Technical Report Documentation Poge 

1. Report No. 2. Government Access ion No. 3. Recipient ' s Catalog No. 

FAA-AM-79-24 

4. Title and Subtitle 5. Report Date 

NOVEMBER 1979 

EFFECTS OF NOISE EXPOSURE ON PERFORMP~CE OF A 6 . Perform ing Organi zotion Code 

SIMULATED RADAR TASK 

8 . Performing Organization Report No. 

7. Author' s) 

RICHARD I. THACKRAY AND R. MARK TOUCHSTONE 

9 . Performing Organization Nome and Address 10. Work Unit No. (TRAIS) 

FAA CIVIL AEROMEDICAL INSTITUTE 

P.O. BOX 25082 11. Contract or Grant No . 

OKLAHOMA CITY, OKLAHOMA 73125 13. Type of Report and Period Covered 

12. Sponsoring Agency Name and Address 

OFFICE OF AVIATION MEDICINE 

FEDERAL AVIATION ADMINISTRATION 

800 INDEPENDENCE AVENUE, s.w. 14 . Sponsoring Agency Code 

WASHINGTON, D.C. 20591 

15 . Supplementary Notes 

Work was performed under Task AM-C-79-PSY-76. 

16. Abstract 

The present study examined the effect of noise (radar control room sounds, 80 dBA) 

on the ability to sustain attention to a complex monitoring task. The visual 

display was designed to resemble that of a highly automated air traffic control 

radar system containing computer-generated alphanumeric symbols. Fifty-six men 

and women were divided into four equal-sized groups. Each group was assigned to 

one of four combinations of noise or quiet condition and easy or difficult version 

of the task. In addition to measuring performance (detection latency to specified changes in the alphanumerics), physiological recordings of heart rate and heart rate 

variability and subjective measures of attentiveness, fatigue, tension, annoyance, and boredom were also obtained. With the exception of heart rate variability, no 

significant effects of noise were obtained. Heart rate variability was signifi- cantly lower under the noise than under the quiet condition. This suggests that, 

although performance was unchanged, effort expenditure may have been greater under 

noise. 

17. Key Words 18. Distribution Statement 

Air Traffic Control Noise Document is available to the public 

Effort Performance through the National Technical Information 

Heart Rate Variability Vigilance Service, Springfield, Virginia 22161. 

Monitoring 

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

Unclassified Unclassified 8 

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized 
• 

EFFECTS OF NOISE EXPOSURE ON PERFORMANCE OF A SIMULATED RADAR TASK 

I. Introduction. 

While a considerable number of vigilance studies have investigated the 

effects of noise on performance, surprisingly little useful information has 

resulted from this research. The findings have ranged from adverse effects 

through no effects to beneficial effects on performance. (See 1,2,5,10,11,17 

for reviews.) 

Given this diversity of findings, some have taken the extreme position 

that noise has little or no effect, not only on vigilance performance, but on 

mental or motor performance in general (10,16). An alternative view, however, 

is that noise effects are real but extremely .elusive, and that even slight 

changes in characteristics of the vigilance or monitoring task and/or in 

characteristics of the noises used may significantly alter the obtained 

results (12). If one adopts this latter view, then it would behoove the 

applied investigator to carefully choose noise and task conditions that 

approximate as closely as possible those of the particular operational 

situation of interest. 

The present study was undertaken with this approach in mind, i.e., the 

study sought to determine the possible effects of normal radar control room 

noises on visual monitoring performance using a task designed to simulate the 

display conditions and functional task requirements of a highly automated air 

traffic control radar system. In essence, the task required the observer to 

simply monitor the visual display for infrequent, "critical" changes in alphanumeric symbols. Two conditions of task difficulty were employed. In one 

condition, a constant, readily identifiable critical stimulus was used, while 

the more difficult condition required the observer to detect changes in 

altitude numbers above or below assigned limits. Performance was measured in 

terms of latency to detect critical stimulus changes. In addition to mean 

latency measurements, maximum and minimum latencies were also obtained. The 

results of several previous studies of complex monitoring suggest that 

maximum latencies reflect lapses of attention or failures to maintain scanning 

while minimum latencies provide an estimate of the individual's maximum state 

of alertness at any given period during the course of a monitoring session 

(8,18,21). 

Noise consisted of recordings of sounds obtained from actual radar control 

rooms. Such noise is a composite of speech sounds, whistles, laughs, coughs, 

The authors wish to thank Dr. Robert N. Thompson and Mr. Noal D. May of the FAA 

Industrial Hygiene Program for supplying the noise tapes used 1n this study 

and their assistance in noise measurement. 

1 
telephone bells, etc. The no~se varied about a mean level of 78-80 dBA. This 

level was chosen for two reasons: (i) It approximates the noise levels for 

large Air Route Traffic Control Center (ARTCC) radar rooms during periods of 

high activity (14); (ii) 80 dBA is below the level at which one can expect 

hearing damage even for long-term exposures. 

In addition to studying performance effects, we included a number of 

subjective measures along with measures of heart rate and heart rate variability. These measures were included in order to assess additional effects 

of noise that might be related to changes in performance. 

II. Method. 

A. Subjects. Fifty-six men and women were randomly assigned to four 

groups of equal size: (i) Noise-Low Task Difficulty, (ii) Noise-High Task 

Difficulty, (iii) Quiet-Low Task Difficulty, and (iv) Quiet-High Task 

Difficulty. All subjects (Ss) were selected from the general population (e.~, 

college students, housewives) and were paid for their participation. Their 

ages ranged from 18 to 29 years. None of the Ss had had prior experience with 

the task used or previous training ~n a~r traffic control. 

B. Apparatus and Design. The basic apparatus and task have been 

described in detail in several previous studies (20,21). 

In essence, all task programing and recording of responses were accomplished using a Digital Equipment Corporation PDP-11/40 computer, interfaced 

with a 17-inch cathode-ray tube that served as the S's display. The stimuli 

(targets) consisted of small rectangular "blips" representing the locations 

of given aircraft. Adjacent to each target was an alphanumeric data block, 

which identified the aircraft and gave its altitude and speed. A simulated 

radar sweepline made one complete clockwise revolution every 6 seconds. A 

target was updated as to location and any change in its data block moments 

after the sweepline passed the target's prior location. Critical stimuli 

consisted of a sudden change in a data block as follows: For the low difficulty condition, the S simply looked for the appearance of a 999 (signifying 

a malfunction) in the-altitude portion of a data block, while in the high 

difficulty condition, the S had to search for any altitude whose value 

exceeded 550 (55,000 ft) or was less than 150 (15,000 ft). For both task 

conditions, 10 critical stimuli occurred in each half-hour period, 5 in the 

first 15 minutes and 5 in the second. The S's response to a critical 

stimulus consisted of pressing a button held in the right 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 value. If the S 

failed to detect a critical stimulus within 1 minute, the data block automatically reverted to its previous value. Marker channels on a Beckman Dynegraph signaled the onset of a critical stimulus and the occurrence of the 

required button press. 

2 
• 

f 

Heart rate was obtained from chest electrodes with the leads connected to 

the Dynograph. Pulses from a cardiotachometer coupler were used as inputs to 

the computer for recording heart rate and heart rate variability. 

C. Background Stimulation (Noise). As noted previously, the noise 

condition consisted of tape-recorded sounds obtained from actual radar rooms. 

The radar rooms used were located in the ARTCCs at Fort Worth, Texas, and 

Albuquerque, New Mexico. Using the recordings from both rooms, a single 

30-minute tape segment was made by mixing these separate recordings. The 

purpose of using this composite was to mask virtually all intelligible 

speech. Additional editing .removed all recognizable words. The 2-hour 

recording used for the noise condition consisted of this 30-minute segment 

repeated four times without any noticeable interruption. Repeating the same 

segment in this manner insured a relatively uniform level and quality of 

background noise throughout the experimental session. 

The amplified noise was led to an Acoustic Research (AR2a) speaker located 

6 feet behind the Sat head height. Average noise level at the S's head location was 78-80 dBA-(re 20 ~Nfm2) as measured with a sound level meter. 

Ambient noise in the room (quiet condition) was measured at the same location 

and found to average approximately 57 dBA. 

D. Procedure. The S was seated at a simulated a1r traffic control 

console, which contained-the visual display. Chest electrodes were attached 

and the task instructions administered. If the S was one assigned to the 

noise condition, he/she was told that a continuo~s recording of actual radar 

control room sounds would be played during the task session. The Ss were 

instructed to try to ignore the noise as much as possible, since they were 

told that would be what an actual controller would tend to do. A 9-point 

subjective rating scale was then administered dealing with present feelings of 

attentiveness, fatigue, tension, annoyance, and boredom, followed by a 

4-minute practice period containing six critical stimuli. 

After the 2-hour task session, the S completed a second form of the 

subjective rating scale. This form was-identical to the first except that the 

S was asked to rate each item on the basis of how the S felt near the end of 

the test period just completed. 

E. Measurement of the Performance and Physiological Data. Performance 

data were computer processed and the following measures were obtained on each 

~ for each 30-minute period (all latency measures refer to the time from 

critical stimulus onset to the button press): 

(i) 

(ii) 

stimulus. 

(iii) 

stimulus. 

Mean response latency to critical stimuli correctly identified. 

Single longest latency to a correctly identified critical 

Single shortest latency to a correctly identified critical 

(iv) Number of critical stimuli missed. 

3 
The computer program described in a previous study (19) was used to obtain 

the mean and standard deviation of heart rate for each successive 5-minute 

period. These were then averaged to give values for the four 30-minute 

periods. 

III. Results. 

Figure 1 shows mean, maximum, and m1n1mum detection latencies for the two 

levels of task difficulty under noise and quiet conditions. Analyses of 

variance revealed significant differences between task difficulty levels for 

mean, F(l,52) = 45.29, £ < .01; maximum, F(l,52) = 48.26, E < .01; and 

minimum, F(l,52) = 15.64, £ < .01 detection latencies. Likewise, there were 

significant main effects for 30-minute periods for all three response measures. 

36 

32 

2 8 

24 

IJJ 

0 20 z 

0 

u 

w 16 IJJ 

12 

8 

4 

0 

,0·-----· 

~ 

~ ~ 

~ ___. HIGH DIFFICULTY- NOISE 

~.~ 1>.-1>. HIGH DIFFICULTY- QUIET 

0---o LOW DIFFI CULTY -NOISE 

6 ·- ·6 LOW DIFFICULTY- QUIET 

MAXIMUM LATEN CIES 

0----------o--- --· -----•--

MEAN LATENCIES .- 6 - .-·-· - 6 

9~-..:..:-==.:...-=8==-..:.-------0----------0 - ·- r:: MINIMUM LATENCIES ~=-~-=='! 

~=-· ~ ==~--:..._ _ _ _:_ ____ o---------0 

2 3 4 

30 - MINUTE PERIODS 

FIGURE 1. Detection latencies for the two levels of task 

difficulty under noise and quiet conditions. 

Obtained values were F(3,156) = 7.38, E < .01; F(3,156) = 5.19, £ < . 01; and 

F(3,156) = 3.24, E < .05, for mean, maximum, and minimum latencies respectively. As with our previous studies using this task (18,20,21}, performance 

appears to remain relatively uniform or even improve during the first hour 

with a general increase in latencies during the second. Although the data 1n 

Figure 1 (especially mean and maximum latencies) suggest a slight, general 

superiority of performance under noise for both levels of task difficulty, 

none of the main effects for noise were significant, nor were any of the 

interactions significant (~ > .05). 

4 
With regard to missed stimuli, there was no apparent effect of noise under 

the low task difficulty condition. Thus, one S under the quiet condition 

missed a critical stimulus and two Ss each mis;ed one stimulus under noise. 

For high task difficulty, 10 of the-14 Ss in the quiet condition missed one or 

more critical stimuli, while only 5 of l4 noise-exposed Ss missed one or more 

stimuli. A comparison of the number of ~s in the high difficulty noise and 

high difficulty quiet groups missing no stimuli with those missing one or more 

yielded a chi-square value of 3.59, df = 1. This value approached(£< .10) 

but did not reach the conventional 5-percent level of statistical significance. 

Heart rate data are shown in Figure 2. Analyses of variance revealed a 

significant decline in heart rate across 30-minute periods (F(3,156) = 26.08, 

79 

77 

w 75 

I-

::::> 

~ 73 ~ 

0:: 

w 71 a_ 

(/) 

ti 9 w 

!D 

7 

5 

0 

HEART RATE 

·--------· 

~------------~~, 

-~---- ......... ---------- ....... _ ---o 

._.HIGH DIFFICULTY- NOISE 

.11.-.11. HIGH DIFFICULTY- QUIET 

0---0 LOW DIFFICULTY- NOISE 

lJ..- .lJ. LOW DIFFICULTY- QUIET 

----. 

. ----· ~·------ ·--·--6 ............ lJ.--·----·-lJ.-·- ..a -:::::--·- ----0 

s~ --~----

HEART RATE VARIABILITY 

I I I 

2 3 4 

30-MINUTE PERIODS 

FIGURE 2. Heart rate and .heart rate variability under 

noise and quiet for the two levels of task 

difficulty. 

£ < .01) and a significant increase in heart rate variability (F(3,156 = 

29.42, £ < .01). However, for heart rate variability, there was also a 

significant main effect for noise (F(l,52) = 5.28, £ < .05). As is evident 

from the figure, heart rate variability was lower in noise for both levels of 

task difficulty . There were no other significant main effects for either 

heart rate or heart rate variability and no significant interactions (£ > .05). 

Analyses of variance were also applied to the subjective rating scale 

data. Significant differences between measurement periods were obtained for 

attentiveness (F(l,52) = 97.63, £ < .01), fatigue (F(l,52) = 82.41, £ < .01), 

5 
annoyance (F(l,S2) = 26.16, £ < .01), and boredom (F(l,S2) = 122.04, £ < .01}. 

The increase in tension was nonsignificant (£ > .OS). No significant main 

effects for noise or task difficulty and no significant interactions were 

obtained for any of the above variables(£ > .OS). Statements on the scales 

corresponding to the mean ratings at the completion of the task period 

suggested that the Ss were only slightly bored, were mildly annoyed, felt more 

tired than usual, a~d felt themselves to be reasonably attentive. The actual 

obtained values are not presented because of the lack of significant 

between-group and interaction effects. 

IV. Discussion. 

The results of the present study indicate that typical radar control room 

noise at an average level of 78-80 dBA does not significantly affect 

monitoring performance. However, although performance was unaffected by noise, 

heart rate variability was significantly lower under the noise than under the 

quiet condition. This was true for both levels of task difficulty. Since 

numerous studies have shown ~n inverse relationship between measures of heart 

rate variability and mental load or attentional demands (3,4,7,9,19), the 

lower heart rate variability under noise suggests that greater effort was 

required to sustain attention under noise than under quiet conditions. That 

increasing levels of noise may affect effort expended without affecting 

performance has recently been reported by Dornic, Sarnecki, Larsson, and 

Svensson (6). In the four different tasks studied, all of which required 

concentrated attention, exposure to 70-90 dB of street and office noise 

significantly increased perceived effort but had no significant effect on 

performance. 

If noise exposure in the present study did indeed affect effort expenditure, it is interesting that none of the subjective rating scale measures 

differed as a function of noise. Thus, although no specific measure of 

perceived effort was included, ratings on such seemingly related variables as 

attentiveness, annoyance, and fatigue did not differ among the noise and 

quiet groups. Perhaps the relationship of these variables to perceived 

effort is not that high. Whatever the reasons for the lack of agreement 

between the physiological, performance, and subjective measures used in this 

study, such a finding is not uncommon. As Broadbent (1) has noted, these 

measures frequently do not agree in studies in which noise or some other 

environmental condition is varied. However, while many noise studies have 

been conducted in which some combination of two of the above three kinds of 

measures are compared within a single investigation (lS), studies 

(especially in the area of vigilance research) in which all three are 

examined in the same experiment are virtually nonexistent. Future studies of 

noise and vigilance performance should endeavor to include selected physiological and subjective measures in order to enable a more comprehensive 

assessment of noise effects than is presently available. 

6 
REFERENCES 

1. Broadbent, D.: Effects of Noise on Behavior. In C. M. Harris (Ed.), 

Handbook of Noise Control, New York, McGraw-Hill, 1957, pp. 10-3 to 10-34. 

2. Broadbent, D. E.: Decision and Stress, London, Academic Press, Inc., 

1971, pp. 400-437. 

3. Coles, M.G. H.: Cardiac and Respiratory Activity During Visual Search, 

JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 96:371-379, 1972. 

4. Coles, M.G. H.: Physiological Activity and Detection: The Effects of 

Attentional Requirements and the Prediction of Performance, BIOLOGICAL 

PSYCHOLOGY, 2:113-125, 1974. 

5. Davis, D. R., and G. S. Tune: Human Vigilance Performance, New York, 

American Elsevier Publishing Company, Inc., 1969, pp. 138-156. 

6. Dornic, S., M. M. Sarnecki, T. J. Larsson, and J. C. Svensson: 

Performance and Perceived Difficulty: The Effect of Noise and Distraction. Institute of Applied Psychology, The University of Stockholm, 

Report No. 51, 1974. 

7. Ettema, J. H., and R. L. Zielhuis: Physiological Parameters of Mental 

Load, ERGONOMICS, 14:137-144, 1971. 

8. Johnston, W. A., W. C. Howell, and I. L. Goldstein: Human Vigilance as a 

Function of Signal Frequency and Stimulus Density, JOURNAL OF EXPERIMENTAL 

PSYCHOLOGY, 72:736-743, 1966. 

9. Kalsbeek, J. W. H.: Measurement of Mental Work Load and of Acceptable 

Load: Possible Applications in Industry, INTERNATIONAL JOURNAL OF 

PRODUCTION RESEARCH, 7:33-45, 1968. 

10. Kryter, K. D.: The Effects of Noise on Man, New York, Academic Press, 

1970, pp. 545-585. 

11. Mackworth, J. F.: Vigilance and Habituation, Baltimore, Penguin Books, 

1970, pp. 144-155. 

12. Mirabella, A., and D. A. Goldstein: The Effects of Ambient Noise Upon 

Signal Detection, HU}UW FACTORS, 9:277-284, 1967. 

13. Mulder, G., and W. R. E. H. Mulder-Hajonides van der Meulen: Mental Load 

and the Measurement of Heart Rate Variability, ERGONOMICS, 16:69-83, 1973. 

7 
14. Semmelink, A., and J. M. Clinch: Study of Noise in Air Route Traffic 

Control Center, Flight Service Station, Air Traffic Control Tower and 

Remote Facilities. FAA Systems Research and Development Service Report 

No. FAA-RD-72-47, 1972. 

15. Sharp, L. F., J. F. Swiney, and M. R. Dansby: Behavioral and Physiological Correlates of Varying Noise Environments: Annotated Bibliography. 

Environmental Protection Agency Report No. EPA-600/1-76-038, 

December 1976. 

16. Stevens, S. S.: Stability of Human Performance Under Intense Noise, 

JOURNAL OF SOUND AND VIBRATION, 21:35-56, 1972. 

17. Stroh, C. M.: Vigilance: The Problem of Sustained Attention, New York, 

Pergamon Press, 1971, pp. 31-33. 

18. Thackray; R. I . , J. P. Bailey, and R. M. Touchstone: The Effect of 

Increased Monitoring Load on Vigilance Performance Using a Simulated 

Radar Display, ERGONOMICS, 22:529-539, 1979. 

19. Thackray, R. I., K. N. Jones, and R. M. Touchstone: Personality and . 

Physiological Correlates of Performance Decrement on a Monotonous Task 

Requiring Sustained Attention, BRITISH JOURNAL OF PSYCHOLOGY, 

65:351-358, 1974. 

20. Thackray, R. I., R. M. Touchstone, and J. P. Bailey: Comparison of the 

Vigilance Performance of Men and Women Using a Simulated Radar Task, 

AVIATION, SPACE, AND ENVIRONMENTAL MEDICINE, 49:1215-1218, 1978. 

21 ._ Thackray, R. I., and R. M. Touchstone: Visual Search Performance During 

Simulated Radar Observation With and Without a Sweepline. FAA Office of 

Aviation Medicine Report No. AM-79-12, 1979. 

8 

•