ArticlePDF Available

The Effect of Noise on Human Performance: A Clinical Trial



Noise is defined as unwanted or meaningless sound that apart from auditory adverse health effects may distract attention from cues that are important for task performance. Human performance is influenced by many job-related factors and workplace conditions including noise level. To study the effect of noise on human performance. The participants included 40 healthy male university students. The experimental design consisted of 3 (sound pressure level) × 3 (noise schedule) × 2 (noise type) factors. To investigate occupational skill performance, some specific test batteries were used: 1) steadiness 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. Speed response obtained from the 4 tests in combined conditions of noise schedule, 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. Treble noise was found significant in reducing human performance; also, intermittent noise, especially at high pressure levels, was responsible for worsening environmental conditions during performing a task. Vol 4 Number 2; April, 2013 87
This work is licensed
under a Creative
Commons Attribution-
NonCommercial 3.0
Unported License.
To review this article online, scan this
QR code with your Smartphone
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-
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@
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.
Background: Noise is dened 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 inuenced 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 specic 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),
Conclusion: Treble noise was found signicant 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
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 Vol 4 Number 2; April, 201388
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
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-
Intermittent noise, especially at high pressure levels, re-
duces human performance significantly.
Treble noise is more important in reducing human perfor-
For more information
on the effect of noise
on children education
For more information
on noise-induced ves-
tibular symptoms see
article/view/124 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 Vol 4 Number 2; April, 201390
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®.
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 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 pres-
sure level
Continuous 75 Positive*
Continuous 75 Negative
28.7±12.0 M
Fluctuating 75 Positive
Fluctuating 75 Negative
Intermittent 75 Positive
Intermittent 75 Negative
Continuous 85 Positive
Continuous 85 Negative
Fluctuating 85 Positive
Fluctuating 85 Negative
42.6±19.1 S
432.0±93.3 T
B. Fouladi Dehaghi, P. Nassiri, et al
article Vol 4 Number 2; April, 201392
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.
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
Table 1: Speed response (test completion time) in various
test conditions
Noise pres-
sure level
Intermittent 85 Positive
32.5±17.3 S
22.1±6.1 M
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
22.5±11.1 M
277.5±61.2 T
Continuous 95 Negative
35.3±16.3 S
67.7±7.0 H
279.9±61.6 T
Fluctuating 95 Positive
22.9±13.7 M
62.3±6.8 H
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
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 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
Noise pres-
sure level
error time
Continuous 75 Positive*
0.2±0 .2 T
Continuous 75 Negative4.4±1.7 S
0.8±1.2 T
Fluctuating 75 Positive
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
Continuous 85 Negative 6.3±3.7 S
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
Intermittent 85 Negative 5.0±2.3 S
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
B. Fouladi Dehaghi, P. Nassiri, et al
article Vol 4 Number 2; April, 201394
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
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
1. Fyhri A, Aasvang GM. Noise, sleep and poor
health: Modeling the relationship between road
traffic noise and cardiovascular problems. Sci Total
Environ 2010;408:4935-42.
2. Hohmann C, Grabenhenrich L, de Kluizenaar Y,
et al. Health effects of chronic noise exposure
in pregnancy and childhood: A systematic
review initiated by ENRIECO. Int J Hyg Envir Heal
3. Atmaca E, Peker I, Altin A. Industrial noise and
its effects on humans. Polish J Environ Studies
4. Ulrich-Lai YM, Herman JP. Neural regulation of
endocrine and autonomic stress responses. Nat
Rev Neurosci 2009;10:397-409.
5. Ahmad Badayai AR. A Theoretical Framework and
Analytical Discussion on Uncongenial Physical
Workplace Environment and Job Performance
among Workers in Industrial Sectors. Procedia Soc
Behav Sci 2012;42:486-95.
6. Cohen S, Weinstein N. Nonauditory effects
Noise and Human Performance
Table 2: Error time in steadiness and two-arm coordination
Noise pres-
sure level
error time
Intermittent 95 Positive
Intermittent 95 Negative
1.3±1.7 T
*Bass; Treble; S: Steadiness test; T: Two-arm coordination test Vol 4 Number 2; April, 2013 95
B. Fouladi Dehaghi, P. Nassiri, et al
of noise on behavoir and health. J Soc Issues
7. Sayli N, Khasawneh MT, Lu S, Koon T. Effect of
industrial noise on occupational skill perfor-
mance capability. UMI 1470346, ProQuest LLC
2009 Available from http://gradworks.umi.
com/14/70/1470346.html (Accessed May 23,
8. Noweir MH. Noise exposure as related to pro-
ductivity, disciplinary actions, absenteeism, and
accidents among textile workers. J Safety Res
9. Chiovenda P, Pasqualetti P, Zappasodi F, et al. En-
vironmental noise-exposed workers: Event related
potentials, neuropsychological and mood assess-
ment. Int J Psychophysiol 2007;65:228-37.
10. Leather P, Beale D, Sullivan L. Noise, psychosocial
stress and their interaction in the workplace. J
Environ Psychol 2003,23:213-22.
11. Melamed S, Fried Y, Froom P. The joint effect of
noise exposure and job complexity on distress and
injury risk among men and women: the cardiovas-
cular occupational risk factors determination in Is-
rael study. J Occup Environ Med 2004;46:1023-32.
12. Kahya E. The effects of job characteristics and
working conditions on job performance. Int J
Indust Ergo 2007;37:515-23.
13. Kim TG, Tochihara Y, Fujita M, Hashiguchi N. Physi-
ological responses and performance of loading
work in a severely cold environment. Int J Indust
Ergo 2007;37:725-32.
14. Meerding WJ, Ijzelenberg W, Koopmanschap
MA, et al. Health problems lead to considerable
productivity loss at work among workers with high
physical load jobs. J Clin Epidemiol 2005;58:517-
15. O’Neill MJ. Measuring Workplace Performance,
2nd ed. Taylor & Francis, New York, 2007.
16. Robertson MM, Huang YH. Effect of a workplace
design and training intervention on individual
performance, group effectiveness and collabora-
tion: the role of environmental control. Work
17. Parsons KC. Environmental ergonomics: A review
of principles, methods and models. Appl Ergo
18. Suter AH. The effects of noise on performance.
Final Report. Gallaudet University Washington DC,
19. Waye KP, Bengtsson J, Kjellberg A, Benton S. Low
frequency noise «pollution» interferes with per-
formance. Noise Health 2001;4:33-49.
20. McCoy JM, Evans G. Physical work environment.
In: Barling J, Kelloway EK, eds. Handbook of Work
Stress. Thousand Oaks, CA, Sage Publication,
21. Vischer J. The effects of the physical environment
on job performance: Towards a theoretical model
of workspace model. J Stress Health 2007;23:175-
22. Melamed S, Fried Y, Froom P. The interactive effect
of chronic exposure to noise and job complexity
on changes in blood pressure and job satisfaction:
A longitudinal study of industrial employees. J
Occup Health Psychol 2001;6:182-95.
23. Szalma JL, Hancock PA. Noise effects on human
performance: a meta-analytic synthesis. Am Psy-
chol Assoc 2011;137:682-707.
24. Smith DG, Baranski JV, Thompson MM, Abel SM.
The effects of background noise on cognitive per-
formance during a 70 hour simulation of condi-
tions aboard the international space station. Noise
Health 2003;6:3-16.
25. Occupational skill assessment test battery.
Available from (Ac-
cessed March 1, 2009).
26. Bies DA, Hansen CH. Engineering Noise Control.
3rd ed. Spon Press. Taylor & Francis, 2003:100-1.
27. Conway GE, Szalma JL, Hancock PA. A quantitative
meta-analytic examination of whole-body vibra-
tion effects on human performance. Ergonomics
28. Hancock PA, Ross JM, Szalma JL. A meta-analysis
of performance response under thermal stressors.
Hum Factors 2007;49:851-77.
29. Loeb M. Noise and human efficiency. Chichester,
England: Wiley, 1986.
30. Cohen S, Evans GW, Stokols D, Krantz DS. Behav-
ior, health and environmental stress. New York,
London: Plenum Press, 1986.
31. Baron RA. The physical environment of work set-
tings: effects on task performance, interpersonal
relations and job satisfaction. Res Organ Behav
32. Kroemer KHE, Grandjean E. Fitting the task to the
human. 5th ed. A textbook of occupational ergo-
nomics. London, Bristol, PA, Taylor and Francis,
33. Broadbent DE, Little EAJ. Effects of noise reduction
in a work situation. Occup Psychol 1960;34:133-
... Noise can be described as "unwanted sound" (Stansfeld & Matheson, 2003, p. 243) and much research has found links between high levels of noise and adverse physical and mental outcomes (for example: Chiovenda et al., 2007;Öhrström & Skånberg, 2004;Saha et al., 1996;Stansfeld & Matheson, 2003;Stansfeld et al., 2005). However, current research is increasingly investigating the non-auditory impact of low-level noise distraction and background noise on aspects of learning (Clausen et al., 2013;Nassiri et al., 2013). ...
... People may not be aware that noise is an issue for them, but may still be less able to concentrate and complete tasks in the presence of background noise. Intermittent noise has been found to be more annoying than constant noise, as attention is continuously diverted from the task to the noise, although changes in intensity can be distracting as well (Nassiri et al., 2013). Further, when noise distraction is intermittent, simply anticipating noise is disruptive for attention and performance (Stansfeld & Matheson, 2003). ...
... All participants in this study said that they were bothered by noise pollution (Minichilli et al., 2018) and went to lengths to eliminate noise distraction in their personal study environments. Intermittent noise is the most distracting noise (Nassiri et al., 2013) and ...
Full-text available
People vary in the way in which they perceive, process and react to environmental factors, and some are more or less sensitive than others. There is a dearth of research investigating the possible impact that environmental sensitivity has in the postsecondary education context. To address this gap in literature, the following research question was posed: What impact does environmental sensitivity have on student learning in tertiary education? To answer this question a two-stage mixed methods research project was undertaken. The first stage involved two studies which used snowball recruitment via social media, and subject inclusion criteria were current or previous postsecondary education experience. Participants completed on-line surveys. Study One is the design, development and validation of a self-report instrument measuring postsecondary students’ perceptions of their learning success, and participants completed the Perceived Success in Study Survey (PSISS) and associated demographic questions. Two phases were undertaken to check for reliability of results, n=225 and n=237. Reliability statistics found a high level of internal consistency, and principal component analysis identified five factors: Intellectual Stimulation, Generic Skills, Work-life Balance; Commitment to Learning and Learning Community. The PSISS was found to be a comprehensive measure of overall success for postsecondary learners. The participants in Study Two (n=365) completed the PSISS and the 12-item Highly Sensitive Person Scale (HSPS-12, Pluess et al., 2020) and related demographic questions. Independent T-tests, ANOVA and Tukey post-hoc calculations identified that high sensitivity is positively associated with success-promoting attitudes and strategies as identified on three of the five PSISS factors. It also found positive associations between total scores on the PSISS and the sensitivity subscales of Aesthetic Sensitivity and Ease of Excitation (Smolewska et al., 2006). This study included a response field to register interest in participation in further research. Those who responded, and who rated as highly sensitive on the HSPS-12, were invited to take part in a semi-structured interview, leading into the second stage of the project. Thirteen Zoom interviews were conducted with participants from a broad range of geographic locations and levels and fields of study in order to exemplify and elaborate on the quantitative findings. Reflexive inductive thematic analysis was employed to analyse the data, and sixteen codes and three themes were identified. Responses were written vi into a semantic narrative, accompanied by pertinent participant quotations, providing a rich and detailed description of participant experience. The results of this study confirmed that there are educational advantages contingent with high sensitivity, including the use of a broad array of metacognitive study and self-care strategies, and the prioritisation of wellbeing and work-life balance. Conversely, it also found that numerous simultaneous study demands can lead to feelings of overwhelm, however, the participants employed a comprehensive array of metacognitive coping strategies to manage these. Low sensory thresholds associated with high sensitivity can present challenges for highly sensitive students who can be negatively impacted by aspects of the physical learning environments including light, noise, indoor environmental pollutants. Additionally, participants highlighted the need for postsecondary institutions to provide education about environmental sensitivity, to allow flexibility in teaching delivery, to explore options to support students who may struggle with group-work and presentations, and to provide assessment accommodations. Overall, the project has identified a number of positive and negative associations between levels of learner sensitivity and student success and suggests that education about environmental sensitivity for students and teaching staff would be helpful for increasing awareness about the benefits and challenges of environmental sensitivity. Institutional commitment to providing optimal physical learning and social environments may enhance the learning experience for all students. Finally, recommendations for policy, practice and institutions highlight elements that will be of benefit to all students, most especially those who sit at the high end of the sensitivity spectrum.
... A large number of experimental and survey studies have been carried out to assess the effect of noise level and exposure duration by field measures [35]. Furthermore, a direct negative relationship between noise level and performance has been validated by several studies [26,36]. The noise level is the most influential parameter but usually centered on a higher level of noise, not a wide range. ...
... Cognitive performance is associated with the dynamic cognitive states. Most articles have concentrated on the direct effects of noise on external performance, error rates, and so on [8,36]. However, the existing evidence is inadequate regarding the noise effects on cognitive performance, which can be assessed by the cognitive state, such as stress level, attention level, cognitive load, annoyance, etc. ...
Task-irrelevant noises pose deleterious effects on task performance, health, and work safety, especially in the construction field. However, the quantitative effects of noise on the cognitive performance in construction remain relatively unexplored. The paper aims to examine the effects of various noise conditions on task performance and cognitive performance via a portable electroencephalography device. A total of 27 subjects participated the experiment to identify hazards under different noise exposure conditions (contents and levels). The behavioral performance (accuracy and reaction time) and electroencephalography were collected and analyzed. The findings indicated a negative relationship between the performance of the participants and the exposure to noise. The intrinsic cognitive states including attention, stress and mental workload have been affected in varying degrees. Evaluating the impact of noise on cognitive functions helps explain the mental effects of the impaired performance. Neurocognitive monitoring with electroencephalography sets the basis for predicting task performance under different noise conditions.
... The effects of noise on performance are particularly noteworthy, as quite different findings exist. Noise-induced effects in performance depend on the difficulty of the task to be processed, the type of noise, the sound pressure level, and the duration of noise exposure (Jahncke et al., 2011;Monteiro et al., 2018;Nassiri et al., 2013). According to a meta-analysis (Szalma & Hancock, 2011), noise impairs performance in more complex tasks, such as cognitive and communication tasks, and primarily affects accuracy and less the speed of processing. ...
Lärm in Schulen gilt aus unterschiedlichen Gründen als massiver Belastungsfaktor für Lehrkräfte und kann deshalb zu Leistungsdefiziten im Beruf, aber auch zu physischen und psychischen Beeinträchtigungen führen. Die Erforschung von Schullärm und seinen Auswirkungen ist daher essentiell. Die drei Studien, die in dieser Arbeit vorgestellt werden, untersuchten die unmittelbaren Auswirkungen von Lärm auf Lehramtsstudierende und die mittelbaren Auswirkungen auf praktizierende Lehrkräfte. In der ersten und zweiten Studie wurde im Rahmen zweier Experimente überprüft, wie sich Pausenlärm auf das Stresserleben, die Leistung in einem Konzentrationstest und auf die Fehlerkorrektur eines Diktats auswirkt. Auf Grundlage des transaktionalen Stressmodells (Lazarus & Folkman, 1984) wurde vermutet, dass Lärm zu einer Erhöhung des Stresserlebens führt. Der Maximal-Adaptability-Theorie (Hancock & Warm, 1989, 2003) nach sollte der Lärm zunächst eine optimale Leistung, langfristig jedoch eine Leistungsbeeinträchtigung verursachen. Um dies zu überprüfen, bearbeiteten in der ersten Studie 74 und in der zweiten Studie 104 Lehramtsstudierende der Universität Passau zwei unterschiedliche Konzentrationstests und korrigierten das Diktat eines Schülers, während sie kurzen, kontinuierlichen oder keinen Pausenlärm hörten. In beiden Experimenten führte kontinuierlicher Lärm zu einer Erhöhung des Stresserlebens. Weder kurzer noch kontinuierlicher Lärm führte zu einer Verschlechterung der Konzentrationsleistung. Weiter zeigten sich unterschiedliche Befunde: Im ersten Experiment führte ein kurzer Konzentrationstest in Kombination mit kontinuierlichem Lärm zu positiven Effekten in der Diktatkorrektur, d.h. die Versuchspersonen wiesen eine bessere Leistung in der Fehlerkorrektur auf. Im zweiten Experiment führte ein langer Konzentrationstest in Kombination mit kurzem oder kontinuierlichem Lärm zu negativen Effekten, d.h. die Probanden machten vergleichsweise mehr Fehler bei der anschließenden Diktatkorrektur. Daraus lässt sich schlussfolgern, dass Schullärm einerseits das Stresserleben erhöhen und andererseits die anschließende Leistungsfähigkeit der Lehrkräfte verbessern oder einschränken kann. Letzteres scheint allerdings von der konkreten Situation abzuhängen. Im ersten Teil der dritten Studie lag der Fokus auf den Bewältigungsstilen und dem erlebten Stress der Lehrkräfte. Da Bewältigungsstile nachweislich einen großen Einfluss auf die psychische Gesundheit haben, lag die Vermutung nahe, dass das durch Lärm verursachte Stresserleben je nach Bewältigungsstil unterschiedlich ausfällt. Auf der Grundlage des Belastungs-Beanspruchungsmodells (Rudow, 2000) und des transaktionalen Stressmodells (Lazarus & Folkman, 1984) wurde angenommen, dass Lehrkräfte mit riskanten Copingstilen mehr Stresssymptome erleben. Deshalb wurde im Rahmen einer Online-Studie untersucht, ob es in Bezug auf psychische und körperliche Symptome Unterschiede zwischen Lehrkräften mit distinkten Bewältigungsstilen gibt. Dazu wurden 99 bayerische Grund- und Mittelschullehrkräfte befragt. Aus den übergeordneten Skalen Engagement und Resilienz resultierten vier berufliche Bewältigungsstile. Der Typ Gesundheit (hohes Engagement, hohe Resilienz), der Schon-Typ (niedriges Engagement, hohe Resilienz), Typ A (hohes Engagement, niedrige Resilienz) und Typ Burnout (niedriges Engagement, niedrige Resilienz) unterschieden sich hinsichtlich Bedrohungseinschätzung, Lärmstress, Stimm- und Hörproblemen sowie lärmbedingtem Burnout. Im Vergleich zum Typ Gesundheit wiesen die Risikotypen Typ A und Typ Burnout ein höheres Stresserleben auf und erwiesen sich generell anfälliger gegenüber Schullärm als der Typ Gesundheit. Dies ist die erste Studie, die zeigen konnte, dass Schullärm besonders für Lehrkräfte mit riskanten Copingstilen eine Gefährdung darstellt. Im zweiten Teil der dritten Studie lag der Fokus auf den Wirkungspfaden von Schullärm. Hier wurden Zusammenhänge zwischen individuellen Eigenschaften der Lehrkräfte und den unterschiedlichen Auswirkungen von Schullärm vermutet. Basierend auf dem vereinfachten Modell von Lehrerstress (van Dick & Wagner, 2001) wurde an 159 bayerischen Grund- und Mittelschullehrkräften untersucht, ob Lärmstress und Stimmermüdung die Verbindung zwischen Lärmempfindlichkeit und lärmbedingtem Burnout vermitteln. Die Ergebnisse zeigten, dass Stress die Beziehung zwischen Lärmempfindlichkeit und Stimmermüdung vermittelte; Stimmermüdung vermittelte die Beziehung zwischen Lärmstress und lärmbezogenem Burnout; Lärmstress und Stimmermüdung vermittelten seriell die Beziehung zwischen Lärmempfindlichkeit und lärmbedingtem Burnout. Dies ist die erste Studie die Verbindungen zwischen lärmempfindlichen Lehrkräften und Lärmstress, Stimmproblemen und lärmbedingtem Burnout aufzeigen konnte.
... Noise has been found as a non-specific biological stressor which can cause negative effects beyond the ones that occur at the auditory system. Non-auditory effects of noise include speech interference [1], annoyance, sleep disturbance [2], cardiovascular problems [3], disorder in cognitive function and memory [4], and effects on behavior [5]. These effects can be observed at exposure to noise levels below those identified as causing hearing impair-ment and inflicted by occupational regulations [6]. ...
Background Gender can affect the relationship between noise exposure and both cognitive function and comfort; however, evidence is still limited. This study aimed to examine the gender differences in cognitive performance and psychophysiological responses during exposure to noise under tasks with different workloads. Methods Thirty-two participants (16 females and 16 males) with normal hearing and good general health were recruited. They were asked to perform the N-Back test at three levels of workload during exposure to four low-frequency noise conditions: 55, 65, 70, and 75 dB(A). The participants were also asked to judge noise-induced annoyance and subjective fatigue using visual analog scales at the end of each noise condition. The heart rate variability was also recorded using Nexus-4 device before and during each trial and the ratio of low to high frequency (LF/HF) power was analyzed. Results The results revealed that the females rated significantly higher levels of annoyance and fatigue than the males. The mean accuracy of the women in the level of 55 dB(A) with a medium workload was higher than that of the men, while in higher noise levels the men showed better performance. The response time to the stimulus was also lower in females at different noise levels and workloads. Furthermore, the findings showed that, with increasing noise level and workload, the LF/HF of the women was higher than that of the men. Conclusion Females and males indicated significant and different responses in exposure to different noise levels and workloads. Therefore, this study suggests that gender criteria should be taken into account particularly in the job selection, work content, and design of workplaces.
... Noise is a source of stress that is always present in the daily lives of the majority of the population and, depending on the presence or absence of noise, which has a direct impact on performance [1]. The interest in this subject mostly began with the discomfort that the Industrial Revolution caused in the workers [2] and questions began to emerge about the influence of noise and its impact on general health [3], general performance [4,5] and, most recently, sport performance [6]. Regarding sport performance, it is known that the noise does not seem to affect the components linked to the performance speed, but it decreases accuracy performance and short-term and/or working memory performance [7]. ...
Full-text available
Considering that athletes constantly practice and compete in noisy environments, the aim was to investigate if performing neurofeedback training in these conditions would yield better results in performance than in silent ones. A total of forty-five student athletes aged from 18 to 35 years old and divided equally into three groups participated in the experiment (mean ± SD for age: 22.02 ± 3.05 years). The total neurofeedback session time for each subject was 300 min and were performed twice a week. The environment in which the neurofeedback sessions were conducted did not seem to have a significant impact on the training’s success in terms of alpha relative amplitude changes (0.04 ± 0.08 for silent room versus 0.07 ± 0.28 for noisy room, p = 0.740). However, the group exposed to intermittent noise appears to have favourable results in all performance assessments (p = 0.005 for working memory and p = 0.003 for reaction time). The results of the study suggested that performing neurofeedback training in an environment with intermittent noise can be interesting to athletes. Nevertheless, it is imperative to perform a replicated crossover design.
... Due to the sound caused by various machines and tools in different agriculture sectors, occupational safety and health should be continuously evaluated. Among the most important adverse effects of sound on humans, in addition to permanent and temporary hearing loss, we can mention such things as reduced work efficiency and increased risk of accidents, sleep disorders, neurological and mental disorders and cardiovascular disease [4][5][6][7][8][9]. This phenomenon has also had detrimental effects on agricultural activists [10]. ...
... For example, Kyriakides and Leventhall reported that low-frequency noise can affect productivity, and Persson-Waye et al. and Bengtsson et al. also reported that low-frequency noise can interfere with proof-reading tasks [33][34][35][36] . It was also found that intermittent and treble noise reduces human performance [37][38] . With regards to background speech intelligibility and noises from human activities, researchers have found that it impairs short-term memory, working memory tasks, and reasoning ability, and also disrupt tasks representing office work [39][40][41][42][43][44][45][46] . ...
Full-text available
Environmental noise in space vehicles, caused by onboard equipment and crew activities, has generated concerns for crew health and safety since early U.S. space missions. The International Space Station (ISS) provides a unique environment where acoustic conditions can be monitored while crewmembers from the U.S. and their international partners work and live for as long as 6 to 12 consecutive months. This review of acoustic dosimetry data collected to date reveals that the noise exposure limits of NASA's stringent noise constraint flight rule have been exceeded in 41% of these dosimetry measurements since ISS Increment 17 (2008), with undefined impacts to crew. These measurements do not take into account the effects of hearing protection devices worn by the crew. The purpose of this paper is to provide an update on ISS noise exposure monitoring approaches and hearing conservation strategies that include acoustic dosimetry data collected since the ISS Increment 55 mission (April 2018). Future directions and recommendations for the ISS noise exposure monitoring program will also be presented, including research initiatives aimed at better defining the impact of ISS noise on crew health and performance.
Background: Existing studies on the impact of background music in the workplace have reported varying results, from improving production and performance to being known as an annoying factor. Given the lack of evidence of the background music influence on the cognitive factors in the work place in previous studies and the lack of study on the effect of background music on skill performance when gender and personality type is considered, research in this area seems necessary. Objective: The purpose of the present study is to investigate the influence of background music on cognitive and skill performance in the work place with regard to gender and personality type. Methods: This study was conducted with the participation of 52 students (26 males and 26 females) aged between 18-30 years old. Sustained attention, working memory, fine finger and gross manual dexterity skills and personality type were assessed. Participants were randomly tested once when being exposed to classical instrumental music and once again when faced with complete silenceRESULTS:Playing background music improved students working memory but had no significant effect on sustained attention. Music also improved skill performance.Overall, memory performance and fine finger dexterity were found significantly better in extroverts when compared to introverts during playing background music. Conclusion: Background music improves working memory and speeds up performance in skill tasks, however the role of personality type in influencing background music on cognitive and skill performance needs further investigation.
Quality of work life and its link to quality of life by noise-exposed workers Objective: It was aimed to evaluate both the quality of work-life and quality of life of factory workers working in noisy environments by using the quality of work-life scale and the WHOQOL-BREF (TR) scale and to examine the correlation of the two scales. The secondary aim of our study is to draw attention to the negative impact of noise-induced hearing loss on quality of life and the necessity of measures to protect individual workers. Material and Method: Forty participants aged between 18-45 with and without noise-induced hearing loss (20 participants) were included in the study. Pure tone audiometry tests were performed on the participants. Then, they were asked to answer the WHOQOL-BREF (TR) and Quality of Work Life Scale items. Results: A statistically significant difference was found between the years of work, quality of life, and quality of work-life scores between participants with and without hearing loss. Moderate to strong correlations were observed between the scales assessing the quality of life and work-life. Conclusion: Occupational noise is an important risk factor for hearing loss in workers. Considering that the quality of life of workers exposed to noise is adversely affected, it is necessary to determine the noise exposure, evaluate the negative psychological effects of noise and reduce exposure to noise if necessary. Keywords: Occupational noise, noise exposure, industrial noise, hearing loss, quality of life, quality of work-life
Full-text available
Noise as one of the most common hazardous physical agents in the work environment causes physical and psychological problems in occupied workers. This study aims to investigate the relationship of demographic variables and noise exposure with mental disorder and work ability index in automotive industry workers. This study aims to investigate the effect of noise exposure on mental disorder and work ability index among industry workers. In this descriptive-analytic study, 325 individuals working in auto parts supplier industry who were exposed to different level of noises were investigated. Personnel’s daily exposure to noise for each group was measured based on ISO-9612 standards using calibrated sound level meter model SVANTEK-971. Workers’ mental disorder and work ability index were determined using Kessler Psychological Distress Scale questionnaire and shortened form of work ability index, respectively. Then, collected data were analyzed using SPSS-22. The mean and standard deviation of mental disorder and work ability index for all employees was 23.46 ± 3.45 and 37.43 ± 6.14, respectively. The results of one-way ANOVA and linear regression analysis showed that there is a significant association between noise exposure with mental disorder and work ability index in term of age groups, working groups, and work experience ( p-value < .05). Regardless the effect of other variables, it can be stated that for each dB increase in noise exposure cause mental disorder increase by 0.32 and work ability index decrease by 0.157. And among the demographic variables, age was the most influential parameter on mental health and work ability index. According to the results of this study, noise exposure could lead to increased psychological distress and decreased work ability index in workers. The ability to work directly and indirectly through mental disorders can be affected by exposure to industrial noise. Considering severe exposure to noise in some units and the negative impact of noise exposure on mental health and work ability index, it is necessary to improve of controlling and protective measures against noise.
Full-text available
The purpose of this research is to explore the theoretical framework of the physical workplace environment and its effects on job performance. Early researchers have classified five factors of the workplace environment that can affect job performances: sound, temperature, air, light and colour, and space. These findings though largely still contradictory; still play a major role in the determinants of workers' job performance. Therefore, a recommendation of a better and congenial physical environmental design has been suggested by describing a new kind of work centre, acoustic privacy and general kind of work setting.
Full-text available
The problem of noise in the industries around Sivas has been examined in this study; and noise measurement and survey studies have been carried out at concrete traverse, cement, iron and steel and textile factories located in this region. A questionnaire was completed by 256 workers during this study in order to determine the physical, physiological, and psycho-social impacts of the noise on humans and to specify what kind of measurements have been taken both by the employers and workers for protection from the effects of noise. It has been specified, during the surveys, that the noise levels detected in all the industries are much above the 80 dBA that is specified in the regulations: 73.83% of the workers in these industries are disturbed from the noise in their workplaces, 60.96% of them have complaints about their nervous situations, 30.96% of these workers are suffering hearing problems although they had not had any periodical hearing tests and they are not using ear protection equipment.
Full-text available
Only 2 chapters are available as full-text: 1. Stress Processes and the Cost of Coping. 2. Correlational Field Methodology in the Study of Stress
Scitation is the online home of leading journals and conference proceedings from AIP Publishing and AIP Member Societies
Noise and Human Efficiency is the sixth volume in this Wiley series on "Studies in Human Performance". It is an account of the effects of noise on human performance. After delineating the physics of sound and noise, and presenting the essentials on the physiology of the ear with its associated brain mechanisms, the book explains the consequences of noise for auditory perception and the comprehension of speech. It also describes the after effects of persistent noise, in the form of various kinds of temporary or permanent deafness. With respect to performance of non-auditory tasks, the book reviews the experiments on annoyance and social disruption, in addition to those on various industrial and laboratory tasks. It brings the record up to date by showing that the effects of noise are not always detrimental. Noise has complex consequences, interacting with such factors as arousal, time-of-day, sex and personality. Although the appropriate psychological theories are reviewed, the author's main aim has been to pick his way through the experimental and methodological complexities in such a way as to show exactly what has been firmly established.