European isolation and confinement study. Cognitive fatigue in complex decision-making.

In six healthy males, confined in a hyperbaric chamber complex for 4 weeks, mental fatigue was assessed by means of a Working Memory Test. This test involved a decision-making task, which concerned the management of the chemical environment of a spacecraft affected by the presence of contaminants. Five items of reference information were shown on a screen and had to be memorized, then five "status" cards were given, upon which the need for corrective action had to be decided. Checking back to the reference information was permitted. The following parameters of the decision-making process were recorded: memorizing time (MT), decision-making time (DT), checking-back time (CT), total time per card (TT), and percent false decision (%E). Data analysis had to compensate for continued learning during the isolation period, because the pre-isolation training period had been too short. For this reason, only the last 3 weeks of isolation were considered. Only data from correct trials were used in data analysis. The group average performance measures were fairly constant over the 3-week period, indicating that there are no strong overall effects of isolation on mental functioning. There is a tendency towards increasing MT and CT and decreasing DT, but these changes are not statistically significant. There was also a tendency for increased mental fatigue on weekends (only the increase in CT was statistically significant). Analysis of the data for the one subject without missing days and with low and constant error rates over the three weeks shows that his behavior became more variable over time (particularly in DT), and that a breakdown of normal cognitive processes occurred on two days during the fourth week of isolation. Further experiments with a longer pre-isolation training period and a longer isolation period are needed to determine whether this is a general or an exceptional phenomenon.