FAA-AM-83-13 

RATE OF INITIAL RECOVERY AND SUBSEQUENT 

RADAR MONITORING PERFORMANCE FOLLOWING 

A SIMULATED EMERGENCY INVOLVING STARTLE 

Richard I Thackray and R. Mark Touchstone 

Civil Aeromedical Institute 

Federal Aviation Administration 

Oklahoma City, Oklahoma 

September 1983 

Document is available to the public through the 

National Technical Information Service 

Springfield, Virginia 22161 

Prepared for 

U.S. DEPARTMENT OF TRANSPORTATION 

Federal Aviation Administration 

Office of Aviation Medicine 

Washington, D.C. 20591 
NOTICE 

This document is disseminated under the sponsorship of the 

Department of Transportation in the interest of information 

exchange. The United States Government assumes no liability 

for its contents or use thereof. 
1. Report No . 2 . Government Access i on No . 

FAA-AM-83-13 

4 . Title and Subtitle 

RATE OF INITIAL RECOVERY AND SUBSEQUENT RADAR 

MONITORING PERFORMANCE FOLLOWING A SIMULATED 

EMERGENCY INVOLVING STARTLE 

Technical Report Documentation Page 

3. Recipient ' s Catalog No. 

5. Report Date 

SEPTEMBER 1983 6. Performing Orgoni zotion Code 

r-:;---:--;---;-;---------------------..C.I ______ --!8 . Performing 0 rgani zati on Report No . 

7. Authorl s) 

Richard I. Thackray and R. Mark Touchstone 

9 . Performing Organi zotion Name and Address 

FAA Civil Aeromedical Institute 

P. 0. Box 25082 

Oklahoma City, Oklahoma 73125 

10. Wo rk Unit No . (TRAIS ) 

11 . Contract or Grant No. 

I 13. Type of Report and Period Covered 

~~------------------------------·------------~----------~ 12. Sponsoring Agency Name and Address 

Office of Aviation Medicine 

Federal Aviation 

800 Independence 

Washington, D.C. 

Administration 

Avenue, S.H. 

20591 

14 . Sponsori ng Agency Code 

15 . Supplementary Notes 

Work was performed under tasks AM-C-82-PSY-89 and AM-C-83-PSY-89. 

16 . Abstract The present study employed auditory startle to simulate the principal 

components (unexpectedness, fear, and physiological arousal) that are common to many 

types of sudden emergencies and compared performance recovery following startle with 

recovery following a nonstartling stimulus. The subject's primary task was to 

monitor a simulated air traffic control radar display. Performance recovery following the emergency (a radar failure signaled by either a loud or low level noise) was 

assessed in terms of response time and error rate on a secondary information processing (serial reaction) task and also in terms of subsequent performance on the radar 

monitoring task. Although the high intensity noise was clearly startling, while 

subjects exposed to the lower intensity noise showed only a surprise reaction, 

subsequent performance of the two noise exposure groups differed significantly in 

only two respects: The variance of initial response times was greater in the 

startled group, and this group had a higher frequency of incorrect responses on the 

serial reaction task during the first minute following stimulation. A comparison of 

these findings with those of other studies of simulated emergencies suggests that 

recovery time for simple perceptual-motor responses during the initial shock phase 

of an emergency is quite rapid (on the order of 1 to 3 s), and this appears to be 

independent of whether or not the emergency is startling and emotionally arousing or 

simply surprising and unexpected. If the shock phase evokes heightened emotionalphysiological arousal as in the case of startle, information-processing ability may 

be impaired for approximately 30 to 60 s following the stimulus event. 

17. Key Words 

Air Traffic Control 

Automation 

Emergency behavior 

Monitoring 

Performance recovery 

19. Security Classif. (of this report) 

Unclassified 

~orm DOT F 1700.7 (8-72) 

Startle 18. Distribution Statement 

Document is available to the public 

through the National Technical 

Information Service, Springfield, 

Virginia, 22161 

20. Security C lassil. (o f th i s page) 21. No . of Pages 2 2. Price 

Unclassified 20 

Reproduction of completed page authorized 
RATE OF INITIAL RECOVERY AND SUBSEQUENT 

RADAR MONITORING PERFORMANCE FOLLOWING 

A SIMULATED EMERGENCY INVOLVING STARTLE 

In proposed highly automated air traffic control systems of the future, 

such as the Automated En Route Air Traffic Control (AERA) concept (6), it is 

anticipated that the controller will become less involved in manual control 

operations and will become more of a systems monitor or systems manager. 

Such a shift in role is not unique to air traffic control; it is becoming 

common to all automated systems as computer technology rapidly advances. In 

some areas, such as nuclear control room operation, these role changes are 

already occurring (13). Operators are being removed from the manual control 

loop to serve as systems monitors whose primary function is to detect 

occasional malfunctions or departures from normal limits, and then take 

corrective action. Thus, in nuclear control rooms and similar highly 

automated systems, a primary responsibility of the operator is to act as a 

backup in case of failure. 

While it is almost axiomatic that engineers and designers of highly 

automated systems will attempt to design such systems as fail-safe as 

possible, it is difficult to anticipate all possible contingencies that may 

arise. As Lees and Sayers (9) point out, there will always remain " ••• a 

residual of events, usually of low probability, against which there is no 

protection either because they were unforeseen or because their probability 

was estimated as below the designer's cutoff level" (p. 332). It is the 

unexpected, low-probability event that the systems monitor is expected to 

handle. Some of these events will undoubtedly be emergency situations, and 

the reliability of humans in rapidly resolving unexpected emergencies, such 

as equipment failures in critical situations, is often stated to be low (9). 

In proposed highly automated air traffic control systems, it is clearly 

important to determine how rapidly and effectively controllers can respond 

to unexpected failure conditions in order to establish redundancy 

requirements and to determine the extent of automated backup needed. 

Although the belief tha~ humans are relatively ineffective in rapidly 

resolving emergency situations is a common one, relatively few studies of 

human performance in emergency situations have actually been conducted. 

Part of this is due to the fact that field data on human reliability in 

general, to say nothing of human reliability in emergencies, are almost 

nonexistent (4). Laboratory studies are difficult to conduct because 

subjects are usually aware that some "emergency" is going to occur and 

because realistic emergencies are extremely difficult to simulate in a 

laboratory environment. 

Of the field studies dealing with emergency behaviors, the earliest 

appears to have been conducted by Ronan (cited in Rigby and Edelman (14)). 

Ronan collected information on 2,790 emergency situations that crew-members 

of multiengine aircraft had encountered. His data suggest that 

approximately 16 percent of the critical actions taken to resolve these 

emergencies either made the situations worse or failed to correct them. 

Rigby and Edelman (14) selected 32 of the more common emergencies listed by 

1 
Ronan and, using a paired-comparison technique, had experienced multiengine 

crew-members identify the most stress-producing item in each pair. The 32 

emergencies were then sc~led according to perceived stress, covering a range 

from mildly stressful to extremely stressful. Since Ronan had listed the 

frequency of effective and ineffective behaviors for each of these 

emergencies, Rigby and Edelman obtained an approximate error rate for each 

emergency by dividing the number of ineffective behaviors by the total 

number of behaviors reported. From a resulting plot of error rates against 

perceived stressfulness of the various emergencies, they arrived at error 

rates ranging from .01 for mildly stressful emergencies to .25 for extremely 

stressful emergencies. The types of emergencies associated with their 

lowest stress category (mildly stressful) appeared to differ little from 

normal behaviors encountered in piloting aircraft. Consequently, they 

consider an error rate of .01 to be a conservative estimate of task 

unreliability under reasonably benign operating conditions. 

Other studies relating to performance recovery in emergency situations 

have dealt with simulated nuclear power plant emergencies. Lees and Sayers 

(9) describe a number of studies carried out by the United Kingdom Atomic 

Energy Authority over a period of years that ranged from relatively simple 

laboratory experiments of response times to warning lights, to simulator 

studies involving response times to realistic fault conditions. Because of 

the differences between experimental situations, it is difficult to 

summarize these results. However, it would appear from the simulator data 

that average response times for the various fault conditions were almost 

always within allowable response times. Thus, values of actual response 

times divided by allowable times ranged from .33 to 2.60, with a mean across 

faults of .87. The mean probability of failing to respond within allowable 

times was .18. A much lower value of .001 was obtained for failure to 

respond rapidly enough to a warning light in the simpler laboratory studies, 

when the allowable response time was 4 s. 

The higher probability of failure obtained in the simulator studies was 

apparently due to the fact that allowable response times were the sum of 

motor or movement times plus the more variable time that it took the 

operator to decide that the fault was uncontrollable, requiring that the 

plant be shut down. In the laboratory studies, decision time was minimal, 

with a mean time to respond (as estimated from the data given) of 

approximately 1 s. 

The remaining studies to be considered have dealt with driver 

response-recovery time to unexpected situations. Ziperman and Smith (26) 

examined driver performance following the unexpected deployment of air bag 

restraining devices. Although there was some initial lateral deviation in 

vehicle travel following deployment (the actual duration and extent of 

deviation were not reported), recovery was quite rapid and no driver's 

lateral deviation exceeded the limits of the driving lane. In a recently 

published study, Muto and Wierwille (11) studied the effects of prolonged 

driving on driver's response time to a simulated emergency. The emergency 

consisted of a sudden deceleration of the lead vehicle in a car-following 

scenario. Mean response time to the initial emergency situation following a 

prolonged driving period was found to be 1.64 s. With repeated practice, 

2 
response times declined significantly to baseline levels. 

From the studies just reviewed, it is apparent that the data on human 

reliability in emergency situations are both extremely meager and, because 

of the different methods and approaches used in assessing reliability, are 

difficult to compare in any meaningful manner. In addition, although 

investigators generally acknowledge the need to incorporate stress into 

studies of performance recovery following simulated emergencies (4), it is 

often very difficult to create in a laboratory the particular 

perceptual-cognitive events that, because of their meaning or significance 

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

associated with real-life emergencies. Yet some way of producing emotional 

stress in simulation studies would appear to be essential if the data are to 

have relevance. 

In an early study by Sternbach (19), it was reasoned that startle 

resulting from a loud auditory stimulus might be used to approximate the 

principal components (unexpectedness, fear, and physiological arousal) that 

are common to many types of sudden emergencies and hence provide a technique 

for studying the time course of behavioral recovery following traumatic 

events under laboratory conditions. It is generally accepted that sudden 

emergencies frequently, if not typically, elicit feelings of fear and 

anxiety, and a number of studies have clearly demonstrated that startle does 

evoke an experience, albeit rather transitory, that is most closely 

identified with fear (2,17). Further, the physiological response to 

startle, 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 (18). This latter pattern has been shown to be the 

characteristic pattern produced by fear-inducing situations (1,15). 

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

response, Sternbach (19) found that behavioral recovery times ranged from 

128 to 3,262 ms with a mean (estimated from the data) of 950 ms. 

Sternbach's primary concern, however, was not with the establishment of mean 

values of response-recovery time to an emotionally disruptive stimulus, but 

rather with investigating psychophysiological correlates of individual 

differences in response time to such stimuli. In this regard, he found that 

greater autonomic response to the high intensity noise was associated with 

slower perceptual-motor recovery from startle. A later study by Thackray 

(20) compared response times to startle with reaction times to nonstartling 

auditory stimuli. The intent of this study was to provide baseline data 

that might be used to establish pilot response times to potentially critical 

situations, such as unexpected clear air turbulence or a sudden failure in 

an automatic control system. Mean response-recovery time (893 ms) to the 

startle stimulus was similar to that obtained by Sternbach, but the 

principal finding was that response times to startle exaggerated differences 

between individuals in their reaction times to low intensity tones, i.e., 

the slow tended to respond slower and the fast responded more rapidly to the 

startle stimulus. 

3 
A subsequent study by Thackray and Touchstone (21) again used startle 

to simulate a sudden aircraft emergency and examined both the magnitude of 

initial disruption in psychomotor coordination and the time course of 

performance recovery. Although tracking performance showed maximum 

impairment during the first 2 s following startle, significant impairment 

was still present 10 s following stimulation. Since the total reflex 

response to startle lasts approximately .3 to 1.5 s (8), it is evident that 

the obtained impairment in tracking, lasting up to 10 s following startle, 

clearly extended beyond the initial disruptive effects of the startle reflex 

itself and would appear to be a manifestation of a longer lasting, more 

general physiological-emotional response to the unexpected noise 

stimulation. 

Other laboratory studies of perceptual-motor recovery following 

startle, however, have failed to find evidence of impairment lasting this 

long. Thus, May and Rice (10) and Vlasak (23), using various types of 

tracking tasks, found that impairment following startle lasted considerably 

less than 10 s, with significant impairment occurring only during the first 

2 to 3 s following stimulation. The longer period of impaired performance 

found by Thackray and Touchstone (21) 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. 

Although perceptual-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 (23) studied the effects of startle on continuous mental subtraction 

and found performance to be signficiantly impaired during the first 30 s 

following stimulation. A similar period of impairment was found by Woodhead 

(24,25) who obtained decrements on a continuous symbol-matching task lasting 

from 17 to 31 s after startle. 

The fact that impairment on some tasks following startle may last for 

at least 30 s clearly indicates that startle effects extend beyond the 

initial period of motor disruption produced by the reflex response itself. 

Given that startle is unexpected, frequently evokes subjective responses 

associated with fear, and produces pronounced physiological arousal, it 

seems reasonable to conclude that startle may indeed provide a laboratory 

technique for studying recovery of functioning following sudden emergency 

situations. 

In all of the startle studies just reviewed, performance recovery 

effects were studied only during the first few min following stimulation. 

While it is entirely possible that performance impairment does not extend 

beyond this time period, startle is known to be accompanied by rather 

massive autonomic (especially cardiovascular) changes, and it is entirely 

possible that such changes could have longer-term effects on performance. 

Thus, a pronounced discharge of the autonomic nervous system might have a 

long-term activating effect resulting in prolonged performance facilitation, 

or, conversely, it might produce a period of parasympathetic 

overcompensation leading to eventual drowsiness and impaired performance. 

4 
The present study was conducted to compare both short- and long-term 

performance recovery effects following a simulated emergency involving 

startle with recovery following a nonstartling emergency situation. This 

latter condition was considered to be a control condition for the purpose of 

establishing a baseline response-recovery pattern to a nonemotional 

"emergency" situation. The subject's primary task was to monitor a 

simulated air traffic control (ATC) radar display. Performance recovery 

following the emergency (a radar failure signaled by either a loud or low 

level noise) was assessed in terms of response time and error rate on a 

simple information processing task and also in terms of subsequent 

performance on the radar monitoring task. In addition to performance, 

physiological and subjective measures of startle and arousal were also 

obtained. It was hypothesized that performance following the high intensity 

noise (expected to elicit a startle reflex) would be significantly impaired 

relative to performance following the low intensity noise (expected to 

elicit an orienting type response). 

Method 

Subjects. Thirty paid university students (16 males and 14 females) 

were randomly assigned, in approximately equal male-female proportions, to 

one of two treatment groups. Subjects ranged in age from 19 to 34 (mean = 

23.5) and none had prior experience with the tasks used or previous training 

in air traffic control. All had 20/20 vision, corrected or uncorrected, and 

all had no reported hearing loss. 

Apparatus. Programing and recording of responses for the primary radar 

task were accomplished using a Digital Equipment Corporation PDP 11/40 

computer. The computer was interfaced with a 17 in (43 em) cathode-ray tube 

(CRT), which served as the subjects' display. The stimuli (targets) 

consisted of 16 alphanumeric data blocks that identified the aircraft and 

gave its altitude and speed. Targets were updated as to location and any 

change in the alphanumerics in a continuous, clockwise manner, such that a 

complete update occurred every 6 s. Critical stimuli consisted of a change 

in a target's displayed altitude to a value greater than 550 or less than 

150. Changes occurred randomly, with 10 critical stimuli in each half-hour 

period. Interstimulus intervals ranged from 1.2 to 7.5 min. Subjects 

responded to a critical stimulus by pressing a button held in their hand and 

then holding a light pen over the critical target. The light pen caused the 

altitude portion of the data block to revert to its previous within-limits 

value. If a critical stimulus was not detected within 1 min, the altitude 

change reverted automatically to its previous value. 

The secondary information-processing task consisted of a simple 

self-paced serial reaction (SR) task. The subject's panel contained four 

lever-actuated microswitches arranged in a row 3 em apart with a 1.9 em 

diameter visual display centrally located over the keys. The visual display 

presented the numbers 1-4 corresponding to keys 1-4 as numbered from left to 

right. A tape reader was used to present the numerical stimuli to the 

subject. Stimuli consisted of a quasi-random series of numbers with the 

restrictions that no number could occur twice in succession and that each 

number occur an equal number of times in the series. The series consisted 

5 
of 300 stimuli and repeated itself automatically. 

Each time a given number appeared, the subject attempted to press the 

corresponding key. If a correct response was made, the tape reader advanced 

and the cycle continued. If an incorrect response was made, the visual 

stimulus did not change until the correct key was pressed. Elapsed time 

between responses as well as incorrect responses were computer recorded. 

The noise burst used to signal the onset of the simulated radar failure 

consisted of a 1 s pulse of amplified white noise produced by a Grason 

Stadler Noise Generator and delivered through an Acoustic Research (AR2a) 

speaker located 1.8 m behind the subject at head height. Noise level at the 

subject's head location was 104 dBA for the high intensity (startle) 

condition and 67 dBA for the low intensity condition. Ambient room noise 

was 57 dBA. 

Heart rate was obtained from chest electrodes placed at midlateral 

locations on the rib cage and the leads connected to a Beckman 

cardiotachometer. Pulses from the cardiotachometer were used as inputs to 

the computer for processing heart rate. Beckman biopotential electrodes 

filled with a saline paste and attached to the volar surfaces of the index 

and middle fingers of the subject's left hand were used for measuring 

conductance level. Leads from these electrodes led to a Beckman Type 9844 

coupler that recorded conductance directly. 

The computer and other recording apparatus were located in an adjacent 

room from which the subject was monitored and video-tape recorded via 

closed-circuit TV. Indirect lighting was used in the subject's room, and 

the level of illumination at the display was 21.5 lux. This level 

approximates that used in operational air traffic control environments. 

Procedure. The subject was seated at a simulated air traffic control 

console containing the visual display, with the SR task located directly to 

the right of the chair. Electrodes were attached and an orientation tape 

played. The orientation stated that this was one of a series of studies 

designed to investigate the role of an air traffic controller in future, 

highly automated systems, and that in this particular study the intent was 

to evaluate performance recovery following an emergency condition (a radar 

failure). 

The instructions for the radar task emphasized the necessity of 

pressing the button immediately upon detection of a critical stimulus. The 

subject was told that a critical stimulus (any altitude value greater than 

550 or less than 150) could occur in any target at any time, regardless of 

the current altitude values of the targets. It was explained that 

occasional large changes in altitude would not normally occur in an actual 

radar system, but that this departure from normal conditions was necessary 

to insure that all targets would be given equal priority in scanning. A 

7-min practice period was then administered. 

6 
Instructions for the SR task described the basic nature of the task and 

emphasized that performance should be as rapid as possible, but not at the 

expense of accuracy. They were told that a noise from the speaker behind 

them would always be the signal to begin performing this task. Three 1-min 

training periods separated by 30-s rest periods were then administered. The 

noise level signaling the start of each training period was always set at 67 

dBA. 

Subjects were then reminded that the purpose of this study was to 

examine performance recovery following an emergency (radar failure) 

condition. They were told that at some time during the 1 1/2- to 2 1/2-h 

period of radar performance (the actual duration of radar performance was 

always 2 h) the targets on the screen would stop moving. At the same time 

they would hear a noise signal from the speaker and a red indicator light on 

the console would be illuminated. When this occurred, they were to 

immediately begin performing the SR task and continue performing it until 

the red indicator light went off. They were informed that the targets on 

the radar screen would commence to move again once the red light was 

extinguished, and they were to resume performance of the radar task at that 

time. Subjects were told that they had been randomly assigned to different 

conditions and that the noise signaling the radar failure would be at the 

same intensity level as used during the practice periods for some subjects, 

but would be at a louder, possibly startling, level for others. 

The radar failure occurred at the end of 1 h of performance on this 

task. The period of time between the failure and resumption of radar 

monitoring was 5 min. After the 5-min period of SR performance, subjects 

resumed radar monitoring for one more hour. At the end of the experiment, 

all subjects rated the degree of startle elicited by the noise signaling the 

failure period. 

Measurement of the Performance and Physiological Data. For the radar 

task, mean time for critical stimuli-correctly detected and the number of 

critical stimuli missed were obtained for each subject for each successive 

30-min of the task. Heart rate was computer processed and the mean rate 

determined for each 30-min period. Conductance level was measured directly 

from the chart recordings at the beginning and end of each of these periods. 

Our previous study of tracking recovery following startle (21) clearly 

suggested that maximum performance effects occurred well within the first 

min following stimulation. Consequently, a fine-line analysis was made of 

mean SR time during each successive 6-s interval for the first min following 

stimulation. To determine the magnitude of change in heart rate and skin 

conductance, as well as the time-course of recovery, maximum heart rate 

(single fastest beat as measured from the cardiotachometer recording) and 

maximum skin conductance level were obtained within each 6-s interval. 

Since it was anticipated that both performance and physiological measures 

would begin to stabilize after the first min following stimulation, mean 

values were used for all measures during the subsequent four, 1-min 

measurement periods of the radar failure period. 

7 
Results 

Initial Performance and Physiological Response to Noise Stimulation. 

Figure 1 shows mean response time for SR performance during successive 6-s 

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

prestimulus levels. (These were obtained from the final min of the initial 

practice period and did not differ significantly (1(28):.18, £ >.05)). 

Relative to prestimulus levels, both noise stimulation groups displayed an 

increase in response time followed by a return to a level at or below 

prestimulus values. Surprisingly, the performance trends shown in this 

figure appear almost identical in the two groups. An analysis of variance 

of the poststimulus data revealed that, although the periods effect was 

significant (f(9/252)=16.17, £ <.01), there was in fact no difference 

between groups and no significant interaction (f <1.00 in both cases). 

0---0 High Intensity Group 

e e Low I ntenslty Group 

1.40 

(/) 

0 

z 1.20 

0 

u 

w 

(/) 

1.80 

1.60 

0 

Pre- 2 3 4 5 6 7 8 9 10 

Stirn. 6-SECOND INTERVALS 

Figure 1. Mean response time for SR performance during successive 6-s 

intervals of the first min following noise stimulation. Also 

shown are prestimulus values. 

Since this finding was not expected, response times during the first 

6-s period were examined more closely. The time from noise stimulation to 

first response (designated the initial response time) was obtained for each 

subject in the two groups. These data, plotted on log normal probability 

paper, are shown in Figure 2. 

For the high intensity group, mean initial response time was 2.91 s, 

while mean time for the low intensity group was 2.84 s. A t test performed 

on these data revealed no difference between the group means (1(28):.24, £ 

8 
>.05). Figure 2 suggests, however, a difference in the variability of 

initial response times in the two groups. Response time variance for the 

high intensity group was .9916, while for the low intensity group the 

variance was .3806. 

>-

I99 

_J 95 

ro 

<{ 

ro 

0 

0::: 75 

a.. 

w 

> 

I-

<{ 25 _J 

:::> 

~ 

:::> 

u 5 

2 3 

t:. High Intensity Group 

• Low Intensity Group 

4 5 6 7 8 9 10 

TIME (SEC) 

Figure 2. Distribution of time to first SR response following noise 

stimulation. 

This difference was significant (f(14/14):2.61, E <.05). The 

significant difference in variances was confined only to initial response 

times. An examination of response time variances during the first 6-s 

period following stimulation revealed variances of .2869 and .1272 for the 

high and low intensity groups respectively. The difference between groups 

was not significant (f(14/14):2.25, E >.05). 

In an attempt to clarify the reasons for this lack of difference in 

initial mean response times accompanied by a significant difference in 

variability, video-tape recordings taken of each subject's response 

following noise stimulation were visually analyzed. In the high intensity 

group, all subjects displayed perceptible movements of the torso, head, and 

arms in accordance with the classic startle pattern described by Landis and 

Hunt (8). Reactions subsequent to the reflex response, however, differed 

markedly among subjects. Some subjects appeared dazed and disorganized by 

the noise, while others recovered almost immediately and rapidly began 

performing the SR task. For the group receiving the low intensity noise 

stimulation, the behavioral response was quite different. There was no 

evidence of startle and, as expected, the typical reaction resembled an 

orienting or surprise response. Following the orienting reaction, virtually 

9 
all subjects in the low intensity group exhibited an almost identical 

pattern. They slowly and deliberately turned in the chair and, in the same 

slow manner, began performing the SR task. There was none of the confusion 

and disorganization displayed by many subjects in the high intensity noise 

group. Thus, analysis of the video-tape recordings clarified the reasons 

for the lack of difference between the groups in mean time to first 

response. The disruptive effect of the loud sound for some subjects 

combined with the rapid recover.y 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. 

Other performance data obtained during the first min following 

stimulation consisted of the mean number of incorrect responses made by each 

group. The obtained mean value for the high intensity group was 3.14 

errors, while the mean for the low intensity group was 1.86. A Mann Whitney 

U test, used because the distributions were highly skewed, revealed this 

difference to be significant (Q=50, E <.05). (There was no difference 

between the groups (Q=70, E >.05) in their frequency of errors during the 

last min of the initial practice period at the beginning of the experiment. 

Mean error rates were 2.07 and 1.36 for the high and low intensity groups 

respectively.) 

Physiological changes during the first min following noise stimulation 

are shown in Figures 3 and 4. Figure 3 shows conductance change and Figure 

4 shows heart rate change. 

w 

u 

z 

16.0 

<{ 14.0 

ru 

::> 

0 12.0 

z 

0 

u 

10.0 

9.0 

--·' '\ 

' 'o ... ...... 0 ... _ 

... o .... .......... o_ o ---o--- ' ....... 

0---0 High Intensity Group 

• • Low Intensity Group 

o .... ..... 0 

0 ~----L---~--~--~--~----~--~--~--~--~ 

PreStim. 

2 3 4 5 6 7 8 

6- SECOND INTERVALS 

9 10 

Figure 3. Mean maximum conductance level during successive 6-s intervals of 

the first min following noise stimulation. Also shown are prestimulus values. 

10 
110 

100 

w 

~ a:: 90 

r0:: 

<( 

w 

I 

0---0 High Intensity Group 

e e Low Intensity Group 

0~--_L __ _L __ _L __ ~--J---~--~--~--~~ 

Pre- 2 3 4 5 6 7 8 9 10 

Stim. 6-SECOND INTERVALS 

Figure 4. Mean maximum heart rate during successive 6-s intervals of the 

first min following noise stimulation. Also shown are prestimulus 

values. 

Prestimulus values are also shown in both figures. Separate ! tests 

performed on the prestimulus values for heart rate and conductance level 

revealed no significant differences (£ >.05) between groups. Analysis of 

variance performed on the poststimulus conductance data of Figure 3 revealed 

a significant periods effect (f(9/252)=75.36, E <.01), but no difference 

between groups and nq interaction effect (f <1.00 in both cases). Quite 

different results were obtained for the heart rate data, however. The 

analysis of variance revealed significant differences between groups 

(F(1/28):10.42, p <.01), periods (F(9/252)=12.22, p <.01), and a significant 

interaction effect (F(9/252:6.61, p <.01). Examination of the data for the 

high intensity group-in Figure 4 reveals a typical heart rate response to 

startle. There is pronounced initial cardiac acceleration followed by an 

abrupt decline or rebound effect of almost equal magnitude. This is 

followed by a rather large secondary acceleration and slow deceleration. 

The data for the low intensity group, on the other hand, show considerably 

less initial acceleration followed by gradual decline and slow recovery to 

prestimulus level. To clarify further the differences in heart rate 

response, beat-by-beat patterns evoked by the two stimulus intensities are 

shown in Figure 5 as deviations from prestimulus beat 1. Since orienting 

responses can be differentiated from startle responses by the direction of 

the initial heart rate change following stimulation (7), only the initial 

changes were analyzed. 

11 
22 

o-o 

I \ 

E 18 I \ Q. I ..c \ I 

0 \ w I \ 1-

<t I o, 0:: I s I 'o-o 1- 10 

~l \ 0:: 

<t \ w \ J: \ z 6 d 0 - \ w I 

C> I z 2 I <t 

J: I u 0 

0--0 High Intensity Group 

-2 .,__.... Low Intensity Group 

-I I 2 3 4 5 6 7 8 9 10 II 12 13 14 15 

SUCCESSIVE BEATS 

Figure 5. Beat-by-beat changes in mean heart rate from prestimulus beat 1. 

Relative to prestimulus rate, heart rate decreased (l(13)=1.82, E <.05, 

one-tailed) in the low intensity group and increased (l(13)=2.71, E <.01, 

one-tailed) in the high intensity group. The direction of these changes is 

consistent with the expected direction of change for orienting and startle 

responses respectively (7). The fact that conductance change did not differ 

in the two groups is not necessarily inconsistent with the heart rate data. 

Although magnitude of skin conductance change is often found to be 

proportional to stimulus intensity (3,12), conductance change, being 

unidirectional, cannot be used to differentiate orienting from startle 

reactions (7), and orienting reactions of magnitudes comparable to startle 

responses are often evoked by weak stimulus intensities (5). 

Subsequent Performance and Physiological Response to Noise Stimulation. 

Mean SR response time, heart rate, and conductance level were also obtained 

for min 2 through 5 following noise stimulation. These data are shown in 

Table 1. SR performance increased significantly (F(3/84):3.74, p <.05) for 

both groups during this time frame and probably reflected a fatigue effect. 

Conductance level also increased (F(3/84)=39.33, p <.01), while heart rate 

showed no change (f(3/84):1.66, £ ).05). There were no differences between 

the groups in serial reaction performance, heart rate, or conductance level, 

and no significant interaction effects (f <1.00 in all cases). 

12 
TABLE 1. Mean Serial Reaction Time, Heart Rate, and Conductance Level for 

Minutes 2 Through 5 Following Noise Stimulation 

Measure 

Serial Reaction 

(seconds) 

Conductance 

(micromhos) 

Heart Rate 

(beats per min) 

Groups 2 

High Intensity .7533 

Low Intensity .7553 

High Intensity 11.56 

"' Low Intensity 11.39 

High Intensity 77.3 

Low Intensity 74.9 

Minutes After Noise --

1 4 5 

• 7393 .7613 .7720 

.7440 .7480 .7673 

10.56 10.06 9. 77 

10.70 10.31 10.21 

77.2 78.4 78.6 

75.7 75.7 75.8 

Frequency of errors (not shown in Table 1) for the serial reaction task 

was summed across min 2 through 5 and divided by 4 to give the mean number 

of incorrect responses per minute of each group. The obtained means were 

2.70 and 2.62 for the high and low intensity groups respectively. A Mann 

Whitney Q test revealed no difference between the groups (Q=82, E >.05). 

Mean performance on the radar task across the 2-h session is shown in 

Figure 6. 

18.0 

0--0 High Intensity Group 

...._._..Low Intensity Group 

16.0 

(/) 

0 14.0 

z 

0 

(.) 

w 12.0 (/) 

10.0 o----

9.0 

0 

2 3 4 

30-MINUTE PERIODS 

Figure 6. Mean target detection time on the radar monitoring task across 

the 2-h session. 

13 
The general increase in detection time, common to both groups across 

the session, is a typical pattern that has been found in all of our previous 

studies with this task, e.g., Thackray & Touchstone (22). An analysis of 

variance showed this period's effect to be significant (F(3/84)=13.02, E 

<.01). However, there was no difference between groups (f <1.00) and, more 

importantly, there was no significant interaction of groups by periods (F 

<1.00). With regard to omission errors, five subjects in each group missed 

one or more critical stimuli during the first hour of radar performance. 

During the second hour, seven subjects in the high intensity and five 

subjects in the low intensity group missed one or more stimuli. A 

chi-square analysis revealed this difference between groups during the 

second hour to be nonsignificant (E >.05). Thus, the different noise 

intensities to which the two groups were exposed had no differential effect 

on either mean performance or omission errors during subsequent radar 

monitoring. 

Mean heart rates and conductance levels across the 2-h radar monitoring 

session are shown in Table 2. 

TABLE 2. Mean Heart Rate and Conductance Level During Each 30 Minute 

Period of Radar Monitoring 

Measure 

Conductance 

(micromhos) 

High Intensity 9.46 

Low Intensity 10. 14 

30 Minute Periods 

2 

9.23 

9.87 

8.58 

9.48 

4 

8.13 

8.80 

High Intensity 80.61 79.53 76.13 

73.65 

75.02 

Heart Rate 

(beats per min) Low Intensity 78.34 76.13 72.76 

Analyses of variance revealed a significant decline in heart rate 

(f(3/84:41.31, E <.01) and in conductance level (f(3/84):18.31, E <.01). 

There were no significant interaction effects for either variable and no 

differences between groups in either heart rate or conductance level (F 

<1.00 in all cases). -

Subjective Response to Noise Stimulation. Subjective ratings of 

startle, obtained at the completion of the experiment, appeared clearly 

different among the groups. The mean value for the high intensity group was 

6.9 (corresponding to a rating of "very startled"), while for the group 

receiving the low intensity noise, the mean value was 2.9 (corresponding to 

a rating of "only slightly startled"). At test performed on these data 

revealed the difference to be significant (1(28):6.56, E <.01). 

14 
Discussion 

Video-tape recordings, heart rate response, and subjective ratings of 

startle were consistent in demonstrating that the high intensity noise 

signal was clearly startling to subjects assigned to this group. 

Conversely, the group exposed to the low intensity noise exhibited no 

behavioral evidence of startle, and the direction of initial heart rate 

change was consistent with the expectation that this level of noise would 

produce only an orienting or surprise reaction. In spite of these 

differences, however, at no time during the first min following the noise 

signaling a radar failure did response times on the secondary SR task differ 

in the two groups. 

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

nonstartled groups in mean performance during the first min following 

stimulation would appear to be inconsistent with the findings of other 

startle studies reviewed earlier. Previous studies of perceptual-motor 

recovery following startle have found a period of impaired performance 

lasting from 1 to 10 s following intense noise stimulation. It should be 

noted, however, that in all of these studies startle was introduced during 

the performance of some form of continuous tracking task and that the period 

of maximum impairment was always confined to the first 1 to 3 s following 

startle. In the present study, the noise used constituted a signal that a 

radar failure had occurred requiring a transition from the primary 

monitoring task to the secondary SR task. Mean time to make this transition 

was 2.91 s in the startled group, a value clearly within the period of 

maximum tracking impairment reported in the earlier studies. Consequently, 

it would appear that the primary disruptive effects of startle occurred 

during, or were confined to, the time period from stimulation to the first 

SR response (the task transition period), and it is thus not too surprising 

that no differences were found between the groups in mean SR performance 

during the first min following noise exposure. Interestingly enough, 

however, task transition time was found to be no greater in the startled 

than in the nonstartled group. As discussed earlier, analysis of the 

video-tape recordings taken during noise stimulation revealed the reason for 

the lack of difference. 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 

startled 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 extreme reactions to the high intensity noise were apparently 

balanced out by the far more uniform behavioral reaction to the low 

intensity noise resulting in a difference between groups in the variance of 

initial response times, but not in mean values. 

Although mean response times were not adversely affected by startle, 

frequency of errors on the SR task was significantly greater in the startled 

than in the nonstartled group during the first min following stimulation. 

This finding is in general agreement with the findings of Vlasak (23) and 

Woodhead (24, 25) reported earlier, that information processing may be 

impaired during recovery from startle for periods ranging from 17 s to over 

30 s. 

15 
There was no evidence that startle affected frequency of errors or mean 

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

min following stimulation. Since neither heart rate nor conductance level 

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

performance, it would appear that the physiological and performance effects 

of startle are quite transitory and are largely confined to the first min 

following the startling event. 

It would be desirable to compare laboratory findings of recovery from 

startle with the time course of performance recovery following other forms 

of simulated emergencies. Unfortunately, few such comparisons can be made 

because of the paucity of published findings. Of the studies that have been 

reported, the most comparable appear to be those dealing with driver 

reactions to sudden emergencies or startling events. As previously noted, 

Ziperman and Smith· (26) found that explosive deployment of air bag 

restraining devices caused only momentary disruption of vehicle travel, and 

Muto and Wierwille (11) found that mean initial braking time to an 

unexpected driving emergency, presented after a prolonged period of 

uneventful driving, was 1.64 s. Other relevant studies have dealt with 

simulated nuclear power plant emergencies. In these studies, process 

operators in nuclear control rooms were instructed to make a pushbutton 

response as rapidly as possible to simulated emergencies signalled by 

audible alarms and visual indicators. With signal rates of .35 to 1.35 per 

hour, response times (estimated from the data given) were quite short and 

ranged from less than 1 s to approximately 2.5 s (9). 

Laboratory studies of performance recovery following startle are not 

completely analogous to studies of simulated nuclear power plant emergencies 

or even driver response to unexpected situations. Yet, all of these studies 

suggest that performance following unexpected, and often traumatic, 

situations is not nearly as disrupted as is frequently believed, with 

initial recovery of perceptual-motor functioning typically occurring within 

the first few s following the emergency or unexpected event. 

In evaluating these findings with regard to their applicability to 

emergency behaviors in real-life situations, it is important to recognize 

that unexpected emergency situations in real life may involve at least two 

phases of behavioral response. The initial phase, which could be termed a 

"shock phase," is one in which the individual attempts to react to the 

unexpected situation as rapidly as possible with immediate behaviors 

designed to cope with or rectify the unexpected event. It is during this 

phase that emotional-physiological reactions to the emergency may produce 

behavioral disruption or even temporary immobility. 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 initial shock phase and is characterized by an 

emerging perception or evaluation of the situation in terms of the 

individual's ability to cope with the emergency. If it becomes apparent 

that there is no satisfactory means of coping with the situation, panic may 

occur. 

16 
It is evident that findings of studies of performance disruption 

following startle, such as the present one, would be relevant only to the 

initial recovery period or shock phase of a sudden emergency event. This 

would seem to be the case also with the studies simulating nuclear control 

room emergencies and driver response to unexpected situations that were 

cited earlier. Taken together, these studies suggest that perceptual-motor 

disruption immediately following a simulated emergency or startling event is 

relatively short-lived; task relevant responses are generally initiated or 

completed within 1 to 3 s following onset of the event, and there is little 

or no evidence of significant perceptual-motor impairment beyond this period 

(9, 10, 11, 19, 20, 23, 26). There is suggestive evidence, however, that 

cognitive behaviors may be impaired for a longer period of time, since 

several startle studies, including the present one, have found impairments 

in information processing lasting from 17 to 60 s following a startling 

event (23, 24, 25). 

If it is accepted that the emotional-physiological response to auditory 

startle can serve to at least approximate the shock-phase reaction normally 

triggered by particular perceptual-cognitive events in real-life 

emergencies, then the use of startle may prove to be a relatively simple 

laboratory technique for studying performance disruption and rate of 

recovery on a wide variety of tasks. In addition, studies of individual 

differences in response-recovery from startle could assist in our 

understanding of some of the extreme reactions displayed by individuals in 

real-life emergencies. In natural disasters, for example, about 12 to 25 

percent of individuals remain completely "cool and collected" during the 

initial response phase, while about the same percentage show maladaptive 

responses such as confusion, paralyzing anxiety, and hysterical reactions 

(16). As noted earlier, previous laboratory studies have isolated several 

individual difference variables (autonomic reactivity and simple reaction 

time) that appear to be correlated with response-recovery from startle (19, 

20, 21, 23). Such variables suggest the existence of inherent, 

constitutional factors that may be related to the ability to respond rapidly 

and effectively to real-life sudden stress situations. Further research is 

needed, however, to determine the extent to which such variables, uncovered 

in laboratory studies of startle, can serve as useful predictors of 

performance recovery following simulated ATC emergencies that closely 

approximate real-life situations. 

17 
1. Ax, A. A. 

in humans. 

REFERENCES 

1953. The physiological differentiation between fear and anger 

Psychosom. Med. 15: 433-442. 

2. Blatz, w. E. 1925. The cardiac, respiratory, and electrical phenomena 

involved in the emotion of fear. ~ Exp. Psycho!. 8: 109-132. 

3. Davis, R. c., A. M. Buchwald, and R. w. Frankmann, 1955. Autonomic and 

muscular responses, and their relation to simple stimuli. Psycho!. Monogr. 

69: 1-71 (20, Whole No. 405). 

4. Embry, D. E. 1976. Human reliability in complex systems: An overview. 

Birmingham, United Kingdom: Applied Psychology Department, University of 

Aston in Birmingham, AP Report No. 61. 

5. Gogan, P. 1970. The startle and orienting reactions in man. A study of 

their characteristics and habituation. Brain Res. 18: 117-135. 

6. Goldmuntz, L. w., J. T. Kefaliotis, L. A. Kleiman, R. A. Rucker, L. 

Schuchman, and D. Weathers, 1981. The AERA concept. Washington, D.C.: 

FAA Office of Systems Engineering Management, Report No. FAA-EM-81-3. 

1. Graham, F. K. 1979. Distinguishing among orienting, defense, and startle 

reflexes. In: H. D. Kimmel, E. H. van Olst, and J. F. Orlebecke 

(Eds.), The-orienting Reflex in Humans. New York: Erlbaum Associates. 

8. Landis, c. and w. A. Hunt, 1939. The startle pattern. New York: Farrar 

and Rinehart. 

9. Lees, F. P. and B. Sayers, 1976. The behavior of process operators under 

emergency conditions. InT. B. Sheridan and G. Johannsen (Eds.), 

Monitoring Behavior and Supervisory Control. New York: Plenum Press. 

10. May, D. N. and C. G. Rice, 1971. Effects of startle due to pistol shots 

on control precision performance. ~ Sound Vib. 15: 197-202. 

11. Muto, w. H. and w. w. Wierwille, 1982. The effect of repeated emergency 

response trials on performance during extended - duration simulated driving. 

Hum. Factors. 24: 693-698. 

12. Raskin, D. c., H. Kotses, and J. 

orienting and defensive reflexes. 

Bever, 1969. Autonomic indicators of 

~ Exp. Psycho!. 80: 423-433. 

13. Rasmussen, J. and w. B. Rouse (Eds)., 1981. Human detection and 

diagnosis of system failures. New York: Plenum Press. 

14. 

15. 

Rigby, L. V. 

emergencies. 

and D. A. Edelman, 1968. A predictive scale of aircraft 

Hum. Factors. 10: 475-482. 

Schacter, J. 1957. Pain, fear, and anger in hypertensives and 

normotensives. Psychosom. Med. 19: 17-29. 

18 
16. Singer, T. J. 1982. 

a psychological nature. 

An introduction to disaster: Some considerations of 

Aviat. Space Environ. Med. 53: 245-250. 

17. Skaggs, E. B. 1926. Changes in pulse, breathing and steadiness under 

conditions of startledness and excited expectancy. ~ Comp. Psychol. 6: 

303-318. 

18. Sternbach, R. A. 1960. A comparative analysis of autonomic responses to 

startle. Psychosom. Med. 22: 204-210. 

19. Sternbach, R. H. 1960. Correlates of differences in time to recover from 

startle. Psychosom. Med. 22: 144-148. 

20. Thackray, R. I. 1965. 

74-80. 

Correlates of reaction time to startle. Hum. 

21. 

Factors. 7: 

Thackray, R. I. and R. M. Touchstone, 1970. 

performance following startle. Percept. Mot. 

Recovery of motor 

Skills. 30: 279-292. 

22. Thackray, R. I. and R. M. Touchstone, 1980. Visual search performance 

during simulated radar observation with and without a sweepline. Aviat. 

Space Environ. Med. 51: 361-366. 

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

40: 124-128. 

24. 

25. 

26. 

Woodhead, M. 

visual task. 

Woodhead, M. 

Acoust. Soc. 

-- Ziperman, H. 

restraints. 

M. 

Br. 

M. 

1958. 

J. 

1959. 

The effects of bursts of noise on a continuous 

Ind. Med. 15: 120-125. 

Effect of brief loud noise on decision making. 

Amer. 31: 1329-1331. --

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

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

19 

Jr.