Multi-Stress And Human Performance: A Refutation Of Inverted-U Hypothesis

The purpose of this paper is to study the consequences of multi-stress (temperature, humidity, noise and whole-body vibration) with different intensities on cognitive and work performance as well as on the discomfort measured by using the Likert scale. Background: So far these effects have been investigated with fewer external stressors and of relatively low intensities. It was necessary a closer approach to the realities of working environments highly threatening to worker’s health. Method: The experiment involved 20 people (10 women and 10 men) aged between 19-28 years, in good health. Each experiment was held for a certain temperature, humidity, noise level and vibration acceleration level transmitted to the subject. The temperature has been selected: 38, 42 and 48 o C; the humidity: 60, 70 and 80%; the sound level: 75, 85 and 95dB; the acceleration of the vibrations transmitted to the subjects (ar.m.s.): 2.38, 2.75 and 3.12m/s 2 . Tests of human performances consisted in: Discomfort determination using Likert scale; Cognitive performance measurement (Attention measurement and Assessment of short-term memory) and Work performance measurement. Human performances were quantified using the results from the test presented above. Results: In the experimental set with 3 stressors the first dropouts appear: 4 in women and 1 in men. The increasingly values of the 3 stressors to which the subjects were exposed proved to be unbearable, especially for women. In the experimental set with 4 stressors were many dropouts, especially among women ending that after 7 experiments all the women gave up. The first man that dropout was the same one that gave up at the last set; the second was forced out of the experiment as he completely lost his balance and could not stand on the vibrating system. The women (sooner) and the men (later) presented dizziness, vomiting and had severe headaches (according to personal statements). Conclusion: in the experimental sets with 1, respectively 2 stressors, the performances curves could be read off using the upper part of „Curve A” from Yerkes–Dodson Law, meaning that the inverted-U hypothesis is correct for some areas. Keywords—multi-stress, temperature, humidity, noise, whole-body vibration, discomfort, Likert scale, cognitive performance, work performance