For the training period, only the performance
data were scored. In order to make the tracking

data comparable to the test phase data, the num- ,

ber of horizontal and vertical resets obtained
during each 2-minute trial. was expressed in
terms of means per 5-second interval. Each $’s
distribution of reaction times to the 15 presenta-
tions of the 1,000 Hz stimulus was obtained and
a median computed. Since no warning signal

was employed with the reaction time stimuli, the
individual distributions were often quite skewed,
and thus the median yielded a better measure of
central tendency than the mean. Medians were
also used for the reaction time data of the test
phase.

The electroencephalographic and eye closure
recordings were used only to monitor possible
changes in levels of wakefulness during the 30-
minute test period. No detailed analyses were
made of these data.

IIL. Results.

Training data. In plotting the data for the
horizontal and vertical tracking error during
training, it was found that the two curves essen-
tially paralleled each other and were highly cor-
related across trials (7=.93; p<.01).. Conse-
quently, there appeared little to be gained by
considering them separately, and they were com-
bined in both the training and subsequent test
phase of the experiment.

The combined error data’ over the 15 training
trials are shown in Figure 2. The scores are
plotted in three-trial blocks with each block rep-
resenting the mean number of integrator resets
per 5-second interval. It is apparent from the
figure that an asymptotic level of performance
was reached at or before the end of training.

For the reaction time data, each S’s median
response time to the 15 stimuli was obtained and
these values averaged across Ss. This yielded a
mean value of 516 msecs.

Response to startle. Figure 3 displays mean
number of integrator resets for the tracking data
during successive 5-second intervals of the first
minute following S,. Also displayed are mean
maximum heart rate and mean conductance level
for each 5-second interval. In addition, mean
spre-stimulus values are given for each variable.
Relative to the pre-stimulus level, tracking error
increased by 65 percent during the first 5-second
interval, This declined to a 16 percent increase
by the second interval. Both increases were sig-
nificant with ¢-values of 5.35 (p<.01) and 3.34
(p<.01) respectively. Error continued to de-
cline up to the fourth interval, with an apparent
rise in tracking error beginning at the fifth in-
terval and then a fall below the pre-stimulus
level by the seventh and for most of the remain-
der of the minute. Of intervals three through


r TRACKING ERROR (TE) 794 13.6
E _~ e—-—o CONDUCTANCE (C) 492 413.4
-* MAX. HEART RATE (MHR) 490 413.2
= 3
488= 413.02
5 €
486 2 412.85
8 =
4842 412.6—
# lead
482% 712.42
5
[ee W223
47ee 41208
476 411.8"
474 16
bec 472. ung
mn L 1 1 1 1 1 1 n 1 1 1 1 0 3 1.2
Peet 2 3 4 5 6 7 8 9 10 WW
Stim.
FIVE - SECOND INTERVALS
Fieure 4. Mean tracking error, maximum heart rate, and conductance level during successive 5-second intervals

following S,. Also shown are pre-startle values for each variable.

to have a facilitative effect on reaction time.
Thus, mean reaction times to S, and S, were
402 msecs. and 401 msecs., respectively, while the
mean of each §’s median reaction time to the
15 nonstartle tones was 462 msecs. Separate com-
parisons of this latter value with mean reaction
times to the two startle stimuli yielded ¢-values
of 3.39 (p<.01) for S; and 4.75 (p<.01) for S:.
The correlations of nonstartle reaction time with
response time to S, and S, were 0.33 (p>.05)
and 0.54 (p<.01) respectively. There was no
evidence of any relationship between either the
nonstartle or startle reaction time measures and
tracking performance as measured either prior
to S, or S. or during the first 5-second interval
following startle. The obtained product-moment
correlations ranged from 0.00 to 0.14.

Although it was not intended to investigate
adaptation effects to startle, and the startle
stimuli were presented only twice with 15 minutes
between presentations to deliberately minimize
any possible adaptation, a comparison of Figures
3 and 4 might suggest that the second startle
stimulus was somewhat less disruptive in its ef-
fects on tracking behavior than the first. Thus,

relative to the pre-stimulus levels, tracking error
rose only 29 percent during the initial 5-second
interval following S., but increased 65 percent
during the same interval following S,. Further,
tracking error following S, was found to be sig-
nificantly less than the pre-stimulus level for
most of the remaining minute; this was not the
case with S,. These differences between S, and
S., however, appeared to be due primarily to
differences in the level of pre-stimulus tracking
error. A comparison of the mean levels revealed
the level prior to S, to be significantly greater
than the level prior to S, (¢=4.71; p<.01). This
increase is interesting in view of the fact that
there were no significant differences between the
pre-stimulus levels for maximum heart rate
(¢=0.29; p>.05) or conductance (t=0.12; p>.05)
which might have indicated a declining arousal
level. Because of the difference in pre-stimulus
tracking performance, it was difficult to compare
the two startle stimuli in terms of either their
immediate effects on performance or possible dif-
ferences in the recovery patterns. There were
several indications, however, which would sug-
gest that S, and S, did not differ appreciably in



AM 69-21

RECOVERY OF MOTOR PERFORMANCE FOLLOWING
STARTLE

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

Approved by Released by
Le. PUSagee uo
J. Roserr Dux, M.D. P. V. Smcxn, M.D.
Cuter, Crvit AEROMEDICAL Feprran Air Surceon
InsrrruTe

October 1969

Department of Transportation

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine



error before startle and vice versa. These find-
ings are consistent with those of several previous
studies. Thus, Vlasak*® found a similar relation-
ship between performance disruption following
startle and level of prior proficiency, with less
proficient Ss being considerably more disrupted
by startle. This held for three out of the four
tasks studied. These included mental subtraction,
choice reaction time, and simple tracing. As
noted earlier, Thackray** also found evidence to
suggest that, with the particular reaction time
task employed, startle tended to exaggerate pre-
existing differences between individuals in their
“nonstartle” response time, i.e., the slow became
slower and the fast responded with even shorter
latencies to startle. Taken together with the
present findings, these results suggest the general
hypothesis that the extent of disruption following
startle is dependent upon the level of task pro-
ficiency prior to startle with greatest disruption
occurring among those who are least proficient
prior to startle.

Although there was some indication of greater
subjective and physiological response to startle
by the HE Ss, the differences were not pro-
nounced and appeared somewhat inconsistent.
Thus, while the differences between the groups
in heart rate response and subjective judgment
were significant for S,, they were not for S.
Also, the two groups did not differ in their con-
ductance change to either S, or S,. Nevertheless,
with the exception of this lack of difference be-
tween the groups in conductance change, the
trends of these differences were in general agree-

10

ment with the previous findings of Sternbach’”
and Thackray.* Both earlier studies found a
tendency for slowness of response to startle
(greater impairment) to be associated with
greater autonomic response. Also, like the pres-
ent study, neither of these previous ones found
any relationship between the extent of perform-
ance disruption to startle and pre-startle levels
of physiological activity.

Evidence of an apparent covariation between
the recovery curves for heart rate and tracking
was found for both S, and S;. For both stimuli
the significant increase in heart rate and tracking
error immediately after startle was followed by
parallel decreases in heart rate and error. The
subsequent secondary heart rate acceleration was
accompanied again by an increase in error, al-
though this was a considerably weaker effect as
shown by the general lack of statistical signifi-
cance. Nevertheless, there are reasons to believe
that the secondary rise in tracking error was
real, Not only did it appear following both
stimuli, but it was also present in the data of
pilot Ss run prior to the experiment. Why the
apparent coupling between these two variables
continued for the initial 20- to 25-second period
following stimulation, and then appeared to dis-
sipate is an interesting question. Certainly there
is evidence to suggest that cardiac-behavioral
coupling can and does occur.****° Lacey®* has
reviewed the evidence for a mechanism whereby
cardiac change can either facilitate or inhibit
sensory input via baroreceptor feedback to the
central nervous system, and the present data may
reflect the operation of such a mechanism.


which the S attempted by means of a stylus, to
trace an irregular line. Startle resulting from
a “klaxon” horn was reported to produce only
momentary disruption of performance lasting
approximately 1 to 2 seconds. It should be noted,
though, that Viasak chose to examine perform-
ance only during the first few seconds following
startle. Thus, the possibility of subsequent dis-
ruption of lesser magnitude was ignored. In
addition, he used what would appear to be a
much simpler “tracking task,” and one which
might reveal more rapid recovery from startle.
Nevertheless, the tracking data of the present
study were re-examined to determine whether the
increase in error during the initial 5-second in-
terval following startle could be attributed pri-
marily to an increase occurring during the first
1 or 2 seconds. The total number of integrations
within each successive second of this interval
was obtained and expressed as a percentage of
the total. For the initial interval following Si,
the percentages were 28, 28, 17, 15, and 12 for
1, 2, 3, 4, and 5 seconds, respectively. Comparable
percentages for S, were 30, 26, 17, 13, and 14.
These data indicate that over 50 percent of the
error during the initial 5-second interval occurred
during the first 2 seconds, and thus tend to sup-
port Vlasak’s findings. Since the total startle
reflex may last from 0.3 to 1.5 seconds, this sug-
gests that at least some of the performance dis-
ruption which takes place within the 5-second
interval following startle may be attributable to
direct. mechanical effects of the startle reflex on
motor control. However, the fact that the present
study showed performance to be significantly
impaired during the second 5-second interval
following startle as well, at least for the first
presentation of the stimulus, would also suggest
that not all of the increase in error can be at-
tributed entirely to a disruption of motor control
resulting from the mechanical effects of the
startle reflex*.

In addition to tracking, Vlasak also studied
the effects- of startle on continuous mental sub-
traction and on simple and choice reaction time.
Subtraction was found to be significantly im-

*Since reaction times were also obtained in the present
study, it could be argued that the response of pressing the
button to the startle stimulus may have contributed to tracking
impairment during the first second following startle. Although
this may have had some effect upon tracking, it is likely that
the effect was quite small, since pilot data indicated that the
actual button response itself resulted in no apparent increase
in tracking error.

paired for 15 seconds following stimulation. For
the reaction time tasks, there were insufficient
data given to determine the precise duration of
impairment, although both were impaired tem-
porarily following startle. As noted earlier,
Woodhead” ** found decrements on a decision
task following sudden noise stimulation which
lasted from 17 to 31 seconds. It would appear
from the results of the present study and from
the few others which also have investigated per-
formance recovery, that the major performance
decrement following startle probably occurs
within the first few seconds. However, a lesser
but significant decrement may last for periods of
from 10 to 30 seconds after startle. There is
some indication that following startle, recovery
of performance on motor tasks may be somewhat
more rapid than recovery of performance on
tasks which are more cognitive in nature, al-
though this must be considered a tentative con-
clusion at present.

Reaction times to the startle stimuli them-
selves were found to be facilitated relative to the
nonstartle reaction times. This was an unex-
pected finding, since two previous studies‘? ** ob-
tained lengthened reaction times to startle. One
possibility might be that the thumb flexion re-
quired as a response in this study was facilitated
by the startle reflex itself, although the mean
reaction times to S, and S, (402 and 401 msecs.,
respectively) were considerably longer than the
times (145 to 195 msecs.) reported by Landis and
Hunt® for the muscular startle reflex to reach the
hand. This would suggest that ‘the obtained
reaction times, while possibly facilitated by
startle, were not simply reflex responses. Puro-
hit! TM has recently argued that reaction time to
startle may be either inhibited or facilitated de-
pending on the extent to which the voluntary
response employed is compatible with the reflex
startle response. This would appear to offer a
reasonable explanation for the discrepancy be-
tween the reaction time data of the present study
and the findings of both Sternbach’” and Thack-
ray,® since these earlier studies employed arm
or hand responses which likely were partially
inhibited by the total startle pattern.

With regard to individual differences, there
was a direct relationship between tracking pro-
ficiency before and after startle, ie., the group
which revealed the greatest error immediately
following startle also had significantly higher



» @ mM DO bh @
T

0. integrator resets/5-sec. int.)
a na nN N © ODO @

TRACKING ERROR (
>
&

TRACKING ERROR (TE) 796 5
513.
e—-—0 CONDUCTANCE (C) 494
413.4
so---* MAX. HEART RATE (MHR) 492
413.2
a 490 _
TN oe Jeg 118°
om=~o a6 412.8 §
4e6 5
We 412.6 =
w 412.48
13 Ji ok
deoe | 8
rea 7!2.08
dg
16" 41g
ns
nn 4
file
fe <A

Pre- 1 2 3 4 5 6

Stim.

FIVE - SECOND INTERVALS

Fievre 3. Mean tracking error, maximum heart rate, and conductance level during successive 5-second intervals
following S,. Also shown are pre-startle values for each variable.

between the initial heart rate and performance
changes, the rise in tracking error (interval four
to interval six) was compared with the heart rate
increase during these same intervals. However,
neither the error increase (¢=1.01; p>.05) nor
the heart rate increase (t=1.81; p>.05) was sig-
nificant.

Figure 4 displays the same variables shown in
Figure 2 except that the data are those for S,..
Tracking error during the first 5-second interval
increased by only 29 percent over the pre-stimulus
level. This increase, however, was significant
(t=2.67; p<.05). By the second interval, error
had decreased below the pre-stimulus level and
remained below during the rest of the 1-minute
period. Comparisons of each interval with the
pre-stimulus value yielded ¢-values which were
significant (p<.05) for intervals three, five, six,
seven, eight, and 11.

Maximum heart rate increased significantly
from a pre-stimulus level of 80.8 b.p.m. to 93.6
b.p.m. during the first interval following startle
(t=7.65; p<.01). It then followed a recovery

pattern similar to that obtained for S, Of in-
tervals two through 12, however, only the third
interval was significantly different from the pre-
stimulus value (¢=2.63; p<.05).

Gonductance level also showed a pattern which
approximated that obtained for the earlier startle
stimulus, and ¢-tests revealed all intervals to dif-
fer significantly (p<.01) from the level at the
time of stimulation.

Once again, it is interesting to note the ap-
parent relationship between heart rate and track-
ing error immediately following stimulation.
After the initial decline, however, the secondary
increase in both heart rate and tracking error
occurred 5 seconds earlier than the corresponding
rise which appeared to follow S;. A comparison
of the heart rate increase between intervals three
and four yielded a significant ¢-value (¢=2.90;
p<.01), but the increase in tracking error which
occurred during these intervals was not significant
(t=1.77; p>.05).

While the immediate effect of startle on track-
ing was a temporary impairment, startle appeared


II. Method.

Subjects. Thirty paid male college students
between the ages of 18 and 25 were employed.
All were right-handed, had no known hearing
loss, and had no prior experience with tracking
tasks.

Apparatus. The basic task apparatus con-
sisted of a console containing an oscilloscope
which constituted the display for a two-dimen-
sional compensatory tracking task. 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 hori-
zontal and vertical deflection plates of the
oscilloscope. The 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 inch in any direc-
tion 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 voltages) 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 track-
ing task was essentially a slightly modified ver-
sion of one previously described by Pearson."

High-intensity noise served as the startle
stimulus and was produced by amplifying the
output of a Grason-Stadler, Model 455B noise
generator. Stimuli for measures of “nonstartle”
reaction time were produced by a General Radio,
Model 1310 oscillator. All auditory stimuli were
presented through Sony Model DR-3A_head-
phones which had been previously calibrated
using an artificial ear. Stimulus levels were
periodically monitored by means of a Ballantine
Labs, Model 300-E voltmeter. Duration of all
stimuli was 114 seconds, and a Friden Model
SP-2 tape reader was used for stimulus sequenc-
ing. Each stimulus activated a Hunter Klockoun-
ter which was stopped when § pressed a button
located on top of the control stick.

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 the S’s chest

and the leads connected to a Beckman Type 9857
cardiotachometer coupler. Skin resistance was
obtained from two Fels zinc-zine sulphate elec-
trodes leading to a Fels Model 22A Dermohm-
meter. One electrode was attached to the palmar
surface of the left hand and the other to the
ventral surface of the left wrist. Current dens-
ity was 22.3 microamps/cm.*. The output of the
Dermohmmeter led to another channel of the
recorder. Beckman miniature biopotential elec-
trodes were attached immediately above and be-
Jow the right eye and direct coupled to the
recorder. This yielded a gross indication of eye
closure as well as blinks. The electroencephalo-
gram was obtained from bipolar placements on
the left occipital and left midcentral regions.
Standard Grass electrodes with Grass electrode
cream were employed.

All equipment, with the exception of that
equipment used by § in actually performing the
tasks, was located outside the S’s room. Figure 1
shows a S instrumented for physiological record-
ing and performing the tracking task.

Procedure. Upon arrival each S received an
audiometric examination, was given a general
description of the tasks he was to perform, and
was told that the purpose of the experiment was
to investigate physiological changes during the
learning and performance of perceptual-motor
tasks. The various electrodes were attached and
S was given detailed instructions concerning the
tasks. He was told that the first or training
phase would consist of a series of 2-minute trials
with a 35-second rest period between each. His
principal task was to try to keep the moving
spot on the oscilloscope as close to center as pos-
sible during the trials. He was further told that
while tracking he would occasionally hear a tone
through his headphones, and that he should re-
spond to each tone by pressing the button located
on top of the control stick. He was informed
that a small red warning light would come on
5 seconds prior to the beginning of each trial.
The S then rested quietly for approximately 8
minutes while the physiological equipment was
adjusted and recordings made of “eyes open”
and “eyes closed” electroencephalographic ac-
tivity.

Fifteen 1,000 Hz, 75 db reaction time stimuli
were presented during the 15-trail training
period. Although the temporal position of each
of these stimuli within trials was randomly de-




RECOVERY OF MOTOR PERFORMANCE FOLLOWING STARTLE

I. Introduction.

Sudden, high-intensity sounds, such as those
produced by sonic booms, can be quite startling.
In view of the increasing interest in possible
detrimental effects of sonic booms, it would ap-
pear important to consider what is presently
known concerning the general effects of startle
on behavior. Although there have been numerous
studies of autonomic or electromyographic re-
sponse to startle,?4°*1* as well as the well-
known work of Landis and Hunt® on the mus-
cular reflex to startle, relatively few studies have
been concerned with the effects of startle on
performance. Thus, while it is generally be-
lieved that startle has a disruptive effect upon
performance, little data are available concerning
the actual extent of disruption resulting from
startle, the rate of recovery, or the characteristics
of subjects (Ss) who differ in their susceptibility
to startle.

Woodhead” **_ employed sudden bursts of
broad-band sound (100-110 db) and studied the
effects of such stimuli on a decision task in which
moving symbols were matched against stationary
ones. Performance was found to be significantly
impaired following stimulation, but recovered to
pre-stimulus levels within 17 to 31 seconds.
Woodhead, however, was more concerned with
the use of sudden, intense noise as a “distractor”
and attempted to reduce the startle qualities of
the stimuli through pre-experimental adaptation.
Consequently there is some question as to whether
these recovery rates would apply to completely
unexpected, startling sounds.

Several other studies have examined the speed
with which individuals can react to startle, with
particular emphasis on identifying possible dif-
ferences between fast and slow reactors. Stern-
bach‘ used a pistol shot and identified a group
of slow reactors (mean response time of 1,695
msecs.) and a group of fast reactors (mean re-
sponse time of 200 msecs.). The slow reactors

were found to be significantly more responsive
to the startle stimulus on a number of autonomic
variables. While the study was not specifically
concerned with determining the over-all mean
response time to startle, it was estimated from
the data given to be approximately 950 msecs.
Thackray’* obtained a mean response time of
893 msecs. to a 120 db auditory stimulus on its
initial presentation, and also obtained evidence
to support Sternbach’s finding of a relationship
between reaction time to startle and autonomic
response. In addition, Thackray found that
startle tended to exaggerate the differences which
exist. between individuals in their “normal” speed
of response, such that Ss classified as slow re-
actors under nonstartle conditions tended to re-
spond more slowly to startle stimuli, while fast
reactors responded more rapidly. This latter
finding, however, was significant only for the
second of the two startle stimuli employed.

The present study was designed to provide ad-
ditional data on the extent and duration of per-
formance disruption following startle, as well as
to examine further the physiological and be-
havioral correlates of Ss who differ in the extent
of disruption. A tracking task requiring con-
tinuous perceptual-motor coordination was chosen
as the principal or primary task. Reaction times
to both startle and nonstartle auditory stimuli
were also obtained as a secondary task. This
latter task was included for purposes of com-
parison with the previous studies of Sternbach”’
and Thackray** and to determine the relationship,
if any, between reaction time to startle and per-
formance impairment on the tracking task. The
startle stimulus was presented twice with suffi-
cient time between presentations to minimize
adaptation effects. A final aspect of the study
was the examination of possible relationships
between the recovery rate of perceptual-motor
performance following startle and the rate of
autonomic recovery.



Qualified requesters may obtain Aviation Medical Reports from Defense Documentation
Center. The general public may purchase from Clearinghouse for Federal Scientific and
Technical Information, U.S. Dept. of Commerce, Springfield, Va. 22151.


REFERENCES

1, Bere, R. L. and Beese-Center, J. G.: Cardiac startle
in man, Journal of Experimental Psychology, 28 :262-
279, 1941.

. Davis, R. C.: Motor effects of strong auditory

stimuli. Journal of Eaperimental Psychology, 38 :257-

275, 1948.

ForsytH, R. P.: Influence of blood pressure on pat-

terns of voluntary behavior. Psychophysiology,

2:08-102, 1965.

. Jones, F. P. and Kennepy, J. L.: An electromyo-

graphic technique for recording the startle pattern.

Journal of Psychology, 32 :63-68, 1951.

Lacey, J. I, and Lacey, B. ©.: The relationship of

resting autonomic activity to motor impulsivity. In,

The brain and human behavior (Proceedings of the

Association for Research in Nervous and Mental

Disease). Baltimore: Williams and Wilkins, 144-

209, 1958.

Lacey, J, I.: Psychophysiological approaches to the

evaluation of psychotherapeutic process and outcome.

In E. A, Rubinstein and M. -B. Parloff (Eds.),

Research in psychotherapy. Washington, D.C.:

American Psychological Association, 1959.

Lacey, J. I,: Somatic response patterning and stress:

Some revisions of activation theory. In M. H.

Appley and R. Trumbull (Eds.), Psychological

stress. New York: Appleton-Century-Crofts, 1967.

Lanpis, OC. and Hunt, W. A.: The startle pattern.

New York: Farrar and Rinehart, Inc., 1939.

Lavmr, A. R. and Surrx, E, A.: A quantitative study

of the relation between pulse and breathing changes

and electrobiochemical responses. American Journal

of Psychology, 44 :732-739, 1932,

Osrist, P. A, Hartman, 8. 1, and Woop, D, M.:

Automatic levels and liability, and performance time

w

~

-

na

10.

11

11,

13.

14.

15.

16.

1.

18.

19.

21.

2. PuROHIT,

on a perceptual task and a sensory-motor task.
Perceptual and Motor Skills, 18 :758-762, 1964,
Pearson, R. G.: Performance tasks for operator-
skills research, FAA Office of Aviation Medicine
Report No, AM 66-19, 1966.

A. P.: Some correlates of inhibition-
facilitation effect on reaction-time due to unexpected
increase in stimulus intensity. Psychonomic Science,
553-54, 1966.

Punonrr, A. P.: Effect of unexpected increase in
stimulus intensity on reaction time of hand with-
drawal. Psychonomic Science, 6:387-388, 1966.
SHocx, N. W. and Scuxarrer, J. M.: Pulse rate
response of adolescents to auditory stimuli. Journal
of Experimental Psychology, 30 :414-425, 1942,
Sixcer, S.: Nonparametric statistics for the behav-
ioral sciences. New York: McGraw-Hill Book Com-
pany, Ine., 1956.

Sxacos, E. B.: Changes in pulse, breathing and
steadiness under conditions of startledness and ex-
cited expectancy. Journal of Comparative Psychol-
ogy, 6 :303-818, 1926.

Srerneacu, R, A.: Correlates of differences in time
to recover from startle. Psychosomatic Medicine,
22 :143-148, 1960.

Tuackray, R. I.: Correlates of reaction time to
startle. Human Factors, 7:74-80, 1965.

Vuiasak, M.: Effect of startle stimuli on performance.
Aerospace Medicine, 40 :124-128, 1969.

Woovurap, M. M.: The effects of bursts of loud
noise on a continuous visual task. British Journal
of Industrial Medicine, 15 :120-125, 1958.

WoopneaD, M. M.: Effect of brief loud noise on
decision making. Journal of the Acoustical Society
of America, 81 :1329-1331, 1959.