A comparative study of introversion and extroversion cognitive functions in three positions before, during, and after exposure to low frequency noise

Sound is one of the most influential exogenous factors affecting the processing mechanisms of the human brain that play a major role in the occurrence of human errors and occupational accidents. Low-frequency noise is one of the most important sources of noise in the environment, and even at low levels it is annoying and affects people's cognitive performance. Some of the individual differences, such as personality type, hand superiority, neuroticism, and individual sensitivity are factors that influence the effect of sound on cognitive functions. The purpose of this study was to investigate the effect of personality type on cognitive functioning in three situations before, during and after exposure to low frequency noise.

The present study is an empirical basic science. The study population was students of Hamadan University of Medical Sciences through purposive sampling (60 extroverted and 60 introverted). All experiments were performed in the Faculty of Health of Hamadan University of Medical Sciences in a room with controlled acoustic and physical conditions in March, 2016. Eiseng personality questionnaire was used to determine personality type. Simulating the real-world environment of each of the subjects in the industry were exposed to the most intense noise in the industry (50 and 70 dB) for 40 minutes. Each of the subjects underwent cognitive performance in three positions before and during and after the exposure using continuous audiovisual performance test. Environmental conditions were maintained under conditions of thermal comfort and equivalent to a humidified temperature of 18 ° C and relative humidity of 50% without disturbing airflow. Also using fluorescent lamps and halogen lamps of 500 lux with optimum luminance levels were provided and kept constant during all tests. In this study, the recording of industrial ventilation in the workplace was performed using the Cool edit Program software in the frequency band. It is a powerful software for generating sound at different frequencies, especially low frequency sound. When playing the sound, the sound pressure equivalent to the ear of the test subjects was measured and in the sitting position. The sound meter used in this study is SVANTEK Model 971 manufactured by Polish-American Company, which operates according to IEC 61672, which has the capability of analyzing 1/1 and 1/8 octaves. The speakers used in this study are spherical-shaped speakers with a SWA-100 amplifier to amplify the sound at low frequencies that produce a sound similar to the workplace. After each step, the groups were replaced to eliminate the noise exposure effect and to avoid cumulative fatigue in the second level, a 24-hour interval was considered. Data were analyzed by SPSS 20 software and repeated measure ANOVA.

The mean age of the subjects was 23.94 with a standard deviation of 3.25. The distribution of the test subjects was gender uniform and 85% of them were single and the rest were married. Most of the participants in this study were undergraduates of health sciences and 80% of them. The results showed that the cognitive functions of extroverted and introverted individuals were different in the three situations before, during and after exposure to noise. The results indicated that introverts in the pre-exposure condition and extroverts performed better in the exposure conditions. Also, with increasing sound level from 45 to 65 dB, there was a significant difference (p <0.05) between extroverted and introverted individuals 'cognitive functions, which improves extroverted individuals' cognitive functions. The findings also showed a significant relationship between sound and sex.

The findings of the present study provide good evidence for the difference between introversion and extroversion in the tendency to environmental stimuli. The results of this study show that exposure to low frequency noise was influential in the components of participants' cognitive functions There is a significant relationship between the increase in sound level and the components of cognitive functioning with personality type. When exposed to noise, extroverts had higher cognitive performance components. The better performance of introverts in later exposure situations indicates their avoidance of stimulation and their tendency to silence a natural and genetic issue. Accordingly, the effects of personality type should be taken into account in job posts and sensitive occupational tasks that require the use of cognitive functions.