Influence of noise on heart rate and quantity of work in mental work

In the present study, we investigated the correlation between the physiological function, heart rate (HR) and the quantity of work performed when A-weighted sound pressure level of factory noise or construction noise was varied during the mental operations of calculation and erosion. Furthermore, we looked for differences in the effects of sound noise and music on the quantity of work performed. The A-weighted sound pressure level was set at four levels of background noise, i.e. 60, 70 and 80 dB (A). The music sound level was set at 70 dB (A). The subjects were exposed to factory noise, construction noise and music during their mental work. A balanced factorial experiment was conducted with a total of 16 combinations of types of mental work (two levels of calculation and erosion), sound noise (two levels of factory and construction sound noise), and A-weighted sound pressure levels (four levels). The order of the experimental procedures was determined at random. The following conclusions were made from the findings of the study. 1) HR elevation occurred due to exposure to sound noise, and further increase in HR resulted from an increase in the A-weighted sound pressure level. This result can be attributed to the action of sound noise as a stressor, which excites sympathetic nerves, leading to an elevation of HR. 2) The quantity of work performed decreased with an increase in the A-weighted sound pressure level. 3) When the subjects were exposed to music with an A-weighted sound pressure level of 70 dB (A) instead of sound noise of the same level, almost no elevation of HR was observed. However, the quantity of work completed when exposed to music was less than that performed when exposed to sound noise of the same A-weighted sound pressure level.