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Original Article
The Effect of Noise on
Human Performance: A
Clinical Trial
P Nassiri1, M Monazam1, B Fouladi Dehaghi1,
L Ibrahimi Ghavam Abadi2, SA Zakerian1, K Azam3
1Department of Occu-
pational Health, School
of Public health, Tehran
University of Medical
Sciences, Tehran, Iran
2Department of Environ-
mental Management,
Islamic Azad University,
Science and Research
Branch, Khouzestan-
Iran
3Epidemiology and Bio-
statistics Department,
School of Public Health,
Tehran University of
Medical Sciences,
Tehran, Iran
Correspondence to
Behzad Fouladi De-
haghi, PhD, Depart-
ment of Occupational
Health, School of Public
Health, Tehran Uni-
versity of Medical Sci-
ences, Tehran, Iran
E-mail: bdehaghi@
gmail.com
Received: Dec 13, 2012
Accepted: Feb 25, 2013
Cite this article as: Nassiri P, Monazam M, Fouladi Dehaghi B, et al. The effect of noise on human perfor-
mance: A clinical trial. Int J Occup Environ Med 2013;4:87-95.
Abstract
Background: Noise is dened as unwanted or meaningless sound that apart from auditory
adverse health effects may distract attention from cues that are important for task perfor-
mance. Human performance is inuenced by many job-related factors and workplace condi-
tions including noise level.
Objective: To study the effect of noise on human performance.
Methods: The participants included 40 healthy male university students. The experimental
design consisted of 3 (sound pressure level) x 3 (noise schedule) x 2 (noise type) factors. To
investigate occupational skill performance, some specic test batteries were used: 1) steadi-
ness test, 2) Minnesota manual dexterity test, 3) hand tool dexterity test, and 4) two-arm
coordination test. Time duration of test completion was measured as speed response; to
determine error response, the time taken during committing an error by participants while
performing a task was measured.
Results: Speed response obtained from the 4 tests in combined conditions of noise sched-
ule, harmonic index, and sound pressure level was highest for (intermittent, treble, 95 dB),
(continuous, treble, 95 dB), (continuous, treble, 85 dB) and (intermittent, treble, 95 dB),
respectively.
Conclusion: Treble noise was found signicant in reducing human performance; also, inter-
mittent noise, especially at high pressure levels, was responsible for worsening environmen-
tal conditions during performing a task.
Keywords: Noise; Occupational employee performance appraisal; Psychomotor perfor-
mance; Environmental exposure
Introduction
Noise—generally defined as un-
wanted and unpleasant sound—
usually disrupts the activity or bal-
ance of human life. Nowadays, with fast
growth of industrial and technological ad-
vancements, humans face noise pollution
in their working and living environments
as a major problem. This growing concern
has proved causing health hazards apart
from hearing loss in exposed people.1-6
Research has demonstrated that the pres-
ence of industrial noise has serious conse-
quences on the performance and produc-
tivity of workers.7-11 Despite this barrier in
achieving maximum productivity and ef-
ficiency, industries try hard to cope with
such problems and achieve the highest
levels of profit.12 Between the measures of
www.theijoem.com Vol 4 Number 2; April, 201388
article
Noise and Human Performance
job performance, worker productivity is
an important one and severe adverse en-
vironmental conditions can restrict work-
er productivity to a large extent.12-16
Human performance is under the influ-
ence of many factors such as job type, job
complexity level, job context and working
conditions such as heat, light, humidity,
dust, pollution and noise.12,15
Constant exposure to these environ-
mental stressors in the workplace can
lead to adverse effects on human perfor-
mance as they would cause problems in
concentration, adverse health outcomes,
etc,11,12,15 which all affect workers' health,
comfort and performance. The latter is of
major concern as it affects productivity
and efficiency of the worker, hence lead-
ing to a loss of profit for any company or
industry.17
As it is stated by many studies, the ef-
fect of noise on human performance is
very complex.18-22 The effect of noise on
task performance depends on various fac-
tors such as external environment, task
complexity and other external stress-
ors.18,21 On the effect of noise on worker
performance, there are controversial
views between researchers.18,22-24 To in-
vestigate occupational skill performance,
some specific test batteries are used: 1)
steadiness test, 2) Minnesota manual
dexterity test, 3) hand tool dexterity test,
and 4) two-arm coordination test. This
battery of tests is basically used to test
the rehabilitation and return to work ca-
pabilities of humans and helps in testing
applicants for assembly work and various
other jobs.25 They cover the hand-eye co-
ordination, steadiness, mechanical skills,
arm dexterity, two-arm coordination, and
motor skills.
Our study was based on the investi-
gation of the effect of various factors of
industrial noise on participants' perfor-
mance and efficiency with the means of
these occupational skill assessment tests.
In other words, the objective of the pres-
ent study was to determine: 1) the effect
of noise harmonic index on human per-
formance, 2) the effect of noise pressure
level on human performance, 3) the effect
of noise schedule on human performance,
and 4) to reveal the interaction of com-
bined effects of the variables.
Materials and Methods
Study population
This study included 40 healthy male uni-
versity students. Ethical aspects were
considered. All the participants received
the information regarding the objective
of the study and enrolled in the study as
volunteers. Furthermore, they were free
to leave the experiments whenever de-
manded. The mean±SD age of partici-
pants was 24.5±3 years. Self-reporting
general health status questionnaire was
completed by all participants. They were
also trained so that they became familiar
with the equipment they had to work with.
Before the participants were asked to take
part in the experiments, their hearing and
vision were checked.
Experimental design
The experimental design consisted of
thee independent factors—3 (sound
pressure level) × 3 (noise schedule) × 2
(noise harmonic index) factors. The in-
dependent variables considered for the
experiments were continuous, fluctuat-
ing and intermittent noise, three differ-
TAKE-HOME MESSAGE
●Intermittent noise, especially at high pressure levels, re-
duces human performance significantly.
●Treble noise is more important in reducing human perfor-
mance.
For more information
on the effect of noise
on children education
see
www.theijoem.com/
ijoem/index.php/ijoem/
article/view/185
For more information
on noise-induced ves-
tibular symptoms see
www.theijoem.com/
ijoem/index.php/ijoem/
article/view/124
www.theijoem.com Vol 4 Number 2; April, 2013 89
B. Fouladi Dehaghi, P. Nassiri, et al
ent levels of noise (75, 85 and 95 dBA);
and two noise harmonic indices (posi-
tive and negative). The two internation-
ally standardized weighting networks for
different frequencies in common use are
the “A” and “C,” which have been built
to correlate to the frequency response of
the human ear for different sound levels
in different frequencies. The “A” network
modifies the frequency response to fol-
low approximately the equal loudness
curve of 40 phones, while the “C” network
approximately follows the equal loud-
ness curve of 100 phones, respectively.26
Thus, noise harmonic index is defined as
the difference between these two weight-
ing networks, i.e., dB(C) – dB(A). When
the result of this equation is positive, the
noise is in “bass” form; when it is nega-
tive, the noise is called “treble.”
The dependent variables of the study
were speed and time duration of com-
mitting errors by the participants while
performing the battery of tests. The speed
was measured as the amount of time tak-
en to perform the test.
Battery of tests
Steadiness test
In this test, the participant is asked to
hold a metal tipped stylus in various sized
holes. The participant is not supposed to
touch the sides of the holes. The steadi-
ness test is mainly used to test the psy-
chomotor phenomenon of steadiness in
various participants. The holes are pro-
gressively reduced in size and the partici-
pant is asked to insert the stylus inside
the holes first from the largest hole to
the smallest hole size and then from the
smallest hole to the largest hole size. The
speed response is the amount of time that
the participant takes to insert the stylus
in the holes and it is measured in seconds
(test completion time). The error time is
measured in terms of duration of time
for committing errors by the participants
while performing the experiment.
Minnesota manual dexterity test
In this experiment, the participant is test-
ed for hand-arm coordination and hand-
eye coordination. The participant's task is
to begin from the right side, pick up the
bottom disk and place it on top of the sec-
ond board. Next, the participant is sup-
posed to pick up the next disk on the right
and place it in the next hole of the second
board. The participant is supposed to
move from right to left and continue from
one column to the other until the entire
board is filled. The response that is re-
corded is speed. Speed is recorded as the
time taken by the participant to perform
the entire experiment.
Two-arm coordination test
The participants' task is to trace the star
pattern in clockwise as well as counter-
clockwise direction. The black star pat-
tern can be traced by spreading the han-
dles, bringing them together, or moving
them left or right so that the stylus traced
the star pattern. The participant is sup-
posed to maintain the stylus on the black
area of the star; if the stylus left the black
star pattern, an error time is recorded by
the recorder attached to the equipment.
The responses measured during this test
are participants' speed, which is the time
taken by him or her to perform the experi-
ment, and error time.
Hand tool dexterity test
The participant's task is to remove all the
bolts starting from left to right and from
top to bottom, completing each row at a
time. Then the participant had to mount
the bolts starting from right side and from
the bottom row moving up to the top. All
of the bolt heads are supposed to be facing
the inside and the bolts had to be removed
and mounted on the wooden frame with
the help of various tools which are pro-
article
www.theijoem.com Vol 4 Number 2; April, 201390
article
vided. In this experiment, the response
measured is the speed. Speed is calculat-
ed as the time taken by the participant to
remove the bolts from one upright side of
the wooden frame and mount them on the
other upright side of the frame.
Study equipment
A stopwatch was used to record the time
taken to perform the experiments. A
sound level meter (B&K model 2236)
was used for frequency analysis and to
determine sound pressure levels in test
room. Also, PULSE Multi-analyzer Sys-
tem (B&K Type 3560) was used to record
real noise in an industrial setting, and for
reproducing the recorded real noise in the
test room with the help of Goldwave soft-
ware (ver 5.1).
Test room layout
The test room consisted of a work desk
with 70 cm in height, where the experi-
mental apparatus was placed; a chair
where the participant was asked to sit
while performing the experiments, and
two speakers placed at a distance of 1.5
meters on the participant's left and right.
The test room conditions were kept at
comfort zone temperature and levels of
humidity, lighting, etc.
Data collection and statistical analyses
The effect of three different attributes of
noise on human performance was ana-
lyzed during this experimental study.
The error response was analyzed only in
the case of two-arm coordination and the
steadiness test. In the hand tool dexterity
test and Minnesota manual dexterity test,
it was difficult to quantify the errors, thus,
they were not reported. The participants
were given sufficient training and prac-
tice before conducting the actual experi-
ments. This helped to make them familiar
with the test equipment and equalizing
their skill level. The participants were
given sufficient rest after conducting each
experimental run.
For the statistical analysis of the exper-
imental data, Student's t test, Tukey test
and three-way ANOVA were used. The
data analyses were performed by SPSS®
ver 19 for Windows®.
Results
Speed response as test completion time
The speed response for the four tests un-
der the effect of three noise pressure lev-
els, two harmonic sound indices, and three
schedules of noise were measured (Table
1). The test completion time was highest
(mean±SD of 44.6±17 sec) in the steadi-
ness test for the combination of intermit-
tent noise, negative harmonic index (tre-
ble) at a pressure level of 95 dBA. For the
same test, the completion time was low-
est (mean±SD of 29.9±16.0 sec) for the
situation in which continuous noise, posi-
tive harmonic index (bass), and 75 dBA
noise pressure level were used. The speed
variable had a normal distribution (Kol-
mogorov-Smirnov test). ANOVA revealed
that the speed response was only affected
by noise harmonic index. To determine
the kind of effective harmonic index, Stu-
dent's t test was used that revealed that a
negative harmonic index was responsible
for reducing the test performance speed
in steadiness test (p<0.001).
In Minnesota manual dexterity test
results (Table 1), the test completion
time was highest (mean±SD of 32.2±14.0
sec) for the combination of continuous
noise, negative harmonic index (treble)
and a pressure level of 95 dBA. It was
lowest (mean±SD of 21.3±7.7 sec) when
continuous noise, a positive harmonic
index (bass), and a pressure level of 75
dBA were combined. ANOVA revealed
that the speed response in this test was
dependent on both the noise schedule
Noise and Human Performance
www.theijoem.com Vol 4 Number 2; April, 2013 91
(p<0.025) and harmonic index (p<0.041)
(the negative harmonic index [treble] was
the only effective one [p<0.038]). Tukey
test was performed to compare the three
noise schedules and revealed a significant
(p<0.04) difference between continuous
and intermittent noise schedules.
The results for the third test, two-arm
coordination test, showed that the test
completion time was highest (mean±SD
of 68.3±5.4 sec) for the combination of
continuous noise, negative harmonic in-
dex (treble) and pressure level of 85 dBA.
It was lowest (mean±SD of 61.9±7.0 sec)
when fluctuating noise, a positive har-
monic index (bass) and a pressure level of
75 dBA were combined. The noise pres-
sure level and harmonic index affected the
speed response significantly (p<0.023).
There was also a significant (p<0.04) dif-
ference between pressure level of 75 dBA
and other noise intensities used.
Speed responses (test completion time)
for the last test, hand tool dexterity test,
was highest (mean±SD of 436.0±106.1
sec) for the combination of intermittent
noise, negative harmonic index (treble)
and a pressure level of 95 dBA. It was
lowest (mean±SD of 244.7±51.6 sec)
when continuous noise, positive harmon-
ic index (bass) and a pressure level of 75
dBA were used. All the three independent
variables—noise schedule, noise pressure
level, and harmonic index—affected the
speed response significantly (p<0.005).
Negative harmonic index was associated
with reduction in the performance speed.
There was a significant (p<0.003) differ-
ence between the pressure level of 75 dBA
and 85dBA. The effect of continuous noise
was significantly (p<0.001) different from
that of other noise schedules used.
Error response (time duration of
committing errors)
The error response was analyzed only in
the case of two-arm coordination and the
Table 1:
Speed response (test completion time) in various
test conditions
Noise
Schedule
Noise pres-
sure level
dB(A)
Harmonic
index
Mean±SD
speed
(sec)
Test
Continuous 75 Positive*
29.9±16.0
S
21.3±7.7
M
66.1±7.1
H
244.7±51.6
T
Continuous 75 Negative†
36.8±12.9
S
28.7±12.0 M
67.5±6.5
H
314.3±67.8
T
Fluctuating 75 Positive
38.4±16.0
S
22.1±8.8
M
61.9±7.0
H
343.4±55.3
T
Fluctuating 75 Negative
38.7±14.3
S
23.9±10.3
M
64.1±6.6
H
384.1±41.4
T
Intermittent 75 Positive
31.5±15.1
S
30.8±13.4
M
62.8±6.5
H
337.2±91.1
T
Intermittent 75 Negative
38.7±14.4
S
23.5±8.8
M
65.2±5.4
H
391.0±88.9
T
Continuous 85 Positive
34.6±18.4
S
21.4±7.5
M
65.7±7.1
H
323.4±66.4
T
Continuous 85 Negative
39.9±19.2
S
22.8±6.6
M
68.3±5.4
H
362.8±102.5
T
Fluctuating 85 Positive
36.5±20.7
S
20.8±8.0
M
62.2±7.3
H
412.8±86.1
T
Fluctuating 85 Negative
42.6±19.1 S
21.9±10.2
M
66.2±9.0
H
432.0±93.3 T
B. Fouladi Dehaghi, P. Nassiri, et al
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www.theijoem.com Vol 4 Number 2; April, 201392
article
steadiness test with the help of an error
time recorder that recorded the time du-
ration of errors committed by the partici-
pant during the experiment.
The error response for the steadiness
test and two-arm coordination test un-
der the effect of three levels of noise, two
harmonic noise indices and three sched-
ules of noise were measured (Table 2). In
steadiness test, the error time duration
was highest (mean±SD of 6.3±3.7 sec)
for the combination of continuous noise,
a negative harmonic index (treble), and
a pressure level of 85 dBA. It was lowest
(mean±SD of 3.8±1.6 sec) when inter-
mittent noise, a positive harmonic index
(bass), and a 75 dBA noise pressure level
were used. The error response was only
affected by noise harmonic index. The
negative harmonic index (treble) was the
main cause of increasing error in perfor-
mance (p<0.001).
In two-arm coordination test, the error
time was highest (mean±SD of 1.4±1.8
sec) when a continuous noise, a negative
harmonic index (treble), and a pressure
level of 85 dBA were used. The error time
was lowest (mean±SD of 0.2±0.2 sec)
when a continuous noise, a positive har-
monic index (bass), and a 75 dBA noise
pressure level were combined. None of
the variables had a significant effect on
the error response.
Discussion
We found that speed responses (time
spent for completion of a task) for all four
occupational skill assessment tests were
mainly affected by the harmonic index.
Of all the three studied factors, a nega-
tive harmonic index was found to be the
most significant factor that affected the
speed performance of participants while
performing the four occupational skill as-
sessment tests.
The interaction between the three
Continued
Table 1: Speed response (test completion time) in various
test conditions
Noise
Schedule
Noise pres-
sure level
dB(A)
Harmonic
index
Mean±SD
speed
(sec)
Test
Intermittent 85 Positive
32.5±17.3 S
22.1±6.1 M
64.0±9.5
H
392.3±69.3
T
Intermittent 85 Negative
42.6±18.8 S
22.4±10.4 M
62.2±9.0 H
409.7±75.7 T
Continuous 95 Positive
32.3±16.3
S
22.5±11.1 M
65.8±9.1
H
277.5±61.2 T
Continuous 95 Negative
35.3±16.3 S
32.2±14.0
M
67.7±7.0 H
279.9±61.6 T
Fluctuating 95 Positive
34.8±19.9
S
22.9±13.7 M
62.3±6.8 H
395.1±79.7
T
Fluctuating 95 Negative
42.9±22.3 S
23.0±12.2 M
65.9±6.4 H
435.2±91.4 T
Intermittent 95 Positive
33.6±14.8 S
21.9±10.3 M
61.5±4.8 H
389.7±78.9
T
Intermittent 95 Negative
44.6±17.0 S
24.3±13.7 M
65.7±10.3 H
436.0±106.1 T
*Bass; †Treble; S: Steadiness test; M: Minnesota manual dexter-
ity test; H: Hand tool dexterity test; T: Two-arm coordination test
Noise and Human Performance
www.theijoem.com Vol 4 Number 2; April, 2013 93
studied factors of noise was not the same
for all the tests: for steadiness test and
Minnesota manual dexterity test, there
was a significant difference between con-
tinuous and intermittent noise sched-
ules. As it is stated by many researchers,
of various noise characteristics studied,
noise schedule is of utmost importance;
intermittent noise is responsible for dis-
traction of attention away from the task
and leads to reduced performance par-
ticularly in performing complex cogni-
tive tasks. When an intermittent noise
occurs at high intensities, the performer
briefly diverts his or her attention to the
noise.23,26-27 Intermittent noise is reported
to be more disruptive than continuous
noise, however, change in the intensity
is also very important.30 Our findings
support this finding as the lowest perfor-
mances were observed with intermittent
noise in different tests. On the other hand,
in two-arm coordination test, the noise
intensity was responsible for variation in
participants' performance as it has been
stated by other researchers.11,29-31 Fluctu-
ating noise, caused no significant effect
probably because the designed tasks test-
ed were simple and this kind of noise was
something between intermittent and con-
tinuous noise. However, more research in
this area seems to be necessary.
In the hand tool dexterity test, it was
found that the speed was affected by all
the studied factors including noise har-
monic index, noise schedule, noise pres-
sure level and the interaction between
them. This could be due to the fact that
the task tested an individual for his or her
mechanic skills, and that the duration for
this task was much longer than the dura-
tion for any other tasks tested. Therefore,
participants received more exposure to
noise while they were performing this
task compared to other tasks.
In assessing the error time while per-
forming the task, we found that harmonic
Table 2: Error time in steadiness and two-arm coordination
tests
Noise
schedule
Noise pres-
sure level
dB(A)
Harmonic
index
Mean±SD
error time
(sec)
Test
Continuous 75 Positive*
4.1±1.9
S
0.2±0 .2 T
Continuous 75 Negative†4.4±1.7 S
0.8±1.2 T
Fluctuating 75 Positive
4.2±1.8
S
0.6±0.9 T
Fluctuating 75 Negative
4.5±1.6 S
0.6±1.0 T
Intermittent 75 Positive
3.8±1.6 S
0.6±0.9 T
Intermittent 75 Negative 5.3±3.0 S
0.2±0.4 T
Continuous 85 Positive 4.7±2.4 S
0.3±0.4
T
Continuous 85 Negative 6.3±3.7 S
1.4±1.8
T
Fluctuating 85 Positive 4.0±2.4 S
0.3±0.5 T
Fluctuating 85 Negative
4.2±2.0 S
0.4±0.5 T
Intermittent 85 Positive 4.2±2.0 S
0.5±0.7
T
Intermittent 85 Negative 5.0±2.3 S
0.6±0.7
T
Continuous 95 Positive
4.4±2.3 S
0.3±0.3 T
Continuous 95 Negative
4.2±2.0 S
0.4±0.5 T
Fluctuating 95 Positive
4.5±2.7 S
0.8±1.3 T
Fluctuating 95 Negative 5.5±2.5 S
1.0±1.2
T
B. Fouladi Dehaghi, P. Nassiri, et al
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www.theijoem.com Vol 4 Number 2; April, 201394
article
index mainly affected the error response
in steadiness test. Therefore, more dura-
tion of errors occurred due to the pres-
ence of negative harmonic index. In the
two-arm coordination test, apart from
negative harmonic index, no other signifi-
cant factors affected the error response of
human performance.
In many of the reported cases of this
study, higher noise pressure levels were
associated with more reduction in per-
formance.24 Moreover, it should be men-
tioned that in this study, real noise from
industrial settings was used in well-con-
trolled experiments. Most of previous
studies used artificially generated noises
in artificial settings with usually very
short exposure times. In an experiment,
it was shown that reducing noise levels
in a factory improved work performance
through reduction of the number of work
errors.33 According to Broadbent,33 now
classic in theoretical treatment of the ef-
fects of noise on performance, loud noise
leads to over-arousal, which narrows at-
tention and restricts one's focus to a lim-
ited range of cues. This inability to attend
to less salient cues would ultimately lead
to deterioration of performance. Our find-
ings supported these results.
Although there are a vast variety of
studies on the effects of noise on human
performance in different conditions and
designs, with of course many controver-
sial results, to the best of our knowledge,
none of them has so far focused on the
effect of noise harmonic index on hu-
man performance. We found that when
the noise harmonic index was negative
(treble noise) the performance was sig-
nificantly affected. The results of the ef-
fects of the two other noise characteristics
we studied, were in keeping with previous
reports. Further controlled studies are
needed to confirm the importance of the
noise characteristics in design of working
environments.
Acknowledgements
The authors appreciate the partici-
pants for their interest and enthusiasm
to participate in the study. We also ac-
knowledge Tehran University of Medical
Sciences and School of Public Health for
their invaluable help and support during
the research.
Conflicts of Interest: None
declared.
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Noise and Human Performance
Continued
Table 2: Error time in steadiness and two-arm coordination
tests
Noise
schedule
Noise pres-
sure level
dB(A)
Harmonic
index
Mean±SD
error time
(sec)
Test
Intermittent 95 Positive
4.6±3.4
S
0.3±0.3
T
Intermittent 95 Negative
5.9±4.3
S
1.3±1.7 T
*Bass; †Treble; S: Steadiness test; T: Two-arm coordination test
www.theijoem.com Vol 4 Number 2; April, 2013 95
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