Research Article, J Ergon Res Vol: 1 Issue: 2
The Role of Personality Type on the Effects of Low-Frequency Noise on Cognitive Performance of Students
*Corresponding Author : Derakhshan Jalil
MSc Occupational Health, School of Public Health, Hamadan University of Medical Sciences, Hamadan, Iran
E-mail: [email protected]
Received: July 24, 2018 Accepted: August 20, 2018 Published: August 27, 2018
Citation: Mohammad B, Majid M, Rostam G, Jalil D, Maryam F, et al. (2018) The Role of Personality Type on the Effects of Low-Frequency Noise on Cognitive Performance of Students. J Ergon Res 1:2.
Background: Noise exposure has harmful effects on physical and mental health as well as cognitive functions. Low-frequency noise is one of the most important sources of noise in the environment. Some individual differences such as extraversion, neuroticism, and sound sensitivity can affect the influences of sound on cognitive functions. The purpose of this study was to investigate the effect of personality type (introversion/extraversion) on cognitive functions in the presence of low-frequency noise.
Materials and Methods: In this interventional study, research population included all students who were studding at Hamadan University of Medical Sciences. For this reason, 120 students were selected through purposive sampling method (60 students with extraverted personality and 60 students with introverted personality). To simulate the real environment of each subject, they were exposed to noise with different sound pressure levels (SPLs) of 50, 60 and 70 dB for 40 min. While the exposure to the determined levels of noise, the continuous visual-auditory performance test was used to evaluate the cognitive functions of the subjects. Data were analyzed using SPSS software (version 20) by independent t-test and ANOVA tests.
Results: The results showed that low-frequency noise negatively affected the components of cognitive functions. These functions decreased with increasing SPL from 50 to 70 dB (P<0.05). The study of the effects of personality type (introversion/extraversion) and gender of the subjects showed that the cognitive functions were more affected in introverts and women and there was a significant difference between the two groups (p<0.05).
Conclusion: The results of this study showed that the SPL of the low-frequency noise has various effects on the cognitive function parameters of individuals with extroverted and introverted personality, and the negative effect of low-frequency noise on introverts was lower than extroverts. Moreover, a significant relationship was observed between noise and gender.
Keywords: Low-frequency noise; Cognitive function; Personality type; Noise pressure level
Many researchers have defined low-frequency noise as a broad band noise (BBN) in the frequency range of 20-200 Hz. Some researchers have considered a wider frequency from about 10 to 250 Hz [1-3]. In addition to the industrial environments, low-frequency noises are present in public environments. The use of new techniques, especially new digital techniques, has reduced the level of sound in the industry. While more use of new devices and technologies in public environments, such as ventilation systems, compressors, computers, printers, etc., are associated with low-frequency noises that are annoying.
Low-frequency noise is generally produced by different sources such as ventilation systems, pumps, compressors, diesel engines, gas turbines and transport vehicles. Therefore, these sounds are also present in industrial areas such as control rooms, as well as in residential and offices areas [2-4].
Among the many reported symptoms of low-frequency noise exposure, irritability and headache have the most correlation with reduced work capacity . The most important effects of lowfrequency noise on human health include fatigue, difficulty in focus and a pressure feeling in the head and eyelids. Many new occupations require special precision during information processing and may face unpredictable situations.
Since noise is an environmental stressor and in combination with other stressors can cause or exacerbate mental disorders, and even it can affect individual performance under certain conditions . The accidents has been recognized by WHO as one of the indicators for reduced performance caused by noise. WHO has introduced the lowfrequency noise as a direct factor affecting mental disorders, which has an accelerating and exacerbating role in mental disorders . Research also showed that the individual differences have an important effect on the individual performance. These studies have reported that there is a relationship between the emotional characteristics of people and the effect intensity of noise on individual performance .
Aizing (This is not in consistent with the mentioned reference) found that extroverts and introverts have differences in term of basic level of brain arousal. This means that extroverts need a lower level of stimulus and they seek it actively. In contrast, introverts avoid the arousal due to the arousal high level of their brain. As a result, the introverts are more sensitive to sensory stimulation than extroverts. So, introverts are more sensitive to low-level stimuli and have lower pain thresholds compared to extroverts . Moreover, previous studies have shown that the performance of introverts in complex cognitive activities is more strongly influenced by intervening factors such as music and background noise compared to extroverts. In a similar study, 118 girl students in high school were evaluated with cognitive tests under quiet conditions, background noise and music, and it was found that in the presence of music and noise, the performance of introverts were less than extroverts. While in a quiet place, both groups had a similar performance. In addition, this study showed that the performance of the subjects in the presence of music and noise was less than in quiet place. On the other hand, they concluded that there was a positive relationship between extraversion and intelligence . Augustin's research also showed that in the presence of noise, extroverts worked significantly faster than in quiet conditions (P<0.05). In addition, they had a higher tolerance against noise compared to introverts. In introverts, the lack of focus power and fatigue were higher in the presence of noise than in quiet (p<0/05) . The study of Raw and Griffiths also indicated that there was a significant correlation between introversion/extraversion of individuals and annoyance caused by noise . Previous studies on the effect of noise on the human performance demonstrated that the noise may cause some work problems and increases the number of mistakes at work, but these effects depend on the type of noise and running work. Meanwhile, meaningful and relevant information attracting attention of the individual results in a decrease in efficiency . Muzet showed that the disruption effects of noise in intellectual activity are more than physical activity, and when it exceeds 90 dB, it could increase the required energy to maintain awareness and alertness . Therefore, the present study aimed to investigate the role of introversion/ extroversion on the influence of low-frequency noise with intensities of 50, 60 and 70 dB (common intensities in the industry) on the cognitive functions.
In this interventional study, research population consisted of all students of Hamadan University of Medical Sciences. For this purpose, 120 students were selected through purposive sampling (60 students with introverted personality and 60 students with extroverted personality). Inclusion criteria included being between 20 to 30 years old, lack of medication consumption affecting the level of consciousness at the time of testing, lack of color blindness, having normal hearing, lack of a history of the cardiovascular diseases, lack of respiratory problems and sleep disorders. After the final selection of the subjects, all tests were completely explained to the participants. Based on the results of similar studies  and according to the equation (1), the required sample size was calculated.
In this study, integrative visual and auditory continues performance test was used to measure the cognitive functions. This tool is one of the continuous performance tests, which was first introduced by Razold et al., in 1956, and quickly became popular . This test has different types. In the present study, its numeric version was used that measures hearing attention item in addition to visual attention item. This test consists of three target motivators for the visual part and five target motivators for auditory part. During the test, the subjects should click after hearing and seeing the target stimulus. The test takes about 10 min and measures the attention types, the time of reaction and focus. The Persian version of this test has a reliability coefficient of Cronbach's alpha of 0.93 .
This cognitive test was performed while the subject was exposed to 50, 60 and 70 dB of noise (common noise in work places). Personality type of subjects was studied using a short version of Eyeing questionnaire, which included 57 double-choice questions (yes-no). This scale was first designed and introduced by Eyeing in 1975. This scale is applicable for people over 16 years old. There was no time limit for responding but it generally takes 10 to 15 min to complete. Scoring was based on three keys in clouding L (polygonal), E (introversion/ extraversion with 24 questions) and N (stability/instability with 24 questions). A score of more than 5 in L subscale indicates that the subject attempted to show him/herself different from what it is. High scores in N sub-scales represents a tendency to psychosocial states and emotional responses, and low scores represents stability behavioral strength, emotional balance, happiness, and peace in the subject. According to the instruction of the test and previous studies in Iran, the score of 13 in E subscale indicates the cut point, and the scores above 13 represent the extraverted personality type. The maximum score in E scale is equal to 24, which represents that the extroversion personality is dominant. The score of 13 represents the introversion personality is dominant. Eyeing has reported that the reliability of the test was 0.9, 0.89 and 0.86. Moreover, Nader Mohammadi reported that the reliability of the test was 0.63, 0.78 and 0.59 for E, N and L sub-scales, respectively .
Tone Generation Program was used to produce the used sounds. This tool is a strong software for producing noise in different frequencies, especially low-frequency noises. While playing the sound, SPL was measured near the ears of the subjects and their sitting places. In this research, a sound level meter (SVANTEK 971 model, made in Poland -America) was used, which is based on the IEC 61672 standard. This device can provide both 1:1 and 1:3 octave band analysis of noise levels. Spherical speakers with a SWA-100 amplifier were used to amplify low-frequency noise that produces a sound similar to the workplace noise.
In this research, an ergonomic laboratory with an internal dimension of 4 × 5 meters and equivalent sound level of less than 30 dB when its door is closed. The inner surfaces of the test area, including walls and ceiling were made from plaster and its floor was made from stone, which was similar to the real environment. The average of noise reduction coefficient for each of the materials used in the central frequency of 1000, 2000, 500 and 250 Hz was determined in accordance with the following equation:
The noise reduction coefficient of the entire test environment was obtained according to the following equation:
Si: Absorbent surface area (m2).
Iα=Absorption coefficient of each absorbent.
S=Total area of the test environment.
The value obtained for the sound absorption coefficient of the whole test environment was equal to 0.60, which was similar to the real environment. All subjects were investigated under all mentioned noise levels. After each step, the groups were changed to remove the effect of sequential exposure to noise. Upon entering the laboratory room, the subject was rested for 15 min until his body returned to the normal cycle. After completing the questionnaire of low-frequency voice sensitivity, the subject was exposed to the noise under the test environment for 40 min. The cognitive performance tests lasted 10 min, which the subject responded to the questions within 30-40 min. There was a 20 min break between each stage, and during this time, they were served with a sweet beverage to prevent low blood sugar distortion of results. The data were analyzed using SPSS software (Version 20) and statistical tests including Independent t and analysis of variance.
The average and standard deviation of the age of the subjects were 23.94 ± 3.25 with a minimum of 20 and a maximum of 30 year. The gender of the subjects was distributed uniformly. Approximately, 85% of the participants were single and the rest were married. Most of the participants were studied in health fields and most of them (80%) were undergraduate (bachelor's degree). Table 1 shows the results of the continuous visual-audit function tests in SPL.
|50 dB||60 dB||70 dB|
|Visual attention||Mean (SD)||(5.58) 29.18||(4.22) 27.10||(2.44) 23.49||0.016|
|Auditory attention||Mean (SD)||(6.66) 25.73||(5.89) 25.49||(2.31) 20.22||0|
|Visual tolerance||Mean (SD)||(5.40) 25.60||(4.63) 24.26||(3.22) 22.85||0.061|
|Auditory tolerance||Mean (SD)||(6.48) 26.30||(3.62) 21.88||(3.75) 16.13||0.001|
|Visual balance||Mean (SD)||(7.30) 29.43||(8.04) 27.85||(7.69) 26.75||0.102|
|Auditory balance||Mean (SD)||(5.44) 30.63||(5.01) 25.82||(7.14) 23.75||0|
|Visual focus||Mean (SD)||(3.93) 28.33||(3.97) 23.57||(7.85) 19.16||0|
|Auditory focus||Mean (SD)||(6.20) 30.28||(5.21) 25.88||(6.12) 21.01||0|
|Visual psycho-physical fatigue||Mean (SD)||(4.37) 28.98||(5.91) 27.46||(6.13) 26.41||0.071|
|Auditory psycho-physical fatigue||Mean (SD)||(5.83) 28.88||(7.88) 21.45||(6.39) 14.34||0|
|Visual reaction time||Mean (SD)||(146.64) 542.7||(101.5) 465.62||(87.14) 434.75||0.001|
|Auditory reaction time||Mean (SD)||(108.2) 562.56||(81.2) 440.19||(41.44) 410.96||0|
|Visual vigilance||Mean (SD)||(5.19) 27.05||(7.16) 24.39||(6.03) 24.14||0.081|
|Auditory vigilance||Mean (SD)||(4.52) 18.03||(6.18) 19.14||(4.05) 21.38||0|
|Visual speed||Mean (SD)||(5.58) 22.18||(7.22) 23.39||(5.55) 27.10||0|
|Auditory speed||Mean (SD)||(6.66) 19.73||(9.15) 22.25||(6.53) 26.10||0|
Table 1: Results of visual-audio continuous performance test (mean ± standard error) by SPL.
As shown, the cognitive functions of individuals decreased with increasing SPL. In addition, the reduction of auditory components was statistically significant (P<0.05). While the visual-auditory components improved significantly, but there was no a significant decrease in the visual components of attention (P<0.05), due to their decrease with the increase of SPL and with regard to the significant level achieved. Also, the visual-auditory components of the reaction time improved with increasing SPL. This result means that the reaction time to target stimuli decreases with increasing the SPL.
According to the results of cognitive performance test by personality type (Table 2) and the significant level obtained (p<0.05), it seems that the noise led to an increase in the function of extroverts compared to those with introverted personality. It should be noted that various researches reported that individual differences affect the sound influence on the performance of individuals . Belojevic showed that extroverts often adapt to boring activities . Eyeing also demonstrated that extroverts have a lower basic level of arousal than introverts. Due to the low level of arousal in the brains of extroverts, they require excitation and stimulation, and seek it actively . Because the arousal level of the extraverts is low, the noise could increase it, and eventually increases attention, focus and tolerance in this group of subjects. The result of this study is consistent with the content presented.
|Visual reaction time||(83.19) 488.13||(98.32) 531.36||0.001|
|Auditory reaction time||(81.79) 444.35||(101.12) 587.56||0|
|Visual attention||(3.56) 24.22||(3.35) 15.97||0.016|
|Auditory attention||(4.05) 25.14||(3.89) 17.35||0|
|Visual tolerance||(3.13) 22.53||(4.05) 18.12||0.251|
|Auditory tolerance||(4.53) 20.98||(5.15) 14.13||0.001|
|Visual balance||(4.48) 23.63||(4.61) 21.78||0.109|
|Auditory balance||(4.41) 27.04||(3.13) 22.01||0|
|Visual focus||(6.66) 21.11||(5.65) 14.95||0.047|
|Auditory focus||(6.51) 26.12||(3.39) 11.46||0|
|Visual psycho-physical fatigue||(4.12) 25.15||(4.19) 23.38||0.251|
|Auditory psycho-physical fatigue||(3.07) 28.12||(3.64) 19.64||0.081|
|Visual vigilance||(2.86) 23.65||(3.48) 19.92||0.061|
|Auditory vigilance||(2.17) 24.42||(2.90) 15.01||0|
|Visual speed||(3.17) 27.62||(4.17) 20.66||0|
|Auditory speed||(3.12) 25.44||(4.62) 15.06||0|
Table 2: shows the results of visual-auditory continuous performance by individual personality type.
There was no significant difference in being alert, tolerance, psychophysical fatigue and balance in the visual part between extroverts and introverts (P<0.05). A similar study has been conducted in this area by Belojevic et al, entitled "Mental responses to traffic noise with respect to personality traits”. They concluded that there was no significant effect between the role of extroversion and introversion on mental responses to noise .
In introverts the level of attention, tolerance, and focus decreased with increasing SPL. Augustin's has reported similar results and showed that in the presence of noise, introverts had more problems in relation to the focus and fatigue variables compared to the quiet conditions [P<0.05] (11). Belojevic showed that the introverted group are more sensitive to noise in intellectual activity compared to extroverted group . R. Megil also reported that extraverts showed faster response times than introverts . As a result, introverts are more susceptible to intrinsic stimuli than extraverts, and it can be concluded that introverts have lower pain thresholds than extroverts .
According to the results obtained (Table 2), there was a significant difference in work speed between introverts and extraverts. This finding is consistent with the results of Belojevic study, which showed that extraverts work significantly faster in the presence of noise compared to quiet conditions (p<0.05) .
In Table 3, the results of the cognitive performance variables were presented by gender, according to the results obtained, there was a significant difference in the functional variables between the male and female (P<0.05). A similar study was conducted by Qnat Abadi, entitled "Investigating the effect of sound on mental performance of students of Tehran University of Medical Sciences". The results of the mentioned study showed that short-term memory was not affected by noise based on the mentioned variables. While there was a relationship between computational memory, personality type, sensitivity to noise, and gender and noise effect . It seems that the mental performance of male and female is not similar in noise exposure. There was a relationship between focus as a cognitive function and gender (P<0.05). In a study that was conducted by Ali Shalchiyan on the noise pollution caused by traffic and its effects on people showed that generally male are more affected than female by the effects of mental resulting from exposure to noise . In contrast, Aniansson et al., reported a contradictory result, they proved that in female the sound sensitivity is higher than that of that of male .
|Variables||Mean (SD)||P value|
|Visual reaction time||(83.19) 528.13||(98.32) 474.06||0.001|
|Auditory reaction time||(81.79) 523.35||(101.12) 479.19||0.001|
|Visual attention||(3.56) 28.26||(3.35) 21.97||0|
|Auditory attention||(4.05) 32.79||(3.89) 22.78||0|
|Visual tolerance||(3.13) 29.35||(4.05) 20.83||0|
|Auditory tolerance||(5.33) 28.11||(4.05) 19.13||0.001|
|Visual tolerance||(4.48) 24.11||(4.61) 24.03||0.681|
|Auditory tolerance||(3.41) 25.11||(5.13) 25.11||0.561|
|Visual balance||(4.66) 28.07||(4.65) 15.15||0|
|Auditory balance||(5.11) 28.47||(5.39) 13.95||0|
|Visual focus||(3.95) 18.47||(6.01) 18.15||0.551|
|Auditory focus||(6.17) 21.84||(7.64) 22.07||0.723|
|Visual psycho-physical fatigue||(6.68) 23.65||(5.48) 22.92||0.251|
|Auditory psycho-physical fatigue||(7.17) 21.98||(6.93) 22.01||0.109|
|Visual vigilance||(4.11) 23.06||(5.01) 22.43||0.001|
|Auditory vigilance||(5.12) 23.44||(3.62) 22.66||0.001|
Table 3: Results of visual-auditory continuous performance (mean ± standard deviation) by gender.
In Table 3, there was a significant correlation between the reaction time and gender (P<0.05), which is not consistent with the finding of Chiovenda et al, study. This difference may be attributed to the differences in the statistical society and sound type. Because in the present study, the statistical society included students exposed to noise, but in the mentioned research, the statistical population consisted of driving guidance officers and control group consisted of administrative staff. Another reason for this contradiction may be related to the noise intensity, which in the present study, the subjects were exposed to the noise with common intensities in the industry, but in the mentioned study, the traffic noise was over 80 dB. They concluded that there was no difference in the emotional and mental characteristics of the participants .
Results indicated that individual differences are an effective factor in the influence of noise on the individual performance. So that, noise in extroverts can improve their performance. While it has different effect on introverts. Moreover, there was a relationship between the noise and gender. The noise acts as a progressive factor in male and distractive factor in female in their work quality.
This study has been adapted from an MSc thesis at Hamadan University of Medical Sciences.
The study was funded by Vice-chancellor for Research and Technology, Hamadan University of Medical Sciences (No. 9510286155).
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