Noise.html

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 Occupational Health, School of Public health, Tehran University of Medical Sciences, Tehran, Iran

2Department of Environmental Management, Islamic Azad University, Science and Research Branch, Khouzestan- Iran

3Epidemiology and Biostatistics Department, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran

Correspondence to
Behzad Fouladi Dehaghi, PhD, Department of Occupational Health, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran

E-mail: bdehaghi@gmail.com

Received: Dec 13, 2012

Accepted: Feb 25, 2013

Abstract

Background: 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.

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 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.

Results: 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.

Conclusion: 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.

Keywords: Noise; Occupational employee performance appraisal; Psychomotor performance; Environmental exposure

Introduction

Noise—generally defined as unwanted and unpleasant sound—usually disrupts the activity or balance of human life. Nowadays, with fast growth of industrial and technological advancements, 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 presence of industrial noise has serious consequences on the performance and productivity of workers.7-11 Despite this barrier in achieving maximum productivity and efficiency, industries try hard to cope with such problems and achieve the highest levels of profit.12 Between the measures of job performance, worker productivity is an important one and severe adverse environmental conditions can restrict worker productivity to a large extent.12-16

Human performance is under the influence 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 environmental stressors in the workplace can lead to adverse effects on human performance 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 leading to a loss of profit for any company or industry.17

As it is stated by many studies, the effect of noise on human performance is very complex.18-22 The effect of noise on task performance depends on various factors such as external environment, task complexity and other external stressors.18,21 On the effect of noise on worker performance, there are controversial views between researchers.18,22-24 To investigate 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 capabilities of humans and helps in testing applicants for assembly work and various other jobs.25 They cover the hand-eye coordination, steadiness, mechanical skills, arm dexterity, two-arm coordination, and motor skills.

Our study was based on the investigation of the effect of various factors of industrial noise on participants' performance and efficiency with the means of these occupational skill assessment tests. In other words, the objective of the present study was to determine: 1) the effect of noise harmonic index on human performance, 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 combined effects of the variables.

Materials and Methods

Study population

This study included 40 healthy male university 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 demanded. The mean±SD age of participants 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 independent variables considered for the experiments were continuous, fluctuating and intermittent noise, three different levels of noise (75, 85 and 95 dBA); and two noise harmonic indices (positive and negative). The two internationally 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 follow approximately the equal loudness curve of 40 phones, while the “C” network approximately follows the equal loudness curve of 100 phones, respectively.26 Thus, noise harmonic index is defined as the difference between these two weighting networks, i.e., dB(C) – dB(A). When the result of this equation is positive, the noise is in “bass” form; when it is negative, the noise is called “treble.”

The dependent variables of the study were speed and time duration of committing errors by the participants while performing the battery of tests. The speed was measured as the amount of time taken 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 steadiness test is mainly used to test the psychomotor phenomenon of steadiness in various participants. The holes are progressively reduced in size and the participant 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 tested 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 second board. Next, the participant is supposed 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 recorded 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 pattern can be traced by spreading the handles, bringing them together, or moving them left or right so that the stylus traced the star pattern. The participant is supposed 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 experiment, 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 provided. In this experiment, the response measured is the speed. Speed is calculated 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 System (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 software (ver 5.1).

Test room layout

The test room consisted of a work desk with 70 cm in height, where the experimental 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 analyzed 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 practice before conducting the actual experiments. 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 experimental 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 under the effect of three noise pressure levels, 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 steadiness test for the combination of intermittent noise, negative harmonic index (treble) at a pressure level of 95 dBA. For the same test, the completion time was lowest (mean±SD of 29.9±16.0 sec) for the situation in which continuous noise, positive harmonic index (bass), and 75 dBA noise pressure level were used. The speed variable had a normal distribution (Kolmogorov-Smirnov test). ANOVA revealed that the speed response was only affected by noise harmonic index. To determine the kind of effective harmonic index, Student'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 (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.

Table 1: Speed response (test completion time) in various test conditions

Noise Schedule

Noise pressure 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

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

 

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 index (treble) and pressure level of 85 dBA. It was lowest (mean±SD of 61.9±7.0 sec) when fluctuating noise, a positive harmonic index (bass) and a pressure level of 75 dBA were combined. The noise pressure level and harmonic index affected the speed response significantly (p<0.023). There was also a significant (p<0.04) difference 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 harmonic 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) difference 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 steadiness test with the help of an error time recorder that recorded the time duration of errors committed by the participant during the experiment.

The error response for the steadiness test and two-arm coordination test under the effect of three levels of noise, two harmonic noise indices and three schedules 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 intermittent 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 performance (p<0.001).

Table 2: Error time in steadiness and two-arm coordination tests

Noise schedule

Noise pressure 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

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

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 harmonic 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 negative harmonic index was found to be the most significant factor that affected the speed performance of participants while performing the four occupational skill assessment tests.

The interaction between the three 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 continuous and intermittent noise schedules. As it is stated by many researchers, of various noise characteristics studied, noise schedule is of utmost importance; intermittent noise is responsible for distraction of attention away from the task and leads to reduced performance particularly in performing complex cognitive 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 performances 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 Fluctuating noise, caused no significant effect probably because the designed tasks tested were simple and this kind of noise was something between intermittent and continuous 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 harmonic index, noise schedule, noise pressure 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 duration 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 performing the task, we found that harmonic index mainly affected the error response in steadiness test. Therefore, more duration of errors occurred due to the presence of negative harmonic index. In the two-arm coordination test, apart from negative harmonic index, no other significant 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 performance.24 Moreover, it should be mentioned that in this study, real noise from industrial settings was used in well-controlled 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 effects of noise on performance, loud noise leads to over-arousal, which narrows attention and restricts one's focus to a limited range of cues. This inability to attend to less salient cues would ultimately lead to deterioration of performance. Our findings 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 controversial results, to the best of our knowledge, none of them has so far focused on the effect of noise harmonic index on human performance. We found that when the noise harmonic index was negative (treble noise) the performance was significantly affected. The results of the effects 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 participants for their interest and enthusiasm to participate in the study. We also acknowledge 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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TAKE-HOME MESSAGE

  • Intermittent noise, especially at high pressure levels, reduces human performance significantly.
  • Treble noise is more important in reducing human performance.

Cite this article as: Nassiri P, Monazam M, Fouladi Dehaghi B, et al. The effect of noise on human performance: A clinical trial. Int J Occup Environ Med 2013;4:87-95.




 pISSN: 2008-6520
 eISSN: 2008-6814

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