In many studied on the relationship between mental load and sinus arrhythmia (SA) scores in binary-choice reaction tasks, most authors disregarded the effect of minor motor actions inevitably accompanying light work. However, because the chemoreceptors for muscle cell activities are directly coupled with the heart rate (HR) control centre in the brain (cardiovascular centre) through neural pathways, even minor motor actions can influence SA.
In this study mental and physical loads were respectively scored by information processing and finger tapping rates. Percentage changes in SA and HR above resting levels were scored from heart beat intervals of subjects. A cost-effective measurement system using 6502 or 8088 microprocessor was developed for accurate heart beat intervals. According to a multivariate regression analysis of SA scores on mental and physical load components, an increase in mental load decreased SA, but did not increase HR significantly. An increase in physical load decrease SA and increased HR significantly. This result implies that a significant effect of minor motor actions often disregarded by other researchers should be separated from SA for precise prediction of mental load.
This study evaluates two types of predictive functions for mental and physical load components of a light work of which performance or subjective response is difficult or impossible to measure in real work situations. Statistical multivariate inverse regression functions based on regressing mental and physical load components on HR and SA scores resulted in smaller predictive errors than algebraic inverse functions of multivariate regression functions based on regressing HR and SA scores on mental and physical load components. A graphical model based on multivariate inverse regression functions is presented or prediction of mental and physical load components equivalent to HR and SA scores.
For total workload comparison, combined total workload scores using weighted averages of mental and physical load components are examined. The weights using entropies of mental and physical load components lead to higher contrast of the combined scores than other weight-determination methods. Hence for clear comparison of combined scores, the weights using entropies will be usefull.