The combined effect of industrial noise type,level and frequency characteristics on hand motor skills: A lab trial study

Abstract

BACKGROUND:

The study aimed to assess the interactive effects of industrial noise type, level and frequency characteristics on hand motor skills using the Minnesota Manual Dexterity Test and the Hand Tool Dexterity Test.

METHODS:

A total of ten nonsmoking male volunteers with normal hearing and vision were selected for this study. The study followed a full 3×3×2 factorial design. Independent variables were noise type (steady, intermittent and fluctuating), noise level (75, 85 and 95 dBA) and frequency characteristics (“roar” <2000 Hz and “hiss” >2000 Hz).

RESULTS:

For Minnesota Manual Dexterity Test, the lowest speed is related to steady hiss noise at 75 dBA and the highest speed is related to fluctuating roar noise at 95 dBA. The speed is being significantly affected by the frequency characteristic (P = 0.041) and noise type (P = 0.025). The effect of hiss noise on speed is greater than roar noise (P = 0.038). There is a significant difference (P = 0.035) between continuous noise and fluctuating noise. For the Hand Tool Dexterity Test, the lowest speed is related to fluctuating hiss noise at 95 dBA and the highest speed is related to steady roar noise at 95 dBA. The speed is being significantly affected by the frequency characteristic (P = 0.002), noise type (P = 0.0001) and noise level (P = 0.005). The effect of hiss noise on response variable to be greater than roar noise (P = 0.008). There is a significant difference (P = 0.0001) between steady noise and the two other types of noise, and also there is a significant difference between 75 dBA and 85 dBA level (P = 0.003).

CONCLUSIONS:

The results showed that on hand motor skills, speed response was influenced by three characteristics: the type of noise, frequency characteristics and noise level. Also, the effect of the hiss noise was more than the roar noise.

Keywords

Industrial noise occupational skills Minnesota Manual Dexterity Test Hand Tool Dexterity Test speed response

1. Introduction

Various harmful agents exist in the work environments that cause worker exposure to physical, chemical, ergonomic, biological, mechanical and psychological hazards. Being exposed to one or a combination of these factors can have adverse effects on the health, safety, comfort and performance of the workers [1, 2]. Exposure to occupational noise is considered to be one of the important stressors in the workplaces [3, 4]. It is reported that 600 million workers are exposed to noise all over the world [5, 6]. Exposure to noise above acceptable thresholds not only adversely affects hearing systems but also reduces level of concentration, performance, awareness and efficiency. Among the non-hearing related effects of noise exposure, reduction in performance and skill is a challenging issue and a grave concern for any company or industry as it can incur unwanted costs and additionally a reduction in profits [7].

Although humans have the ability to adapt to these types of noise, the reality is that noise is a cause of fatigue and can reduce performance in physical and/or mental tasks. The effects of occupational noise on workers’ performance is also dependent on personal traits, type of occupation, environmental factors, complexity of task and the existence of other stressors in the work environment [1].

The effects of occupational noise on performance are as follows:

Masking - a condition where hearing is affected as a result of noise exposure.

Lack of focus - the existence of any noise that causes a specific response and reaction to its source, so leads to reduced focus.

Irritability level - noise increases the threshold of excitement, so result in over-activity and receiving the selective information [8].

Various studies have shown that noise induced stress can affect focus, awareness, productivity and efficiency [9]. But in most studies noise level is considered as a singular variable while other sound characteristics such as frequency range, type of noise and their combined effects are neglected. Changes in any of these characteristics can subsequently cause changes in the aforementioned harmful effects caused by them. For instance, noise may be continuous or intermittent, the latter having a more pronounced effect, meaning that environments where workers were exposed to continuous noise, the lower effects have been observed [10].

It must be noted that most studies that assess the effect of noise exposure on performance have been focused on mental performance, showing noise-induced impairments on specific cognitive functions [11]. Few studies have investigated the role of noise characteristics on hand skill performance. Most industries have at least some tasks that are done by hand, such as assembly, packaging, repair, maintenance or casting, to name a few. Noise may have a negative effect on hand-arm and heavy movement skills and reduce working speed [12].

In most industries, maximizing the performance and efficiency of the work force for the purpose of increasing profits is highly preferred. Adverse environmental conditions are an important factor in this regard. Thus, it is essential to understand how these conditions affect human performance so that adequate solutions can be implemented to retain performance.

As such, the purpose of this study is to investigate the interactive effects of industrial noise type, level and frequency characteristics on hand motor skills using manual tests such as the Minnesota Manual Dexterity Test and the Hand Tool Dexterity Test. This study seeks to determine which of these three characteristics has the strongest effect on hand dexterity tasks and also whether there is any interaction among them or not.

2. Materials and Methods

2.1 Participants

A total of ten nonsmoking male volunteer with normal hearing and vision were selected for this study. They had no history of any other health problem that may affect brain and muscle function, no drug dependencies such as nicotine, alcohol or other drugs and also no use of sleep inducing pharmaceutical drugs or drugs that weaken the central nervous system during the testing period. The nonsmoking male participants were entered the study, because this research may have taken place in a country where men are highly represented in the paid workforce and as the literatures, the effects of smoking may be toxic to the brain and cognitive function [13].

All subjects had at least 8 hours of sleep before taking the test and were instructed to fill out a form detailing demographic information and functional vision and hearing assessment along with a consent form. All candidates were between 20 to 30 years of age and the average age of participants was 24.5±3 years. Participants were briefed on how the experiment would be carried out, and testing was conducted after being informed fully about it. A signed informed consent has been obtained from all subjects. Ethical approval was granted by the Research Ethics Committee of Tehran University of Medical Sciences (Research project no. 89-04- 27-1187).

2.2 Study design

In this study independent variables were noise type (steady, intermittent and fluctuating), noise level (75, 85 and 95 dBA) and frequency characteristics (“roar” < 2000 Hz and “hiss” > 2000 Hz). The study followed a full 3×3×2 factorial design (Table 1). The dependent variable was considered to be the speed at which the task could be completed. Then, the combined effects of the aforementioned characteristics on human performance were evaluated.

Table 1
The study design

Frequency characteristics Roar Hiss

Noise level 75 85 95 75 85 95

dBA dBA dBA dBA dBA dBA

Noise type Steady A G M B H N

Intermittent C I O D J P

Fluctuating E K Q F L R

Frequency characteristics	Roar	Hiss
Noise type	Steady	A	G	M	B	H	N
	Intermittent	C	I	O	D	J	P
	Fluctuating	E	K	Q	F	L	R

The experiment was conducted in the Physical Hazardous Agents Laboratory of the School of Public Health, University of Medical Sciences. In order to limit any interference with the performance of the test taker, noise levels and other parameters were selected and applied using a computer interface located outside of the test site. The participant was first seated in a chair in their respective location with the test tool in front of him on a work bench. Two separate noise sources were used in the test. Figure 1 shows the test setup including the work bench where the participant takes the test. The noise sources are located approximately one meter away from the participant.

Fig. 1

A schematic of the experimental layout [1].

To prevent any errors, the source noise was categorized using software programs and a unique code was assigned to each sample type. Noise characteristics and their interactions along with their respective codes are presented in Table 1. A total of 18 sample types and an additional “no exposure” condition makes for a combined number of 19 tests per each individual. On average, three minutes of rest time between each test was applied. In order to prevent bias, noise samples were played at random for each participant. Sound insulation was applied to the door to prevent any leakage.

2.3 Equipment

2.3.1 Industrial noise recording device

After reviewing the literature, the required noise source was determined considering sound characteristics. Then for the purpose of recording the samples, a manufacturing plant was selected where noise was recorded using a Bruel & Kjaer Data Acquisition Device Type 3560 B, C, D, E version 12. The intended industrial noise was recorded at the hearing height of the workers at the same distance as the operator stood from the noise source considering the variables related to noise.

2.3.2 Noise measurement device

In order to perform frequency analysis and also to measure the level of noise produced, a Bruel & Kjaer model 2236 was used.

2.3.3 Noise production software

Steady, intermittent and fluctuating noise was produced using the Gold Wave software version 4.26 which enables editing, setting the duration and also customizing the level of sound produced.

2.3.4 Chronometer

The time needed to complete the test was considered a dependent variable in this study and was mea-sured using a chronometer. To start the test, a signal was played for the participants and the chronometer was set as they begun. The chronometer was stopped immediately after completion and the time recorded.

2.4 Test used

2.4.1 Minnesota Manual Dexterity Test

In the Minnesota Manual Dexterity Test (Fig. 2), hand/arm dexterity is evaluated in coordination with eye. The test consists of two 3×9 boards connected by a hinge with 60 holes that fit 1.5-inch rods inside. Rods are located at the top of the board in 15 columns and the participant is asked to fill the holes from the right side in a way that the rod located at the bottom of the column sits on the top of the board. The participant must place the rods in the particular order instructed (Placing Test). The only variable that is measured in this test is the time taken to complete the test (speed response) [12].

Fig. 2

Minnesota Manual Dexterity Test [14].

2.4.2 Hand Tool Dexterity Test

This test is used to assess an individual’s ability to use ordinary mechanics tools (Fig. 3). For doing the test, the participant is instructed to open twelve nuts and bolts located on the left side of a wooden board, in a particular order (top to bottom), and refit them on the right side of the board in reverse order. Participant must utilize tools such as screwdrivers and spanners and must ensure that the nuts and bolts are tightly secured in their location. The variable that is measured in this test is speed [12].

Fig. 3

Hand Tool Dexterity Test [14].

2.5 Data analysis

Statistical analysis was conducted using the SPSS version 18 software (Chicago, IL, USA). The normality of data was examined by 1-sample Kolmo-gorov–Smirnov test. The significance level was set at 0.05. Descriptive statistics including mean and standard deviation and statistical analyses including T-test and one-way analysis of variance (ANOVA) for comparing the results between the groups and multi-factor analysis of variance (three-way ANOVA) for determining an interaction effect between three independent variables on the dependent variable were used.

3. Results

Figure 4 shows mean speed response for the Minnesota Manual Dexterity Test across the experimental conditions. As can be seen, the longest times (lowest speed) is related to steady hiss noise at 75 dBA and the shortest times (highest speed) is related to fluctuating roar noise at 95 dBA.

Fig. 4

Speed response for all the treatment combinations in the Minnesota Manual Dexterity Test.

The results of the multi-factor analysis of variance indicate that the variable “speed” is being significantly affected by the frequency characteristic (P = 0.041) and noise type (P = 0.025) in the Minne-sota Manual Dexterity Test. The t-test results regarding frequency characteristic showed the effect of hiss noise on speed to be greater than roar noise (P = 0.038), so that hiss noise decreases the speed response in the Minnesota Manual Dexterity Test. The results of the one-way analysis of variance (post-hoc Tukey test) on noise type showed there to be a significant difference (P = 0.035) between continuous noise and fluctuating noise.

Figure 5 shows the effect of different noise characteristics on the variable “speed” in the Minnesota Manual Dexterity Test. As can be seen, the hiss noise has a greater effect than the roar noise on the response variable. Comparing noise types, one can see the effect of steady noise as being greater than the other two. Also, regarding noise level, 95 dBA has a more pronounced effect.

Fig. 5

Speed across the noise characteristics in the Minnesota Manual Dexterity Test.

Using t-test for the variable “speed”, a significant difference was observed (P = 0.035) between the non-exposure and exposure condition. It was observed that the average time to complete the test was higher in non-exposure condition as opposed to when industrial noise is played.

Figure 6 shows the mean speed in the Hand Tool Dexterity Test for each test condition. As can be seen, the longest test times (lowest speed) is related to fluctuating hiss noise at 95 dBA and the shortest test time (highest speed) is related to steady roar noise at 95 dBA.

Fig. 6

Speed response for all the treatment combinations in the Hand Tool Dexterity Test.

The results of the three-way ANOVA indicate that the variable “speed” is being significantly affected by the frequency characteristic (P = 0.002), noise type (P = 0.0001) and noise level (P = 0.005) in the Hand Tool Dexterity Test. Also, a significant interaction was observed between noise type and level (P = 0.035), though this interaction was not statistically significant among the others (P > 0.05). The t-test results regarding frequency characteristic showed the effect of hiss noise on response variable to be greater than roar noise (P = 0.008) in the Hand Tool Dexterity Test. The results of the one-way analysis of variance (post-hoc Tukey test) on noise type showed there to be a significant difference (P = 0.0001) between steady noise and the two other types of noise, and also that there is a significant difference between 75 dBA and 85 dBA level (P = 0.003).

Figure 7 shows the variable “speed” in different noise characteristics for the Hand Tool Dexterity Test. As can be seen, the effect of hiss noise on the variable ‘speed’ is greater than that of roar one. As for noise type, the effect of intermittent noise is more pronounced than the other two. Also, regarding noise level, 85 dBA has a more pronounced effect.

Fig. 7

Speed across the noise characteristics in the in the Hand Tool Dexterity Test.

The t-test results regarding the “speed” showed a significant difference (P = 0.035) between the non-exposure and exposure condition. It was observed that the mean time to complete the test was higher in non-exposure condition as opposed to exposure ones.

4. Discussion and conclusion

This study was conducted with the aim of inves-tigating the interactive effect of three noise characteristics including frequency range, noise level, and noise type on arm-hand skill performance. The strengths of this study are that unlike other studies, a wide range of characteristics related to noise and its effect on performance are considered and investigated. Also, instead of using environmental noise (for instance traffic noise), industrial noise was specifically intended. Furthermore, instead of focusing on mental performance like most studies have, we focused on hand motor skills.

In the Minnesota Manual Dexterity Test, frequency characteristics and noise type were affecting task completion speed among the factors. In the study conducted by Narvane on 8 participants, type of noise source was determined to be the most effective factor [12]. In the present study, unlike the Narvane study, frequency characteristics were examined as a new factor. We observed that low frequency noise (roar) had a lesser effect as compared to high frequency noise (hiss). This may be due to the fact that hiss noise covers a more expansive range of frequencies and as such has a more pronounced effect on the ears, increasing test times [1]. It was also observed that steady noise had a more pronounced effect than other types and that noise level was most effective at 95 dBA. In a study conducted on the effect of the noise types (continuous, intermittent and fluctuating) on inspection performance, it was determined that human error rises when exposed to continuous or fluctuating noise [15].

In the Hand Tool Dexterity Test, the effects of the three intended factors became apparent as the relation between noise level and noise type became significant. As in the previous test, hiss noise was more effective than its counterpart. As for intensity, 85 dBA caused an increase in test completion times. Intermittent noise was most effective among other types.

The results of Lercher et al. show that steady noise have a lesser negative effect on complex tasks (memory or attention) as opposed to intermittent noise [16]. Clark et al. have shown that a noise source that is perceptibly fluctuating through time has a more adverse effect on cognitive functions as compared to a noise source that is continuous and steady [10]. Since the Hand Tool Dexterity Test is more complex than the Minnesota Dexterity Test, the effect of intermittent noise is higher in the former test while steady noise was more effective in the later test due to its less complexity.

In a study by Nassiri et al., the effect of noise on cognitive skills was evaluated using steadiness and uniformity tests. The results showed frequency characteristics to be the most effective factor, and that hiss noise was more effective than the roar one. The study also showed that intermittent noise at 85 dBA had the most negative effects [1].

In a study that assessed the effect of noise on circuit board inspections, it was observed that among various noise intensities, performance was mostly affected at 90 dBA [15].

In another study conducted by Gorzin et al. on the effects of steady and intermittent noise on students’ problem-solving skills, it was observed that intermittent noise was more effective than steady noise and relative performance can still be maintained when expose to steady noise [17].

Defects in performance is occurred whenever there was exposure to a long intermittent noise. This does not happen when exposed to continuous noise as individuals get used to this type of noise and thus regain their performance after a while but not if the noise source is intermittent [18].

Driskell et al. discovered that noise can have negative effects on performance and have noted that effective factors in this regard include its level, being steady or intermittent, duration of exposure and type of activity being performed [19].

Using the t-test on the variable “speed” showed a significant difference between the non-exposure and exposure condition. It was observed that the mean time needed to complete the test was higher under non-exposure condition as opposed to when industrial noise is played. The study by Jafari et al. showed that loud noise (65 dBA) increases performance speed as compared to relatively quiet conditions (45 dBA) [20].

The results of the Finkelman et al. [21] and Fisher et al. [22] studies showed that performance speeds increased in the presence of loud noise (65 dBA) as opposed to quiet conditions, however, this also increased the number of incorrect responses due to the defense mechanism that pushes individuals to finish the task faster in order to escape the stressful condition they are under [23].

This study confirms the harmful effects of noise on hand skill performance. High intensity, high frequency noise can cause a change in the exposed subjects’ speed due to decreased focus and attention while also causing stress. The performance and efficiency of individuals at workplaces may be affected in this situation. This can threaten occupational health and safety health if suitable preventive measures and controls are not adopted [24].

The tests used in this study, including the Minnesota Manual Dexterity Test and the Hand Tool Dexterity Test, can be useful for selecting the candidates (considering the including criteria of the present research) who intended for positions that need team work or positions intended for rehabilitation and aid for getting back to work. These tests can be very useful for appointing people that are most suited to a particular occupational role.

The effects of other workplace environmental factors such as heat, cold, vibration and lighting, gender, BMI, smoking status, doing sports, personal trait, noise sensitivity, and other factors, are all potential influences on the hand motor skills are not considered in present study; however, these factors are outside the scope of this paper. Moreover, small sample size may be another limitation of present work. Future research might look to field studies exploring how the effect of these factors or combinations of factors is implicated in hand motor skills.

Conflict of interest

The authors confirm that there is no conflict of interests.

Funding

This study was financially supported by the Tehran University Medical Sciences (Grant No. 89-04- 27-1187).

Footnotes

Acknowledgments

The present study was part of a M.S. thesis funded by Tehran University of Medical Sciences (Grant no.89-04- 27-1187). The authors wish to thank all the participants who took part in the study.

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The combined effect of industrial noise type,level and frequency characteristics on hand motor skills: A lab trial study

Abstract

BACKGROUND:

METHODS:

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Materials and Methods

2.1 Participants

2.2 Study design

Table 1 The study design Frequency characteristics Roar Hiss Noise level 75 85 95 75 85 95 dBA dBA dBA dBA dBA dBA Noise type Steady A G M B H N Intermittent C I O D J P Fluctuating E K Q F L R

2.3.1 Industrial noise recording device

2.3.2 Noise measurement device

2.3.3 Noise production software

2.3.4 Chronometer

2.4 Test used

2.4.1 Minnesota Manual Dexterity Test

3. Results

Conflict of interest

Funding

Footnotes

Acknowledgments

References

Table 1
The study design

Frequency characteristics Roar Hiss

Noise level 75 85 95 75 85 95

dBA dBA dBA dBA dBA dBA

Noise type Steady A G M B H N

Intermittent C I O D J P

Fluctuating E K Q F L R