* DOT/FAA/AM-88/4 Performance Recovery Following Star

Office of Aviation Medicine A Laboratory Approach To The Study Washington, D.C. 20591 OF Behavioral Response To Sudden

Aircraft Emergencies

(0

MRichard I. Thackray, Ph.D.

Civil Aeromedical Institute

Federal Aviation Administration

•* Odahoma City, OK 73125

*• August 1988

This document is available to the public

through the National Technical Information

Service, Springfield, Virginia 22161.

F)TIC

r Ai:ro~l)- 2e i. LECTE

-- jOCT 2 8 1988p

U.S Department of Transportation

Federal Aviation Administration

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'E FOR,%NNCE RFCOVF7Y FOL. LO8NC STARTLE: A At ,ist 1Q8

!\30RArORY APPROACH TO HE S71UDY OF BEH\VIORA. -'I, ; - ,.

RE,PONSE To SUDDEN .ArRCRAFT ,'.ERrENC1ES

Richard [. T hackra,

F.XA Civil Atr,,medicaL rnsz:iJte

P. 0. Box 25082 4n 3.C I, ;.in,

:)klthoma Cit:,, OK 731_'5

aDomoouig Ager~c., Name 3jmd a.011

Office of Aviation Medicine

Federal Aviation Administration

800 Independence Avenue, S.W.. :4 1,9 ASge-o, &g

Washington, D.C. 2059" I_ I Supplementary 4,11S

This work was performed under tasks AXM-C-69-PSY-21.; AYM-C-82/83-PSY-106 and

XM-C-88-HRR-121.

16 Abitruct

This paper deals with the use of response/recovery rate to auditory start

as a laboratory technique for simulating some of the principal aspects 

the initial shock phase of sudden emergency situations. It is submitt

that auditory startle, with its unexpectedness, pronounced autonom

reaction, fear-like subjective experience, and frequent behavior

disruption, approximates the response pattern to be expected in the initi

shock phase of sudden traumatic emergencies, and that by studying the ti

course of performance recovery following startle, as well as individu

differences in response/recovery rate, we may gain a better understandi

of some of the variables related to extreme reactions displayed 

individuals in real-life emergency situations. Research studies conduct

in our laboratory and in others on performance impairment/recove

following startle are reviewed. These studies include those dealing wi

initial reaction time to the startle stimulus itself, disruption a

recovery rate of perceptual-motor (tracking) performance following startl

and the time-course of performance recovery in information processing tas

after exposure to startle. Data are also presented showing a relationsh

of several individual difference variables to performance response/recove

following startle. These variables include autonomic response to t

startle stimulus and level of task proficiency prior to startle.,/ 

1 7. ey Nord%,1 '),sr,.butom , en

\cc tdento. Document is available to the public -.nerzencv behavior, thr-iih the National Technical

ReDnse time lnflr-nation Service, Snrinvfield, S ca rt1e, ';ryi t n ia 22616.

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Form DOT F 1700.7 8-721 Reproduction of completed page authorised
PERFORMANCE RECOVERY FOLLOWING STARTLE: A LABORATORY APPROACH

TO THE STUDY OF BEHAVIORAL RESPONSE TO SUDDEN AIRCRAFT EMERGENCIES

INTRODUCTION

Aircraft emergencies often occur without prior warning and require rapid

response. Although it is commonly accepted that response times to unexpected

events generally exceed those to comparable events that are anticipated,

actual data on response times to unexpected stimuli or events occurring

infrequently in real-life settings are surprisingly sparse. In one of the

few studies in which such data were obtained, Warrick, Kibler, and Topmiller

(1965) examined the time that it took secretaries to press a button located

9.5 in from their typewritters when the stimulus (buzzer) was sounded without

warning once or twice a week over a 6-month period. Relative to alerted

conditions, the increase in response times when the buzzer was unannounced

was surprisingly small. During the first month, unalerted response times

(Mdn=.8 sec) were about 33 percent longer than response times under alerted

conditions. By the end of the 5-month period, the median unalerted time was

.6 sec, representing only a 22-percent increase over alerted times.

Other stucies of response times to unexpected events have been conducted by

investigators concerned with driver reactions to simulated emergencies. Muto

and Wierwi le (1982), for example, found that braking time to an unexpected

* event, prcsented after prolonged driving, averaged about 1.64 sec when the

event first occurred. By the time the fourth "emergency" occurred, response

times were about equal to baseline response times (approximately 1.40 sec).

Thus, unexpectedness resulted in braking times that were 23 percent longer,

at most, than braking times when the events were anticipated. In a somewhat

similar study, Johansson and Rumar (1971) alst compared braking response

times to expected and unexpected situations. On the average, braking time to

unexpected situations averaged .73 sec; this decreased to .54 sec when the

events were anticipated. Unexpectedness, thus, resulted in response times

that were approximately 35% longer than response times for anticipated

events.

A few reported studies have dealt with simulated nuclear power plant

emergencies. In these studies, process operators in nuclear control rooms

were instructed to respond as rapidly as possible to simulated emergencies

signaled by audible alarms and visual indicators. With signal rates of 1.35

to .35 per hour, response times (estimated from the data given) ranged from

less than I sec to approximately 2.5 sec (Lees and Sayers, 1976).

Of the studies Just discussed, those that have compared response times to

* both expected and unexoerted stimuli are relatively consistent in their

findings. Maximum percent increase in response time due to the factor of

unexpectedness has been found to range from 22 to 35 percent. When the

influence of repetition has been examined, reduction in uncertainty caused

response times to approximate baseline (alerted) conditions. Such findings

lend support to the conclusion reached by Warrick, Kibler, and Topmiller that

* one may be able '% extrapolate to unalerted conditions from data collected

under comparable alerted conditions.

In many types of emergency situations, however, one has not only the factor

of unexpectedness to contend with, but also the additional and potentially

* . .,i i i m i i i I | I I 1 ..
disruptive factor of intense emotional arousal. Actual data with regard to

response time to traumatic emergency events, to say nothing of the

time-course of behavioral recovery following such experiences, are virtually

nonexistent. Part of this is clearly due to the extreme dil'ficulty of

creating under controlled, experimental conditions the particular

perceptual/cognitive events that, because of their meaning or significance to

the individual, are the usual triggers for the emotional reactions assuciated

with real-life emergencies.

RATIONALE FOR THE USE OF STARTLE

A possible technique for circumventing this dilemma involves the use of

startle. Before considering this approach, however, a brief review of the

startie response is warrantea. in essence, the startle reflex is primarily a

muscular response where the complete reaction consists of a series of

involuntary contractions beginning at the head with the eyeblink and rapidly

progressing to the legs. It is typically evoked by impulsive auditory

stimuli (e.g., a pistol shot), although other, and generally less effective

stimuli, such as a jet of ice water, photoflash, and electric shock have also

been found to elicit it (Landis and Hunt, 1939). It always begins within 100

msec of the eliciting stimulus, and may have a duration of .3 sec for a mild

but complete response to approximately 1 to 1.5 sec for an intense reaction

(Ekman, Friesen, and Simons, 1985; Landis and Hunt, 1939). Although the

muscle reflex, described in detail by Landis and Hunt (1939), is often

considered to define the startle pattern in its entirety, the total pattern

includes physiological as well as subjective components. The physiological

response consists of a pronounced, generalized increase in autonomic and

central nervous system activity and has been described in detail by Sternbach

(1960a). This pattern of physiological response, when compared with

autonomic response patterns produced by exercise, the cold pressor test, and

injections of epinephrine and norepinephrine, has been found to closely

resemble the pattern produced by epinephrine injection (Steribach, 1960b).

The feeling state evoked by startle is more difficult to classify. While

often considered to be related to the emotion of surprise (Ekman, Friesen,

and Simons, 1985), others have identified it not only with surprise, hit with

fear and onger as well (Blatz, 1925; Landis and Hunt, 1939; Skaggs, 1926).

Interestingly enough, the epinephrine-like physiological pattern to startle

0 that was noted above is also the characteristic pattern found to be produced

by fear-inducing situations (Ax, 1953; Schacter, 1957). Although agreeing

that the feeling state associated with startle appears closest to fear and

anger, Landis and Hunt (1939) consider that it may be best to define startle

as preemotional. They note that "It does not stand in the same group of

0 phenomena as the major emotions, yet it seems to be closely related to them

and to belong generically in the same field. It is an immediate reflex

response to sudden, intense stimulation which demands some

out-of-the-ordinary treatment by the organism. As such It partakes of the

nature of an emergency reaction, but it is a rapid, transitory response much

more simple In its organization and expression than the so-called 'emotions'"

0 (Landis and Hunt, 1939, p. 153).

In a study concerned with the question of why some individuals seem to

"freeze," while others appear to react almost instantaneously In emergency

situations, Sternbach (1960a) reasoned that startle resulting from a loud

auditory stimulus might be used to approximate the principal components

* 2
(surprise, fear, intense physiological arousal, and temporary behavioral

disruption) that are common to many types of sudden emergencies and hence

provide a technique for studying behavioral recovery following traumatic

events under laboratory conditions. It is generally accepted that sudden

emergencies frequently, if not typically, elicit feelings of fear or anxiety,

and, as we have just noted, a number of studies have demonstrated that

startle does evoke an experience, albeit rather transitory, that has been

identified not only with surprise, but with fear as well. Further, the

physiological response to startle, when compared with the autonomic response

patterns produced by a number of other stressors, has been found to closely

resemble the epinephrine pattern associated with fear-inducing situations.

Taken in conjunction with the Landis and Hunt (1939) belief that the total

startle pattern resembles that of an emergency reaction, it would not seem

unreasonable to believe that studies of response to startle might provide a

useful laboratory approach to the study of human behavior in sudden stress

situations. The present paper adopts this position and reviews research

findings relevant to performance recovery from startle. No attempt is made

here to document the methodological considerations (e.g., stimulus

parameters, modifying variables, differentiation of startle from orienting

and defensive reflexes, measurement requirements) that must be recognized in

carrying out research in this area. Relevant methodological considerations

are reviewed or described by Graham, 1979; Landis and Hunt, 1939; Ekman,

Friesen, and Simons, 1985; Raskin, Kotses, and Bever, 1969, and Thackray,

1972.

RESPONSE TIME TO STARTLE

Using a pistol shot as the stimulus for a required button press response,

Sternbach (1965a) found that response times to startle ranged from 128 to

3,262 msec with a mean (estimated from the data) of 950 msec. Sternbach's

primary concern, however, was not with establishing the actual range or

limits of response time to startle, but rather with investigating

psychophysiological correlates of individual differences in time to respond.

In this regard, he examined physiological resting and response levels of the

10 fastest and slowest reactors to startle. While there was no meaningful

relationship of resting physiological levels to reaction time, fast and slow

reactors differed significantly in their physiological response to startle on

a number of variables; slow reactors showed a significantly greater increase

in systolic blood pressure, pulse pressure, palmar skin conductance, and

heart rate than did fast reactors. In addition to greater autonomic

response, informal statements made by slow reactors (e.g., 01 knew I was

supposed to do something, but I couldn't think of it at first." "I thought I

pressed it at first, then I realized I hadn't." "It took me a moment to

realize what I had to do.') suggested greater cognitive disruption as well;

no such statements were made by the group of fast reactors.

A subsequent study by Thackray (1965) extended the Sternbach study by

including a comparison of response times to high-intensity, startling stimuli

with reaction times to nonstartling auditory stimuli. The principal intent 

of this investigation was to provide baseline data that might be used to

estimate pilot response times to potentially critical situations, such as

unexpected clear air turbulence or a sudden failure in an automatic control

system. Subjects were instructed to respond to any auditory stimulus by

moving a control stick as rapidly as possible to the left and simultaneously 

flipping back a response button located on top of~the stick. The firstd

3 t pecial

.INP I I

/ 91V.
stimulus consisted of an unexpectedly loud burst of 120-db noise; this was

followed by a series of 50 low-intensity auditory stimuli at constant 15 sec

intervalq and a final 120-db stimulus. The mean (893 msec) and range (356 to

1800 msec) of response times to the initial high-intensity stimulus were

similar to those obtained by Sternbach. Like Sternbach, autonomic reactivity

to startle was found to be positively correlated with response time to

startle. The second high-intensity stimulus presented 15 sec after the

series of low-intensity stimuli, and with no indication that anything other

than another low-intensity stimulus would occur, yielded a mean (416 msec)

and range (187 to 1550 msec) of response times that were considerably lower

than that obtai~ied to the first high-intensity stimulus. Interestingly

enough, autonomic response to the second loud stimulus was found to be

inversely related to response time. Thus, while magnitude of autonomic

response to the initial high-intensity sound was directly related to

performance disruption, autonomic response to the second, and subjcctively

less startling sound, was associated with performance facilitation. OCr

might hypothesize that, in accordance with the predictions of activation

theory (Malmo, 1959), arousal level to the initial startle was sufficiently

high to disrupt performance, while the lower arousal associated with the

second startle acted to facilitate performance.

Although positive correlations were found between reaction times to the

low-intensity sounds (Mn=368 msec) and response times to the high-intenslty,

startling stimuli, the most interesting aspect of this finding was that

startle appeared to magnify differences between individuals in their reaction

times to the low-intensity, nonstartlig tones; i.e., slow responders tended

to respond even more slowly, while the fast responded more rapidly to startle

stimulation.

RESPONSE/RECOVERY OF CONTINUOUS PSYCHOMOTOR PERFORMANCE FOLLOWING STARTLE

While the studies described above provide basic information on the time

required to make a discrete, voluntary response to startle, they fail to

indicate whether this time frame encompasses all of the disruptive effects of

startle or whether some disruption may extend beyond this period. Since the

reflex muscle response to startle, depending upon the Intensity of the

reaction, may last from .3 to 1.5 sec (Landis and Hunt, 1939), it is evident

that a major portion of the time required to complete a voluntary response

following startle is a direct result of this reflex interference. To provide

* information on possible disruptive effects of startle beyond this period,

Thackray and Touchstone (1970) studied the recovery rate of continuous

psychomotor performance following startle. In this study, subjects performed

a compensatory tracking task continuously during a 30-min period. A 115-db

burst of white noise occurred unexpectedly 2 min into the session and again

at the middle of the session. Tracking error during the first min following

* the initial startle stimulus is shown in Figure 1. Also shown in this figure

are the response/recovery curves for heart rate and skin conductance.

Although maximum performance disruption occurred during the first 5-sec

measurement period following stimulation, significant (p<.05) impairment was

still present 10 sec after startle.

4
- TRACKING ERROR (TE) 96

-8.8 - .---- CONDUCTANCE (C) 194 3.6

13.4 8.4 -. 0 MAX. HEART RATE (IMHR) -92

8.0 - 15.2

J 8.0 ~ *--.--.-..90 ~ _

~7.6 -* 0I.8

7.2 86

G 12.6E

6.8 -1- 84 5

- -12.4 ' 6.4 o 82 z .... ... 6.0 0 MHR / 2C5.6 - - w 12.0 z

5.2 , 76

4.8 TE "174 11.6

C 1 1.4

"72

4"O-0 70 11.2

Pre- I 2 3 4 5 6 7 8 9 ;0 II 12

Slim

FIVE -SECOND INTERVALS

Figure 1. Mean tracking error, maximum heart rate, and conductance level

during successive 5-sec intervals following startle. Also shown are pre- startle values for each variable.

The disruption in tracking performance, persisting into the 10-sec period following startle stimulation, clearly extended beyond the initial disruption caused by the reflex response itself and would appear to be a manifestation

of a longer lasting, more general physiological/emotional response to the

unexpected noise stimulation. Support for this view is suggested by the

apparent covariation of heart rate with performance that is shown in Figure 1

and that appears to extend at least into the first 30 sec following stimulation. (Incidently, it is of interest to note in this figure that

significant performance improvement occurred during the 8th 5-sec interval

following startle; facilitation at this same location also occurred following

the second startle stimulus. Since neither of the autonomic measures showed

any corresponding change during this time period, some central nervous system

facilitory process is suggested.)

The pattern of performance change and physiological response to the second of

the two startle stimuli, although of somewhat lower magnitude, was quite similar to that shown in Figure 1. Of interest was the finding that

magnitude of tracking error to the two startle stimuli was significantly

correlated (r=.60, p<.01). This enabled us to form two subgroups of subjects whose tracking error following both startle events placed them in either the

top third (high impairment) or bottom third (low impairment) of the combined

distributions. Relative to prestartle tracking performance, it was found

that the high-impairment group almost doubled in their tracking error scores

immediately following startle; the low-impairment group showed little

difference between their prestartle and poststartle levels of tracking error.

With regard to physiological response to startle, the high-impairment group showed significantly greater heart rate acceleration, but the groups did not

differ significantly (p>.05) in conductance change.

5

0 l i • mn llml l H i l ' ..
A study by Vlasak (1969) likewise evaluated individual differences in

psychomotor disruption to startle. Using a simple line-tracing task, Vlasak

studied differences in performance disruption to an unexpected 100-db sound

from a Klaxon horn. His findings were similar to those of Thackray and

Touchstone (1970); performance impairment following startle was related to

prior task proficiency, with less proficient subjects being considerably more

disrupted by startle. As noted earlier, Thackray (1965) also found evidence

to suggest that, with the particular reaction time task employed, startle

tended to exaggerate preexisting 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, the results of these

three studies suggest the general hypothesis that the extent of disruption

following startle is dependent upon prestartle level of performance, with the I greatest impairment occurring among those who are either slowest or least

proficient prior to startle.

Before concluding this section it should be noted that both Vlasak and a

subsequent study by May and Rice (1971) found the total duration of tracking

impairment following startle to be only 2 to 3 sec, which is considerably

* less than that found in the Thackray and Touchstone study. In a

reexamination of their data, Thackray and Touchstone likewise found maximum

impairment to occur within this same time period and concluded that at least

some of the disruption that takes place within the 5-sec period following

startle is attributable to direct mechanical effects of the muscle reflex on

motor control. However, the fact that Thackray and Touchstone found tracking

performance to be significantly impaired for up to 10 sec following startle

clearly demonstrates that disruptive effects transcend the time period that

one might rzasonably attribute to mechanical effects of the startle reflex.

The longer eriod of disruption found by Thackray and Touchstone may have

been due to the use of a more difficult tracking task and/or the use of a

more refined measure of tracking error than was used in either th1 Vlasak or

the May and Rice study.

RECOVERY OF COGNITIVE FUNCTIONING FOLLOWING STARTLE

Although oerceptual-motor recovery following startle appears to be quite

rapid, there is evidence that tasks involving decision making or information

* processing may be impaired for a longer period of time. Thus, Vlasak (1969)

studied the effects of startle on continuous mental subtraction and found

performance to be significantly impaired during the first 30 sec following

stimulation. A similar period of impairment was found by Woodhead (1959,

1969), who obtained decrements on a continuous symbol-matching task lasting

from 17 to 31 sec after startle. The fact that impairment on some tasks

* •following startle may last for at least 30 sec lends further support to our

belief that startle effects may extend considerably beyond the initial period

of motor disruption produced by the reflex response itself.

In all of the startle studies Just reviewed, however, performance recovery

effects were studied only during some portion of the first 60 sec following

*e stimulation. While it is certainly possible that performance impairment does

not extend beyond this time period, startle is known to be accompanied by

rather pronounced autonomic (especially cardiovascular) changes (e.g.,

Thackray and Touchstone, 1970. 1983), and it is conceivable that such changes

could have more lasting effects on performance. Thus, a pronounced discharge

of the autonomic nervous system might have a long-term activating effect l 6
leading to performance facilitation, or, conversely, it might produce a

period of parasympathetic overcompensation resulting In eventual drowsiness

and impaired performanr.

In our most recent study (Thackray and Touchstone, 1983), we used monitoring

and information processing tasks to examine both short- and long-term

performance recovery effects following a simulated emergency situation (a

radar failure) that was accompanied by either a startling or a nonstartling

auditory signal. The subject's primary task was to monitor a simulated air

traffic control (ATC) radar display. One hr into the session a radar failure

occurred that was accompanied by either a loud (10A db) or low level (67 db)

burst of white noise acting as an alarm signal. Subjects were then required

to turn in the chair and begin performing a simple informaticn processing

(serial reaction) task. (The serial reaction task consisted of a self-paced,

four-choice reaction time task in which the subject pressed one of four keys

in response to a centrally displayed number.) Five min of performance on this

task was followed by a return to radar monitoring. In addition to

performance, physiological and subjective measures of startle and arousal

were also obtained. It was hypothesized that performance following the

high-intensity alarm signal (expected to elicit a startle reflex) would be

significantly impaired relative to performance following the low intensity

signal (expected to elicit an orienting-type response).

Heart rate response and subjective ratings of startle were consistent in

demonstrating that the high-intensity signal was clearly startling to

subjects in this group. Conversely, the group exposed to the low-intensity

signal did not rate the signal as startling, and the slight heart rate

deceleration that occurred immediately following stimulation was consistent

with the expectation that this level of noise would produce only an orienting

or s-,rnrira reaction frraham. JQ79). In spite of these differences, however,

both groups showed almost identical patterns of response during the first min

foilowing noise stimulation. Relative to prestimulus performance levels,

mean response times on the serial reaction (SR) task were significantly

elevated only during the first 6 sec following noise; thereafter, performance

returned to prestimulus levels for the remainder of the 60-sec period. A

comparison of the response patterns obtained for the two groups is shown in

Figure 2.

At first glance, this lack of any difference between the startled and

nonstartled groups in mean performance during the first 6 sec following

stimulation would appear to be inconsistent with the findings of our previous

studies and those of others reviewed earlier. Since these results were not

expected, response times during the first 6-sec period were examined more

closely. The time from the onset of the noise signal to Jhe first SR

response was obtained for each subject. These initial SR response times,

which encompass the time required to transition from the radar to the SR

task, were plotted on log probability paper and are shown in Figure 3.

7
.80-

0-- -0 High Itensity Group

.60- 0--- Low Intenlsity Group

1.40 /

Z 1.20-

U

1fl.00 I

.80-/

U .60

0 III IL

Pre- 1 2 3 4 5 6 7 8 9 10

StIm. 6-SECOND INTERVALS

Figure 2. Mean response time for SR performance during successive 6-sec

intervals of the first minute following noise stimulation. Also shown are

prestimulus values.

99

-J 95-

M

0

Cr 75

0-

Li.J 50-

< 25 -

D A High Intensity Group

D 0 Low Intensity Group

I 2 3 4 5 6 7 89 10

TIME (SEC)

Figure 3. Task transition times for the two groups.
AlLnough mean time to make this initial response (designated task transition

time) did not differ among the two groups (2.91 and 2.84 for the means of the

high- and low-intensity groups respectively), Figure 3 clearly suggests a

difference between the groups in range or variability of transition times.

An F test of the variances of the two groups revealed the startled group to

be significantly more variable (F(14/14)=2.61, p<.05) in the time required to

make this initial response. An examination of variability of responses on

the SR task subsequent to this first response, but still within the first

6-sec period following stimulation, revealed variances of .2869 and .1272 for

the high- and low-intensity groups respectively. These values, although in

the same direction as the transition time variances, failed to reach

significance (F(14/14)=2.25, p>.05). The difference between groups in

response variability was thus confined to task transition time.

Analyses of the video-taped recordings taken during noise stimulation

clarified these findings. In the group receiving the nonstartling noise

signal, behavior following stimulation was extremely uniform; subjects slowly

turned in the chair and began performing the SR task. In the high-intensity

(startle) group, there were pronounced individual differences following

stimulation with some subjects appearing dazed and confused by the noise

while others recovered almost immediately and rapidly began performing the

task. The disruptive effect of the loud sound for some subjects combined

with the rapid recovery shown by others apparently balanced the generally

uniform response of the low-intensity group. This also explained the

difference in the variance of response times of the two groups. The

increased range or variability of initial response to startle that was found

in this study is clearly similar to that discussed earlier in the context of

both voluntary reaction time to startle and tracking performance following

startle.

Unlike response times which, except for the initial task transition time,

were largely unaffected by startle, the frequency of incorrect responses

(representing errors in information processing) was found to be significantly

greater in the startled than in the nonstartled group during the first minute

following stimulation. This finding is in general agreement with the

findings of Vlasak (1969) and Woodhead (1959, 1969) mentioned earlier, that

information processing may be impaired during recovery from startle for

periods ranging from 17 sec to over 30 sec. Woodhead (1969) has noted that

30 to 60 sec is the period that it generally takes for autonomic responses

such as heart rate to recover to approximate prestimulus levels following

startle and that it may not be mere coincidence that this corresponds to the

recovery period of cognitive performance.

There was no evidence that startle affected frequency of errors or mean

performance on either the SR taik or on the radar task subsequent to the

first minute following stimulation. Since neither heart rate nor conductance

level differed among the groups during these subsequent periods of SR and

radar performance, it may be concluded that both the physiological and

performance effects of startle are largely confined to the initial 1-min

period following startle stimulation.

9
FIELD STUDIES OF RESPONSE/RECOVERY TO STARTLE

It would be desirable to compare laboratory findings of performance recovery

from startle with the findings of comparable studies conducted in the field.

Unfortunately, such comparisons are few because of the paucity of published

findings. In one of the few field studies of which I am aware that

specifically investigated the effects of startle on performance, Ziperman and

Smith (1975) compared the extent of disruption of driving behavior produced

by unexpected air-bag deployment with that resulting from hood fly-up.

Fifty-one male and female drivers ranging in age from 19 to 74 years were

tested. Although air-bag deployment, accompanied by a shot-like sound, was

experienced as being considerably more startling than hood fly-up, both types

of events produced similar, marked changes in heart rate, blood pressure, and

skin conductance. In spite of pronounced subjective and physiclogical

evidence of startle, drivers apparently retained control of the test vehicle

and were reported to be lucid on questioning less than 10 seconds after

cushion deployment. As stated in their paper, "The average steering-wheel

rotation was 85 degrees during hood fly-up and 72 degrees during cushion

deployment. This degree of steering-wheel rotation would correspond to

approximately 3 to 4 degrees at the tire. In combination with the

lateral-deviation data, it shows that adequate steering control can be and is

maintained in the startle modes tested" (p. 439). Although the effects of

these startling events might appear to be less than one might have expected,

it should be noted that the actual time-course of performance reco,_-y cannot

be determined from the data as reported in this study. There is no

indication, however, that the duration of performance disruption found by

Ziperman and Smith would differ appreciably from that found in our laboratory

stuales.

CONCLUSIONS

If we combine the results of all studies considered thus far, certain

generalizations concerning response/recovery following startling events can

be made:

1. Simple, voluntary responses to startling stimuli or events can generally

be made within 1 to 3 sec following stimulation (Sternbach, 19BOa;

Thackray, 1965). In this regard, mean time to respond to a startling

stimulus may not differ appreciably from mean time to respond to an

unexpected event or stimulus that is simply surprising. It is likely,

however, that the range of response times to the former type of event

will significantly exceed the range of response times to the latter type

of event (Thackray, 1965; Thackray and Touchstone, 1983).

2. More complex perceptual-motor behavior, such as that requiring continuous

psychomotor control, is likely to show maximum disruption during this

same I- to 3-sec period (May and Rice, 1971; Thackray and Touchstone,

1970, 1983; Vlasak, 1969; Ziperman and Smith, 1975), although

significant, but lesser, disruption may still be present for up to 10 sec

following stimulation (Thackray and Touchstone, 1970).

3. Evidence from several studies suggests that the ability to process

information may be impaired for 17 to 60 sec following the occurrence of

a startling event (Thackray and Touchstone, 1983; Vlasak, 1969; Woodhead,

1959, 1969).

10
4. Individual differences in the magnitude of performance impairment

following startle appear (a) directly related to physiological reactivity

to startle (Sternbach, 1960a; Thackray, 1965; Thackray and Touchstone,

1970) and (b) inversely related to level of prestartle task proficiency

(Thackray, 1965; Thackray and Touchstone, 1970; Vlasak, 1969).

In order to evaluate the relevance of the above laboratory and field findings

of response/recovery following startle to behavioral response following

real-life emergencies, it is important to recoSiize that unexpected and

traumatic emergency situations in real life probably involve at least two

phases. The first phase, which could be termed a "shock phase," constitutes

the initial reaction. In this phase, the individual attempts to respond with

immediate behaviors that are intended to cope with or rectify the unexpected

event. While the behaviors employed may appear to be irrational and actually

wcrsen the situation, this is clearly not the intent. With some individuals,

behavior seems to become suspended (affective immobility or "freezing"),

although numerous studies of response to disaster (e.g., Singer, 1982)

suggest that this type of response is the exception rather than the rule.

When it does occur, it appears to be a rather temporary or momentary

response. In some emergencies, the shock phase is followed by a second phase

which could be termed an "evaluative phase." This phase occurs if the

emergency situation has not been resolved during the intial shock phase and

is characterized by an emerging perception or evaluation of the situation in

terms of the individual's ability, or lack of ability, to cope with the

emergency. It is during this phase that panic, if no solution or escape

seems possible, may occur. However, panic, like affective immobility, also

appears to be a relatively infrequent form of disaster response (Singer,

1982).

If one is willing to accept that the emotional/physiological response to

startle can serve to at least approximate the initial shock phase of

traumatic, real-life emergencies, then findings of laboratory studies of

performance recovery following startle may have relevance in predicting the

time course of behavioral recovery following such events and may assist in

our understanding of some of the extreme reactions displayed by individuals

in real-life emergency situations, As we have t.oted, laboratory studies have

isolated several individual difference variables (autonomic reactivity and

level of prior task proficiency) tnat appear to be correlated with

performance recovery from startle. The first of these, autonomic reactivity,

suggests that inherent, constitutional factors undoubtedly play some role in

startle recovery; tie second variable, task proficiency or skill level, would

suggest that some of the performance disruption following startle may be

amenable to training. Research is needed, however, to determine the extent

to which individual differences in response/recovery found in laboratory

studies of startle can serve as useful predictors of disruption/recovery

following simulated emergencies that closely approximate real-life

situations.

11

Thackray, R. I. 1965. Correlates of reaction time to startle. Hum.

Factors. 7: 74-80.

Thackray, R. 1. 1972. Sonic boom exposure effects 11.3: Startle

responses. In R. Rylander (Ed.), Sonic boom exposure effects: Report

from a worksho-p on methods and criteria, Stockholm 1971. J. Sound Vib.

20: 477-544.

A Thackray, R. I. and R. M. Touchstone. 1970. Recovery of motor

performance following startle. Percept. Mot. Skills. 30: 279-292.

Thackray, R. I. and R. M. Touchstone. 1983. Rate of recovery and

subsequent radar monitoring performance following a simulated emergency

involving startle. FAA Office of Aviation Medicine Report No.

l FAA-AM-83-13.

Vlasak, M. 1969. Effect of startle stimuli on performance. Aerosp. Med.

40: 124-128.

Warrick, M. J., A. W. Kibler, and D. A. Topmiller. 1965. Response time

* to unexpected stimuli. Hum. Factors. 7: 81-86.

Woodhead, M. M. 1959. Effect of brief noise on decision making. J.

Acoust. Soc. Am. 31: 1329-1331.

Woodhead, M. M. 1969. Performing a visual task in the vicinity of

reproduced sonic bangs. J. Sound Vib. 9: 121-125.

Ziperman, H. H. and G. R. Smith. 1975. Startle reaction to air-bag

restraints. J. Amer. Med. Assn. 233: 436-440.

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