Subjective-activity correlations. Subjective scale correlations for the signal changes of the visual (A, B) and auditory (C, D) cortices are shown. Activity change rate or normalised activity change ratio were plotted against pre-experiment visual analogue scale score (pre-experiment VAS) (A, C) or change rate of visual analogue scale score after the experiment (ΔVAS) (B, D). Activity change rate was calculated as change of activity of the visual cortices during the visual search from pre-fatigue to post-fatigue sessions divided by the session time (hour) of the fatigue-inducing period. Normalised activity was calculated as activity of the auditory cortices in a given section divided by that in the first section. Normalised activity change ratio was calculated from the slope of regression fitted to a scatter plot of the time course (section) against normalised activity. Subjects were asked to rate subjective sensation of fatigue on the VAS from 0 to 10. Squared Pearson correlation (R2) and P value are displayed. Closed circles, normal subjects; open circles, CFS subjects.