A Factor-Analytic Study of Phase Discrimination in Mental Fatigue

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Abstract
In dealing with observed data of fatigue studies, it is essential to distinguish ‘ overfatigued ’ phases. To compare the data with the test results before work, for instance, is not always recommended, since the latter themselves represent merely a cross-section of the variation. Discrimination of phases in the course of diurnal variation of cortical functions was attempted for operators in the train control centre. Critical flicker fusion frequency was measured at different periods of a 24.hour shift. Correlation coefficients among periods w-ere computed and three underlying factors were extracted by factor analysis (principal component analysis and varimax rotation). In accordance with these three factors, the shift periods could be classified into (I) the morning-rise phase, (II) the intermediate phase, (III) night-and-early-morning phase, and (IV) after-overnight-vigil phase. Phase IV, although in the morning hours, did not show the features of phase I, but was characterized by markedly different factors as compared with the early morning. Distribution of observed fusion frequencies was not normal in the phases of night or intermediate factors. Similar factors and phases could be demonstrated also for choice reaction time. It was concluded that phase discrimination of cortical functions by means of factor analysis would be of use for detecting the overfatigued conditions in operators.